The responses of hypovolemic patients would be expected to be similar to experimental animals that were hypovolemic. Normovolemic patients would be expected to respond as do the normovolemic experimental animals. Hypovolemic patients do not necessarily respond the same as do normovolemic patients or volunteers. The amount of external pressure applied by the device is directly proportional to the amount of tissue pressure increase. Tissue pressure is transmitted to the vessel as reduction transmural pressure, or in change in the size of the vessels and subsequent increase in SVR. Patient response to external pressure varies with the amount of device pressure. The optimal pressure of the PASG is in the range of 60 to 80 torr. Although exceeding this value does not appear to be necessary, it is not harmful in the short term (less than 90 minutes). Using less pressure reduces the SVR and, therefore, the blood pressure response. Keeping the external pressure at approximately 40 torr appears to be ideal for hemorrhage control. Of the more than 300 articles that have appeared in the recent literature addressing the PASG, at least 190 have discussed specific scientific experiments in the animal laboratory, in the human laboratory, or in the clinical environment, in which results gathered addressed how, why, or if the PASG worked. These studies demonstrate that the PASG does, in fact, improve blood pressure, control hemorrhage, improve carotid and upper body blood flow, improve the ability of the prehospital provider to start IV lines, and improve survival (particularly short-term) with few hospital and even fewer prehospital complications. The device produces its blood pressure response by improving preload, increasing SVR, and mobilizing some blood (500 to 1,000 mL) to the upper body compartment above the device. These responses are most probably produced by decreasing the radius of the vessels compressed by the device, decreasing the compartment volume, and differentially affecting the blood flow without and within the device. Hemorrhage is controlled by increasing the external pressure on the vessel by the transmitted increased tissue pressure, reducing the vascular lumen, and reducing the area of the laceration. Short-term survival is improved by decreasing intra-abdominal hemorrhage and improving perfusion (maintaining better oxygenation in the heart-brain-lung circulation.) Long-term survival is improved because the device controls hemorrhage, maintains blood pressure, and allows delivery of the severely injured patient to the trauma center and within the hospital while awaiting an OR, as in the case of a leaking aortic aneurysm.(ABSTRACT TRUNCATED AT 400 WORDS)