Resistance training in men is associated with increased arterial stiffness and blood pressure but does not adversely affect endothelial function as measured by arterial reactivity to the cold pressor test

Resistance training is a popular mode of exercise, but may result in stiffening of the central arteries. Changes in carotid artery diameter were determined using the cold pressor test (CPT), which results in production of nitric oxide via sympathetic activation and is one of the novel methods available for assessing endothelial function in the carotid artery. To investigate the effect of resistance training on endothelial function, we designed a cross-sectional study of carotid arterial vasoreactivity to CPT in men participating in regular resistance training with increased carotid arterial stiffness compared with age-matched control subjects. Twelve resistance-trained middle-aged men (age 38.7 +/- 1.7 years) and 17 age-matched control subjects (age 36.8 +/- 1.2 years) were studied. The direction and magnitude of changes in carotid artery diameter were measured by B-mode ultrasonography during sympathetic stress induced by submersion of the foot in ice slush for 90 s. Carotid arterial beta-stiffness index, and systolic and mean arterial blood pressure were higher (7.7 +/- 0.7 versus 6.0 +/- 0.4 arbitrary units, 116 +/- 2 versus 131 +/- 4 mmHg and 86 +/- 2 versus 95 +/- 2 mmHg, respectively, all P < 0.05) in the resistance training group compared with control subjects. There were, however, no significant differences in the amount or percentage change in carotid artery diameter in CPT between the two groups (resistance training group, 0.33 +/- 0.07 mm and 5.2 +/- 1.1%; control group, 0.37 +/- 0.06 mm and 5.8 +/- 0.9%, respectively). These findings suggest that while carotid arterial stiffening and higher blood pressure are observed in regular resistance-trained men, these are not associated with abnormalities in carotid arterial vasoreactivity to sympathetic stimulus, which implies intact endothelial function.     

Prolonged strenuous exercise alters the cardiovascular response to dobutamine stimulation in male athletes

Prolonged strenuous exercise has been associated with transient impairment in left ventricular (LV) systolic and diastolic function that has been termed 'cardiac fatigue'. It has been postulated that cardiac β-adrenoreceptor desensitization may play a central role; however, data are limited. Accordingly, we assessed the cardiovascular response to progressive dobutamine stimulation after prolonged strenuous exercise (2 km swim, 90 km bike, 21 km run). Nine experienced male athletes were studied: PRE (2–3 days before), POST (after) and REC (1–2 days later). The cardiovascular response to progressive continuous dobutamine stimulation (0, 5, 20, and 40 μg kg⁻¹ min⁻¹) was assessed, including heart rate (HR), systolic blood pressure (SBP), LV cavity areas (two-dimensional echocardiography) and contractility (end-systolic elastance, SBP/end-systolic cavity area (ESCA)). POST there was limited evidence of myocardial necrosis (measured by troponin I), while catecholamines were elevated. HR was higher POST (mean ± s.d. ; PRE, 58 ± 9; POST, 79 ± 9; REC, 57 ± 7 beats min⁻¹; P < 0.05), while SBP was lower (PRE, 127 ± 15; POST, 116 ± 9; REC, 121 ± 12 mmHg; P < 0.05). A blunted HR, SBP and LV contractility (SBP/ESCA; PRE 29 ± 6 versus POST 20 ± 6 mmHg cm⁻²; P < 0.05) response to dobutamine was demonstrated POST, with values returning towards baseline in REC. Following prolonged strenuous exercise, the chronotropic and inotropic response to dobutamine stimulation is blunted. This study supports the hypothesis that beta-receptor downregulation and/or desensitization may play a major role in prolonged-strenuous-exercise-mediated cardiac fatigue.     

Mechanisms of hypotensive effects of a posture change from seated to supine in humans.

