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Cardiac systolic and diastolic function during whole body heat stress
R Matthew Brothers1, Paul S Bhella, Shigeki Shibata
1Presbyterian Hospital of Dallas, Institute of Exercise and Environmental Medicine, 7232 Greenville Ave., Ste. 435, Dallas, TX 75231, USA.
Insights
Whole body heat stress enhances systolic function in healthy individuals, improving atrial and ventricular performance. Diastolic function remains unchanged, contrary to expectations of reduced filling pressures.
Area of Science:
- Cardiovascular Physiology
- Thermoregulation
- Exercise Physiology
Background:
- Heat stress can affect cardiac function, with known benefits in heart failure patients.
- The impact of heat stress on cardiac function in healthy individuals is less understood.
- Previous studies suggest potential improvements in stroke volume during heat stress.
Purpose of the Study:
- To investigate the effects of whole body heat stress on diastolic and systolic cardiac function in healthy individuals.
- To test the hypothesis that heat stress improves cardiac function in healthy adults.
- To compare cardiac function before and after a controlled passive heat stress intervention.
Main Methods:
- Nine healthy male volunteers participated in the study.
- Echocardiographic measurements of diastolic and systolic function were recorded at rest and during heat stress.
- Passive heat stress was applied to increase core body temperature by approximately 1.0°C.
Main Results:
- Heat stress did not alter key diastolic function indexes, including early diastolic mitral annular velocity (E') and the E/E' ratio.
- Late diastolic mitral annular velocities (A') and mitral inflow velocity during atrial contraction increased, indicating improved atrial systolic function.
- Ventricular systolic function improved, evidenced by increased septal and lateral mitral annular systolic velocities and isovolumic acceleration.
Conclusions:
- Whole body heat stress improves both atrial and ventricular systolic function in healthy individuals.
- Diastolic function was maintained during heat stress, despite expected reductions in filling pressures.
- Findings support previous research indicating heat stress enhances systolic performance, while diastolic function remains stable.
Abstract:
During a whole body heat stress, stroke volume is either maintained or slightly elevated despite reduced ventricular filling pressures and central blood volume, suggestive of improved cardiac diastolic and/or systolic function. Heat stress improves cardiac systolic and diastolic function in patients with congestive heart failure, although it remains unknown whether similar responses occur in healthy individuals, which is the hypothesis to be tested. Nine male volunteers underwent a whole body heat stress. Echocardiographic indexes of diastolic and systolic function were performed following a supine resting period, and again following an increase in internal temperature of approximately 1.0 degrees C via passive heat stress. Despite previous reports of heat stress-induced decreases in ventricular filling pressures and central blood volume, no changes in indexes of diastolic function were identified during heating [i.e., unchanged early diastolic mitral annular tissue velocity (E'), mitral inflow during the early diastolic phase (E), the E/E' ratio, and isovolumetric relaxation time]. Heat stress increased late diastolic septal (P = 0.03) and lateral (P = 0.01) mitral annular tissue velocities (A'), mitral inflow velocity during atrial contraction (P < 0.001), and the relative contribution of atrial contraction to left ventricular filling during diastole (P = 0.01), all indicative of improved atrial systolic function. Furthermore, indexes of ventricular systolic function were increased by heat stress [i.e., increased septal (P = 0.001) and lateral (P = 0.01) mitral annular systolic velocities and isovolumic acceleration at the septal (P = 0.03) and lateral (P < 0.001) mitral annulus]. These data are suggestive of improved atrial and ventricular systolic function by the heat stress. Together these data support previous findings, which used the less precise measure of ejection fraction, that heat stress improves indexes of systolic function, while diastolic function is maintained.
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