Investigating short-term blood pressure regulation : peripheral baroreceptor sensitivity

Autonomically-mediated baroreflex control of heart rate has been extensively studied (cardiac BRS, cBRS), but peripheral control of blood pressure is less well known. Total peripheral resistance (TPR) was derived from pulse contour stroke volume (SVPC) using non-invasive blood pressure (Finapres). The beat-to-beat variability of Finapres SVPC was evaluated in cardiac catheterisation patients against aortic blood pressure SVPC. Correlations were generally good (mean R = 0.75), but regression slopes tended to be less than unity and several aortic recordings were significantly affected by the dynamic response of the measurement system. Finapres SVPC was also compared to Doppler stroke distance (SD) in healthy volunteers. Both measures followed respiratory movements well, although SVPC had higher coherence with respiration. Discrepancies between the results were considered to be mainly due to errors in the Doppler method. Coherence thresholds for spectral cBRS were determined as a function of the number of subrecords available for ensemble averaging and the effect of ventricular ectopics on cBRS estimates was investigated. Pulse contour TPR data was then used to determine peripheral BRS (pBRS) in healthy controls and neurocardiogenic syncope patients (NCS) using methods adapted from cardiac BRS analysis. Diastolic pressure produced greater pBRS estimates than systolic pressure and pBRS was generally higher in patients and fainters than in controls and non-fainters. Tilt did not have a consistent effect on pBRS and it was not linearly related to age or resting blood pressure, although it may be increased in hypertension and the elderly. pBRS was able to discriminate between the subject groups when cBRS methods showed no difference.