Table 1—

Humidity and water loss

ParameterNo humidifierCold humidifierHeated humidifierp‐value
 Hrel %24.0±9.134.5±10.1#53.9±13.2¶,+<0.001
 Habs mg·L−19.4±3.513.4±3.9#21.3±5.1¶,+<0.001
 υ hygrometer °C34.8±1.034.6±1.0#35.0±1.1¶,+<0.001
 υ mask °C31.1±1.431.3±1.632.4±1.7¶,+<0.001
 Hrel %75.5±14.479.8±10.2#82.2±8.9¶,+<0.001
 Habs mg·L−130.8±5.532.2±4.0#33.6±3.5¶,+<0.001
 υ hygrometer °C35.6±0.735.3±0.9#35.6±0.9¶,+<0.001
 υ mask °C32.4±1.132.6±1.2#33.7±1.1¶,+<0.001
VT L0.58±0.370.59±0.370.81±1.50.42
 Bf L·min−121.9±10.221.2±10.218.9±9.90.26
 VE L·min−110.5±4.010.1±4.49.6±3.20.43
 Water loss mg·min−1226.3±49.4190.8±46.9#118.0±48.5¶,+<0.001
Impedance of the total respiratory system
 Z 5 Hz cmH2O·L−1·s−15.7±1.86.4±2.16.7±1.80.025
 R 5 Hz cmH2O·L−1·s−15.5±1.46.1±1.76.3±1.50.012
 R 20 Hz cmH2O·L−1·s−15.4±0.75.3±0.75.3±0.60.62
 X 5 Hz cmH2O·L−1·s−1−1.7±1.3−2.1±1.4−2.1±1.20.21
  • Hrel: relative humidity

  • Habs: measured absolute humidity in the capacitive hygrometer

  • υ hygrometer: temperature in the hygrometer

  • υ mask: temperature in the mask

  • VT: total volume

  • Bf: breathing frequency

  • VE: minute volume

  • water loss: amount of water lost on the basis of measurements of absolute humidity in expired and inspired air

  • Z 5 Hz: impedance of the total respiratory system at an oscillation frequency of 5 Hz

  • R 5 Hz: resistance at 5 Hz

  • R 20 Hz: resistance at 20 Hz

  • X 5 Hz: reactance at 5 Hz. The p-values were determined according to the repeated-measure one-way analysis of variance (p<0.05)

  • #: cold humidifier versus no humidifier

  • +: heated humidifier versus cold humidifier

  • The post hoc significance (p<0.05)

  • : heated humidifier versus no humidifier