Forehead cooling activates the sympathetic nervous system and can trigger angina pectoris in susceptible individuals. However, the effect of forehead cooling on coronary blood flow velocity (CBV) is not well understood. In this human experiment, we tested the hypotheses 1) that forehead cooling reduces CBV (i.e., coronary vasoconstriction); and 2) this vasoconstrictor effect would be enhanced under systemic beta-adrenergic blockade. A total of 30 healthy subjects (age range 23-79 years) underwent Doppler echocardiography evaluation of CBV in response to 60 seconds of forehead cooling (1°C ice bag on forehead). A subset of subjects (n = 10) also underwent the procedures following an intravenous infusion of propranolol. Rate pressure product (RPP) was used as an index of myocardial oxygen demand. Consistent with our first hypothesis, forehead cooling reduced CBV from 19.5 ± 0.7 to 17.5 ± 0.8 cm/sec (P < 0.001) while MAP increased by 11 ± 2 mmHg (P < 0.001). Consistent with our second hypothesis, forehead cooling reduced CBV under propranolol despite a significant rise in RPP. The current studies indicate that forehead cooling elicits a sympathetically-mediated pressor response and a reduction in CBV and this effect is augmented under beta-blockade. The results are consistent with sympathetic activation of beta-receptor coronary vasodilation in humans, as has been demonstrated in animals.
- sympathetic nervous system
- blood flow
- cold temperature
- Copyright © 2013, American Journal of Physiology - Heart and Circulatory Physiology