Different contributions from lungs and chest wall to respiratory mechanics in mice, rats, and rabbits

Changes in lung mechanics are frequently inferred from intact-chest measures of total respiratory system mechanics without consideration of the chest wall contribution. The participation of lungs and chest wall in respiratory mechanics has not been evaluated systematically in small animals commonly used in respiratory research. Thus, we compared these contributions in intact-chest mice, rats, and rabbits and further characterized the influence of positive end-expiratory pressure (PEEP). Forced oscillation technique was applied to anesthetized mechanically ventilated healthy animals to obtain total respiratory system impedance (Zrs) at 0, 3, and 6 cmH2O PEEP levels. Esophageal pressure was measured by a catheter-tip micromanometer to separate Zrs into pulmonary (ZL) and chest wall (Zcw) components. A model containing a frequency-independent Newtonian resistance (RN), inertance, and a constant-phase tissue damping (G) and elastance (H) was fitted to Zrs, ZL, and Zcw spectra. The contribution of Zcw to RN was negligible in all species and PEEP levels studied. However, the participation of Zcw in G and H was significant in all species and increased significantly with increasing PEEP and animal size (rabbit > rat > mice). Even in mice, the chest wall contribution to G and H was still considerable, reaching 47.0 ± 4.0(SE)% and 32.9 ± 5.9% for G and H, respectively. These findings demonstrate that airway parameters can be assessed from respiratory system mechanical measurements. However, the contribution from the chest wall should be considered when intact-chest measurements are used to estimate lung parenchymal mechanics in small laboratory models (even in mice), particularly at elevated PEEP levels. NEW & NOTEWORTHY In species commonly used in respiratory research (rabbits, rats, mice), esophageal pressure-based estimates revealed negligible contribution from the chest wall to the Newtonian resistance. Conversely, chest wall participation in the viscoelastic tissue mechanical parameters increased with body size (rabbit > rat > mice) and positive end-expiratory pressure, with contribution varying between 30 and 50%, even in mice. These findings demonstrate the potential biasing effects of the chest wall when lung tissue mechanics are inferred from intact-chest measurements in small laboratory animals.

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Effects of lung volume on lung and chest wall mechanics in rats

Journal of Applied Physiology ◽

10.1152/jappl.1999.86.1.16 ◽

1999 ◽

Vol 86 (1) ◽

pp. 16-21 ◽

Cited By ~ 81

Author(s):

T. Hirai ◽

K. A. McKeown ◽

R. F. M. Gomes ◽

J. H. T. Bates

Keyword(s):

Chest Wall ◽

Respiratory System ◽

Lung Volume ◽

Small Animal ◽

Tissue Mechanics ◽

Lung Mechanics ◽

Open Chest ◽

Pressure Volume Relationship ◽

Volume Resistance ◽

Relationship Of

To investigate the effect of lung volume on chest wall and lung mechanics in the rats, we measured the impedance (Z) under closed- and open-chest conditions at various positive end-expiratory pressures (0–0.9 kPa) by using a computer-controlled small-animal ventilator (T. F. Schuessler and J. H. T. Bates. IEEE Trans. Biomed. Eng. 42: 860–866, 1995) that we have developed for determining accurately the respiratory Z in small animals. The Z of total respiratory system and lungs was measured with small-volume oscillations between 0.25 and 9.125 Hz. The measured Z was fitted to a model that featured a constant-phase tissue compartment (with dissipation and elastance characterized by constants G and H, respectively) and a constant airway resistance (Z. Hantos, B. Daroczy, B. Suki, S. Nagy, and J. J. Fredberg. J. Appl. Physiol. 72: 168–178, 1992). We matched the lung volume between the closed- and open-chest conditions by using the quasi-static pressure-volume relationship of the lungs to calculate Z as a function of lung volume. Resistance decreased with lung volume and was not significantly different between total respiratory system and lungs. However, G and H of the respiratory system were significantly higher than those of the lungs. We conclude that chest wall in rats has a significant influence on tissue mechanics of the total respiratory system.

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Respiratory mechanical effects of surgical pneumoperitoneum in humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.00552.2014 ◽

2014 ◽

Vol 117 (9) ◽

pp. 1074-1079 ◽

Cited By ~ 19

Author(s):

Stephen H. Loring ◽

Negin Behazin ◽

Aileen Novero ◽

Victor Novack ◽

Stephanie B. Jones ◽

...

