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., 2000). End-tidal carbon dioxide pressure (PETCO2) was clamped at 1-2 mmHg above the usual resting value for 11 min of euoxia (PETO2 100 mmHg), followed by 22 min of hypoxia (PETO2 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 O2 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.
Lucy
S Deborah
SD
Department of Physiology, Faculty of Medicine, The University of Western Ontario, London, Ontario N6G 1H1, Canada.
Kowalchuk
John M
JM
Hughson
Richard L
RL
Paterson
Donald H
DH
Cunningham
David A
DA
D000368:Aged; D000375:Aging; D001341:Autonomic Nervous System / Q000503:physiopathology*; D001794:Blood Pressure; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006706:Homeostasis; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012119:Respiration; D012146:Rest; D013312:Stress, Physiological / Q000503:physiopathology*