Initial Positive End-expiratory Pressure Research Articles

Inflating Pressure and Not Expiratory Pressure Initiates Lung Injury at Birth in Preterm Lambs.

Rationale: Inflation is essential for aeration at birth, but current inflating pressure settings are without an evidence base. Objectives: To determine the role of inflating pressure (ΔP), and relationship with positive end-expiratory pressure (PEEP), in initiating early lung injury pathways in the preterm lamb lung. Methods: 124-127d steroid exposed preterm lambs (n=45) were randomly allocated (8-10/gp) to 15 min of respiratory support with placental circulation and 20 or 30 cmH2O ΔP, with an initial high PEEP (maximum 20 cmH2O) recruitment manoeuvre known to facilitate aeration (dynamic PEEP), and compared to dynamic PEEP with no ΔP or 30 cmH2O ΔP and low (4 cmH2O) PEEP. Lung mechanics and aeration were measured throughout. after an additional 30 min of apnoeic placental support, lung tissue and bronchoalveolar fluid were analysed for regional lung injury, including proteomics. Results: 30 cmH2O ΔP and dynamic PEEP resulted in quicker aeration, better compliance, but higher tidal volumes (often >8 ml/kg, all p<0.0001; mixed effects) and injury. ΔP 20 cmH2O with dynamic PEEP resulted in the same lung mechanics and aeration, but less energy transmission (tidal mechanical power), as ΔP 30 cmH2O with low PEEP.. Dynamic PEEP without any tidal inflations resulted in the least lung injury. Use of any tidal inflating pressures altered metabolic, coagulation and complemented protein pathways within the lung. Conclusions: Inflating pressure is essential for the preterm lung at birth, but also the primary mediator of lung injury. Greater focus is needed on strategies that identify safest application of pressure in the delivery room.

Implementation of Bubble Continuous Positive Airway Pressure in the Delivery Room and NICU.

Implementation of Bubble Continuous Positive Airway Pressure in the Delivery Room and NICU.

Correlation of Positive End-Expiratory and Intracranial Pressure Using the Ultrasonographic-Guided Measurement of Optic Nerve Sheath Diameter in Traumatic Brain Injury Patients.

In brain injury patients, positive end-expiratory pressure (PEEP) may potentially increase the intracranial pressure (ICP). ICP can be noninvasively assessed from the sonographic measurement of the optic nerve sheath diameter (ONSD). Herein, we aim to evaluate the association between PEEP and ICP via measuring ONSD in traumatic brain injury (TBI) patients. TBI patients with age ≥18 years, severe brain injury (GCS 8 or less), receiving mechanical ventilation, initial PEEP ≤4 mmHg and no history of severe cardiopulmonary disease were included in this study. Patients with intracranial hypertension (defined as ICP >20 mmHg) and already receiving PEEP >15 cm H2O at enrollment were excluded from the study. ONSD measurement was performed when hemodynamic parameters were most stable. Variables included central venous pressure, invasive blood pressure, heart rate, saturation, and ventilator parameters. The ONSD and ICP did not increase significantly while PEEP increased from 0-5 cm and 5-10 cm H2O. However, ONSD and ICP significantly increased when PEEP increased from 10-15 cm H2O. There was no significant difference noted while comparing measurements of optic nerve sheath (ONS) diameter in both eyes at all PEEP values in cases as well as control patients. Mean arterial pressure (MAP) decreased with an increase in PEEP value. Highly significant decrease occurred in MAP change from PEEP 10-15 in cases (P < 0.001) and control (P < 0.001). The PEEP up to 10 cm H2O can be safely applied in patients with TBI. In addition, the increment of PEEP might further increase the oxygenation, at the cost of ICP accentuation.

