Individuals with persisting post-concussion symptoms with physiological subtype demonstrate altered cardiovascular and autonomic responses to face cooling.

Abstract

Individuals with persisting post-concussion symptoms with physiological subtype (PPCS-P) demonstrate exercise intolerance due to exacerbation of concussion-like symptoms during incremental exercise. We tested the hypothesis that individuals with PPCS-P (n = 12) would have a blunted cardiac autonomic response to face cooling compared to healthy controls (CTRL, n = 12). Participants were supine and performed a 5 min baseline, then experienced a 3 min face cold pressor test followed by 5 min of recovery. A three-lead electrocardiogram was used to measure heart rate and root mean square of successive differences in R-R intervals (RMSSD), finger photoplethysmography was used to measure mean arterial pressure (MAP), and laser-Doppler flowmetry was used to measure finger skin blood flux. The PPCS-P group had a lower exercise tolerance (9.9 ± 3.2 min, P < 0.001) and lower peak heart rate (170.0 ± 14.0 beats·min^-1, P < 0.001) compared to CTRL (19.6 ± 2.5 min; 193.0 ± 5.0 beats·min^-1). PPCS-P demonstrated a blunted mean heart rate (CTRL: ∆-4.0 ± 5.0 beats·min^-1, PPCS-P: ∆2.0 ± 4.0 beats·min^-1; group effect: P < 0.001) and mean RMSSD (CTRL: ∆26.6 ± 34.7 ms, PPCS-P: ∆-1.8 ± 33.9 ms; group effect: P = 0.026) responses at 2 min of face cooling compared to CTRL. Both groups had a significant increase in MAP during face cooling, where at 2 min, MAP was higher in PPCS-P (∆+13.2 ± 5.5 mmHg) compared to CTRL (∆+8.7 ± 6.9 mmHg, group effect: P < 0.001). Furthermore, PPCS-P had a sustained lower finger skin blood flux (group effect: P < 0.001) during face cooling (PPCS-P: ∆-48.2 ± 27.1%, CTRL: ∆-12.8 ± 24.7% at 2 min). These data suggest that individuals with PPCS-P demonstrate altered cardiac and peripheral autonomic function during face cooling compared to healthy controls.