The Effects of Changes in PaCO2 Cerebral Blood Volume, Blood Flow, and Vascular Mean Transit Time
The relationships between cerebral blood volume (CBV), cerebral blood flow (CBF), and the cerebral vascular mean transit time (tv) during acute changes in the PaCO2 over a range of 15 to 76 torr were investigated in vivo in rhesus monkeys by serially determining the mean transit time of a vascular tracer, 15O-labeled carboxyhemoglobin, and the mean transit time of a diffusible tracer, 15O-labeled water. Over this range of PaCO2, a significant linear relationship of CBV = 0.041 PaCO2 + 2.0 was found. For each one torr change in PaCO2, there is a change in CBV of 0.041 ml/100 gm of perfused tissue. At a normocarbic value of PaCO2 (37 torr), an average value of 3.5 ml/100 gm was found. A nonlinear relationship of CBV and CBF was found. This relationship is expressed in the equation, CBV = 0.80 CBF0.38. A significant linear relationship was found between CBF and PaCO2. This was described by the equation, CBF = 1.8 PaCO2 - 16.75. For each one torr change in the PaCO2, there is a 1.8 ml/100 gm per minute change in the CBF. At a normocarbic value of PaCO2(37 torr), an average value of CBF of 50 ml/100 gm per minute was found. The relationship of CBV and tv was nonlinear and was expressed in the equation, tC15O = 41 CBF-0.62.
- © 1974 American Heart Association, Inc.