Comparing spectral and invasive estimates of baroreflex gain

One of the new methods to evaluate the sensitivity of the baroreceptor-heart rate (HR) reflex involves the use of power spectral analysis to calculate the transfer function between blood pressure and HR. We assess the applicability and reproducibility of the baroreflex gain estimated by this method with traditional invasive techniques that induce ramp changes in mean arterial pressure (MAP) in conscious rabbits. Renal sympathetic nerve activity recordings are used to identify the mid-frequency band, and we also identify coherent fluctuations of MAP and HR with a 1.8 s phase delay, consistent with a baroreflex relationship and therefore appropriate to estimate the cross spectral transfer function.