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Title: Aspects of respiratory heat transfer in asthma
Author: Farley, Robert
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1988
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During the winter some asthma suffers are incapable of exertion without provoking bro nchoconstriction. The rate of respiratory heat exchange (RHER) is proposed as a stimulus of exercise induced asthma. A respiratory test was required to determine heat loss sensitivity. A pumped cold air supply was developed (-22°C, 150 1/min air flowrate) to effect airway cooling during either a hyperventilation or exercise challenge. A microcomputer based data acquisition unit was programmed to record the real-time RHER and permit a trend analysis of expirate temperatures. In two independent hyperventilation challenges, both involving asthmatic and normal subjects, RHER in the asthmatics correlated with the post challenge fall in FEV^ (r=0.96 n = 7 ; r=0.85 n=9). Evidence of an air conditioning deficiency in asthma was found. Attenuation of RHER was by a purpose built humidifier (38°C 100%RH, 150 1/min air flowrate). The device was combined with a numerical model of simultaneous heat and water vapour transfer in order to describe the thermodynamic factors influencing airway heat exchange. Minimising RHER inhibited airway dysfunction in 11 asthmatics after exercise. Invasive measurement in 11 anaesthetised patients of airway temperature was undertaken to determine the site of maximal heat loss. An oral-pharyngeal temperature gradient of 15°C during tidal inspiration of ambient air was found. A catheter-like humidity probe was developed. In 6 subjects tidally inspired ambient air was found to be subsaturated (minima: 80% RH, 34°C) at the mid trachea. Trans mucosal water flow proximal to the trachea was measured as 0.21 ml/min. The larynx may host the airway site from which the bronchial response to heat loss is triggered.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available