Effects of changes in arterial O2 content on cerebral blood flow in the lamb

Abstract

The effect of variations in arterial O2 content (CaO2) on the cerebrovascular bed of seven unanesthetized newborn lambs was studied as the hematocrit and arterial PO2 (PaO2) were varied. Each subject was studied at a high hematocrit [44 +/- 3% (SD)] and a low hematocrit [24 +/- 3%]. At each hematocrit level the PaO2 was changed over a range of 30-150 mmHg. The relationship between cerebral blood flow and PO2 depended on hematocrit and vice versa. To the contrary, the relationship of blood flow to CaO2 was independent of hematocrit and/or PO/. As CaO2 fell, regardless of whether this was due to a fall in PO2 hematocrit or both, there was a reciprocal increase in cerebral blood flow such that cerebral O2 delivery (cerebral blood flow x CaO2) was constant. These data show that CaO2 is a variable of fundamental importance to the regulation of cerebral blood flow. Changes in CaO2 are accompanied by reciprocal changes in cerebral blood flow to maintain constant cerebral O2 delivery. Data among species with differing cerebral O2 consumption show that cerebral O2 delivery, in turn, is regulated according to cerebral O2 consumption.

An Initial Sustained Inflation Improves the Respiratory and Cardiovascular Transition at Birth in Preterm Lambs

“…Numerous previous studies have demonstrated that, after birth, CBF gradually decreases, which is considered to be an autoregulatory process in response to an increase in oxygenation (14,17,18). This response was observed in SI lambs, with CBF gradually decreasing from 40.2 Ϯ 7.8 mL/min/kg at 1 min after birth to 19.9 Ϯ 4.3 mL/min/kg by the end of the experiment.…”

Cerebral Blood Flow and O2 Metabolism after Asphyxia in Neonatal Lambs

“…Parameters compared included measured physiologic variables (oxygen contents, blood gases, microsphere whole brain, and regional blood flows) as well as calculated variables. CMR0 2 , 00, fractional extraction of oxygen, CBF per unit Oz consumption [1/(CaOz-CvOz)] were calculated as described previously (10,15).…”

“…The neonatal lamb was chosen for these studies because it is a well-established model for the evaluation of the cerebral circulation (l0, 15,26). The surgical procedures are tolerated nicely and an indwelling sagittal sinus catheter for sampling cerebral venous drainage can be reliably placed.…”

Pathogenesis of hypoxic-ischemic brain injury

“…Thus, interruption of placental blood flow with hypoxia and hypercarbia both independently increase CBF. [11][12][13] In addition, the vascular responses to both partial pressure of carbondioxide (PaCO 2 ) and partial pressure of oxygen (PaO 2 ) vary widely amongst brain regions. For example, cerebral white matter as compared to brainstem and cortical structures has limited vasodilatory responses to both PaCO 2 and hypoxia.…”