Sympathetic nervous system and exercise tolerance response in normotensive and hypertensive adolescents

Cardiac performance during exercise in hypertensive patients without ventricular hypertrophy

BACKGROUND

Reduced systolic reserve on effort may be present in subjects with hypertension but no evidence of hypertensive cardiomyopathy. We assessed the determinants of abnormal cardiac performance during exercise in hypertensive patients without left ventricular hypertrophy.

MATERIALS AND METHODS

Thirty-five newly diagnosed, never-treated-earlier hypertensive patients without definite indication for left ventricular hypertrophy at echocardiography underwent radionuclide ambulatory monitoring of left ventricular function at rest and during upright bicycle exercise testing.

RESULTS

The patients were classified into two groups according to their ejection fraction response to exercise. In 21 patients (group 1), the ejection fraction increased > or = 5% with exercise and in 14 patients (group 2), the ejection fraction either increased < 5% or decreased with exercise. Patients of group 1 had lower peak filling rate at rest and less augmentation in end-diastolic volume during exercise (both P < 0.01) when compared with patients of group 2. A significant relationship between the magnitude of change in ejection fraction with exercise and both peak filling rate at rest (r = 0.58, P < 0.01) and exercise-induced change in end-diastolic volume (r = 0.45, P < 0.01) was found.

CONCLUSIONS

In newly diagnosed, never-treated-earlier hypertensive subjects with no evidence of hypertensive cardiomyopathy, the cardiac response to exercise is dependent on adequate diastolic filling volume to maintain systolic performance.

Left ventricular performance during prolonged exercise and early recovery in healthy subjects

The effect of semi-supine long lasting exercise to exhaustion [61 (SD 10) min] on left ventricular systolic performance was studied by echocardiography in 16 young healthy volunteers. During the incremental phase of exercise, the ejection fraction increased from 65.2 (SD 4.1)% to 80.1 (SD 4.8)% (P < 0.0001), then it levelled off up to the end of exercise [81.7 (SD 4.4)%, P < 0.0001 vs rest]. During recovery, the ejection fraction rapidly and steadily decreased to a value similar to that at rest [66.1 (SD 5.0)%, n.s.). A similar pattern was shown by the systolic blood pressure/end-systolic volume coefficient, which rose from 3.2 (SD 0.8) mmHg.ml-1 to 7.5 (SD 2.7) mmHg.ml-1 (P < 0.0001) in the initial phase and subsequently did not change until the end of exercise [7.0 (SD 2.2) mmHg.ml-1, P < 0.0001 vs rest], to fall sharply after the cessation of exercise [2.9 (SD 1.1) mmHg.ml-1 at the 10th min, n.s. vs rest]. Exercise and recovery indices of left ventricular performance were not correlated with exercise duration, maximal heart rate and increase in free fatty acids. The present results indicated that, after the initial increase, left ventricular performance remained elevated during prolonged high intensity exercise and that conclusions on exercise cardiac performance drawn from postexercise data can be misleading.

Left ventricular systolic response to exercise in patients with systemic hypertension without left ventricular hypertrophy

Supine exercise radionuclide angiography was performed in 367 men to assess left ventricular (LV) systolic response to exercise; 58 had systemic hypertension without LV hypertrophy on a resting electrocardiogram and 309 were normotensive. All patients met the following criteria defining a low pretest likelihood of coronary artery disease: age less than 50 years; normal electrocardiographic response to exercise; absence of typical or atypical chest pain; and exercise heart rate greater than 120 beats/min. Patients taking beta-receptor blockers were excluded. There were no significant differences between hypertensive and normotensive groups in peak exercise heart rate, workload or exercise duration. However, hypertensive patients had significantly higher peak exercise systolic blood pressures and peak exercise rate-pressure products. There were no differences between patients with and without hypertension in resting ejection fraction, peak exercise ejection fraction (hypertensive patients 0.71 +/- 0.01, normotensive patients 0.70 +/- 0.05) or change in ejection fraction at peak exercise (hypertensive patients 0.07 +/- 0.01, normotensive patients 0.07 +/- 0.04). Diastolic and systolic ventricular volumes tended to be smaller in the hypertensive patients, but the difference was not statistically significant. The change in systolic volume with exercise was similar in the 2 groups (hypertensive -10 +/- 3 ml/m2, normotensive -10 +/- 1 ml/m2). In the absence of electrocardiographic evidence of LV hypertrophy, systemic hypertension does not influence LV systolic response to exercise.

