IS THE MEASUREMENT OF STATIC COMPLIANCE DIFFERENT IN MECHANICAL AND SPONTANEOUS BREATHING?

Abstract

A recent report demonstrated that the values of dynamic compliance measured in mechanical breaths are lower than those evaluated in spontaneous ones (Mammel Ped Pulmonol B:222, 1990). To evaluate the influence of mechanical and spontaneous ventllation on respiratory function values we measured and compared static compliance of the respiratory system (Crs) in these two different states, performing 44 studies in 33 stable intubated infants (age 3 days±1 SD, weight 2000 g±400 SD). All infants had acute or chronic lung disease, no sedat ion was given. We used the single breath occlusion technique and a computerized system (SensorMedics 2600); compliance measurements (atleast 7 breaths) were performed during mechanical (CrsV) and spontaneous (CrsS) breaths (after a brief disconnection of the infant from the ventilator). In both situations the exalation is externa) to the ventilator circuit. The mean values of CrsV resulted 0.46±0.06 ml/cmH20/kg (mean coefficient of variation cv; 9.35±3-8%, ranee 3.3-16%> and there was no significant difference (p=NS paired t-test) from the values of CrsS (0.43±0.07 ml/cmH20/kg, cv: 9.85±3.5%, range 4-17%). Assuming that the lung is on the same part of the pressure-volume curve, we conclude that measuring static compliance by the single breath occlusion technique is not necessary to obtain measurements performed both during mechanical and spontaneous breaths as suggested for dynamic compliance.