Diaphragmatic movement using ultrasound during spontaneous and mechanical ventilation: effect of tidal volume.

Using ultrasound (US) the effect of various tidal volumes on the movement of ventral, dome and dorsal parts of the right hemidiaphragm was studied, both during spontaneous and mechanical ventilation. Six healthy non-medicated volunteers who were in the supine position breathed spontaneously shallowly (tidal volume (VT) being 400 ml) (SB), and deeply (VT 1000 ml) (SB-deep). In addition, they were mechanically ventilated with intermittent positive pressure ventilation at three different VT's: 500 ml (IPPV-500), 1000 ml (IPPV-1000) and 1700 ml (IPPV-1700). The maximal movement was recorded in the ventral part in 2 volunteers during SB, in 3 during SB-deep, and in 3 and 5 subjects during IPPV-500 and IPPV-1700, respectively. The movement in dome was 100% during SB (all others standardized to this), 303 +/- 107% during SB-deep, 82 +/- 30% during IPPV-500, 165 +/- 70% during IPPV-1000 and 266 +/- 153% during IPPV-1700. An increased tidal volume is associated with an increase in the diaphragmatic movement studied by US. However, a larger VT is needed during mechanical ventilation to achieve the same amount of change as occurred with deep spontaneous breathing.