Pressure–Volume Curve Does Not Predict Steady-State Lung Volume in Canine Lavage Lung Injury

Downie, John M.; Nam, Arthur J.; Simon, Brett A.

doi:10.1164/rccm.200305-614oc

Cited by 54 publications

(48 citation statements)

References 28 publications

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“…Static pressure volume curves have been advocated to predict end-expiratory recruitment by examining the measured end-expiratory pressure in relation to the critical closing pressure on the expiratory limb of the static pressurevolume curve (56,57) or, alternatively, in relation to the maximal tidal compliance in a decremental PEEP trial (12,27,29). The prediction of dynamic behavior based on static pressure-volume relationships, however, does not take into account the dynamics of end-expiratory collapse.…”

Section: Discussionmentioning

confidence: 99%

Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

Syring

Otto²,

Spivack³

et al. 2007

Journal of Applied Physiology

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Cyclical recruitment of atelectasis with each breath is thought to contribute to ventilator-associated lung injury. Extrinsic positive end-expiratory pressure (PEEPe) can maintain alveolar recruitment at end exhalation, but PEEPe depresses cardiac output and increases overdistension. Short exhalation times can also maintain end-expiratory recruitment, but if the mechanism of this recruitment is generation of intrinsic PEEP (PEEPi), there would be little advantage compared with PEEPe. In seven New Zealand White rabbits, we compared recruitment from increased respiratory rate (RR) to recruitment from increased PEEPe after saline lavage. Rabbits were ventilated in pressure control mode with a fraction of inspired O(2) (Fi(O(2))) of 1.0, inspiratory-to-expiratory ratio of 2:1, and plateau pressure of 28 cmH(2)O, and either 1) high RR (24) and low PEEPe (3.5) or 2) low RR (7) and high PEEPe (14). We assessed cyclical lung recruitment with a fast arterial Po(2) probe, and we assessed average recruitment with blood gas data. We measured PEEPi, cardiac output, and mixed venous saturation at each ventilator setting. Recruitment achieved by increased RR and short exhalation time was nearly equivalent to recruitment achieved by increased PEEPe. The short exhalation time at increased RR, however, did not generate PEEPi. Cardiac output was increased on average 13% in the high RR group compared with the high PEEPe group (P < 0.001), and mixed venous saturation was consistently greater in the high RR group (P < 0.001). Prevention of end-expiratory derecruitment without increased end-expiratory pressure suggests that another mechanism, distinct from intrinsic PEEP, plays a role in the dynamic behavior of atelectasis.

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Section: Discussionmentioning

confidence: 99%

Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

Syring

Otto²,

Spivack³

et al. 2007

Journal of Applied Physiology

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“…We chose the lung lavage model because it presents the vertical distribution of lung density characteristic of ALI (34,35) and maintains significant recruitment with sufficient PEEP (36)(37)(38)(39). Therefore, this model appeared likely to allow investigation of the relation between shunt and gas fractions over a wide spectrum of lung inflation, especially with varying levels of PEEP.…”

Section: Rationale and Critique Of The Experimentsmentioning

confidence: 99%

“…Because lower PEEP was set according to oxygenation and could hence be expected to differ between animals, we chose a single higher PEEP to assess whether any interanimal variability present at lower PEEP was maintained at a uniform PEEP. Although the lavage model does not encompass the pathophysiologic complexity of human ALI, it is likely to reflect several of its features, such as surfactant dysfunction (40,41), atelectasis (18), and edema (36,38). Addition of a detergent (19,21,39) allows the target hypoxemia to be reached with a lower volume of fluid than pure saline (34,35,41).…”

Section: Rationale and Critique Of The Experimentsmentioning

confidence: 99%

Relation between Shunt, Aeration, and Perfusion in Experimental Acute Lung Injury

