Comparison of simultaneous indirect (auscultatory) and direct (intra-arterial) measurements of arterial pressure in man: Steele, J. M.: p. 1042

Abstract

While it is well known that too narrow a sphygmomanometer cuff may give erroneously high indirect blood pressure readings, particularly in subjects with thick arms, it has not been generally appreciated that a cuff supplied with a rubber bag which is too short to encircle the upper arm may cause a similar error. Auscultatory pressure readings obtained with two cuffs, one with a bag 12 by 23 cm. and the other with that of 14 by 40 cm., were compared with direct intraarterial pressure recording in 53 subjects. The large bag gave systolic values 3.0 ± 1.16 mm. Hg too low, and diastolic (phase v) values 1.4 ± 1.26 mm. Hg too high. With the small bag the error depended on the site of wrapping; as applied on the biceps it gave a better agreement with the systolic (0.5 ± 1.71 mm. Hg too high), but a poorer one with the diastolic pressure (7.6 ± 2.0 mm. Hg too high). As applied on the triceps, the small bag gave systolic values 5.5 ± 1.91 mm. Hg too high; the diastolic values were also 4.6 ± 2.36 mm. Hg on the high side.With the large bag the random error was significantly smaller than with the smaller bag in either position, both for systolic and diastolic pressure.The disappearance of the sounds (phase v) was closer than muffling (phase iv) to the intraarterial diastolic pressure.In this series, the arm circumference as such had no effect on the error of the indirect blood pressure measurement. However, the thickness of the triceps skinfold was negatively correlated with the error of the systolic measurement when a small cuff was used, and with that of the diastolic phase IV measurement with both cuffs. With the large cuff and the phase V criterion, the thickness of the subcutaneous fat introduced no systematic error.