Lower Peripheral Resistance Research Articles

Autonomic neuropathy in end-stage cirrhotic patients and evolution after liver transplantation

Autonomic neuropathy (AN), which is frequently observed in cirrhosis patients, has been associated with a higher mortality. We have prospectively evaluated the prevalence of AN, its relationship with the degree of liver dysfunction and circulatory disturbances, and the evolution of AN after liver transplantation (LT) in 62 end-stage liver cirrhosis patients. AN was evaluated by seven cardiovascular tests assessing sympathetic or parasympathetic function before and 6 months after LT. Patients were classified as showing absent (A), early (E), or definite dysfunction (D). AN appeared in 67.7% of cases (E: 24.2%, D: 43.5%) without relation to liver disease etiology. Parasympathetic dysfunction was more prevalent than sympathetic dysfunction (59.7% vs. 20.9%). AN was significantly related to Child-Pugh score. Hyperdynamic circulation was more marked in the D than the A group as shown by a greater cardiac output (CO)(9 vs. 7.3 L/min) and a lower peripheral resistance (SVR)(666 vs. 866 dyn.s.cm −5). Moreover, AN scores significantly correlated with CO and SVR. Overall the prevalence of AN decreased 6 months after LT (67.7 % vs 48%) due to a significant reduction in definite AN (43.5 vs. 14.8%; P < .05). AN improved in 70% of cases after LT. Sympathetic dysfunction remained in only one patient. We conclude that AN is frequent in liver transplant candidates; its severity is associated with the degree of liver failure. Systemic circulatory disturbances seem to correlate with the severity of AN. AN is clearly improved by LT. The evaluation of AN may contribute to a better selection of LT recipients.

Microcirculatory hemodynamics of the rat cremaster muscle flap in reduced blood flow states.

Recent studies revealed that muscle and musculocutaneous flaps have the lowest peripheral resistance and best flap survival. The critical values of flow rates responsible for this survival have not been established. The authors evaluated the effect of prolonged arterial flow reduction on flow hemodynamics and muscle flap survival, independent of neovascularization using the rat cremaster muscle island flap model for microcirculatory studies. Muscle flaps were implanted into a transparent Plexiglas chamber to allow prolonged observation of the microcirculation. Twenty-six male Sprague-Dawley rats were studied in three experimental groups. In group I (control; no occlusion), after flap isolation, the cremaster muscle was implanted into the tissue chamber and microcirculatory measurements were performed from day 0 to day 3. In group II, after flap isolation, flow in the main feeding artery (the iliac) was reduced with a silk suture loop between 47% and 62%. In group III, arterial flow was reduced between 63% and 80%. Vessel diameters, red blood cell velocities, number of perfused capillaries, and number of rolling, sticking, and transmigrating leukocytes were reduced daily for each rat. Immediately after flow reduction, mean arteriolar (A1) diameters were significantly smaller in group II (25%) and group III (29%) compared with the controls (p<0.05). This reduction was confirmed by a drop in red blood cell velocities of 37% and 58% in groups II and III respectively (p<0.05). At day 1, more than 60% of group III flaps had no arterial flow, whereas normal flow was observed in control flaps for as long as 3 days. In addition, the number of perfused capillaries dropped significantly (by 42%) in group II flaps after 3 days (p<0.05). The authors conclude that continuous arterial blood flow reduction exceeding 60% of the normal volume, independent of angiogenesis, is incompatible with flap viability in the rat cremaster muscle model.

Associations of Insulin Levels With Left Ventricular Structure and Function in American Indians

