Purpose of the Study: The sounds associated with the five classical Korotkoff phases are clinically important for measuring systolic and diastolic blood pressures. The frequency ranges of the sounds have been described using the overall peak frequencies within each phase by simple Fourier methods. However, such analysis may be missing potentially useful clinical information. The aim of this study was to use a time-frequency analysis (TFA) technique to extract features associated with the Korotkoff sounds obtained during blood pressure measurement and to compare these with the phases allocated by an expert cardiologist.
Methods: A single operator recorded Korotkoff sounds from 6 healthy subjects using a measurement system comprising: cardiology stethoscope, microphone, amplifier, a recording system for computer sound digitization and a MiniDisc system for playback to the cardiologist for phase classification.
Results: TFA demonstrated three main types of frequency components: low frequency (<80Hz), high frequency (100-250Hz) spike and murmurs, which when present, followed the spike for up to 150mS. Qualitatively, the phase changes within subjects showed that phase 2 was most complex, having the greatest degree of murmur and phase 4 having the lowest frequency range.
Conclusion: The TFA approach to Korotkoff phase analysis was able to identify characteristic differences associated with the different phases classified by the expert cardiologist.
Allen J, Gehrke T, O'Sullivan J, King ST, Murray A. Time and frequency analysis of the Korotkoff sounds. Third International Workshop on Non-invasive Haemodynamic, Autonomic and Vascular Monitoring, Graz, Austria, May 2003. Abstract published in: Clinical Autonomic Research, 2003; 13:67.
Dr. John Allen, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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