The OKA-MT pressure chambers were used. External respiration was studied by spirography by means of the SG-2M spirograph. From the results of examination of 53 patients with acute cerebral circulatory disorders it was established that hyperbaric oxygen normalizes the initially abnormal external respiration: corrects the periodical rhythms and reduces hyperventilation; the hyperbaric oxygenation sessions have no effect on initially normal respiration; the reaction of external respiration to hyperbaric oxygen changes during the course of treatment depending on the number of sessions; the appearance or intensification of the hyperventilation syndrome after one or three hyperbaric oxygenation sessions in the absence of negative neurological dynamics cannot be assessed as a contraindication for hyperbarotherapy.