Tadalafil

Continual or extraurethral incontinence buy 20 mg tadalafil overnight delivery erectile dysfunction pump for sale, It is of two types: Acute retention and chronic e discount 2.5 mg tadalafil otc erectile dysfunction doctor in hyderabad. Pelvic foor exercises and weight • Acute retention is the sudden inability Tis type of incontinence also occurs in reduction if the patient is obese purchase tadalafil with a visa erectile dysfunction drugs australia. Overfow incontinence is an uncon- • In stress incontinence, there is loss of Local or systemic estrogen reduces trollable leakage and dribbling of urine urine during coughing, sneezing, strain- urine leakage by proliferation of ure- from the urethra in a case of chronic ing, weight lifing, etc. Conservative measures: Before a catheter the fstula is better seen with a contrast enema. If all the above measures fail, the bladder It is the diversion of urine temporarily or per- b. Diabetes-progressive lower motor between one hollow viscus and another or stage incontinence that is not other- neuron pattern (faccid bladder). Drugs like narcotics, anticholiner- lowing neglected obstructed child- birth bladder cancer. Nephrostomy (open and percutaneous • Blood urea and electrolytes estimation to disease and postirradiation necrosis. Intestinal conduit using either ileum or • Plain abdominal X-ray to see bladder cal- Tere is escape of urine in both vesicovaginal colon. In vesicoenteric fstula, the most striking Suprapubic Cystostomy • Urodynamics-allows identifcation and feature is the passage of turbid urine, containing It is commonly indicated for: assessment of neurologic bladder dys- recognizable fecal contents and fecal organisms. The catheter is connected to a closed drainage system and is changed every 4 weeks due to occurrence of encrus- tation and obstruction by phosphate debris. The technique involves division of the ureters which are pulled into the sigmoid fig. As a result this Here the ureters are mobilized and a loop the pons, the pontine micturition center center becomes excited and the desire to of ileum with intact vascularity is isolated. The middle portion is formed into a urethrae (external urethral sphincter) is reservoir. Tus, the bladder is analogous to the skel- • Anticholinergic drugs like oxybutynin, etal muscle in that neural control can be propantheline bromide, etc. A neurogenic or cord bladder is one in which The features of neurogenic bladder Bladder (fig. Tumors • Voluntary micturition is under the con- This is due to lesions above the sacral mic- 3. Following this phase the blad- der may become either spastic or remains faccid depending on the level of spinal cord injury as mentioned above. During the stage of spinal shock, the blad- der has to be drained preferably by intermit- tent catheterization. If there is severe spinal cord injury, there is Complications Tere is accumulation of huge residual a stage of faccid paralysis, below the level • Recurrent urinary tract infections. Hypotension due to cardiogenic shock hemoglobinemia and antibodies (Myocardial infarction, constrictive peri- against red cells. Renal causes: (intrinsic renal failure) multiple factors are involved ing over a period of hours to days resulting i. Loss of fuid and salt drome in which there is severe arterial thrombosis, emboli or stenosis, a. From the gut in severe vomiting, contusion of the muscles of the bilateral renal vein thrombosis. Section 12  Urology by stones and tumor, or bladder outfow pyelography may help in assessing the vi. Antibiotics may be needed to avert infec- obstruction due to prostatic hypertrophy nature and site of the obstruction. Improved urine output may be obtained lesions by the appropriate means may gives information about excretion and by infusion of dopamine (2–5 µg/kg/min) result in rapid resolution of the acute renal diferential function between the two and frusemide (10–15 mg/kg/hour) and failure. Almost 80 percent of acute renal failure is cially in the early phase despite azotemia. Clinical Microscopically, there is mitochondrial cal drainage either endoscopically or by open 1. The recovery phase may last (postdiuretic patient alive till recovery of the renal lesion Peritoneal Dialysis Versus phase) from 3 to 12 months during which takes place. Fluid replacement - Intake of fuid is Peritoneal dialysis is the simplest form of lar function gradually improve to nearly restricted to replacing the lost volumes treatment, although hemodialysis may be baseline levels. Preexisting Dialysis Acute renal failure usually comes to the atten- over hydration should be taken note of. Both forms of dialysis are efective when tion of the physician either because of a raised Fluid is best given orally. A low protein diet with additional calo- who cannot tolerate hypotensive episodes ries (daily intake of 3000kcal) is generally or the heparinization required to perform Clinical Evaluation recommended and should be ordered in hemodialysis. Hemodialysis, on the other hand, achieves