The effects of sympathetic activity induced by ice water on blood flow and brachial artery flow-mediated dilatation response in healthy volunteers

OBJECTIVE: To investigate the association between sympathetic activity, reactive hyperemia and brachial artery flow-mediated dilation (FMD). BACKGROUND: It is claimed that major surgery has an impact on endothelial function, as observed by post-operative reduced brachial artery FMD response. However, another explanation for the observed reduced FMD response post-operatively may be sympathetic stress-induced reduction in blood flow. METHODS: Seventeen healthy volunteers with a median age (25(th)-75(th) percentiles) of 23.5 (23–24.8) years were recruited. Participants’ brachial blood flow and FMD response were measured (i) during normal non-stress conditions (Normal(1)); (ii) during exposure to ice water; and (iii) afterwards, under normal non-stress conditions (Normal(2)). We continuously measured arterial blood pressure (Finometer), heart rate (ECG), skin blood flow of the index finger (laser Doppler), and brachial artery blood flow and diameter (Ultrasound Doppler). Measurements were taken at baseline; before a 5-min suprasystolic forearm occlusion; and following a 3-min post-occlusion, to measure reactive hyperemia and FMD. RESULTS: Median (25(th)-75(th) percentiles) FMD response after exposure to ice water was reduced compared to non-stress conditions [4.9 (2.9–8.4) % during ice water vs. 9.7 (7.6–12.2) % Normal(1) and 9.7 (6.4–10.3) % Normal(2), P < 0.001]. Blood flow 60 s after cuff-deflation during ice water exposure was significantly reduced to 328 (289–421) mL compared to non-stress conditions (both P < 0.05). No differences were observed between Normal(1) [446 (359–506) mL] and Normal(2) [455 (365–515) mL] (both P > 0.05). Heart rate significantly increased during ice water exposure [67 (59–69) beats/min)] compared to 55 (49–60) beats/min during Normal(1) and 54 (47–60) beats/min during Normal(2) (both P < 0.05). MAP did not change during Normal(1) [72 (64–84)] or during Normal(2) [71 (65–81) mm Hg] (both P > 0.05), but increased to 86 (75–98) mm Hg during ice water exposure (P < 0.05). CONCLUSIONS: Increased sympathetic activity resulted in decreased blood flow and brachial artery FMD response in healthy volunteers, independent of endothelial dysfunction. Future studies should adjust for blood flow when interpreting the FMD response.