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STUDENT DIGITAL NEWSLETTER ALAGAPPA INSTITUTIONS |
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Jonathon D. Truwit MD
David Barker and colleagues postulated that impaired fetal growth may be a key determinant of later development of adult diseases such as obesity medicine quest 400mg gabapentin fast delivery, insulin resistance medicine to stop vomiting cheap gabapentin 600mg line, type 2 diabetes mellitus section 8 medications buy cheap gabapentin 400 mg, and cardiovascular disease stroke treatment 60 minutes cheap 600 mg gabapentin. Postmaturity refers to an infant born of a post-term pregnancy medications for fibromyalgia discount 300 mg gabapentin with mastercard, defined as a pregnancy beyond 42 weeks of gestation lb 95 medications effective gabapentin 300 mg. Dysmaturity may occur in term or preterm infants and describes an infant who exhibits characteristics of placental insufficiency, such as loss of subcutaneous fat and muscle mass or meconium staining of the amniotic fluid, skin, and nails. By 32 weeks of gestation, the fetus consistently responds to temperature, pressure, and pain. By 25 weeks of gestation, response to intense vibroacoustic stimuli can be elicited. Sensitivity and frequency resolution approach adult level by 30 weeks of gestation and are indistinguishable from the adult by term. Five parameters are assessed: n Fetal breathing movements (one or more episodes of rhythmic fetal breathing movement of 30 seconds or more within 30 minutes) n Gross body movements (three or more discrete body or limb movements within 30 minutes) n Fetal tone (one or more episodes of extension of a fetal extremity with return to flexion, or opening or closing of a hand) n Qualitative amniotic fluid volume (a single pocket of amniotic fluid exceeding 2 cm) n Reactive fetal heart rate by nonstress test the presence of a normal assessment is scored as 2 points, and the absence of the finding is scored as 0. A regular pattern of fetal breathing movements is observed by 20 to 21 weeks of gestation. Fetal breathing movement is controlled by centers on the ventral surface of the fourth ventricle. As a result, the presence of fetal breathing indicates an intact central nervous system. Fetal breathing movements appear to assist the movement of fetal lung fluid into the amniotic cavity and also tone the respiratory muscles for the initiation of breathing at the time of birth. How does one differentiate pathologic absence of fetal breathing movements from periodic breathing that occurs during fetal sleep Nonreactive fetal heart rate activity should be the first sign of fetal compromise, followed by absence of fetal breathing movements, gross body movement, and, lastly, tone. Minor anomalies are those that may have cosmetic significance but rarely require medical or significant surgical treatment. In contrast, major anomalies are those that have a serious impact on the health, development, or functional ability of the affected individual. Although some women-such as those with diabetes, those born with a congenital anomaly, or those who have had a prior affected child-are at higher risk of having a baby with a birth defect, the majority of infants with congenital anomalies are born to women with no risk factors. The goal of prenatal screening is the early detection of major birth defects before delivery. Prenatal detection of anomalies allows time for referral to a tertiary care facility for consultation with appropriate pediatric subspecialists, delivery planning, and coordination of neonatal care. Although the majority of anomalies are detected in the second or third trimester, some major birth defects can be diagnosed already in the first trimester. Measurement of the nuchal translucency between 11 and 14 weeks of gestation can be used as an early screening tool for aneuploidy, fetal congenital heart disease, and other structural anomalies. Although many birth defects can be diagnosed prenatally, some major and many minor anomalies are not detected until birth (or later). In general, major anomalies are generally more likely to be detected before birth than minor abnormalities, but some major anomalies-such as congenital heart disease and orofacial clefts-have relatively low detection rates despite routine prenatal screening. In addition to the nature of the ultrasound facility and the experience of the sonographer or sonologist, ultrasound detection rates can also be affected by maternal factors, such as obesity and abdominal wall scarring, which can make it difficult to see fetal structures prenatally. Furthermore, some anomalies cannot be detected early in gestation either because the structure is not developed at the time the ultrasound is performed or because the abnormality may develop after the scan was done. Aside from two-dimensional ultrasound, what other imaging tools can be used to diagnose anomalies prenatally Fetal echocardiogram is recommended in all cases of suspected fetal congenital heart disease as well as in women at increased risk of fetal cardiac anomalies. Usefulness of additional fetal magnetic resonance imaging in the prenatal diagnosis of congenital abnormalities. The severity of clinical presentation is modulated by the degree of bidirectional flow from superficial anastomoses. Complications specific to the recipient twin are polycythemia, systemic hypertension, biventricular cardiac hypertrophy, and congestive heart failure. The donor twin is at risk for growth failure, anemia, high-output cardiac failure, and hydrops. Both twins are at increased risk of congenital anomalies, in utero demise, and cerebral palsy. When cardiac output is compromised, maternal antiarrhythmic therapy may be initiated. If the fetal arrhythmia remains refractory, direct fetal therapy with antiarrhythmic medications may be considered. Cystic adenomatoid malformation volume ratio predicts outcome in prenatally diagnosed cystic adenomatoid malformation of the lung. Congenital diaphragmatic hernia: an evaluation of the prognostic value of the lung-to-head ratio and other prenatal parameters. Congenital diaphragmatic hernia: An evaluation of the prognostic value of the lung-to-head ratio and other prenatal parameters. The major neonatal diseases that may benefit from fetal intervention are listed in Table 2-2. Fetal intervention for congenital diaphragmatic hernia is currently investigational. What are the key principles in determining the potential value of a prenatal therapy for a fetal anomaly What are the major considerations for fetal intervention in cases of congenital cardiac lesions Right-sided lesions n Pulmonary atresia/severe pulmonary valve stenosis with intact ventricular septum: In utero balloon valvuloplasty may preserve cardiac function by decompressing the right ventricular load and ensuring adequate right-sided heart blood flow and right ventricular growth. The procedure is currently used for the delivery and management of fetal airway compromise resulting from extrinsic mass compression or intrinsic airway defect. Maternal mirror syndrome is a preeclampsia-like state that occurs in the setting