The hypothesis tested was that the hydrostatic stimulation of carotid baroreceptors is pivotal to decrease mean arterial pressure at heart level during a posture change from seated to supine. In eight males, the cardiovascular responses to a 15-min posture change from seated to supine were compared with those of water immersion to the xiphoid process and to the neck, respectively. Left atrial diameter and cardiac output (rebreathing) increased similarly during the posture change and water immersion to the xiphoid process and further so during neck immersion. Mean arterial pressure decreased by 12 +/- 2 mmHg during the posture change, by 5 +/- 1 mmHg during xiphoid immersion, and was unchanged during neck immersion. Arterial pulse pressure increased by 12 +/- 3 mmHg during the posture change (P < 0.05) and less during xiphoid and neck immersion by 7 +/- 3 mmHg (P < 0.05). Total peripheral vascular resistance decreased similarly during the posture change and neck immersion and slightly less during xiphoid immersion (P < 0.05). In conclusion, the hydrostatic stimulation of carotid baroreceptors combined with some additional increase in arterial pulse pressure, which also stimulates aortic baroreceptors, accounts for more than half of the hypotensive response at heart level to a posture change from seated to supine.     

Intima-media thickness and pulse wave velocity in hypertensive adolescents

Increased intima-media thickness (IMT) and pulse wave velocity (PWV) are noninvasive markers of early arterial wall alteration and are more widely used in adult clinical research. We investigated whether IMT and PWV are useful predictors of cardiovascular risk in hypertensive adolescents. Fifteen hypertensive adolescents (13-18 yr old, systolic BP > or = 140 mmHg, diastolic BP > or = 90 mmHg) and seventeen normotensive subjects were included. Height, weight, obesity index, body mass index (BMI), and fat distribution were obtained from each group. Serum lipid, insulin, vitamine B12, folate, renin, aldosterone, angiotensin-converting enzyme (ACE), and homocysteine levels were compared. The carotid IMT and PWV were measured. Arterial wall compliance and distensibility were calculated with the equation. High systolic blood pressure significantly correlated with height, weight, BMI, obesity index, arm circumference, fat mass, and fat distribution. Hypertensive adolescents had significantly greater cIMT (carotid intima-media thickness) and lower elastic properties such as cross-sectional compliance and distensibility of the carotid artery. The carotid IMT significantly correlated with brachial-ankle PWV. In conclusion, the measurement of carotid IMT and brachial-ankle PWV might be useful to predict the development of atherosclerosis in hypertensive adolescents.     

Effects of a 4-week training with voluntary hypoventilation carried out at low pulmonary volumes

This study investigated the effects of training with voluntary hypoventilation (VH) at low pulmonary volumes. Two groups of moderately trained runners, one using hypoventilation (HYPO, n=7) and one control group (CONT, n=8), were constituted. The training consisted in performing 12 sessions of 55 min within 4 weeks. In each session, HYPO ran 24 min at 70% of maximal O(2) consumption ( [V(02max)) with a breath holding at functional residual capacity whereas CONT breathed normally. A V(02max) and a time to exhaustion test (TE) were performed before (PRE) and after (POST) the training period. There was no change in V(O2max), lactate threshold or TE in both groups at POST vs. PRE. At maximal exercise, blood lactate concentration was lower in CONT after the training period and remained unchanged in HYPO. At 90% of maximal heart rate, in HYPO only, both pH (7.36+/-0.04 vs. 7.33+/-0.06; p<0.05) and bicarbonate concentration (20.4+/-2.9 mmolL(-1) vs. 19.4+/-3.5; p<0.05) were higher at POST vs. PRE. The results of this study demonstrate that VH training did not improve endurance performance but could modify the glycolytic metabolism. The reduced exercise-induced blood acidosis in HYPO could be due to an improvement in muscle buffer capacity. This phenomenon may have a significant positive impact on anaerobic performance.     