Keyword(s):

Chest Wall ◽

Respiratory System ◽

Transpulmonary Pressure ◽

Esophageal Pressure ◽

Pleural Pressure ◽

Abdominal Pressure ◽

Positive End Expiratory Pressure ◽

Before And After ◽

Show Evidence ◽

Obese Subjects

Pneumoperitoneum for laparoscopic surgery is known to stiffen the chest wall and respiratory system, but its effects on resting pleural pressure in humans are unknown. We hypothesized that pneumoperitoneum would raise abdominal pressure, push the diaphragm into the thorax, raise pleural pressure, and squeeze the lung, which would become stiffer at low volumes as in severe obesity. Nineteen predominantly obese laparoscopic patients without pulmonary disease were studied supine (level), under neuromuscular blockade, before and after insufflation of CO2 to a gas pressure of 20 cmH2O. Esophageal pressure (Pes) and airway pressure (Pao) were measured to estimate pleural pressure and transpulmonary pressure (Pl = Pao − Pes). Changes in relaxation volume (Vrel, at Pao = 0) were estimated from changes in expiratory reserve volume, the volume extracted between Vrel, and the volume at Pao = −25 cmH2O. Inflation pressure-volume (Pao-Vl) curves from Vrel were assessed for evidence of lung compression due to high Pl. Respiratory mechanics were measured during ventilation with a positive end-expiratory pressure of 0 and 7 cmH2O. Pneumoperitoneum stiffened the chest wall and the respiratory system (increased elastance), but did not stiffen the lung, and positive end-expiratory pressure reduced Ecw during pneumoperitoneum. Contrary to our expectations, pneumoperitoneum at Vrel did not significantly change Pes [8.7 (3.4) to 7.6 (3.2) cmH2O; means (SD)] or expiratory reserve volume [183 (142) to 155 (114) ml]. The inflation Pao-Vl curve above Vrel did not show evidence of increased lung compression with pneumoperitoneum. These results in predominantly obese subjects can be explained by the inspiratory effects of abdominal pressure on the rib cage.

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Respiratory mechanics of horses measured by conventional and forced oscillation techniques

Journal of Applied Physiology ◽

10.1152/jappl.1994.76.6.2467 ◽

1994 ◽

Vol 76 (6) ◽

pp. 2467-2472 ◽

Cited By ~ 23

Author(s):

S. S. Young ◽

D. Tesarowski

Keyword(s):

Resonant Frequency ◽

Respiratory System ◽

Respiratory Mechanics ◽

Forced Oscillation ◽

Dynamic Compliance ◽

Close Correlation ◽

Esophageal Pressure ◽

Forced Oscillation Technique ◽

Pulmonary Resistance ◽

Oscillation System

Respiratory mechanics were compared using conventional and forced oscillation techniques in six conscious horses and a mechanical model of the equine respiratory system. The parameters calculated from conventional airflow and esophageal pressure measurements were pulmonary resistance and dynamic compliance. The impedance of the respiratory system was measured at 1, 2, and 3 Hz with the forced oscillation technique, and respiratory system resistance, compliance, inertance, and resonant frequency were calculated. Pulmonary resistance was 1.0 +/- 0.3 cmH2O.l-1.s, and pulmonary dynamic compliance was 2.4 +/- 0.6 l/cmH2O. With the use of the forced oscillation system, respiratory resistance was 1.61 +/- 0.50 cmH2O.l-1.s at 1 Hz, compliance was 0.195 +/- 0.075 l/cmH2O, inertance was 0.026 +/- 0.0095 cmH2O.l-1.s2, and resonant frequency was 2.40 +/- 0.25 Hz. Data collected from a model of the respiratory system showed a close correlation between resistance and compliance measured with the two systems. This study demonstrates that the forced oscillation technique is a useful method for noninvasive measurement of respiratory mechanics in horses.

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Effect of pressure-controlled ventilation-volume guaranteed mode combined with individualized positive end-expiratory pressure on respiratory mechanics, oxygenation and lung injury in patients undergoing laparoscopic surgery in Trendelenburg position

Journal of Clinical Monitoring and Computing ◽

10.1007/s10877-021-00750-9 ◽

2021 ◽

Author(s):

Jianli Li ◽

Saixian Ma ◽

Xiujie Chang ◽

Songxu Ju ◽

Meng Zhang ◽

...

