Decay of inspiratory muscle pressure during expiration in anesthetized cats

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Abstract
In 6 spontaneously breathing anesthetized cats (pentobarbital sodium, 35 mg/kg), the antagonistic pressure developed by the inspiratory muscles during expiration (PmusI) was studied. This was accomplished in 2 ways: with a previously reported method based on the measurement of changes in lung volume and airflow during spontaneous expiration, together with determination of the total passive respiratory system elastance and resistance; and measurement of the time course of changes in tracheal pressure after airway occlusion at end-inspiration, up to the moment when the inspiratory muscles become completely relaxed. The agreement between the 2 methods is generally good, both in the amplitude of PmusI and in its time course. The 1st method was also applied to spontaneous expirations through added linear resistive loads. These did not alter the relative decay of PmusI. In anesthetized cats the braking action of the inspiratory muscles does not decrease when expiratory resistive loads are added, i.e., when such braking is clearly not required.