Effects of different training intensities on the cardiopulmonary baroreflex control of forearm vascular resistance in hypertensive subjects

Improvements in insulin sensitivity and muscle blood flow in aerobic-trained overweight-obese hypertensive patients are not associated with ambulatory blood pressure

To verify whether there are relationships between vascular and hormonal responses to aerobic training in hypertensive persons, sedentary hypertensive patients were randomized to an aerobic training or a callisthenic exercise group. The patients' 24-hour blood pressure, arterial compliance, forearm blood flow, and hormonal profile were evaluated at baseline and after 3-month training protocols. Mean maximal oxygen consumption (VO(2) max) increased by 8% in the aerobic group (P<.001), while no change was observed in the control group. There was a decrease in insulin resistance (homeostatic model assessment of insulin resistance, P=.039) and plasma cortisol (P=.006) in the aerobic group only, that also demonstrated an increase in forearm blood flow (P<.001) after training. No relationship was observed between change in blood pressure or change in body mass and other parameters. Aerobic training can promote a decrease in cardiovascular risk in hypertensive adults by improving vascular function and insulin resistance, despite no changes in ambulatory blood pressure after a 3-month intervention.

Cardiorespiratory fitness and laboratory stress: a meta-regression analysis

We performed a meta-regression analysis of 73 studies that examined whether cardiorespiratory fitness mitigates cardiovascular responses during and after acute laboratory stress in humans. The cumulative evidence indicates that fitness is related to slightly greater reactivity, but better recovery. However, effects varied according to several study features and were smallest in the better controlled studies. Fitness did not mitigate integrated stress responses such as heart rate and blood pressure, which were the focus of most of the studies we reviewed. Nonetheless, potentially important areas, particularly hemodynamic and vascular responses, have been understudied. Women, racial/ethnic groups, and cardiovascular patients were underrepresented. Randomized controlled trials, including naturalistic studies of real-life responses, are needed to clarify whether a change in fitness alters putative stress mechanisms linked with cardiovascular health.

Limb vasodilatory capacity and venous capacitance of trained runners and untrained males

Aerobically trained athletes possess enhanced vasodilatory capacity and venous capacitance in their exercising muscles. However, whether they also possess these characteristics in their non-specific exercising muscles is undetermined. This study examined vasodilatory capacity and venous capacitance of specific (legs) and non-specific exercising muscles (arms) of ten trained runners and ten active but untrained males aged 18-35 years. Venous occlusion plethysmography determined baseline and peak blood flow after 5 min of reactive hyperaemia. Forearm and leg venous capacitance were determined as the difference between baseline and 2 min of venous occlusion at 50 mmHg. During reactive hyperaemia, trained runners had higher leg (48.4+/-5.3 ml.100 ml tissue(-1).min(-1)) and arm (40.8+/-2.1 ml.100 ml tissue(-1).min(-1)) vasodilatory capacity compared to the untrained (leg: 37.3+/-2.5 ml.100 ml tissue(-1).min(-1); arm: 34.2+/-2.2 ml.100 ml tissue(-1).min(-1); P<0.05), and higher calf vascular conductance (0.51+/-0.06 ml.100 ml tissue(-1).min(-1).mmHg(-1) versus 0.35+/-0.03 ml.100 ml tissue(-1).min(-1).mmHg(-1); P<0.05). The trained also had higher venous capacitance in both arms (3.5+/-0.2 ml 100.ml(-1)) and legs (4.8+/-0.1 ml.100 ml(-1)) compared to the untrained (3.0+/-0.2 ml 100.ml(-1); 4.2+/-0.2 ml.100 ml(-1); P<0.05). These findings show that vasculature adaptations to running occur in both specific and non-specific exercising muscles.

