Regulation of peripheral circulation during muscular exercise

Transcutaneous neuromuscular electrical stimulation effect on the degree of microvascular perfusion in autonomically denervated rat skeletal muscle

OBJECTIVE

To determine the effect of transcutaneous neuromuscular electrical stimulation (TNMES) on the degree of microvascular perfusion in autonomically denervated skeletal muscle.

DESIGN

A completely randomized experimental design was used to compare the effects of TNMES on the degree of microvascular perfusion in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles from autonomically denervated rats (Ch-TES) to the degree of microvascular perfusion in the same muscles of untreated controls, rats receiving only TNMES (TES), and rats receiving only autonomic denervation (shams).

INTERVENTION

All electrical stimulation treatments were delivered via carbon silicone surface electrodes, and evoked sustained tetanic contraction of the TA and EDL muscles. Autonomic denervation was achieved by the application of chlorisondamine.

MAIN OUTCOME MEASURES

The degree of microvascular perfusion was determined for the deep (DTA) and superficial (STA) region of the TA muscle and the EDL muscle by calculating their perfused microvessel/muscle fiber (PV/F) ratio.

RESULTS

The PV/F ratio in the DTA from Ch-TES animals was greater (p < or = .05) than that in the same muscle from control and sham animals. The PV/F ratios in the STA and EDL from Ch-TES animals were not significantly (p > .05) different from the PV/F ratio in the respective muscles of shams.

CONCLUSIONS

The response of the microvasculature in autonomically denervated skeletal muscle to TNMES that evokes muscle contraction is variable, and (2) mechanisms other than autonomic regulation may be involved in this hyperemic response.

Peripheral action of spironolactone: plethysmographic studies

The relation between vasodilation and the blood pressure-reducing action of spironolactone was studied in a randomized, placebo-controlled, double-blind, crossover study using 9 patients with essential hypertension. Vasodilation was studied by measuring blood flow in finger and calf (representative of skin and muscle circulation) by an electrocardiographic-triggered venous-occlusion plethysmograph. Treatment with spironolactone (100 mg twice daily for 4 weeks) produced significant decreases in systolic and diastolic blood pressure without significantly affecting heart rate. Blood flow through finger and calf increased, sometimes markedly, in 6 of the 9 patients, while vascular resistance decreased. This study confirms that the antihypertensive action of spironolactone is associated with vasodilation in many patients.

Blood glucose turnover during high- and low-intensity exercise

We hypothesized that whole body glucose uptake (Rd) during exercise is not related in a simple, linear manner to O2 uptake (VO2). To test this, seven healthy male subjects (age range 23-34 yr) were studied in the postabsorptive but not glycogen-depleted state. Three conditions were examined: 1) rest, 2) 40 min of constant exercise in which the work rates were carefully chosen to consist of low-intensity exercise (no elevated blood lactate, a mean of 40% maximal VO2), and 3) 40 min of high-intensity exercise (markedly elevated blood lactate, 79% maximal VO2). Gas exchange was measured breath by breath, and glucose uptake and production were measured using [6,6-2H2]glucose. Low-intensity exercise (n = 7) resulted in a small but not statistically significant increase in mean Rd [3.06 +/- 0.37 (SE) mg.min-1.kg-1] compared with resting values (2.87 +/- 0.39 mg.min-1.kg-1) despite a fourfold increase in the production of CO2 and VO2. By contrast, the high-intensity exercise Rd (n = 5, 6.98 +/- 0.67 mg.min-1.kg-1) was significantly greater than the resting value (3.03 +/- 0.56 mg.min-1.kg-1). Results of glucose production were virtually the same. Similarly, mean levels of epinephrine and norepinephrine increased significantly above resting values during high- but not low-intensity exercise. Our data demonstrate that whole body glucose dynamics and regulation during 40 min of exercise do not change in a simple linear manner with respect to metabolic rate.

Differential control of heart rate and sympathetic nerve activity during dynamic exercise. Insight from intraneural recordings in humans

We used microelectrode recordings of muscle sympathetic nerve activity (MSNA) from the peroneal nerve in the leg during arm exercise in conscious humans to test the concept that central command and muscle afferent reflexes produce mass sympathetic discharge at the onset of exercise. Nonischemic rhythmic handgrip and mild arm cycling produced graded increases in heart rate and arterial pressure but did not increase MSNA, whereas ischemic handgrip and moderate arm cycling dramatically increased MSNA. There was a slow onset and offset of the MSNA responses, which suggested metaboreceptor mediation. When forearm ischemia was continued after ischemic handgrip, MSNA remained elevated (muscle chemoreflex stimulation) but heart rate returned to control (elimination of central command). The major new conclusions are that: the onset of dynamic exercise does not produce mass, uniform sympathetic discharge in humans, and muscle chemoreflexes and central command appear to produce differential effects on sympathetic and parasympathetic responses.