to make the diagnosis of acute renal failure. Nephrotoxic drugs should be discontin- more rapid clearance of the plasma and is The background factors and the etiology ued or avoided. Hypertension (Nephrosclerosis) • Metabolic acidosis results as the hydro- fold and can be of biological origin, e. Diabetic nephropathy gen ion excretion (40 – 60 mcg/day) is arterial and heart valve grafs or syn- 3. Interstitial nephritis ing the arterial pH to nearly normal Preparation of the Recipient 6. Active tuberculosis or other systemic disease is progressive, leading to end stage infection. Extremes of age (Elderly people > 65 years Conservative treatment-In case of estab- or very young children). Coagulopathy-due to decreased platelet transplantation are used when conservative Donor Selection adhesiveness. The majority of donated kidneys come from efective treatment of platelet dysfunction. Electrolyte disturbance – The most serious transplants are taken from live related donors. Renal trans- fcial ventilation but have no evidence of magnesium levels may accompany plantation means transplantation of a kidney malignant disease. Preoperative Management Chronic hypocalcemia will lead to • Heterotopic graf is a graf placed at a site 1. Tissue typing hyperparathyroidism with resulting diferent from that where the organ is nor- i. The behavior of organs and tissues bone decalcifcation, development of mally located. Infection due to immunosuppression Antibodies and cellular immune mech- similar to a nephrectomy for other rea- 2. Acute rejection - Tis occurs between The most important transplanta- length of the artery, vein and ureter as 1 and 8 weeks afer transplantation.

buy tadalafil 20 mg online

The influences of these postganglionic fibers on key cardiovascular variables are summarized in Figure 9-1 purchase tadalafil online from canada cost of erectile dysfunction injections. In the sympathetic pathways purchase online tadalafil erectile dysfunction treatment time, the cell bodies of the preganglionic fbers are located within the spinal cord discount tadalafil 5mg fast delivery impotence at 55. These preganglionic neurons have spon­ taneous activity that is modulated by excitatory and inhibitory inputs, which arise from centers in the brainstem and descend in distinct excitator and inhibitor spi­ nal pathways. In the parasympathetic system, the cell bodies of the preganglionic fbers are located within the brainstem. Their spontaneous activity is modulated by inputs from adjacent centers in the brainstem. Major concentrations of these receptors are found near the arch of the aorta (the aortic baroreceptors) and at the bifurcation of the common carotid artery into the internal and external carotid arteries on either side of the neck (the carotid sinus baroreceptors). The receptors themselves are mechanoreceptors that sense arterial pressure indirectly from the degree of stretch of the elastic arterial walls. In general, increased stetch causes an increased action potential generation rate by the arterial baroreceptors. Baroreceptors actually sense not only absolute stretch but also the rate of change of stretch. For this reason, both the mean arterial pressure and the arterial pulse pressure afect baroreceptor firing rate, as indicated in Figure 9-2. The dashed curve in Figure 9-2 shows how baroreceptor fring rate is afected by diferent levels of a steady arterial pressure. The solid curve in Figure 9-2 indicates how baroreceptor firing rate is afected by the mean value of a pulsatile arterial pres­ sure. Note that in the presence of pulsations (that of course are normal), the baro­ receptor firing rate increases at any given level of mean arterial pressure. Note also that changes in mean arterial pressure near the normal value of 100 mm Hg pro­ duce the largest changes in baroreceptor discharge rate. If arterial pressure remains elevated over a period of several days for some rea­ son, the arterial baroreceptor fring rate will gradually return toward normal. Thus, arterial baroreceptors are said to adpt to long-term changes in arterial pres­ sure. For this reason, the arterial baroreceptor refex cannot serve as a mechanism for the long-term regulation of arterial pressure. The neural interconnec­ tions between the difuse structures in this area are complex and not completely mapped. Moreover, these structures appear to serve multiple functions including respiratory control, for example. For example, as indicated in Figure 9-1, the aferent sensory information from the arterial baroreceptors enters the medullary nuceus tractus solitarius, where it is relayed via polysynaptic pathways to other structures in the medulla (and higher brain centers, such as the hypothalamus, as well). The cell bodies of the eferent vagal parasympathetic cardiac nerves are located primarily in the medul­ lary nuceus ambigus. The sympathetic autonomic eferent information leaves the medulla predominantly from the rostral ventrolteral medull group of neurons (via an excitatory spinal pathway) or