Transient analysis of the canine cerebrovascular response to carbon dioxide.

Cerebral venous outflow and carbon dioxide transients were studied during five different transitional states: (1) on and off 10% carbon dioxide breathing, (2) on and off hyperventilation, (3) on 7% carbon dioxide breathing, (4) on 10% carbon dioxide breathing initiated from 7% carbon dioxide breathing, and (5) on 10% carbon dioxide breathing initiated during intracarotid papaverine infusion, in pentobarbital anesthetized, paralyzed, mechanically ventilated dogs. Plots of the temporal relationships between these variables indicated that cerebral blood flow is closely related with cerebral venous carbon dioxide tension but not arterial carbon dioxide tension. The rate at which flow changed upon transition from one steady state to another was phase dependent, in that longer times were required to establish stable conditions in the on phase than in the off phase.

Analysis of the effect of bilateral sympathetic stimulation of cerebral and cephalic blood flow in the dog.

Unilateral stimulation of the cervical sympathetic in dogs had no effect on cerebral blood flow (CBF) measured by the venous outflow technique. Since this technique measured CBF from both cerebral hemispheres, small changes induced by unilateral stimulation could have been masked by a large constant CBF measured from the contralteral hemisphere. To test this possibility the effect of simultaneous bilateral sympathetic stimulation was studied when the dog was breathing either normal air or a gas mixture of 10%CO2.

Computer-assisted method for multi-exponential curve fitting for determining cerebral blood flow.

A computer program has been developed for use in determining cerebral blood flow using an inert radioactive gas. The basic algorithm involves the determination of multiple exponential coefficients from the complex concentration-time function. The exponential coefficients are determined by 'peeling' away slower exponentials complex function one at a time.

Microvascular control in intestinal mucosa of normal and hemorrhaged rats.

The mucosal microcirculation in innervated and denervated small intestine was studied using anesthetized rats. Denervation did not cause significant (P greater than 0.05) diameter changes in the precapillary vasculature; however, venules did constrict significantly.