Exercise response in young women with borderline hypertension

We compared the response to dynamic exercise in 157 females (mean age 19 +/- 3 years) with borderline hypertension (BH) to findings in 105 normotensive controls. Near-maximal physical working capacity was 90 +/- 17 W in females with BH and 71 +/- 23 W for the controls (p less than 0.001). Mean heart rate, systolic and diastolic blood pressure, and pulse pressure levels both at rest and at exercise were significantly higher in BH patients (p less than 0.001 for all). Mean change between rest and exercise for all the above parameters was not significantly different among BH patients compared with controls. Nonspecific ST-T changes at rest (p less than 0.001) and exercise (p less than 0.005) were more common and mean corrected QT interval was significantly longer (p less than 0.001) in BH patients. The parallel exercise response that we found in BH and normotensives would not appear to substantiate the view that ergometry is particularly useful as a modality for diagnosing hypertension in young females.

Left ventricular ejection fraction response during exercise in asymptomatic systemic hypertension

To study the effect of mild-to-moderate elevations in diastolic blood pressure (BP) on systolic left ventricular (LV) function, 28 hypertensive patients and 20 normal subjects underwent upright exercise first-pass radionuclide angiography. All were asymptomatic, had normal rest and exercise electrocardiographic findings and no evidence of LV hypertrophy or coronary artery disease. LV function at rest was similar in the 2 groups, but with exercise hypertensive patients had a greater end-systolic volume (69 +/- 19 vs 51 +/- 19 ml, p less than 0.002) and lower ejection fraction (EF) (0.59 +/- 0.09 vs 0.72 +/- 0.07, p less than 0.0001), stroke volume (101 +/- 28 vs 130 +/- 36 ml, p less than 0.005) and peak oxygen uptake (23 +/- 7 vs 33 +/- 9 ml/kl/min, p less than 0.05). Hypertensive patients were separated into 3 groups: group 1-12 patients with an increase in EF with exercise greater than or equal to 0.05; group 2-7 patients with a change in EF with exercise less than 0.05; and group 3-9 patients with a decrease in EF with exercise greater than or equal to 0.05. Group 3 hypertensive patients were older, had a higher heart rate at rest and lower peak oxygen uptake. Rest LV function was similar in the 3 hypertensive subgroups, but exercise end-systolic volumes were higher in groups 2 and 3. Exercise thallium-201 images was normal in all but 1 of 14 hypertensive group 2 or 3 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Function of the autonomic nervous system in young, untreated hypertensive patients

The reactivity of the sympathetic nervous system was studied in 10 young, adult patients with labile hypertension and compared with a normotensive age-matched control group. Upon graded exercise on a constant speed bicycle ergometer, the hypertensive subjects reacted with an exaggerated blood pressure response and a significantly greater increase in the plasma adrenaline and noradrenaline levels. The basal catecholamine levels, however, were similar in both observation groups. This was in spite of an intact baroreceptor reflex in the hypertensives as indicated by a normal hemodynamic response to angiotensin II. This apparent discrepancy may be explained by an enhanced uptake of adrenaline during stress into the neuron, where it acts as a cotransmitter and facilitates the release of noradrenaline via presynaptic beta 2-adrenoceptors. Similar blood pressure and heart rate responses to isoproterenol and atropine were observed in both groups. This indicates normal beta-adrenoceptor sensitivity and vagal nerve activity in the hypertensive subjects.