Field evaluation of the Copal UA-231 automatic sphygmomanometer.

Automated sphygmomanometers should be evaluated in field studies before being recommended for epidemiological use. In this study an automated sphygmomanometer, the Copal UA-231, was evaluated on the basis of duplicate blood pressure measurements, one with this machine and one with a Hawksley random zero machine, taken on 1536 participants in a health survey. The Copal-random zero differences had a mean of 2.3 mm Hg for systolic blood pressure and 1.9 mm Hg for diastolic pressure, the Copal reading higher than the random zero. The standard deviations of these differences were similar to the standard deviations of the differences between two random zero measurements taken on subjects in a separate survey. However, Copal-random zero differences varied systemically with blood pressure levels. In this study a 10 mm Hg increase in systolic blood pressure was associated with a 1.22 mm Hg increase in the Copal-random zero difference and a 10 mm Hg increase in diastolic blood pressure was associated with a 1.15 mm Hg increase in the Copal-random zero difference. The Copal UA-231 is recommended for use in field surveys, but it should be recognised that a small systematic increase in Copal-random zero difference with increasing blood pressure may complicate interpretation of epidemiological associations.