Effect of positive end expiratory pressure level selection in prone position ventilation on lung recruitment and inflammatory factors in patients with severe acute respiratory distress syndrome

To investigate the effect of positive end expiratory pressure (PEEP) level selection on prone position ventilation and inflammatory factors in patients with severe acute respiratory distress syndrome (ARDS). A prospective randomized controlled study was conducted. The 100 patients with severe ARDS admitted to Union Jiangbei Hospital, Huazhong University of Science and Technology from March 2016 to March 2019 were enrolled. Patients were divided into two groups according to the random number table method, with 50 cases in each group. All patients were given lung protective ventilation strategy and prone position ventilation treatment on the basis of treatment of primary disease. The lower level of PEEP [8-12 cmH2O (1 cmH2O = 0.098 kPa)] was the control group, and the higher level of PEEP (13-17 cmH2O) was the observation group. Patients' vital signs were continuously monitored during mechanical ventilation. The indexes of pulmonary recruitment were recorded, including the dynamic lung compliance (Cdyn), pulmonary drive pressure (DP), heart rate and lactate (Lac) levels before and 48 hours after the treatment. The levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), high sensitivity C-reaction protein (hs-CRP) in serum were detected by enzyme linked immunosorbent assay (ELISA). Arterial blood gas was detected, including arterial partial pressure of oxygen (PaO2), oxygenation index (PaO2/FiO2), and arterial partial pressure of carbon dioxide (PaCO2). The occurrence of pleural effusion and heart, liver and kidney dysfunction were recorded. In the control group, the PEEP level was (10.9±1.2) cmH2O, and the observation group PEEP level was (15.6±1.5) cmH2O. There was no significant difference in the index of lung recruitment, the levels of inflammatory factors and the arterial blood gas analysis index between the two groups before treatment. After prone ventilation, the index of lung recruitment and the arterial blood gas analysis index were much better in both groups. The effect of lung recruitment and oxygenation in the observation group with higher PEEP level were significantly superior to the control group with lower PEEP level [Cdyn (mL/cmH2O): 37.61±5.09 vs. 32.51±4.97, DP (cmH2O): 10.36±1.51 vs. 12.55±1.35, heart rate (bpm): 93.13±10.56 vs. 108.56±12.49, Lac (mmol/L): 2.34±0.41 vs. 3.41±0.57, PaO2 (mmHg, 1 mmHg = 0.133 kPa): 95.13±3.33 vs. 91.81±2.75, PaO2/FiO2 (mmHg): 180.12±7.25 vs. 150.29±8.52, PaCO2 (mmHg): 38.31±2.13 vs. 45.22±2.61, all P < 0.05]. The levels of inflammatory factors after treatment were higher than before treatment in both groups. Higher PEEP level will cause increased inflammatory factor level than the control group [IL-6 (ng/L): 526.24±125.18 vs. 465.18±130.52, TNF-α (ng/L): 42.47±2.20 vs. 34.12±1.89, hs-CRP (mg/L): 101.24±23.26 vs. 83.56±25.51, all P < 0.05]. Furthermore, the occurrence of pleural effusion and heart, liver, kidney dysfunction in the observation group were lower than that of the control group (4.0% vs. 8.0%, 10.0% vs. 16.0%, 2.0% vs. 10.0%, 2.0% vs. 6.0%, respectively, all P < 0.05). The higher PEEP level combined with prone position ventilation is beneficial to the severe ARDS patients with better lung recruitment effect and arterial blood gas improvement, thus promote the patients' recovery. But the higher initial PEEP will induce the release of inflammatory factors to a certain extent.

Recruitability and effect of PEEP in SARS-Cov-2-associated acute respiratory distress syndrome

BackgroundA large proportion of patients with a SARS-Cov-2-associated respiratory failure develop an acute respiratory distress syndrome (ARDS). It has been recently suggested that SARS-Cov-2-associated ARDS may differ from usual non-SARS-Cov-2-associated ARDS by higher respiratory system compliance (CRS), lower potential for recruitment with positive end-expiratory pressure (PEEP) contrasting with severe shunt fraction. The purpose of the study was to systematically assess respiratory mechanics and recruitability in SARS-Cov-2-associated ARDS.MethodsGas exchanges, CRS and hemodynamics were assessed at 2 levels of PEEP (15 cmH2O and 5 cmH2O) within 36 h (day1) and from 4 to 6 days (day 5) after intubation. The recruited volume was computed as the difference between the volume expired from PEEP 15 to 5 cmH2O and the volume predicted by compliance at PEEP 5 cmH2O (or above airway opening pressure). The recruitment-to-inflation (R/I) ratio (i.e. the ratio between the recruited lung compliance and CRS at PEEP 5 cmH2O) was used to assess lung recruitability. A R/I ratio value higher than or equal to 0.5 was used to define highly recruitable patients.ResultsThe R/I ratio was calculated in 25 of the 26 enrolled patients at day 1 and in 15 patients at day 5. At day 1, 16 (64%) were considered as highly recruitable (R/I ratio median [interquartile range] 0.7 [0.55–0.94]) and 9 (36%) were considered as poorly recruitable (R/I ratio 0.41 [0.31–0.48]). The PaO2/FiO2 ratio at PEEP 15 cmH2O was higher compared to PEEP 5 cmH2O only in highly recruitable patients (173 [139–236] vs 135 [89–167] mmHg; p < 0.01). Neither PaO2/FiO2 or CRS measured at PEEP 15 cmH2O or at PEEP 5 cmH2O nor changes in PaO2/FiO2 or CRS in response to PEEP changes allowed to identify highly or poorly recruitable patients.ConclusionIn this series of 25 patients with SARS-Cov-2 associated ARDS, 64% were considered as highly recruitable and only 36% as poorly recruitable based on the R/I ratio performed on the day of intubation. This observation suggests that a systematic R/I ratio assessment may help to guide initial PEEP titration to limit harmful effect of unnecessary high PEEP in the context of Covid-19 crisis.

