BREATHING DURING EXERCISE IN DOGS - PASSIVE OR ACTIVE

The activation patterns of the costal and crural diaphragm and transve rsus abdominis muscle and their relationship to esophageal pressure (P es) changes and footplant were examined in five chronically instrument ed dogs which breathed at high frequencies at rest and during exercise . In two tracheostomized dogs, measurements were made of diaphragmatic length via sonomicrometry and of airflow and were related to diaphrag matic electrical activity and Pes. Dogs exhibited either a high-freque ncy breathing pattern, characterized by Pes changes occurring at 2-6 H z, or a mixed-frequency breathing pattern, characterized by low-amplit ude Pes oscillations (4-6 Hz) superimposed on a slower breathing rate of 0.5-1 Hz. Regardless of the type of breathing pattern elected or of the various breathing-to-stride frequency ratios observed during exer cise, decreases in Pes were always associated with phasic electromyogr ahic activity of the costal and crural diaphragm and with phasic diaph ragmatic muscle shortening. The transversus abdominis electromyographi c activity coincided with an increasing Pes from peak negative values in resting dogs and exhibited both an expiratory and a locomotory modu lation during exercise. Although footplant may have contributed to som e airflow generation when dogs utilized the mixed-frequency pattern, t hese data demonstrate that the movement of air into and out of the lun gs in stationary or exercising dogs requires phasic neural activation of the diaphragm and other respiratory muscles.