Effects of high-intensity and blood flow-restricted low-intensity resistance training on carotid arterial compliance: role of blood pressure during training sessions

We examined the effects of high-intensity resistance training (HIT) and low-intensity blood flow-restricted (LI-BFR) resistance training on carotid arterial compliance. Nineteen young men were randomly divided into HIT (n = 9) or LI-BFR (n = 10) groups. The HIT and LI-BFR groups performed 75 and 30 %, respectively, of one-repetition maximum (1-RM) bench press exercise, 3 days per week for 6 weeks. During the training sessions, the LI-BFR group wore elastic cuffs around the most proximal region of both arms. Muscle cross-sectional area (CSA), 1-RM strength, and carotid arterial compliance were measured before and 3 days after the final training session. Acute changes in systolic arterial pressure (SAP), plasma endothelin-1 (ET-1), nitrite/nitrate (NOx), and noradrenalin concentrations were also measured during and after a bout of training session. The training led to significant increases (P < 0.01) in bench press 1-RM and arm and chest muscle CSA in the two training groups. Carotid arterial compliance decreased significantly (P < 0.05) in the HIT group, but not in the LI-BFR group. There was a significant correlation (r = ?0.533, P < 0.05) between the change in carotid arterial compliance and the acute change in SAP during training sessions; however, ET-1 and NOx did not correlate with carotid arterial compliance. Our results suggest that muscle CSA and strength increased following 6 weeks of both HIT and LI-BFR training. However, carotid arterial compliance decreased in only the HIT group, and the changes were correlated with SAP elevations during exercise sessions.     

体外反搏对犬血流脉动性和血管阻力的影响

为了评价体外反搏是否具有扩张血管和增加血流脉动性的作用 ,制造了犬急性心肌梗塞模型 ,并使犬存活 6周。麻醉后 ,测定左侧颈总动脉血流量和右侧颈总动脉血压。计算反搏前和反搏中脉压差、血压脉动指数、血压的标准差、流量差、流量脉动指数、流量标准差和平均血管阻力。结果显示脉压差、血压脉动指数和血压标准差三个血压脉动性指标分别由反搏前的 30± 9mm Hg、1.2 6± 0 .0 5、8.7± 2 .5 mm Hg升高到反搏中的 4 3± 8mm Hg(P<0 .0 5 )、1.5 4± 0 .13、12 .4± 2 .0 mm Hg (P<0 .0 5 )。流量差、流量脉动指数和流量标准差三个血流脉动性指标分别由反搏前的 317± 4 8ml/ min、2 .85± 0 .2 1、96± 2 1ml/ min升高到反搏中的 4 4 7± 88m l/ min、4 .5 6± 0 .90、131±39m l/ m in,P值均于小 0 .0 5。平均血管阻力由反搏前的 5 78± 72 Wood单位降低到反搏中的 4 76± 85 Wood单位(P<0 .0 5 )。这表明体外反搏可使血管阻力下降 ,血压和血流脉动性增强。     

Role of arterial baroreceptors in mediating cardiovascular response to exercise.

The role played by the major arterial baroreceptor reflexes in the cardiovascular response to exercise was examined by comparing the responses of untethered conscious dogs instrumented for the measurement of aortic pressure and cardiac output with those of dogs with total arterial barorecptor denervation (TABD). Moderately severe levels of exercise (12 mph) in intact dogs increased cardiac output from 111 +/- 17 ml/kg per min, increased heart rate from 101 +/- 5 to 265 +/- 8 beats/min, and reduced total peripheral resistance from 0.039 +/- 0.003 to 0.015 +/- 0.002 mmHg/ml per min. Dogs with TABD responded in a very similar fashion; exercise increased cardiac output from 119 +/- 8 to 356 /+- 23 ml/kg per min, increased heart rate from 122 +/- 7 to 256 +/- 5 beats/min, and decreased total peripheral resistance from 0.042 +/- 0.005 to +/- 0.015 +/- 0.001 mmHg/ml per min. The reflex heart rate responses to intravenous bolus doses of methoxamine were also examined in intact animals, both at rest and during exercise. Methoxamine caused striking bradycardia at rest, but little bradycardia during exercise. These results suggest that the arterial baroreceptor reflex is normally turned off during severe exercise and thus does not modify significantly the cardiovascular response to exercise.     

