Acute effects of cigarette smoking on cerebral oxygenation and hemodynamics:

Abstract 

Cigarette smoking has been shown to increase cerebral blood flow velocity (CBFV) and reduce vasomotor reactivity temporarily. The aim of our study was to clarify whether this results from dilation of resistance vessels alone with subsequent increase in regional cerebral blood flow (rCBF), or an additional constriction of basal cerebral arteries.

In 24 healthy smokers (mean age±S.D., 32.7±10.5 years), cerebral oxygenation and hemodynamics were monitored by transcranial Doppler sonography and near-infrared spectroscopy before, during, and after smoking a cigarette (nicotine 0.9 mg). We simultaneously recorded CBFV of both middle cerebral arteries, mean arterial blood pressure, skin blood flow, end-tidal CO₂, changes in concentration of cerebral oxyhemoglobin, deoxyhemoglobin, and total hemoglobin (μmol/l), and a cerebral tissue oxygenation index.

Smoking increased CBFV (p<0.01), oxyhemoglobin (p<0.01), and total hemoglobin (p<0.01). After smoking, the increase in CBFV and total hemoglobin persisted (p<0.01), while oxyhemoglobin returned to baseline. Deoxyhemoglobin and cerebral tissue oxygenation index did not change during the whole procedure. During, but not after smoking, CBFV increase was correlated to ipsilateral changes in oxyhemoglobin and total hemoglobin (p<0.05).

The increase in oxyhemoglobin only during smoking and the lack of changes in deoxyhemoglobin and cerebral tissue oxygenation index indicate that smoking did not substantially increase rCBF. The smoking-induced elevation in CBFV might therefore be due to an additional constriction of the middle cerebral artery. The combined effects of smoking on basal cerebral arteries and arterioles might contribute to the increased stroke risk in smokers.

Keywords:  Risk factors, Cigarette smoking, Spectroscopy, near-infrared, Ultrasonography, Doppler, transcranial

Abbreviations:  CBFV, cerebral blood flow velocity, [HHb], deoxyhemoglobin (μmol/l), MAP, mean arterial blood pressure, NIRS, near-infrared spectroscopy, [O₂Hb], oxyhemoglobin (μmol/l), rCBF, regional cerebral blood flow, [tHb], total hemoglobin (μmol/l), TOI, tissue oxygenation index