Korean J Crit Care Med.  2017 May;32(2):174-181. 10.4266/kjccm.2016.00738.

Evaluation of Respiratory Dynamics in an Asymmetric Lung Compliance Model

• Yun SH
• Lee HJ
• Lee YH
• Park JC

• KMID: 2384042
• DOI: http://doi.org/10.4266/kjccm.2016.00738

Abstract

BACKGROUND
Unilateral lung hyperinflation develops in lungs with asymmetric compliance, which can lead to vital instability. The aim of this study was to investigate the respiratory dynamics and the effect of airway diameter on the distribution of tidal volume during mechanical ventilation in a lung model with asymmetric compliance.
METHODS
Three groups of lung models were designed to simulate lungs with a symmetric and asymmetric compliance. The lung model was composed of two test lungs, lung1 and lung2. The static compliance of lung1 in C15, C60, and C120 groups was manipulated to be 15, 60, and 120 ml/cmHâ‚‚O, respectively. Meanwhile, the static compliance of lung2 was fixed at 60 ml/cmHâ‚‚O. Respiratory variables were measured above (proximal measurement) and below (distal measurement) the model trachea. The lung model was mechanically ventilated, and the airway internal diameter (ID) was changed from 3 to 8 mm in 1-mm increments.
RESULTS
The mean ± standard deviation ratio of volumes distributed to each lung (VL1/VL2) in airway ID 3, 4, 5, 6, 7, and 8 were in order, 0.10 ± 0.05, 0.11 ± 0.03, 0.12 ± 0.02, 0.12 ± 0.02, 0.12 ± 0.02, and 0.12 ± 0.02 in the C15 group; 1.05 ± 0.16, 1.01 ± 0.09, 1.00 ± 0.07, 0.97 ± 0.09, 0.96 ± 0.06, and 0.97 ± 0.08 in the C60 group; and 1.46 ± 0.18, 3.06 ± 0.41, 3.72 ± 0.37, 3.78 ± 0.47, 3.77 ± 0.45, and 3.78 ± 0.60 in the C120 group. The positive end-expiratory pressure (PEEP) of lung1 was significantly increased at airway ID 3 mm (1.65 cmHâ‚‚O) in the C15 group; at ID 3, 4, and 5 mm (2.21, 1.06, and 0.95 cmHâ‚‚O) in the C60 group; and ID 3, 4, and 5 mm (2.92, 1.84, and 1.41 cmHâ‚‚O) in the C120 group, compared to ID 8 mm (P < 0.05).
CONCLUSIONS
In the C15 and C120 groups, the tidal volume was unevenly distributed to both lungs in a positive relationship with lung compliance. In the C120 group, the uneven distribution of tidal volume was improved when the airway ID was equal to or less than 4 mm, but a significant increase of PEEP was observed.

Keyword

airway obstruction; lung compliance; positive-pressure respiration, intrinsic; ventilation

MeSH Terms

Airway Obstruction
Compliance
Lung Compliance*
Lung*
Positive-Pressure Respiration
Positive-Pressure Respiration, Intrinsic
Respiration, Artificial
Tidal Volume
Trachea
Ventilation

Figure

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  Figure 1. Schematic diagram of the two-lung model. (A) Proximal measurement setting. (B) Distal measurement setting. a: spirometer; b: filter; c: endotracheal tube with an internal diameter of 8 mm; d: connector with a variable internal diameter ranging from 3 mm to 8 mm; e: breathing circuit.

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  Figure 2. Change of plateau pressure time in (A) C15, (B) C60, and (C) C120 groups. P1: start point of plateau pressure; P2: end point of plateau pressure; C15: static compliance of lung1 was manipulated as 15 ml/cmH2O; C60: static compliance of lung1 was manipulated as 60 ml/cmH2O; C120: static compliance of lung1 was manipulated as 120 ml/cmH2O. * P < 0.05 vs. proximal measurement.

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  Figure 3. Change of plateau pressure time at (A) proximal and (B) distal measurements during change of internal diameter. P1: start point of plateau pressure; P2: end point of plateau pressure; C15: static compliance of lung1 was manipulated as 15 ml/cmH2O; C60: static compliance of lung1 was manipulated as 60 ml/cmH2O; C120: static compliance of lung1 was manipulated as 120 ml/cmH2O. * P < 0.05 vs. airway internal diameter of 8 mm.

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  Figure 4. Distal measurements showing response of positive endexpiratory pressure according to internal diameter change. C15: static compliance of lung1 was manipulated as 15 ml/cmH2O; C60: static compliance of lung1 was manipulated as 60 ml/cmH2O; C120: static compliance of lung1 was manipulated as 120 ml/cmH2O. * P < 0.05 vs. airway internal diameter of 8 mm. Cross section area: internal diameter of 3, 4, 5, 6, 7 and 8 mm were measured to be 7.1, 12.6, 19.6, 28.3, 38.5, 50.3 mm2 respectively. † P < 0.05 vs. C60 group.

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  Figure 5. Flow-time curve of distal measurement in (A) C15, (B) C60, and (C) C120 groups. The area under the curve represents volume distributed to lung1. ID: internal diameter; C15: static compliance of lung1 was manipulated as 15 ml/cmH2O; C60: static compliance of lung1 was manipulated as 60 ml/cmH2O; C120: static compliance of lung1 was manipulated as 120 ml/cmH2O.

Reference

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