Minor change in initial PEEP setting decreases rates of ventilator-associated events in mechanically ventilated trauma patients.

BackgroundSurveillance of ventilator-associated events (VAEs) as defined by the National Healthcare Safety Network (NHSN) is performed at many US trauma centers and considered a measure of healthcare quality. The surveillance algorithm relies in part on increases in positive end-expiratory pressure (PEEP) to identify VAEs. The purpose of this cohort study was to evaluate the effect of initiating mechanically ventilated trauma patients at marginally higher PEEP on incidence of VAEs.MethodsAnalysis of level-1 trauma center patients mechanically ventilated 2+ days from 2017 to 2018 was performed after an institutional ventilation protocol increased initial PEEP setting from 5 (2017) to 6 (2018)cm H2O. Incidence of VAEs per 1000 vent days was compared between PEEP groups. Logistic regression modelling was performed to evaluate the impact of the PEEP setting change adjusted to account for age, ventilator days, injury mechanism and injury severity.Results519 patients met study criteria (274 PEEP 5 and 245 PEEP 6). Rates of VAEs were significantly reduced among patients with initial PEEP 5 versus 6 (14.61 per 1000 vent days vs. 7.13 per 1000 vent days; p=0.039). Logistic regression demonstrated that initial PEEP 6 was associated with 62% reduction in VAEs.ConclusionsOur data suggest that an incrementally increased baseline PEEP setting was associated with a significantly decreased incidence of VAEs among trauma patients. This minor change in practice may have a major impact on a trauma center’s quality metrics.Level of evidenceIV.

Positive end-expiratory pressure titration with electrical impedance tomography and pressure\u2013volume curve in severe acute respiratory distress syndrome

BackgroundThe study objective was to compare titration of positive end-expiratory pressure (PEEP) with electrical impedance tomography (EIT) and with ventilator-embedded pressure–volume loop in severe acute respiratory distress syndrome (ARDS).MethodsWe have designed a prospective study with historical control group. Twenty-four severe ARDS patients (arterial oxygen partial pressure to fractional inspired oxygen ratio, PaO2/FiO2 < 100 mmHg) were included in the EIT group and examined prospectively. Data from another 31 severe ARDS patients were evaluated retrospectively (control group). All patients were receiving medical care under identical general support guidelines and protective mechanical ventilation. The PEEP level selected in the EIT group was the intercept point of cumulated collapse and overdistension percentages curves. In the control group, optimal PEEP was selected 2 cmH2O above the lower inflection point on the static pressure–volume curve.ResultsPatients in the EIT group were younger (P < 0.05), and their mean plateau pressure was 1.5 cmH2O higher (P < 0.01). No differences in other baseline parameters such as APACHE II score, PaO2/FiO2, initial PEEP, driving pressure, tidal volume, and respiratory system compliance were found. Two hours after the first PEEP titration, significantly higher PEEP, compliance, and lower driving pressure were found in the EIT group (P < 0.01). Hospital survival rates were 66.7% (16 of 24 patients) in the EIT group and 48.4% (15 of 31) in the control group. Identical rates were found regarding the weaning success rate: 66.7% in the EIT group and 48.4% in the control group.ConclusionIn severe ARDS patients, it was feasible and safe to guide PEEP titration with EIT at the bedside. As compared with pressure–volume curve, the EIT-guided PEEP titration may be associated with improved oxygenation, compliance, driving pressure, and weaning success rate. The findings encourage further randomized control study with a larger sample size and potentially less bias in the baseline data.Trial Registration NCT03112512

Positive end-expiratory pressure-induced increase in external jugular venous pressure does not predict fluid responsiveness in laparoscopic prostatectomy.