of fetal hydrops; other terms that are used interchangeably are Ballantyne syndrome and pseudotoxemia. Although the symptoms are similar to those of true preeclampsia, mothers with this syndrome typically exhibit anemia caused by hemodilution rather than hemoconcentration and do not commonly develop thrombocytopenia. Amniocentesis is a procedure that involves the aspiration of amniotic fluid from the amniotic sac during pregnancy. National Institutes of Child Health and Human Development National Registry for Amniocentesis Study Group. Amniocentesis can be classified by the time in the pregnancy when it is done and by its indication. In the second trimester amniocentesis is most often performed for genetic indications. However, early amniocentesis is gradually being abandoned because it is associated with a high rate of subsequent amniotic fluid leakage (premature rupture of membranes). In the third trimester amniocentesis is most often performed for fetal lung maturity testing. In the setting of preterm labor or preterm rupture of the membranes, amniocentesis can be used to evaluate possible intraamniotic infection or inflammation. Amniocentesis can be helpful in reducing amniotic fluid volume in the setting of polyhydramnios with either premature labor or maternal respiratory difficulty. It is also used for twin-twin transfusion associated with polyhydramnios in one fetus. In this setting amniocentesis is used to determine whether the fetus is Rh positive or positive for the sensitized antigen so that testing can be avoided if the fetus is not at risk. Randomised trial to assess safety and fetal outcome of early and mid-trimester amniocentesis. Miscarriage risk from amniocentesis performed for abnormal maternal serum screening. Fetal loss rate after chorionic villus sampling and amniocentesis: an 11-year national registry study. Immediate and preliminary (1- to 3-day) results can be obtained for cytogenetics using fluorescence in situ hybridization. Definitive chromosome studies require cultured amniocytes (cells from amniotic fluid) and therefore usually require 10 to 14 days. One or more cells are removed from the developing embryo 2 to 4 days after fertilization and then analyzed. When the parents are carriers of an adverse genetic trait, it may obviate the need for testing during pregnancy. It is not considered "diagnostic" for karyotype, however, because of the high rate of mosaicism. Introduced in late 2011, this testing is currently very expensive and recommended only for women who have one or more risk factors for aneuploidy (based on maternal serum screening, ultrasound screening, advanced maternal age, family history). Other defects, such as major cardiac defects, can be seen most of the time depending on the sophistication of the center, type of equipment, patient body habitus, and other factors. In addition, many fetuses with chromosome abnormalities including trisomy 13, 18, and 21 syndromes will have findings that will lead to subsequent amniocentesis to confirm the diagnosis. Before conception: preimplantation diagnosis (in in vitro fertilization pregnancies) 2. Depending on which combination of tests is performed, detection of Down syndrome is 60% to 95% with a 5% screen positive rate. Reasonable detection rates are also achieved for trisomy 18 and open neural tube defects. Randomised study of risk of fetal loss related to early amniocentesis versus chorionic villus sampling. The preterm prediction study: cervical lactoferrin concentration, other markers of lower genital tract infection, and preterm birth. The preterm prediction study: granulocyte colony-stimulating factor and spontaneous preterm birth. National Institute of Child Health and Human Development Maternal-Fetal Units Network. The preterm prediction study: sequential cervical length and fetal fibronectin testing for the prediction of spontaneous preterm birth. National Institute of Child Health and Human Development MaternalFetal Medicine Units Network. Third-trimester hemorrhage refers to any bleeding from the genital tract during the third trimester of pregnancy. In practice, it refers to any bleeding that occurs from the time of viability. The common causes are classified as placenta previa (7%), placental abruption (13%), and other bleeding (80%), including local lesions of the lower genital tract, vasa previa, early labor, trauma, neoplasia, and marginal placental separation. Ultrasound visualization is the method of choice for diagnosis of placenta previa. Multiple reports show a transvaginal approach to be safe and superior in its accuracy compared with transabdominal ultrasound. Abnormal placentation: evidence-based diagnosis and management of placenta previa, placenta accreta, and vasa previa. Digital vaginal examination is not recommended when bleeding occurs until placenta previa is excluded by performing an ultrasound examination. Pearls If ultrasound is not available in late pregnancy, a useful approach is the double setup examination in which two teams prepared to administer anesthesia are in the operating room. If bleeding results from a placenta previa, an emergency cesarean section is performed by the second team. Complete placenta previa is detected in 5% of second-trimester gestations, with 90% resolving by term; partial placenta previa is seen in 45% of second-trimester gestations and resolves in more than 95% of cases. This apparent resolution is most likely related to the growth of the lower uterine segment in late pregnancy, so the placenta appears to move away from the os. Placental abruption is the separation of the normally implanted placenta before the birth of the fetus. It is termed a revealed abruption when vaginal bleeding is present (90%) and a concealed abruption if no bleeding is visible (10%). It is uniquely dangerous to the fetus and the mother because of its serious pathophysiologic sequelae. Abruption severe enough to cause fetal death is less common (approximately 1 in 420 deliveries). Women who have a placental abruption severe enough to cause fetal death have a 7% risk of a similar outcome in a subsequent pregnancy. Most mortality is caused by prematurity n Fetomaternal hemorrhage with resultant fetal anemia: more common in abruption associated with maternal trauma 16. Fetomaternal hemorrhage is caused by a disruption of the normal barrier at the placental-decidual interface. It may occur with abruptio placentae; however, it occurs more commonly with abruptio placentae associated with maternal trauma, with maternal trauma without abruptio placentae, or spontaneously without an apparent precipitating event. Approximately 5% of stillbirths without apparent cause are the result of fetomaternal hemorrhage. In patients with spontaneous fetomaternal hemorrhage, the presenting symptom is decreased fetal movement. Treatment can consist of immediate delivery if the fetus is near term or intrauterine transfusion if the fetus is premature and no abruption is apparent. Bleeding at any time during pregnancy is cause for concern and should always be carefully investigated. During the third trimester, however, onset of hemorrhage may be particularly ominous.
