Lulling, J., Delwiche, J. P., & Prignot, J. (1981). Early Bronchodilating Effect of Oxitropium Bromide in Comparison With Ipratropium Bromide. Respiration (English Edition) : international journal of thoracic medicine, 42(3), 188-192. https://doi.org/10.1159/000194427 (Original work published 1981)