Effect of Low Oxygen on Muscular Contraction.

Abstract

This study deals with effects of lowered alveolar oxygen on muscular activity of the dog. Twin rebreathing tanks were used containing room air and low oxygen mixtures respectively. Super-maximal stimuli were applied with an automatic stimulator to the peripheral end of the sartorius muscle whose motor nerve was severed to insure direct muscular stimulation. The results of 3-5% mixtures in most animals revealed increased respiration with a corresponding increase of amplitude of muscular response, this passing into a gradual decline to nearly zero with the continuing but declining hyperpnea. The subsequent administration of room air gave a decided rise of muscular activity to a nearly normal level of contraction accompanied by the usual respiratory changes. When the condition of the animal became more critical, post administration level was gradually lowered below previous starting levels. In some animals both the muscular and respiratory responses were well augmented over long periods of administration of low oxygen mixtures. Other animals gave no initial rise in muscular activity. The muscular response gradually decreased until room air was administered though the usual hyperpnea prevailed.

It is suggested that the augmented respiratory movements of lowered alveolar oxygen in most of the observations may be partly accounted for by peripheral chemical changes occurring within the respiratory muscles themselves. In other cases the hyperpnea was maintained despite decreased muscular response to direct stimulation.