Degree Type

Thesis

Degree Name

Doctor of Philosophy (Medical Science)

Department

Medical Sciences (Division of Physiology/Pharmacology)

Supervisor

Luke J. Janssen

Co-Supervisor

Mark Inman

Language

English

Committee Member

Gerard Cox

Abstract

Asthma is a disease characterized by transient airway smooth muscle contraction leading to episodes of reversible airway narrowing. It affects over 300 million people worldwide and is implicated in over 250 000 deaths annually. The primary clinical features of asthma include airway inflammation, hyperresponsiveness, and remodeling. Generally, asthmatic patients experience exacerbations between periods of diminished symptoms. Interestingly, in addition to these above mentioned hallmarks, asthmatics have also been shown to react differently to ventilatory mechanical strain. This is most evident when assessing the effect of a deep inspiration (DI), clinically measured as a breath taken from functional residual capacity to total lung capacity, in healthy individuals versus asthmatics. These deep inspiratory efforts have been shown to produce a bronchodilatory response in healthy individuals, whereas in asthmatics, DIs are less effective in producing bronchodilation, can cause more rapid airway re-narrowing, and even bronchoconstriction in moderate to severe asthmatics. The mechanism by which a DI is able to cause bronchoconstriction remains ambiguous. Previous theories suggest that this phenomenon is intrinsic to airway smooth muscle (ASM) itself. However, the airway inflammation present in asthmatic airways may also add to the increased ASM contractility following stretch, by the release of mediators that can prime the contractile apparatus to react excessively in the presence of stretch.

Thus, collectively, the studies contained in this thesis are linked to the general theme of greater characterization of the signalling mechanisms that regulate airway stretch-activated contractions using a pharmacological approach in intact bovine bronchial segments, with the hope of providing novel insights into the mechanisms that regulate the DI-induced bronchoconstriction seen in asthmatics.

McMaster University Library

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