Initial responses to added viscous resistance to inspiration in dogs

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Abstract
Respiratory mechanics and diaphragm electromyograms in six anesthetized dogs were studied to determine the immediate nonchemical responses to three levels of added airflow resistance to inspiration. Inspiratory time, intrathoracic pressure amplitude, diaphragm activity, and inspiratory work all increased in the first breath with added resistance. The adjustments to added viscous resistance are interpreted as indicating an immediate active response which tends to maintain an adequate tidal volume. Even though Vt decreased with added resistance, the area under the inspiratory volume curve was unaltered on the first resistance breath. Thus, during the initial response, inspiratory duration may depend primarily upon the accumulated or summated information related to change in volume. Work done on the lung and apparatus was greater with added resistance. The increase resulted from the increased inspiratory time rather than change in rate at which work developed during the inspiration. After two to three breaths on resistance the inspiratory work rate began to increase, probably reflecting the addition of secondary chemical drive. airflow resistance; diaphragm electromyogram; respiratory control Submitted on February 14, 1964