Biologically variable or naturally noisy mechanical ventilation recruits atelectatic lung

Biologically variable mechanical ventilation ((V) over dot bv)-using a comp uter-controller to mimic the normal variability in spontaneous breathing-im proves gas exchange in a model of severe lung injury (Lefevre, G. R., S. E. Kowalski, L. G. Girling, D. B. Thiessen, W. A. C. Mutch. Am. J. Respir. Cr it. Core Med. 1996;154:1567-1572). Improved oxygenation with (V) over dot b v, in the face of alveolar collapse, is thought to be due to net volume rec ruitment secondary to the variability or increased noise in the peak inspir atory airway pressures (Ppaw). Biologically variable noise can be modeled a s an inverse power law frequency distribution (y proportional to l/f(a)) (W est, B.)., M. Shlesinger. Am. Sci. 1990;78:40-45). In a porcine model of at electasis-right lung collapse with one-lung ventilation-we studied if (V) o ver dot bv (n = 7) better reinflates the collapsed lung compared with conve ntional monotonously regular control mode ventilation ((V) over dot c; n = 7) over a 5-h period. We also investigated the influence of sigh breaths wi th (V) over dot c ((V) over dot s; n = 8) with this model. Reinflation of t he collapsed lung was significantly enhanced with (V) over dot bv-greater P a-O2 (502 +/- 40 mm Hg with (V) over dot bv versus 381 +/- 40 mm Hg with (V ) over dot c at 5 h; and 309 +/- 79 mm Hg with (V) over dot s; mean +/- SD) , lower Pa-CO2 (35 +/- 4 mm Hg versus 48 +/- 8 mm Hg and 50 +/- 8 mm Hg), l ower shunt fraction (9.7 +/- 2.7% versus 14.6 +/- 2.0% and 22.9 +/- 6.0%), and higher respiratory system compliance (Crs) (1.15 +/- 0.15 ml/cm H2O/kg versus 0.79 +/- 0.19 ml/cm H2O/kg and 0.77 +/- 0.13 ml/cm H2O/kg)-at lower mean Ppaw (15.7 +/- 1.4 cm H2O versus 18.8 +/- 2.3 cm H2O and 18.9 +/- 2.8 cm H2O). (V) over dot bv resulted in an 11% increase in measured tidal volu me (V-Tm) over that seen with (V) over dot c by 5 h (14.7 +/- 1.2 ml/kg ver sus 13.2 ml/kg). The respiratory rate variability programmed for (V) over d ot bv demonstrated an inverse power law frequency distribution (y proportio nal to 1/f(a)) with a = 1.6 +/- 0.3. These findings provide strong support for the theoretical model of noisy end-inspiratory pressure better recruiti ng atelectatic lung. Our results suggest that using natural biologically va riable noise has enhanced the performance of a mechanical ventilator in con trol mode.