Exercise-induced arterial hypoxaemia in endurance athletes: case report and review

Abstract Exercise-induced arterial hypoxaemia (EIAH) is a well-described phenomenon typically occurring in highly trained endurance athletes. It is characterized by a reduction in arterial oxygenation during intense exercise despite normal resting conditions. Its pathophysiology is multifactorial and may involve relative hypoventilation, ventilation-perfusion mismatch with an increased alveolar-arterial oxygen gradient, and pulmonary diffusion limitation during exercise. EIAH may represent a physiological limitation of oxygen transport in otherwise healthy endurance athletes and should be distinguished from exercise-induced desaturation due to underlying disease. Clinically relevant or otherwise unexplained exercise-induced desaturation should prompt appropriate evaluation for potential cardiopulmonary causes before being attributed to physiological EIAH. We report the case of a 47-year-old male endurance cyclist (approximately 16,000 km/year) referred for unexplained performance decline associated with poor adaptation to high altitude, with subsequent detection of exercise-induced desaturation also at sea level. Cardiopulmonary exercise testing (CPET) with serial arterial blood gas analysis demonstrated excellent functional capacity (peak VO 2 58.5 mL/kg/min, 153% of predicted value), without evidence of cardiac, pulmonary vascular, or ventilatory limitation; however, it revealed progressive exercise-induced hypoxaemia (PaO 2 70 mmHg and SpO 2 92% at peak effort). Comprehensive cardiac and pulmonary investigations excluded structural abnormalities or alternative causes of hypoxaemia. The final diagnosis, after exclusion of organic cardiopulmonary disease, was consistent with exercise-induced arterial hypoxaemia (EIAH). This case highlights the importance of interpreting exercise-induced arterial desaturation within the individual clinical context and of excluding relevant cardiopulmonary disease before attributing the finding to EIAH. In otherwise healthy endurance athletes, EIAH may represent a physiological limitation of pulmonary gas exchange rather than a pathological condition requiring specific treatment.