the raphe nucleus (via an inhibitory spinal path­ way). The intermediate processes involved in the actual integration of the sensory information into appropriate sympathetic and parasympathetic responses are not well understood at present. Although much of this integration takes place within the medulla, higher centers such as the hypothalamus are probably involved as well. In this context, knowing the details of the integration process is not as impor­ tant as appreciating the overall efects that changes in arterial baroreceptor activity have on the activities of parasympathetic and sympathetic cardiovascular nerves. Several functionally important points about the central control of the auto­ nomic cardiovascular nerves are illustrated in Figure 9-1. The major external infuence on the cardiovascular centers comes from the arterial baroreceptors. Because the arterial baroreceptors are active at normal arterial pressures, they sup­ ply a tonic input to the central integration centers. As indicated in Figure 9-1, the integration process is such that increased input from the arterial baroreceptors tends to simultaneously (I) inhibit the activity of the spinal sympathetic excitatory tract, (2) stimulate the activity of the spinal sympathetic inhibitory tract, and (3) stimulate the activity of parasym­ pathetic preganglionic nerves. Tus, an increase in the arterial baroreceptor dis­ charge rate (caused by increased arterial pressure) causes a decrease in the tonic activity of cardiovascular sympathetic nerves and a simultaneous increase in the tonic activity of cardiac parasympathetic nerves. Conversely, decreased arterial pres­ sure causes increased sympathetic and decreased parasympathetic activity. The arterial baroreceptor refex mechanism acts to regulate arterial pressure in a negativefed­ back manner that is analogous in many ways to the manner in which a thermo­ statically controlled home heating system operates to regulate inside temperature despite disturbances such as changes in the weather or open windows. Because home thermostats do not usually regulate the operation of the windows, there is no analogy to the reflex medullary control of arterioles. The pressure that the arterial baroreflex strives to maintain is analogous to the temperature setting on the thermostat dial. Immediate cardiovascular adjustments caused by a decrease in arterial blood pressure. Circled numbers indicate the chapter in which each interaction was previously discussed. Figure 9-3 shows many events in the arterial baroreceptor reflex pathway that occur in response to a disturbance of decreased mean arterial pres­ sure. All the events shown in Figure 9-3 have already been discussed, and each should be carefully examined (and reviewed if necessary) at this point because a great many of the interactions that are essential to understanding cardiovascular physiology are summarized in this figure. Note that in Figure 9-3 the overall response of the arterial baroreceptor refex to the disturbance of decreased mean arterial pressure is increased mean arte­ rial pressure (ie, the response tends to counteract the disturbance). One should recall that nervous control of vessels is more important in some areas such as the kidney, the skin, and the splanchnic organs than in the brain and the heart muscle. Thus, the refex response to a fall in arterial pressure may, for example, include a signifcant increase in renal vascular resistance and a decrease in renal blood fow without changing the cerebral vascular resistance or blood fow. The peripheral vascular adjustments associated with the arterial barorecep­ tor refex take place primarily in organs with strong sympathetic vascular control. Other Cardiovascular Reflexes and Responses Seemingly in spite of the arterial baroreceptor reflex mechanism, large and rapid changes in mean arterial pressure do occur in certain physiological and pathological situations. Tese reactions are caused by influences on the medullary cardiovascular centers other than those from the arterial barorecep­ tors. The analogy was made earlier that the arterial baroreceptor refex operates to control arterial pressure somewhat as a home heating system acts to control inside temperature. Such a system automatically acts to counteract changes in tempera­ ture caused by such things as an open window or a dirty furnace. Consequently, the arterial baroreceptor reflex does not resist most of these pressure disturbances but actually assists in producing them. The role of these cardiopulmonar receptors in neurohumoral control of the car­ diovascular system is, in most cases, incompletely understood, but they are likely to be importantly involved in regulating blood volume and body fuid balance. One general function that the cardiopulmonary receptors perform is sensing the pressure {or volume) in the atria and the central venous pool. Increased central venous pressure and volume cause receptor activation by stretch, which elicits a refex decrease in sympathetic activity.