We evaluated the association of insulin and echocardiographic left ventricular (LV) measurements in 1,388 (45% men) nondiabetic American Indian participants in the Strong Heart Study (SHS). Significant (all P < 0.05) relations were found in men and women between log(10) fasting insulin and LV mass (r = 0.24 and 0.26), left atrial diameter (r = 0.25 and 0.28), posterior wall thickness (r = 0.20 and 0.26), septal thickness (r = 0.19 and 0.24), LV diameter (r = 0.17 and 0.16), and cardiac output (r = 0.20 and 0.24) and in women relative wall thickness (r = 0.11) and peripheral resistance (r = -0.17). In regression analyses, adjusting for BMI, age, height, and systolic pressure, fasting insulin was independently correlated with cardiac output in men and relative wall thickness and septal thickness in women (all P < 0.05). The 97th percentiles of fasting insulin (25 microU/ml for men, and 23 microU/ml for women) in 163 apparently normal (BMI <26; blood pressure <140/90; and absence of diabetes, valvular disease, LV wall motion abnormality, or antihypertensive treatment) SHS participants were used to separate normal from elevated fasting insulin levels. Adjusting for age, BMI, and height, men with elevated insulin levels had larger LV diameters (5.41 vs. 5.16 cm; P = 0.05), higher cardiac output (5.5 vs. 4.9 l/min; P < 0.001), and lower peripheral resistance (1,487 vs. 1,666; P = 0.01), paralleling results of regression analyses. Positive relations between insulin and heart size in nondiabetic adults are largely due to associations with body size; after adjustments for covariates, fasting insulin levels are related to greater LV size and cardiac output in men and more concentric LV geometry in women.

Role of the endothelium in viral hemorrhagic fevers.

To describe endothelial participation in the pathogenesis of viral hemorrhagic fevers and certain other acute infectious diseases. Survey of published literature on viral hemorrhagic fevers interpreted in light of observations in patients and research on those diseases. Endothelial involvement is an extremely important factor in the clinical syndrome termed viral hemorrhagic fever. Endothelial dysfunction is important in the genesis of bleeding, which is not universal and is commonly seen only in the presence of thrombocytopenia or severe platelet dysfunction. The pathogenesis of endothelial dysfunction varies in the different diseases. In some situations, direct endothelial infection is important in increased vascular permeability, changes in the procoagulant vs. anticoagulant balance, or cytokine production. In all the viral hemorrhagic fevers studied to date, cytokine induction is an important factor and also acts on the endothelium. Poor myocardial contractility is a very important issue in viral hemorrhagic fever and is not caused by direct viral infection of the heart; it is increasingly being recognized that these patients present with low cardiac output and high peripheral resistance and that they respond poorly to fluid infusion. The clinical findings in viral hemorrhagic fever differ from those in the sepsis syndrome and should be studied and interpreted separately; this approach will sharpen therapeutic approaches and could shed light on the problems of sepsis in general.

Sodium in preascitic cirrhosis: please pass the salt

See article on page 847 The relationship between sodium retention, hyperactivity of the neurohumoral vasoactive systems, and ascites formation in cirrhosis is intriguing and still remains a subject of interest...

The influence of recovery posture on post-exercise hypotension in normotensive men.

Postexercise hypotension may be the result of an impaired vasoconstrictor response. This hypothesis was investigated by examining the central and peripheral hemodynamic responses during supine and seated recovery after maximal upright exercise. After supine or seated baseline measurements, seven normotensive male volunteers completed a graded upright cycling protocol to volitional exhaustion. This was immediately followed by either supine or seated recovery. Measurements of pulsatile arterial blood pressure and central and peripheral hemodynamic variables recorded 30 min before exercise were compared with those taken throughout 60 min of recovery. Compared with baseline, mean arterial pressure (MAP) was reduced after exercise (P < 0.05) although the degree of change was not different between the supine (-9 +/- 4 mm Hg) and seated positions (-6 +/- 2 mm Hg). This change in MAP was associated with a reduction in diastolic blood pressure (DBP) (P < 0.05) and arterial pulse pressure (APP) (P < 0.01) for the supine and seated positions, respectively. The reduction in APP during seated recovery was accompanied by a decline in stroke volume (SV) (P < 0.05), not seen in the supine position, that limited the contribution of cardiac output (CO) to the maintenance of MAP. This effect of seated recovery was compensated by greater systemic (SVR) and regional vascular resistances in the forearm (FVR) and the forearm skin (SkVRA). There was also evidence of an augmented return of FVR and SkVRA to resting levels in the seated position after exercise. The lower peripheral resistance in the supine compared with seated recovery position suggests there is potential for greater vasoconstriction, although this is not evoked to increase blood pressure. This further suggests that the arterial baroreceptor reflex is reset to a lower operating pressure after exercise.

