| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 102 === SUMMARY
This paper proposes a signal processing method for evaluating arteriovenous shunt (AVS) stenosis in hemodialysis patients. AVSs are surgically created pathological or physiological fistulas serving as access routes for end-stage renal disease patients. The distinct and periodic bruit of vascular shunts is clearly audible over the access routes. Thus, a bruit spectral analysis could be considered a valuable noninvasive method for quantifying the severity of vessel stenosis. We intend to determine a more precise relationship of phonography to stenotic lesions; therefore, we must conduct an additional in vitro study to simplify the relationships. To achieve this goal, we must set up a specific mock to simplify the blood flow condition and analyze the stenotic lesions-to-phonoangiography relationship.
Keywords—arteriovenous shunt (AVS) , phonoangiographic signal, AVS stenosis, SPL, mean artery pressure.
INTRODUCTION
Chronic kidney disease (CKD) is typically an irreversible and progressive process, and the final stage is kidney failure. Arteriovenous (AV) accesses (surgically created pathological fistula) serve as critical access routes for providing hemodialysis treatment for these ESRD patients. However, after prolonged use of these routes, pathological changes can occur, include: such as venous high pressure (caused by venous outflow obstruction) or insufficient blood flow (arterial inflow or in-graft stenosis). Prompt detection of these pathological conditions is critical for patients, physicians, and nurses. The AV access can be evaluated by feeling thrill and pulsation through palpation, listening for the bruit by using a stethoscope, or by direct examination employing vascular echography or angiography. Therefore, we sought to develop a phonography method for use in a home-based care system.
MATERIALS AND METHODS
A simplified geometric model of AV access was integrated in a closed circuit. The mock loops will offer pulsatile flow and physiological conditions for silicone tubing to simulate cardiovascular cycle. The reduction of the pipe as the stenotic site of AV access will be used as the independent variables in the mock circulatory loop. According to the hemodialysis condition, 600-1000 mℓ/min blood flow and 60-90 beat/min heart rates, different stenotic lesion will be conducted to different the hemodynamic parameters (velocity and pressure) and phonographic signal. However, the degree of stenosis (DOS) is used as an index to classify the AV access condition, and is determined by the narrowing percentage of the normal vessels. The definition of the DOS can be represented as , D is the diameter of the normal vessel and d is the diameter of the stenosis lesion. In this experimental, the DOS was varied from 50%, 70%, 80%, 85%, 90%, 92.5% to 95%. To analysis the bruit signal that includes experiment and clinical signal in SPL method.
RESULTS AND DISCUSSION
1. Hemodynamic parameters measured in varied DOS:
In this experiment, the pressure decreased when the fluid passed across the stenosis under the variant DOS conditions (from 50% to 95%). The pressure increased up-stream of the stenotic site according to the severity of the stenosis. In particular, the differential pressures increased substantially, exceeding 40 mmHg in the range of DOS up to 90% to 95%, as Fig. 1 illustrates. However, the effect on the distance parameters (1D, 5D, 10D and 17D) was inconsequential under the same DOS conditions. In the summation of differential pressure, under different DOS conditions (from 50% to 95%), up-stream pressures were higher than the down-stream pressures.
2. Phonography signal analyzed in various DOS status:
Based on our previous clinical study [20][21], the intensity and power spectral density of bruits are associated with the severity of AV access stenosis. The frequency spectra of phonography varied according to the increase in DOS. Based on this experimental study, we proposed that the auditory spectrogram could be represented by the bruits in the time-frequency domain. The experimental results showed that the high frequency occurred. Phonography is a noninvasive and scientific method for investigating the local fluid motion in arterial narrowing and distinguishes arterial dysfunction. The SPL value of the bruits was decreased when the DOS gradually increased. (figure 2)
CONCLUSION
The experimental result shows strongly correlation between phonoangiography and the severity of AV access, the trend of the experimental pressure and flow data correlated to the clinical phenomenon. The analytic method may be helpful for clinician for reference.
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