FOREARM VASCULAR RESPONSES TO MENTAL STRESS AND DEVICE GUIDED BREATHING ASSOCIATE WITH PLASMA CONCENTRATIONS OF NORMETADRENALINES IN SUBJECTS WITH ESSENTIAL HYPERTENSION

Abstract

Objective: Forearm vasodilator responses to mental stress (MS) are impaired in hypertensive compared to normotensive individuals by a mechanism that may relate to peripheral alpha-adrenergic activity antagonising that of neuronal nitric oxide. We investigated whether the response to MS may be dependent on the level of basal sympathetic activity as measured by plasma concentrations of normetadrenaline (NM) and how responses to slowing respiratory rate by device guided breathing (DGB, which reduces sympathetic activity) vary according to NM concentrations. Design and method: Subjects with essential hypertension were stratified according to concentrations of plasma NM into those with low NM (< or = 500pmol/L) and high NM (> or = to 750pmol/L). Forearm blood flow (FBF) was measured by venous occlusion plethysmography after 15 minutes of rest, during MS elicited by the Stroop word-colour test and during supervised DGB with breathing rate < 10 breaths/minute. Results: Subjects with high NM (n = 30, 15 men) had greater body mass index than those with low NM (n = 30, 17 men): (mean ± SD) 31 ± 7 vs 27 ± 4 kg/m2 (P < 0.05), but the two groups were similar with respect to age and brachial blood pressure (BP). During MS and DGB, changes in BP were similar in subjects in both low NM and high NM groups. MS increased FBF in both groups but the response in high NM was impaired as compared to subjects with low NM (34 ± 3 vs. 49 ± 3 %, P < 0.05). DGB increased forearm vascular resistance to a lesser extent in subjects with high compared to low NM (1.21 ± 7.95 vs 5.50 ± 6.32 mmHg.100 mL/mL, P < 0.05). Conclusions: These results are consistent with greater sympathetic vascular tone in patients with higher NM that antagonises forearm vascular responses to MS. Circulating concentrations of NM may identify subjects with impaired neuronal nitric oxide signalling.