Accessory muscle activity and respiration.

The relationship between the accessory muscle activity (sternohyoid and sternothyroid) and respiration was studied in canines. These animals do not have an omohyoid muscle such as found in primates. Therefore, chair-trained monkeys that have all three accessory muscles were used in a portion of the study. Findings in canines supported those previously reported. The sternothyroid muscle fired spontaneously with the onset of inspiration, but there was no similar activity in the sternohyoid. The activity of both muscles was observed after sectioning the recurrent laryngeal nerves and inducing hypoxia and hypercarbia. The severely hypoxic animals produced some negligible activity in the sternohyoid muscle. The data obtained from the chair-trained monkeys showed no consistent accessory muscle activity during normal respiration with recordings taken immediately after electrode placement, at 24 hours, and one week later. Respiratory activity was consistent in the omohyoid and sternothyroid but not in the sternohyoid muscle when partial airway obstruction and hypoxia were induced.