Does it matter whether blood pressure measurements are taken with subjects sitting or supine?

Abstract

Several guidelines for the management of hypertension do not give special preference to a specific position of the patient during blood pressure measurement, suggesting that blood pressure readings taken with patients sitting and with patients supine are interchangeable. To test whether there is any difference between the blood pressure readings with patients sitting and supine. Blood pressure and heart rate were measured three times each for 245 subjects (171 hypertensives), with subjects both sitting and supine, simultaneously on both arms, with a Hawksley random-zero sphygmomanometer on the right arm and a semi-automatic oscillometric device (Bosomat) on the left arm. The sequence of the two positions was randomized. The procedure was repeated on a second occasion for 49 subjects (41 hypertensives) with the sequence of the positions reversed. Because there was no systematic difference among the three readings per position, the averages of the three blood pressure and heart rate readings with subjects sitting and supine were compared and the influences of age, body mass index, hypertension and medication on the difference were examined. We found no influence of the subject's body posture on the systolic blood pressure. We found a higher diastolic blood pressure [by 5.2+/-0.4 mmHg (mean+/-SEM), P< 0.001 with Hawksley random-zero sphygmomanometer] and a greater heart rate [by 1.5+/-0.3 beats/min (mean+/-SEM), P< 0.001] with subjects sitting. The sitting minus supine differences for diastolic blood pressure and heart rate decreased significantly with increasing age (P< 0.001). We found no effect of body mass index, hypertension and medication on the sitting - supine differences. The subject's body posture influenced especially the diastolic blood pressure and heart rate, both of them being significantly higher with patients sitting rather than supine. This effect decreased with age. Thus, for indirect blood pressure measurement, diastolic blood pressure values obtained with subjects sitting and supine cannot automatically be regarded as equivalent.