Dynamic change in central venous pressure (CVP) was associated with fluid responsiveness. External jugular venous pressure (EJVP) may reliably estimate CVP and have the advantages of being less invasive. We investigated whether increase in EJVP induced by positive end-expiratory pressure (PEEP) could be a reliable predictor of fluid responsiveness in patients undergoing robot-assisted laparoscopic prostatectomy (RALP). Fifty patients who underwent RALP with steep Trendelenburg position were enrolled. PEEP of 10cmH2O was applied for 5min and then 300ml of colloid was administered. EJVP, stroke volume variation (SVV), and cardiac index calculated by pulse contour method were measured before and after the PEEP challenge and colloid administration. Increase in cardiac index>10% was used to define the fluid responsiveness. Twenty-six patients were fluid responders. Neither the increase in EJVP after the initial PEEP nor SVV was significantly different between responders and non-responders. They were not significantly correlated with an increase in cardiac index. The areas under the receiver operating characteristic curve (AUC) of these two variables were not significantly greater than 0.5. However, a post hoc analysis revealed that AUC of a decrease in EJVP after removal of PEEP was significantly greater than 0.50. Our study results suggested that SVV and increase in EJVP after applying PEEP were not accurate predictors of fluid responsiveness during RALP. Further studies are required to find an adequate preload index in robot-assisted urologic surgery with steep Trendelenburg position.

Development of a Predictive Pulmonary Elastance Model to Describe Lung Mechanics throughout Recruitment Manoeuvres

Abstract Mechanical ventilation is a primary therapy for patients with acute respiratory failure. However, poorly selected ventilator settings can cause lung damage due to the heterogeneity of healthy and damaged alveoli. A commonly used lung protective strategy is titrating PEEP (positive end expiratory pressure) to minimum elastance. However, in clinical practice this initial PEEP is rarely changed. As lung disease evolves over time, the optimal PEEP required to maintain recruitment also changes. A predictive elastance model could be used to assess whether or not the current PEEP level should be changed based on whether a nearby PEEP had lower elastance. In this study, a physiologically relevant basis function model is developed and tested across the entirety of 18 recruitment manoeuvres. Accurate prediction of pressure and PIP to 10% across each of these data sets validates the functionality of this model.

Efficacy of Lung Recruitment Maneuver with High-Level Positive End-Expiratory Pressure in Patients with Influenza-Associated Acute Respiratory Distress: A Single-Center Prospective Study

BackgroundThe latest data released to the public from the Chinese Ministry of Health reported 120,940 confirmed H1N1 cases and 659 deaths on the Chinese mainland. ObjectiveWe performed a prospective, single-center study to investigate the efficacy of lung recruitment maneuver (RM) with high-level positive end-expiratory pressure (PEEP) in patients with the 2009 influenza A (H1N1)-associated acute respiratory distress syndrome (ARDS). MethodsEighty-four patients with H1N1-associated ARDS were admitted to emergency intensive care units between October 2009 and February 2012. During pressure control ventilation, if arterial oxygen saturation (SpO2) is consistently <88% for >30 minutes, an RM with high-level PEEP is performed to normalize lung volume at 30 cmH2O for 60 seconds. The RM was considered initially a responder if SpO2 increased >3% within 15 minutes; otherwise, an SpO2 increase <3% would be considered initially a nonresponder. Variations on oxygen metabolism and hemodynamic parameters were also measured before and after initial RM with high-level PEEP. ResultsAfter the initial RM, 40 patients (47.6%) with influenza-associated ARDS displayed an increase (≥3%) in SpO2 (the responder group), and 44 patients (52.4%) had no significant improvement (<3%) in SpO2 (the nonresponder group). Among 84 patients with influenza-associated ARDS, 56 patients survived and 28 patients died. There was significant difference in mortality rate between the responder group and the nonresponder group (7 out of 40 vs 18 out of 44; P = 0.019). The initial PEEP level in the responder group was lower than that of the nonresponder group (P = 0.028). The initial mean duration of mechanical ventilation in the responder group was also shorter than that of the nonresponder group (P = 0.011). Furthermore, the initial dynamic lung-thorax compliance was obviously higher in the initially responder group than in the nonresponder group (P = 0.038). ConclusionsInitial response of lung RM with high-level PEEP may be associated with good clinical outcome of patients with influenza-associated ARDS. The initial PEEP level, duration of mechanical ventilation, and dynamic lung-thorax compliance dynamic lung-thorax compliance may be potential factors in influencing the initial response to RM.

