Robert H Brown, Robert A Wise, Kirk Gregory, Drummond M Bradley, Mitzner Wayne
Department of Anesthesiology, Johns Hopkins University, Baltimore, MD; Department of Medicine, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD; Environmental Health Sciences, Division of Physiology, Johns Hopkins University, Baltimore, MD.
Department of Medicine, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD.
Chest. 2015 Oct;148(4):995-1002. doi: 10.1378/chest.15-0264.
With body growth from childhood, the lungs can enlarge by either increasing the volume of air in the periphery (as would occur with inspiration) or by increasing the number of peripheral acinar units. In the former case, the lung tissue density would decrease with inflation, whereas in the latter case, the lung density would be relatively constant as the lung grows. To address this fundamental structural issue, we measured the CT scan density in human subjects of widely varying size at two different lung volumes.
Five hundred one subjects were enrolled in the study. They underwent a chest CT scan at full inspiration and another scan at end expiration. Spirometry, body plethysmography, and diffusing capacity of the lung for carbon monoxide were also measured.
There was a strong correlation between the size of the lungs measured at full inspiration on CT scan and the mean lung density (r = -0.72, P = .001). People with larger lungs had significantly lower mean lung density. These density changes among different subjects overlapped the density changes within subjects at different lung volumes.
Lung structure in subjects with larger lungs is different from that in subjects with smaller lungs. Tissue volume does not increase in proportion to lung size, as would be required if larger lungs just had more alveoli. These observations suggest that the growth of the lung into adulthood is not accompanied by new alveoli, but rather by enlargement of existing structures. The presence of greater air spaces in larger lungs could impact the occurrence and pathogenesis of spontaneous pneumothorax or COPD.
随着儿童时期身体的生长，肺部可以通过增加外周空气量（如吸气时那样）或增加外周腺泡单位数量来扩大。在前一种情况下，肺组织密度会随着充气而降低，而在后一种情况下，随着肺的生长，肺密度会相对恒定。为了解决这个基本的结构问题，我们在两个不同的肺容积下测量了不同体型人类受试者的CT扫描密度。
501名受试者参与了该研究。他们在深吸气时进行了胸部CT扫描，并在呼气末进行了另一次扫描。还测量了肺活量、体容积描记法和肺一氧化碳弥散量。
CT扫描在深吸气时测量的肺大小与平均肺密度之间存在很强的相关性（r = -0.72，P = 0.001）。肺较大的人平均肺密度显著较低。不同受试者之间的这些密度变化与同一受试者在不同肺容积下的密度变化重叠。
肺较大的受试者的肺结构与肺较小的受试者不同。组织体积并不与肺大小成比例增加，而如果较大的肺仅仅有更多肺泡则会需要这种比例增加。这些观察结果表明，肺生长到成年期并非伴随着新肺泡的产生，而是现有结构的扩大。较大肺中存在更大的气腔可能会影响自发性气胸或慢性阻塞性肺疾病（COPD）的发生和发病机制。
