Carbon dioxide is a triple vasodilator.

AIMS: Carbon dioxide (CO2) can regulate blood flow and is applied therapeutically in intensive care units to treat brain injury, as well as in balneotherapy for peripheral arterial disease (PAD) and diabetic angiopathy; however, its mode of action remains unclear.

METHODS AND RESULTS: The vasoactive CO2 effects were tested in arteries of healthy C57BL/6J mice, hypertensive apolipoprotein E-deficient mice, and soluble guanylyl cyclase (sGC) knockout mice in a small vessel myograph with and without pharmacologically intervening in endothelium- and/or vascular smooth muscle-mediated vasodilation. CO2-based near-infrared spectroscopy (NIRS-CO2) was developed to assess vasoreactivity of the skin microcirculation to CO2 in healthy individuals, PAD and coronary artery disease (CAD) patients, and was compared with flow-mediated dilation (FMD). We identified CO2 as a triple vasodilator mimicking the actions of endothelium-derived relaxing factor (nitric oxide, NO), endothelium-derived hyperpolarization factor, and direct myogenic vasodilators. CO2 engaged endothelial NO/sGC, endothelial small-/intermediate-conductance calcium-activated potassium channels (SKCa/IKCa), and myogenic voltage-gated (KV) and IKCa potassium channels, respectively, acting as a triple vasodilator. CO2-evoked vasodilator responses were blunted and delayed in diseased human and murine arteries. In the human cohort, the NIRS-CO2-derived time-to-intersection of the HbO2 and HHb curves, capturing the delay phenotype, showed a strong association with PAD/CAD status and, in exploratory analyses, also distinguished young individuals with cardiovascular risk factors, supporting NIRS-CO2 as a physiological readout that integrates endothelial and myogenic components of microvascular reactivity. Duration and extent of CO2 vasodilation were coupled to tissue metabolism through vascular carbonic anhydrases (CAs), providing a mechanism for vasculometabolic coupling and one for clinically approved CA inhibitors.

CONCLUSION: NIRS-CO2 provides a feasible readout of CO2-evoked microvascular responsiveness and shows disease-associated alterations in our PAD/CAD cohort. Larger studies will validate generalizability across vasculopathies and clarify the relative contributions of NO-sGC vs. K+ channel-linked mechanisms for future therapeutic translation.