Profil étiologique et épidémiologique des granulomatoses systémique dans un service de médecine interne

Although maintaining some amount of positive end-expiratory pressure (PEEP) seems essential, selecting and titrating a specific level for patients with ARDS remains challenging despite extensive research on the subject. Although an “open lung” approach to ventilation is popular and has some degree of biological plausibility, it is not without risk. Furthermore, there is no clear evidence-based guidance regarding initial PEEP settings or how to titrate them early in the course of the illness. Many busy clinicians use a “one-size-fits-all” approach based on local medical culture, but an individualized approach has the potential to offer significant benefit. Here we present a pragmatic approach based on simple measurements available on all ventilators, focused on achieving balance between the potential risks and benefits of PEEP. Acknowledging “best PEEP” as an impossible goal, we aim for a straightforward method to achieve “better PEEP.”

Reproducibility of regional lung ventilation distribution determined by electrical impedance tomography during mechanical ventilation

Electrical impedance tomography (EIT) has the potential to become a new tool for bedside monitoring of regional lung ventilation. The aim of our study was to assess the reproducibility of regional lung ventilation distribution determined by EIT during mechanical ventilation under identical ventilator settings. The experiments were performed on 10 anaesthetized supine pigs ventilated in a volume-controlled mode. EIT measurements were performed with the Goe-MF II device (Viasys Healthcare, Höchberg, Germany) during repeated changes in positive end-expiratory pressure (PEEP) from 0 to 10 cm H2O. Regional lung ventilation was determined in the right and left hemithorax as well as in 64 regions of interest evenly distributed over each chest side in the ventrodorsal direction. Ventilation distributions in both lungs were visualized as ventrodorsal ventilation profiles and shifts in ventilation distribution quantified in terms of centres of ventilation in relation to the chest diameter. The proportion of the right lung on total ventilation in the chest cross-section was 0.54 ± 0.04 and remained unaffected by repetitive PEEP changes. Initial PEEP increase resulted in a redistribution of ventilation towards dorsal lung regions with a shift of the centre of ventilation from 45 ± 3% to 49 ± 3% of the chest diameter in the right and from 47 ± 2% to 50 ± 2% in the left hemithorax. Excellent reproducibility of the results in the individual regions of interest with almost identical patterns of ventilation distribution was found during repeated PEEP changes.

Avaliação da função pulmonar de recém-nascidos com síndrome do desconforto respiratório em diferentes pressões finais expiratórias positivas

To verify the alterations of pulmonary function in preterm newborn infants with respiratory distress syndrome (RDS). The parameters analyzed were Dynamic Compliance (Cdyn), Inspiratory Tidal Volume (TVinsp), partial arterial pressure of carbon dioxide (PaCO2). Eleven preterm newborn infants, with gestational age <35 weeks, and birth weight <2,500 g, were include in a control case study. All infants presented RDS and were treated with 120 mg/Kg of porcine surfactant. The initial positive end expiratory pressure (PEEP) was 3 cm H2O. A pneumotachograph with a graphical monitor was used to assess the pulmonary function. After each increase in the PEEP (4 and 6 cm H2O), there was an interval of 20 minutes before measuring the arterial data of pulmonary function and arterial gases. There were three males and eight females (1:2.7) among the infants with RDS. The mean gestational age was 30.78. +/- 2.05 weeks, ranging from 26 to 34 weeks. The increase in the PEEP from 3 to 6 cm H2O caused significant decrease in the TVinsp (6.46 +/- 3.43 to 4.20 +/- 2.35, P=0.0262). With the increase in the PEEP from 4 to 6 cm H2O, there was also a decrease in the TVinsp (5.98 +/- 3.33 to 4.20 +/- 2.35), (P=0.0044). Regarding the Cdyn, when there was an increase in the PEEP from 3 to 6 cm H2O, the reduction was statistically significant (0.58 +/- 0.27 to 0.46 +/- 0.25, P=0.0408) and from 4 to 6 cm H2O, the reduction in the Cdyn was also important (0.77 +/- 0.27 to 0.46 +/- 0.25), (P=0.0164). Increases in the PEEP from 4 to 6 cm H2O caused increases in the PaCO2 (52.81 +/- 15.49 to 64.90 +/- 12.69), (P= 0.0141). A more significant increase was observed when the PEEP was elevated from 3 to 6 cm H2O (41.45 +/- 7.87 to 64.90 +/- 12.69, P=0.0033). The study showed that the PEEP from 3 to 4 cm H2O produces better results in terms of Cdyn and less collateral effects regarding respiratory acidosis and pulmonary hyperventilation with impairment of the alveolar ventilation, evidenced by the increase in the PaCO2 and the decrease in the TVinsp.