The acute post-exercise response of blood pressure varies with time of day

The reactivity of ambulatory blood pressure following a given change in everyday physical activities is highest in the morning. Whether the acute response of blood pressure following a controlled bout of steady-state exercise is influenced by time of day is examined in this study. After 45 min of supine rest, 12 male normotensives completed 30 min of cycling at 70% [Formula: see text] which began at either 0800 or 1600 hours. Arterial blood pressure, cardiac output, total peripheral resistance, cutaneous blood flow and temperature were determined before, and up to 90 min after, exercise. Mean +/- SE arterial pressure, averaged over the acute (20-min) period, reduced by 7 +/- 2 mmHg following exercise at 1600 hours but increased by 3 +/- 3 mmHg following exercise at 0800 hours (P = 0.03). Total peripheral resistance fell by 4.2 +/- 0.8 mmHg l(-1) min(-1) after exercise at 1600 hour, but increased slightly by 0.1 +/- 0.5 mmHg l(-1) min(-1) after morning exercise (P = 0.02). We conclude that the acutely hypotensive effects following 30 min of steady state exercise are less marked in the morning, probably because the exercise-mediated decrease in peripheral resistance is not as apparent at this time of day.     

Behaviour of the carotid wall in menopausal women with and without arterial hypertension

OBJECTIVE: A study was conducted on the carotid vascular wall to evaluate its behaviour in postmenopausal women suffering from arterial hypertension compared to normotensive postmenopausal women. METHOD: Intima-media thickness(IMT) of carotid artery was determined by ecoduplex scanner in 182 postmenopausal women (age range 40-60 years) divided in four age classes (40-45, 46-50, 51-55, 55-60 years). Ninety-one women presented normal arterial blood pressure (SBP 136.6+/-11.7 and DBP 82.3+/-8.9 mmHg) and 91 were hypertensive (SBP 172.6+/-11.7 and DBP 97.4+/-6.6 mmHg). RESULTS: The normotensive women presented the following IMT values: 1.19+/-0.21 mm (40-45 years), 1.21+/-0.25 mm (46-50 years), 1.25+/-0.20 mm (51-55 years), 1.25+/-0.20 mm (55-60 years). IMT values in hypertensive women were: 1.75+/-0.25 mm (40-45 years), 1.77+/-0.30 mm (45-50 years), 1.91+/-0.28 mm (51-55 years), 2.02+/-0.33 mm (55-60 years). ANOVA test was performed in both groups of women and did not show any significant difference in the four age classes of normotensive women. On the other hand it revealed a statistical significance between 40-45 and 46-50-year-old hypertensive classes (P<0.001) and between 51-55 and 55-60-year-old hypertensive clases (P<0.02). CONCLUSIONS: There was a correlation between age and IMT in the arterial hypertensives, especially in two older classes, and between the duration of menopause and IMT values. The results indicated that carotid wall thickening was constantly higher in hypertensive women compared with normotensive ones.     

Involvement of endothelin-1 in habitual exercise-induced increase in arterial compliance