order tadalafil line

Chest X-ray The only sign of an early effusion Endoscopy (around 500mL) may be blunting of the costo- phrenic angle (Fig 14 tadalafil 2.5 mg fast delivery erectile dysfunction. Bronchoscopy should be performed to exclude Larger effusions may have a fluid level or show a endobronchial disease cheap tadalafil 2.5 mg overnight delivery erectile dysfunction causes heart disease. An ultrasound scan of the chest is more sensi- Management tive and specific than an X-ray buy generic tadalafil on-line erectile dysfunction treatment videos. If a chest provide diagnostic information regarding any drain is to be inserted, intravenous access should be underlying thoracic pathology. This may also apply to the fluid should be sent for microbiological, bio- some exudates, e. Gram stain insertion of an intercostal drain may be more and culture will help diagnose an empyema. Talc This is a rare malignant tumour arising from the slurry is the most effective, with a response rate of mesothelial layer of the pleura. Side-effects include pain, fever factor in almost all cases is exposure to asbestos and infection. A pleurodesis should not be per- inhalation, typically 30–40 years prior to presen- formed in the presence of an infected pleural space. Investigation Further investigation is essential if there is any Clinical diagnostic indicators doubt about the diagnosis or if conservative treat- There is chest pain and dyspnoea usually caused by ment fails to control the effusion. Surgical treatment Imaging The role of surgery is to establish a diagnosis and A chest X-ray will usually reveal a pleural effu- prevent reaccumulation of pleural fluid. Contraction of the Open pleural biopsy can be performed via a hemithorax may be present. The pleurodesis success rate of talc poudrage is Cytological examination of the pleural effusion if 90 per cent. Complications include empyema, death and tumour seeding in the surgical wounds or drain sites. The use of the more radical surgery sometimes appropriate for empyema and pleural malignancy is controversial. This is usually second- ary to malignancy, pleural infection (empyema) or chylothorax. The cause is a thick layer of tumour, fibrin or fibrotic tissue overlying and incorpo- rating the visceral pleura that encases the lung. The mortality is lower with a lung-preserving Management radical pleurectomy/decortication. However, there are reports of long-term A combination of cisplatin and pemetrexed can survivors following radical surgical treatment com- prolong survival and is indicated in patients with a bined with chemoradiotherapy. A Drain-site and operation-site prophylactic radio- pleural effusion should be managed by talc pleurod- therapy is still advocated by some centres to prevent esis or a long-term indwelling pleural catheter. Radiotherapy can be useful in palliating symptomatic chest wall Surgical treatment involvement. This is usually possible with life-threatening condition, even in young people, video-assisted thorascopic techniques. An iatrogenic empyema may complicate cated a more radical approach with the hope of chest surgery or chest drain insertion. It is estimated that over 50 per cent of patients An extrapleural pneumonectomy (en bloc with pneumonia develop a para-pneumonic effu- resection of the lung, visceral and parietal pleura, sion but only a small proportion of these effusions diaphragm and pericardium) combined with pre- become infected. Both the visceral and parietal pleura become thickened and the lung is encased by a fibrous peel or cortex. Streptococcus pneumoniae and Staphylococcus aureus are the main causes of community-acquired pneumonia. Bacteroides fragilis) are nodule; P, benign asbestos pleural plaque; E, blood-stained also commonly isolated. Untreated, an empyema can become compli- Antibiotic therapy should be dictated by Gram cated by: stain and culture results. It is a widely held, but unsub- invasion through the chest wall with stantiated belief, that a large-bore drain should be spontaneous external drainage (empyema used. Drains should remain in place until contraction there is radiological and clinical improvement and osteomyelitis. The cor- rect duration of antibiotic treatment is unknown Investigation but 3 weeks appears to be an appropriate length of time. Clinical diagnostic indicators Although trials are still ongoing, the use of intra- Patients with an empyema develop shortness of pleural fibrinolytic agents (e. The indications for surgery include the failure of There may be respiratory compromise secondary to conservative measures, the presence of a multilocu- both the causative pneumonia and the compression lated pleural collection, and the presence of a thick of underlying lung by the effusion/pus. The resection of a small portion Blood tests of rib in a dependent position allows the manual The white cell count and C-reactive protein will breakdown of loculations, the evacuation of fluid, usually be elevated. It is indicated in those patients in whom either a rib resection has failed or who Bacteriology clearly have a trapped lung from the outset. This A lung abscess is a localized collection of pus in may