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Described here are the progressive changes in blood-flow distribution that accompany four-hour heart-lung bypass in dogs and the effects of perfusion rate on flow distribution and oxygen consumption. The corresponding changes produced by anesthesia alone and by the thoracotomy needed for a bypass procedure are also shown for comparison purposes. These data indicate that the bypass procedure itself puts a very significant stress on the test animals and that perfusion rates in excess of resting cardiac output are required to prevent hypoxia induced irreversible tissue damage.

There are two conventional approaches available for the investigation of placental transfer. The first is to derive a mathematical model of the placenta. On the basis of this model, the response of the placenta to a change can be predicted. The second method is to perform experiments on living animals, and observe the response of the animal to a change. Sometimes the two methods are compatible and sometimes they are not. Where there is disagreement, it is often due to the complex nature of the animal response. The response that was predicted from the mathematical model may exist, the the ability of the investigator to observe this response will be hindered by compensatory reflexes which mask the predicted response.