Effects of elastase-induced emphysema on histochemical properties of guinea pig diaphragm.

We studied the changes of histochemical properties of diaphragm in guinea pigs with elastase-induced emphysema. Using myofibrillar ATPase staining, three types of diaphragmatic muscle fibers were classified as slow-twitch, oxidative (SO), fast-twitch, oxidative, glycolytic (FOG), and fast-twitch, glycolytic (FG). Capillaries adjacent to individual fibers were also demonstrated by ATPase reaction. After 24 weeks of tracheal instillation of elastase, both the size and number of SO and FOG fibers were increased, thereby indicating the increase in relative areas occupied by these oxidative fibers in the diaphragm (p less than 0.01 in each case). Moreover, these changes were accompanied by the increased capillary density (p less than 0.01). These results suggest that chronic respiratory load with emphysema may establish the diaphragm more resistant to fatigue by increasing oxidative capacity of the diaphragmatic muscle fibers.