Aim: Habitual aerobic exercise results in a significant increase in central arterial compliance. Endothelin‐1 (ET‐1) is a potent endothelium‐derived vasoconstrictor peptide and could play a role in mediating the habitual aerobic exercise‐induced increase in central arterial compliance. The aim of the present study was to examine whether ET‐1 is involved in the mechanisms underlying the increase in central arterial compliance with aerobic exercise training. Methods: Seven apparently healthy middle‐aged and older (60 ± 3 years) adults underwent systemic endothelin‐A/B (ET_A/B)‐receptor blockade (500 mg of Tracleer^®) before and after 12 weeks of aerobic exercise training (70 ± 1% of maximal heart rate, 44 ± 2 min day^?1, 4.4 ± 0.1 days week^?1). Results: Basal carotid arterial compliance (via simultaneous B‐mode ultrasound and arterial applanation tonometry on the common carotid artery) increased significantly after exercise training. Resting plasma ET‐1 concentration decreased significantly after exercise training. Before exercise intervention, carotid arterial compliance increased significantly with the administration of the ET_A/B‐receptor blockade. After training, however, increases in carotid arterial compliance previously observed with the ET_A/B‐receptor blockade before training were abolished. Conclusions: Regular aerobic exercise training enhances central arterial compliance in middle‐aged and older humans. The increase in arterial compliance was associated with the corresponding reduction in plasma ET‐1 concentration as well as the elimination of ET‐1‐mediated vascular tone. These results suggest that reductions in ET‐1 may be an important mechanism underlying the beneficial effect of exercise training on central artery compliance.     

Effects of diazepam on the carotid sinus baroreflex control of circulation in rabbits

To examine the effects of diazepam on the carotid sinus baroreflex control of circulation, bilateral carotid occlusion was performed on 14 conscious rabbits with aortic denervation. The responses of mean arterial pressure, heart rate, cardiac output and total peripheral resistance were obtained. The haemodynamic responses to carotid occlusion were evaluated at cumulative doses of 0.5 and 1.0 mg kg-1 of diazepam. The administration of diazepam decreased cardiac output and increased total peripheral resistance significantly, but did not affect the arterial pressure and heart rate. The response of total peripheral resistance to carotid occlusion was significantly increased from 0.118 +/- 0.018 (mean +/- SE) to 0.154 +/- 0.026 mmHg min ml-1 at 1.0 mg kg-1 of diazepam. The heart rate response was attenuated significantly from 41 +/- 5 to 24 +/- 4 beats min-1 at 1.0 mg kg-1 of diazepam. Diazepam did not alter the response of arterial pressure to carotid occlusion. We suggest that the dissociated effects of diazepam on the reflex control of circulation reflect the dissociated influences of diazepam on the central sympathetic and vagal-mediated pathways.     

Role of total arterial compliance and peripheral resistance in the determination of systolic and diastolic aortic pressure.

The goal of the study was to define the major arterial parameters that determine aortic systolic (Ps) and diastolic (Pd) pressure in the dog. Measured aortic flows were used as input to the two-element windkessel model of the arterial system, with peripheral resistance calculated as mean pressure over mean flow and total arterial compliance calculated from the decay time in diastole. The windkessel model yielded an aortic pressure wave from which we obtained the predicted systolic (Ps, wk) and diastolic (Pd, wk) pressure. These predicted pressures were compared with the measured systolic and diastolic pressures. The measurements and calculations were carried out in 7 dogs in control conditions, during aortic occlusion at four locations (the trifurcation, between trifurcation and diaphragm, the diaphragm and the proximal descending thoracic aorta) and during occlusion of both carotid arteries. Under all conditions studied the predicted systolic and diastolic pressure matched the experimental ones very well: Ps, wk = (1.000 +/- 0.0055) Ps with r = 0.958 and Pd, wk = (1.024 +/- 0.0035) Pd with r = 0.995. Linear regression for pulse pressure gave PPwk = (0.99 +/- 0.016) PP (r = 0.911). We found the accuracy of prediction equally good under control conditions and in presence of aortic or carotid artery occlusions. Multiple regression between pulse pressure and arterial resistance and total arterial compliance yielded a poor regression constant (r2 = 0.19) suggesting that the two arterial parameters alone cannot explain pulse pressure and that flow is an important determinant as well. We conclude that, for a given ejection pattern (aortic flow), two arterial parameters, total arterial resistance and total arterial compliance are sufficient to accurately describe systolic and diastolic aortic pressure.     

