The random-zero versus the standard mercury sphygmomanometer: a systematic blood pressure difference

Area of Science:

• Cardiovascular research
• Medical instrumentation

Background:

• Sphygmomanometers are crucial for blood pressure measurement in epidemiological studies.
• Frequent interchangeable use of random-zero and standard mercury devices raises concerns about data consistency.

Purpose of the Study:

• To investigate systematic differences between random-zero and standard mercury sphygmomanometers.
• To determine if these devices can be used interchangeably in epidemiological research.

Main Methods:

• Simultaneous measurement of systolic and diastolic blood pressures using both sphygmomanometers.
• Controlled experiments with calibrated devices, double stethoscopes, and blinded technicians.
• Analysis of readings at a deflation rate of 2 mmHg/second, with adjustments for confounding factors.

Main Results:

• Random-zero sphygmomanometers yielded systematically lower readings: -0.9 mmHg (systolic), -1.8 mmHg (diastolic phase IV), -1.8 mmHg (diastolic phase V).
• Differences remained significant (p < 0.001) after adjusting for age, sex, heart rate, blood pressure, observer, and temperature.
• Eliminating residual mercury from random-zero devices reduced the observed measurement discrepancies.

Conclusions:

• A systematic difference exists between random-zero and standard mercury sphygmomanometers.
• The discrepancy is likely due to the mercury column height in the random-zero device.
• Interchangeable use of these sphygmomanometers in epidemiological studies is not recommended.