Cerebral Hemodynamics Assessed by means of Transcranial Doppler and Near - Infrared Spectroscopy in Healthy Smokers and non-Smokers

The assessment of cerebral vasomotor reactivity (VMR) is a valuable tool for the early detection of risk condition in healthy subjects and for the non-invasive bedside evaluation of patients. Typically, cerebral hemodynamics assessment is performed in correspondence of CO₂ reactivity. We studied the VMR of a population of young healthy non-smokers (n=10, age 27 plusmn 4.1) and healthy smokers (n=4, age 28 plusmn 4.5) using a joint approach based on transcranial Doppler ultrasonography and near-infrared spectroscopy, to monitor cerebral blood flow velocity (CBFV) and concentrations of oxygenated (O₂Hb) and reduced (CO₂Hb) haemoglobin. VMR was induced by means of voluntary breath-holding (BH). We quantified VMR using the breath-holding index (BHI). Smokers BH duration was significantly lower than that of non-smokers (p < 10^-4; their BHI did not significantly differ from that of non-smokers in terms of CBFV, but differed in terms of O₂Hb and CO₂Hb concentrations changes. Specifically, with respect to non-smokers, smokers presented a delayed VMR that took place only around 60% of the apnoea phase. This delayed response could reveal an impaired autoregulatory mechanism and could be a risk condition when the subjects need to compensate an abrupt change in the cerebral blood flow