Precise control of end‐tidal carbon dioxide and oxygen improves BOLD and ASL cerebrovascular reactivity measures

Abstract

In-depth investigation of cerebrovascular blood flow and MR mechanisms underlying the blood oxygenation level dependent signal requires precise manipulation of the arterial partial pressure of carbon dioxide and oxygen, measured by their noninvasive surrogates, the end-tidal values. The traditional methodology consists of administering a fixed fractional concentration of inspired CO 2 , but this causes a variable ventilatory response across subjects, resulting in different values of end-tidal partial pressures of CO 2 and O 2 . In this study, we investigated whether fine control of these end-tidal partial pressures would improve stability and predictability of blood oxygenation level dependent and arterial spin labeling signals for studying cerebrovascular reactivity. In 11 healthy volunteers, we compared the MR signals generated by the traditional fixed fractional concentration of inspired CO 2 method to those of an automated feed-forward system, a simpler, safer, and more compact alternative to dynamic end-tidal forcing systems, designed to target constant end-tidal partial pressures of CO 2 and O 2 . We found that near square-wave changes in end-tidal partial pressure of CO 2 of 5, 7.5, and 10 mm Hg (61.01 mm Hg within two to three breaths) and constrained changes in the end-tidal partial pressure of O 2 (<10 mm Hg) induced cerebral vascular reactivity measurements with faster transitions, together with improved stability and gradation, than those achieved with the traditional fixed fractional concentration of inspired CO 2 method. Magn Reson Med 64:749-756,

Quantitative mapping of cerebrovascular reactivity using resting-state BOLD fMRI: Validation in healthy adults

“…This method was chosen to maximize steadystate PETCO 2 -targetting accuracy and stability while minimizing PETO 2 confounds during CO 2 -based CVR measurements (Chen and Pike, 2010b;Halani et al, 2015;Mark et al, 2010;Prisman et al, 2008), and is the most established method clinically (Pillai and Mikulis, 2015).…”

“…While acetazolamide injections are invasive and have been associated with adverse and potentially long-lasting side effects (Asghar et al, 2011;Mancino et al, 2011), respiratory manipulations are relatively non-invasive and safe. They induce changes in the subject's end-tidal CO 2 pressure (PETCO 2 ), a surrogate for intravascular CO 2 (Mark et al, 2010;Poulin et al, 1996). CO 2 is a potent vasodilator, triggering changes in vascular tone through the arterial baroflex.…”

“…CO 2 is a potent vasodilator, triggering changes in vascular tone through the arterial baroflex. PETCO 2 changes can be induced through manually adjusted administration of blended gases (Bandettini and Wong, 1997 ;Cohen et al, 2004;Yezhuvath et al, 2009), end-tidal forcing (Poulin et al, 1996) or more recently, computerized PETCO 2 targeting (Conklin et al, 2011;Han et al, 2011;Mandell et al, 2011;Mandell et al, 2008;Mark et al, 2010;Mikulis et al, 1989;Mutch et al, 2012;Prisman et al, 2008;Slessarev et al, 2007;Spano et al, 2013;Vesely et al, 2001). The latter method provides immediate and robust PETCO 2 changes, and we have used it extensively in our own work (Chen and Pike, 2010a;Chen and Pike, 2010b;Halani et al, 2015).…”

Indication of BOLD-Specific Venous Flow-Volume Changes from Precisely Controlled Hyperoxic vs. Hypercapnic Calibration

“…In the context of the widely used dHb dilution model, we recently introduced a precise, repeatable computer-controlled iso-oxic HC method for reduced methodological variations in calibration and M-estimates (Mark et al, 2010(Mark et al, , 2011. Because M represents the theoretical maximum achievable BOLD signal at baseline dHb, it would ideally be more accurately found at high HC levels (Hoge et al, 1999a).…”

Comparison of pulsed and pseudocontinuous arterial spin‐labeling for measuring CO2‐induced cerebrovascular reactivity

“…HYPERCAPNIA is known to elicit a global increase in cerebral blood flow (CBF) (1,2), a phenomenon that has been exploited in various magnetic resonance imaging (MRI) applications including measures of cerebrovascular reactivity (CVR) (3,4) and calibrated MRI for estimation of task-induced cerebral metabolic rate of oxygen (CMRO 2 ) changes (5,6). These techniques rely on arterial spin-labeling (ASL), which provides dynamic and noninvasive images of CBF.…”