Left ventricular systolic and diastolic function during orthostatic heat stress

Abstract

During supine passive heat stress, stroke volume (SV) and early diastolic filling are maintained, due to increased left ventricular (LV) contractility and associated LV suction. The LV response to heat combined with orthostatic stress has not been studied. We hypothesized that orthostatic heat stress results in reduced early diastolic filling coupled with an inability to further reduce end-systolic volume (ESV). 2D and Doppler ultrasound was used to measure LV end-diastolic (EDV) and ESV, ejection fraction (EF), early diastolic filling velocities (E), and lateral annular tissue velocities during systole (S′) and early diastole (E′). Twelve healthy men (25 ± 5 yr) were studied under normothermia and hyperthermia, in the supine and 30° head-up tilt (HUT) positions. HUT reduced EDV (20%), E (22%), E′ (26%), and SV (29%), whereas S′ increased (14%), and EF and ESV were unchanged. HUT + heat stress further reduced EDV (12%) and E′ (12%) vs. HUT, while ESV was reduced by 51%, and EF and S′ were augmented (15% and 26%, respectively). SV and E were unchanged from HUT. Contrary to our hypothesis, early diastolic filling velocity was not significantly reduced, and systolic function was augmented with heat during orthostatic stress.