Kevin Kwong

Acoustic transmission in normal human hips : structural testing of joint symmetry

An acoustical technique has been developed for the measurement of structural symmetry of the hip joints. A mild vibratory force was applied to the sacrum and sound signals were picked up at both hips by a pair of microphones installed in two stethoscopes. These stethoscope-microphone assembles were calibrated to achieve a difference in relative sensitivity of less than 0.2 dB. The relative transmission of sound signals was analysed and compared between both hips by a dual-channel signal analyser. Twenty-seven healthy adults, 20 healthy pre-school children and 19 normal neonates were tested. Results from these three groups showed high coherence of the sound signals and that the discrepancy between both hips was smallest in the frequency range of 200-315 Hz. For normal neonates, the sound signals maintained a high coherence (gamma2>0.97) and small discrepancy (D<1.25 dB) between both hips. This study has shown that the acoustical technique provides a practical structural testing for bony symmetry of the hips and the results offer a baseline for further investigation into developmental dysplasia of the hip (DDH) in neonates. Clinical screening for DDH is still problematic in developing countries.

New Technique for Early Screening of Developmental Dysplasia of the Hip: Pilot Study

An acoustical technique has been developed for early screening of developmental dysplasia of the hip (DDH) in neonates by comparing the sound transmitted across the hips while a vibratory force was applied to the sacrum. The baseline for 90 normal neonates has been established and tests in the frequency bands of 200, 250, and 315 Hz were found to be most effective, achieving high coherence and smallest discrepancy. Sixteen patients with unilateral DDH were examined and the results suggested that coherence below 0.8 in at least one of these frequency bands was strongly indicative of structural asymmetry between both hips, and there was a significant difference between normal neonates and patients with unilateral DDH. By setting the cut-off discrepancy at 2.0 dB, the best sensitivity (100%) would be achieved, and this could be proposed as the threshold for wide-scale screening of DDH.

Acoustic performance of three stethoscope chest pieces

This study compared the spectral response of three different stethoscope chest pieces (Tycos Harvey, Littmann Classic II, Tollot Dual Head) to both pink noise and normal human breath sounds recorded from the chest wall of 12 subjects breathing at an average peak inspiratory flow rate of 1.5 L/s. The sound data was subjected to fast Fourier transform (FFT) algorithm analysis. The pink noise data showed frequency accentuation between 100 and 1250 Hz occurred with all the chest pieces but was most prominent with the Littmann and least with the Tycos Harvey chest piece. Inspiratory breath sound analysis showed that the peak intensity (PI) recorded using the Littmann chest piece was highest and the Tollot lowest, whilst the frequency at maximum power (F/sub max/) recorded using the Tycos Harvey chest piece was highest and the Tollot lowest. There was no difference in the frequency (F/sub 50/) and band width at half power during inspiration between the three chest pieces. All parameters measured during inspiration were significantly different from that measured during expiration, except for F/sub 50/. This study demonstrates that the acoustic performance of stethoscope chest pieces is different, with the Littmann displaying the highest gain in intensity at adventitial sound frequencies and appears most suitable for lung sound auscultation in the clinical setting. However, the superior F/sub max/ of the Tycos Harvey chest piece suggests superior diaphragmatic auscultation of high frequency sounds such as wheezes.

The development and clinical application of acoustical technique in hip joint

SummaryA non-invasive acoustical system was developed for the measurement of transmission properties of acoustic waves in the hip joints. The instrumentation consisted of three sub-systems. An excitation system employed a vibratory force at the sacrum of the test subjects. A transduction system included a pair of identical microphones installed in the tubes of two stethoscopes, which were placed at the greater trochanters on both sides for picking up the acoustical signals transmitted across the hip joints. The data acquisition and analysis system was a portable signal analyzer with a program of dual channel digital filter for measuring the power of acoustical signal in 1/3-octave frequency bands. 27 normal adults, 20 normal pre-school children and 40 normal neonates were randomly selected for testing. Coherence function (CF) and discrepancy (D) was measured during the testing. Results from the three groups showed that there was a high coherence of the signals (CF>0.9) and a small discrepancy (D<3 dB) between bilateral hips in the frequency range of 200–315 Hz. For normal neonates, there was a wider frequency range of 160–315 Hz in which the acoustical signals maintained a high coherence (CF>0.93) and a smaller discrepancy (D<2 dB) was observed. This study showed that the development of the acoustical technique provided a practical method with objective parameters. The results obtained in this study can offer a baseline for further investigation of hip disorders particularly those related to structural abnormalities of the hip.