Non-invasive assessment of the sensitivity of cardiac baroreflex was performed by recording each RR-interval and each blood pressure cycle (Finapres®). In sequences of at least three cardiac cycles in which systolic blood pressure and RR-interval had changed in the same direction, the slope of linear regression of RR duration as a function of the change in systolic arterial pressure was taken for estimating the sensitivity of the spontaneous cardiac baroreflex. This technique was used in healthy humans to examine how a postural change from supine to upright by either active standing up or 60° head-up tilting modified the sensitivity of the spontaneous baroreflex. We observed that the slope of the spontaneous baroreflex averaged 14.6 ±2 ms.mm Hg_1 during 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 position. Head-up tilting by 60° led to values similar to those following active standing. The adjustment of baroreflex slope to either postural change occurred in a few seconds, so that posture-characteristic values were obtained from five-minute records. We conclude that non- invasive 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 position. This easy and reliable determination of the sensitivity of the cardiac baroreflex might prove to be useful when assessment of baroreflex function is needed.
The cold pressor test (CPT) triggers in healthy subjects a vascular sympathetic activation and an increase in blood pressure. The heart rate (HR) response to this test is less well defined, with a high inter-individual variability. We used traditional spectral analysis together with the non-linear detrended fluctuation analysis to study the autonomic control of HR during a 3-min CPT. 39 healthy young subjects (23.7 ± 3.2 years, height 180.4 ± 4.7 cm and weight 73.3 ± 6.4 kg) were divided into two groups according to their HR responses to CPT. Twenty subjects have a sustained increase in HR throughout the test with reciprocal autonomic interaction, i.e. increase in sympathetic activity and decrease vagal outflow. In the 19 remainders, HR decreased after an initial increase, with indication of involvement of both sympathetic and vagal outflow. Baseline evaluation of the subjects revealed no difference between the two groups. Nevertheless, a higher sympathetic activity at the skin level during CPT was present in the group with decreased HR. Further studies are needed to explain why healthy subjects react differently to the CPT and if this has potential clinical implications., L. Mourot, M. Bouhaddi, J. Regnard., and Obsahuje seznam literatury