Isolation of the arterial supply to the carotid and central chemoreceptors in the sheep.
The aim of our study was to develop and validate a simple surgical model in the sheep which allows control of the gas composition of the blood supplying the carotid and central chemosensitive area independently of the rest of the body. This approach was made possible due to the specific features of the cranial circulation in the sheep. An extracorporeal circuit, consisting of a pump and a gas exchanger, was placed at the level of the two common carotid arteries to create a pressure gradient between the carotid and the systemic systems and to reverse blood flow in the vertebral vessels via the occipital arteries. When a pressure gradient of about 40 Torr was created between the systemic and carotid circulation, we found that no blood could reach the carotid bodies and the medulla without passing though the extracorporeal circulation. This was established (1) by measuring vertebral blood flow; and (2) by injecting either a coloured suspension or particles labelled with (99m*)Tc into the systemic or the carotid circulation. The slope of the relationship between minute ventilation (V(E)) and systemic arterial P(CO2) (P(a,CO2)) during high CO(2) inhalation in seven hyperoxic vagotomised and anaesthetised sheep was dramatically reduced, but remained above zero, when P(a,CO2) was maintained constant in the cephalic circuit (0.11 +/- 0.15 vs. 0.70 +/- 0.35 l min(-1) Torr(-1) for the control tests). This residual V(E) response to CO(2) inhalation remains to be explained since it could not be accounted for by any of the chemical or circulatory changes occurring in the cephalic circulation. Nevertheless, this preparation provides an easy method of maintaining chemical and circulatory homeostasis at the chemoreceptor level.
Haouzi
Philippe
P
Laboratoire de Physiologie, EA 3450, Faculté de Médecine de Nancy, Université Henry Poincaré, 54505 Vandoeuvre-lès-Nancy Cedex, France. p.haouzi@chu-nancy.fr
Chenuel
Bruno
B
Chalon
Bernard
B
Braun
Marc
M
Bedez
Yvonne
Y
Tousseul
Bernard
B
Claudon
Michel
M
Gille
Jean-Pierre
JP
D000818:Animals; D001158:Arteries / Q000502:physiology / Q000601:surgery; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002339:Carotid Arteries / Q000502:physiology* / Q000601:surgery*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002628:Chemoreceptor Cells / Q000502:physiology*; D005112:Extracorporeal Circulation / Q000295:instrumentation / Q000379:methods*; D006706:Homeostasis / Q000502:physiology*; D023421:Models, Animal; D012119:Respiration; D012756:Sheep; D014711:Vertebral Artery / Q000502:physiology*
D002245:Carbon Dioxide