Care should be taken as the Nyquist frequency will be different for images with different pixel sizes purchase discount propranolol cardiovascular nursing questions. Tomography based on detection of the dual annihilation photons that originate from positron emission cheap propranolol line kelly cardiovascular group. The set of projec- tions, recorded at different angles, form the data that are used for tomographic reconstruction. These instruments analyse the size of the energy signal and produce an output only if the size of the energy signal is within the range specified by the predefined energy windows. This is the process of obtaining a cross-sectional image from a set of projections. This refers to the ability of imaging systems to distinguish between two closely spaced small sources. By use of an appropriate filter the loss of resolution due to some measurable effect (e. These are a common error in reconstructed images which are caused by a localized non-uniformity in the detector. When one or both photons originating from a positron event are detected in coincidence, the path defined by the points of detection does not necessarily correspond to the point of positron emission. A gamma ray which has changed direction at least once due to Compton interaction and loss of energy in the material through which it is travelling. Fraction of the emitted gamma rays which pass through the collimator (collimator sensitivity) or are detected by the gamma camera (system sensitivity). Owing to the probability of detection, there are many more single events detected than coincidences. Cross-sectional slices of the radionuclide distribution in the patient are generated by taking images of the patient from various angles and then using these to construct the slices with a computer. It is so called since the projections from a single point describe a perfect sine wave when plotted in this form. Smoothing is an operation that involves spreading values across neighbouring pixels; the averaging effect reduces statistical noise but degrades resolution. Frequency normally refers to cyclic variations as a function of time (units: s–1). Tomography involves measurement from different angles around an object with the intention to ‘reconstruct’ an image of the internal distribution of some parameter (e. When two annihilation photons originating from a single positron annihilation are detected in coincidence (without being scattered), this is referred to as a true coincidence. Differential uniformity is a measure of the maximum rate of change over a specified distance. If one considers a digitized 3-D volume rather than a digitized 2-D image, each digital value within the volume can be considered to occupy a small volume element (e. One therefore refers to planar projections as having pixels, but to each reconstructed slice as having voxels, which also have a thickness corresponding to the spacing between adjacent slices. Purpose The purpose of this chapter is to provide nuclear medicine practitioners with general guidelines on imaging using a single photon scintillation camera. Recommendations specific to individual procedures are included in their respective procedure guidelines. Peaking The scintillation camera must be peaked correctly for the energy (energies) of the emitted photon for the radionuclide used. This should be checked at least once daily and when different radionuclides are used. The window is placed symmetrically about the photopeak, or asymmetrically if an appropriate energy correction is available, in order to minimize scattered radiation. A physicist can help in determining the limits of asymmetry that are desirable for a range of energies. Multiple energy windows The use of multiple energy windows for radionuclides that have more than one energy peak is advantageous. It is necessary to check the spatial regis- tration for the combination of windows. A physicist can help determine if the co-registration is adequately adjusted for all of the windows in order to maintain the best spatial resolution and contrast. A collimator offering adequate resolution for the most energetic photons must be used. Intrinsic uniformity should be checked for imaging multiple energy windows for such radionuclides. Again, a physicist can help determine the need for special uniformity corrections. Dual radionuclide studies When using two radionuclides in a sequential study, images from the lower energy radionuclide should be obtained first. In principle, it is possible to use multiple energy windows to image two radionuclides simultaneously. Such a technique involves many pitfalls however, and the results will depend on the equipment used and special