• Y Yamazaki, M Yamakage, Y Ujike, and A Namiki.
• Department of Anesthesiology, Sapporo Medical University and Hospital, School of Medicine, Japan.
• Chest. 1994 Mar 1;105(3):860-3.

Study ObjectivesTo describe the importance of measuring work of breathing (WOB) in patients with high airway resistance (Raw) during continuous positive airway pressure (CPAP) support.DesignFundamental study using an advanced model lung and a pulmonary function monitor.SettingA research laboratory at the ICU of a university hospital.InterventionsSpontaneous breathing (tidal volume x respiratory rate: 400 ml x 15 min-1) was simulated with a time-cycled jet-flow generator. The CPAP and Raw were adjusted to 0, 5, and 10 cm H2O and to 5, 10, and 20 cm H2O.L-1.s-1, respectively.Measurements And ResultsUsing four advanced demand-flow system type ventilators (Evita, 7200a, Servo 900C, and Servo 300), a two-bellows-in-a-box type model lung, and a pulmonary function monitor with an esophageal catheter (CP-100), we measured WOB during CPAP with increased Raw. The WOB of the model lung increased significantly with increase in CPAP. The WOB of the model lung also increased significantly with increase in Raw for all ventilators tested in this study; some values showed over 1 J.L-1. The WOB under the Servo 300 exhibited the lowest values in all situations of all the ventilators tested in this study.ConclusionsPatients with high Raw may suffer excessive WOB even during CPAP with advanced demand-flow system type ventilators. It is vital to monitor WOB continuously using an adequate pulmonary function monitor such as that used in this study.

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