Background: Amyotrophic lateral sclerosis results in respiratory muscle weakness, hypoventilation, and eventually chronic hypercapnic respiratory failure that initially manifests during deep sleep. There is limited evidence that existing clinical surrogates are sensitive to detect nocturnal hypoventilation. In this study, assessments of daytime and nocturnal transcutaneous CO2 (tCO2) are compared to clinical respiratory surrogates and patient-reported symptoms.
Patients with FVC of 50-90% predicted and who did not use noninvasive ventilator support and did not have other pulmonary disease were enrolled at Penn State Hershey and University of Pennsylvania ALS clinics. While in ALS clinic, participants recorded forced vital capacity (FVC), maximal inspiratory pressure (MIP) and completed a 15-minute tCO2/SpO2 “spot check”. Participants were provided a home tCO2 device to perform overnight recordings for 3 consecutive nights.
Results: 13 participants have been enrolled (4F, median age 66 years, range 50-78 years). No pairwise correlations were found at baseline between respiratory surrogates, SpO2, tCO2, and dyspnea symptoms. Of the total 51 overnight recordings performed, 39 (76.5%) were valid, with invalid recordings having no tCO2 registered (n=7) or tCO2 that was not corrected for drift (n=5). Mean overnight tCO2 values were 2.7 mmHg higher than daytime values (p = 0.07). The median time spent hypercapnic per night (tCO2>45 mmHg) was 49.7 minutes, and the median time spent hypoxemic (SpO2<88%) was 2.9 minutes. Seven individuals had at least one overnight recording which displayed normal pulse oximetry (<88% for <5 minutes) and abnormal tCO2 (>45 mmHg for >10 minutes).
Preliminary results provide early evidence that overnight tCO2 measurements could be a more sensitive measure of hypoventilation than oximetry alone. Completion of this study will involve improving methods for collecting complete and valid home data, and the analysis of longitudinal changes in nocturnal tCO2 alongside standard clinical respiratory measures.