quality control tests. The procedure must account for the detection of scatter from the higher energy photons into the energy window used for lower energy photons (normally referred to as downscatter). This procedure should be designed carefully by an individual with the necessary expertise. If, on the other hand, the two radio- nuclides are imaged separately, it will be necessary to consider the effects of motion, especially if subsequent processing of the two images assumes co-registration. Matrix size for planar imaging The matrix size is primarily dependent on resolution and is independent of counting statistics. Static imaging The specific imaging parameters for a given static acquisition will vary in accordance with the above sampling considerations, depending on the desired clinical information. For computer acquired images, matrix size will depend on the specific requirements of each type of study. For example, whole body scans require large matrices to ensure that sampling is maintained over the large area scanned. When large matrices are used for smaller areas, statistical fluctuation (noise) may be excessive unless reduced by smoothing: this will result in decreased spatial resolution. The digital appearance of smaller matrix sizes can be improved by interpolation to large matrices for display, although this will not improve resolution. Whole body imaging Scan time varies depending on the count rate and count density required. Because a whole body image covers about 200 cm, the matrix dimension along the length of the patient should be at least 512 pixels. Acquisition times greater than about 30 min are not practical for routine use in unsedated patients. Dynamic imaging The time per frame selected depends on the temporal resolution needed for the processing of the study and the organ function under investigation. Shorter times are preferred for quantitative functional studies, provided adequate statistics are obtained, in order to measure physiological changes.
Clinicoanatomic Correlation • Anterior Circulation • Anterior circulation strokes rarely have associated symptoms; neurologic deficits accompanied by headache order genuine propranolol line blood vessels from the heart, nausea 80mg propranolol overnight delivery capillaries diseases, and vomiting are more suggestive of intracere- bral hemorrhage or posterior circulation stroke. In addition, complications of cerebellar infarcts, such as edema compressing brainstem structures, may cause rapid deterioration (i. Voluntary eye opening, vertical eye movements, and ocular convergence are preserved. Neurologic Emergencies 103 • Neurologic exam may reveal nystagmus; ipsilateral Horner’s syndrome, paralysis of the soft palate and posterior pharynx, and limb ataxia; and impaired pain/ temperature sensation in the ipsilateral face and contralateral limbs. Scope of the Problem • Disruption in the flow of blood to the brain results in ischemia and cell death. The central area of infarction is surrounded by a region of salvageable tissue, referred to as the penumbra. Identifying the etiology of the patient’s symptoms is critical for determining therapy. Risk Factors • Vascular Disorders • Atherosclerosis • Diastolic or isolated systolic hypertension • Hyperlipidemia (hypercholesterolemia) • Cigarette smoking • Oral contraceptive use • Diabetes mellitus • Hereditary predisposition (i. Vital Signs • Hypotension may be the underlying cause of a stroke; markedly elevated blood pres- sure is suggestive but not diagnostic of a hemorrhagic stroke. Neurologic Emergencies 105 Physical Examination • Focus on searching for an underlying systemic cause, especially a treatable one. A patient with a cere- bral hemispheric stroke will typically gaze toward the side of the insult; a brainstem infarct will cause the patient to gaze away from the side of the lesion. Whenever possible, lower extremity strength should be assessed by observing the patient’s gait. Double simultaneous stimulation: assess sensation on both sides of the body simultaneously; patients with cortical infarcts will only notice the unaf- fected side. Evaluation • Pulse Oximetry • Rapid determination of oxygen saturation may reveal impending respiratory failure and the need for mechanical ventilation. Patients with severely depressed mental Neurologic Emergencies 107 status and patients with an unprotected airway may require intubation and me- chanical ventilation. How- ever, in the absence of hypoxia, supplemental oxygen has not been shown to affect outcome. Over the next few hours to days, the blood pressure generally 4 declines spontaneously. The ischemic penumbra may be dependent upon a moder- ately increased blood