A-14 Free Communication/Slide - Cardiac: JUNE 2, 2010 9:30 AM - 11:30 AM: ROOM: 331
The combined stress of prolonged exercise, dehydration and hyperthermia leads to a reduced stroke volume (SV) in humans, yet the precise left ventricular (LV) diastolic and systolic responses remain unclear. This reduction in SV may be underpinned by lower LV strain rates and/or twist rates (LV mechanics), which have been shown to link LV filling with ejection.
PURPOSE: To examine diastolic and systolic LV strain and twist rates at rest and during exercise with hyperthermia and progressive levels of dehydration.
METHODS: Echocardiographic images were obtained, from seven healthy young men (VO2max 58±8 ml.kg-1.min-1) at rest and during sub-maximal one-legged knee-extensor exercise, to estimate end-diastolic volume (EDV), end-systolic volume (ESV), SV, strain rates, systolic twist rate, diastolic untwisting rate in four experimental conditions: 1) Control (euhydration, core temperature ∼37°C), 2) ∼2% Dehydration (∼38°C), 3) ∼3.5% Dehydration (∼38°C), and 4) after Rehydration (∼37°C).
RESULTS: At rest, 3.5% Dehydration significantly reduced EDV and SV by 34±15 and 22±15 ml, respectively (P<0.01). In contrast, peak systolic twist rate increased from 77±21 to 148±35 deg.sec-1 (P<0.01) while peak diastolic untwisting rate tended to increase (P=0.11) and was significantly delayed from 7±3% to 23±8% of diastole (P<0.01). Delayed peak untwisting rate at rest was paralleled by a delay in peak diastolic strain rates (P<0.01). Similar to rest, during exercise, EDV and SV were reduced (32±9 and 23±9 ml, respectively, P<0.01). However, the significant change in twist rate observed at rest with dehydration was not apparent during exercise as LV twist rate was already enhanced during Control exercise and did not increase further with superimposed hyperthermia and dehydration.
CONCLUSIONS: Maintained strain rates coupled with reduced EDV and enhanced twist rates suggest that the lowering of SV with dehydration and hyperthermia at rest and during small muscle mass exercise is associated with reductions in LV filling likely due to hypovolemia rather than reduced contractility or LV mechanics.
This study was Supported by the Gatorade Sports Science Institute.