Highly sensitive electronic stethoscope based on non-uniform PVDF curvature structure

Electronic stethoscope is an instrument used for auxiliary determination of patients＇ physical condition by collecting and processing heart sounds and lung sounds.Since traditional electronic stethoscopes have low sensitivity and poor low-frequency response,a novel electronic stethoscope is provided in this paper using curved PVDF clamping structure with non-uniform curvature based on the structure of PVDF and silicone rubber substrate.Theoretical analysis and comparison by means of the corresponding inhomogeneous string vibration model show that sensitivity significantly increases for non-uniform curvature than the uniform one.Furthermore,a new electronic stethoscope pickup is developed based on the optimal parameters at the point of maximum sensitivity of non-uniform curvature.Experiment results show that the sensitivity of the pickup can reach1.7mV/Pa,which increases by 13.3%compared to the one with the structure of uniform curvature PVDF and silicone rubber substrate that has been studied in recent years.Moreover,flat frequency response characteristics can be retained within the frequency band range of 2-2kHz,which covers the frequency response range of cardiopulmonary sound collection,thus provides a strong guarantee for complete acquisition of heart and lung sound signals.

Spectral analysis of bowel sounds in intestinal obstruction using an electronic stethoscope

AIM: To determine the value of bowel sounds analysis using an electronic stethoscope to support a clinical diagnosis of intestinal obstruction. METHODS: Subjects were patients who presented with a diagnosis of possible intestinal obstruction based on symptoms, signs, and radiological findings. A 3MTH Littmann Model 4100 electronic stethoscope was used in this study. With the patients lying supine, six 8-second recordings of bowel sounds were taken from each patient from the lower abdomen. The recordings were analysed for sound duration, soundto-sound interval, dominant frequency, and peak frequency. Clinical and radiological data were reviewed and the patients were classified as having either acute, subacute, or no bowel obstruction. Comparison of bowel sound characteristics was made between these subgroups of patients. In the presence of an obstruction, the site of obstruction was identified and bowel calibre was also measured to correlate with bowel sounds. RESULTS: A total of 71 patients were studied during the period July 2009 to January 2011. Forty patientshad acute bowel obstruction (27 small bowel obstruction and 13 large bowel obstruction), 11 had subacute bowel obstruction (eight in the small bowel and three in large bowel) and 20 had no bowel obstruction (diagnoses of other conditions were made). Twenty-five patients received surgical intervention (35.2%) during the same admission for acute abdominal conditions. A total of 426 recordings were made and 420 recordings were used for analysis. There was no significant difference in sound-to-sound interval, dominant frequency, and peak frequency among patients with acute bowel obstruction, subacute bowel obstruction, and no bowel obstruction. In acute large bowel obstruction, the sound duration was significantly longer (median 0.81 s vs 0.55 s, P = 0.021) and the dominant frequency was significantly higher (median 440 Hz vs 288 Hz, P = 0.003) when compared to acute small bowel obstruction. No significant difference was seen between acute large bowel obstruction and large bowel pseudoobstruction. For patients with small bowel obstruction, the sound-to-sound interval was significantly longer in those who subsequently underwent surgery compared with those treated non-operatively (median 1.29 s vs 0.63 s, P < 0.001). There was no correlation between bowel calibre and bowel sound characteristics in both acute small bowel obstruction and acute large bowel obstruction. CONCLUSION: Auscultation of bowel sounds is nonspecific for diagnosing bowel obstruction. Differences in sound characteristics between large bowel and small bowel obstruction may help determine the likely site of obstruction.