pressure for adequate perfusion; thus, use of antihypertensive agents may exacerbate the patient’s condition. Aspirin is recommended in patients who are not candidates for thrombolytics or other anticoagulants. However, because this modality is now being described by certain groups as the standard of care, the 108 Emergency Medicine inclusion and exclusion criteria are included here. For this reason, many neurologists are describing symptoms that persist for more than 1 h as an acute stroke. Various guidelines exist, ranging 4 from keeping the diastolic blood pressure at approximately 100 mm Hg to basing the target systolic and diastolic levels on the patient’s premorbid blood pressure. Potential surgical candidates are those with neurologic deterioration, superficial cerebral hemorrhages causing mass effect, and cerebellar hematomas. Neurosurgical consultation is recommended in all patients with intracerebral hemorrhage. Preventing rerupture, by maintaining adequate blood pressure control, is the mainstay of treatment. Eleva- tion of the head of the bed, mild sedation, and analgesics (for headache) may suffice. The blood pressure should be reduced to approximately 160/100 mm Hg, using rap- idly titratable, parenteral medications if necessary. The timing and outcome of sur- gical intervention are determined by the patient’s clinical grade and medical stability, among other factors. Is admission medically justified for all patients with acute stroke or transient ischemic attack? Part F: Dizziness and Vertigo Basic Anatomy • The vestibular system provides input to the brain regarding movement of the head. The vestibular portion of the 8th cranial nerve is composed of the utricle, the saccule, and three semicircular canals that lie at right angles to each other. Abnormal information, or improper integration, results in a complaint of “dizziness” or vertigo. Scope of the Problem • The complaint of “dizziness” can be attributed to numerous disorders, both benign and life-threatening. For patients with true vertigo, the next task is to determine the source of the symptoms; is it a peripheral or central vestibular process? Central lesions involve the vestibular nuclei (located in the brainstem) and their connections (e. Patients with nonvestibular lesions explain the feeling as one of spinning inside the head, near-faint, floating, swimming in the head, or giddiness. Peripheral vestibular disorders are associated with intermittent episodes of vertigo that are sud- den, brief, and severe; symptoms from central lesions have a more gradual onset, last longer, and are less intense. Pe- ripheral lesions are commonly initiated by turning the head to the side or tilting the head up, whereas central causes are not positional. Cervical vertigo refers to the symptom complex of neck pain, vertigo, and nystagmus that is worse with movement of the neck. Peripheral vestibular lesions are commonly associated with nausea or vomiting; hearing loss, tinnitus, or ear fullness; other neurologic deficits (e. Loss of coordination between attacks indicates 8th cranial nerve or brainstem disease. Vestibular neuritis and acute labyrinthitis are com- monly preceded by a viral illness. Post-traumatic posi- tional vertigo, labyrinthine concussion, and perilymphatic fistula are all caused by head trauma. A rapid, twisting injury of the neck can cause vertebral artery dissection or occlusion. Uremia, Parkinson’s disease, dia- betes, and chronic alcohol abuse are causes of peripheral neuropathy and orthostasis. Frequently, elderly patients with poor vision and sensa- tion—especially after starting sedating medications—describe a feeling of being off balance and stumbling (dysequilibrium), without true vertigo or presyncopal symptoms. Patients with ill-defined light-headedness often have extensive work-ups without an explanation for their symptoms. With the patient looking straight forward, ensure that the eyes are properly aligned.
Changed incidence and trol of the established risk factors for stroke will result case-fatality rates of first-ever stroke between 1970 and in prevention of a very large number of stroke events 1993 in Tartu buy propranolol 80 mg free shipping cardiovascular system jeopardy, Estonia cheap 80mg propranolol free shipping cardiovascular technologist bls. Stroke incidence and mortality in rural and urban Shanghai from 1984 through 1991. Sarti C, Stegmayr B, Tolonen H, Mahonen M, 86 2: Stroke event registration data component. Are changes in mortality Cardiovascular Diseases, World Health Organization; from stroke caused by changes in stroke event rates Chapter 5: Basic epidemiology of stroke and risk assessment or case fatality? Jousilahti