Cerebral blood flow velocity in patients with subclinical portal-systemic encephalopathy

Alterations in cerebral blood flow (CBF) are implicated in the etiology of portal-systemic encephalopathy. We hypothesized that CO2 reactivity of the cerebral circulation may be impaired in subjects with chronic liver disease (CLD) who also had subclinical portal-systemic encephalopathy (SPSE). We compared the relationship between PETCO2 and cerebral blood flow velocity in 10 patients with CLD with those of 10 healthy control subjects. Middle cerebral artery mean blood flow velocity (MCAMFV) was measured using transcranial Doppler during rest, hyperventilation, and hypoventilation. The degree of SPSE was quantified by using psychometric testing. Patients with CLD had poorer psychometric test scores compared with control subjects. Patients with CLD had lower PETCO2, MCAMFV, and blood pressure values and higher heart rates, differing from control subjects in all ventilation states. However, CO2 reactivity, the rate of change in MCAMFV to changes in ventilation (expressed as percent change in CBF velocity per mm Hg change in PETCO2) was similar for both groups (4.6% +/- 0.6% vs 4.2% +/- 0.5% for patients with CLD versus control subjects, P = 0.15).

Psychometric test scores in patients with chronic liver disease revealed subclinical impairment compared with control subjects. Transcranial Doppler measurements of middle cerebral artery blood flow with varying PETCO2 were conducted, but the CO2 response of patients with liver disease was within the range of control subjects.