Sympathetic activity and the heterogenous blood pressure response to exercise training in hypertensives

To test whether changes in sympathetic nervous system (SNS) activity or insulin sensitivity contribute to the heterogeneous blood pressure response to aerobic exercise training, we used compartmental analysis of [3H]norepinephrine kinetics to determine the extravascular norepinephrine release rate (NE2) as an index of systemic SNS activity and determined the insulin sensitivity index (S(I)) by an intravenous glucose tolerance test, before and after 6 mo of aerobic exercise training, in 30 (63 +/- 7 yr) hypertensive subjects. Maximal O2 consumption increased from 18.4 +/- 0.7 to 20.8 +/- 0.7 ml x kg(-1) x min(-1) (P = 0.02). The average mean arterial blood pressure (MABP) did not change (114 +/- 2 vs. 114 +/- 2 mmHg); however, there was a wide range of responses (-19 to +17 mmHg). The average NE2 did not change significantly (2.11 +/- 0.15 vs. 1.99 +/- 0.13 microg x min(-1) x m(-2)), but there was a significant positive linear relationship between the change in NE2 and the change in MABP (r = 0.38, P = 0.04). S(I) increased from 2.81 +/- 0.37 to 3.71 +/- 0.42 microU x 10(-4) x min(-1) x ml(-1) (P = 0.004). The relationship between the change in S(I) and the change in MABP was not statistically significant (r = -0.03, P = 0.89). When the changes in maximal O2 consumption, percent body fat, NE2, and S(I) were considered as predictors of the change in MABP, only NE2 was a significant independent predictor. Thus suppression of SNS activity may play a role in the reduction in MABP and account for a portion of the heterogeneity of the MABP response to aerobic exercise training in older hypertensive subjects.

Resetting of the cardiopulmonary baroreflex 10 years after surgical repair of coarctation of the aorta

OBJECTIVE

To characterise cardiopulmonary baroreflex responses and examine the effects of a 45 minute cycling bout late after successful repair of coarctation of the aorta.

SUBJECTS

10 young adults (mean (SEM) age 18.1 (2.6 years)) operated on for coarctation of the aorta 12.7 (3.5) years earlier, and 10 healthy controls.

DESIGN

Forearm blood flow (venous occlusion plethysmography) and vascular resistance, left ventricular internal diastolic diameter, and central venous pressure estimated from an antecubital vein were measured in the supine position at baseline and during five minute applications of lower body negative pressure (LBNP) at -15 mm Hg (LBNP(-15)) and -40 mm Hg (LBNP(-40)). Venous samples were obtained at baseline and during LBNP(-40) for noradrenaline (norepinephrine), adrenaline (epinephrine), renin activity, and aldosterone. The tests were repeated after 45 minutes of moderate exercise.

RESULTS

Baseline heart rate (78 (9) v 64 (6) beats/min), echocardiographic cardiac output (6.9 (1.1) v 5.0 (0.2) l/min), shortening fraction (41.7 (1.8)% v 33.3 (1.3)%), and forearm blood flow (3.4 (0.4) v 2.3 (0.3) ml/100 g/min) were higher in the coarctation group than in the controls (p < 0.05). Changes in forearm blood flow and forearm vascular resistance from baseline to LBNP(-40) were similar in both groups, but the relation between forearm vascular resistance and estimated central venous pressure or left ventricular internal diastolic diameter was shifted downward in the coarctation group. Plasma adrenaline was increased in the coarctation group (baseline: 3.2 (0.6) v 2.4 (0.3) pmol/l in controls; LBNP(-40): 687 (151) v 332 (42) pmol/l) (p < 0.05). Both groups showed a similar downward displacement of forearm vascular resistance (p < 0.05) after exercise.

CONCLUSIONS

There appears to be resetting of the cardiopulmonary baroreflex to a lower forearm vascular resistance in young adults operated on for coarctation of the aorta, associated with hyperdynamic left ventricular function. Raised circulating adrenaline could contribute to the lower forearm vascular resistance.

