Further, we examined whether it would suffice to apply RM only every 60 min instead of every 5 min. This was studied in the low V T group (lowV T RM60) only. In this group, respiratory conditions were instable. R and C worsened comparable to the lowV T noRM group, but improved significantly after each RM. These alterations were reflected in changes in G and H. However, even though each RM was beneficial, after six hours tissue elastance had increased permanently, indicating that one deep inflation per hour is not sufficient to maintain lung volume at base line values. This is illustrated by the finding that H (p,0.001), R, C, G (all p,0.01) and R aw (p,0.05) were significantly different between the lowV T RM60 and the lowV T RM5 group.