P, Rastenyte D, Tuomilehto J, Sarti C, Group; Cardiovascular Nursing Council; Clinical Vartiainen E. Parental history of cardiovascular disease Cardiology Council; Nutrition, Physical Activity, and and risk of stroke. A prospective follow-up of 14371 Metabolism Council; and the Quality of Care and middle-aged men and women in Finland. Prenatal influences on survival: secular trends in Rochester, Minnesota, stroke mortality in England and Wales. Neuroepidemiology 2003; of risk factors for stroke and transient ischemic attack 22(3):196–203. Broderick J, Brott T, Kothari R, Miller R, Khoury J, J Neurol 2007; 254(3):315–21. Cerebrovascular disease in African cohorts of young adult and middle-aged men and Americans. Do trends in mortality between non-Hispanic whites, Hispanic population levels of blood pressure and other whites, and blacks. The National Longitudinal cardiovascular risk factors explain trends in stroke Mortality Study. Stroke World Health Organization Monitoring of Trends and incidence and survival among middle-aged adults: Determinants in Cardiovascular Disease. J Clin Epidemiol 2005; study of early risk of stroke after transient ischaemic 58(9):951–8. Neurology 2004; evaluation of the Finnish Diabetes Risk Score: a tool to 62(11):2015–20. Transient prediction of dementia risk in 20 years among middle ischaemic attacks: which patients are at high (and low) aged people: a longitudinal, population-based study. Lancet 2005; Meta-analysis of genetic studies in ischemic stroke: 366(9479):29–36. The strategy in primary preven- Lifestyle modifications have a high potential to tion is to lower stroke risk attributed to these factors prevent at low cost and low risk the development of through education, lifestyle changes and medication. Thus, they should be an such as atrial fibrillation or diabetes mellitus can be important issue in stroke prevention. Targets of primary stroke prevention can Five low-risk lifestyle factors with a high potential to prevent stroke: be the entire population or high-risk – but stroke- non-smoking free – individuals partly suffering from disorders moderate activity! Lifestyle factors Stroke prevalence has been associated with individual lifestyle factors (e. Healthy lifestyle in general was considered in one Projections estimate the mortality attributed to large prospective cohort study of healthy women. Nearly one-third from smoking, low-normal body mass index, moder- of these deaths are caused by cardiovascular diseases ate alcohol consumption, regular exercise and healthy and 8% by cerebrovascular diseases . Large observational studies have the data of two large cohort studies, the Nurses’ shown cigarette smoking to be an independent risk Health Study (71 243 women) and the Health Profes- factor for stroke in both men and women [e. Smoking is a well-established risk factor for ischemic Smoking may have additive effects and potentiate stroke . This may suggest a lower middle-aged patients (18–49 years) and with the risk tolerance for high blood pressure in smokers . Another between fatal stroke cases and other men were only population-based case-controlled study including 432 found for non-smokers . In the Non-smokers exposed to tobacco smoke were Nurses’ Health Study total and ischemic stroke excess estimated to absorb only the equivalent of 0. Nevertheless passive for former smokers compared to never smokers was smoking was associated with a greater progression 1. Only ever, due to its addictive effect the success in smoking a few studies investigated stroke risk due to environ- cessation is only modest. A meta-analysis of pharmacological therapies are available to assist 16 studies of variable design and quality suggests that smokers in quitting and their effects are the subject Chapter 6: Common risk factors and prevention of a number of Cochrane reviews (e. All Beneficial effects on lipids and hemostatic factors forms of nicotine replacement therapy (nicotine gum, have been reported . Their effect seems, however, to be inde- drinking seems to influence the vascular risk; binge pendent of their antidepressant effect and they are drinking, even when alcohol consumption was other- of similar efficacy to nicotine replacements . The wise light, increases the risk of ischemic and total nicotine receptor partial agonist varenicline was also stroke [32, 25]. Psychosocial intervention such as behavioral jects stroke risk was increased significantly by heavy therapy, self-help or telephone counseling are effect- drinking. Even passive smoking was associated with drinking and light-drinking hypertensive subjects, increased risk for stroke. The relationship between alcohol and overall and ischemic stroke