Keyword(s):

Laparoscopic Surgery ◽

Lung Injury ◽

Respiratory Mechanics ◽

Lung Mechanics ◽

Trial Registry ◽

Positive End Expiratory Pressure ◽

Clinical Trial Registry ◽

Trendelenburg Position ◽

Pressure Controlled Ventilation ◽

Pressure Controlled

AbstractThe study aimed to investigate the efficacy of PCV-VG combined with individual PEEP during laparoscopic surgery in the Trendelenburg position. 120 patients were randomly divided into four groups: VF group (VCV plus 5cmH2O PEEP), PF group (PCV-VG plus 5cmH2O PEEP), VI group (VCV plus individual PEEP), and PI group (PCV-VG plus individual PEEP). Pmean, Ppeak, Cdyn, PaO2/FiO2, VD/VT, A-aDO2 and Qs/Qt were recorded at T1 (15 min after the induction of anesthesia), T2 (60 min after pneumoperitoneum), and T3 (5 min at the end of anesthesia). The CC16 and IL-6 were measured at T1 and T3. Our results showed that the Pmean was increased in VI and PI group, and the Ppeak was lower in PI group at T2. At T2 and T3, the Cdyn of PI group was higher than that in other groups, and PaO2/FiO2 was increased in PI group compared with VF and VI group. At T2 and T3, A-aDO2 of PI and PF group was reduced than that in other groups. The Qs/Qt was decreased in PI group compared with VF and VI group at T2 and T3. At T2, VD/VT in PI group was decreased than other groups. At T3, the concentration of CC16 in PI group was lower compared with other groups, and IL-6 level of PI group was decreased than that in VF and VI group. In conclusion, the patients who underwent laparoscopic surgery, PCV-VG combined with individual PEEP produced favorable lung mechanics and oxygenation, and thus reducing inflammatory response and lung injury.Clinical Trial registry: chictr.org. identifier: ChiCTR-2100044928

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Respiratory mechanics in the anesthetized rat

Journal of Applied Physiology ◽

10.1152/jappl.1978.45.2.255 ◽

1978 ◽

Vol 45 (2) ◽

pp. 255-260 ◽

Cited By ~ 51

Author(s):

Y. L. Lai ◽

J. Hildebrandt

Keyword(s):

Chest Wall ◽

Respiratory System ◽

Esophageal Pressure ◽

Gas Content ◽

Lung Capacity ◽

Consistent Change ◽

Residual Capacity ◽

Wall Compliance ◽

The Difference ◽

Body Plethysmograph

Functional residual capacity (FRC) and pressure-volume (PV) curves of the lung, chest wall, and total respiratory system were studied in 15 anesthetized rats, weighing 307 +/- 10 (SE) g. Pleural pressure was estimated from the esophageal pressure measured with a water-filled catheter. The FRC determined by body plethysmograph was slightly and significantly larger than FRC determined from saline displacement of excised lungs. The difference may be accounted for by O2 uptake by lung tissue, escape of CO2 through the pleura, and abdominal gas. Paralysis in the prone position did not affect FRC, and abdominal gas content contributed only slightly to the FRC measured by body plethysmograph. Values of various pulmonary parameters (mean +/- SE) were as follows: residual volume, 1.26 +/- 0.13 ml; FRC, 2.51 +/- 0.20 ml; total lung capacity, 12.23 +/- 0.55 ml; compliance of the lung, 0.90 +/- 0.06 ml/cmH2O; chest wall compliance, 1.50 +/- 0.11 ml/cmH2O; and respiratory system compliance, 0.57 +/- 0.03 ml/cmH2O. The lung PV curve did not show a consistent change after the chest was opened.

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Lung Mechanics in Type L CoVID-19 Pneumonia: A Pseudo-Normal ARDS.

10.21203/rs.3.rs-78234/v1 ◽

2020 ◽

Author(s):

Lorenzo Viola ◽

Emanuele Russo ◽

Marco Benni ◽

Emiliano Gamberini ◽

Alessandro Circelli ◽

...

Keyword(s):

Mechanical Properties ◽

Respiratory System ◽

Respiratory Mechanics ◽

Blood Gases ◽

Lung Mechanics ◽

Prone Positioning ◽

Arterial Blood Gases ◽

Arterial Blood ◽

Esophageal Balloon ◽

Early Phases

Abstract Background. This study was conceived to provide systematic data about lung mechanics during early phases of CoVID-19 pneumonia, as long as to explore its variations during prone positioning. Methods. We enrolled four patients hospitalized in the Intensive Care Unit of “M. Bufalini” hospital, Cesena (Italy); after the positioning of an esophageal balloon, we measured mechanical power, respiratory system and transpulmonary parameters and arterial blood gases every 6 hours, just before decubitus change and 1 hour after prono-supination. Results. Both respiratory system and transpulmonary compliance and driving pressure confirmed the pseudo-normal respiratory mechanics of early CoVID-19 pneumonia (respectively, CRS 40.8 ml/cmH2O and DPRS 9.7 cmH2O; CL 53.1 ml/cmH2O and DPL 7.9 cmH2O). Interestingly, prone positioning involved a worsening in respiratory mechanical properties (CRS,SUP 56.3 ml/cmH2O and CRS,PR 41.5 ml/cmH2O – P 0.37; CL,SUP 80.8 ml/cmH2O and CL,PR 53.2 ml/cmH2O – P 0.23). Conclusions. Despite the severe ARDS pattern, respiratory system and lung mechanical properties during CoVID-19 pneumonia are pseudo-normal and tend to worsen during pronation. Trial registration. Restrospectively registered.

