Effect of Alterations in the Arterial Carbon Dioxide Tension on the Blood Flow Through the Cerebral Cortex at Normal and Low Arterial Blood Pressures

Abstract

It is well known that the cerebral blood flow alters in response to changes in the arterial carbon dioxide tension. However, it is not yet clear whether there are upper and lower limits of Paco, beyond which the cerebral vessels do not react. In addition, there have been no reports on the response of cerebral blood flow to alterations in Paco, in hypotensive states.The recent development by Ingvar (1961, 1962) of a rapid, easily repeatable, and relatively untraumatic method of estimating the blood flow through the cerebral cortex has enabled us to make multiple estimations of blood flow in lightly anaesthetized dogs at varying tensions of arterial carbon dioxide and varying arterial blood pressures. METHODThree hundred and two measurements of blood flow through the cerebral cortex were made on 41 unselected mongrel dogs. The animals were anaesthetized with thiopentone. A cuffed endotracheal tube was inserted and connected to a Starling respiratory pump, through which a 4:1 mixture of N20 and oxygen was delivered in open circuit. Suxamethonium chloride was administered at intervals. Repeated small doses of thiopentone were given during the actual operation. A cannula was inserted into the femoral artery and connected to a damped mercury manometer for the measurement of the systemic blood pressure. This cannula was also used for the withdrawal of arterial blood samples.The thyroid branch of the common carotid artery was cannulated centripetally, the distal end being tied. The temporal muscle was excised and a trephine hole made over the parietal bone. A cruciate incision was made in the dura and the exposed brain cortex was covered with a plastic membrane (Melinex) 6,& in thickness. A thin lead shield was placed over the surrounding dura and bone, leaving exposed only the area of cortex covered by the membrane. An end window Geiger counter, mounted 1 mm. above the exposed cortex, was connected to a ratemeter and a direct writing recorder. After the operation was completed, thiopentone administration was discontinued and the preparation remained undisturbed for one hour before the first measurements of blood flow were made. Plasma substitute (Dextran), saturated with 85 Krypton, was injected, rapidly at first and then more slowly, into the carotid artery over two to three minutes. The blood flow through the brain cortex was calculated from the half-life of the initial slope of a semilogarithmic plot of the clearance curve using the formula of Lassen and Ingvar (1961, 1962

Hydrogen Clearance Method for Determining Local Cerebral Blood Flow. II. Effect of Heterogeneity in Cerebral Blood Flow

“…This has been exactly ob served repeatedly by many investigators (lngvar and Lassen, 1962;Fieschi et aI. , 1965;Harper and , 1965;Lassen, 1965a;Jamieson and Halsey, 1973;Pasztor et aI., 1973;Meyer et aI., 1980) using krypton, xenon, or H2 as an indicator and was also confirmed by us in another series of experiments (von Kummer, 1984b).…”

Regional Neurovascular Coupling and Cognitive Performance in Those with Low Blood Pressure Secondary to High-Level Spinal Cord Injury: Improved by Alpha-1 Agonist Midodrine Hydrochloride

“…11,12 Although resting CBF may be preserved after SCI, cerebrovascular reserve (i.e., the ability of the cerebrovascular system to respond to acute increases in metabolic demand, mechanical or neural stimuli) may be affected, resulting in an insufficient CBF response. 13 Supporting this contention, elegant work by Harper and Glass 14 showed that progressive hypotension abolishes the capacity of the cerebrovasculature to dilate or constrict.…”

“…18 As cerebral perfusion pressure is a critical component of CBF control, it is possible that NVC mediates the relationship between reduced BP and cognitive function in SCI. 14 Wecht et al 19 partially examined this relationship by showing the MCA flow velocity response to cognition (i.e., Stroop test) was not different between AB and SCI. Although the internal carotid/MCA provides 475% of total CBF, arteries responsible for perfusing the brainstem (i.e., vertebral/posterior cerebral arteries (PCA)) have been shown to be more responsive to various cognitive stimuli.…”

Measurement of Cerebral Blood Flow in the Rat with Intravenous Injection of [11C]Butanol by External Coincidence Counting: A Repeatable and Noninvasive Method in the Brain

“…In using a P aco2 change to produce changes in CBF, it seemed reasonable to choose values at the ex tremes of variations that might occur under physi ological stress and not to employ extremes which result in indeterminate secondary effects or are be yond those attainable by a physiological situation. For Paco2, this range probably extends from 15-30 mm Hg to 60-70 mm Hg (Reivich, 1964;Harper and Glass, 1965;James et aI., 1969;Sage et aI., 1981). This range includes the straight-line portion of the curves published by many investigators for CBF versus Paco2 in a variety of animals.…”