Augmented cardiopulmonary baroreflex control of forearm vascular resistance in young athletes

The aim of this study was to examine the effect of exercise training on reflex control of vascular resistance in human males. Forearm vascular responses to lower body negative pressure (LBNP) at -10 and -40 mm Hg were compared between highly trained young athletes (21.5 +/- 0.5 years old, n = 14) and age-matched nonathletes (20.7 +/- 0.5 years old, n = 16). Resting heart rate was lower in athletes than in nonathletes. Resting blood pressure, central venous pressure, forearm blood flow, and forearm vascular resistance were not different between the two groups. The magnitude of reflex forearm vasoconstriction in response to LBNP at -10 mm Hg, which decreased central venous pressure but did not alter blood pressure or heart rate, was greater in athletes than in nonathletes. The slope of the regression line relating changes in central venous pressure and forearm vascular resistance was steeper in athletes than in nonathletes. Vasoconstrictive responses to intraarterially administered norepinephrine and angiotensin II did not differ between athletes and nonathletes. These results suggest that the tonic inhibitory influence of the cardiopulmonary receptors is augmented in athletes. This augmentation may contribute to some of cardiovascular and endocrine adaptations that occur with exercise training.

Regional blood flow responses to stimulation of the subthalamic locomotor region

Recent studies have suggested that descending central command from an area in the diencephalon (subthalamic locomotor region - STLR) is involved in the control of ventilation, arterial pressure and heart rate during exercise. The purpose of this study was to determine if electrical activation of the STLR in anesthetized cats elicits changes in regional blood flow and vascular resistances similar to those evoked by exercise. Therefore, organ blood flows (radioactive microsphere technique), arterial pressure (AP), heart rate (HR), and respiratory output (quantified from phrenic nerve activity) were recorded during resting conditions and during STLR stimulation. Stimulation of the subthalamic locomotor region produced increases in AP, HR and respiratory output similar to those reported previously. These changes were accompanied by increased blood flow to the heart, diaphragm and limb skeletal muscles. A concomitant decrease occurred in blood flow to the kidneys. In addition, the vascular resistances of the intestines, gallbladder and stomach increased. These vascular and respiratory responses are similar to those occurring during static exercise in conscious cats.

Effects of upright and supine position on cardiac rest and exercise response in aortic regurgitation

The effects of upright and supine position on cardiac response to exercise were assessed by radionuclide ventriculography in 15 patients with moderate to severe aortic regurgitation (AR) and in 10 control subjects. In patients with AR, heart rate was higher during upright exercise, but systolic and diastolic blood pressure and left ventricular (LV) output were similar during both forms of exercise. LV stroke volume and end-diastolic volume were not altered during supine exercise. LV end-systolic volume increased and ejection fraction decreased during supine exercise, but both were unchanged during upright exercise. Of 15 patients, 5 in the upright and 12 in the supine position had an abnormal LV ejection fraction response to exercise (p less than 0.01). Right ventricular ejection fraction increased and regurgitant index decreased with both forms of exercise and was not significantly different between the 2 positions. Thus, posture is important in determining LV response to exercise in patients with moderate to severe AR.

Effect of felodipine and metoprolol on muscle and skin arteries in hypertensive patients

The antihypertensive and vasodilator effects of felodipine, a new calcium antagonist of the dihydropyridine group, were examined in 15 patients with moderate to severe hypertension. Flow was measured simultaneously at the calf and finger using a venous occlusion ECG-triggered plethysmograph. Measurements were made at rest, during handgrip and during reactive hyperaemia. Felodipine (12.5 mg, orally) was given after placebo treatment and after 3 weeks' treatment with metoprolol. It was also given for 3 weeks in combination with metoprolol. Felodipine caused a significant decrease in blood pressure which was similar in the supine, sitting and standing positions without causing any orthostatic reaction. The antihypertensive effect was accompanied by an increase in heart rate, dilatation of calf arteries and, to a lesser degree, dilatation of finger arteries. However, the degree of vasodilatation diminished with long term treatment. Metoprolol prevented the increase in heart rate but not vasodilatation. Felodipine decreased the potential for further dilatation in certain situations, as shown during reactive hyperaemia, although vasoconstrictor responses during the handgrip test remained unimpaired.

