title: Relationship between oxygen supply and cerebral blood flow assessed by transcranial Doppler and near-infrared spectroscopy in healthy subjects during breath-holding.
abstract: BACKGROUND
  Breath-holding (BH) is a suitable method for inducing cerebral vasomotor reactivity (VMR). The assessment of VMR is of clinical importance for the early detection of risk conditions and for the follow-up of disabled patients. Transcranial Doppler ultrasonography (TCD) is used to measure cerebral blood flow velocity (CBFV) during BH, whereas near-infrared spectroscopy (NIRS) measures the concentrations of the oxygenated (O2Hb) and reduced (CO2Hb) hemoglobin. The two techniques provide circulatory and functional-related parameters. The aim of the study is the analysis of the relationship between oxygen supply and CBFV as detected by TCD and NIRS in healthy subjects performing BH.
  
  
  METHODS
  20 healthy subjects (15 males and 5 females, age 33 +/- 4.5 years) underwent TCD and NIRS examination during voluntary breath-holding. VMR was quantified by means of the breath-holding index (BHI). We evaluated the BHI based on mean CBFV, O(2)Hb and CO(2)Hb concentrations, relating the baseline to post-stimulus values. To quantify VMR we also computed the slope of the linear regression line of the concentration signals during BH. From the NIRS signals we also derived the bidimensional representation of VMR, plotting the instantaneous O(2)Hb concentration vs the CO(2)Hb concentration during the BH phase. Two subjects, a 30 years old current smoker female and a 63 years old male with a ischemic stroke event at the left middle cerebral artery, were tested as case studies.
  
  
  RESULTS
  The BHI for the CBFV was equal to 1.28 +/- 0.71 %/s, the BHI for the O(2)Hb to 0.055 +/- 0.037 micromol/l/s and the BHI for CO2Hb to 0.0006 +/- 0.0019 micromol/l/s, the O2Hb slope was equal to 0.15 +/- 0.09 micromol/l/s and the CO(2)Hb slope to 0.09 +/- 0.04 micromol/l/s. There was a positive correlation between the CBFV and the O(2)Hb increments during BH (r = 0.865). The bidimensional VMR pattern shows common features among healthy subjects that are lost in the control studies.
  
  
  CONCLUSIONS
  We show that healthy subjects present a common VMR pattern when counteracting cerebral blood flow perturbations induced by voluntary BH. The proposed methodology allows for the monitoring of changes in the VMR pattern, hence it could be used for assessing the efficacy of neurorehabilitation protocols.
authors.affiliation: Biolab, Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy. filippo.molinari@polito.it
authors.forename: Filippo
authors.initials: F
authors.lastname: Molinari
authors.forename: William
authors.initials: W
authors.lastname: Liboni
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Grippi
authors.forename: Emanuela
authors.initials: E
authors.lastname: Negri