Nervous output from the respiratory center during obstructed breathing.

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Abstract
The present study was concerned with measuring the nervous output from the respiratory center of dogs during obstructed breathing. An assessment of this output was obtained by measuring electrical activity in the phrenic nerve before and after complete obstruction and the introduction of "threshold" loads. Indirect assessments were obtained by measuring electrical activity in the diaphragm with needles inserted in the muscle and with esophageal electrodes. The results show that, during unobstructed breathing, tidal volumes are proportional to the activity in the phrenic nerve, diaphragm, and esophagus. Conversely, during complete obstruction and during inspiratory loading, tidal volume decreases even though activity in the phrenic nerve increases. The activity recorded from diaphragm and esophagus parallels that in the phrenic nerve. These observations indicate that the minute ventilation may not measure the nervous output from the respiratory center during airway obstruction. A more reliable measure of this output may be obtained by recording electrical activity in the phrenic nerve or in the diaphragm. The activity in the diaphragm may be measured directly by needles inserted in the muscle, or indirectly by an esophageal lead introduced to the level of diaphragm.