When core body temperature was lowered to 15°C, both hypothermic groups experienced a similar reduction in circulating blood volume. And both showed that the physiological mechanisms that help transport oxygen and help unload oxygen from hemoglobin were working. "As a consequence, oxygen supply was not a limiting factor for survival in the present experiments," the authors wrote.
The rats in the one-hour group spontaneously normalized their blood pressure, cardiac output and heart rate after they were rewarmed, Tveita noted. However, the rats in the five-hour group, which were significantly more likely to experience heart failure during rewarming, experienced substantial lowering of cardiac output and other cardiac functions.
"We conclude that the heart failure we see after rewarming is not due to a lack of oxygen supply or oxygen transportation because unloading of oxygen at the cell level from hemoglobin is functioning," Tveita stated. Thus, it appears that the problem comes as a result of the lower cardiac output, he added.
"Thus, efforts aimed at elevating cardiac output in this phase seem advisable in order to optimize oxygen supply, reperfuse (restore blood flow to) vascular beds (minute blood vessels) and prevent rewarming shock formation," the authors wrote
Source and funding
"Is oxygen supply a limiting factor for survival during rewarming from profound hypothermia?" by Timofei V. Kondratiev, Kristina Flemming, and Mikhail A. Sovershaev, University of Tromsø, Norway; Eivind S.P. Myhre, Sørlandet Hospital, Kristiansand; and Torkjel Tveita, University of Tromsø and University Hospital of Nor
Source:American Physiological Society