When matched for heart rate using low-dose atenolol, mild hyperthermia increased stroke volume by 7% during the final 20 minutes of prolonged exercise compared with normothermia (P=0.03).
RCT (n=11)
Does preventing heart rate elevation with atenolol during hyperthermic prolonged exercise affect stroke volume in men?
By preventing heart rate drift with a low-dose beta-blocker, this study demonstrates that mild hyperthermia actually increases stroke volume during exercise, and the typical reduction in stroke volume is secondary to elevated heart rate.
valor p: p=0.03
People who become hyperthermic during exercise display large increases in heart rate (HR) and reductions in stroke volume (SV). It is not clear if the reduction in SV is due primarily to hyperthermia or if it is a secondary effect of an elevation in HR reducing ventricular filling. In the present study, the upward drift of HR during prolonged exercise was prevented by a very small dose of the β1-adrenoreceptor blocker (atenolol; βB), thus allowing SV to be compared at a given HR during normothermia and hyperthermia. Eleven men cycled for 60 min at 57% of peak O2 uptake after receiving placebo control (PL) or a low dose (0.2 mg/kg) of βB. Hyperthermia was induced by reducing heat dissipation during exercise. Four experimental conditions were studied: normothermia-PL, normothermia-βB, hyperthermia-PL, and hyperthermia-βB. Hyperthermia increased skin and core temperature by 4.3 degrees C and 0.8 degrees C (P<0.01), respectively. βB prevented HR elevation with hyperthermia: HR values were similar at minute 60 during normothermia-PL and hyperthermia-βB (155±11 and 154±13 beats/min, respectively, P=0.82). However, SV was increased by 7% during the final 20 min of exercise during hyperthermia-βB compared with normothermia-PL (treatment×time interaction, P=0.03). In conclusion, when matched for HR, mild hyperthermia increased SV during exercise. Furthermore, the reduction in SV throughout prolonged exercise under normothermic and mildly hyperthermic conditions appears to be due to the increase in HR.
Trinity et al. (Mon,) conducted a rct in Exercise-induced hyperthermia (n=11). Atenolol and hyperthermia vs. Placebo and normothermia was evaluated on Stroke volume during the final 20 min of exercise (p=0.03). When matched for heart rate using low-dose atenolol, mild hyperthermia increased stroke volume by 7% during the final 20 minutes of prolonged exercise compared with normothermia (P=0.03).
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