Respiration and blood pressure variability: mechanical and autonomic influences.

The transfer function between broad-band respiratory activity and the heart rate (HR) response can be used to elucidate the frequency dependent phase and magnitude characteristics of the respiratory sinus arrhythmia (RSA). To understand the complex links between respiratory activity and arterial blood pressure (ABP), the transfer functions between instantaneous lung volume (ILV), parameters of arterial pressure, and central venous pressure (CVP) were determined in healthy human volunteers during 6-minute periods in which the respiratory rate was voluntarily controlled in a predetermined but erratic fashion, or CVP was perturbed with a similar pattern. Pharmacologic autonomic blockade was used to dissect the direct mechanical links between respiration and ABP from the effects of RSA on ABP. The results suggest that with HR fluctuations eliminated, respiration affects ABP in proportion to the rate of change of ILV; however, when neural control of HR remains intact, the RSA plays an important role in the genesis of ABP fluctuations.