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New Lung Tissue Growth Discovered: Is Some Lung Regeneration Possible?
Lung regeneration has never been thought possible in adults. But Steven Mentzer et al from Brigham and Women's at Harvard reported a case of a 33 year old woman who had an apparent 64% increase in the number of functioning alveoli in her left lung, during 15 year follow-up after a right pneumonectomy in 1995 for adenocarcinoma (despite her young age, she had a 30+ pack-year smoking history).
Although existing lung parenchymal tissue was known to expand after lung resection, in adults this was thought to occur through dilation of existing alveoli and supporting tissues, not de novo growth of new alveoli. However, experiments in dogs suggested lung regeneration was possible, and so researchers turned their attention to closely following this patient and her lung function after her surgery.
The woman described had an initial FEV1 of 35% and FVC of 49% after pneumonectomy. But for 15 years, steady improvements in her spirometry resulted in a final FEV1 of 60% and FVC of 73%. (According to expectations, she should have had about a 10% decline over 15 years, due to aging.) Her left lung grew larger and larger on annual surveillance CT scans, partially herniating into the right hemithorax.
The authors used experimental MRI scan techniques (diffusion of inhaled hyperpolarized helium-3 gas) to determine alveolar dimensions. Larger alveoli look different than smaller alveoli with this technique, owing to differences in "clumping" of concentrated gas molecules.
The authors speculated that the woman's young age at the time of surgery and active lifestyle with vigorous exercise including cycling, walking, and yoga in the years following surgery may have contributed to the growth of lung tissue, saying:
"We hypothesize that, reminiscent of the role of stretch in lung development, cyclic stretch as such may be an important trigger for new lung growth. Regardless of the specific mechanism, the findings in this patient support the concept that new lung growth can occur in adult humans."
James P. Butler et al. Evidence for Adult Lung Growth in Humans. NEJM 2012; 367:244-247.