Syndromes
This is important so that in a stress response medications routes gabapentin 600 mg discount, such as the flight or fight response (p medications not to be crushed gabapentin 800 mg line. The length of the vessels and viscosity of blood also contribute to peripheral resistance medicine 3601 discount 600 mg gabapentin otc, but in health these are constant and are therefore not significant determinants of changes in blood flow medications during pregnancy cheap gabapentin 800 mg without a prescription. The ability of an organ to control its own blood flow according to need is called autoregulation symptoms of the flu discount 600mg gabapentin. Some organs jnc 8 medications cheap gabapentin 400 mg fast delivery, including the central nervous system, liver and kidneys receive proportionately higher blood flow as a matter of course. Other tissues, such as resting skeletal muscle, receive much less, but their blood supply can increase by as much as 20-fold during heavy exercise. Other examples include blood flow through the gastrointestinal tract increasing after a meal to allow for increased activity in the tract, and adjustments to blood flow through the skin in the control of body temperature (p. Blood flow is increased through individual organs by vasodilation of the vessels supplying it, and decreased through vasoconstriction. The main mechanisms associated with this local control of blood flow include: release of metabolic waste products. An active tissue releases more wastes than a resting one, and increased levels of waste increase blood flow into the area tissue temperature: a rise in metabolic activity increases tissue temperature, which in turn causes vasodilation release of vasodilator chemicals. Inflamed and metabolically active tissues release a number of vasodilators, which increase blood supply to the area. One important vasodilator is nitric oxide, which is very short lived, but which is important in opening up the larger arteries supplying an organ. Other agents include substances released in the inflammatory response, such as histamine and bradykinin (p. The sympathetic hormone adrenaline (epinephrine), released from the adrenal medulla, is a powerful vasoconstrictor. Oxygen is carried from the lungs to the tissues in combination with haemoglobin as oxyhaemoglobin. Exchange in the tissues takes place between blood at the arterial end of the capillaries and the tissue fluid and then between the tissue fluid and the cells. Oxygen diffuses down its concentration gradient, from the oxygen-rich arterial blood, into the tissues, where oxygen levels are lower because of constant tissue consumption. Oxyhaemoglobin is an unstable compound and breaks up (dissociates) easily to liberate oxygen. Carbon dioxide is one of the waste products of cell metabolism and, towards the venous end of the capillary, it diffuses into the blood down the concentration gradient. Exchange of other substances the nutrients required by the cells of the body are transported round the body in the blood plasma. In passing from the blood to the cells, the nutrients pass through the semipermeable capillary walls into the tissue fluid bathing the cells, then through the cell membrane into the cell. The mechanism of the transfer of water and other substances from the blood capillaries depends mainly upon diffusion and osmosis. Diffusible substances include dissolved oxygen and carbon dioxide, glucose, amino acids, fatty acids, glycerol, vitamins, mineral salts and water. The force of the osmotic pressure depends on the number of non-diffusible particles in the solutions separated by the membrane. The main substances responsible for the osmotic pressure between blood and tissue fluid are the plasma proteins, especially albumin. Capillary fluid dynamics the two main forces determining overall fluid movement across the capillary wall are the hydrostatic pressure (blood pressure), which tends to push fluid out of the bloodstream, and the osmotic pressure of the blood, which tends to pull it back in, and is due mainly to the presence of plasma proteins. At the arterial end, the hydrostatic pressure is about 5 kPa (35 mmHg), and the opposing osmotic pressure of the blood is only 3 kPa (25 mmHg). The overall force at the arterial end of the capillary therefore drives fluid out of the capillary and into the tissue. Blood flow is slower than at the arterial end because the hydrostatic pressure drops along the capillary to only 2 kPa (15 mmHg). The osmotic pressure remains unchanged at 3 kPa (25 mmHg) and, because this now exceeds hydrostatic pressure, fluid moves back into the capillary. This transfer of substances, including water, to the tissue spaces is a dynamic process. As blood flows slowly through the large network of capillaries from the arterial to the venous end, there is constant change. Of the 24 litres or so of fluid that moves out of the blood across capillary walls every day, only about 21 litres returns to the bloodstream at the venous end of the capillary bed. The excess is drained away from the tissue spaces in the minute lymph capillaries which originate as blind-end tubes with walls similar to , but more permeable than, those of the blood capillaries. Extra tissue fluid and some cell waste materials enter the lymph capillaries and are eventually returned to the bloodstream (Ch. Heart Learning outcomes After studying this section, you should be able to: describe the structure of the heart and its position within the thorax trace the circulation of the blood through the heart and the blood vessels of the body outline the conducting system of the heart relate the electrical activity of the cardiac conduction system to the cardiac cycle describe the main factors determining heart rate and cardiac output. It lies obliquely, a little more to the left than the right, and presents a base above, and an apex below. The apex is about 9 cm to the left of the midline at the level of the 5th intercostal space, i. Structure the heart wall the heart wall is composed of three layers of tissue. The outer sac consists of fibrous tissue and the inner of a continuous double layer of serous membrane. The outer fibrous sac is continuous with the tunica adventitia of the great blood vessels above and is adherent to the diaphragm below. The outer layer of the serous membrane, the parietal pericardium, lines the fibrous sac. The inner layer, the visceral pericardium, or epicardium, which is continuous with the parietal pericardium, is adherent to the heart muscle. A similar arrangement of a double membrane forming a closed space is seen also with the pleura, the membrane enclosing the lungs. It secretes serous fluid into the space between the visceral and parietal layers, which allows smooth movement between them when the heart beats. The space between the parietal and visceral pericardium is only a potential space. In health the two layers lie closely together, with only the thin film of serous fluid between them. Myocardium the myocardium is composed of specialised cardiac muscle found only in the heart. This arrangement gives