Toward safer skies - the role of NIRS and capnography in G-tolerance monitoring: A narrative review

G-force-induced loss of consciousness (G-LOC) is a significant concern in high-performance aviation, where rapid gravitational shifts impair cerebral perfusion and oxygenation. The resulting physiological decline can originate from both peripheral (e.g., systemic hypoperfusion, ventilation-perfusion mismatch) and central (e.g., cerebral hypoxia, impaired autoregulation) mechanisms. Peripheral impairments involve cardiovascular redistribution and reduced end-tidal CO 2 , while central disruptions reflect compromised oxygen delivery to brain tissue. Recent advancements in physiological Monitoring, particularly Near-Infrared Spectroscopy (NIRS) and capnography, offer real-time, non-invasive assessment of these critical variables. NIRS enables continuous monitoring of regional cerebral oxygen saturation (rSO 2 ), while capnography measures end-tidal CO 2 (EtCO 2 ) as a proxy for ventilation and perfusion efficiency. When used in combination, these modalities offer a synergistic view of pilot physiology under G-stress, supporting early detection of hypoxic decline and informing targeted countermeasures. As aerospace operations expand in intensity and complexity, wearable and integrative monitoring solutions become increasingly relevant. This narrative review explores the physiological mechanisms underlying G-tolerance, the technological advancements in NIRS and capnography, and the potential of these tools to mitigate G-LOC risk through individualized diagnostics, predictive modeling, and enhanced anti-G training protocols.