Another version of the nasal breathing valve designed by Tissot with  an electical switch that was activated during expiration. Used one-way valves so exhaled air could be collected and analyzed.  From J. Tissot, “Nouvelle méthode de mesure et d’inscription du débit et des mouvements respiratoires de l’homme et des animaux”, Journal de physiologie et de pathologie générale, 1904, vol 6, pp. 691.