Effects of Altitude Exposure on Cardiovascular Autonomic Indices in Endurance-Trained Women

Women's engagement in high-altitude activities is increasing across disciplines. Physiological responses to exercise under hypoxia and cold remain under-researched. We evaluated heart rate variability indices and brachial artery flow-mediated dilation at baseline and after 30 minutes of exercise at a simulated altitude of 11,000 feet, 40 ºC. Participants included endurance-trained(n=5, 22±0 years, 168.7±4.30 cm, 61.00±5.60 kg, resting SBP 118±4 mmHg, resting DBP 76±5 mmHg, 21.46±5.08 % body fat, V̇O2max of 49.24±4.04 ml/kg/min) and untrained(n=5, 21±1.79 years, 167.68±4.41 cm, 71.68±8.36 kg, resting SBP of 118±2 mmHg, resting DBP of 76±3, 30.7±4.17 % body fat, V̇O2max of 32.64±6.65 ml/kg/min). Trained group RMSSD and PNN50 significantly increased (PNN50 stand-up pre 4.27±1.64 ms, post 11.67±12.06 ms, p=0.001; sit-down pre 11.67±12.08 ms, post 21.43±23.72 ms, p=0.001). (RMSSD pre 25.06±1.06 ms, post 39.29±20.56 ms, p=0.0254). Both groups increased sympathetic activity, evidenced by elevated low-frequency and very-low-frequency bands post-exposure. Brachial artery diameter(BAD) rose significantly in both groups, larger increase in the trained group. The BAD significantly increased from baseline to exposure in the trained(pre 0.29±0.05 mm, post 0.33±0.03 mm, p=0.005) and untrained group(pre 0.30±0.07 mm, post 0.33±0.06 mm p=0.006). Results help understand cardiovascular autonomic responses in women at high-altitude and have implications for their performance and safety.<p></p>