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Stress distribution in a three dimensional, geometric alveolar sac under normal and emphysematous conditions.

de Ryk J, Thiesse J, Namati E, McLennan G - Int J Chron Obstruct Pulmon Dis (2007)

Bottom Line: Using the model numerical analysis of the stress distribution in normal conditions could be compared with those resulting in emphysematous conditions.When internal alveolar pressure was increased along with the adjustment of the material properties to represent a weakening of one wall in the acinus, increased stress resulted at the perimeters of the weakened area.It was also found that under the proposed simulated emphysematous conditions, a significant disruption in the stress distribution within the acinus model occurred at low, rather than high, lung volumes.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA.

ABSTRACT
Pulmonary emphysema is usually the result of chronic exposure to cigarette smoke in at risk individuals. To investigate the hypothesis that lung damage in emphysema results from coincident weakening in the structural properties of the tissue and increased mechanical forces--as one explanation of the continued development of pulmonary emphysema after smoking cessation--we developed a three dimensional, geometric dodecahedron-based acinar model. Using the model numerical analysis of the stress distribution in normal conditions could be compared with those resulting in emphysematous conditions. Finite element analysis was used to evaluate the model at a number of lung inflation levels, using quasi-static loading of the alveolar pressure. When internal alveolar pressure was increased along with the adjustment of the material properties to represent a weakening of one wall in the acinus, increased stress resulted at the perimeters of the weakened area. In particular this increased stress was localized at the junction points of the internal alveolar septa. It was also found that under the proposed simulated emphysematous conditions, a significant disruption in the stress distribution within the acinus model occurred at low, rather than high, lung volumes. This is supportive of the physiological observation that destruction of the diseased tissue can occur under less stress than those existing in the normal state.

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Related in: MedlinePlus

The stress distributions for the emphysematous alveolar sac models at two different lung volumes. A single area of the alveolar sac has the emphysematous material properties applied as highlighted in the figure. The low lung volume (A) and the high lung volume (B) reveal very different stress distributions. Specifically, very high stress levels are induced in the emphysematous area and the airway inlet at the low lung volume.Abbreviations: TLC, total lung capacity.
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f4-copd-2-81: The stress distributions for the emphysematous alveolar sac models at two different lung volumes. A single area of the alveolar sac has the emphysematous material properties applied as highlighted in the figure. The low lung volume (A) and the high lung volume (B) reveal very different stress distributions. Specifically, very high stress levels are induced in the emphysematous area and the airway inlet at the low lung volume.Abbreviations: TLC, total lung capacity.

Mentions: While the pattern of stress distribution for the normal alveolar sac appears to remain unchanged from 40% to 100% TLC, the value of the stress within the model does increase. It appears as though the magnitude of stress in the normal alveolar sac changes at different lung volumes while the stress distribution remains relatively constant (Figure 3). However, the emphysematous alveolar sac contour plots demonstrate the drastic disruption in the stress distribution induced through the mimicking of emphysema in one alveolar wall accompanied by a slight elevation in internal alveolar pressure (Figure 4). The single rhombic area to which the simulated emphysematous material properties were applied is labled in Figure 4. At 40% TLC the irratic stress pattern is more evident than at 100% TLC. At low lung volumes the Young’s modulus of the tissue is small (2 kPa) and extremely small in the alveolar wall modelled as having emphysematous properties (90 Pa). These relatively small Young’s moduli make the tissue less capable of withstanding the increased internal alveolar pressure than the stronger tissue at higher lung volumes, resulting in nontypical stress distributions. This observation is in support of the work conducted by Kononov and colleagues (2001) which indicate that the combination of weakening in the strucutral properties of the tissue along with increased mechanical forces can cause the tissue to breakdown under stresses less than those observed in the normal physiological state.


Stress distribution in a three dimensional, geometric alveolar sac under normal and emphysematous conditions.

de Ryk J, Thiesse J, Namati E, McLennan G - Int J Chron Obstruct Pulmon Dis (2007)

The stress distributions for the emphysematous alveolar sac models at two different lung volumes. A single area of the alveolar sac has the emphysematous material properties applied as highlighted in the figure. The low lung volume (A) and the high lung volume (B) reveal very different stress distributions. Specifically, very high stress levels are induced in the emphysematous area and the airway inlet at the low lung volume.Abbreviations: TLC, total lung capacity.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2692121&req=5

f4-copd-2-81: The stress distributions for the emphysematous alveolar sac models at two different lung volumes. A single area of the alveolar sac has the emphysematous material properties applied as highlighted in the figure. The low lung volume (A) and the high lung volume (B) reveal very different stress distributions. Specifically, very high stress levels are induced in the emphysematous area and the airway inlet at the low lung volume.Abbreviations: TLC, total lung capacity.
Mentions: While the pattern of stress distribution for the normal alveolar sac appears to remain unchanged from 40% to 100% TLC, the value of the stress within the model does increase. It appears as though the magnitude of stress in the normal alveolar sac changes at different lung volumes while the stress distribution remains relatively constant (Figure 3). However, the emphysematous alveolar sac contour plots demonstrate the drastic disruption in the stress distribution induced through the mimicking of emphysema in one alveolar wall accompanied by a slight elevation in internal alveolar pressure (Figure 4). The single rhombic area to which the simulated emphysematous material properties were applied is labled in Figure 4. At 40% TLC the irratic stress pattern is more evident than at 100% TLC. At low lung volumes the Young’s modulus of the tissue is small (2 kPa) and extremely small in the alveolar wall modelled as having emphysematous properties (90 Pa). These relatively small Young’s moduli make the tissue less capable of withstanding the increased internal alveolar pressure than the stronger tissue at higher lung volumes, resulting in nontypical stress distributions. This observation is in support of the work conducted by Kononov and colleagues (2001) which indicate that the combination of weakening in the strucutral properties of the tissue along with increased mechanical forces can cause the tissue to breakdown under stresses less than those observed in the normal physiological state.

Bottom Line: Using the model numerical analysis of the stress distribution in normal conditions could be compared with those resulting in emphysematous conditions.When internal alveolar pressure was increased along with the adjustment of the material properties to represent a weakening of one wall in the acinus, increased stress resulted at the perimeters of the weakened area.It was also found that under the proposed simulated emphysematous conditions, a significant disruption in the stress distribution within the acinus model occurred at low, rather than high, lung volumes.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA.

ABSTRACT
Pulmonary emphysema is usually the result of chronic exposure to cigarette smoke in at risk individuals. To investigate the hypothesis that lung damage in emphysema results from coincident weakening in the structural properties of the tissue and increased mechanical forces--as one explanation of the continued development of pulmonary emphysema after smoking cessation--we developed a three dimensional, geometric dodecahedron-based acinar model. Using the model numerical analysis of the stress distribution in normal conditions could be compared with those resulting in emphysematous conditions. Finite element analysis was used to evaluate the model at a number of lung inflation levels, using quasi-static loading of the alveolar pressure. When internal alveolar pressure was increased along with the adjustment of the material properties to represent a weakening of one wall in the acinus, increased stress resulted at the perimeters of the weakened area. In particular this increased stress was localized at the junction points of the internal alveolar septa. It was also found that under the proposed simulated emphysematous conditions, a significant disruption in the stress distribution within the acinus model occurred at low, rather than high, lung volumes. This is supportive of the physiological observation that destruction of the diseased tissue can occur under less stress than those existing in the normal state.

Show MeSH
Related in: MedlinePlus