The valve characteristics were studied by connecting it to an electric blower and measuring flow at the air intake by means of a pneumotachograph, pressure at the mouthpiece, and plunger mass on electronic scales.
For any given mass there is a threshold opening pressure. At pressures less negative than threshold, the valve is completely closed (this occurs at flows less than 0.05 L/s). Once the inspiratory pressure reaches threshold, the valve opens and thereafter pressure changes by less than 1 cm HtO/L/s for flows up to 3.0 L/s.
Flow volume curves, single breath carbon monoxide transfer, and arterial blood gas tensions were determined for each patient entering the study.
Eight patients underwent IMT. Spirometry (Godart water-filled spirometer), cycle exercise performance, 12 minute walking distance (MWD), maximum sustained breathing capacity (MSBC), and MIP were determined before and after the six week training period.
Exercise performance was assessed using 8W increments each minute on an electrically-braked cycle ergometer. During the last 20 seconds of each minute of exercise, expiratory flow (pneumotachograph) was electrically integrated to provide minute ventilation. Mixed expired gas was analyzed to determine oxygen uptake and carbon dioxide output. All signals were recorded on a chart recorder.
Duty cycle (Ti/Ttot) which is the ratio of inspiratory muscle contraction time to total respiratory cycle time, was determined from a flow-time trace at rest and during maximal cycle exercise.
Twelve minute walking distance* was measured in an air-conditioned hospital corridor of 60 meters length. The patient was asked to walk as far as he could, resting if he so desired, and was given standardized verbal encouragement.
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