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Respiratory Mechanics

10.1093/med/9780190670085.003.0001 ◽

2017 ◽

Author(s):

John W. Kreit

Keyword(s):

Mechanical Ventilation ◽

Respiratory System ◽

Respiratory Mechanics ◽

Pressure Change ◽

Equation Of Motion ◽

Positive End Expiratory Pressure ◽

Elastic Recoil ◽

Viscous Forces ◽

Equilibrium Volume ◽

Complex Process

Ventilation can occur only when the respiratory system expands above and then returns to its resting or equilibrium volume. This is just another way of saying that ventilation depends on our ability to breathe. Although breathing requires very little effort and even less thought, it’s nevertheless a fairly complex process. Respiratory Mechanics reviews the interaction between applied and opposing forces during spontaneous and mechanical ventilation. It discusses elastic recoil, viscous forces, compliance, resistance, and the equation of motion and the time constant of the respiratory system. It also describes how and why pleural, alveolar, lung transmural, intra-abdominal, and airway pressure change during spontaneous and mechanical ventilation, and the effect of applied positive end-expiratory pressure (PEEP).

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Positive End-expiratory Pressure Improves Respiratory Function in Obese but not in Normal Subjects during Anesthesia and Paralysis

Anesthesiology ◽

10.1097/00000542-199911000-00011 ◽

1999 ◽

Vol 91 (5) ◽

pp. 1221-1221 ◽

Cited By ~ 256

Author(s):

Paolo Pelosi ◽

Irene Ravagnan ◽

Gabriella Giurati ◽

Mauro Panigada ◽

Nicola Bottino ◽

...

Keyword(s):

Body Mass Index ◽

Chest Wall ◽

Body Mass ◽

Respiratory System ◽

Respiratory Function ◽

Normal Subjects ◽

Intraabdominal Pressure ◽

Morbidly Obese ◽

Obese Patients ◽

Positive End Expiratory Pressure

Background Morbidly obese patients, during anesthesia and paralysis, experience more severe impairment of respiratory mechanics and gas exchange than normal subjects. The authors hypothesized that positive end-expiratory pressure (PEEP) induces different responses in normal subjects (n = 9; body mass index < 25 kg/m2) versus obese patients (n = 9; body mass index > 40 kg/m2). Methods The authors measured lung volumes (helium technique), the elastances of the respiratory system, lung, and chest wall, the pressure-volume curves (occlusion technique and esophageal balloon), and the intraabdominal pressure (intrabladder catheter) at PEEP 0 and 10 cm H2O in paralyzed, anesthetized postoperative patients in the intensive care unit or operating room after abdominal surgery. Results At PEEP 0 cm H2O, obese patients had lower lung volume (0.59 +/- 0.17 vs. 2.15 +/- 0.58 l [mean +/- SD], P < 0.01); higher elastances of the respiratory system (26.8 +/- 4.2 vs. 16.4 +/- 3.6 cm H2O/l, P < 0.01), lung (17.4 +/- 4.5 vs. 10.3 +/- 3.2 cm H2O/l, P < 0.01), and chest wall (9.4 +/- 3.0 vs. 6.1 +/- 1.4 cm H2O/l, P < 0.01); and higher intraabdominal pressure (18.8 +/-7.8 vs. 9.0 +/- 2.4 cm H2O, P < 0.01) than normal subjects. The arterial oxygen tension was significantly lower (110 +/- 30 vs. 218 +/- 47 mmHg, P < 0.01; inspired oxygen fraction = 50%), and the arterial carbon dioxide tension significantly higher (37.8 +/- 6.8 vs. 28.4 +/- 3.1, P < 0.01) in obese patients compared with normal subjects. Increasing PEEP to 10 cm H2O significantly reduced elastances of the respiratory system, lung, and chest wall in obese patients but not in normal subjects. The pressure-volume curves were shifted upward and to the left in obese patients but were unchanged in normal subjects. The oxygenation increased with PEEP in obese patients (from 110 +/-30 to 130 +/- 28 mmHg, P < 0.01) but was unchanged in normal subjects. The oxygenation changes were significantly correlated with alveolar recruitment (r = 0.81, P < 0.01). Conclusions During anesthesia and paralysis, PEEP improves respiratory function in morbidly obese patients but not in normal subjects.

