The thorax provides physiological protection to the thoracic organs and also provides a platform for the respiratory muscles to function as a continuous “respiratory pump”. The respiratory muscles expand the thorax to create a negative pressure in the pleural cavity, which is the actual driving force for breathing. Therefore, any structural or functional abnormality of the chest wall can potentially affect respiration and thoracic organs significantly. 1. Effects on lung development and airway function Some studies have reported reduced lung volumes in patients with funnel chest, suggesting the presence of restrictive lung defects. It has been hypothesized that this restriction is the result of irregular and narrow thoracic shape, which prevents normal lung growth and development. However, recent studies have shown that although there is some reduction in spirometry, it is still within the normal range. More importantly, lung function performance varies widely from patient to patient. According to a recent study, 54% of patients had normal spirometry and airway function, while 41% had airway obstruction manifestations and only 5% had restrictive effects. Completely normal lung function was seen mainly in children <9 years of age. Conversely, the incidence of airway obstruction and restriction increases with the age of the child. Rapid lung growth and development occurs mainly in the first years of life, so it can be assumed that funnel chest has little effect on lung growth and development. A surprising finding is the increase in residual lung air volume and total residual ratio in patients with funnel chest, which suggests the presence of airflow limitation. Interestingly, airflow expiratory limitation is not only present in patients with manifestations of airway obstruction, but also in patients with normal lung function and airway limitation. Since patients with funnel chest have increased residual volume with concomitant decreased spirometry, there is often a decrease in exertional spirometry that may be due to restricted airflow expiration rather than the generally presumed restricted lung growth and development. 2. Effects on cardiovascular system function The sternal recess significantly reduces the anterior and posterior diameter of the thorax. This alteration impedes the diastole of the heart, and to some extent limits the increase in beat-to-beat output to meet the demands of increased metabolism (e.g., physical activity). Cardiac displacement and possible transposition of the great vessels may further lead to complications of the cardiovascular system. 3. Effects on the spine The thorax consists of the sternum in front, the thoracic vertebrae in the back, and the ribs that connect the two. The ribs are connected to the sternum and thoracic vertebrae by joints, allowing a certain degree of freedom of movement during the respiratory cycle. The depressed sternum limits the movement of the ribs, especially the low ribs, which prevents horizontal expansion of the lower thorax, and the thorax may only move longitudinally. In addition, due to the asymmetric depression of the sternum, the ribs exert a certain pressure on the spine, which may eventually lead to vertebral body displacement and thus scoliosis. 4.Impact on respiratory muscles The rib cage is covered by the internal and external intercostal muscles, which are separated from the abdominal cavity by the diaphragm. Although funnel chest does not directly affect any respiratory muscle group, the twisted deformation of the rib cage and the possible presence of abdominal protrusion cause a decrease in the mechanical movement of the thorax, which is manifested by a significant decrease in the maximum inspiratory pressure and maximum expiratory pressure (MIP and MEP). This respiratory muscle strength and function abnormality could explain the high incidence of increased residual gross ratio in patients with funnel chest. Although the general respiratory strength reduction is not severe, the reduction in thoracic compliance makes normal lung expansion require higher than normal pressures, so these effects may be much more complex. Therefore, reduced lung volume may be the result of impaired thoracic mechanomotor function rather than impaired lung development.