Abstract
During hypoxic exposure, humans with high-affinity hemoglobin (and compensatory polycythemia) have blunted increases in heart rate compared with healthy humans with typical oxyhemoglobin dissociation curves. This response may be associated with altered autonomic control of heart rate. Our hypothesis-generating study aimed to investigate cardiac baroreflex sensitivity and heart rate variability among nine humans with high-affinity hemoglobin [6 females, O2 partial pressure at 50% SaO2 (P50) = 16 ± 1 mmHg] compared with 12 humans with typical affinity hemoglobin (6 F, P50 = 26 ± 1 mmHg). Participants breathed normal room air for a 10-min baseline, followed by 20 min of isocapnic hypoxic exposure, designed to lower the arterial partial pressure O2 (PaO2) to ∼50 mmHg. Beat-by-beat heart rate and arterial blood pressure were recorded. Data were averaged in 5-min periods throughout the hypoxia exposure, beginning with the last 5 min of baseline in normoxia. Spontaneous cardiac baroreflex sensitivity and heart rate variability were determined using the sequence method and the time and frequency domain analyses, respectively. Cardiac baroreflex sensitivity was lower in humans with high-affinity hemoglobin than controls at baseline and during isocapnic hypoxic exposure (normoxia: 7 ± 4 vs. 16 ± 10 ms/mmHg, hypoxia minutes 15–20: 4 ± 3 vs. 14 ± 11 ms/mmHg; group effect: P = 0.02, high-affinity hemoglobin vs. control, respectively). Heart rate variability calculated in both the time (standard deviation of the N-N interval) and frequency (low frequency) domains was lower in humans with high-affinity hemoglobin than in controls (all P < 0.05). Our data suggest that humans with high-affinity hemoglobin may have attenuated cardiac autonomic function.
Original language | English (US) |
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Pages (from-to) | R625-R634 |
Journal | American Journal of Physiology - Regulatory Integrative and Comparative Physiology |
Volume | 324 |
Issue number | 5 |
DOIs | |
State | Published - May 2023 |
Keywords
- baroreflex sensitivity
- blood pressure regulation
- cardiovascular
- heart rate variability
- hypoxia
ASJC Scopus subject areas
- General Medicine