The oscillotonometer in theory and practice.

The accuracy of the Scala Alternans Altera oscillotonometer was investigated by comparison with direct intra-arterial pressures. It was found that the traditional criteria for detecting systolic and diastolic pressures were in error. A slow deflation rate was essential for the accurate measurement of systolic pressure, the maximum amplitude of needle oscillation correlated closely with mean pressure, and the determination of diastolic pressure was so inaccurate as to be clinically useless. The response of the oscillotonometer was also found to be dependent upon the individual combination of oscillotonometer and patient.