Respiratory activity of upper airway muscles and oro-nasal flow partitioning

This thesis examines the coordinated respiratory activity of various upper airway muscles in awake, normal subjects. The dimensional changes of the oropharyngeal airway were measured during exposure to negative intraluminal pressures. In the absence of an inspiratory effort, there was marked narrowing and cephalad displacement of the upper airway. This suggested a complex interaction of upper airway and thoracic muscle activity, critical to the maintenance of upper airway patency. The respiratory related EMG activity of the cricothyroid muscle was compared with that of the alae nasi. During quiet breathing and various respiratory manoeuvres, the electrical activity of the cricothyroid was analagous to that of the alae nasi, and hence simulated predominantly that of an upper airway dilator. During increased chemical drive, the cricothyroid and alae nasi patterns of response were similar, and were related to the inspiratory muscle response in a curvilinear manner. The relationship between alae nasi activity and breathing route was studied during progressive exercise. As ventilation increased, alae nasi activity and nasal ventilation were tightly correlated, independently of flow through the mouth. However, our findings were not explained by reflex control of alae nasi activity sensitive to nasal flow, temperature or pressure and were more consistent with a centrally controlled, feed forward modulation of activity. The partitioning of oro-nasal breathing during exercise was reproducible within an individual. The flow partitioning was not directly related to the exercise itself and was uninfluenced by the direction of upper airway flow, suggesting tightly controlled modulation of the relative oral and/or nasal resistances. The inspiratory and expiratory pressure-flow relationships of the oral and nasal airways were curvilinear, well described by a power function, and suggested a similar degree of flow turbulence at rest. Decreases in nasal resistance occurred following exercise and were associated with a change in flow regime from fully turbulent to orifice flow. These studies elucidate some specific interactions of upper airway muscles, and provide new insight into their activity during respiration