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1 Research and Development, John D. Dingell Veterans Administration Medical Center, Detroit, MI, USA
2 Department of Internal Medicine, Wayne State University, Detroit, MI, USA; Research and Development, John D. Dingell Veterans Administration Medical Center, Detroit, MI, USA; Department of Biomedical Engineering, Wayne State University, Detroit, MI, USA
3 Department of Internal Medicine, Wayne State University, Detroit, MI, USA; Research and Development, John D. Dingell Veterans Administration Medical Center, Detroit, MI, USA; Department of Physiology, Wayne State University, Detroit, MI, USA
* To whom correspondence should be addressed. E-mail: jmateika{at}med.wayne.edu.
We hypothesized that the acute ventilatory response to carbon dioxide in the presence of low and high levels of oxygen would increase to a greater extent in males compared to females following exposure to episodic hypoxia. Eleven healthy males and females of similar race, age and body mass index completed a series of rebreathing trials before and after exposure to eight 4-min episodes of hypoxia. During the rebreathing trials, subjects initially hyperventilated to reduce the partial pressure of carbon dioxide(PETCO2) below 25 Torr. Subjects then rebreathed from a bag containing a normocapnic (42 Torr), low (50 Torr) or high oxygen gas mixture (150 Torr). During the trials, PETCO2 increased while the selected level of oxygen was maintained. The point at which ventilation began to rise in a linear fashion as PETCO2 increased was considered to be the carbon dioxide set-point. The ventilatory response below and above this point was determined. The results showed that the ventilatory response to carbon dioxide above the set-point was increased in males compared to females before exposure to episodic hypoxia, independent of the oxygen level that was maintained during the rebreathing trials (50 Torr: male - 5.19 ± 0.82 vs. female - 4.70 ± 0.77 L/min/Torr; 150 Torr: male - 4.33 ± 1.15 vs. female - 3.21 ± 0.58 L/min/Torr). Moreover, relative to baseline measures, the ventilatory response to carbon dioxide in the presence of low and high oxygen levels increased to a greater extent in males compared to females after exposure to episodic hypoxia (50 Torr: male - 9.52 ± 1.40 vs. female - 5.97 ± 0.71 L/min/Torr; 150 Torr: male - 5.73 ± 0.81 vs. female - 3.83 ± 0.56 L/min/Torr). Thus, we conclude that enhancement of the acute ventilatory response to carbon dioxide after episodic hypoxia is sex dependent.
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