Influence of respiration on metabolic, hemodynamic, psychometric, and R-R interval power spectral parameters.

Because respiration modulates autonomic activity, we determined the magnitude of perturbation of changing breathing frequency and tidal volume on metabolic, hemodynamic, psychometric, and R-R interval power spectral parameters. Seated subjects breathed at three different rates and five different volumes with each of the different rates. Breathing rates and volumes were percentages of the subject's resting breathing pattern and, therefore, identical across all subjects. Increases in rate and volume resulted in significant perturbations in end-tidal CO2 production, CO2 production, ventilatory equivalent for O2, comfort levels, and R-R interval power spectra (P < 0.05). The magnitude of the perturbations in the above parameters indicated a substantial upset in all subjects' metabolic, hemodynamic, and comfort homeostasis, precipitating a significant loss of vagal tone. The implications of our findings are that imposed breathing patterns used to modulate autonomic outflow should be tailored to the individual's resting breathing pattern. These data further support the urgent need for concomitant metabolic and respiratory measurements when analyzing and interpreting heart rate variability data.