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Fetal lung growth requires distension, supported by reduced thoracic volume causing pulmonary hypoplasia. Impaired fetal breathing movements also suggest growth depends on both tonic and phasic forces.
Area of Science:
- Developmental biology
- Fetal development
- Pulmonary medicine
Background:
- Pulmonary hypoplasia is consistently observed when fetal thoracic volume is reduced by congenital or acquired disorders.
- Reduced thoracic volume supports the hypothesis that fetal lung distension is crucial for normal lung growth.
- Many disorders causing reduced thoracic volume also impair fetal breathing movements, indicating growth depends on both tonic and phasic forces.
Purpose of the Study:
- To investigate the role of fetal lung distension and breathing movements in normal lung growth.
- To test the hypothesis that lung distension is necessary for pulmonary development.
Main Methods:
- Review of conditions causing reduced thoracic volume and pulmonary hypoplasia.
- Analysis of the impact of impaired fetal breathing movements on lung growth.
- Examination of animal experiments involving obstruction or facilitation of lung fluid outflow.
- Assessment of the effects of interrupting breathing movements via upper motor neurone lesions.
Main Results:
- Reduced thoracic volume consistently leads to pulmonary hypoplasia, supporting the lung distension hypothesis.
- Impaired fetal breathing movements are associated with lung hypoplasia, suggesting dependence on phasic and tonic forces.
- Animal experiments obstructing lung fluid outflow were inconclusive.
- Interrupting fetal breathing movements through upper motor neurone lesions, while preserving diaphragmatic tone, resulted in lung hypoplasia.
- Breathing episodes may distend lungs by retaining fluid; individual breaths can redistribute lung fluid.
Conclusions:
- Fetal lung distension is necessary for normal lung growth.
- Both tonic and phasic forces, mediated by fetal breathing movements, are important for lung development.
- Further research is needed to clarify the role of lung fluid dynamics in fetal lung growth.
Abstract:
Pulmonary hypoplasia occurs consistently when thoracic volume is reduced by any of a variety of congenital and acquired disorders and supports the hypothesis that distension of the fetal lung is necessary for normal growth. Many of these disorders also impair fetal breathing movements suggesting that growth is dependent on phasic as well as tonic forces. Results of animal experiments to test the hypothesis by obstructing or facilitating outflow of lung fluid are inconclusive but interrupting breathing movements by upper motor neurone lesions that preserve diaphragmatic tone causes hypoplasia. Episodes of breathing may distend the lungs by retaining secreted lung fluid while single breaths may redistribute fluid within the lungs.