Response of Pial Precapillary Vessels to Changes in Arterial Carbon Dioxide Tension

Abstract

A quantitative study of responses of pial precapillary vessels to changes in arterial blood carbon dioxide tension was made in anesthetized cats. All vessels examined ranging in diameter from 13 to 90/ x responded to hypercapnia with increases in diameter and to hypocapnia with decreases in diameter. The onset of the response to hypercapnia was earlier, its speed was faster, and its magnitude greater with higher concentrations of CO 2 . In response to the same increase in arterial blood Pco 2l smaller vessels (13 to 40/i) increased in diameter by 47.7 ± 10.8% of the control value while the increase in diameter of larger vessels (41 to 90/x) was significantly lower and equal to 29.5 ± 6.3% of the control value. In the steady state the relation between pial vessel diameter expressed as percent of the control value (Y) and arterial blood Pco 2 (X) was given by the equation Y = 53.07 + 1.587X -0.00715X 2 . The relatively large magnitude of the response of pial arteries and arterioles to CO 2 and the fact that it was dependent on vessel size show that there must be significant readjustments in the pressure gradients in these vessels when CO 2 tension is changed. KEY WOKDScat hypercapnia cerebral blood vessels hypocapnia arterioles B In view of the generally acknowledged importance of the action of carbon dioxide on cerebral blood vessels in the regulation of blood flow to this vascular bed, and because of the well-recognized principle that normal adjustments in the vascular resistance in most vascular beds are usually carried out by alterations in the caliber of the small precapillary blood vessels, it appeared important to study the effect of CO 2 on small precapillary cerebral blood vessels. There are only two previous studies in which this aspect of the cerebral vascular action of CO 2 was From the Department of Medicine, Medical College of Virginia, Health Sciences Division, Virginia Commonwealth University, Richmond, Virginia 23219. This work was supported by Contract NGL 47-002-001 from the National Aeronautics and Space Administration, by Grant HE-11077 from the National Heart and Lung Institute, and by a grant from the Virginia Heart Association. Dr. Kontos is the recipient of a Research Career Development Award from the National Heart and Lung Institute, and Markle Scholar in Academic Medicine. Dr. Patterson is the recipient of a Research Career Award from the National Heart and Lung Institute.Received October 27, 1970. Accepted for publication February 23, 1971. examined systematically. In one study (1) it was found that the inhalation of the CO 2 by anesthetized or unanesthetized cats and monkeys produced vasodilation, but the results were reported only qualitatively. In the other study (2) quantitative results were presented, but only arteries larger than 150/JL in diameter were examined. Furthermore, methods presently available allow more accurate and complete studies than were possible in the past. The present study was undertaken to investigate the effect of changes in blood CO 2 tension on ...

Reactivity of Rat Pial Arterioles and Venules to Adenosine and Carbon Dioxide: With Detailed Description of the Closed Cranial Window Technique in Rats

“…tension. In contrast, the small arterioles were more sensitive to CO2, These results are consistent with reports by Raper et al (1971), Gregory et al (1980), and Wei et al (1980) fore represent the initial effects of adenosine-free artificial CSF (i.e., the previous washout of aden osine in endogenous CSF). This observation could be in keeping with our findings that theophylline causes a decrease in resting CBF (Morii et aI., 1983) and in pial diameter (Winn et aI., 1985), implying a role for adenosine in the regulation of CB F during normoxia.…”

The Velocities of Red Cell and Plasma Flows through Parenchymal Microvessels of Rat Brain are Decreased by Pentobarbital

“…All of these changes could affect blood flow and flow ve locity through capillaries. Pial arteries and arteri oles dilate in response to hypercapnia (Raper et aI., 1971;Heistad and Kontos, 1983;Wei et aI., 1984). Furthermore, Levasseur and Kontos (1989) re ported that the extent of pial arteriolar dilation at Pco2 of 50 mm Hg (the partial pressure measured in our experimental rats) was similar in awake and pentobarbital-anesthetized (45 mg/kg) rabbits.…”

Role of Large Arteries in Regulation of Cerebral Blood Flow in Dogs

“…An interesting observation is that large (>100 ,um) but not small (<60 gm) pial arteries dilate when arterial pressure Is reduced from 120 to 80 mm Hg in cats (18). Small arteries (40-90 ,um) have also been reported (19) to dilate during hypercapnia, although not as much as arterioles (13-40 ,um). These studies provide strong support for the concept that large arteries participate in regulation of cerebral blood flow; however, as blood flow was not measured in these studies, it is not possible to estimate quantitatively the changes in resistance.…”