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Title: Measurement of airway blood flow by laser Doppler flowmetry
Author: Godden, David J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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Laser Doppler flowmetry (LDF) is a non-invasive method of measuring microcirculatory blood flow based on quantifying the Doppler frequency shift imparted to laser light by moving red blood cells. The object of this study was to examine whether a laser Doppler flow probe could be used to measure airway wall blood flow during bronchoscopy. Studies were performed in dogs, sheep and humans. Artifactual LDF flow signals were identified due to inadequate contact between the probe head and the mucosa, ventilatory and cardiac movement, and ambient light interference. Measurement technique was modified to minimise these artifacts. Site-to-site variation in LDF flow signals under baseline conditions was observed in all species (mean coefficient of variation = 36%), and, in humans, variation was similar in awake subjects during breath-holding, and in anaesthetised subjects during cardiopulmonary bypass, in whom ventilatory and cardiac artifacts are absent. When the probe was held at a single site, linear flow-pressure relationships (r = 0.63 - 0.9, p< 0.001) were observed in the trachea in 7 dogs during acute changes in mean systemic blood pressure and airway pressure. In 4 sheep, average LDF flow signals within regions of the bronchi varied in a linear fashion with changes in blood flow through a cannulated bronchial artery perfused by a roller pump. However, site-to-site variation in response occurred, and a substantial signal persisted when bronchial arterial flow was stopped, or when the artery was perfused by a cell-free solution of dextran which would, in theory, be expected to produce no LDF signal. These results may be explained in part by collateral blood flow, but also indicate detection of 'noise'. In 5 dogs, blood flow was measured in 6 regions of the trachea by both LDF and by the radiolabelled microsphere reference flow technique during resting ventilation (baseline), application of 15 cm H2O positive end-expiratory pressure (PEEP) and during hyperventilation of dry air (HV). When regional measurements were examined, weak, but significant, correlations were observed between LDF and reference flow measurements during each condition. However, during PEEP, although both techniques indicated a similar mean reduction in blood flow (63%) from baseline, there was no correlation between the techniques in the magnitude of reduction measured in individual regions. During HV, LDF measurements showed variable responses between regions, and the mean change from baseline was not significantly different from zero. In contrast, reference flow values increased in most regions, and the mean increase was 87% from baseline. Sectioning of the tracheal wall indicated that this increase was localised to the mucosal layer. The results indicate that acute changes in blood flow at single sites in the airway may be detected by LDF applied in the present fashion. However, detection of 'noise' and site-to-site variation in LDF signals preclude quantitative measurements of airway wall blood flow using this probe design, particularly when the probe is moved between sites during an intervention.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available