Hemodynamic effects of isometric exercise in hypertrophic cardiomyopathy: comparison with normal subjects

Isometric stress in cardiovascular magnetic resonance-a simple and easily replicable method of assessing cardiovascular differences not apparent at rest

INTRODUCTION

Isometric exercise may unmask cardiovascular disease not evident at rest, and cardiovascular magnetic resonance (CMR) imaging is proven for comprehensive resting assessment. This study devised a simple isometric exercise CMR methodology and assessed the hemodynamic response evoked by isometric exercise.

METHODS

A biceps isometric exercise technique was devised for CMR, and 75 healthy volunteers were assessed at rest, after 3-minute biceps exercise, and 5-minute of recovery using: 1) blood pressure (BP) and 2) CMR measured aortic flow and left ventricular function. Total peripheral resistance (SVR) and arterial compliance (TAC), cardiac output (CO), left ventricular volumes and function (ejection fraction, stroke volume, power output), blood pressure (BP), heart rate (HR), and rate pressure product were assessed at all time points.

RESULTS

Image quality was preserved during stress. During exercise there were increases in CO (+14.9 %), HR (+17.0 %), SVR (+9.8 %), systolic BP (+22.4 %), diastolic BP (+25.4 %) and mean BP (+23.2 %). In addition, there were decreases in TAC (-22.0 %) and left ventricular ejection fraction (-6.3 %). Age and body mass index modified the evoked response, even when resting measures were similar.

CONCLUSIONS

Isometric exercise technique evokes a significant cardiovascular response in CMR, unmasking physiological differences that are not apparent at rest.

KEY POINTS

• Isometric exercise unmasks cardiovascular differences not evident at rest. • CMR is the reference standard for non-invasive cardiovascular assessment at rest. • A new easily replicable method combines isometric exercise with CMR. • Significant haemodynamic changes occur and differences are unmasked. • The physiological, isometric CMR stressor can be easily replicated.

Heat stress attenuates the increase in arterial blood pressure during isometric handgrip exercise

The purpose of this study was to examine arterial blood pressure responses during isometric handgrip (IHG) exercise performed at increasing levels of heat stress. Ten male subjects performed 1 min of IHG exercise at 60 % of maximal voluntary contraction under no heat stress (NHS), moderate heat stress [MHS, 0.6 °C increase in esophageal temperature (T (es))] and high heat stress (HHS, 1.4 °C increase in T (es)). For all conditions, IHG exercise significantly elevated mean arterial pressure (MAP) (NHS: 124 ± 6 vs. 90 ± 4 mmHg, MHS: 112 ± 6 vs. 89 ± 6 mmHg, HHS: 107 ± 7 vs. 91 ± 5 mmHg, P ≤ 0.05) and cardiac output (CO) (NHS: 9.0 ± 1.5 vs. 6.1 ± 0.6 L/min, MHS: 9.8 ± 1.8 vs. 7.6 ± 1.3 L/min, HHS: 10.0 ± 2.0 vs. 8.5 ± 1.9 L/min, P ≤ 0.05) relative to baseline, whereas no differences in total peripheral resistance (TPR) were observed (P > 0.05). However, the relative increases in MAP and CO were significantly reduced during MHS (MAP: 23 ± 6 mmHg, CO: 2.1 ± 0.9 L/min) and HHS (MAP: 16 ± 7 mmHg, CO: 1.5 ± 0.8 L/min) compared to NHS (34 ± 5 mmHg, CO: 2.9 ± 1.1 L/min, P ≤ 0.05). Furthermore, these elevations were significantly attenuated during HHS compared to MHS (P ≤ 0.05). Our findings show that heat stress attenuates the increase in arterial blood pressure during isometric handgrip exercise and this attenuation is cardiac output dependent, since TPR did not change during exercise for all heat stress conditions.

PET/CT assessment of symptomatic individuals with obstructive and nonobstructive hypertrophic cardiomyopathy

Patients with obstructive hypertrophic cardiomyopathy (HCM) exhibit elevated left ventricular outflow tract gradients (LVOTGs) and appear to have a worse prognosis than those with nonobstructive HCM. The aim of this study was to evaluate whether patients with obstruction, compared with nonobstructive HCM, demonstrate significant differences in PET parameters of microvascular function.

