Frequency Domain Causal Interactions Between Heart Period and Systolic Arterial Pressure During Baroreflex Loading

Frequency domain causality analysis based on multivariate autoregressive (MAR) and multivariate dynamic adjustment (MDA) models were applied to typify directional dynamic interactions between heart period (HP) and systolic arterial pressure (SAP) during the baroreflex loading induced by head-down tilt (HDT). We studied 12 healthy men (age: from 41 to 71 yrs, median: 57 yrs) at rest in supine condition and during HDT with a tilt table inclination equal to −25°. We observed a reduction of the involvement of the baroreflex in governing HP-SAP dynamic interactions during HDT. This finding was evident only in the low frequency (LF, from 0.04 to 0.15 Hz) band. We suggest that frequency domain causality analysis allows the investigation of cardiovascular control mechanisms and HDT can be fruitfully utilized to reduce the relevance of baroreflex control, thus raising the chance of observing different cardiovascular regulatory mechanisms.