Phrenic nerve conduction studies as a biomarker of respiratory insufficiency in amyotrophic lateral sclerosis.

Our objective was to examine the value of phrenic nerve conduction studies (PNCS) in quantifying diaphragm dysfunction in ALS, as no ideal test of respiratory insufficiency exists in ALS. We prospectively recorded bilateral PNCS, forced vital capacity (FVC), maximum inspiratory pressure (MIP), sniff nasal inspiratory pressure (SNIP), respiratory rate, ALSFRS-R, and respiratory symptoms in 100 ALS patients attending our clinic over a nine-month period. Survival data were collected for two years. Results showed that PNCS were reproducible and well tolerated. When the Pamp was abnormal (<0.3 mV), the relative risk of a respiratory rate >18 was 7.2 (95% CI 2.2-37.2, p <0.01) compared with a Pamp ≥0.3 mV. Similarly, the relative risk of orthopnea was 3.5 (95% CI 1.6-8.7, p <0.01) and dyspnea 2.4 (95% CI 1.4-4.0, p <0.01). FVC had the strongest correlation with Pamp (R(2) = 0.48 (p <0.001)). Fourteen of 15 patients with a FVC <50% had a Pamp <0.3 mV. However, eight with a Pamp <0.3 had a FVC >80%. The median survival was 1.07 years when the Pamp was <0.3 mV and >2 years when the Pamp was >0.3 mV (p <0.001). In conclusion, the phrenic Pamp correlated closely with multiple symptoms, signs, and laboratory measures of respiratory insufficiency and may prove to be a useful biomarker of respiratory dysfunction in ALS.

Effects of noninvasive ventilation on sleep outcomes in amyotrophic lateral sclerosis.

STUDY OBJECTIVES: The objective was to study the effects on noninvasive ventilation on sleep outcomes in patient with ALS, specifically oxygenation and overall sleep quality. METHODS: Patients with ALS who met criteria for initiation of NIV were studied with a series of 2 home PSG studies, one without NIV and a follow-up study while using NIV. Primary outcome was a change in the maximum overnight oxygen saturation; secondary outcomes included change in mean overnight oxygen saturation, apnea and hypopnea indexes, sleep latency, sleep efficiency, sleep arousals, and sleep architecture. RESULTS: A total of 94 patients with ALS were screened for eligibility; 15 were enrolled; and 12 completed study procedures. Maximum overnight oxygen saturation improved by 7.0% (p = 0.01) and by 6.7% during REM sleep (p = 0.02) with NIV. Time spent below 90% oxygen saturation was also significant-ly better with NIV (30% vs 19%, p < 0.01), and there was trend for improvement in mean overnight saturation (1.5%, p = 0.06). Apnea index (3.7 to 0.7), hypopnea index (6.2 to 5.7), and apnea hypopnea index (9.8 to 6.3) did not significantly improve after introducing NIV. NIV had no effect on sleep efficiency (mean change 10%), arousal index (7 to 12), or sleep stage distribution (Friedman chi-squared = 0.40). CONCLUSIONS: NIV improved oxygenation but showed no significant effects on sleep efficiency, sleep arousals, restful sleep, or sleep architecture. The net impact of these changes for patients deserves further study in a larger group of ALS patients.