Local vascular response to change in carbon dioxide tension. Long term observation in the cat's brain by means of the hydrogen clearance technique.

Abstract

(617) ALTHOUGH ARTERIAL carbon dioxide tension (PaCO 2 ) has often been confirmed as a prominent factor of circulatory control in the central nervous system (CNS) since regional CBF measurements were performed, 1 " 12 the quantitative relationship between local cerebral blood flow (ICBF) and PaCO 2 is not yet clear. Within physiologic ranges of PaCO 2 , the vascular response has been described to be linear 2 "5 l0 " but also as an exponential function.' 8 9 n This has led to uncertainty in calculations of CBF when adjustments for changes in PaCO 2 are necessary. It is also uncertain whether CCyreactivity (CO 2 -R) in different regions of the CNS is uniform or not.6 -7 ' 3 ' 6 Recently Meyer et al 17 stated from stable xenon-CT measurements that ICBF of both gray and white matter decreased "diffusely and homogenously throughout the brain," although they registered a 3.9% flow reduction/mmHg PaCO 2 change in occipital cortex but only a 2.6% flow reduction/mmHg PaCO 2 change in occipital white matter.For these reasons the present study was designed to determine the quantitative response of ICBF to PaCO, From the Neurologische Universitatsklinik Heidelberg. Address correspondence to: Dr. R. v. Kummer, Neurologische Universitatsklinik, Voss-Str. 2, D-6900 Heidelberg, West-Germany.Received January 6, 1983; revision accepted June 22. 1983. change in gray and white matter as well as in the deep nuclei of the brain. The hydrogen clearance technique was chosen for lCBF-determination because this method enables direct and repeated measurements. As previous observations 18 l9 and preliminary data of this study showed, 20 the vascular reactivity is not impaired by small hydrogen sensitive electrodes. To minimize and measure any possible influence of tissue trauma, in this study the electrodes were implanted chronically and the CO 2 -R was repeatedly determined over a period of 12 weeks. MethodsThe experiments were carried out in 6 cats of either sex within the weight range of 2.4 to 3.7 kg. Anesthesia was induced with sodium pentobarbital (30 mg per kg) and maintained with 70% N 2 O-30% O 2 -gas via an endotracheal tube. The animals were paralyzed with pancuroniumbromide administered intravenously, repeated as necessary. Ventilation was maintained by a Schuler pump. Where the PaCO 2 was to be raised, this was done by adding CCygas to the input of the pump.

Comparison of regional vasomotor responses to acetazolamide and CO2 in rabbit cerebrum and cerebellum, measured by a hydrogen clearance method

“…A considerable difference was found between the caudate nucleus and the cerebellar cortex in CBFr and the absolute CO 2 reactivity, but the relative CO 2 responses in the cerebrum and the cerebellum were similar. These results are in agreement with those in earlier studies, which showed that, although the absolute values of CO 2 reactivity might be different due to a greater CO 2 response in better perfused areas, the relative CO 2 reactivity is uniform throughout the CNS (Ackerman 1973, von Kummer 1984. In agreement with our results, in the two studies where the cerebral cortical and basal ganglion CO 2 reactivities were compared in cats using the HC method, no difference was found , von Kummer 1984.…”

“…In agreement with our results, in the two studies where the cerebral cortical and basal ganglion CO 2 reactivities were compared in cats using the HC method, no difference was found (Symon et al. 1973, von Kummer 1984). The CO 2 response in the cerebellum has been determined in only a few studies.…”

Control for Carbon DioxideRelated Changes in Flow Velocity by Transcranial Doppler Monitoring

“…This mean velocity value is the time-averaged mean calculated from the spectral outline of the maximal velocities by the TC2-64 instrument [3]. End-tidal carbon dioxide correlates to arterial Pco 2 , reflecting the intrinsic effects of carbon dioxide at the arteriolar site, that is, the resistance vessels in the MCA territory [5,6]. The vasodilatory effect of carbon dioxide is attributed to the effect on these resistance vessels, rather than to the minute changes in the diameter of the basal cerebral arteries [7,8].…”