Masking of Korotkoff sounds used in blood pressure measurement through auscultation.

Measurement of blood pressure (BP) through manual auscultation and the observation of Korotkoff sounds (KSs) remains the gold standard in BP methodology. Critical to determining BP levels via auscultation is the determination of KS audibility. While absolute sound level audibility is well researched, the problem has not been approached from the point of view of psychoacoustic masking of the sounds. Here, during manual auscultation of BP, a direct comparison is made between what an observer perceives as audible and the electronic analysis of audibility level determined from masking of sound signal levels. KSs are collected during auscultation with an electronic stethoscope, which allows simultaneously observing sound audibility and recording the sound electronically. By time-segmenting the recorded sound around Korotkoff peaks into a test segment and a masking segment, performing Fourier transforms on the segments, and comparing frequency-band sound energy levels, signal-to-noise ratios of a sound to its masking counterpart can be defined. Comparing these ratios to difference limen in the psychoacoustic masking literature, an approximate threshold for sound audibility is obtained. It is anticipated that this approach could have profound effects on future development of automated auscultation BP measurements.

Optimum waveform envelopes and amplitude ratios in oscillometric blood pressure estimation.

OBJECTIVE: To determine if, when using the oscillometric method, there is a specific range of amplitude ratios in the fixed-ratio algorithm that will result in blood pressure estimates that consistently fall within a mean error ≤5 mmHg and a SD of the error <8 mmHg. Additionally, to apply different representations of the oscillometric waveform envelope to verify if this will affect the accuracy of the results. METHODS: SBP and DBP were obtained using the fixed-ratios method applied to a dataset of 219 oscillometric measurements obtained from 73 healthy volunteers and compared to their corresponding auscultation values. Ratio and envelope analysis were done on Matlab (The MathWorks, Inc., Natick, Massachusetts, USA). RESULTS: Depending on the envelope representation, ratios between 0.44-0.74 for systolic pressure and 0.51-0.85 for diastolic pressure yield results within the limits mentioned above. When a set of optimum envelope representations and ratios are selected based on population mean, the highest percentage of subjects presenting blood pressure estimates within the limits were 72.6% for systolic and 69.9% for diastolic. CONCLUSION: The range of ratios presenting optimum results appears to be independent of the degree of arterial stiffness given the wide range of ages of the subjects in the study. Different representations of the oscillometric waveform envelope may improve the accuracy of the method. However, there remains a considerable percentage of the population with unreliable results. It is therefore important to only use devices that have been properly validated according to standard protocol.