Essential cerebral distribution of cardiac output in infants

Introduction

The major regulatory mechanisms for CBF in infants are autoregulation, arteriolar CO2, oxygen delivery, blood glucose and neural activity. Furthermore, the cardiovascular system regulates CBF through variation in cardiac output (CO) and distribution of blood flow. In this study, the usefulness of multi-channel near-infrared spectroscopy (MNIRS) and pulse dye densitometry with indocyanine green (lCG) for determing CBF and left ventricle CO in infants was investigated.

Subjects and methods

We measured CBF and CO in 17 infants (mean gestational age ± SD: 32. 9 ± 4.3 weeks) without neural abnormalities on day 0 to day 82 after birth. A bolus of ICG (0.2 mg/kg) was injected into the peripheral vein of each infant. Changes in the cerebral ICG concentration in a 6 cm × 6 cm field of the parieto-temporal region were recorded using MNIRS. Simultaneously, pulse dye densitometry, using the general principles of pulse oximetry, was used to measure the arterial blood concentration of ICG. The CBF was calculated using Fick's equation. CO was calculated from the first dilution curve on a dye densitogram.

Results and Discussion

CO and CBF in the parieto-temporal region were 202.8 ± 90.6 mL/kg/min (mean ± SD) and 15.3 ± 4.2 mL/100 g/min, respectively. The relationship between CO and CBF was CBF = 0.03 CO + 8.71 (r = 0.70, p = 0.002). The blood flow distribution to the brain of left ventricular CO is estimated to be 11% if the brain weight is assumed to be 15% of body weight. When CO was high (300 mL/kg/min) the CBF was 20.1 mL/100 g/min, which calculated to 7.8% of CO. When CO fell to ∼100 mL/kg/min, CBF also fell (to 12.0 mL/100 g/min), the percentage of CBF to CO was calculated to 21.2%. The brain is considered an essential organ defined as one whose blood supply is preferentially maintained during periods of reduced CO. We conclude that control of CO important for regulation of CBF during the acute phase of illness in infants.