Adaptation of respiratory muscle perfusion during exercise to chronically elevated ventilatory work

Pneumonectomy (PNX) leads to chronic asymmetric ventilatory loading of resp iratory muscles (RM). We measured RM energy requirements during exercise fr om RM blood flow ((Q) over dot) using a-fluorescent microsphere technique i n dogs that had undergone right PNX as adults (adult R-PNX) or as puppies ( puppy R-PNX), compared with dogs subjected to right thoracotomy without PNX as puppies (Sham) and to left PNX as adults (adult L-PNX). Ventilatory wor k ((W) over dot) was measured during exercise. RM weight was determined pos t mortem. After adult and puppy R-PNX, the right hemidiaphragm becomes gros sly distorted, but (W) over dot and right costal muscle mass increased only after adult R-PNX. After adult L-PNX, the diaphragm was undistorted; (W) o ver dot and left hemidiaphragm RM (Q) over dot were elevated, but muscle ma ss did not increase. Mass of parasternal muscle did not increase after adul t R-PNX, despite increased (Q) over dot. Thus muscle mass increased only in response to the combination of chronic stretch and dynamic loading. There was a dorsal-to-ventral gradient of increasing (Q) over dot within the diap hragm, but the distribution was unaffected by anatomic distortion, hypertro phy, or workload, suggesting a fixed pattern of neural activation. The diap hragm and parasternals were the primary muscles compensating for the asymme tric loading from PNX.