I Laryngeal Resistance to Air Flow

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Abstract
A method is described for measuring flow through and pressure drop across the larynx of the decerebrate or anesthetized cat with simultaneous determination of the width and, if desired, the length and area of the glottis. An instantaneous measure of resistance to flow and the state of the glottis is thus made possible. The nerve and blood supply is retained intact. The distribution in time, of pressure flow, "resistance" and glottic width is readily plotted. Where this is done the following observations are possible: Each respiratory cycle appears different from its immediate neighbors. The wave forms of pressure and flow are not simple sine waves at any respiratory rate but become less complex as the rate increases. The "resistance" (hindrance) to air flow is greater (at a given glottic aperture) during inspiration than during expiration. Gases with a density lower than air from a theoretical viewpoint should lower the resistance to flow. When the source of the flow through the glottis comes from the respiratory apparatus and there is no deep respiratory depression, the average resistance is greater during inspiration than during expiration. A lack of exact synchronism between respiratory and glottic movements may account for this in part. The lack of anatomical streamlining of the inspiratory pathway (as compared with the expiratory pathway) is also a factor. The resistance values found vary from less than 1 to about 10 cgs ohms or ohms (acoustic) in the absence of central depression. This is of the same magnitude as the impedances of the tracheopulmonary apparatus found at frequencies below 40 per second. In general more energy is dissipated in the larynx during the inspiratory flow. The exception is seen when the respiratory rate is low and expiration approaches the "gasping." Since here the expiratory phase is much shorter than the inspiratory the power discrepancy is greater than that calculated as work. The power consumption is less than 1 milliwatt in all cases.