Abstract
We measured the oxygen cost of breathing during voluntary hyperventilation in 13 subjects to test the hypothesis that the oxygen cost of breathing at a given level of ventilation would vary, dependent on the combination of tidal volume and respiratory frequency. We also measured thoracoabdominal asynchrony indices with respiratory inductive plethysmography. Prior to experiments, resting tidal volume (100%VT) was determined in each subject. Subjects voluntarily increased ventilation with tidal volume fixed (100%VT, 150%VT, or 300%VT). Increased ventilation increased VO2 in proportional to the level of ventilation. Changes in VO2 during hyperventilation (delta VO2) were compared between VTs. Delta VO2 was significantly higher during 100%VT breathing than 300%VT breathing. These results suggest that the oxygen cost of breathing during hyperventilation is high when VT is fixed at the resting level. Respiratory inductive plethysmography showed that thoracoabdominal asynchrony indices (PhAng, PhRIB, PhREB, and PhRTB) significantly increased during 100%VT breathing with the level of ventilation increased. Such an increase was not found during 150%VT breathing or 300%VT breathing. However, correlation analyses revealed no significant correlation between delta VO2 and delta PhAng, delta PhRIB, delta PhREB, or delta PhRTB, suggesting that thoracoabdominal asynchrony does not explain differences in the oxygen cost of breathing between VTs. [J Physiol Sci. 2008;58 Suppl:S116]
