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Table 6: Acceptability criteria for measurement of intrathoracic gas volume (functional residual capacity). |
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Tidal volume breathing before shutter closure and gasping |
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Acceptable |
Before shutter closure: • Stable end-expiratory tidal volume During shutter closure: • Gasping maneuvers • Superimposed straight lines without hysteresis • Parallel straight lines with minimal hysteresis • Gasping respiratory rate between 0.5 to 1 Hz or between 1.0 and 1.5 Hz with normal spirometry or mild obstruction |
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Usable |
Any of: Before shutter closure: • End-expiratory tidal volume unstable, but no significant change in either direction During shutter closure: • Partially closed gasping maneuver • Partially overlapping straight lines • Parallel straight lines with hysteresis • Respiratory rate >1.5-2.0 Hz with normal spirometry or mild obstruction |
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Not acceptable or rejected |
Any of: Before shutter closure: • Unstable end-expiratory tidal volume with significant change in either direction (e.g., increase in end-expiratory lung volume with each breath) During shutter closure: • Gasping maneuver with mouth opening • No straight lines • Excessive hysteresis • Force to perform the gasping maneuver exceeded the range of the oral pressure transducer • Gasping respiratory rate < 0.5 Hz, > 2 Hz with normal spirometry or mild obstruction or > 1.5 with significant obstruction |