Direct and indirect blood pressure in normotensive and hypertensive subjects

To compare intrabrachial blood pressure (I-BP) with simultaneously measured contralateral auscultatory (A-)BP in hypertensive and normotensive subjects. The question was whether differences between direct and indirect BP are influenced by the BP levels.

Hypertensive subjects treated with either placebo (n = 10) or metoprolol (n = 8) and age-matched normotensive subjects (n = 15), selected from a defined patient population waiting for cholecystectomy or hernia repair. Measurements were performed pre-induction of anaesthesia.

In the hypertensive subjects, cuff systolic BP (SBP) was lower than I-BP by an average of 8 mmHg (placebo-) and 7 mmHg (metoprolol-treated), whereas diastolic A-BP (A-DBP) was 3 and 7 mmHg higher, respectively. In the normotensive subjects, mean A-SBP and I-SBP agreed closely, whereas A-DBP was 11 mmHg higher. Thus, SBP differences (i.e. indirect-direct BP) were significantly less and DBP differences significantly greater in the normotensive than in the hypertensive subjects (P < 0.05). Plasma renin activity and adrenalin showed better correlations with A-MBP than with I-MBP.

The drift of cuff systolic readings fell progressively below the intrabrachial values when BP increased, whilst diastolic cuff values approached the direct pressures. Since A-MBP did not significantly differ from I-MBP in any group, one must ask whether hypertension would be more correctly defined according to MBP criteria.