Effects of acute hypercapnia on the amplitude of cerebrovascular pulsation in humans registered with a non-invasive method Andrzej F. Frydrychowski a , Magdalena Wszedybyl-Winklewska a , Wojciech Guminski b , Piotr Lass c , Tomasz Bandurski c , Pawel J. Winklewski a, ⁎ a Institute of Human Physiology, Faculty of Health Sciences, Medical University of Gdansk, Tuwima Str. 15, 80-210 Gdansk, Poland b Department of Computer Communications, Faculty of Electronics, Telecommunications and Informatics, Technical University of Gdansk, Gabriela Narutowicza Str. 11/12, 80-233 Gdansk, Poland c Department of Nuclear Medicine and Radiological Informatics, Faculty of Health Sciences, Medical University of Gdansk, Debinki Str. 7, 80-211 Gdansk, Poland abstract article info Article history: Accepted 13 August 2011 Available online 19 August 2011 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 1 g 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 transcra- nial 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 al- lows for non-invasive bedside monitoring of the amplitude of CVP. NIR-T/BSS is consistent with transcranial Doppler and SPECT. © 2011 Elsevier Inc. All rights reserved. Introduction Cerebrovascular vasodilation caused by hypercapnia increases ce- rebral blood flow (Kagstrom et al., 1983; Brian, 1998). Although hy- percapnia induces relatively uniform vasodilation for the entire arterial–arteriolar bed, the arterioles play a major role in the control of cerebral blood flow (Kontos et al., 1978; Narayanan et al., 2008). To date, cranial window installation and microscopic examination re- main the methods of choice to investigate the pial microvessels in vivo (Levasseur et al., 1975). Not surprisingly, the influence of acute hypercapnia on the pulsation of human pial arteries has not yet been investigated. Hypercapnia-induced vasodilation has been shown to result in a decrease in pial arteriolar bed resistance in piglets (Domoki et al., 2008; Narayanan et al., 2008) and to significantly increase the ampli- tude of cerebrovascular pulsation (CVP) in rabbits (Frydrychowski et al., 2002a; Frydrychowski et al., 2011a). The amplitude of CVP can be measured non-invasively using near-infrared transillumina- tion/backscattering sounding (NIR-T/BSS), a new method based on infrared radiation (IR) that has been developed in the last decade by our team (Plucinski et al., 2000; Pluciński and Frydrychowski, 2007; Frydrychowski et al., 2001a,b, 2002a,b,c; Frydrychowski and Plu- ciński, 2007). Contrary to near-infrared spectroscopy (NIRS), which relies on absorption of IR by haemoglobin (Li et al., 2010, 2011), NIR-T/BSS uses the subarachnoid space (SAS) filled with translucent cerebrospinal fluid as a propagation duct for IR. Cerebral microcirculation is significantly affected by several path- ological conditions: traumatic brain injury (Wei et al., 2009), ische- mia and reperfusion (Hauck et al., 2004), and arterial hypertension (Castellani et al., 2006), to name a few. Therefore, non-invasive bed- side measurement of parameters describing functional status of the pial arteries, like the amplitude of pulsation, potentially constitutes Microvascular Research 83 (2012) 229–236 ⁎ Corresponding author. Fax: +48 58 3491515. E-mail address: pawelwinklewski@wp.pl (P.J. Winklewski). 0026-2862/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.mvr.2011.08.005 Contents lists available at SciVerse ScienceDirect Microvascular Research journal homepage: www.elsevier.com/locate/ymvre