Effects of hyperventilation on cerebral blood flow and brain tissue metabolism in normotensive and spontaneously hypertensive rats.

Abstract

SUMMARY Cerebral vascular carbon dioxide (CO2) reactivities were compared in normotensive (NTR) and hypertensive (SHR) rats. Cerebral bloodflow (CBF) in cortex and thalamus were evaluated before and during one hour of hyperventilation. After one hour of hyperventilation brain lactate, pyruvate, and ATP concentrations were also determined. Significant and similar reductions of CBF due to hyperventilation induced hypocapnia were found in both NTR and SHR groups. In contrast the percent increase in cerebrovascular resistance (CVR) per unit decrease in paC0 2 was significant, indicating that hypocapnia induced vasoconstriction is greater in NTR than in SHR groups. During hyperventilation the average value for lactate in the NTR group was 3.98 mM/kg. In contrast it was 3.15 mM/kg in the SHR group, a significant difference (p < 0.05). When paCC>2 fell below 15 mm Hg the cerebral lactate increased strikingly in the NTR group and cortical CVR was reduced suggesting that an accumulation of the ischemic metabolites caused dilatation of the constricted cerebral vessels. In contrast the SHR group disclosed no such changes. The increase CVR characteristic of SHR appeared to diminish the cerebral vasoconstrictive response to hypo capnia. As a result ischemic metabolites in the brain do not increase in this group to the degree that they do in NTR.Stroke Vol 13, No 5, 1982 IT HAS BEEN KNOWN that hyperventilation leads to cally ventilated with a gas mixture of 70% N 2 0 and vasoconstriction of cerebral arteries with reduced cere 30% of 0 2 . One femoral artery was cannulated to bral blood flow (CBF) and cerebral oxygen tension, 1 ' 2 measure blood pressure and for anaerobic sampling of and consequently alters the brain metabolism. '• 3 4 The arterial blood for pC0 2 , p0 2 and pH determinations electroencephalographic changes during hyperventila with a Model 113 IL meter. The body temperature, tion are indistinguishable from those observed during measured in the rectum, was kept close to 37°C cerebral hypoxia. 5,6 throughout the experiment. Our previous studies 7-10 have demonstrated that The animals were divided into two experimental spontaneously hypertensive rats (SHR) are more sus groups: one for measurements of local CBF and the ceptible to cerebral ischemia than normotensive rats other for determinations of brain tissue metabolites. (NTR) following bilateral carotid occlusion, suggest ing that the cerebral vasoreactivities to changes of the Cerebral Blood Flowperfusion pressure might be different between SHR Twenty-two NTR and 22 SHR were used for this and NTR. In fact, the lower limit of cerebral autoregupurpose. The animal's head was fixed in a head holder, lation is significantly higher in SHR than NTR, and the and two small burr holes were made on the skull 2 mm increased cerebral vascular resistance due to the persis lateral to the bregma on each side for stereotaxic inser tent high blood pressure is responsible for such upward tion of teflon-coated platinum electrodes, one in the shift of the autoregulation in SHR...

Cerebrospinal Fluid Lactate in Patients with Hepatic Encephalopathy

“…Since hyperven tilation gives rise to cerebral vasoconstric tion, leading to a reduction in cerebral blood flow and increase in tissue lactate [18], the decreased arterial C 0 2 tension in hepatic encephalopathy might be one of the factors for the elevated CSF lactate. Our previous study showed, however, that hypocapnia as low as 29.0 mm Hg does not affect brain lac tate levels [19]. We assume, therefore, that an increase in CSF lactate in hepatic enceph alopathy may be caused by excess produc tion of lactate in the brain.…”

Cerebral physiological and metabolic effects of hyperventilation in the neonatal dog

“…Studies of a variety of adult animals including rat (8, 13, Hg, respectively, in the rat. Ishitsuka [13] suggests that in the hyperventilated rat, lactate accumulation results from both decreased brain perfusion and a decrease in transfer of oxygen from blood to tissue (Bohr effect).…”

“…Marked hypocarbia in the neonatal dog produces an elevated brain lactate level that may be related to changes in glycolytic rate rather than to tissue ischemia or hypoxia. [13,14, 191 that accompany prolonged hyperventilation in the adult human and laboratory animal have been ascribed to tissue ischemia resulting from marked vasoconstriction and to decreased oxygen availability during alkalosis (the Bohr effect). To determine whether prolonged hyperventilation may also lead to brain ischemia and elevation of brain lactate levels in the neonate, we measured CBF and levels of brain glucose, lactate, ATP, and phosphocreatine (PCr) after 90 minutes of hyperventilation in neonatal dogs.…”

Autoregulation of spinal cord blood flow: is the cord a microcosm of the brain?

“…Regional cerebral blood flow in the rat has also been investigated by Nystrom and Norl6n. ' 8 They found the following values for regional flows: cerebellar flow of 58 ml/100 g/min; brainstem flow of 54 ml/100 g/min; right hemisphere flow of 33 Author De Ley et al, 1985 17 NystrSm et al, 1983 18 Ishitsuka et al, 1982 19 Nilsson et al, 1976 20 Hernandez et al, 1976 21 Matsumoto et al, 1976 22 Gjedde et al, 1975 23 Eklofetal, 1973 24 Goldman et al, 1973 25 Pannier et al, 1973 26 Haining ml/100 g/min and left hemisphere flow of 38 ml/100 g/min. Although the values reported are lower than those found in our study, the same tendency was observed, namely higher flows in the cerebellum and brainstem than in the cortical regions.…”