cardiac muscle the appearance of being a sheet of muscle rather than a very large number of individual cells. Because of the end-to-end continuity of the fibres, each one does not need to have a separate nerve supply. This reflects the amount of work each chamber contributes to the pumping of blood. Fibrous tissue in the heart the myocardium is supported by a network of fine fibres that run through all the heart muscle. In addition, the atria and the ventricles are separated by a ring of fibrous tissue, which does not conduct electrical impulses. Consequently, when a wave of electrical activity passes over the atrial muscle, it can only spread to the ventricles through the conducting system that bridges the fibrous ring from atria to ventricles (p. It is a thin, smooth, glistening membrane that permits smooth flow of blood inside the heart. It consists of flattened epithelial cells, and it is continuous with the endothelium lining the blood vessels. Interior of the heart the heart is divided into a right and left side by the septum. Each side is divided by an atrioventricular valve into the upper atrium and the ventricle below. The atrioventricular valves are formed by double folds of endocardium strengthened by a little fibrous tissue. The right atrioventricular valve (tricuspid valve) has three flaps or cusps and the left atrioventricular valve (mitral valve) has two cusps. Flow of blood in the heart is one way; blood enters the heart via the atria and passes into the ventricles below. The valves between the atria and ventricles open and close passively according to changes in pressure in the chambers. During ventricular systole (contraction) the pressure in the ventricles rises above that in the atria and the valves snap shut, preventing backward flow of blood. The valves are prevented from opening upwards into the atria by tendinous cords, called chordae tendineae, which extend from the inferior surface of the cusps to little projections of myocardium into the ventricles, covered with endothelium, called papillary muscles. This blood passes via the right atrioventricular valve into the right ventricle, and from there is pumped into the pulmonary artery or trunk (the only artery in the body which carries deoxygenated blood). The opening of the pulmonary artery is guarded by the pulmonary valve, formed by three semilunar cusps. This valve prevents the backflow of blood into the right ventricle when the ventricular muscle relaxes. After leaving the heart the pulmonary artery divides into left and right pulmonary arteries, which carry the venous blood to the lungs where exchange of gases takes place: carbon dioxide is excreted and oxygen is absorbed. Two pulmonary veins from each lung carry oxygenated blood back to the left atrium. Blood then passes through the left atrioventricular valve into the left ventricle, and from there it is pumped into the aorta, the first artery of the general circulation. The opening of the aorta is guarded by the aortic valve, formed by three semilunar cusps. From this sequence of events it can be seen that the blood passes from the right to the left side of the heart via the lungs, or pulmonary circulation. However, it should be noted that both atria contract at the same time and this is followed by the simultaneous contraction of both ventricles. The muscle layer of the walls of the atria is thinner than that of the ventricles. The atria, usually assisted by gravity, propel the blood only through the atrioventricular valves into the ventricles, whereas the ventricles actively pump the blood to the lungs and round the whole body. The pulmonary trunk leaves the heart from the upper part of the right ventricle, and the aorta leaves from the upper part of the left ventricle. The coronary arteries receive about 5% of the blood pumped from the heart, although the heart comprises a small proportion of body weight. This large blood supply, especially to the left ventricle, highlights the importance of the heart to body function. The coronary arteries traverse the heart, eventually forming a vast network of capillaries. Venous drainage Most of the venous blood is collected into a number of cardiac veins that join to form the coronary sinus, which opens into the right atrium. The remainder passes directly into the heart chambers through little venous channels. Conducting system of the heart the heart possesses the property of autorhythmicity, which means it generates its own electrical impulses and beats independently of nervous or hormonal control, i. However, it is supplied with both sympathetic and parasympathetic autonomic nerve fibres, which increase and decrease respectively the intrinsic heart rate. In addition, the heart responds to a number of circulating hormones, including adrenaline (epinephrine) and thyroxine. Small groups of specialised neuromuscular cells in the myocardium initiate and conduct impulses, causing coordinated and synchronised contraction of the heart muscle. The sinoatrial cells generate these regular impulses because they are electrically unstable. This instability leads them to discharge (depolarise) regularly, usually between 60 and 80 times a minute. This depolarisation is followed by recovery (repolarisation), but almost immediately their instability leads them to discharge again, setting the heart rate. Within the ventricular myocardium the branches break up into fine fibres, called the Purkinje fibres. Nerve supply to the heart As mentioned earlier, the heart is influenced by autonomic (sympathetic and parasympathetic) nerves originating in the cardiovascular centre in the medulla oblongata. Parasympathetic stimulation reduces the rate at which impulses are produced, decreasing the rate and force of the heartbeat. Stages of the cardiac cycle Taking 74 bpm as an example, each cycle lasts about 0. The superior vena cava and the inferior vena cava transport deoxygenated blood into the right atrium at the same time as the four pulmonary veins bring oxygenated blood into the left atrium. The atrioventricular valves are open and blood flows passively through to the ventricles. This delay means that the mechanical result of atrial stimulation, atrial contraction, lags behind the electrical activity by a fraction of a second. This allows the atria to finish emptying into the ventricles before the ventricles begin to contract. This results in a wave of contraction which sweeps upwards from the apex of the heart and across the walls of both ventricles pumping the blood into the pulmonary artery and the aorta (ventricular systole 0. The high pressure generated during ventricular contraction is greater than that in the aorta and forces the atrioventricular valves to close, preventing backflow of blood into the atria. After contraction of the ventricles there is complete cardiac diastole, a period of 0. During this time the myocardium recovers in preparation for the next heartbeat, and the atria refill in preparation for the next cycle. The valves of the heart and of the great vessels open and close according to the pressure within the chambers of the heart.
