In 1922, Beams and Christie<sup>12 Christie C.D., Beams A.J. The estimation of normal vital capacity with special reference to the effect of posture Arch Intern Med 1922 ;  30 : 34-39

Cliccare qui per andare alla sezione Riferimenti</sup> first reported that vital capacity was lower when measured in the supine than in the upright posture. In 1933, Hurtado and Frey<sup>28 Hurtado A., Frey W.W. Studies of total pulmonary capacity and its subdivisions. III: Changes with body posture J Clin Invest 1933 ;  12 : 825-831

Cliccare qui per andare alla sezione Riferimenti</sup> extended this observation to include functional residual capacity (FRC), and McMichael and McGibbon attributed the difference to the weight of the abdomen in 1939.<sup>39 McMichael J., McGibbon J.P. Postural changes in the lung volume Clin Sci 1939 ;  4 : 175-183

Cliccare qui per andare alla sezione Riferimenti</sup> In 1955, Blair and Hickham<sup>5 Blair E., Hickham J.B. The effect of change in body position on lung volume and intrapulmonary gas mixing in normal subjects J Clin Invest 1955 ;  34 : 383-389  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> first noted that body position alters gas mixing. The fact that the prone position might counter these adverse effects dates to 1961, when Moreno and Lyons noted that the FRC measured prone was higher than that measured supine.<sup>42 Moreno F., Lyons H.A. Effect of body posture on lung volumes J Appl Physiol 1961 ;  16 : 27-29

Cliccare qui per andare alla sezione Riferimenti</sup>

Mellins referred to the aforementioned observations in a presentation at a conference on the scientific basis of respiratory therapy in 1974,<sup>40 Mellins R.B. Pulmonary physiotherapy in the pediatric age group Am Rev Respir Dis 1974 ;  110 : 137-142

Cliccare qui per andare alla sezione Riferimenti</sup> and concluded that the transpulmonary pressure opposing lung collapse could vary markedly depending on body position. In discussing this presentation, Bryan<sup>10 Bryan A.C. Comments of a devil's advocate Am Rev Respir Dis 1974 ;  110 : 143-144

Cliccare qui per andare alla sezione Riferimenti</sup> reviewed the results of a study he and Froese had recently completed<sup>18 Froese A.B., Bryan A.C. Effects of anesthesia and paralysis on diaphragmatic mechanics in man Anesthesiol 1974 ;  41 : 242-255  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> that suggested the reduction in FRC that occurred when lying supine was primarily localized to dorsal lung regions, and was the first to suggest that the only “feasible” method of expanding these regions would be to ventilate patients in the prone position.

The first documentation that the prone position actually improved oxygenation was provided in 1976 and 1977,<sup>15References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti, 48References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti</sup> in patients with the acute respiratory distress syndrome (ARDS), but these observations went largely unrecognized until 1987, when the effects of prone positioning were first studied mechanistically,<sup>1References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti</sup> and the clinical observations were repeated by Langer and colleagues in 1988.<sup>34References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti</sup> Additional laboratory studies were published in the early 1990s<sup>24References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti, 33References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti, 44References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti, 45References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti, 58References 6,9,11,17,27,30,43,46,49,53,54,55,56.

Cliccare qui per andare alla sezione Riferimenti</sup> and were followed by numerous confirmatory clinical reports from around the world, which continue to date.^{*References 6,9,11,17,27,30,43,46,49,53,54,55,56.}

This article reviews the clinical information regarding the effects of prone ventilation on gas exchange in patients with ARDS, discusses the mechanisms by which this improvement occurs, and considers how prone ventilation might also reduce ventilator-induced lung injury.