EFFECT OF GROUP-B STREPTOCOCCAL MENINGITIS ON RETINAL AND CHOROIDAL BLOOD-FLOW IN NEWBORN PIGS

Purpose. To assess the effect of group B streptococcal (GBS) meningiti s on retinal blood flow (RetBF) and choroidal blood flow (ChBF) autore gulation in sedated newborn piglets (1 to 5 days of age). Methods. Fou rteen study animals injected with 0.5 ml heat-killed GBS (10(9)) were compared to 10 control animals injected with 0.5 mi saline. The site o f injection for both groups was the cerebral lateral ventricles. RetBF and ChBF were measured by radioactive microspheres (Ce-141, Cr-51, Sn -113, Sr-85, Nb-95, Sc-46) over a mean arterial blood pressure (MABP) range of 20 to 150 mm Hg. Hypertension and hypotension were induced 2 hours apart in random sequence on each animal by inflating balloon-tip ped catheters placed at the descending aorta and the aortic root, resp ectively. RetBF and ChBF were measured 15 minutes before and after inj ection of GBS or saline (baseline) and during hypotension or hypertens ion. Results. Fifth-order polynomial regression analyses of RetBF and ChBF (ml/100 g per minute) versus MABP showed that in control animals, blood flows were constant at MABP of 60 to 110 mm Hg for RetBF and wa s pressure passive above and below these ranges. However, no autoregul ation was observed for ChBF throughout the MABP range. In contrast, Re tBF of GBS-treated animals increased with increasing blood pressure th roughout range of MABP studied, and absence of autoregulation was main tained in the choroid. Vascular resistance (mm Hg/ml per minute/100 g) increased as MABP was raised to maintain constant flow and was correl ated linearly with MABP at 60 to 110 mm Hg (r = 0.6682, P = 0.0003) in RetBF of control animals but not in GBS-treated animals (r = -0.291, P = NS). Vascular resistance did not change with MABP for ChBF of cont rol animals (r = -0.264, P = NS) but decreased as MABP was raised in G BS-treated animals (r = -0.548, P < 0.0001). GBS did not alter oxygen delivery, which varied directly with MABP in control animals (RetBF: r = 0.74, P < 0.001; ChBF: r = 0.68, P < 0.001) and in GBS-treated anim als (RetBF: r = 0.55, P < 0.001; ChBF: r = 0.68, P < 0.001). Conclusio n. Group B streptococcal meningitis significantly impairs eye blood fl ow autoregulation and may contribute to increased risk of retinal dama ge in infants with meningitis.