Effect of labetalol on cerebral blood flow, oxygen metabolism and autoregulation in healthy humans.
Level 4 - case-series / case-control
Prospective before-and-after physiological study in healthy humans without a separate control group
PubMed 7669469 · doi:10.1093/bja/75.1.51
What was done
Eight healthy volunteers received an infusion of labetalol to evaluate its effects on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2). CBF was measured using single photon emission computerized tomography (SPECT) before and during the infusion. CMRO2 was calculated from CBF and cerebral arteriovenous oxygen content difference (CaO2-CvO2). CBF autoregulation was tested during labetalol infusion by altering arterial pressure and estimating relative changes in global CBF from changes in CaO2-CvO2.
What was found
CBF before and during labetalol infusion was 67 and 65 ml/100 g min-1, respectively (P > 0.05). CMRO2 was 2.9 and 2.8 ml/100 g min-1, respectively (P > 0.05). CBF autoregulation was preserved in all subjects, with a lower limit of CBF autoregulation of 88 mm Hg (94% of baseline mean arterial pressure).
Why it matters
The findings demonstrate that acute labetalol administration does not adversely affect global cerebral perfusion, oxygen consumption, or autoregulation in healthy individuals.
Limits
The sample size is very small (n = 8) and restricted to healthy volunteers, limiting generalizability to patients with chronic hypertension or acute cerebrovascular pathology. The study lacked a placebo or parallel control group, and autoregulatory changes were estimated via arteriovenous oxygen differences rather than direct continuous flow measurements.
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