Can resting lung function predict the response of a person living with motor neuron disease to a hypoxic challenge test?

Objective: People living with MND (PlwMND) are at risk of altitude-related hypoxia during flight. The Hypoxic Challenge Test (HCT) determines whether in-flight oxygen is required but can be expensive and inaccessible. To assist with travel recommendations, we investigated the relationship between altitude simulation-induced hypoxemia and baseline lung function.

Methods: Retrospective audit of clinical database of PlwMND who had HCT and lung function. Pearson's correlation assessed relationships between oxygen saturation at altitude (AltSpO₂) and lung function. Univariate logistic regression analysis and receiver operator characteristic (ROC) curves determined associations between lung function and HCT pass or fail.

Results: Between 2004-2023, 50 PlwMND were identified (median (IQR) diagnosis to HCT = 11.6 (16.9) months, mean ± SD forced vital capacity (FVC) = 2.4 ± 0.9 liters). Ten patients dropped below 85% SpO₂ during testing (HCT fail). Baseline SpO₂ was associated with AltSpO₂ (r = 0.64) and predicted HCT pass or fail (OR 2.0 [95% CI 1.2-3.4], area under ROC curve (AUC) =0.8 [0.6-1.0]), as did FVC (AUC = 0.8 [0.6-0.9]). PlwMND with a FVC > 2.7L or a resting SpO₂ > 97% are likely to pass HCT, whereas all those with FVC < 1L and SpO₂ < 92% failed.

Conclusion: PlwMND with FVC >2.7L or SpO₂ >97% are unlikely to require oxygen or ventilatory supports for airline travel. A FVC below 2.7L will require a HCT to confidently determine HCT outcome, with testing still required for FVC <1L or baseline SpO₂ <92%, to provide evidence to the airlines for in-flight respiratory support.