Differences in Echocardiographic Findings and Systemic Hemodynamics among Non-Diabetic American Indians in Different Regions: The Strong Heart Study

PURPOSE: This study was undertaken to determine whether differences in left ventricular (LV) and systemic hemodynamic findings exist between American Indians in different regions that might contribute to known differences in cardiovascular morbidity rates among American Indians. METHODS: We compared echocardiography results in 290 non-diabetic Strong Heart Study (SHS) participants in Arizona, 595 in Oklahoma and 572 in North/South Dakota (ND/SD). RESULTS: Participants in the 3 regions were similar in age and gender but those in Arizona had the highest body mass indices and lowest heart rates while those in ND/SD had the lowest diastolic blood pressures (BP). In analyses that adjusted for significant covariates, ND/SD participants had larger aortic (Ao) anular, Ao root, and LV chamber size as well as higher cardiac output and lower peripheral resistance, whereas Arizona participants had increased LV wall thickness and mass and reduced LV myocardial contractility. These findings may contribute to the known high rates of cardiovascular events in ND/SD Indians and to the proportionately higher rate of cardiovascular death than of non-fatal cardiovascular events that has been recently documented in Arizona Indians. CONCLUSIONS: Application of echocardiography to non-diabetic SHS participants reveals that LV chamber and arterial size are larger in ND/SD Indians and that LV wall thicknesses and mass are higher and LV myocardial contractility lower in Arizona Indians, possibly contributing to the higher than expected rates of cardiovascular morbidity and mortality among Indians in Arizona.

Peak exercise hemodynamics in exercising postmenopausal women taking versus not taking supplemental estrogen.

The purpose of this study was to determine whether supplemental estrogen influences cardiovascular hemodynamics at peak exercise in endurance trained and sedentary postmenopausal women. Subjects were 22 women between 3 and 10 yr past menopause who had engaged in endurance exercise at least three times per week for one or more years. Twelve of the women had taken estrogen replacement for at least 1 yr (ER) while the other 10 had never taken supplemental estrogen (NOER). Peak cardiac output (Qpeak) and, subsequently, peak cardiac index (QIpeak) were calculated by regressing submaximal cardiac output values on corresponding oxygen consumptions and extrapolating to peak exercise. Peak oxygen consumption in the two groups were almost identical; however, the ER group demonstrated a higher QIpeak in conjunction with a lower arteriovenous oxygen difference and a lower peripheral resistance. It was concluded that estrogen supplementation may be associated with higher peak cardiac outputs in exercise trained postmenopausal women via alterations in the peripheral vascular and oxygen kinetic responses to maximal exercise.

Arterial and venous compliance in obese and nonobese subjects

In conclusion, the present study shows that, compared with their nonobese counterparts, obese patients have higher stroke volume, cardiac output, central blood volume, and total blood volume, and lower peripheral resistance. The ratio of central blood volume to total blood volume, as an index of peripheral venous distensibility, did not differ between the 2 groups, whereas arterial compliance was better in obese patients and correlated with body mass index only in the hypertensive population.

Significance and pathogenesis of septic shock.

Septic shock is a state of inadequate tissue perfusion induced by microbial products and characterized by low blood pressure and biochemical signs of oxygen deficit. The reduced oxygen and nutrient transport to vital organs is caused by a generalized intravascular inflammatory response resulting in vasodilation. Septic shock evolves through different stages and is initially characterized by a hyperdynamic circulation, i.e., high cardiac output and after volume loading low peripheral resistance (Parillo 1993). Most patients dying of septic shock remain in this circulatory state to the end (Parillo 1993). In patients with overwhelming bacteremia caused by Neisseria meningitidis, Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and certain other bacteria the initial hyperdynamic circulation is gradually transformed into a hypodynamic circulation due to reduced cardiac performance. These patients die in a state of irreversible vasodilation combined with myocardial failure often with a terminal arrhythmia (Mercier et al. 1988; Brandtzaeg 1995).

Refluxes in orthotopic neobladders: Canthe ileocecal sphincter be considered an adequate antireflux mechanism?

