Effects of subfascial pressure in experimental deep pectoral myopathy of the fowl: An angiographic study

1. Angiography of the supracoracoid muscles of broiler breeder hens after neurostimulation of the breast muscles showed that complete ischaemia developed within 10 min and persisted for at least 1 h. After 24 h ischaemia remained only in the middle 1/4-1/3 of the muscle, coinciding with the main site of necrotic lesions found in experimental and spontaneous deep pectoral myopathy. 2. The development of ischaemia was prevented when the deep pectoral fascia was incised along its length before neurostimulation. 3. An increase in subfascial pressure in the supracoracoid was observed during 30 min after neurostimulation in both broiler breeder and lightweight hens. This was greater in the broiler breeder hens and more than sufficient to arrest blood flow. 4. During the first hour after neurostimulation an increase of 20% occurs in the weight of the supracoracoid muscle of both types of hen but only the broiler hens developed ischaemia. 5. It is suggested that the immediate cause of the ischaemia following neurostimulation is a rise in intramuscular pressure due to the increased muscle volume within an osteofascial compartment of limited size. The basic difference betweeen the two types of bird in their susceptibility to this type of ischaemia and to deep pectoral myopathy probably lies in the relative development of the supracoracoid and its overlying fascia.