The generation and function of microvesicles in blast injury
File(s)
Author(s)
Sharrock, Anna
Type
Thesis
Abstract
Blast is the most common mechanism of injury in combat casualties and these patients are more likely to develop multiorgan failure and coagulopathy and die than those injured by penetrating mechanisms. Anecdote suggests that the former group of patients are also more likely develop post-arterial repair thrombosis. Civilian trauma patients develop prothrombotic microvesicles (MV). The hypotheses were that:
1. Clinical outcomes following vascular reconstruction are worse in blast-injured than non-blast injured patients, that;
2. Procoagulant MV are generated from blast-activated vascular endothelium and that;
3. Blast-injured combat casualties have higher plasma procoagulant microvesicles than healthy controls or those with penetrating injuries.
To establish clinical outcomes, two national databases (JTTR, RCDM, UK and GWOT-VII, US Army Institute of Surgical Research and Joint Battlefield Health Institute, USA) were merged to provide admission (including mechanism of injury) intervention and outcome data from patients with lower limb arterial injuries sustained in Iraq and Afghanistan operational theatres. Overall, injuries were most frequently sustained due to explosive mechanisms, and autologous vein grafting was the most common method of arterial reconstruction. No evidence of a difference in mortality, arterial repair thrombosis or local infection could be found.
The vascular endothelium’s response to blast was assessed using In vivo (rat) and in vitro (human endothelial cell) shock tube blast models. Following exposure to a shock wave, human endothelial cells exhibited cytoskeletal reorganisation, and MV were visualised on confocal microscopy. MVs were counted and phenotyped using flow cytometry in both models, and were shown to increase in vivo at 3 and 24 h post 14 bar blast (p<0.05). The in vitro model revealed an insignificant MV rise 24 h post 6–8 bar blast, and more tissue factor activity as measured by calibrated automated thrombography at 24 h post 6 vs 2 bar blast (p<0.05). Platelet function was concurrently assessed by optical aggregometry within the in vivo model, which revealed diminished function 1 hr post blast compared to controls (p<0.05).
To address the final hypothesis, patients with blast injuries sustained during operations in Afghanistan in 2013 were compared with age and sex matched controls and patients with penetrating mechanisms of injury alone. Blood was drawn from patients on arrival in the Emergency Department, 45 and 90 minutes later, in intensive care, and during aeromedical repatriation to the UK. Plasma was processed for MV detection by flow cytology and calibrated automated thrombography. MVs were at their highest levels in early time points, whilst later time points and MV titres were similar. Tissue factor positive events increased 4.7 (p<0.01) and 4.4 (p<0.05) fold in blast vs control and penetrating groups respectively. Platelet microvesicles were most commonly identified MV lineage.
In summary prothrombotic microvesicles have been demonstrated in blast models in vivo and in vitro, and in a clinical setting. However no differences were detected in clinical outcomes (mortality, thrombosis, infection) following arterial injury by explosive versus penetrating mechanisms alone.
1. Clinical outcomes following vascular reconstruction are worse in blast-injured than non-blast injured patients, that;
2. Procoagulant MV are generated from blast-activated vascular endothelium and that;
3. Blast-injured combat casualties have higher plasma procoagulant microvesicles than healthy controls or those with penetrating injuries.
To establish clinical outcomes, two national databases (JTTR, RCDM, UK and GWOT-VII, US Army Institute of Surgical Research and Joint Battlefield Health Institute, USA) were merged to provide admission (including mechanism of injury) intervention and outcome data from patients with lower limb arterial injuries sustained in Iraq and Afghanistan operational theatres. Overall, injuries were most frequently sustained due to explosive mechanisms, and autologous vein grafting was the most common method of arterial reconstruction. No evidence of a difference in mortality, arterial repair thrombosis or local infection could be found.
The vascular endothelium’s response to blast was assessed using In vivo (rat) and in vitro (human endothelial cell) shock tube blast models. Following exposure to a shock wave, human endothelial cells exhibited cytoskeletal reorganisation, and MV were visualised on confocal microscopy. MVs were counted and phenotyped using flow cytometry in both models, and were shown to increase in vivo at 3 and 24 h post 14 bar blast (p<0.05). The in vitro model revealed an insignificant MV rise 24 h post 6–8 bar blast, and more tissue factor activity as measured by calibrated automated thrombography at 24 h post 6 vs 2 bar blast (p<0.05). Platelet function was concurrently assessed by optical aggregometry within the in vivo model, which revealed diminished function 1 hr post blast compared to controls (p<0.05).
To address the final hypothesis, patients with blast injuries sustained during operations in Afghanistan in 2013 were compared with age and sex matched controls and patients with penetrating mechanisms of injury alone. Blood was drawn from patients on arrival in the Emergency Department, 45 and 90 minutes later, in intensive care, and during aeromedical repatriation to the UK. Plasma was processed for MV detection by flow cytology and calibrated automated thrombography. MVs were at their highest levels in early time points, whilst later time points and MV titres were similar. Tissue factor positive events increased 4.7 (p<0.01) and 4.4 (p<0.05) fold in blast vs control and penetrating groups respectively. Platelet microvesicles were most commonly identified MV lineage.
In summary prothrombotic microvesicles have been demonstrated in blast models in vivo and in vitro, and in a clinical setting. However no differences were detected in clinical outcomes (mortality, thrombosis, infection) following arterial injury by explosive versus penetrating mechanisms alone.
Version
Open Access
Date Issued
2018-12
Date Awarded
2019-05
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Rankin, Sara
Sponsor
Drummond Foundation
University Hospitals Birmingham NHS Foundation Trust
Royal British Legion
Publisher Department
The Royal British Legion Centre for Blast Injury Studies and The National Heart and Lung Institute
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Medicine (Research) MD (Res)