Effects of changes in end‐tidal PO ₂ and PCO ₂ on neural responses during rest and sustained attention

Abstract

Impairments of cognitive function during alterations in arterial blood gases (e.g., high‐altitude hypoxia) may result from the disruption of neurovascular coupling; however, the link between changes in arterial blood gases, cognition, and cerebral blood flow (CBF) is poorly understood. To interrogate this link, we developed a multimodal empirical strategy capable of monitoring neural correlates of cognition and CBF simultaneously. Human participants performed a sustained attention task during hypoxia, hypercapnia, hypocapnia, and normoxia while electroencephalographic (EEG) activity and CBF (middle and posterior cerebral arteries; transcranial Doppler ultrasound) were simultaneously measured. The protocol alternated between rest and engaging in a visual target detection task that required participants to monitor a sequence of brief‐duration colored circles and detect infrequent, longer duration circles (targets). The target detection task was overlaid on a large, circular checkerboard that provided robust visual stimulation. Spectral decomposition and event‐related potential (ERP) analyses were applied to the EEG data to investigate spontaneous and task‐specific fluctuations in neural activity. There were three main sets of findings: (1) spontaneous alpha oscillatory activity was modulated as a function of arterial CO2 (hypocapnia and hypercapnia), (2) task‐related neurovascular coupling was disrupted by all arterial blood gas manipulations, and (3) changes in task‐related alpha and theta band activity and attenuation of the P3 ERP component amplitude were observed during hypocapnia. Since alpha and theta are linked with suppression of visual processing and executive control and P3 amplitude with task difficulty, these data suggest that transient arterial blood gas changes can modulate multiple stages of cognitive information processing.

Neurovascular coupling is optimized to compensate for the increase in proton production from nonoxidative glycolysis and glycogenolysis during brain activation and maintain homeostasis of pH, pCO2, and pO2

“…The critical importance of homeostasis for brain cognitive and electrical function has been long known from patient studies (Meyer et al, 1966). More recently, magneto/electro‐encephalography (MEG/EEG), as well as resting state functional magnetic resonance (fMRI) studies, have found that small (few ) increases in end‐tidal significantly alter brain electrical activity (Driver et al, 2016; Hall et al, 2011; Halpern et al, 2003; Jones et al, 2005; Xu et al, 2011; Zappe et al, 2008) as well as cognitive function (Bullock et al, 2021). In the most sensitive measurements performed, MEG measurements during hypercarbia found the level of spontaneous neural oscillations in alpha (8–13 Hz), beta (13–30 Hz) and low gamma (30–50 Hz) band power is altered by end‐tidal changes of as little as (Driver et al, 2016).…”

Habituation of the stress response multiplex to repeated cold pressor exposure

“…Statistical significance in all tests (except the rank order analysis) was assessed by using a non-parametric permutation-based resampling approach to empirically approximate null distributions for F and t statistics ( Foster et al, 2016 ; Bullock et al, 2017 ; Bullock et al, 2021 ). This testing approach was adopted because it has the advantage of being robust to violations of normality.…”

Decreased CO2 saturation during circular breathwork supports emergence of altered states of consciousness

“…These studies suggest that circular breathwork increases blood oxygenation (Bednarczyk et al, 1990;Zwaag et al, 2022) while reducing CO2 saturation (Bednarczyk et al, 1990;Inbar et al, 2022;Kox et al, 2014;Krapf et al, 1991;Stäubli et al, 1994;Tercero et al, 2021;Zwaag et al, 2022). This in turn renders blood pH more alkaline (respiratory alkalosis, (Bednarczyk et al, 1990;Kox et al, 2014;Krapf et al, 1991;Nuding et al, 2015;Stäubli et al, 1994;Zwaag et al, 2022)), causing vasoconstriction (Ainslie & Duffin, 2009;Bednarczyk et al, 1990;Bullock et al, 2021;Ito et al, 2003;Kety & Schmidt, 1946;Kontos et al, 1977;Mueller et al, 1977;Stäubli et al, 1994;K. Szabo et al, 2011;Tercero et al, 2021), particular throughout the neocortex (Posse et al, 1997;Terekhin & Forster, 2006;Wise et al, 2007).…”