Introduction: Through a variety of causes the function of the diaphragm can become unilaterally impaired resulting in lower lung volumes and exercise performance. Questions remain to what extent a bilateral dysfunction will exacerbate these effects.

Aim: Assessing severity of bilateral in comparison to unilateral diaphragm-dysfunction with respect to cardiopulmonary exercise performance.

Methods: Diaphragm dysfunction was established by ultrasound imaging of excursion and thickness-variation of the diaphragm. Results were corroborated by diaphragm-fluoroscopy. Spirometry was performed according to ATS/ERS 2005 criteria for acceptability and reproducibility. Exercise testing was done using stepwise incremental load on a bike-ergometer. Bilaterally impaired (8) were compared to unilaterally impaired subjects (11).

Results: Bilateral diaphragm-dysfunction results in lower spirometric volumes (p=0.043), poorer exercise performance in comparison with unilateral dysfunction (maximum work 31% vs 73% of predicted, p=0.020). Low respiratory exchange ratio (<1.00) indicates absence of lactic acidosis and high heart-rate reserve implies absence of cardiovascular limitation in the bilaterally impaired group. The bilateral-dysfunction group shows a higher change in oxygen uptake per unit work (p=0.004) consistent with higher energy expenditure per unit labour, probably caused by inefficient breathing mechanics.

Conclusion: Findings suggest that bilateral diaphragm paralysis has a devastating effect on exercise tolerance as compared to unilateral paralysis and a high probability to result in ventilatory limitation in exercise.