Single cuff comparison of two methods for indirect measurement of arterial blood pressure: standard auscultatory method versus automatic oscillometric method.

With the introduction of automatic oscillometric systems for indirect measurement of arterial blood pressure (e.g. DINAMAP), the problem of correspondence between that method and the standard auscultatory method arose. For an exact and valid comparison of two methods, for physiological and methodological reasons, both measurements have to be performed simultaneously and using only one single cuff. Applying a methodological approach fulfilling these preconditions and offering in addition the advantage of a graphic documentation of the individual measurement cycles, we were able to investigate both methods in a sample of 216 comparative experiments. We found a mean difference (auscultatory method minus oscillometric method) between the methods (bias) of -0.82 mm Hg (-0.109 kPa) for systolic pressure, 1.25 mm Hg (0.166 kPa) for diastolic pressure and 1.00 mm Hg (0.133 kPa) for mean pressure. Except for systolic pressure, the differences were statistically significant (paired t-test and analysis of variance). We also obtained a significant negative correlation between the differences and the average of both pressure values (decreasing error with increasing pressure) and a significant negative correlation between differences and heart rate (decreasing differences with increasing heart rate). The conclusions drawn from the comparative study are that, although the oscillometric method exhibited a tendency to higher systolic and lower diastolic measurement values compared to the auscultatory method, both methods are well comparable and the differences are below the level of physiological and clinical significance.