Variations in End-Expiratory Pressure During Partial Liquid Ventilation: Impact on Gas Exchange, Lung Compliance, and End-Expiratory Lung Volume

To determine the effects of different levels of positive end-expiratory pressure (PEEP) during partial liquid ventilation (PLV) on gas exchange, lung compliance, and end-expiratory lung volume (EELV). Prospective animal study. Animal physiology research laboratory. Nine piglets. Animals underwent saline solution lavage to produce lung injury. Perflubron was instilled via the endotracheal tube in a volume estimated to represent functional residual capacity. The initial PEEP setting was 4 cm H(2)O, and stepwise changes in PEEP were made. At 30-min intervals, the PEEP was increased to 8, then 12, then decreased back down to 8, then 4 cm H(2)O. After 30 min at each level of PEEP, arterial blood gases, aortic and central venous pressures, heart rates, dynamic lung compliance, and changes in EELV were recorded. Paired t tests with Bonferroni correction were used to evaluate the data. There were no differences in heart rate or mean BP at the different PEEP levels. CO(2) elimination and oxygenation improved directly with the PEEP level and mean airway pressure (Paw). Compliance did not change with increasing PEEP, but did increase when PEEP was lowered. EELV changes correlated directly with the level of PEEP. As previously reported during gas ventilation, oxygenation and CO(2) elimination vary directly with PEEP and proximal Paw during PLV. EELV also varies directly with PEEP. Dynamic lung compliance, however, improved only when PEEP was lowered, suggesting an alteration in the distribution of perflubron due to changes in pressure-volume relationships.

An intrinsic positive end-expiratory pressure lung model, with and without flow limitation

To design an intrinsic positive end-expiratory pressure (PEEP) lung model that has the property of air flow limitation. Mechanical lung model study of intrinsic PEEP. Lung models were set up in the research laboratory. Intrinsic PEEP lung models were created with and without flow limitation. In the model with flow limitation, intrinsic PEEP was created by replacing a portion of the expiratory circuit with a collapsible Penrose tube and by placing this portion the circuit under water. The expiratory circuit became a part of the respiratory airway, with flow limitation occurring at the Penrose drain. In the model without flow limitation, intrinsic PEEP was generated with a fixed linear resistor, which was inserted in the expiratory circuit to produce a similar level of intrinsic PEEP. Multiple levels of external PEEP, both above and below the initial intrinsic PEEP, were applied. At each level of external PEEP, peak airway pressure, plateau airway pressure, isovolume air flow, internal lung pressure, and intrinsic PEEP were measured. Peak airway pressure, plateau pressure, and internal lung pressure were minimally affected if the external PEEP was less than the intrinsic PEEP in the lung model with flow limitation. Intrinsic PEEP was reduced with external PEEP. However, if intrinsic PEEP was induced without dynamic airway closure or flow limitation, any level of external PEEP caused an immediate increase in peak airway pressure, plateau airway pressure, and internal lung pressure and a decrease in isovolume flow. External PEEP has little effect on the levels of intrinsic PEEP. We demonstrated two different models of an intrinsic PEEP lung model. The interactions between intrinsic PEEP and externally applied PEEP were different. The lung model with collapsible tube closely simulated the human respiratory system with flow limitation. This lung model may be useful for the future study of intrinsic PEEP and pulmonary mechanics.