Table 3.
Frequency domain responses to progressive lower body negative pressure (LBNP) to presyncope (PS) in high tolerant (HT) and low tolerant (LT) subjects.
| LBNP Stage | LMM P-Value | ||||
|---|---|---|---|---|---|
| 0 | PS 3-min | Time | Tolerance | Interaction | |
| RRI LF, ms2 | |||||
| HT | 2448.1 ± 4911.5 | 322.6 ± 425.1* | 0.01 | 0.49 | 0.21 |
| LT | 1369.5 ± 1088.9 | 633.5 ± 717.4 | |||
| SAP LF, mmHg2 | |||||
| HT | 7.6 ± 6.6 | 20.8 ± 15.7* | <0.0001 | 0.28 | 0.25 |
| LT | 7.0 ± 7.1 | 15.4 ± 15.6* | |||
| SAP-RRI LF coherence | |||||
| HT | 0.61 ± 0.13 | 0.61 ± 0.15 | 0.62 | 0.44 | 0.70 |
| LT | 0.64 ± 0.15 | 0.62 ± 0.14 | |||
| SAP-RRI LF Gain, ms/mmHg | |||||
| HT (n = 23) | 15.4 ± 8.8 | 3.2 ± 2.0* | <0.0001 | 0.36 | 0.17 |
| LT (n = 17) | 14.7 ± 5.8 | 6.4 ± 5.4* | |||
| MAP LF, mmHg2 | |||||
| HT | 5.6 ± 3.6 | 15.7 ± 11.9* | <0.0001 | 0.30 | 0.06 |
| LT | 6.4 ± 5.4 | 11.0 ± 9.2 | |||
| MCAv LF, (cm/s)2 | |||||
| HT | 3.5 ± 2.8 | 4.8 ± 3.5 | 0.14 | 0.11 | 0.78 |
| LT | 5.0 ± 3.7 | 5.8 ± 4.7 | |||
| MAP-mean MCAv LF coherence | |||||
| HT | 0.63 ± 0.12 | 0.71 ± 0.11 | 0.23 | 0.71 | 0.17 |
| LT | 0.66 ± 0.18 | 0.66 ± 0.19 | |||
| MAP-mean MCAv LF gain, (cm/s).mmHg−1 | |||||
| HT (n = 25) | 0.75 ± 0.38 | 0.55 ± 0.14*,† | 0.02 | 0.13 | 0.13 |
| LT (n = 18) | 0.80 ± 0.21 | 0.75 ± 0.39 | |||
Data are presented as absolute means ± SD. LF, low frequency; RRI, R-to-R interval; SAP, systolic arterial pressure; MAP, mean arterial pressure; MCAv, middle cerebral artery velocity. PS 3-min refers to the 3-min prior to presyncope. A two-factor linear mixed model analysis with repeated measures from baseline to PS-3 was performed, followed by Holm-corrected post-hoc tests for multiple comparisons (run on the least squared means generated by the linear mixed model analysis).
P ≤ 0.03 compared to baseline within a group.
P ≤ 0.09 between HT and LT groups. Exact P values are reported for all comparisons.