Influence of gender on the sympathetic neural adjustments to alterations in systemic oxygen levels in humans

The purpose of this investigation was to determine whether gender influences the muscle sympathetic nerve activity (MSA) and systemic cardiovascular adjustments to alterations in systemic oxygen levels. To accomplish this, we performed direct (intraneural) measurements of muscle sympathetic nerve activity in 11 male and seven female young healthy adults during room air breathing, moderate isocapnic hypoxaemia and hyperoxaemia. During hypoxaemia, arterial oxygen saturation declined similarly in men and women. The magnitudes of the peak increases in MSA and stimulus-response 'gain' were not different between groups. However, the women had a shorter latency of response (P < 0.05). Women also demonstrated a greater increase in heart rate and a modest elevation in diastolic blood pressure, whereas the ventilatory responses were identical in the two groups. During normoxic recovery, MSA returned to baseline more quickly in women than in men (P < 0.05). During hyperoxaemia, muscle sympathetic nerve activity decreased only in the men (P < 0.05). Heart rate decreased slightly (P < 0.05) in both men and women, whereas blood pressure and minute ventilation were unchanged from normoxic control levels. Our findings fail to support an effect of gender on the peak muscle sympathetic nerve activity response to moderate isocapnic hypoxaemia in healthy young adult humans, although women demonstrate a shorter latency for sympathoexcitation and recovery under these conditions. In response to hyperoxaemia, women fail to demonstrate the sympathoinhibition consistently observed in men, possibly because of the low resting levels of MSA characteristic of young adult women. Thus, gender appears to contribute to the interindividual variability in sympathetic and cardiovascular responses to alterations in systemic oxygen levels.