Augmentation of cardiopulmonary baroreflex control of forearm vascular resistance in borderline hypertension.

Arterial baroreflex control of heart rate is impaired in young men with borderline or mild hypertension. Despite this impairment, these subjects often have exaggerated increases in vascular resistance during orthostatic stress. We considered the possibility that this exaggerated reflex vasoconstriction might reflect augmented cardiopulmonary baroreflex control of vascular resistance in borderline hypertension (BHT). Accordingly, we studied cardiopulmonary baroreflex control of forearm vascular resistance in nine BHT men with blood pressure intermittently above 150/90 mm Hg and in seven normotensive (NT) men. Cardiopulmonary baroreceptor input was reduced with lower body negative pressure (LBNP-5 to-20 mm HG), which decreases cardiac filling pressures. Baseline mean arterial pressure was 99 /+- 3 mm Hg (mean /+- SE) in BHT vs 83 /+- 2 mm Hg in NT (p less than 0.05). Baseline forearm resistance was also higher in BHT than in NT: 19 /+- 2 vs 13 /+-1 mm Hg/ml/min/100 ml or units (p less than 0.05). Reflex increases in forearm resistance during LBNP were greater (p less than 0.05) in BHT than in NT 8.6 /+- 1.7 vs 4.5 /+- 1.1 units during LBNP-20). Increases in arterial pressure and forearm resistance during a cold pressor test were not significantly different in the two groups. Thus, the augmented response to LBNP could not be attributed to a nonspecific influence of increased baseline resistance or a generalized abnormality in reflex control. In summary, the results of this study suggest that there is augmentation of the tonic inhibitory influence of cardiopulmonary baroreceptors in humans with BHT.