Cardiorespiratory interactions during resistive load breathing

The addition to the respiratory system of a resistive load results in breat hing pattern changes and in negative intrathoracic pressure increases. The aim of this study was to use resistive load breathing as a stimulus to the cardiorespiratory interaction and to examine the extent of the changes in h eart rate variability (HRV) and respiratory sinus arrhythmia (RSA) in relat ion to the breathing pattern changes. HRV and RSA were studied in seven hea lthy subjects where four resistive loads were applied in a random order dur ing the breath and 8-min recording made in each condition. The HRV spectral power components were computed from the R-R interval sequences, and the RS A amplitude and phase were computed from the sinusoid fitting the instantan eous heart rate within each breath. Adding resistive loads resulted in 1) i ncreasing respiratory period, 2) unchanging heart rate, and 3) increasing H RV and changing RSA characteristics. HRV and RSA characteristics are linear ly correlated to the respiratory period. These modifications appear to be l inked to load-induced changes in the respiratory period in each individual, because HRV and RSA characteristics are similar at a respiratory period ob tained either by loading or by imposed frequency breathing. The present res ults are discussed with regard to the importance of the breathing cycle dur ation in these cardiorespiratory interactions, suggesting that these intera ctions may depend on the time necessary for activation and dissipation of n eurotransmitters involved in RSA.