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

Aim: The aim of the study was to assess non-invasively the effects of acute hypercapnia on the amplitude of cerebrovascular pulsation (CVP) in humans.

Methods: Experiments 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% CO(2) for 2 minutes 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.

Results: Inhalation of a gas mixture containing 5% CO(2) 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%).

Conclusion: Acute 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.