title: Assessment of dynamic mechanical properties of the respiratory system during high-frequency oscillatory ventilation*.
abstract: OBJECTIVE
  1) To investigate the possibility of estimating respiratory system impedance (Zrs, forced oscillation technique) by using high-amplitude pressure oscillations delivered during high-frequency oscillatory ventilation; 2) to characterize the relationship between Zrs and continuous distending pressure during an increasing/decreasing continuous distending pressure trial; 3) to evaluate how the optimal continuous distending pressure identified by Zrs relates to the point of maximal curvature of the deflation limb of the quasi-static pressure-volume curve.
  
  
  METHODS
  Prospective laboratory animal investigation.
  
  
  METHODS
  Experimental medicine laboratory.
  
  
  METHODS
  Eight New Zealand rabbits.
  
  
  METHODS
  The rabbits were ventilated with high-frequency oscillatory ventilation. Zrs was measured while continuous distending pressure was increased and decreased between 2 and 26 cm H2O in 1-minute steps of 4 cm H2O. At each step, a low-amplitude (6 cm H2O) sinusoidal signal was alternated with a high-amplitude (18 cm H2O) asymmetric high-frequency oscillatory ventilation square pressure waveform. Pressure-volume curves were determined at the end of the continuous distending pressure trial. All measurements were repeated after bronchoalveolar lavage.
  
  
  RESULTS
  Zrs was estimated from flow and pressure measured at the inlet of the tracheal tube and expressed as resistance (Rrs) and reactance (Xrs). Linear correlation between the values, measured by applying the small-amplitude sinusoidal signal and the ventilator waveform, was good for Xrs (r = 0.95 ± 0.04) but not for Rrs (r = 0.60 ± 0.34). Following lavage, the Xrs-continuous distending pressure curves presented a maximum on the deflation limb, identifying an optimal continuous distending pressure that was, on average, 1.1 ± 1.7 cm H2O below the point of maximal curvature of the deflation limb of the pressure-volume curves.
  
  
  CONCLUSIONS
  Xrs can be accurately measured during high-frequency oscillatory ventilation without interrupting ventilation and/or connecting additional devices. An optimal continuous distending pressure close to the point of maximal curvature of the deflation limb of quasi-static pressure-volume curve can be identified by measuring Zrs during a decreasing continuous distending pressure trial. Zrs might constitute a useful bedside tool for monitoring lung mechanics and improving the continuous distending pressure optimization during high-frequency oscillatory ventilation.
authors.affiliation: 1TBM Lab, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano University, Milano, Italy. 2Neonatal Intensive Care Unit, MBBM Foundation, Monza, Italy. 3Department of Health Sciences, Università di Milano Bicocca, Monza, Italy.
authors.forename: Raffaele L
authors.initials: RL
authors.lastname: Dellacà
authors.forename: Emanuela
authors.initials: E
authors.lastname: Zannin
authors.forename: Maria L
authors.initials: ML
authors.lastname: Ventura
authors.forename: Giulio
authors.initials: G
authors.lastname: Sancini
authors.forename: Antonio
authors.initials: A
authors.lastname: Pedotti
authors.forename: Paolo
authors.initials: P
authors.lastname: Tagliabue
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Miserocchi
mesh_terms: D000818:Animals; D017097:Electric Impedance; D006612:High-Frequency Ventilation / Q000379:methods*; D008168:Lung / Q000502:physiology*; D011817:Rabbits; D012119:Respiration; D012129:Respiratory Function Tests