Objectives To evaluate the usefulness of the ileocecal sphincter in preventingureteral refluxes in ileocecal orthotopic neobladder, thus avoiding the use of antireflux technique for ureteroileal anastomosis. Methods. From 1980 to 1992, 95 patients underwent orthotopic bladder substitution. In 30 our detubularized ileal reservoir was used and in 65 first only an integral ileocecal segment was used and subsequently multiple transverse teniamyotomies on the cecal portion to increase the capacity and reduce the pressure. The upper urinary tract was indirectly protected in the ileal reservoir technique by leaving an integral 8 to 10 cm long afferent segment folded behind the reservoir and in the ileocecal technique by the ileocecal sphincter, thus keeping the anastomosis between ureters and ileum simple and direct. Results. The mean follow-up of the 65 patients with ileocecourethrostomy is 37 ± 33months (range, 2 to 141 months); in 13.8% of the patients (9/65) monolateral refluxes appeared, but without any evident clinical consequences. The appearance of monolateral stenosis on the ureterointestinal anastomosis requiring treatment occurred in 4 patients (6%): 3 underwent an endoscopic treatment and 1 a surgical one. Modifications of renal function with respect to the preoperative status were not verified in any of the patients. Conclusions. The ileocecal sphincter is an effective antireflux mechanism for an orthotopicneobladder in which multiple transverse teniamyotomies (5 to 7) increase the capacity of the neobladder itself, reduce its internal pressure, and confer a nearly spherical configuration. Moreover, a correct anastomosis between the cecum and membranous urethra decisively reduces the resistance to emptying of the neobladder, thus avoiding too strong pressures against the ileocecal sphincter. The integrity of the circular muscular layer maintains a healthy tonic wall: this fact, combined with the low peripheral resistances, ensures good emptying and a stable capacity. The procedure is easy to perform and not time-consuming; these considerations lead us to consider the ileocecal unit an excellent structure for bladder substitution.

Lowered peripheral resistance in arteries of legs with venous ulcer.

In the literature there is disagreement concerning the existence of arteriovenous shunting in legs with venous ulcer(s). The aim of this study was to find out if there are differences in resistance in the arteries of ulcer legs and non-ulcer legs and if it is possible to investigate this with a non-invasive Doppler method. Eleven patients, aged 34-87 years, with venous ulcer only in one leg, were investigated using angiography and duplex scanning. Angiography showed premature venous filling and Doppler examination showed lowered peripheral resistance in the arteries of every ulcer leg. Lowered peripheral resistance was found only in one non-ulcer leg, which, however also had signs of venous stasis. Our results clearly show that there is lowered peripheral resistance in arteries of legs with venous stasis. The possible significance of this phenomenon in the pathogenesis of venous leg ulcer is discussed.

Persistent pulmonary hypertension in high-risk congenital diaphragmatic hernia patients: Incidence and vasodilator therapy

Survival of congenital diaphragmatic hernia patients depends on the gravity of pulmonary hypoplasia and persistent pulmonary hypertension (PPH). Many vasoactive drugs have been used in the treatment of PPH, but often they also lower peripheral resistance, leading to a significant drop in arterial blood pressure. The incidence of PPH in 52 high-risk diaphragmatic hernia patients and the results of treatment with tolazoline and prostacyclin were evaluated in a study lasting 52 months and involving 52 patients. High-risk patients require ventilatory support within 6 hours after birth. Study parameters were alveolar-arterial oxygenation difference (AaDO 2), oxygenation index (OI), and mean arterial blood pressure (MABP), measured at set times before and after administration of tolazoline or prostacyclin. Twenty-one patients had documented episodes of PPH (46%), and 18 of them died. Tolazoline did not lower AaDO 2 and OI values, but MABP dropped significantly. Prostacyclin caused a significant decrease of AaDO 2 and OI values without an effect on MABP. We concluded: (1) PPH presented in 46% of our patients, associated with a high mortality rate; (2) tolazoline is not an effective dilator of the pulmonary vascular bed and lowers MABP; and (3) prostacyclin is an effective pulmonary vasodilator as reflected by ventilation parameters without systemic side effects; it does not affect overall outcome but can used as a “bridge” to extracorporeal membrane oxygenation.

Ascites as a marker for the hyperdynamic heart of Laennec's cirrhosis.

The purpose of this study was to determine the relation of the circulatory findings of cirrhosis to hepatic decompensation. Twenty individuals with biopsy-proven cirrhosis and 15 aged-matched controls underwent echocardiographic evaluation of cardiac function. Cardiac dimensions and indices derived from echocardiograms were related to various measures of liver decompensation. Cirrhotics had a higher heart rate, left ventricular end-diastolic volume, left ventricular ejection fraction, and cardiac output and a lower mean blood pressure and peripheral resistance than aged-matched subjects. On multiple regression analyses mean blood pressure, peripheral resistance, and cardiac output were all found to be related to estimates of ascites. Also, cirrhotics with ascites had a lower peripheral resistance than those without this finding. In clinically stable patients with cirrhosis, the presence of ascites indicates an intense vasodilatory state with a hyperdynamic circulation.

