title: Haemophilus influenzae type B impairment of pial vessel autoregulation in rats.
abstract: To examine the mechanisms of autoregulatory impairment in meningitis, we studied the effects of Haemophilus influenzae type b (Hib) on pial vessels during hemorrhagic hypotension in rats, using a cranial window technique. We prepared cranial windows in barbiturate-anesthetized, mechanically ventilated rats. Artificial cerebrospinal fluid or 10(5) Hib in cerebrospinal fluid (n = 7 each group) was suffused over the pial surface. Pial arteriolar diameter was measured hourly for 4 h. Autoregulation was assessed as the ability of pial arterioles to dilate in response to graded hemorrhagic hypotension at 2 and 4 h. Pial arterioles exposed to Hib dilated progressively to 149 +/- 27% of baseline at 4 h. Vessel diameter in the Hib group was significantly greater than in the control group beginning at 2 h. Autoregulation was progressively impaired in Hib-exposed rats compared with control rats [-5.85 +/- 1.38 versus -8.02 +/- 2.02 and -3.82 +/- 1.57 versus -8.53 +/- 1.72% dilation/kPa fall in mean arterial blood pressure at 2 and 4 h, respectively (p < 0.05)]. These data suggest that autoregulation is impaired in pial arterioles exposed to Hib because involved vessels have a finite dilatory capacity and are close to maximal dilation before hypotensive challenge.
authors.affiliation: Department of Anesthesiology/Critical Care Medicine and Pediatrics, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287.
authors.forename: I D
authors.initials: ID
authors.lastname: Berkowitz
authors.forename: W R
authors.initials: WR
authors.lastname: Hayden
authors.forename: R J
authors.initials: RJ
authors.lastname: Traystman
authors.forename: M D
authors.initials: MD
authors.lastname: Jones
mesh_terms: D000818:Animals; D001160:Arterioles / Q000503:physiopathology; D002543:Cerebral Hemorrhage / Q000503:physiopathology; D006193:Haemophilus influenzae; D006706:Homeostasis / Q000502:physiology; D007022:Hypotension / Q000503:physiopathology; D008297:Male; D008583:Meningitis, Haemophilus / Q000503:physiopathology*; D010841:Pia Mater / Q000098:blood supply*; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000502:physiology