Real-time Detection Of Breath Ammonia In Vivo Based On Photoacoustic Spectroscopy

Measurement of breath ammonia is an important non-invasive diagnostic technique for end-stage renal disease (ESRD). According to a good linear relationship between NH3 in exhaled breath and blood urea nitrogen (BUN), this technique not only can realize real-time monitoring for hemodialysis (HD), but also can give an estimated effect of HD on renal failure patients. Photoacoustic spectroscopy is widely applied in trace gas detection of medical diagnosis area for its advantages such as high sensitivity and multi component in vivo detection.In this paper, many kinds of methods, used to measure the breath ammonia in vivo, are reviewed. The advantages of the photoacoustic spectroscopy are introduced. The theory of photoacoustic spectroscopy including the generation and detection of photoacoutic signal is discussed in detail. And also, technologies of wavelength modulation and harmonic detection are introduced to improve the signal to noise ratio. The relationship between the breath ammonia and renal failure patients is discussed, and this forms the theoretical basis on photoacoustic spectroscopy used for breath ammonia detection in vivo.Photoacoustic spectrometer based on tunable erbium doped fiber laser (TEDFL) and erbium doped fiber amplifier (EDFA) is optimized, including realizing real-time wavelength demodulation and completing system control through programming by LabVIEW. Considering that high concentration of H2O and CO2 in exhaled breath may cause interferences to the measurement of ammonia. The absorption line at 1522.44nm for NH3 is chosen as a feature line, based on the spectrum analysis of NH3,H2O and CO2, specific at 1.5μm. And then stimulated breath ammonia is detected. The experimental results demonstrated that at room temperature and atmospheric pressure, the detection limit of ammonia reaches 8ppb and the interferences of H2O and CO2 is successfully eliminated. Based on the stimulated breath ammonia measurement, the system is applied to measure real breath ammonia of three healthy volunteers. And the concentrations of the ammonia are 313ppb,208ppb and 559ppb respectively. These preliminary results demonstrate that the photoacoustic spectrometer can roughly meet the requirement of clinical monitoring for kidney dialysis. In conclusion, the photoacoustic spectrometer in this dissertation realized real-time monitoring for breath ammonia in vivo. It can give an estimated effect of HD by non-invasive diagnostic technique. This work would be helpful for pushing the wide application of photoacoustic spectroscopy in exhaled breath diagnosis.