Conti G, Cavaliere F, Costa R, Craba A, Catarci S, Festa V, Proietti R, Antonelli M. Respir Care. 2007 Nov;52(11):1463-71
Comparison of the efficacy of NPPV delivered to 25 patients via helmet, matched with 25 controls chosen from historical patients treated with face mask. Authors conclude that NPPV by helmet can be 'an alternative to conventional ventilation'.
Link to abstract.