The statistically significant short-term decrease in breathing frequency in our study is consistent with previous studies.7,19,25,26 While improved thoraco-abdominal synchrony might be a mechanism of breathing-frequency reduction,
we found no significant reduction in PaCO2. Roca and colleagues similarly reported that HFNC significantly reduced breathing frequency, but with no reduction in PaCO2
.7 We did not perform quantitative calibrations for respiratory inductive plethysmography, so we were unable to obtain accurate VT from each subject with respiratory inductive plethysmography. Even so, the product of the sum signal and breathing frequency was statistically significantly reduced by HFNC (P .001). If minute volume was reduced by HFNC without any change in alveolar ventilation, it is likely that HFNC reduced anatomical dead space.