Aim: 

The sex–linked differences in the respiratory system as well as in the haemoglobin oxygen saturation in normoxia are well documented. Also ventilatory response to hypoxia has been found different in men and women. Studies of cardiac autonomic nervous system (ANS) function during acute exposure to hypobaric hypoxia have suggested a shift in the sympatho-vagal balance towards relatively more sympathetic and less parasympathetic activity at higher hypoxic levels.

Methods: 

In the present study the effects of moderate hypoxia on cardiac ANS function and haemoglobin oxygen saturation (SaO2) in 14 young healthy subjects (eight women and six men) were evaluated.

Results: 

The exposure to 30-min acute normobaric hypoxia (FiO2 = 12.86%) provoked a significant increase of the heart rate in females (p<0.007) as well as in males (p<0.03). The power spectral analysis (autoregressive spectra) and the Poincaré plot analysis of the heart rate variability, used as assessment of cardiac ANS activity, showed a significant reduction of vagal activity (p<0.05) in women but not in men, comparing hypoxia to normoxia. In normoxia the SaO2 values was slightly higher in females than in males. Compared hypoxia to normoxia, the SaO2 decrease was statistically more significant in females (p<0.0001) than in males (p<0.02).

Conclusion: 

These results indicate a different sex response of the cardiac ANS during the exposure to hypoxia, suggesting in females a relevant reduction of the vagal activity concomitant with higher SaO2 decrease