Direct vascular actions of hydrochlorothiazide and indapamide in isolated small vessels

The mechanism by which thiazides lower peripheral resistance is unresolved. The aim of this study was to investigate the mechanisms of the acute vasodilator action of hydrochlorothiazide and the ‘thiazide-like’ diuretic indapamide on human, guinea pig and rat small arteries. Vessels were mounted on a myograph and the relaxation profile of both drugs and interactions with K + channels and the vascular eicosanoid system were studied. Neither drug had any relaxant effect in rat mesenteric vessels and indapamide did not relax human arteries. Hydrochlorothiazide in both human and guinea pig vessels produced significantly more relaxation of noradrenaline than K +-constricted vessels (P < 0.001). Relaxation to hydrochlorothiazide was reduced in the presence of charybdotoxin. Maximal-induced hydrochlorothiazide relaxation was reduced by 64% in human arteries (P < 0.001) and by 91% in guinea pig vessels (P < 0.001). Incubation with glibenclamide and indomethacin had no effect on the relaxant activity of hydrochlorothiazide and indapamide. Indapamide-induced relaxation was unaffected in the presence of charybdotoxin. These results show marked differences in the acute vasodilator action of hydrochlorothiazide and indapamide. There appears to be involvement of Ca 2+-activated K + channels in the acute vasorelaxant activity of hydrochlorothiazide.

Duplex sonography in splenomegaly

The aetiology of splenomegaly is seldom clear from either clinical or imaging assessment of the spleen. In the majority of cases sonographic assessment of the spleen produces a homogeneous enlargement of variable echodensity, but with very poor correlation with pathology. A study has been undertaken to assess the Doppler characteristics of the splenic artery in splenomegaly, excluding cases of portal hypertension in an attempt to provide further diagnostic information. Duplex assessment of 18 normal subjects and 10 patients with splenomegaly due to five different causes was undertaken. Analysis of waveform, peak frequency and pulsatility index were compared and failed to demonstrate any significant change. In the normal subject there is a broad systolic spectrum related to the tortuosity of the splenic artery, with persistence of forward flow throughout diastole, a reflection of the low peripheral resistance of the spleen. In splenomegaly the broad systolic spectrum is unchanged, since vessel tortuosity persists. Pathological and physiological assessment of the spleen in splenomegaly shows that a low resistance circulation persists, explaining maintenance of the diastolic flow pattern in splenomegaly. Increased blood flow to the spleen in splenomegaly occurs either as a result of an increase in vessel diameter or an increase in flow velocity, or a variable combination of the two which does not seem to be governed by specific pathology. An increase in peak frequency in some cases reflected some increase in flow velocity but provided no useful correlation. Analysis of the pulsatility index supported the above findings without adding further information.

The salvage of rabbit ischaemic epigastric free flaps using the vasodilator calcitonin gene-related peptide

The rabbit epigastric free flap, subjected to 21 hours of warm (25°C) ischaemia, was used as an experimental model to test the ability of two endothelium-dependent vasodilators, calcitonin gene-related peptide (CGRP) and carbamyl β-methylcholine chloride (MCh, bethanechol chloride, the stable acetylcholine analogue) to improve flap viability. After the period of ischaemia, flaps were infused intra-arterially with either Hanks balanced salt solution (controls), CGRP or MCh for 30 minutes, and received additional intravenous boluses of these drugs at 2 and 32 minutes after revascularisation. The area of flap surviving improved significantly (p < 0.025) from 39.9% (n = 18) for controls to 70.2% (n = 14) for CGRP treatment at 2 μg/kg, but was unchanged at 47.1% (n = 14) for MCh treatment at 50 μg/kg. Both CGRP and MCh significantly increased blood flow (p < 0.05) resulting in 34% lower peripheral resistances compared with controls. These results suggest that CGRP has considerable clinical potential for the salvage of ischaemic flaps. CGRP must have several, as yet undefined, beneficial effects on the ischaemic tissue, since MCh invoked a vasodilatory response but failed to salvage ischaemic flaps.

