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

Abstract

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 27.7 kg/m 2 , ambulatory daytime BP 139/87 mmHg, and 276 were male (65%). As supine-to-upright changes in SBP ranged from -52 to +30 mmHg, and in DBP from -21 to +32 mmHg, 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 +1 mmHg), while mean(supine+upright) DBP was 4 mmHg lower ( P < 0.05) than ambulatory value. Correlograms indicated that laboratory 136/82 mmHg corresponded to ambulatory 135/85 mmHg. When compared with ambulatory 135/85 mmHg, the sensitivity and specificity of laboratory 136/82 mmHg to define hypertension were 71.5% and 77.3% for SBP, and 71.7% and 72.8%, for DBP, respectively. The laboratory cutoff 136/82 mmHg 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 136/82 mmHg 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.

Fig. 1

Line graphs show radial and aortic tonometric SBP (a), and DBP (b) in the study population consisting of normotensive subjects (n = 69), unmedicated hypertensive patients (n = 151), and medicated hypertensive patients (n = 190) during 10-minute laboratory recordings; minutes 1–5 in supine position, minutes 6–10 during passive head-up tilt; mean and 95% confidence interval of the mean.

Fig. 2

Line graphs show radial tonometric SBP (a) and diastolic blood pressure (b) of study participants divided into tertiles according to the magnitude of the change in radial SBP during head-up tilt; minutes 1–5 in supine position, minutes 6–10 during passive head-up tilt; mean and 95% confidence interval of the mean.

Fig. 3

Correlograms of mean ambulatory daytime blood pressure (BP) versus mean(supine+upright) radial tonometric BP; SBP (a), DBP (b), dotted black lines represent cutoff points for hypertension, green numbers denote the proportion of subjects classified similarly, and red numbers denote the proportion of subjects classified dissimilarly to hypertensive and normotensive subjects.

Fig. 4

Receiver operating characteristic curves depicting the prediction of brachial ambulatory blood pressure (BP) ≥135/85 mmHg by the mean(supine+upright) radial tonometric SBP (red line) and DBP (red line) (a), and by the mean(supine+upright) aortic SBP (red line) and DBP (red line) (b).