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Pulmonary microembolism: a cause of lung injury
S L Beal1, R L Reed, D Heimbach
1Department of Surgery, University of Washington School of Medicine.
Abstract:
Microthrombi found in the pulmonary capillaries in patients dying with post-traumatic pulmonary insufficiency suggests that pulmonary microembolism (PME) may be etiologically important, but a temporal relationship has not been demonstrated. We used a modified Lim-Blaisdell model of PME to cause a severe ischemic soft tissue injury in dogs. The appearance of microaggregates (MA) in the venous circulation was measured using a laser optical scanning technique. The effect of MA on pulmonary physiologic and histologic parameters was measured and compared to control animals. In the ischemic soft tissue injury group, following restoration of local circulation, the platelet count dropped by 72% (P less than 0.00002), the number of MA increased by 800% (P less than 0.00002), the mean pulmonary artery pressure (PA) increased from 15.6 to 32 mm Hg (P less than 0.00002), and electron micrographs of lung obtained at 4 hr after ischemic insult revealed PM with severe lung injury that was consistent with a capillary membrane leak. The control group never demonstrated a significant change in platelets, MA, PA, or histologic lung injury. These findings imply that MA found in the pulmonary microcirculation are temporally related to the development of physiologic and anatomic lung abnormalities.
Insights
Severe soft tissue injury causes microaggregates, leading to increased pulmonary artery pressure and lung injury. This study demonstrates a temporal link between microaggregates and lung abnormalities in post-traumatic pulmonary insufficiency.
Area of Science:
- Trauma and Injury Research
- Pulmonary Medicine
- Vascular Biology
Background:
- Post-traumatic pulmonary insufficiency is linked to microthrombi in pulmonary capillaries.
- The direct temporal relationship between microembolism and lung injury remains unclear.
Purpose of the Study:
- To investigate the temporal relationship between microaggregate formation and pulmonary dysfunction following ischemic soft tissue injury.
- To establish a causal link between microembolism and lung injury in a canine model.
Main Methods:
- A modified Lim-Blaisdell model was used to induce severe ischemic soft tissue injury in dogs.
- Laser optical scanning measured microaggregate (MA) appearance in venous circulation.
- Pulmonary physiologic and histologic parameters were assessed and compared to controls.
Main Results:
- Ischemic injury led to a 72% drop in platelets and an 800% increase in MA (P < 0.00002).
- Mean pulmonary artery pressure increased significantly (15.6 to 32 mm Hg, P < 0.00002).
- Lung histology revealed severe injury consistent with capillary membrane leak.
Conclusions:
- Microaggregates in the pulmonary microcirculation are temporally related to lung abnormalities.
- This study provides evidence for microembolism as a key factor in post-traumatic pulmonary insufficiency.