The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

THE EFFECT OFINSPIRATORY RISE TIME ON TOTAL PATIENT WORK OF BREATHING (TPWOB) DURING PRESSURESUPPORT VENTILATION (PSV) IN A SPONTANEOUS BREATHING LUNG MODEL

David L.Vines,MHS, RRT, Warren Kolenda, CRT, Faustino Ramos, CRT, David C. Shelledy, PhD,RRT. The University of Texas Health Science Center, San Antonio, Tx.

BACKGROUND:Limmited information is available concerning the use of rise time on the SERVO300 ventilator (SiemensMedical, Danvers, Massachusetts). We compared variousrise time settings during PSV to determine which setting resulted in the lowestTPWOB using a two-compartment mechanical lung model (Michigan Instruments Inc.,Grand Rapids, MI) to simulate spontaneous breathing.

Methods: WOBwas first measured on lung B alone at tidal volumes of 200, 400, 600, and 800while peak flow was varied from 30, 60, 80, and 100 L/min with a sine wave flowpattern using the Ventrak 1550 Respiratory Mechanics Monitoring System (NovametrixMedical Systems, Inc., Wallingford CT). Then WOB was measured at these volumesfor lung B to drive lung A at normal compliance (0.05 L/cmH2O) and resistance(2.7 cmH2O/L/sec), decreased compliance (0.02 L/cmH20), and increased resistance(17.6 cmH2O/L/sec) while lung A received assistance through an 8.0 endotrachealtube from either PSV of 5, 10, 15 or 20 cmH2O, while the rise time setting wasvaried from 0 to 10 for each level of PSV. TPWOB was calculated using the followingformula: [TPWOB= WOB(B+A) ? WOBB]

Results:

Mean WOB(J/L)
Rise Time Normal C/RC ­ Raw
0 0.34 (0.31)+,++,+++0.83 (0.44)+,++0.64 (0.42)+,++
2 0.42 (0.33)+,++ 0.90 (0.43)+ 0.73 (0.43)
5 0.50 (0.34)0.99 (0.44)0.81(0.44)
8 0.58 (0.36) 1.05 (0.43)0.87 (0.45)
10 0.63 (0.37) 1.10 (0.43)0.92 (0.45)

+ significantly < rise time?10,p<0.05, ++ significantly < rise time?8, p<0.05, +++ significantly <rise time?5, p<0.05

CONCLUSION: The lower therise time the lower TPWOB in our spontaneous breathing model. A rise time settingof 0 should result in lowest TPWOB under most patient conditions.

OF-01-267

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