A portable respirator, of the volume cycle type, is powered by and supplied with compressed medicinal gas, requiring no electric power. The respirator is capable of operating in an automatic mode in which a fixed volume of gas is supplied to the patient for a first selected period of time, exhalation is prevented for a subsequent second period of time, and then the patient is allowed to exhale for a subsequent third selected period of time. The respirator can also operate in a demand mode, in which each cycle is triggered by the attempt of the patient to inhale. The respirator shifts automatically from demand mode to automatic mode cycling and triggers an alarm in the event that the patient becomes too feeble to attempt to inhale. The respirator may also be used as an anesthesia ventilator during surgery.  www.jiuxin-med.com