Effects of acute hypercapnia on the amplitude of cerebrovascular pulsation in humans registered with a non-invasive method

Abstract

AimThe aim of the study was to assess non-invasively the effects of acute hypercapnia on the amplitude of cerebrovascular pulsation (CVP) in humans. MethodsExperiments were carried out in four male volunteers aged 25, 26, 31 and 49. Changes in blood flow through the pial arteries were induced using two interventions: (A) breathing a gas mixture containing 5% CO2 for 2minutes and (B) intravenous administration of 1g acetazolamide. The amplitude of CVP and width of subarachnoid space (SAS) were measured non-invasively using near-infrared transillumination/backscattering sounding (NIR-T/BSS), while cerebral blood flow was assessed by single photon emission computed tomography (SPECT) and mean blood flow velocity in the left anterior cerebral artery by transcranial Doppler. ResultsInhalation of a gas mixture containing 5% CO2 evoked an increase in the amplitude of CVP (202.5%±SE 10.1), normalized number of counts (22.6%±SE 3.5%) and mean blood flow velocity in the left cerebral anterior artery (37.6%±SE 11.7%), while resistive index decreased (−8.7%±SE 2.3%) and the width of SAS decreased (−8.0±SE 0.45). Acetazolamide also produced an increase in the amplitude of CVP (23.7%±SE 5.4%), normalized number of counts (7.9%±SE 1.1%), and mean blood flow velocity in the left cerebral anterior artery (62.8%±SE 13.7%), while resistive index decreased (−7.9%±SE 1.7%), and the width of SAS decreased (−13.4%±SE 3.4%). ConclusionAcute hypercapnia causes an increase in the amplitude of CVP pulsation in humans. NIR-T/BSS allows for non-invasive bedside monitoring of the amplitude of CVP. NIR-T/BSS is consistent with transcranial Doppler and SPECT.