risk was described as J-shaped [25, Excessive alcohol drinking increases all-cause mor- tality, as well as the risk of coronary heart disease 26]. This suggests that benefits overcome the harmful and stroke, but benefits overcome the harmful effect of alcohol at light-moderate alcohol consump- effect at light-moderate alcohol consumption levels. Obesity is associated with an increased risk of 53, 54–56]; others found a U-shaped relationship or hypertension, diabetes and dyslipidemia. Adjusting no difference between moderate and high physical for these confounding risk factors often attenuates activity [e. This may be explained by differ- the effect of body mass without eliminating it [38– ent definitions of physical activity and levels of activ- 40, 42, 44, 47]. Additionally there may be different metabolic whether obesity is an independent risk factor of stroke effects of different types of exercise. Overall only a or mediated through blood pressure, diabetes and few studies have evaluated the influence of occupa- cholesterol levels. However, in a meta-analysis systolic blood muting physical activity (walking or cycling to work) pressure was reduced by 4. No randomized controlled trial has stud- ied the effect of regular controlled exercises on stroke risk. There is not enough evidence for the type and Physical inactivity intensity of fitness training protecting best against Several prospective longitudinal population studies stroke. In a meta- partly mediated through beneficial effects on other analysis of 18 cohort and five case–control studies, risk factors. Similarly, moder- Additionally physically more active people were ately active individuals had a lower risk of stroke, found to be more often non-smokers [e. Regular physical activity has a protective effect for stroke, probably mediated through beneficial A similar relationship was found in ischemic effects on other risk factors. Only a few studies investigated Dietary factors the effect of activity on hemorrhagic stroke. However, Poor dietary habits contribute to the development of in a meta-analysis high and moderate activity signifi- other stroke risk factors such as obesity, diabetes, cantly decreased hemorrhagic stroke risk when com- hypertension and dyslipidemia.
Aneurysms can occur anywhere in the thoracic or abdominal aorta order propranolol online pills capillaries leaving alveoli, but the large majority occur in the abdomen generic propranolol 40mg mastercard cardiovascular system vocabulary list, below the renal arteries. Sometimes referred to as a “dissecting aneurysm,” although the term is misleading because the dissection typically produces the aneurysmal dilation rather than the reverse. It receives most of the shear forces generated by the heart with every heartbeat throughout the lifetime of an individual. The wall of the aorta is composed of three layers: the intima, the media, and the adventitia. These specialized layers allow the aortic wall to distend under the great pressure created by every heartbeat. Some of this kinetic energy is stored as potential energy, thus allowing forward flow to be maintained during the cardiac cycle. One must consider the great tensile stress that the walls of this vessel faces when considering the pathologic processes that affect it. Cystic degeneration of the elastic media predisposes patients to aortic dis- section. This occurs in various connective tissue disorders that cause cystic medial degeneration, such as Marfan and Ehlers-Danlos syndrome. Other fac- tors predisposing to aortic dissection are hypertension, aortic valvular abnor- malities such as aortic stenosis and congenital bicuspid aortic valve, coarctation of the aorta, pregnancy, and atherosclerotic disease. Aortic dissection may occur iatrogenically after cardiac surgery or catheterization. A dissection occurs when there is a sudden intimal tear or rupture followed by the formation of a dissecting hematoma within the aortic media, separat- ing the intima from the adventitia and propagating distally. The presence of hypertension and associated shear forces are the most important factors caus- ing propagation of the dissection. It can produce an intraluminal intimal flap, which can occlude branch arteries and cause organ ischemia or infarction. The hematoma may rupture into the pericardial sac, causing cardiac tampon- ade, or into the pleural space, causing exsanguination. It can produce severe acute aortic regurgitation leading to fulminant heart failure. Differentiating the pain of dissection from the pain of myocardial ischemia or infarction is essential because the use of anticoagulation or thrombolytics in a patient with a dissection may be devastating. In