Development of a point-of-care breath ammonia device and its application to non-invasive monitoring of haemodialysis patients
Hibbard, Troy (2012) Development of a point-of-care breath ammonia device and its application to non-invasive monitoring of haemodialysis patients. PhD thesis, Dublin City University.
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Initial investigation into diagnostic breath ammonia monitoring, and the current status of technology, indicated that breath analysis would have great potential as a non-invasive means of diagnosis. The ideal breath ammonia monitoring device would be one that is sensitive to the specific gas and capable of detecting it at the physiologically relevant concentrations in the ppb range with (1) good precision and accuracy, (2) insensitivity to
interferences, (3) is ideally portable for point-of-care use, (4) provides ease-of-use to the user, (5) displays real-time measurements, and (6) is of low cost. To begin assessment, the normal range of human breath ammonia was defined via photoacoustic laser spectroscopy (PALS) which identified baseline concentrations to be from 29 to 688 ppb. Following this, a system was developed to simulate breath interferents such as humidity and temperature
over a human range encompassing normal and abnormal breath ammonia concentrations (18 to 2,993 ppb). This instrumentation assisted in evaluating the performance of an
ammonia sensitive electrode based on print-fabrication technology and polyaniline nanoparticles. The electrodes displayed an intra-variability from 0.05 to 1.67%, and
generated a 0.99 correlation across a range of 40 to 2,175 ppbv ammonia (LOD=6.3 ppbv) fulfilling the analytical and biomedical requirements necessary for sensing ammonia in
exhaled breath. Having optimised the ammonia sensor, a breath sampling system (AmBeR) was engineered and optimised which was capable of performing measurement of breath
ammonia at the point-of-care. Observations of breath from a healthy population demonstrated a 0.97 correlation between AmBeR and PALS. Clinical evaluation followed in a haemodialysis patient cohort. While the clinical results did not show strong population correlations with measures of blood nitrogen (r=0.64 BUN, r=0.62 creatinine, p<0.01), it did show strong significant intra-individual correlations (range 0.86 - 0.96 with BUN, 0.78 - 0.97 with creatinine) which may indicate potential for clinical application.
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