Effects of sphygmomanometer type and position of the arm on blood pressure measurement.

Random zero and standard sphygmomanometers were compared in a balanced study performed by 36 members of a General Practitioner Clinical Research Group. In addition the influence of arm position, supported versus dependent, was examined. There was minimal difference between the mean blood pressures measured by the two sphygmomanometers, although the results from the random zero were more variable. The mean blood pressures with the arm supported were consistently lower than with the arm dependent: 127/79 mmHg arm supported vs 131/83 mmHg arm dependent. It is recommended that the position of the arm should be standardised to that of being supported roughly horizontally at heart level. The random zero machine should be used for clinical trial work where the elimination of observer bias is important, and when proper training of observers can be undertaken.