Effect of spironolactone on systemic blood pressure, limb blood flow and response to sympathetic stimulation in hypertensive patients

Since there is only scanty, indirect information about the mechanism of the hypotensive effect of spironolactone, 9 patients with essential hypertension were studied according to a randomised double-blind, cross-over protocol. Spironolactone 100mg b.i.d. and placebo were each given for one month and the following parameters were studied: blood pressure, heart rate, response to cold pressure and handgrip tests, as well as blood flow in the calf and finger vessels. Flow in the calf and fingers representing muscle and skin arteries, respectively, was measured semicontinuously with an ECG-triggered venous occlusion plethysmograph. After spironolactone there was a significant decrease in the systolic and diastolic blood pressures in the supine, sitting and standing positions; the sitting systolic and diastolic blood pressure decreased by (mean +/- SE) 27 +/- 4mm Hg (p less than 0.001) and 11 +/- 4mm Hg (p less than 0.02), respectively. No orthostatic response was observed. Heart rate remained unchanged. Blood flow through muscle and skin vessels increased in 6 out of 9 patients, and in these patients calculated vascular resistance in these areas decreased. Spironolactone did not significantly change the response of systemic blood pressure to the handgrip and cold pressure tests. The present data confirm the hypotensive properties of spironolactone and show that this effect is associated with dilatation of muscle and skin arteries in many but not in all the patients. The data do not support the hypothesis that spironolactone decreases the responsiveness of systemic blood pressure to orthosympathetic stimulation.

The behavior of the Nicoladoni-Branham sign at rest and under effort

The Nicoladoni-Branham sign may change because of exercise. Both dogs with femoral AVF and patients with lower-extremity AVF showed an increase in the Nicoladoni-Branham reaction after exercise as compared with its magnitude at rest. In both groups the AVFs were located near active muscles. We did not find this behavior in 3 patients with AVFs at points distant from the muscles used in exercise.

Effects of exercise on plasma viscosity in athletes and sedentary normal subjects

To assess the immediate and long-term effects of exercise on factors regulating blood flow, we measured plasma viscosity (eta p) and plasma renin activity (PRA) in 17 trained runners and 16 sedentary healthy subjects before and 10 min after graded treadmill exercise. Resting eta p was lower in runners primarily because of significantly lower fibrinogen concentration. Compared to nonrunners with similar 24-h urine electrolyte excretion rates, runners were characterized by lower PRA at rest. In view of the overall correlation between heart rate and PRA before exercise, reduced adrenergic tone was probably a major factor contributing to the lower PRA in runners. After exercise, plasma viscosity and PRA exceeded control levels, and were similar in magnitude in runners and sedentary subjects. Changes in plasma viscosity were less than expected from the degree of hemoconcentration, primarily because enhanced fibrinolysis maintained fibrinogen level constant. To the extent that plasma viscosity affects viscous flow resistance, the results suggest that tissue perfusion and oxygen delivery rate at rest are greater in trained runners than in sedentary subjects, but these variables become similar after maximum exertion.

Cardiac output distribution during induced static muscular contractions in the dog

Previous experiments in the dog have shown that static contractions of the muscles of one limb elicit a reflex increase of resistance in the vessels of the opposite limb, along with an increase of systemic blood pressure. The aim of the present experiments was to examine whether this reflex can cause a redistribution of cardiac output from the resting areas, in favor of the working parts. In 17 anesthetized and ventilated dogs, static contraction of the muscles of the right thigh was elicited with electrodes inserted into these muscles. The carotid sinuses were kept at constant pressure and the vagi cut. During static contractions systemic blood pressure and cardiac output increased by 17.7 +/- 3.1 and 24.2 +/- 5.5%, respectively. The blood flow measured with an electromagnetic flowmeter decreased by 21.9 +/- 5.3% in the femoral artery of the resting limb and increased by 101 +/- 21% in the femoral artery of the "active limb". Data obtained in six dogs with injection of radioactive microspheres during stimulations show that blood flow decreased not only in the muscles of the rising limb (34 +/- 10%), but also in several other resting areas, such as skin (38 +/- 8%), kidney (24 +/- 8%), gut (38 +/- 6%), and tongue (23 +/- 3%). The results show that the reflex under study causes a redistribution of the cardiac output during static muscular contractions.

The role of the central nervous system in chronic congestive heart failure

Even though congestive heart failure is extremely common, the mechanisms responsible for the clinical manifestations remain a puzzle. The central and autonomic (sympathetic) nervous systems are responsible for a large part of the clinical manifestations. The role of the nervous system in CHF is discussed briefly. It is evident that there are many gaps in knowledge that remain concerning the role of the central, peripheral, and autonomic nervous systems in congestive heart failure. The peripheral vascular constriction, increase in venous tone and pressure, tachycardia, sweating, dermal pallor, and tension and anxiety in patients with CHF reflect generalized sympathetic nervous system activity and the influence of the central and autonomic nervous systems on the clinical syndrome of CHF.