Sex Differences in Macrovascular Responsiveness: Acute Effects of Hot Water Immersion vs. Aerobic Exercise in Overweight Older Adults

Recent studies have focused on the potential benefits of heat exposure for cardiovascular health. However, the acute effects of heat therapy on conduit arteries remain unclear, particularly in overweight and obese older males and females. This study aimed to compare core temperature (Tc), heart rate (HR), and brachial, femoral, and carotid artery diameter and velocity (Doppler ultrasound) responses to an acute exercise (EXE) session versus hot water immersion (HWI), and to determine whether physiological responses are sex-dependent. Twenty-five overweight older adults (10♂/15♀; age:59±7, BMI:29.4±3.4kg/m2) underwent two experimental sessions (30 minutes): EXE (60-70%HRmax) and HWI(40°C). HWI resulted in a larger increase in Tc across the session with the largest difference at 30 minutes (0.9±0.3 vs 0.7±0.3°C;p=0.024). No differences were observed in Tc between males and females (interaction p=0.271). HWI induced a lower rise in HR (♂40±18 vs ♀51±12bpm at 30 mins;p=0.013) than EXE, and females exhibited a larger change in HR after HWI than males (♂27±12 vs ♀48±17bpm;p=0.003). HWI also induced a larger reduction in systolic (-6±10 vs 1±7mmHg;p=0.012) and diastolic BP (-10±9 vs -2±5mmHg;p=0.001) than EXE, but with no sex differences. HWI induced a larger increase in brachial diameter, brachial and femoral velocity, brachial and femoral flow, and shear rate than EXE. Females exhibited significantly higher change in femoral velocity (♀26±8 vs ♂17±6cm/s;p=0.011) and shear rate (♀157±55 vs ♂98±38cm/s;p=0.008) in response to HWI than males. A single session of HWI induced larger vascular responses than exercise. Males and females both benefit, but somewhat differently and possibly via different mechanisms.