Components of respiratory resistance monitored in mechanically ventilated patients

B. Babik, F. Peták, T. Asztalos, Z. I. Deák, G. Bogáts, Z. Hantos

Research output: Contribution to journalArticle

10 Citations (Scopus)


The interrupter technique is commonly adopted to monitor respiratory resistance (Rrs,int) during mechanical ventilation; however, Rrs,int is often interpreted as an index of airway resistance (Raw). This study compared the values of Rrs,int provided by a Siemens 940 Lung Mechanics Monitor with total respiratory impedance (Zrs) parameters in 39 patients with normal spirometric parameters, who were undergoing elective coronary bypass surgery. Zrs was determined at the airway opening with pseudorandom oscillations of 0.2-6 Hz at end inspiration. Raw and tissue resistance (Rti) were derived from the Zrs data by model fitting; Rti and total resistance (Rrs,osc=Raw+Rti) were calculated at the actual respirator frequencies. Lower airway resistance (Rawl) was estimated by measuring tracheal pressure. Although good agreement was obtained between Rrs,osc and Rrs,int, with a ratio of 1.07±0.19 (mean±SD), they correlated poorly (r2=0.36). Rti and the equipment component of Raw accounted for most of Rrs,osc (39.8±11.9 and 43.0±6.9%, respectively), whereas only a small portion belonged to Rawl (17.2±6.3%). It is concluded that respiratory resistance may become very insensitive to changes in lower airway resistance and therefore, inappropriate for following alterations in airway tone during mechanical ventilation, especially in patients with relatively normal respiratory mechanics, where the tissue and equipment resistances represent the vast majority of the total resistance.

Original languageEnglish
Pages (from-to)1538-1544
Number of pages7
JournalEuropean Respiratory Journal
Issue number6
Publication statusPublished - Dec 1 2002


  • Airway resistance
  • Forced oscillations
  • Interrupter technique
  • Respiratory monitoring
  • Tissue resistance

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine

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