Regional heterogeneity and differential vulnerability of cerebral and spinal vascular CO2-responsiveness during graded haemorrhagic hypotension.
Regional inhomogeneity of cerebrovascular CO2-sensitivity as well as its changes at three different levels of standardized haemorrhagic hypotension were studied in ten distinct brain and spinal cord regions of anesthetized, ventilated cats. Regional cerebral blood flow was measured with radiolabelled microspheres in hypocapnic, normocapnic, and hypercapnic conditions, and CO2-responsiveness was determined from the equation of the slopes of the best fit regression lines to the obtained flow values. It was concluded that in normotensive, normoxic cats response of the cerebral and spinal vessels to PaCO2 alterations can be assigned to four major categories. The CO2-responsiveness of a brain region is not solely determined by the rate of its basal steady state blood flow: CO2-reactivity of the hypothalamus was significantly different from that of any other investigated regions with almost identical steady state flow values. Vulnerability of the cerebrovascular CO2-sensitivity during hypotension was different from region to region, with the vessels of the pons-medulla oblongata region being the most sensitive to haemorrhage. Reduced regional cerebral and spinal CO2-responsiveness during haemorrhage is not a consequence of a reduced L-arginine supply for nitric oxide generation since administration of an excess amount of the precursor L-arginine failed to restore the haemorrhage-induced reduction of regional CO2-sensitivity at the 60 mm Hg mean arterial pressure level.
Komjáti
K
K
Experimental Research Department, Semmelweis University of Medicine, Budapest, Hungary.
Sándor
P
P
Reivich
M
M
Greenberg
J H
JH
Kovách
A G
AG
Jaggi
J L
JL
Nyáry
I
I
D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D001808:Blood Vessels / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D002415:Cats; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D005740:Gases / Q000097:blood; D006470:Hemorrhage / Q000503:physiopathology*; D006935:Hypercapnia / Q000503:physiopathology; D016857:Hypocapnia / Q000503:physiopathology; D007022:Hypotension / Q000503:physiopathology*; D008297:Male; D012016:Reference Values; D013116:Spinal Cord / Q000098:blood supply*
D005740:Gases; D002245:Carbon Dioxide; D001120:Arginine