[Oscillometric wrist devices: comparison with the standard mercury sphygmomanometer and estimate of the "supine" error].

Before introducing a wrist device (NAIS-Matsushita) for blood pressure (BP) measurement in our Unit, we formally tested its validity. Since the wrist position is critical and BP in the clinical setting is often measured with patients lying in bed, we also estimated the error introduced by allowing the wrist to lay flat at the bed level. Ten normal subjects and 20 hypertensive patients took part in two consecutive studies. In the first study the subjects were sitting and the blood pressure was simultaneously taken with the auscultatory mercury sphygmomanometer on the left arm and with the NAIS on the right wrist. The wrist was kept at the heart level. In the second study two NAIS devices were used with the subjects lying in bed; the left wrist was allowed to stay at the bed level, while the right one was kept at the heart level. The diastolic BP was consistently underestimated (P< 0.001) by the wrist device (79 mmHg 95%CI: 75-83) as compared to the values obtained with the standard mercury sphygmomanometer (85 CI: 79-88). No significant difference was found in systolic BP (mercury: 135 CI: 127-143; wrist 134 CI: 126-141). In the second study the BP (systolic and diastolic) was markedly higher (P<0.001) when the wrist was kept at the bed level (systolic bed level: 144 CI: 135-152; systolic heart level: 135 CI:126-141; diastolic bed level: 83 CI:78-88; diastolic heart level: 76 CI:71-79).