involve the administration of oxygen, respira- a cavity formed by the disintegration of the lung tory support, intravenous fluid and/or vasoactive parenchyma. The causes of cavitating lung lesions Secondary lung abscesses occur as a result of another pathology such as metastatic septic emboli, Lung abscess an obstructing bronchial carcinoma or an infected Lung cancer (especially squamous cell carcinoma) bulla. Tuberculosis Anaerobic bacteria (particularly the Bacteroides species) are commonly isolated from the pus. Aspergillus, Histoplasmosis) Aerobic bacteria such as Staphylococcus aureus and Hydatid cyst (caused by the Echinococcus tapeworm) Streptococcus pneumoniae (and occasionally colif- Empyema with bronchopleural fistula orms) are sometimes found. Bronchogenic cyst Investigation Clinical diagnostic indicators drainage techniques. The essentials of conservative Patients with a lung abscess usually have a cough treatment are: that becomes productive of pus later in its natural history, especially if the abscess drains spontane- a prolonged course of antibiotics (6–8 weeks) ously into the bronchial tree. They have a fever, dependent on repeated bacterial cultures night sweats and weight loss. Surgical treatment Only approximately 10 per cent of cases now require Sputum culture and antibiotic sensitivities surgical intervention. In the acute phase, surgery Full bacteriological studies are essential and is indicated for complications of the abscess such may demonstrate a heavy growth of a single as a bronchopleural fistula, empyema or bleeding organism. Surgical treatment entails a thoracotomy and Management resection of the abscess, often with the affected Conservative treatment lobe of lung. However, if the patient has been unwell The majority of lung abscesses can be treated and is not a suitable candidate for such major sur- without surgical intervention especially since the gery, it may be safer to exteriorize the abscess cavity advent of radiologically guided percutaneous and allow external drainage. It may be congenital or acquired of bronchial dilatation and peribronchial inflam- (Table 14. Bronchoscopy The result is transmural inflammation, mucosal Pus may be seen originating from the affected lobar oedema and bronchial neovascularization.

proven tadalafil 5 mg

At the end of the 19th century order generic tadalafil on line natural erectile dysfunction treatment remedies, the English physiologist Ernest Starling first postulated the role of hydrostatic and colloid osmotic pressures in determining fluid movement across capillaries purchase tadalafil once a day impotence grounds for annulment philippines. In the 1920s buy discount tadalafil 2.5 mg online erectile dysfunction treatment singapore, the American physiologist Eugene Landis obtained experimental proof for Starling’s hypothesis. The relationship is defined for a single capillary by the Starling-Landis equation: (5) 3 J is the net volume of fluid moving across the capillary wall per unit of time (μm /min). K is theV h hydraulic conductivity for water, which is the fluid permeability of the capillary wall. K is expressed as μm /min/mm Hg (μm ofh capillary surface area per minute per mm Hg pressure difference). The value of K increases up toh fourfold from the arterial to the venous end of a typical capillary. A, in equation 5, is the vascular surface area, P is the capillary hydrostatic pressure, and P is the tissue hydrostatic pressure. This coefficient is included because the microvascular wall is slightly permeable to plasma proteins, preventing the full expression of the two colloid osmotic pressures. The reflection coefficient is normally relatively constant but can be decreased dramatically by hypoxia, inflammatory processes, and tissue injury. This leads to increased fluid filtration because the effective fluid-retaining power of the colloid osmotic pressure is reduced when the vessel wall becomes more permeable to plasma proteins. The extrapolation of fluid filtration or absorption for a single capillary to fluid exchange in a whole tissue is difficult. Within organs, there are regional variations in microvascular pressures, possible filtration and absorption of fluid in vessels other than capillaries, and physiologically and pathologically induced variations in the available surface area for capillary exchange. Therefore, for whole organs, a measurement of total fluid movement relative to the mass of the tissue is used. To take into account the various hydraulic conductivities and total surface areas of all vessels involved, the volume (mL) of fluid moved per minute for a change of 1 mm Hg in net capillary filtration pressure for each 100 g of tissue is determined. For example, during the intestinal absorption of products of digestion, especially lipids, both capillary fluid permeability and perfused surface area increase. The hydrostatic and colloid osmotic pressure differences across capillary walls, called the Starling forces, cause the movement of solutes along with the water into the interstitial spaces. However, most solutes transferred to the tissues move across capillary walls by simple diffusion, not by bulk flow of