Effect of inspiratory volume on intrathoracic pressure generated by an L-1 maneuver.

Since each muscle has an optimal length at which it can generate the maximum tension, an optimal inspiratory volume may exist for producing the maximum intrathoracic pressure during the L-1 maneuver. Intrathoracic pressures were measured in eight healthy men after they inspired various volumes of air and performed the L-1 straining maneuver in a 1-G environment. Both the peak and mean intrathoracic pressures increased at greater inspiratory volumes, except for the mean intrathoracic pressure at the highest volumes. The ability to increase intrathoracic pressure with larger inspiratory volumes may improve +Gz tolerance.