Carotid baroreceptor reflexes in humans during orthostatic stress

Orthostatic stress, including standing, head-up tilting and lower body suction, results in increases in peripheral vascular resistance but little or no change in mean arterial pressure. This study was undertaken to determine whether the sensitivity of the carotid baroreceptor reflex was enhanced during conditions of decreased venous return. We studied eight healthy subjects and determined responses of pulse interval (ECG) and forearm vascular resistance (mean finger blood pressure divided by Doppler estimate of brachial artery blood velocity) to graded increases and decreases in carotid transmural pressure, effected by a neck suction/pressure device. Responses were determined with and without the application of lower body negative pressure (LBNP) at -40 mmHg. Stimulus-response curves were determined as the responses to graded neck pressure changes and the differential of this provided estimates of reflex sensitivity. Changes in carotid transmural pressure caused graded changes in R-R interval and vascular resistance. The cardiac responses were unaffected by LBNP. Vascular resistance responses, however, were significantly enhanced during LBNP and the peak gain of the reflex was increased from 1.2 +/- 0.3 (mean +/- S.E.M.) to 2.2 +/- 0.3 units (P < 0.05). The increased baroreflex gain may contribute to maintenance of blood pressure during orthostatic stress and limit the pressure decreases during prolonged periods of such stress.     

Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise

Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to – 65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.     

Effects of chronic dobutamine administration on the response to acute exercise in dogs

The effects of chronic dobutamine administration on haemodynamic and metabolic responses to submaximal and maximal exercise were studied in dogs. Dobutamine was infused at a rate of 40 micrograms/kg min-1, 2 h day-1, 5 days week-1 for a period of 6 weeks. Acute infusion of dobutamine for 1 h increased heart rate by 73 +/- 30 beats min-1 and cardiac output by 143 +/- 141 ml/min kg-1, reduced mean arterial blood pressure by 12 +/- 10 mmHg and arterial-venous O2 difference by 1.5 +/- 1 vol%. Maximal oxygen consumption, heart rate, stroke volume, cardiac output and arterial-venous O2 difference were unchanged after 6 weeks of treatment. Reductions in heart rate at rest and during submaximal exercise following chronic dobutamine treatment were small and significant only at the lowest exercise level studied. Mixed venous lactate concentrations measured at rest, during submaximal and maximal exercise and at 2 min of recovery were not different after dobutamine treatment. Chronic dobutamine infusion did not change the citrate synthase activity in the lateral gastrocnemius muscle. These results suggest that chronic dobutamine therapy in healthy dogs does not produce aerobic training responses.     

Variations in carotid arterial compliance during the menstrual cycle in young women

The effect of menstrual cycle phase on arterial elasticity is controversial. In 10 healthy women (20.6+/-1.5 years old, mean+/-s.d.), we investigated the variations in central and peripheral arterial elasticity, blood pressure (carotid and brachial), carotid intima-media thickness (IMT), and serum oestradiol and progesterone concentrations at five points in the menstrual cycle (menstrual, M; follicular, F; ovulatory, O; early luteal, EL; and late luteal, LL). Carotid arterial compliance (simultaneous ultrasound and applanation tonometry) varied cyclically, with significant increases from the values seen in M (0.164+/-0.036 mm2 mmHg-1) and F (0.171+/-0.029 mm2 mmHg-1) to that seen in the O phase (0.184+/-0.029 mm2 mmHg-1). Sharp declines were observed in the EL (0.150+/-0.033 mm2 mmHg-1) and LL phases (0.147+/-0.026 mm2 mmHg-1; F=8.51, P<0.05). Pulse wave velocity in the leg (i.e. peripheral arterial stiffness) did not exhibit any significant changes. Fluctuations in carotid arterial elasticity correlated with the balance between oestradiol and progesterone concentrations. No significant changes were found in carotid and brachial blood pressures, carotid artery lumen diameter, or IMT throughout the menstrual cycle. These data provide evidence that the elastic properties of central, but not peripheral, arteries fluctuate significantly with the phases of the menstrual cycle.     

