Cerebral vasoreactivity and arterial gas embolism.

Compression regimens effect redistribution of entrapped cerebral arterial gas emboli by reducing embolus length and/or by increasing local perfusion pressure. Embolus length is related to embolus volume and vessel diameter. It has been assumed without evidence that cerebral arterial gas emboli induce local vasoparalysis and hence that the relevant vessel diameter will not be affected by the treatment regimen. This study tested that assumption. Infusion of gas microbubbles into the femoral artery of upright rabbits caused significant but transient hypertension, respiratory depression, cardiac bradyarrythmia, inhibition of cerebrovascular autoregulation to blood pressure changes, and cerebral arterial gas embolism, with entrapment of long emboli in arterioles of 50-200 micron diameter. Cerebral arterioles constricted and dilated appropriately with sequential changes in ventilation gas mixture both before and after gas embolism. The study demonstrated that cerebral arterial gas emboli did not necessarily inhibit cerebrovascular reactivity and that the effect a compression regimen has on cerebral arteriole diameter should be included in any assessment of its efficacy.