A laboratory technician is found unconscious in a poorly ventilated garage. Arterial blood shows pH 7.39, PaO2 13.0 kPa (reference 10.7–13.3 kPa), and PaCO2 5.1 kPa (reference 4.7–6.0 kPa). Pulse oximetry reads 99%, but calculated oxygen content is markedly reduced and venous blood appears unusually bright red. Which mechanism best explains the tissue hypoxia?
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