contrast to anginal pain, which often builds over minutes, the pain of dissection is often maximal at onset. In addition, myocardial ischemia pain usually is relieved with nitrates, whereas the pain of dissection is not. Also, because most dissections begin very close to the aortic valve, a dissection may produce the early diastolic murmur of aortic insufficiency; if it occludes branch arteries, it can produce dramatically different pulses and blood pressures in the extremities. Most patients with dissection are hypertensive; if hypotension is present, one must suspect aortic rupture, cardiac tamponade, or dissection of the subclavian artery supplying the arm where the blood pressure is being measured. Often a widened superior mediastinum is noted on plain chest film because of dissec- tion of the ascending aorta. When aortic dissection is suspected, confirming the diagnosis with an imaging study is essential. Because of the emergent nature of the condition, the best initial study is the one that can be obtained and interpreted quickly in the given hospital setting. Several classification schemes describe the different types of aortic dissec- tions. Type A dissection always involves the ascending aorta but can involve any other part. Type B dissec- tion does not involve the ascending aorta but can involve any other part. Two-thirds of aortic dissections originate in the ascending aorta a few cen- timeters above the aortic valve. Virtually all type A (proximal or ascending) dissections require urgent surgical therapy with replacement of the involved aorta and sometimes the aortic valve. Type B dissections do not involve the ascending aorta and typically origi- nate in the aortic arch distal to the left subclavian artery. Type B dissections usually are first managed medically, and surgery usually is performed only for complications such as rupture or ischemia of a branch artery of the aorta. The aim of medical therapy is to prevent propagation of the dissection by reducing mean arterial pressure and the rate of rise (dP/dT) of arterial pressure, which cor- relates with arterial shear forces. Intravenous vasodilators, such as sodium nitro- prusside to lower blood pressure, can be administered, along with intravenous beta-blockers, such as metoprolol, to reduce shear forces. Alternatively, one can administer intravenous labetalol, which accomplishes both tasks. It is a degenerative condition typically found in older men (>50 years), most com- monly in smokers, who often have atherosclerotic disease elsewhere, such as coronary artery disease or peripheral vascular disease. The risk of rupture is related to the size of the aneurysm: the annual rate of rupture is low if the aneurysm is smaller than 5 cm but is at least 10% to 20% for 6-cm aneurysms. The risk of rupture must be weighed against the surgical risk of elective repair, which traditionally required excision of the diseased aorta and replacement with a Dacron graft. Recently, endovascular grafts with stents have been used as a less invasive pro- cedure with less risk than the traditional surgical repair, but the exact role of this procedure remains to be defined. Surgery is urgently required in the event of aortic root or other proximal (type A) dissections. Unrecognized and hence untreated aortic dissection can quickly lead to exsanguination and death. For asymptomatic aneurysms smaller than 5 cm, the 5-year risk of rupture is less than 1% to 2%, so serial noninvasive monitoring is an alternative strategy. A bicuspid aortic valve is usually asymptomatic and does not place the patient at risk for aortic aneurysms. Other patients at risk include those with Marfan syndrome,congenital aortic anomalies,or otherwise normal women in the third trimester of pregnancy. Uncomplicated,stable,type B (transverse or descending) aortic dissections can be managed medically. For the last 2 to 3 weeks he has had fever and a nonproductive cough, and he has felt short of breath with mild exertion, such as when cleaning his house. On examination his blood pressure is 134/82 mm Hg, pulse 110 bpm, and respiratory rate 28 breaths per minute. His oxygen saturation on room air at rest is 89% but drops to 80% when he walks 100 feet, and his breathing becomes quite labored. He is not undergoing any antiretroviral therapy or taking pro- phylactic medications. Diffuse bilateral pulmonary infiltrate is seen on chest X-ray, and he is tachypneic and hypoxemic. An arterial blood gas meas- urement can be obtained to quantify his degree of hypoxemia, as it will impact the treatment. Be familiar with indications for antiretroviral therapy and for prophylactic medications against opportunistic infections.