ACTIVE STANDING AND PASSIVE TILTING SIMILARLY REDUCE THE SLOPE OF SPONTANEOUS BAROREFLEX IN HEALTHY-SUBJECTS

Non-invasive assessment of the sensitivity of cardiac baroreflex was p erformed by recording each RR-interval and each blood pressure cycle ( Finapres(R)). In sequences of at least three cardiac cycles in which s ystolic blood pressure and RR-interval had changed in the same directi on, the slope of linear regression of RR duration as a function of the change in systolic arterial pressure was taken for estimating the sen sitivity of the spontaneous cardiac baroreflex. This technique was use d in healthy humans to examine how a postural change from supine to up right by either active standing up or 60 degrees head-up tilting modif ied the sensitivity of the spontaneous baroreflex. We observed that th e slope of the spontaneous baroreflex averaged 14.6+/-2 ms.mm Hg-1 dur ing rest in the supine position, and decreased to 7.8 +/- 1.2 ms.mm Hg -1 (p< 0.05) after active standing, while the number of sequences was significantly increased in the upright as compared to the supine posit ion. Head-up tilting by 60 degrees led to values similar to those foll owing active standing. The adjustment of baroreflex slope to either po stural change occurred in a few seconds, so that pasture-characteristi c values were obtained from five-minute records. We conclude that noni nvasive recording of spontaneous sequences of related changes in blood pressure and RR-interval during several minutes provides reproducible values of the slope of cardiac baroreflex in the supine and upright p osition. This easy and reliable determination of the sensitivity of th e cardiac baroreflex might prove to be useful when assessment of baror eflex function is needed.