DOES THE HAWKSLEY RANDOM ZERO SPHYGMOMANOMETER UNDERESTIMATE BLOOD-PRESSURE, AND BY HOW MUCH

The study objective was to compare blood pressure (BP) measurement by the Hawksley random-zero sphygmomanometer and the standard mercury sph ygmomanometer. Comparison of simultaneous 'blind' BP measurements were made using the Hawksley random-zero sphygmomanometer and the standard mercury sphygmomanometer linked by a Y-connector to a single cuff, in the general practice and office environments. Sixty five healthy volu nteers and general practice patients, aged between 20 and 50 years (SE P range 82-184 mm Hg, DBP range 38-112 mm Hg), were studied. Each had three blood pressure measurements taken. Mean BPs recorded by the Hawk sley random-zero sphygmomanometer were lower than those recorded by th e standard mercury sphygmomanometer. The Hawksley random-zero sphygmom anometer underestimated SEP by 1.3 mm Hg (95% CI 0.9-1.8 mm Hg) and DB P by 1.7 mm Hg (95% CI 1.1-2.3 mm Hg). These differences between instr uments were independent of BP level both for systolic and diastolic me asurements. An overview including this study and six other published r eports describing nine studies examining the performance of the Hawksl ey random-zero sphygmomanometer suggested a similar degree of underest imation for SEP (mean difference 1.35 mm Hg, 95% CI 1.24-1.46 mm Hg). Underestimation of DBP appeared greater (mean difference 2.54 mm Hg, 9 5% CI 2.43-2.65 mm Hg) but was reduced when two outlying studies were removed from analysis (mean 1.97, 95% CI 1.85-2.09 mm Hg). We conclude that the Hawksley random-zero sphygmomanometer underestimates systoli c and diastolic pressure, when compared with the standard mercury sphy gmomanometer. However, the degree of underestimation is small and appe ars consistent across a wide range of blood pressure levels. These fin dings do not preclude careful use of the instrument in future epidemio logical studies, with adjustment for underestimation where necessary.