The influence of a heart level pillow on the result of blood pressure measurement.

Measurement of blood pressure is subject to two sources of variation: biological variation between and within individuals and measurement variation introduced by the observers. Concerning the latter variation it is important to take into consideration arm position in relation to heart level. To improve the standardisation of arm position in relation to the heart level in the supine position, a special pillow--the heart level pillow--was developed. The distances between the examination couch, the centre of the right cardiac atrium, and the sternum were measured by computerised tomography. The upper arm diameter was determined with vernier callipers. These values were then used to design and manufacture a heart level pillow. Blood pressures were then measured on 78 adult patients both with and without the pillow. When blood pressure was measured with the arm at heart level diastolic blood pressure was on average 5.5 mmHg lower compared with measurements performed without the pillow. Therefore, we conclude that a heart level pillow may reduce one common and important error in the indirect measurement of blood pressure.