The application of positive and negative pressures to the neck has been used to study reflex changes in forearm blood flow following stimulation of the carotid sinus baroreceptors. However, the results of such investigations have been equivocal. Increases (Lindblad et al. 1982), decreases (Ernsting & Parry, 1957; Duprez et al. 1987; Ebert, 1982), or no change (Bevegard et al. 1977; Escourrou et al. 1993) in forearm blood flow or forearm vascular resistance have been reported during carotid sinus baroreceptor stimulation. The present study assessed forearm blood flow responses to a wide range of positive and negative pressures applied to the carotid sinus regions of the neck.

With ethical approval (DMU, Bedford), twelve normotensive subjects (5 male, 7 female) with mean (± S.D.) systolic blood pressure (SBP) 118 ± 15 mmHg and diastolic blood pressure (DBP) 64 ± 8 mmHg, had suction at -12, -24, -36, -48 and -60 mmHg, and pressure at 10, 20 and 30 mmHg applied to the carotid sinus region of the neck. Each pressure level was repeated five times, with approximately 15 s between each stimulus. During an end expiration breath hold, five ECG R waves were recorded, after which an electronic solenoid was activated to initiate the pressure change within the neck chamber and the simultaneous inflation of an upper arm venous occlusion cuff. Pressure change was sustained while a further three ECG R waves were recorded, for a total of 8 s. Forearm blood flow (FBF) was estimated from changes in forearm circumference during venous drainage occlusion. experiments were carried out at a consistent lab temperature of 22°C.

Mean (± S.D.) FBF (in ml dl^-1 min^-1), did not change when the carotid sinus baroreceptors were stimulated by negative pressures (2.68 ± 0.77 at -12 mmHg vs. 2.60 ± 0.69 at -24 mmHg vs. 2.69 ± 0.69 at -36 mmHg vs. 2.54 ± 0.82 at -48 mmHg vs. 2.68 ± 0.89 at -60 mmHg), or by positive pressures (2.74 ± 1.55 at +10 mmHg vs. 2.66 ± 0.71 at +20 mmHg vs. 2.43 ± 0.60 at +30 mmHg) when compared with a control value of 2.57 ± 0.61 ml dl^-1 min^-1 (P > 0.05 with repeated measures ANOVA). Negative neck pressures induced increases in the change in RÐR interval (72 ± 94 ms at -12 mmHg vs. 130 ± 104 ms at -24 mmHg vs. 177 ± 106 ms at -36 mmHg vs. 218 ± 102 ms at -48 mmHg vs. 254 ± 115 ms at -60 mmHg), whereas positive neck pressures did not affect the change in RÐR interval.

Given the expected response in RÐR interval following application of positive and negative pressures to the carotid sinus region, the lack of any changes in FBF may suggest that these baroreceptors do not influence forearm vascular resistance during this type of stimulation.

All procedures accord with current local guidelines and the Declaration of Helsinki.