Barocontrol in healthy subjects

Abstract

Background: In the poorly understood relation between orthostatic hypotension and impaired physical performance and falls, baroreflex sensitivity (BRS) and cerebral autoregulation (CAR) may play a key role. Non-invasive ambulatory assessment of BRS and CAR is necessary to account for the time-varying nature of these parameters. We assessed the reliability and validity of combined photoplethysmography (PPG), electrocardiography (ECG) and near-infrared spectroscopy (NIRS) measurements for non-invasive ambulatory monitoring of BRS and CAR during postural changes. Methods: In 34 healthy adults (mean age 25 years, inter quartile range 22-45; 10 female), PPG (arteries in wrist and finger), ECG, bifrontal NIRS and continuous blood pressure (Finapres) were measured during postural changes varying in center of mass displacement (sit to stand versus supine to stand), speed (3 versus 10 seconds) and leg muscle use (supine to stand versus head up tilt). Pulse wave velocity (PWV) was computed as the time between the ECG R-peak and the steepest point in the PPG signal. Sensitivity was defined as a significant signal difference with baseline after postural change; test-retest reliability as the intra-class correlation (ICC) for repeats of the same postural change; and BRS and CAR as the respective change in inter beat interval and oxygenated haemoglobin relative to systolic and mean arterial blood pressure (SBP and MAP). Pearson correlations higher than 0.4, 0.6 and 0.75 were regarded as fair, good and excellent, respectively. Results: Finger PPG showed good correlation with MAP, but had poor test-retest reliability. NIRS had good to excellent reliability and good correlation with MAP. PWV had good test-retest reliability and correlation with MAP. Test-retest reliability and validity were fair for BRS and fair to excellent for CAR during the rapid supine to stand maneuver. Conclusion: The good correlation between PPG and MAP indicates the potential use of PPG for non-invasive BP estimation during postural changes. Measurement of PPG, ECG and NIRS during the rapid supine to stand maneuver produces reliable and valid estimates of BRS and CAR, indicating the potential clinical value of these measurements for non-invasive ambulatory BRS and CAR estimation.