At its proximal end administering medications 7th edition ebook buy gabapentin 100mg mastercard, the ulna presents the olecranon process treatment 4 pimples cheap gabapentin 100 mg on-line, found at the proximal and posterior end of the semilunar (trochlear) notch medicine nobel prize 2015 cheap 600mg gabapentin otc. The coronoid process is seen at the distal and anterior end of the semilunar notch medications for high blood pressure gabapentin 100mg visa. Specifically medical treatment 80ddb generic gabapentin 800 mg mastercard, the semilunar notch of the ulna articulates with the trochlea of the distal medial humerus symptoms esophageal cancer trusted 300mg gabapentin. The capitulum is lateral to the trochlea and articulates with the radial head (Saia, p. The lateral aspect of the distal humerus presents a raised, smooth, rounded surface, the capitulum (E), that articulates with the superior surface of the radial head (A). The trochlea (F) is on the medial aspect of the distal humerus and articulates with the semilunar notch of the ulna. Just proximal to the capitulum and trochlea are the lateral (D) and medial (C) epicondyles; the medial is more prominent and palpable. The coronoid fossa is found on the anterior distal humerus and functions to accommodate the coronoid process (B) with the elbow in flexion (Saia, p. In general, at 1 m from the patient, the intensity is reduced by a factor of 1000, to approximately 0. Successive scatterings can render the intensity to unimportant levels (Bushong, p. Anatomic parts within the body are at various distances from the image receptor and therefore have various degrees of magnification. The oblique position (approximately 15 degrees) opens the joint closest to the image receptor. The lateral projection of the humerus places the shoulder in extreme internal rotation with the epicondyles perpendicular to the image receptor and demonstrates the lesser tubercle in profile (Ballinger & Frank, Vol 1, p. Left and right decubitus positions are usually employed only in double-contrast barium enemas to better demonstrate double contrast of the medial and lateral walls of the ascending and descending colon (Ballinger & Frank, Vol 2, pp. Patients who have suffered burns have lost a very important means of protection, their skin, and therefore have increased susceptibility to bacterial invasion. Patients whose immune systems are depressed lose the ability to combat infection, and hence are more susceptible to infection. A laser camera records the displayed image by exposing a film with laser light; it can also record several images on one film. There are, therefore, fewer x-ray photons interacting with the image receptor, with a resulting decrease in optical/radiographic density as grid ratio increases. Scale of contrast would decrease with an increase in grid ratio (Carlton & Adler, p. Once patients understand what is needed, most will cooperate to the best of their ability (by suspending respiration and holding still for the exposure). Certain body functions and responses, such as heart action, peristalsis, pain, and muscle spasm, cause involuntary motion uncontrollable by the patient. The best way to control involuntary and voluntary motion is by always selecting the shortest possible exposure time. Voluntary motion may also be minimized by careful explanation, immobilization, and (as a last resort and only in certain cases) restraint (Ballinger & Frank, Vol 1, pp. The vertebra prominens is at the level of the seventh cervical vertebra (Ballinger & Frank, Vol 1, p. Circuit breakers and fuses are circuit devices used to protect circuit elements from overload. In case of current surge, the circuit will be broken (opened), thus preventing equipment damage. The cassette front should be made of a sturdy material with a low atomic number, because attenuation of the remnant beam is undesirable. The high atomic number of tungsten makes it inappropriate as a cassette front material (Selman, p. The pelvic outlet is wider and more circular in the female, the ischial tuberosities and acetabula are farther apart, the angle formed by the pubic arch is also greater in the female. This may be accomplished with the patient lying on either the affected or unaffected side (usually affected), that is, mediolateral or lateromedial. The talofibular articulation is best demonstrated in the medial oblique projection of the ankle (Ballinger & Frank, Vol 1, p. A foreign body in the cassette or within the body part will cast its image on the radiographic image. As the exposed film is removed from the cassette, static electrical discharge will expose the film in a characteristic manner. Processor artifacts are not placed on the film during image formation, but rather during chemical processing. Several kinds of artifacts can be produced by careless handling during production of the radiographic image. Tree-like, branching black marks on a radiograph are usually caused by static electrical discharge, especially prevalent during cold dry weather (Saia, p. Radiographic density is directly proportional to mAs (milliampere-seconds); if the mAs is cut in half, the radiographic density will decrease by one-half. Although kilovoltage is used primarily to regulate radiographic contrast, it may also be used to regulate radiographic density in variable kV (kilovolts) techniques, according to the 15% rule (Selman, p. A penetrometer (aluminum step-wedge) is used to illustrate the effect of kV on contrast. A star pattern is used to measure resolving power of the imaging system (Selman, pp. The crash cart is a supply cart with various medications and equipment necessary for treating a patient who is suffering from a myocardial infarction or other serious medical emergencies. It is periodically checked and restocked, usually by nursing, although radiographers may be responsible for a daily check of the plastic throwaway locks. These locks are used to ensure that the cart has not been tampered with or supplies inadvertently used in nonemergency situations. A resuscitation bag is used for ventilation, as during cardiopulmonary resuscitation (Tortora & Derrickson, p. Cephalad refers to that which is toward the head, and