Lungs and hypoxia: a review of the literature

Abstract

Acute, intermittent or chronic hypoxia have negative effects on lung maturation during the embryological period which has been shown by many experimental models designed on animal studies. The receptors responsible from the development of lungs in fetal period are affected from hypoxia. Hypoxia also affects the morphometry, anatomy and microscopy of lung tissue in the adults. In acute phase of hypoxia; lung parenchyma showed destructive oxidative changes. However, in later phases repair and proliferative processes were observed in the lung tissue. Damage to the lining layer of alveoli, accumulation of alveolar macrophages, oedematous changes in the lung parenchyma, mild oedema, inflammatory cell infiltration, increased number of type II pneumocytes and pulmonary fibrosis are the main findings in cases of hypoxia. Chronic hypoxia accentuates lung growth by increasing the lung parenchyma. Decrease of capillary volume and suppression of elastin repair in lung fibroblasts are other clinically important microscopic findings in hypoxia. Many molecular studies found in the literature revealed micro-RNAs to be involved in modulation of hypoxia-induced pulmonary hypertension. In animal models submitted to acute hypobaric hypoxia; the researchers detected an increase in eNOS mRNA which is responsible of the immediate response, producing nitric oxide that caused vasodilation and bronchodilation in lung tissue. In other molecular studies; suppression of many immune molecules, major changes at the levels of various enzymes and growth factors were detected in the researches. Additionally; hypoxia causes to an increase in the amount of lung cancer cells and therefore; induces the metastases of lung cancer cells to brain tissues.