Association of left ventricular end-diastolic volume with core temperature and heart rate during very hot and dry heat stress in older adults.

There is considerable heterogeneity in the thermal and cardiovascular responses to heat stress, even among older adults within a similar age range; hence, age alone may not predict heat-related risks. This variability may be in part explained by differences in cardiorespiratory fitness. We aimed to identify whether left ventricular end-diastolic volume (LVEDV), a characteristic of cardiorespiratory fitness, was associated with core temperatures and heart rate responses in older adults exposed to 3 h of very hot and dry heat stress. We hypothesized that individuals with smaller LVEDV would exhibit higher ending core temperature and heart rates following heat stress. Twenty-two older adults (73 ± 5 yr; 10 females) were exposed to 3 h of very hot and dry ambient heat stress (47°C, 15% relative humidity) with accompanying activities of daily living. We assessed thermal and cardiovascular responses at baseline and end-heating. End core temperature ranged from 37.4°C to 38.9°C, whereas end heart rate ranged from 53 to 113 beats/min. Baseline LVEDV was associated with end-heating core temperature (β = -0.018, SE = 0.004; P = 0.003) after controlling for body surface area and baseline core temperature. Likewise, LVEDV was associated with end-heating heart rate (β = -0.595, SE = 0.126; P < 0.001), after controlling for body surface area. However, LVEDV was not associated with whole body sweat rate (P = 0.100) or the change in forearm blood flow (P = 0.331) indexed to changes in core temperature. These findings suggest that individuals with small LVEDV may be susceptible to hyperthermia and tachycardia associated with environmental heat stress.NEW & NOTEWORTHY There is considerable heterogeneity in the thermal and cardiovascular responses to heat stress, even among older adults within a similar age range; hence, age alone may not predict heat-related risks. This variability may be in part explained by differences in physical fitness. Our findings show that individuals with low left ventricular end-diastolic volumes have greater core temperature and heart rate responses to environmental heat stress.