Musch¹,

Bellani²,

Melo³

et al. 2008

Am J Respir Crit Care Med

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Rationale: In a pulmonary process characterized by spatially heterogeneous loss of aeration, the impairment of gas exchange is expected to depend on the regional distribution of perfusion relative to that of aeration. Objectives: To investigate how regional aeration, shunt, and perfusion are interrelated at different levels of end-expiratory pressure and how their interplay relates to global shunt fraction in acute lung injury. Methods: Regional shunt and perfusion were assessed by imaging with positron emission tomography the pulmonary kinetics of [ 13 N]nitrogen infused in saline solution in five sheep after lung lavage. The lung field was divided in six horizontal regions. Measurements and Main Results: Each animal showed an inverse relation between regional shunt (FS) and gas (FG) fractions: FS 5 2m Á FG 1 FS 0 . This relation was similar among animals (m 5 1.25 6 0.14, FS 0 5 0.75 6 0.15) and invariant with end-expiratory pressure, despite lack of correlation between global shunt and gas fractions and large interanimal variability in global shunt fraction. When this relation was used to estimate global shunt fraction as a perfusion-weighted average of the estimates of regional shunt fraction derived from regional gas fraction, 72% of the interanimal variability in global shunt fraction could be explained. Conclusions: Despite large interanimal variability in global shunt fraction, there was a consistent inverse relation between regional shunt and gas fractions, independent of end-expiratory pressure. Most of the interanimal variability in global shunt fraction could be explained by the combined effect of this relation and the distribution of perfusion on regional shunt, rather than by differences in global aeration.

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“…We used the saline lavage model, which represents a highly recruitable model of acute lung injury (15). After lung lavage, the damage to alveolar epithelial, endothelial, and perivascular cells is probably less than that of other lung injury models, such as the oleic acid or the endotoxin infusion models (16,17), in which the primary insult is delivered from the pulmonary vascular side.…”

Section: Limitations Of the Studymentioning

confidence: 99%

Effect of Prone Position on Regional Shunt, Aeration, and Perfusion in Experimental Acute Lung Injury

Richter

Bellani

Harris

et al. 2005

Am J Respir Crit Care Med

177

133

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Rationale:The prone position is used to improve gas exchange in patients with acute respiratory distress syndrome. However, the regional mechanism by which the prone position improves gas exchange in acutely injured lungs is still incompletely defined. Methods: We used positron emission tomography imaging of [ 13 N]nitrogen to assess the regional distribution of pulmonary shunt, aeration, perfusion, and ventilation in seven surfactant-depleted sheep in supine and prone positions. Results: In the supine position, the dorsal lung regions had a high shunt fraction, high perfusion, and poor aeration. The prone position was associated with an increase in lung gas content and with a more uniform distribution of aeration, as the increase in aeration in dorsal lung regions was not offset by loss of aeration in ventral regions. Consequently, the shunt fraction decreased in dorsal regions in the prone position without a concomitant impairment of gas exchange in ventral regions, thus leading to a significant increase in the fraction of pulmonary perfusion participating in gas exchange. In addition, the vertical distribution of specific alveolar ventilation became more uniform in the prone position. A biphasic relation between regional shunt fraction and gas fraction showed low shunt for values of gas fraction higher than a threshold, and a steep linear increase in shunt for lower values of gas fraction. Conclusion: In a surfactant-deficient model of lung injury, the prone position improved gas exchange by restoring aeration and decreasing shunt while preserving perfusion in dorsal lung regions, and by making the distribution of ventilation more uniform.Keywords: adult respiratory distress syndrome; emission-computed tomography; nitrogen isotopes; prone position; pulmonary gas exchange Despite increasing use of the prone position as a means to improve gas exchange in patients with acute respiratory distress syndrome (ARDS) (1, 2), few studies have investigated the regional mechanism of this improvement in acutely injured lungs (3, 4). Using single-photon emission computed tomography in an oleic acid model of lung injury, Lamm and coworkers (4) showed that the prone position was associated with a narrower distribution of the ventilation-to-perfusion ratio and with an increase in the relative (i.e., mean-normalized) ventilation-to-perfusion ratio in dorsal lung regions. However, because regional shunt could not be measured directly by single-photon emission computed tomography, whether the increase in relative ventilation-to-perfusion ratio in dorsal regions corresponded to reversal of shunt and, more importantly, the magnitude of the associated improvement of regional gas exchange could not be determined. Furthermore, single-photon emission computed tomography did not allow assessment of regional aeration. Combining measurement of regional aeration with measurement of regional shunt and perfusion is important for two reasons. First, it allows determination of whether the improvement of gas exchange in the prone position is d...

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Pressure–Volume Curve Does Not Predict Steady-State Lung Volume in Canine Lavage Lung Injury

Cited by 54 publications

References 28 publications

Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

Relation between Shunt, Aeration, and Perfusion in Experimental Acute Lung Injury

Effect of Prone Position on Regional Shunt, Aeration, and Perfusion in Experimental Acute Lung Injury

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