Midwest Special Instruments---distributor of Grason-Stadler, MedRx, Micromedical, Maico, Interacoustics, Benson Mediacal, CMI, OHD, Tremetrics, Pehratek Products, nSpire, Depiiteo, Acoustics Systems for Minnesota, Iowa, South Dakota, North Dakota, Nebraska, NIOSH approved spirometer training and respirator FIT tester