![]() ![]() ![]() Even in health, submissive hypercapnia ensues during CO 2 breathing/rebreathing when the inhaled CO 2 renders normocapnia difficult to restore even with maximal respiratory effort, hence the respiratory controller’s ‘ ain’t fresh, so won’t breathe’ modus operandi. In severe/very severe COPD, submissive hypercapnia epitomizes the respiratory controller’s ‘ can’t breathe, so won’t breathe’ say-uncle policy when faced with insurmountable ventilatory limitation. Submissive hypercapnia is an emerging paradigm for understanding optimal ventilatory control and cost/benefit decision-making under prohibitive respiratory chemical-mechanical constraints, where the need to maintain normocapnia gives way to the mounting need to conserve the work of breathing. In severe COPD, the augmented exercise ventilation progressively reverses as the disease advances, resulting in hypercapnia at peak exercise as ventilatory limitation due to increasing expiratory flow limitation and dynamic lung hyperinflation sets in. ![]() However, patients with mild-to-moderate COPD or chronic heart failure (CHF) also suffer similar ventilatory inefficiency but they remain near-normocapnic at rest and during exercise with an augmented respiratory effort to compensate for the wasted dead space ventilation. Patients with late-stage chronic obstructive pulmonary disease (COPD) are prone to CO 2 retention, a condition which has been often attributed to increased ventilation-perfusion mismatch particularly during oxygen therapy.
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