Effect of Hypercapnia on Cerebral Blood Flow and Blood Volume in Pigs Studied by Positron Emission Tomography

Pigs are increasingly used as in vivo models in neuroscience, including studies using positron emission tomography. During anesthesia, cerebral blood flow (CBF) and cerebral blood volume (CBV) are mainly regulated by the partial pressure of CO₂ (pCO₂) in arterial blood. We sought to determine the effects of increased arterial pCO₂ (hypercapnia) on CBF and CBV in anesthetized domestic pigs. We anesthetized 4 pigs and manipulated the tidal volume of the ventilator to different pCO₂ levels. Baseline pCO₂ was on average 6.5 kPa (n = 9 periods) and hypercapnia pCO₂ ranged from 11 to 20 kPa, mean 18.5 kPa (n = 9 periods). Series of dynamic PET scans with H₂¹⁵O (CBF measurements) and C¹⁵O (CBV measurements) were performed. CBF increased on average 54%, from mean 0.48 ml blood/min/ml brain tissue during normoxia to 0.74 ml blood/min/ml brain tissue during hypercapnia. CBV increased 41% from mean 0.061 ml blood/ml brain tissue (n = 6) during normoxia to 0.086 ml blood/ml brain tissue (n = 6) during hypercapnia. Our observations indicate that pCO₂ levels have a major influence on porcine CBF and CBV and should be controlled in studies where a constant level is crucial.