The effects of exercise and training on human cardiovascular reflex control

During physical activity, there is a graded withdrawal of vagal cardiac tone and a graded increase in sympathetic cardiac and vasomotor tone, initiated through both central command from the somatic motor cortex and muscle chemoreceptive and mechanoreceptive inputs. In parallel, there is an upward resetting of the operating point of the arterial baroreflex, with preserved reflex sensitivity. In contrast to the traditional interpretation that blood flow through exercising muscle is independent of vasomotor neural influences because of the dominance of local dilator metabolites, recent evidence suggests that both constrictor and dilator sympathetic neural influences may be involved in determining absolute levels of perfusion. Post-exercise, there is a period of relative hypotension that is associated with decreased peripheral resistance. Some, but not all, evidence indicates a causal role for reduced sympathetic drive. Chronic exercise training appears to reduce resting sympathetic activity, with parallel changes in the gain of a variety of cardiovascular autonomic reflexes initiated from cardiovascular sites. These changes may be attributable at least partly to masking of arterial baroreflexes by the impact of elevated blood volume on low-pressure baroreceptors. The reductions in sympathetic drive that follow training are more pronounced in patients with essential hypertension than in normotensive individuals and are likely to underlie the anti-hypertensive effect of exercise.

Vascular structure in the forearm and calf after 6 months of angiotensin converting enzyme inhibition in elderly hypertensive subjects with left ventricular hypertrophy

OBJECTIVE

To investigate the effects of angiotensin converting enzyme inhibition on the structure of resistive arteries assessed from minimal vascular resistance in the forearm and the calf and on left ventricular mass index of elderly hypertensive subjects with left ventricular hypertrophy.

DESIGN AND METHODS

We evaluated 23 elderly patients [12 women and 11 men, aged 70 +/- 1 years (mean +/- SEM)] with essential hypertension assessed with ambulatory blood pressure monitoring and left ventricular hypertrophy before and at the end of 6 months' treatment with quinapril. Minimal vascular resistance was calculated as the ratio of mean arterial pressure to regional blood flow measured upon restoration of circulation after 13 min of ischaemia combined with exercise and taken as an index of resistive vessel structure (i.e. media:lumen ratio).

RESULTS

Daytime ambulatory blood pressure had decreased from 164 +/- 2/95 +/- 1 to 147 +/- 3/86 +/- 2 mmHg (P < 0.001) and left ventricular mass index decreased from 138 +/- 4 to 120 +/- 5 g/m2 (P < 0.001) at the end of treatment. Minimal vascular resistance in the forearm had decreased from 3.1 +/- 0.3 to 2.4 +/- 0.2 mmHg/ml per 100 ml per min (P < 0.01) whereas we observed no change in minimal vascular resistance in the calf after treatment (4.6 +/- 0.7 versus 4.2 +/- 0.4 mmHg/ml per 100 ml per min, NS). The decrease in minimal vascular resistance in the forearm was correlated significantly to the fall in 24 h ambulatory mean arterial pressure (r = 0.58, P < 0.01). Changes in left ventricular mass index were not correlated to those in ambulatory blood pressure or to those in minimal vascular resistance in the forearm.

CONCLUSIONS

A 6-month reduction in blood pressure under quinapril treatment was associated with decreases in left ventricular hypertrophy and in minimal vascular resistance in the forearm of elderly hypertensive patients. Absence of structural changes in leg vasculature could be related to the greater arterial pressure prevalent in the lower limbs while patients stood upright and, consequently, a proportionately smaller decrease in blood pressure, as well as greater structural changes and fibrous damage than those of the upper limbs.

Regular walking increases peak limb vasodilatory capacity of older hypertensive humans: implications for arterial structure

BACKGROUND

Although regular aerobic exercise has been shown to lower arterial blood pressure in older adult humans with essential hypertension, the mechanisms responsible for this hypotensive effect remain largely unknown.

OBJECTIVE

To examine the hypothesis that the reduction in arterial blood pressure in older hypertensive humans with regular exercise is accompanied by evidence of a change in arterial structure.

