Comparison of repeatability of blood pressure measurements between oscillometric and auscultatory methods

Oscillometric and auscultatory methods are two main non-invasive blood pressure measurement methods in routine examinations and monitoring. There is currently little information available on the comparison of their repeatabilities when performing more than three repeat measurements. This study aimed to provide this information. Oscillometric cuff pressure waveforms and Korotkoff sound signals were simultaneously and digitally recorded from 20 normotensive subjects. Eight repeat measurements were performed for each subject. SBP, MAP and DBP values were determined from the digitally recorded oscillometric cuff pressure and Korotkoff sound signals using oscillometric and auscultatory methods respectively. The standard deviation of eight SBP, MAP and DBP measurements was calculated for each subject as the index of repeatability (SBPSD, MAPSD and DBPSD respectively). The results showed that SBP from the oscillometric method were 2 mmHg higher than those from the auscultatory method (P=0.2). MAP and DBP values from the oscillometric method were significant lower than those from the auscultatory method (both P<0.01) by 7 mmHg and 6 mmHg respectively. The key results were that the repeatability indices from the oscillometric method were all greater for oscillometric measurement by 1.5 mmHg for SBPSD (mean±SD: 4.4±1.8 vs 2.9±0.9 mmHg), by 1.3 mmHg for MAPSD (3.6±1.1 vs 2.3±0.9 mmHg), and by 0.8 mmHg for DBPSD (3.4±1.6 vs 2.6±1.0 mmHg), suggesting that the widely used oscillometric method can not replace the auscultatory method in clinical applications.