Ambulatory daytime blood pressure versus tonometric blood pressure measurements in the laboratory: effect of posture

Objective To compare blood pressure (BP) in tonometric radial artery recordings during passive head-up tilt with ambulatory recordings and evaluate possible laboratory cutoff values for hypertension. Methods Laboratory BP and ambulatory BP were recorded in normotensive (n=69), unmedicated hypertensive (n=190), and medicated hypertensive (n=151) subjects. Results Mean age was 50.2 years, BMI 27.7kg/m², ambulatory daytime BP 139/87mmHg, and 276 were male (65%). As supine-to-upright changes in SBP ranged from -52 to +30mmHg, and in DBP from -21 to +32mmHg, the mean values of BP supine and upright measurements were compared with ambulatory BP. The mean(supine+upright) systolic laboratory BP was corresponding to ambulatory level (difference +1mmHg), while mean(supine+upright) DBP was 4mmHg lower (P<0.05) than ambulatory value. Correlograms indicated that laboratory 136/82mmHg corresponded to ambulatory 135/85mmHg. When compared with ambulatory 135/85mmHg, the sensitivity and specificity of laboratory 136/82mmHg to define hypertension were 71.5% and 77.3% for SBP, and 71.7% and 72.8%, for DBP, respectively. The laboratory cutoff 136/82mmHg classified 311/410 subjects similarly to ambulatory BP as normotensive or hypertensive, 68 were hypertensive only in ambulatory, while 31 were hypertensive only in laboratory measurements. Conclusion BP responses to upright posture were variable. When compared with ambulatory BP, mean(supine+upright) laboratory cutoff 136/82mmHg classified 76% of subjects similarly as normotensive or hypertensive. In the remaining 24% the discordant results may be attributed to white-coat or masked hypertension, or higher physical activity during out-of-office recordings.