Static pressure volume curves and body posture in severe chronic bronchitis

¹ University of Athens Medical School, Evaggelismos Hospital, Athens, Greece
² Medicine, University of Athens Medical School, Evaggelismos Hospital, Athens, Greece

^* To whom correspondence should be addressed. E-mail: szakynthinos{at}yahoo.com.

	Abstract

Previously-demonstrated, beneficial pronation-effects on gas-exchange and respiratory mechanics might be maximised in severely hyperinflated chronic bronchitis patients. We sought to elucidate underlying mechanisms and to determine whether pronation-effects are reflected by postural changes in inspiratory pressure-volume curve characteristics.

Sixteen mechanically ventilated (for 16-36 h) patients with chronic bronchitis-exacerbation were studied in preprone semirecumbent, prone, and postprone semirecumbent postures. Respiratory system intrinsic positive end-expiratory pressure (PEEPi,rs) exceeded 12 cm H₂O. Haemodynamics, partitioned respiratory mechanics, gas-exchange, and lung volumes were determined at zero external PEEP. Pressure-volume curves were constructed from functional residual capacity.

End-expiratory lung volume exceeded opening volume. Prone position versus preprone semirecumbent resulted in 20% reduced pressure at lower inflection point (LIP) and 17% increased volume at upper inflection point (UIP) of lung pressure-volume curve (both P<0.05), improved lung mechanics and volumes, oxygenation, and PaCO₂. In multiple linear regression, postural decreases in PEEPi,rs and additional lung resistance independently predicted postural decreases in lung LIP-pressure and PaCO₂, respectively (r²=0.93 and 0.83, respectively, both P<0.001).

Conclusively, in severely hyperinflated patients, pronation reduces lung LIP-pressure and increases lung UIP-volume. Pronation-effects on ventilation homogeneity and PaCO₂ are maximised, implying that pronation can be useful during early controlled ventilation.