Hand-free stethoscope--method and instrument for more reliable blood pressure measurements.

Measurement of blood pressure is subject to two sources of variation: biological and measurement variation. It is important to bear in mind that the ability to interpret the Korotkoff sounds correctly determines the levels of both systolic and diastolic blood pressure. To improve the ability to distinguish between the Korotkoff phases, the handfree stethoscope and the hand-free method were developed. The improved stethoscope head was fixed under the edge of the cuff, thus reducing the noise generated from physiological tremor and other movements. This resulted in more distinct Korotkoff sounds. Furthermore, the new method reduced the spreading of blood pressure values. In 107 patients the average systolic blood pressure recording was 3.1 mmHg higher and the average diastolic blood pressure was 3.5 mmHg lower. We conclude that the new stethoscope and technique provide a means of significantly improving the indirect measurement of blood pressure.

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.