Cumulative Aspects of Repeated HSG Exposure.

A system is described for acceleration treatment of domestic fowl. A reasonable end point for acceleration tolerance is provided by a bradycardia that occurs fairly close to the lethal limit. In a group of 61 male Rhode Island Red chickens exposed to 6 G sub z, the mean tolerance or - SD was 11.1 or - 10.6 minutes. Among individuals, the acceleration tolerance was inversely related to both body size and age, and positively to the pretreatment heart rate. In some individuals the acceleration induced cardiac lesions subendocardial hemorrhage or congestion and at the subcellular level, further degenerative changes became apparent, including regions of hypercontraction of cardiac myocytes, mitochondrial swelling, and necrosis in some cells. Discrete regions of fibrous tissue proliferation and regions with increased frequency of intercalated discs were also observed. In other experiments, chickens were given a single 1-minute exposure to a field that increased from 5 to 18 G sub z for the series. Acceleration-induced changes were observed inheart rate during and after the treatment and subsequently in lymphocyte frequency and body-mass maintenance. Generally, bradycardia and lymphopenia increased proportionally to field strength. Above 13 G, normal growth and even maintenance of pretreatment body mass were impaired.