Characterization of the Korotkoff sounds using joint time–frequency analysis

Abstract

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 already been described simply using the overall peak frequencies within each phase by Fourier methods. However, such analysis may be missing potentially useful clinical information. The aim of this study was to compare features associated with the different phases of the Korotkoff sounds obtained during blood pressure measurement using a joint time-frequency analysis (JTFA) technique. A single operator recorded Korotkoff sounds from 25 healthy subjects using a measurement system comprising cardiology stethoscope, microphone, amplifier and recording system for computer sound digitization, and a MiniDisc system for playback to the cardiologist for Korotkoff phase classification. We have shown that using this system the phase classification by the cardiologist is repeatable, with no significant differences found in the number of sounds allocated to phases on two separate recording assessments. The digitized sounds were processed using a MATLAB-based short-time Fourier transform JTFA technique and differences in time, frequency and amplitude characteristics between the phases compared. It was found that on average, phase III had the largest overall amplitude and high frequency energy. Phase II had the greatest high frequency component and longest murmur, and was visibly the most complex phase in terms of time and frequency content. In contrast, phases IV and V had the lowest amplitude and frequency components. Overall, the statistically significant transitions between phases were: phase I to II with increases in high frequency (224 to 275 Hz) (p < 0.01) and sound duration (49 to 98 ms) (p < 0.0001), II to III with a significant decrease in sound duration (to 37 ms) (p < 0.0001), III to IV with decreases in maximum amplitude (0.95 to 0.25), highest frequency (262 to 95 Hz), and relative high frequency energy of the sounds (0.61 to 0.10) (all p < 0.0001), and IV to V with decreases in the maximum amplitude (0.25 to 0.13) (p < 0.0002) and high frequency energy (0.10 to 0.03) (p < 0.005). This study has demonstrated that joint time-frequency analysis of Korotkoff sounds was able to identify characteristic differences associated with the different phases classified by the expert cardiologist. Ultimately, exploiting the joint time and frequency characteristics of the sounds may improve blood pressure measurement and help to assess the stiffness of the peripheral arteries.

A pilot application of Korotkoff sound delay time in evaluating cardiovascular status

“…The Korotkoff sound transducer (Shengwangsheng MPA201) and the stethoscope bell (3 M Littman 2144 L) are connected together by a tube. Since the Korotkoff sound's energy concentrates mainly below 400 Hz, the passband of the bandpass filter (BPF) for Korotkoff sound channel is 16 Hz-400 Hz [2,5,[10][11][12][13] The invasive blood pressure transducer (Yixinda DPT-248) is connected to the cannula to measure the pressure of the brachial artery. To avoid aliasing distortion, the four signals then pass a low-pass filter (LPF) with a cut-off frequency of 500 Hz before starting A/D converting.…”

“…In the last years, most of the previous researches about Korotkoff sound were focused on the origin and frequency component analyzing of the Korotkoff sounds signal [4,5]. Some other researchers utilized the Korotkoff sound to replace the distal pulse in the peripheral artery and the QRS wave in electrocardiogram to obtain the pulse transit time (PTT), which was named QKd interval [6,7].…”

Noninvasive measurement of beat-to-beat arterial blood pressure by the Korotkoff sound delay time

“…The Korotkoff sound was sensed by the transducer with a frequency range of 15-20 000 Hz. Because most of the Korotkoff sound energy was concentrated below 400 Hz, the frequency range of the band-pass filter was 16-400 Hz [17,20,25]. The IBP transducer (Yixinda model DPT-248, Shenzhen, China) was connected to the cannula, which is inserted in the radial artery.…”

“…In recent years, most of the research concerning Korotkoff sounds was concentrated on the genesis and power spectra analysis of Korotkoff sound signals [16][17][18][19][20]. Some other researchers regarded the Korotkoff sound as a pulse arrival marker in the peripheral artery to calculate the pulse transit time, which was denoted as the QKd interval [21][22][23].…”

Introduction of an electronic aneroid sphygmomanometer that could meet both professional and unprofessional demands

“…The author claimed that the blood pressure could be measured accurately but only in laboratory not in clinical practice. A joint time-frequency analysis (JTFA) technique was reported as an algorithm to characterize the different phases of the Korotkoff-sounds by Allen et al [1]. The JTFA is very useful to identify the first phase and the fifth phase of the Korotkoff-sounds, which are the two key points to mark the systolic and diastolic blood pressure in KSM.…”