METHODS

PET was performed in 33 symptomatic HCM patients at rest and during dipyridamole stress (peak) for the assessment of regional myocardial perfusion (rMP), left ventricular ejection fraction (LVEF), myocardial blood flow (MBF), and myocardial flow reserve (MFR). Myocardial wall thickness and LVOTG were measured with an echocardiogram. Patients were divided into the following 3 groups: nonobstructive (LVOTG < 30 mm Hg at rest and after provocation test with amyl nitrite), obstructive (LVOTG ≥ 30 mm Hg at rest and with provocation), and latent HCM (LVOTG < 30 at rest but ≥ 30 mm Hg with provocation).

RESULTS

Eleven patients were classified as nonobstructive (group 1), 12 as obstructive (group 2), and 10 as latent HCM (group 3). Except for age (42 ± 18 y for group 1, 58 ± 7 y for group 2, and 58 ± 12 y for group 3; P = 0.01), all 3 groups had similar baseline characteristics, including maximal wall thickness (2.3 ± 0.5 cm for group 1, 2.2 ± 0.4 cm for group 2, and 2.1 ± 0.7 cm for group 3; P = 0.7). During peak flow, most patients in groups 1 and 2, but fewer in group 3, exhibited rMP defects (73% for group 1, 100% for group 2, and 40% for group 3; P = 0.007) and a drop in LVEF (73% for group 1, 92% for group 2, and 50% for group 3; P = 0.09). Peak MBF (1.58 ± 0.49 mL/min/g for group 1, 1.72 ± 0.46 mL/min/g for group 2, and 1.97 ± 0.32 mL/min/g for group 3; P = 0.14) and MFR (1.62 ± 0.57 for group 1, 1.90 ± 0.31 for group 2, and 2.27 ± 0.51 for group 3; P = 0.01) were lower in the nonobstructive and higher in the latent HCM group. LVOTGs demonstrated no significant correlation with any flow dynamics. In a multivariate regression analysis, maximal wall thickness was the only significant predictor for reduced peak MBF (β = -0.45, P = 0.003) and MFR (β = -0.63, P = 0.0001).

CONCLUSION

Maximal wall thickness was identified as the strongest predictor of impaired dipyridamole-induced hyperemia and flow reserve in our study, whereas outflow tract obstruction was not an independent determinant.

Endothelial Function as a Possible Significant Determinant of Cardiac Function during Exercise in Patients with Structural Heart Disease

This study was investigated the role that endothelial function and systemic vascular resistance (SVR) play in determining cardiac function reserve during exercise by a new ambulatory radionuclide monitoring system (VEST) in patients with heart disease. The study population consisted of 32 patients. The patients had cardiopulmonary stress testing using the treadmill Ramp protocol and the VEST. The anaerobic threshold (AT) was autodetermined using the V-slope method. The SVR was calculated by determining the mean blood pressure/cardiac output. Flow-mediated vasodilation (FMD) was measured in the brachial artery to evaluate endotheilial function. FMD and the percent change f'rom rest to AT in SVR correlated with those from rest to AT in ejection fraction and peak ejection ratio by VEST, respectively. Our findings suggest that FMD in the brachial artery and the SVR determined by VEST in patients with heart disease can possibly reflect cardiac function reserve during aerobic exercise.

Short-term isometric exercise reduces systolic blood pressure in hypertensive adults: Possible role of reactive oxygen species

OBJECTIVE

A short-term isometric exercise protocol was tested in ten hypertensive individuals to determine its efficacy as a high blood pressure-reducing intervention.

DESIGN

The study was a prospective case study of 10 hypertensive individuals (8 men, 2 woman, mean age = 52 + 5 years) who underwent six weeks of isometric exercise training (three sessions/week).

METHODS

Blood pressure, blood lipids and markers of oxidative stress were monitored before, during and following the isometric intervention. Electron spin resonance spectroscopy was used to directly measure radicals in the blood samples.

RESULTS

After six weeks, systolic blood pressure decreased an average 13 mm Hg (p < 0.05) from a mean blood pressure of 146 to 133 mm Hg, a level that is below the usual 140 mm Hg hypertension threshold. Blood lipids were unchanged, but markers of oxidative stress were affected, with a dramatic decrease in exercise-induced oxygen centered radicals (-266%), (p < 0.05) and an increased resting whole blood glutathione:oxidized glutathione (+61%) in hypertensive adults following six weeks of isometric exercise.

CONCLUSION

Six weeks of isometric exercise training was effective in lowering systolic but not diastolic blood pressure in pre-hypertensive and hypertensive individuals, and enhanced antioxidant protection is a likely underlying mechanism.