Effects of Beta‐Blockers on Thermal and Cardiovascular Strain of Adults With Coronary Artery Disease During Extreme Heat Events

Abstract

IntroductionExtreme heat is associated with a greater risk of adverse cardiovascular events, especially in people with cardiovascular disease. Many patients with cardiovascular disease are prescribed beta‐blockers. Some research suggests that in young healthy adults, cardio‐selective beta‐blockers may alter heat loss capacity. However, the effects of beta‐blockers on temperature regulation in older adults during an extreme heat event are unknown. The objective of this study was to compare thermal and cardiovascular responses during simulated extreme heat events between older adults with coronary artery disease (CAD) who use and do not use beta‐blockers. It was hypothesised that the increase in heart rate and skin blood flow would be smaller in CAD patients who use beta‐blockers compared to those who do not use beta‐blockers.Method25 older adults (23 males/2 females) with stable CAD, 18 taking cardio‐selective beta‐blockers (BB: 66±8 y; 85.7±13.3 kg; 28.0±4.6 kg/m2) and 7 not taking beta‐blockers (NBB: 66±7 y; 77.1±14.6 kg; 26.1±3.9 kg/m2), were exposed to two 3‐hour simulated extreme heat events; one hot and humid (38°C, 60% relative humidity) and one hot and dry (45°C, 10% relative humidity). Rectal and mean skin temperatures, heart rate, and skin blood flow were continuously recorded. Whole body sweat losses were calculated from changes in nude body weight.ResultsAt the end of the 3‐h hot and humid heat exposure, relative to pre‐exposure baseline the change in heart rate (BB: +7±5 bpm; NBB: +11±9 bpm, p=0.20), rectal (BB: +0.57±0.27°C; NBB: +0.60±0.31°C, p=0.76) and mean skin (BB: +5.1±1.2°C; NBB: +5.1±1.1°C, P=0.91) temperatures, and whole body sweat losses (BB: 771±480 g; NBB: 798±172 g, p=0.88) did not differ between groups. The change in skin blood flow from baseline was greater in the NBB (+32±23 arbitrary units) compared to the BB (+9±7 arbitrary units; p=0.01) group. At the end of the 3‐h hot and dry heat exposure, the increase in heart rate (BB: +9±8 bpm; NBB: +9±5 bpm, p=0.93), rectal (BB: +0.61±0.40°C; NBB: +0.62±0.22°C, p=0.91) and mean skin (BB: +5.9±0.9°C; NBB: +5.7±1.3°C; p=0.79) temperatures, whole body sweat losses (BB: 1252±174 g; NBB: 1207±169, p=0.56) and skin blood flow (BB: +26±22 arbitrary units; NBB: +26±39 arbitrary units; p=0.98) from baseline did not differ between groups.ConclusionOur preliminary evidence indicates that cardio‐selective beta‐blocker use does not alter thermal or cardiovascular strain in adults with stable coronary artery disease during simulated hot and humid or hot and dry extreme heat events.