The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

LUNG VOLUME AND TIDAL VENTILATION ARE MARKEDLY AFFECTED BY RECENT LUNG VOLUME HISTORY,

Alexander Adams MPH, RRT, Dana Simonson BA, Alain Broccard MD, David Dries MD, John Marini MD, John Hotchkiss MD. Regions Hosp./Univ of MN, St. Paul, MN.

Background: During pressure-cycled ventilation (PCV), tidal volume (VT) and end expiratory lung volume (EELV) are determined by pressure settings and respiratory system mechanics. However, recent lung volume history may also affect VT and EELV, therefore, we ventilated rat lungs over a range of settings after either lung collapse or lung recruitment.

Methods: Lungs from Sprague rats (n=4) were extracted and suspended within an air-tight jar; the tracheas were in communication with a pressure cycled ventilator. VT and EELV were monitored by tracking the jar pressure as calibrated to volume by a calibration syringe. VT and EELV were obtained for a range of PCV settings (10/5, 15/5, 20/5, 25/5, 30/5, 35/5) after either lung collapse between settings (-10 cmH2O for 5 minutes between settings) or after lung recruitment (PCV of 35/5).

Results: When lung collapse was induced between PCV settings, mean VT increased with increasing Pset (left figure-ascending or lower limb) and mean VT was significantly greater after lung volume recruitment (left figure - descending limb). EELV also increased with increasing peak PCV settings (right figure - ascending or lower limb)) when lung collapse was induced between settings but EELV was maintained as peak PCV settings were decreased after lung recruitment. Thus, the lungs remained open after lung recruitment in spite of decreasing Pset.

Conclusions: VT and EELV were markedly affected by recent lung volume history. Therefore, lung mechanics are dynamic and VT/EELV may be altered by activities such as suctioning or recruitment maneuvers. AHA SDG 9930184N;NIH SCOR 50152.

OF-02-068

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