Effect of independent changes in mixed-venous PCO2 or PO2 on cardiac output in anesthetized sheep.
To determine whether changes mixed-venous PCO2 or PO2 affect cardiac output independent of changes in arterial blood gases, we used extracorporeal gas exchange to increase mixed-venous PCO2 or decrease mixed-venous PO2 in adult sheep. Sheep were anesthetized, mechanically ventilated, and connected to a veno-venous extracorporeal circuit. The circuit included a gas exchanger which was used to increase mixed-venous PCO2 or decrease mixed-venous PO2; the native lungs were ventilated to maintain arterial PCO2 and PO2 at control levels. When mixed-venous PCO2 was increased by 32% above control levels for a period of 60 min, cardiac output increased significantly to 28% above control levels. Cervical vagotomy abolished this response. In contrast, decreasing mixed-venous PO2 by 29% did not increase cardiac output. These results demonstrate that increasing mixed-venous PCO2 can increase cardiac output independent of changes in arterial blood gases and that intact vagus nerves are necessary for this response to occur.
Shanley
C J
CJ
Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109, USA.
Shah
N L
NL
Overbeck
M C
MC
Kulkarni
N B
NB
Bartlett
R H
RH
D000758:Anesthesia; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D002302:Cardiac Output; D010100:Oxygen / Q000097:blood*; D012121:Respiration, Artificial; D012756:Sheep
D002245:Carbon Dioxide; D010100:Oxygen