Blunted Cardiac Autonomic Responsiveness to Hypoxemic Stress in Healthy Older Adults

Supine resting cardiac dynamics and responses to steady-state hypoxemia were investigated in six healthy older (59-72 yrs) adults using coarse-graining spectral analysis of heart rate variability (HRV) and were compared to six young (22-29 yrs) adults studied previously (Lucy et al<normal + trebuchet ms char,12 pt char, black char, condensed by 0.05 pt char>.,</normal + trebuchet ms char,12 pt char, black char, condensed by 0.05 pt char> 2000). End-tidal carbon dioxide pressure (P ET CO 2 ) was clamped at 1-2 mmHg above the usual resting value for 11 min of euoxia (P ET O 2 100 mmHg), followed by 22 min of hypoxia (P ET O 2 55 mmHg). During euoxia, vagally mediated harmonic and fractal power of HRV of older adults was minimal. Hypoxia induced an increase in ventilation, p < 0.01, and heart rate, p < 0.05. The heart rate increase (mean ± SE) of 0.23 ± 0.08 beats•min −1 per 1% decrease in arterial O 2 saturation was 25% of that demonstrated previously by young subjects, p < 0.001. In older adults, HRV spectral power remained unchanged during hypoxia, providing further evidence of an age-related blunting of cardiac autonomic function.