Mechanisms of hypotensive effects of a posture change from seated to supine in humans

The hypothesis tested was that the hydrostatic stimulation of carotid baroreceptors is pivotal to decrease mean arterial pressure at heart level during a posture change from seated to supine. In eight males, the cardiovascular responses to a 15‐min posture change from seated to supine were compared with those of water immersion to the xiphoid process and to the neck, respectively. Left atrial diameter and cardiac output (rebreathing) increased similarly during the posture change and water immersion to the xiphoid process and further so during neck immersion. Mean arterial pressure decreased by 12 ± 2 mmHg during the posture change, by 5 ± 1 mmHg during xiphoid immersion, and was unchanged during neck immersion. Arterial pulse pressure increased by 12 ± 3 mmHg during the posture change (P < 0.05) and less during xiphoid and neck immersion by 7 ± 3 mmHg (P < 0.05). Total peripheral vascular resistance decreased similarly during the posture change and neck immersion and slightly less during xiphoid immersion (P < 0.05). In conclusion, the hydrostatic stimulation of carotid baroreceptors combined with some additional increase in arterial pulse pressure, which also stimulates aortic baroreceptors, accounts for more than half of the hypotensive response at heart level to a posture change from seated to supine.     

Reductions in resting blood pressure after 4 weeks of isometric exercise training

There is some evidence to suggest isometric training can reduce resting blood pressure in a shorter period than the typical 8 weeks, reported most commonly. The purpose of the present study was to explore whether 4 weeks of bilateral-leg isometric training can reduce resting blood pressure, and whether these changes are associated with altered cardiac output or total peripheral resistance. Thirteen participants volunteered for a 4-week crossover training study, involving three sessions per week (each session involving 4 × 2 min bilateral-leg isometric exercise). The training intensity used (95% peak HR) was equivalent to 24% MVC. In addition to blood pressure, resting heart rate, cardiac output, stroke volume, and total peripheral resistance were measured. Results demonstrated that bilateral-leg isometric exercise training for 4 weeks caused significant reductions in systolic, diastolic, and mean arterial pressure. Changes were −4.9 ± 5.8, −2.8 ± 3.2, and −2.7 ± 2.4 mmHg, respectively. No differences were observed in the other resting measures. In conclusion, this study has shown that it is possible to induce reductions in arterial blood pressure after 4 weeks of bilateral-leg isometric exercise.     

Can human cardiovascular regulation during exercise be learnt from feedback from arterial baroreceptors?

During dynamic exercise, a large fall in systemic vascular resistance occurs. Arterial pressure (AP) is, however, maintained through a combination of central command and neural activity from muscle afferents that adjust the autonomic outflow to the circulation. How these signals are calibrated to provide accurate regulation of AP remains unclear. This study tests the hypothesis that the calibration can be 'learnt' through feedback from the arterial baroreceptors arising over multiple trials of exercise. Eight healthy subjects undertook three different protocols in random order. The test protocol consisted of 7 days' training, when subjects were exposed on 70 occasions to 4 min of exercise (50% of maximal oxygen uptake capacity) paired with neck suction (-40 mmHg) to mimic an excessive rise in AP at the carotid baroreceptors with exercise. Two control protocols involved training with either exercise or neck suction alone. No significant changes in mean AP, diastolic AP or heart rate during normal exercise were detected following training with any protocol. However, the rise in systolic AP with exercise was attenuated by an average of 7.3 +/- 2.0 mmHg (mean +/- s.e.m., P < 0.01) on the first and second days following training with the test protocol, but not with either control protocol (P < 0.05 for difference between protocols, ANOVA). In conclusion, this study failed to show that mean AP during normal exercise could be reduced through prior conditioning by overstimulation of the baroreceptors during exercise. However, a reduction in systolic AP was observed that suggests the presence of some plasticity within the autonomic response, consistent with our hypothesis.