Muscular circulation

In conscious rats, the blood flow in the striated muscles of the limbs has been found to decrease in hyperoxia10'60. In dogs, however, it is hardly affected46.

Actually, muscular blood flow depends on the level of muscular activity. Thus in conscious rats in spontaneous ventilation, the blood flow in the abdomen and thorax muscles decreases in normobaric hyperoxia and increases in hyperbaric hyperoxia, as well as in hyperbaric normoxia. This increase in local blood flow is probably due to the increase in VO2 induced by the increase in muscular work caused by an increase in work of breathing due to gas density-related ventilation resistance under hyperbaric condition.

In summary, HBO induces generalized vasoconstriction affecting all organ systems. Global cardiac output decreases and so do the regional blood flows. However, all regional blood flows are not affected equally. Cerebral blood flow seems to decrease in greater proportion to the global cardiac output, and this has a protective effect against the toxic effects of hyperoxia. Coronary blood flow decreases too, but following a decrease in myocardial work. The other regional blood flows drop proportionally except in the organs where the work is increased by hyperbaric condition (i.e. respiratory muscles) or in the organs that are shielded from hyperoxia by venous admixture (i.e. liver).

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