MEASUREMENTS OF PEEP-INDUCED CHANGES IN LUNG-VOLUME - EVALUATION OF ALASER MONITOR

Study objective: To evaluate a newly developed laser monitor in the me asurement of positive end-expiratory pressure (PEEP)-induced changes i n end-expiratory lung volume (EELV) in spontaneously breathing subject s. Design: An open comparison between two different methods to assess breathing parameters. Setting: A respiratory research unit. Participan ts: Six spontaneously breathing, healthy volunteers. Interventions: St epwise increases of PEEP from 0 to 0.8 to 1.6 kPa during spontaneous b reathing; repeated validation of the laser monitor in each subject. Me asurements and results: Pressure and flow were recorded at the airway opening, Abdominal wall displacement (AWD) measured by the laser senso r was recorded simultaneously, The time lag between the volume and the laser signals during baseline was 0.068+/-0.052 s and during maximal PEEP, 0.108+/-0.093 s, There was no baseline drift in either the PEEP or the AWD signals. Mean EELV decreased by 290 mL to 1,157 mL after th e PEEP valve was removed. Within each individual, the ratio between EE LV and AWD showed only small variations. Measurements of tidal volume (VT) and AWD showed good agreement at all PEEP levels. Mean VT decreas ed in all but one subject during PEEP. With the increase in PEEP, the end-expiratory abdominal baseline increased linearly over a large rang e of end-expiratory pressures with a flattening of the curve at high P EEP levels in all subjects. Conclusions: The laser monitor is sufficie ntly accurate for measuring PEEP-induced changes in EELV during sponta neous breathing in healthy adult subjects, Monitors incorporating mult iple laser sensors may have considerable clinical promise.