Determination of blood pressure level and changes in physiological situations: comparison of the standard cuff method with direct intra-arterial recording.

Blood pressure changes during a test series (sitting, supine, standing, bicycle ergometer test, recovery) were determined in a group of normotensive and borderline hypertensive subjects simultaneously with the continuous intra-arterial registration (Oxford method) and the indirect cuff methods. The mean method difference between the direct and indirect method varied considerably in tests, from -2.3 to 12.9 mmHg in systolic pressure and from -4.3 to 18.2 mmHg in diastolic pressure. There was also a large scatter in the method difference between subjects. Analysis of the blood pressure responses to the other tests using values measured in the sitting position as the reference also revealed considerable variation between the methods. The accuracy of the indirect method was also tested by classifying the population in two subgroups along the median (high/low group) in all tests by each method. The classification discrepancy between the methods varied from 9 to 33% in systolic pressure and from 0 to 25% in diastolic pressure. The results indicate that the data gathered using the indirect measuring method from the arterial blood pressure level and changes in varying physiological conditions may differ considerably from direct intra-arterial readings. On the other hand, the repeatability of the indirect method in stabile conditions was found to be acceptable indicating that the indirect method is useful in blood pressure follow-up.