Table 4.
Comparison of changes in baroreflex sensitivity (BRS) and cerebral autoregulation (CA) in the time and frequency domain between high tolerant (HT) and low tolerant (LT) subjects.
| Time domain metrics | t-test P-Value | |
|---|---|---|
| tBRS (ΔHR/ΔSAP), bpm/mmHg | ||
| HT | −1.9 ± 0.9 | P < 0.01 |
| LT | −1.2 ± 0.8 | |
| tCA (ΔMCAv/ΔMAP), (cm/s).mmHg−1 | ||
| HT | 1.2 ± 0.9 | P = 0.45 |
| LT | 1.5 ± 1.8 | |
| Frequency domain metrics | t-test P-Value | |
| fBRS (ΔSAP-RRI LF Gain), ms/mmHg | ||
| HT (n = 14) | −13.0 ± 9.6 | P = 0.47 |
| LT (n = 13) | −10.8 ± 5.6 | |
| fCA (ΔMAP-mean MCAv LF Gain), (cm/s).mmHg−1 | ||
| HT (n = 14) | −0.29 ± 0.41 | P = 0.13 |
| LT (n = 13) | −0.06 ± 0.32 | |
Data are presented as the mean ± SD change from baseline to pre-syncope. HR, heart rate; SAP, systolic arterial pressure; MAP, mean arterial pressure; MCAv, middle cerebral artery velocity; RRI, R-to-R interval; LF, low frequency; tBRS, time domain cardiac baroreceptor sensitivity; tCA, time domain cerebral autoregulation; fBRS, frequency domain cardiac baroreceptor sensitivity; fCA, frequency domain cerebral autoregulation. Group differences in the absolute change from baseline to presyncope were assessed using unpaired t-tests (tBRS, tCA, and fBRS) and Kruskal-Wallis test (fCA). Exact P values are reported for all comparisons.