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Ann Thorac Surg 1997;64:808
© 1997 The Society of Thoracic Surgeons
DR THOMAS M. EGAN (Chapel Hill, NC): That was a very nice study, and it adds to the body of literature supporting the hypothesis that lungs may be useful for transplantation even at intervals after death. I am a little curious about the group of lungs that were fully deflated. I gather from your manuscript that these lungs were deflated because, as part of the preparation, you opened both pleural spaces. I wonder if another control group might have been useful as well, that is, lungs maintained at functional residual capacity, because a fully deflated lung does not really mimic the clinical scenario of a cadaver unless the body dies of bilateral stab wounds to the chest. Do you think there would have been any difference had you studied lungs in a noninflated state, but lungs that were allowed to maintain volume at functional residual capacity?
As I have said, this was an interesting study. It does suffer from one serious limitation, and that is that the duration of your perfusion was relatively short, and no gas exchange data could be accrued.
DR VAN RAEMDONCK: Thank you, Dr Egan, for your kind remarks. It is well appreciated that your group has revived interest in the use of lungs from non–heart-beating donors.
In regard to your first question about the group with deflated lungs, it is true that the lungs were deflated because we opened both pleural spaces after sternotomy. We started doing these experiments by killing the animals with an overdose of pentobarbital, and we observed that even in the control animals without any ischemia, we had a massive amount of lung edema. That is why we started to look for another method to kill the rabbits.
Indeed, these lungs were not at functional residual capacity but below functional residual capacity. Before sacrifice, the lungs were ventilated with room air; as you know, room air is a gas mixture of 21% oxygen and 79% nitrogen. These lungs will not become fully deflated to the complete zero level as nitrogen will not be absorbed. But indeed, as you suggested, we should study another group of animals with lungs at functional residual capacity.
In regard to your second comment, we studied a relatively gross estimate of lung function during a very short period; the Flush was only 5 minutes. Gas exchange after reperfusion with deoxygenated blood is probably the most reliable variable to study the quality of lung preservation and can distinguish between well-preserved and poorly preserved lungs. We first used these flush experiments as a screening model to rapidly define the length of tolerable warm ischemia in all study groups. We have now extended these rabbit experiments in an isolated, pressure-limited, and homologous deoxygenated blood reperfusion and room air–ventilated model using the same study groups.
After an ischemic period of 4 hours, we compared lungs that were deflated versus lungs that were inflated with room air and lungs ventilated with room air, and we looked at oxygenation capacity, defined as the arteriovenous oxygen pressure gradient. During a reperfusion period of 4 hours, there was a highly significant difference in oxygenation capacity between the lungs that were inflated with room air and ventilated with room air versus the deflated lungs.
Also, the wet to dry weight ratio in the deflated lungs after 4 hours of reperfusion with homologous blood was significantly higher than in the lungs inflated with room air and those ventilated with room air. However, there was no significant difference in oxygenation capacity between the group ventilated with room air and the group ventilated with nitrogen, nor was there a difference in wet to dry weight ratio between these same two groups. We think this study confirms the conclusion of our present study that alveolar expansion itself, not continued oxygen supply, represents a functional advantage in postmortem lung preservation.
Related Article
Ann. Thorac. Surg. 1997 64: 801-808.
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