caudad to that which is toward the feet. Structures close to the source or beginning are said to be proximal, while those lying close to the midline are said to be medial (Ballinger & Frank, Vol 1, p. One electron group initiates immediate luminescence during the excited state of Eu2+. However, the "heel" of the focal track prevents x-ray photons from diverging toward the anode end of the tube. This results in varying intensity from anode to cathode, fewer photons at the anode end, and more photons at the cathode end. With the arm abducted, the elbow flexed, and hand supinated, much of the scapula is drawn away from the ribs. The patient should not be rotated toward the affected side, as this causes superimposition of ribs on the scapula. The exposure is made during quiet breathing to obliterate pulmonary vascular markings (Ballinger & Frank, Vol 1, p. This occurs in cases of trauma to the central nervous system resulting in decreased arterial resistance and pooling of blood in peripheral vessels. Cardiogenic shock is related to cardiac failure, as a result of interference with heart function. It can occur in cases of cardiac tamponade, pulmonary embolus, or myocardial infarction. Hypovolemic shock is related to loss of large amounts of blood, from either internal bleeding or hemorrhage associated with trauma. Septic shock, as well as anaphylactic shock, is generally classified as vasogenic shock (Torres et al. The central ray enters the plantar surface and exits the dorsal surface (Ballinger & Frank, Vol 1, pp. The fourth lumbar vertebra is approximately at the same level as the iliac crest (Saia, p. Once the film is processed, a densitometer is needed to read the resulting densities. Log relative exposure is charted along the x (horizontal) axis; an increase in log relative exposure of 0. Optical density is plotted on the y (vertical) axis and represents the amount of light transmitted through a film compared to the amount of light striking the film (expressed as a logarithm) (Bushong, p. First, if the high-speed electron is attracted by the nucleus of a tungsten atom and changes its course, the energy given up as the electron is "braked" in the form of an x-ray photon. This is called bremsstrahlung ("braking") radiation and is responsible for the majority of x-ray photons produced at the conventional tungsten target. Second, a high-speed electron may eject a tungsten K-shell electron, leaving a vacancy in the shell. An electron from a higher energy level, for example, the L shell, drops down to fill the vacancy, emitting the difference in energy as a K characteristic ray. Characteristic radiation comprises only approximately 15% of the primary beam (Saia, p. The central ray is directed through the sphenoid sinuses and exits the open mouth. The routine parietoacanthial projection (with mouth closed) is used to demonstrate the maxillary sinuses projected above the petrous pyramids. Because a great deal of heat is produced at the target, the material should have a high melting point so as to avoid damage to the target surface. The cathode filament receives low-voltage current to heat it to the point of thermionic emission. Then high voltage is applied to drive the electrons across to the focal track (Selman, pp. Radiographic density can vary considerably in appearance depending on which phase of respiration the exposure is made (Ballinger & Frank, Vol 1, p. The opposite is true of the hypersthenic individual: organs are located high, transverse, and laterally (Saia, p. The entrance roller is the first roller of the transport system located at the end of the feed tray; this is where the microswitch that determines amount of replenishment is located. Accurate adjustment of these structures will usually allow good visualization of the odontoid process and the atlantoaxial articulation. Too much flexion superimposes teeth on the odontoid process; too much extension superimposes the base of the skull on the odontoid process (Bontrager, p. Vertigo refers to the feeling of "whirling" or the sensation that the room is spinning. Some possible causes of vertigo include inner ear infection or an acoustic neuroma. Urticaria is a vascular reaction resulting in dilated capillaries and edema that cause the patient to break out in hives. An aura may be classified as either a feeling or a motor response (such as flashing lights, tasting metal, smelling coffee) that precedes an episode such as a seizure or a migraine headache (Adler & Carlton, p. Positive, or radiopaque, contrast agents have a higher atomic number than the surrounding soft tissue, resulting in a greater attenuation or absorption of x-ray photons, thereby producing a higher radiographic contrast. Because the atomic number of air is also quite different from that of soft tissue, an artificially high subject contrast can be produced. The advantage of carbon dioxide over air is that it is absorbed more rapidly by the body (Bushong, p. Unless preventative measures are taken, severe abdominal cramping and urge to defecate can occur. The Trendelenburg position is frequently used to separate redundant loops of bowel (Ballinger & Frank, Vol 2, p. It also states that cells with a high rate of proliferation (mitosis) are more sensitive to radiation. Radiation exposure, especially between the second and sixth week following conception (the period of major organogenesis) can cause organ damage, mental and growth retardation, microcephaly, and genital deformities (Sherer et al. However, as more scattered radiation is absorbed, more primary radiation is absorbed as well. This accounts for the increase in mAs required when changing from 8:1 to 16:1 grid. Additionally, precise centering and positioning become more critical; a small degree of inaccuracy is more likely to cause grid cutoff in a high-ratio grid (Selman, pp. The radiographer selects a processing algorithm by selecting the anatomical part and particular projection on the computer. The filter (made of aluminum or lead acrylic) is constructed so as to absorb much of the primary radiation that would expose the low-tissuedensity area, while allowing the primary radiation to pass unaffected to the high-tissue-density area.