fluid. Capillary hydrostatic pressure is altered by changes in precapillary and postcapillary resistance as well as arteriolar and venule blood pressure. Normal physiologic processes in the body do not control plasma colloid osmotic pressure, tissue hydrostatic pressure, or tissue colloid osmotic pressure. Thus, manipulation of these parameters cannot be used to regulate filtration and reabsorption of fluid at the capillary. Such regulation is accomplished, therefore, by the adjustment of capillary hydrostatic pressure. Capillary hydrostatic pressure (P ) is influenced by four major variables: precapillary resistancec (Rpre), postcapillary resistance (Rpost), arterial blood pressure (P ), and venous blood pressure (P ). To demonstrate the effect of precapillary and postcapillary resistances on capillary pressure, we use the equations for the precapillary and postcapillary resistances to solve for blood flow: (8) The two equations to the right of the flow term can be solved for capillary pressure: (9) Equation 9 indicates that the ratio of postcapillary to precapillary resistance, rather than the absolute magnitude of either resistance, determines the effect of arterial pressure (P ) on capillary hydrostatica pressure. It also shows that venous pressure substantially influences capillary pressure and that the denominator influences both pressure effects. As can be seen by equation 9, capillary hydrostatic pressure will increase with arteriolar vasodilation. Furthermore, with increased tissue metabolism, the postcapillary to precapillary resistance ratio increases because precapillary resistance decreases more than postcapillary resistance. The increased filtration associated with microvascular dilation is usually associated with a large increase in lymph production, which removes excess tissue fluid. When sympathetic nervous system stimulation causes a substantial increase in precapillary resistance and a proportionately smaller increase in postcapillary resistance, the capillary pressure can decrease up to 15 mm Hg and, thereby, greatly increase the absorption of tissue fluid. This process is an important compensatory mechanism the body uses to combat the early stages of circulatory shock (see Chapter 17). Changes in capillary hydrostatic pressure and plasma protein concentration can have a profound effect on filtration at the capillary. The hydrostatic pressure involved in transcapillary fluid exchange depends on how the microvasculature dissipates the prevailing arterial and venous pressures. As seen above, certain interplay of these variables can lead to substantial filtration across the capillaries. Although plasma protein concentration does not vary moment to moment, its circulating value in normal circumstances is determined largely by the rate of protein synthesis in the liver, where most of the plasma proteins are made. Disorders that either impair albumin synthesis or promote the loss of albumin result in reduced plasma protein concentration, a lowered plasma colloid osmotic pressure, and excessive fluid filtration at the capillaries. Edema is a condition in which there is excessive accumulation of fluid in tissue spaces (i. Edema interferes with capillary transport by increasing diffusion distances between capillaries and tissue cells. Sometimes this accumulation can be substantial, and in addition to affecting capillary transport, this extreme can cause circulatory collapse if the edematous fluid was derived from a loss of plasma volume. For example, edema formation in the abdominal cavity (known as ascites) can allow large quantities of fluid to collect in the abdominal space. Anything that causes excess fluid filtration at the capillaries or impairs fluid transport through the lymph channels can create edema (Fig. This is common in diseases in which the liver is unable to manufacture albumin or in kidney diseases in which albumin and other proteins are lost into the urine. Burns, by destroying capillary integrity, cause edema through increased capillary permeability, loss of albumin through damaged vessels, and inflammatory vasodilation. Hives, which are a form of localized edema associated with allergic reactions, result from an increase in capillary permeability, venule permeability, and arterial dilation, all caused by histamine release during the allergic response. Obstruction of veins, usually from blood clot formation after surgery, is another common cause of edema, as is the obstruction of lymph channels at lymph nodes by infections. Factors that increase lymph flow or favor the formation of edema are listed in the figure. Myogenic regulation causes arterioles to actively contract or relax in response to changes in intravascular pressure. This process, called myogenic regulation, is activated in arterioles (and somewhat in venules) when microvascular pressure is increased or decreased. Myogenic mechanisms are extremely fast and appear to be able to adjust to the most rapid pressure changes. These responses are known to persist for as long as the initial stimulus is present, unless vasoconstriction reduces blood flow to the extent that tissue becomes severely hypoxic and nonfunctional.