EFFECTS OF DIAPHRAGM SHORTENING ON THE MEAN ACTION-POTENTIAL CONDUCTION-VELOCITY IN CANINES

1. The present study was designed to test if the mean muscle fibre act ion potential conduction velocity (<(V)over bar (APC)>) in the costal diaphragm changes with muscle length, in spontaneously breathing mongr el dogs. 2. <(V)over bar (APC)> was determined by the electromyogram ( EMG) power spectrum 'dip' method, which is based on the bipolar electr ode transfer function. A bipolar EMG electrode with a 20 mm fixed inte relectrode distance was sutured to the costal diaphragm in the fibre d irection, and in a region with a low density of motor endplates. Diaph ragm length was measured with piezoelectric crystals positioned next t o the EMG electrode. Seven dogs were vagotomized and spinally anaesthe tized in order to increase diaphragmatic shortening, reduce velocity o f shortening and abolish possible cross-talk signals from adjacent mus cles. 3. Our results showed that <(V)over bar (APC)> in the canine cos tal diaphragm wax 3.4 m s(-1) and was not significantly related to dia phragmatic shortening.