Because grids remove many x-ray photons that would have contributed to image density treatment ibs order 600 mg gabapentin mastercard, the addition of a grid requires a significant increase in mAs symptoms adhd gabapentin 400mg free shipping. When implementing a grid or changing grid ratio medications not to take when pregnant generic 800mg gabapentin fast delivery, a gridconversion factor must be used to determine required mAs change in order to avoid undesirable changes in radiographic/image density symptoms 14 days after iui gabapentin 100mg with visa. In general-purpose radiographic tubes conventional medicine order 600mg gabapentin otc, the glass envelope usually accounts for approximately 0 treatment dynamics discount 800 mg gabapentin amex. This type of filter serves to remove the diagnostically useless xray photons that contribute only to patient (skin) dose. Because this radiation is "soft" (low energy) and would not reach the image receptor anyway, the x-ray tube total filtration has no effect on radiographic/image density. Compensating filters can be used to provide more uniform radiographic density when radiographing structures with widely different attenuation coefficients (x-ray absorbing properties) because of thickness or tissue composition. Usually made of aluminum or clear leaded plastic, they slide into tracks in the collimator housing similar to a cylinder cone, or attach magnetically to the undersurface of the collimator housing. If an x-ray image of a foot demonstrates well-exposed tarsals, the toes will frequently be overexposed. If the exposure is adjusted to improve the image of the toes, the tarsals will then be underexposed. Abdominal tissues often shift to the dependent side in the decubitus position, making the "down" side thicker than the "up" side. The thicker lateral portions of the trough reduce the intensity of the beam directed toward the lungs, while the thinner central portion does not attenuate the beam directed to the more dense mediastinal structures. The filter is attached to the collimator housing so that the thin portion is over the tarsals and the thick portion over the toes. Exposure factors appropriate for tarsals are used, and the thick portion of the filter removes enough of the primary beam to prevent overexposure of the toes. A wedge filter is also useful for femur examinations and decubitus abdomen images. A trough filter can be used in chest radiography to permit visualization of the denser mediastinal structures without overexposing the more radiolucent lungs and pulmonary vascular markings. Another simple, yet effective, application of compensating filtration is the use of a saline or similar solution bag. The saline bag is placed over the thinner body part and serves to filter out excessive exposure. Compensating filters are available in various shapes: their thicker portions absorb more of the x-ray beam and are therefore placed over thinner body parts, while their thinner portions (absorbing fewer x-rays) are placed over thicker body parts. The radiographer must be aware of these variants and processes to make an appropriate and accurate selection of technical factors. Walter Mills presented a paper at the American Roentgen Ray Society meeting in Chicago (published in American Journal of Roentgenology, April 1917) describing "The Relation of Bodily Habitus to Visceral Form, Position, Tonus and Motility. He noted that most physicians came into the field prejudiced by their early anatomic teachings and had fixed conceptions, "which the revelations of the roentgen ray ruthlessly outraged. Knowledge of each of the body types and its associated tissue characteristics, position and tonus of associated organs, and so on, helps us position more accurately and select appropriate technical factors. The same body part, such as the stomach, in two different individuals will require very different central ray points of entry if one individual is hypersthenic and the other asthenic. A particular body part, such as the shoulder, might measure the same on two different individuals, yet it may not be appropriate to select identical exposure factors for each if one is a muscular sthenic build and the other a hyposthenic type with little muscle tone. Other factors that influence radiographic density, and consequently the selection of technical factors, are age, gender, and pathology. Various abnormal pathologic conditions, disease processes, and trauma can affect tissue density and, hence, radiographic density. Normal variants of muscle development result from different lifestyles, occupations, and age, and will affect radiographic density. Some pathologic conditions are referred to as destructive, such as osteoporosis and conditions involving necrosis or atrophy. These conditions can cause an undesirable increase in radiographic density unless they are recognized and appropriate changes made in exposure factors. Other conditions such as ascites, rheumatoid arthritis, and Paget disease are additive, and an increase in exposure factors is required to maintain adequate radiographic density. Abnormal density differences exist as a result of trauma or pathologic conditions. The radiographer must be knowledgeable about the conditions affecting normal and abnormal changes in tissue density to make accurate selection of technical factors. Three-phase equipment has a small voltage ripple, and thus produces more high-energy x-ray photons. Therefore, if two x-ray images were made of the same part and using the same factors, one made with a single-phase machine and one with a three-phase machine, the three-phase image would show considerably more radiographic density. Consequently, to reproduce similar image densities when using different generators, exposure factor adjustment is necessary. If 92 kV and 60 mAs were used for a particular abdominal exposure using single-phase equipment, what mAs would be required to produce a similar image using three-phase, six-pulse equipment The correction table in the box in this section indicates that only two-thirds of the original single-phase mAs would be required to produce similar radiographic/image density with three-phase equipment. When technical factors are modified for single-phase or threephase changes, it is usually the mAs that is adjusted; however, kV adjustment is also workable. Changing from single-phase to three-phase requires a 12% decrease in kV; conversely, changing from three-phase to single-phase requires a 12% increase in kV. Conventional 60-Hz full-wave rectified power is converted to a higher frequency of 500 to 25 000 Hz in the most recent generator design-the high-frequency generator. The high-frequency generator is small in size, in addition to producing an almost constant potential waveform. The reverse is also true: as field size increases, image density