Static pressure-volume curves and body posture in severe chronic bronchitis

Abstract

Based on prior data, the current authors hypothesised that beneficial pronation effects on gas exchange and respiratory mechanics might be maximised in severely hyperinflated chronic bronchitis patients. The current authors also sought to elucidate underlying mechanisms and to determine whether pronation effects are reflected by postural changes in inspiratory pressure-volume (P-V) curve characteristics.A total of 16 mechanically ventilated patients (for 16-36 h) with chronic bronchitis exacerbation were studied in pre-prone semirecumbent (SREC), prone and post-prone SREC postures. Static respiratory system intrinsic positive end-expiratory pressure (PEEPi,rs) was .12 cmH 2 O. Haemodynamics, partitioned respiratory mechanics, gas exchange, and lung volumes were determined at zero external positive end-expiratory pressure. P-V curves were constructed from functional residual capacity.End-expiratory lung volume exceeded opening volume. Prone position versus pre-prone SREC resulted in 20% reduced pressure at the lower inflection point (LIP) and 17% increased volume at the upper inflection point of the lung P-V curve, improved lung mechanics and volumes, oxygenation, and carbon dioxide arterial tension (Pa,CO 2 ). In multiple linear regression, postural decreases in PEEPi,rs and additional lung resistance independently predicted postural decreases in lung LIP pressure and Pa,CO 2 , respectively.In conclusion, in severely hyperinflated patients, pronation reduces lung lower inflection point pressure and increases lung upper inflection point volume. Pronation effects on ventilation homogeneity and carbon dioxide arterial tension are maximised, implying that pronation can be useful during early controlled ventilation.

S2e guideline: positioning and early mobilisation in prophylaxis or therapy of pulmonary disorders

“…The significant physiological effects of the prone position are: (a) changes of the respiratory mechanics, (b) the reduction of the pleural pressure gradient [ 126 , 127 , 166 , 183 , 206 , 227 ] and (c) the reduction of tidal hyperinflation [ 62 ] as well as the ventilation induced lung injury (‘stress and strain’) [ 193 ]. They may lead to the homogenisation of pulmonary gas exchange [ 5 , 102 , 203 ], to a reduction of ventilation-perfusion mismatch [ 102 , 215 ], to an increase of lung volume involved in gas exchange in CT analyses due to a reduction of marginally or non-ventilated areas (atelectasis) [ 104 , 107 ] and to a reduction of ventilation-associated lung injury [ 5 , 45 , 46 , 194 , 228 , 278 ]. The assumption is made that an improvement of the drainage of bronchoalveolar secretion is affected.…”