Effects On Regional Circulations

Thus the effects of high pressures of oxygen on central haemodynamics include a decrease in cardiac output mainly through a decrease in heart rate and an increase in peripheral resistance. However, the way this decrease in blood flow is distributed between the various organs has led to controversy. Once again it should be emphasised that regional blood flow, just like global cardiac output, is regulated by the metabolic requirements of the respective organ system. Experimental protocols can produce great variations in regional blood flow distribution depending on the choice of subjects (small mammals such as rats vs large mammals such as dogs, ewes and human beings) the state of consciousness (conscious or anaesthetized), the drugs administered (type of anaesthesia) and whether subjects are resting or exercising (controlled or spontaneous ventilation).

First we shall analyse the effects of high pressures of oxygen on the various regional circulations, then we shall attempt to describe the mechanisms involved.

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