Cardiovascular effects of acute normovolemic hemodilution in rats with disopyramide-induced myocardial depression

The effect of myocardial depression on the circulatory response to acute normovolemic hemodilution (hematocrit 23%) with hetastarch was evaluated in 28 anesthetized Sprague-Dawley rats. Cardiac output was recorded using an electromagnetic flow probe. Mild, moderate, and severe myocardial depression were achieved by infusing disopyramide 50, 75, and 85 mg/kg. This resulted in a dose-dependent decrease in cardiac output (r = -0.73, p less than 0.05) and mean arterial pressure (r = -0.65, p less than 0.05), and an increase in left ventricular end-diastolic pressure (r = 0.77, p less than 0.05) and total peripheral resistance (r = 0.46, p less than 0.05). Following hemodilution, cardiac output and mean arterial pressure were significantly lower and total peripheral resistance significantly higher in animals with myocardial depression compared with saline anemic controls. These differences were dose-dependent for cardiac output (r = -0.83, p less than 0.05), mean arterial pressure (r = -0.68, p less than 0.05), and total peripheral resistance (r = 0.51, p less than 0.05). Although control animals were able to significantly increase their cardiac output and stroke volume after hemodilution compared with baseline, animals with severe myocardial depression were unable to do so. This resulted in marked hypotension after hemodilution in controls compared with severely depressed animals. The results suggest a diminished ability of the pharmacologically depressed heart to tolerate acute normovolemic hemodilution.

Effects of aluminum on the parathyroid hormone receptors of bone and kidney

Aluminum intoxication is associated with low osseous remodeling rate and peripheral resistance to parathyroid hormone (PTH). The pathophysiological mechanism of these aluminum induced changes was investigated using cultured clonal osteoblastic UMR-106 cells as well as dog renal cortical membrane. Both systems possess high-affinity PTH receptors that are coupled to adenylate cyclase. The UMR-106 cells have typical osteoblastic features, including receptors for the tissue-specific hormones, formation and mineralization of a bone-like ground substance and exclusive synthesis of type 1 collagen. The results show that aluminum at a concentration of 4 microM and 40 microM significantly inhibits the cyclic AMP responses to PTH challenge in UMR-106 cells, and this is associated with significant decrease in the binding to the PTH receptor. At 200 microM, no PTH-responsive adenylate cyclase or binding to receptor can be demonstrated. The effect of aluminum on UMR-106 rat osteosarcoma cells is not due to changes in cell number, cell viability or rate of mitogenesis. Similar results are obtained with dog kidney membrane. At a concentration of 10 microM and 400 microM, there is significant inhibition of the binding of PTH to kidney membrane and proportional decrease in PTH-stimulated adenylate cyclase. With higher concentration of aluminum, no response or binding can be demonstrated. In conclusion, aluminum at concentrations of 4 to 400 microM is associated with a decrease in affinity of PTH receptor and concomitant suppression of PTH-stimulated adenylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of posture on upper and lower limb peripheral resistance following submaximal cycling.

The purpose of this study was to determine postural effects on upper and lower limb peripheral resistance (PR) after submaximal exercise. Twelve subjects (six men and six women) completed submaximal cycle ergometer tests (60% age-predicted maximum heart rate) in the supine and upright seated positions. Each test included 20 minutes of rest, 20 minutes of cycling, and 15 minutes of recovery. Stroke volume and heart rate were determined by impedance cardiography, and blood pressure was measured by auscultation during rest, immediately after exercise, and at minutes 1-5, 7.5, 10, 12.5, and 15 of recovery. Peripheral resistance was calculated from values of mean arterial pressure and cardiac output. No significant (p less than 0.05) postural differences in PR were noted during rest for either limb. Immediately after exercise, PR decreased (55% to 61%) from resting levels in both limbs, independent of posture. Recovery ankle PR values were significantly different between postures. Upright ankle PR returned to 92% of the resting level within four minutes of recovery, compared to 76% of the resting level after 15 minutes in the supine posture. Peripheral resistance values in the supine and upright arm were not affected by posture and demonstrated a gradual pattern of recovery similar to the supine ankle recovery response (85% to 88% of rest within 15 minutes). The accelerated recovery rate of PR after upright exercise may result from local vasoconstriction mediated by a central regulatory response to stimulation from gravitational pressure on lower body circulation.