Sex‐Specific Heart Rate Responses to Apneic Manipulations in Young Healthy Subjects

Abstract

Contributions of lung stretch and chemoreflex stimulation to heart rate (HR) responses to apnea have not been elucidated independently in men and women. We tested the hypothesis that HR responses to apnea would be exaggerated in men relative to women. Relative changes in HR (ECG) were analyzed during 4 maximal apneic maneuvers: 1) end‐inspiratory (INSP), 2) end‐tidal expiratory (ETE), 3) INSP following hyperoxic breathing (HX), and 4) INSP following hyperventilation (HV). HR data from all apneas were analyzed in 10s bins. The first 5 bins (50s) of each apnea were compared between sexes in these analyses. INSP caused similar changes in HR between sexes (‐8 ± 11 and ‐7 ± 6 bpm, P=0.8), and the time courses of the changes in HR were also similar. Although the nadir bradycardic response to ETE (designed to unload lung stretch receptors) was similar between men and women (‐9 ± 7 and ‐9 ± 8 bpm, P=0.9) onset of bradycardia was delayed in women (30s bin) compared with men, in whom the bradycardia was immediate (10s bin). During HX (eliminating the influence of O2) and HV (eliminating the influence of CO2) both the time courses of the HR responses and the HR nadirs (HX: ‐17 ± 13 and ‐14 ± 11 bpm, P=0.6; HV: ‐33 ± 12 and ‐35 ± 17 bpm, P=0.9) were similar between men and women, respectively. These data suggest that sex differences in HR responses to apnea are not dependent on changes in O2 or CO2 but, rather, are unveiled during the unloading of lung stretch receptors. Supported by NSERC, AIHS, Mount Royal University Innovation Grant, and the University of Alberta Human Performance Scholarship Fund.