increases as a result of increased production of scattered radiation fog. Therefore, as changes are made in the size of the irradiated field, an accompanying change in mAs is required to maintain the same image density. When using general x-ray tubes at standard distances, the heel effect is noticeable only when imaging parts of uneven thickness, such as the femur and thoracic spine. In these cases, the heel effect may be used to advantage by placing the thicker body portion under the cathode end of the x-ray beam, thus having the effect of "evening out" tissue densities. Note the gradual increase in radiographic density toward the cathode end of the beam. Radiographic density is also directly related to length of development and replenishment rate; that is, density increases as development time increases or as replenishment rate increases. Although a diagnostic radiograph might be produced by reducing the film exposure, higher-than-recommended processing temperatures are not advised because they can produce inconsistent results. The relative position of the lower temperature (90 F) curve is to the right of the optimal temperature (95 F) curve; to achieve the same density, the exposure must be increased to compensate for decreased development. The 100 F curve illustrates a shift to the left of the optimal curve, illustrating that less exposure is required to compensate for decreased development. The anode heel effect can be used to compensate for a difference in tissue density/thickness. Radiographic density increases as developer temperature increases, and as the replenishment rate and/or length of development increase. Grid ratio is defined as the relationship between the height of the lead strip and the: (A) width of the lead strip (B) distance between the lead strips (C) number of lead strips per inch (D) angle of the lead strip 2. Of the following groups of exposure factors, which will produce the greatest radiographic density If the radiographer is unable to adjust the mAs, yet needs to reduce the image density of a particular image by one-half, which of the following would best accomplish this An x-ray image demonstrating poor contrast resolution can be attributable to insufficient: 1. The term used to describe image density in digital imaging is: (A) blackening (B) gray scale (C) brightness (D) resolution 8. Each of the following changes will effectively double radiographic density, except: (A) change to 0. The lead strips are used to trap scattered radiation before it reaches the image receptor, thus decreasing the effect of scattered radiation fog on the image. Grid ratio is defined as the height of the lead strip to the distance between the strips (or width of the interspace material). Groups A and C should produce identical radiographic density, according to the inverse square law, because group C is twice the distance and four times the mAs of group A. Group B has twice the distance of group A, but only twice the mAs; it has, therefore, less density than groups A and C. Group D has the same distance as group A, and twice the mAs, making it the group of technical factors that will produce the greatest radiographic density. Thus, as distance from the source of radiation increases, exposure rate decreases. Because exposure rate and radiographic density are directly proportional, if the exposure rate of a beam directed to an image receptor is decreased, the resultant image density would be decreased proportionally. When correct adjustment of mAs is not possible, a decrease in kV by 15% will effectively halve the radiographic density. Insufficient kilovoltage would produce an image with too much (too high) contrast. The degree of resolution transferred to the image receptor is a function of the resolving power of each of the system components and is expressed in line pairs per millimeter (lp/mm). If the kV is increased by 15%, from 75 to 86 kV, image density will double according to the 15% rule. Because the original mAs was 36, reducing the speed of the system to half (from 200 to 100) will require a doubling of the mAs, to 72, in order to maintain density. Using the density maintenance formula (remember 72 is now the old mAs), we find that the required new mAs at 48 inches is 103. For example, a 12:1 ratio grid will absorb more scattered radiation than an 8:1 ratio grid. Thickness of the lead strips refers to its lead content, which is unrelated to grid ratio. When there is a big difference between shades of densities, radiographic contrast is said to be high. An electronic/digital imaging term is contrast resolution-the ability to record/see adjacent similar anatomic tissues, i. Radiographic (screen/film) contrast is the sum of subject contrast and film contrast. Subject contrast is a result of differential absorption by tissues of varying densities and thicknesses. Hence, subject contrast produces the various density differences visible on the radiographic image and is exhibited as a scale of grays having varying tones representative of differential tissue absorption. Exposure factor selection and various other methods are used to modify the effect of differential absorption properties of tissue, thereby enabling the radiographer to produce the desired scale of contrast. Film/screen subject contrast is regulated by the quality (energy, wavelength, penetrability) of x-ray photons. Images were made of a circular phantom having a variety of wedge-shaped thicknesses; a circular "lesion" of greater density is embedded in each wedge. Note that the level of contrast between adjacent areas is strongly related to the degree of visibility of the "lesions. Methods that can be used to adjust the level of contrast between adjacent areas include (1) increasing kV, (2) using compensating filtration, and (3) using lower contrast (higher latitude) film. Film contrast is affected by the manufacturing process (film type, base fog), processing conditions, and fluorescent properties of the intensifying screens. Film contrast characteristics are illustrated by the sensitometric (D log E) curve. An x-ray image exhibiting a variety/range of different shades of gray possesses long-scale (low) contrast; that is, there is little difference among the various shades. Most anatomic structures have an infinite number of details that compose the image and these structural details often represent a variety of tissue densities having different absorption properties. If the anatomic part is represented radiographically by only a few shades of gray, then many anatomic details are not being visualized at all. If, however, the image displays a wide range of gray tones, more anatomic details will be represented and visualized. A number of factors affect the production of image contrast and each is discussed individually.
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