METHODS

We measured peak limb vascular conductance, a well-established noninvasive measure of arterial structure, both in the forearm (untrained limb) and in the calf (exercise-trained limb) of 22 older adults (aged 51-74 years) with stage 1 or 2 essential hypertension. Eleven subjects walked 3-4 days/week at a mild exercise intensity (45% of heart rate reserve) for 6 months. Eleven other subjects served as nonexercising controls.

RESULTS

Maximal oxygen consumption of subjects in the exercise group increased by 17% (P < 0.05) with no change in body mass and body fat. Systolic and diastolic arterial blood pressures at rest were reduced by 7 +/- 4 and 5 +/- 2 mmHg, respectively (P < 0.05). There were roughly 20% increases in peak forearm blood flow and peak forearm vascular conductance (both P < 0.05). Similar increases in peak calf blood flow and vascular conductance were observed (both P < 0.01). There were no significant changes in any of these variables over the same time period for the nonexercising controls.

CONCLUSIONS

The decrease in resting blood pressure in older adults with stage 1 or 2 essential hypertension in response to regular aerobic exercise is associated with an increase in peak limb vascular conductance, which could be due in part to favorable changes in arterial structure. These exercise-induced functional and, possibly, structural changes are not confined to the exercise-trained limbs, but rather are more systemic in nature. These apparent beneficial changes in limb vasodilatory capacity and vascular structure can be produced with a mode, intensity, and frequency of aerobic exercise that can be tolerated and is commonly performed by older adults.

Diminished forearm vasomotor response to central hypervolemic loading in aerobically fit individuals

The aim of this study was to test the hypothesis that cardiopulmonary baroreflex control of forearm vascular resistance (FVR) during central hypervolemic loading was less sensitive in exercise trained high fit individuals (HF) compared to untrained average fit individuals (AF). Eight AF (age: 24 +/- 1 yr and weight: 78.9 +/- 1.7 kg) and eight HF (22 +/- 1 yr 79.5 +/- 2.4 kg) voluntarily participated in the investigation. Maximal aerobic power (determined on a treadmill), plasma volume and blood volume (Evans blue dilution method) were significantly greater in the HF than AF (60.8 +/- 0.7 vs. 41.2 +/- 1.9 ml.kg-1.min-1, 3.96 +/- 0.17 vs 3.36 +/- 0.08 1, and 6.33 +/- 0.23 vs 5.28 +/- 0.13 1). Baseline heart rate (HR), central venous pressure (CVP), mean arterial pressure (MAP, measured by an intraradial catheter or a Finapres finger cuff), forearm blood flow (FBF, plethysmography), and FVR, calculated from the ratio (MAP-CVP)/FBF, were not different between the HF and the AF. Lower body negative pressure (LBNP, -5, -10, -15, and -20 torr) and passive leg elevation (LE, 50 cm) combined with lower body positive pressure (LBPP, +5, +10, and +20 torr) were utilized to elicit central hypovolemia and hypervolemia, respectively. Range of CVP (from LBNP to LE+LBPP) was similar in the AF (from -3.9 to +1.9 mm Hg) and HF (from -4.0 to +2.2 mm Hg). However, FVR/CVP was significantly less in the HF (-1.8 +/- 0.1 unit.mm Hg-1) than AF (-34 +/- 0.1 unit.mm Hg-1). The FVR decrease in response to increase in CVP was significantly diminished in the HF (-1.46 +/- 0.45 unit.mm Hg-1) compared to the AF (-4.40 +/- 0.97 unit.mm Hg-1), and during LBNP induced unloading the FVR/CVP of the HF (-2.01 +/- 0.49 unit.mm Hg-1) was less (P < 0.08) than the AF (-3.28 +/- 0.69 unit.mm Hg-1). We concluded that the cardiopulmonary baroreceptor mediated FVR reflex response was significantly less sensitive to changes in CVP in individuals who practice exercise training.