Arm position as a source of error in blood pressure measurement.

The present study was designed to assess the value of correct positioning of a patient's arm when measuring blood pressure (BP). A total of 181 subjects were examined, 141 hypertensives on treatment, 25 untreated hypertensives, 15 normotensives. All the subjects underwent three BP measurements after a 5-min resting period in supine position. Then two BP readings were recorded in standing position with the arm either positioned by the patient's side or supported passively at patient's heart level. Average systolic BP (SBP) in standing position were 144.6 +/- 20.2 mmHg with the arm at the side and 136.4 +/- 21.1 mmHg with the arm at the heart level (p less than 0.001); average diastolic pressures were 99.0 +/- 12.0 mmHg and 90.2 +/- 12.3 mmHg (p less than 0.001), respectively. A fall in SBP greater than or equal to 20 mmHg from the supine to the upright position was detected in 18.2% of cases when measurement was performed at heart level; such a reduction was inapparent in two-thirds of cases when the arm was placed at the patient's body side. Incorrect positioning of a patient's arm during BP measurements in standing position leads to overestimation of BP values and masks the presence of postural hypotension.