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 H(2)15O (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.