TITLE:
Modeling the effects of stretch-dependent surfactant secretion on lung recruitment during variable ventilation
AUTHORS:
Samir D. Amin, Arnab Majumdar, Phil Alkana, Allan J. Walkey, George T. O’Connor, Béla Suki
KEYWORDS:
Computational Modeling; Mechanical Ventilation; Variable Ventilation; Surfactant Secretion Dynamics
JOURNAL NAME:
Journal of Biomedical Science and Engineering,
Vol.6 No.12A,
December
27,
2013
ABSTRACT:
Variable ventilation (VV) is a novel strategy of ventilatory
support that utilizes random variations in the delivered tidal volume (VT) to improve lung function.
Since the stretch pattern during VV has been shown to increase surfactant
release both in animals and cell culture, we
hypothesized that there were combinations of PEEP and VT during VV that led to
improved alveolar recruitment compared to conventional mechanical ventilation
(CV). To test this hypothesis, we developed a computational model of stretch-induced
surfactant release combined with abnormal alveolar mechanics of the injured
lung under mechanical ventilation. We modeled the lung as a set of distinct
acini with independent surfactant secretion and thus pressure-volume
relationships. The rate of surfactant secretion was modulated by the stretch
magnitude that an alveolus experienced per breath. Mechanical ventilation was
simulated by delivering a prescribed VT at each breath. The fractional VT that each acinus received depended on its local compliance relative to the
total system compliance. Regional variability in VT thus developed through feedback between stretch and
surfactant release and coupling of regional VT to ventilator settings. The model allowed us to simulate patient-ventilator
interactions over a wide range of PEEPs and VTs
during CV and VV. Full recruitment was achieved through VV at a lower PEEP than
required for CV. During VV, the acini were maintained under non-equilibrium
steady-state conditions with breath-by-breath fluctuations of regional VT. In CV, alveolar injury
was prevented with high-PEEP-low-VT or low-PEEP-high-VT combinations. In contrast, one contiguous region of PEEP-VT combinations allowed for full recruitment without
overdistention during VV. We found that maintaining epithelial cell stretch
above a critical threshold with either PEEP or VT may help stabilize the injured lung. These results demonstrate the significance of patient-ventilator
coupling through the influence of cellular stretch-induced surfactant
release on the whole lung stability.