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Can you calculate the total respiratory, lung, and chest wall respiratory mechanics?

Journal of Mechanical Ventilation ◽

10.53097/jmv.10007 ◽

2020 ◽

Vol 1 (1) ◽

pp. 24-26

Author(s):

Mia Shokry ◽

Kimiyo Yamasaki ◽

Ehab Daoud

Keyword(s):

Mechanical Ventilation ◽

Tidal Volume ◽

Chest Wall ◽

Airway Pressure ◽

Respiratory Mechanics ◽

Peak Inspiratory Pressure ◽

Esophageal Pressure ◽

Horizontal Line ◽

Pulmonary Pressure ◽

Volume Controlled

Figure: Waveforms for a patient undergoing mechanical ventilation with volume controlled mode. Tidal Volume of 500 ml, PEEP 15, Constant inspiratory flow of 45 l/min A: Airway pressure in cmH2O, B: Esophageal pressure in cmH2O, C: Trans-pulmonary pressure in cmH2O, D: Flow in l/min, E: Tidal volume in ml Red dashed horizontal line: values at end of expiratory occlusion maneuver, White solid horizontal line: values at end of inspiratory occlusion maneuver, Green dashed horizontal line: values during peak inspiratory pressure.

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Positive end-expiratory pressure in COVID-19 acute respiratory distress syndrome: the heterogeneous effects

Critical Care ◽

10.1186/s13054-021-03839-4 ◽

2021 ◽

Vol 25 (1) ◽

Author(s):

Davide Chiumello ◽

Matteo Bonifazi ◽

Tommaso Pozzi ◽

Paolo Formenti ◽

Giuseppe Francesco Sferrazza Papa ◽

...

Keyword(s):

Gas Exchange ◽

Respiratory System ◽

Dead Space ◽

Respiratory Mechanics ◽

Peep Level ◽

Lung Mechanics ◽

Mechanical Power ◽

Respiratory System Compliance ◽

Lung Elastance ◽

Lung Stress

Abstract Background We hypothesized that as CARDS may present different pathophysiological features than classic ARDS, the application of high levels of end-expiratory pressure is questionable. Our first aim was to investigate the effects of 5–15 cmH2O of PEEP on partitioned respiratory mechanics, gas exchange and dead space; secondly, we investigated whether respiratory system compliance and severity of hypoxemia could affect the response to PEEP on partitioned respiratory mechanics, gas exchange and dead space, dividing the population according to the median value of respiratory system compliance and oxygenation. Thirdly, we explored the effects of an additional PEEP selected according to the Empirical PEEP-FiO2 table of the EPVent-2 study on partitioned respiratory mechanics and gas exchange in a subgroup of patients. Methods Sixty-one paralyzed mechanically ventilated patients with a confirmed diagnosis of SARS-CoV-2 were enrolled (age 60 [54–67] years, PaO2/FiO2 113 [79–158] mmHg and PEEP 10 [10–10] cmH2O). Keeping constant tidal volume, respiratory rate and oxygen fraction, two PEEP levels (5 and 15 cmH2O) were selected. In a subgroup of patients an additional PEEP level was applied according to an Empirical PEEP-FiO2 table (empirical PEEP). At each PEEP level gas exchange, partitioned lung mechanics and hemodynamic were collected. Results At 15 cmH2O of PEEP the lung elastance, lung stress and mechanical power were higher compared to 5 cmH2O. The PaO2/FiO2, arterial carbon dioxide and ventilatory ratio increased at 15 cmH2O of PEEP. The arterial–venous oxygen difference and central venous saturation were higher at 15 cmH2O of PEEP. Both the mechanics and gas exchange variables significantly increased although with high heterogeneity. By increasing the PEEP from 5 to 15 cmH2O, the changes in partitioned respiratory mechanics and mechanical power were not related to hypoxemia or respiratory compliance. The empirical PEEP was 18 ± 1 cmH2O. The empirical PEEP significantly increased the PaO2/FiO2 but also driving pressure, lung elastance, lung stress and mechanical power compared to 15 cmH2O of PEEP. Conclusions In COVID-19 ARDS during the early phase the effects of raising PEEP are highly variable and cannot easily be predicted by respiratory system characteristics, because of the heterogeneity of the disease.

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