Development and clinical assessment of a heat and moisture exchanger with a multi-magnet automatic tracheostoma valve (Provox FreeHands HME) for vocal and pulmonary rehabilitation after total laryngectomy. - Hilgers,F.J.; Ackerstaff,A.H.; Van As,C.J.; Balm,A.J.; Van den Brekel,M.W.; Tan,I.B. (Acta Otolaryngol, 2003)