How does respiratory muscle weakness affect breathing?
The diaphragm is the key muscle for inspiration (breathing in). When it is weakened by polio, the work of breathing becomes harder, especially when a person is lying down. With each breath, the abdominal contents have to be pushed down, but when sitting upright, gravity assists the diaphragm by pulling the contents down. Polio survivors, especially those with scoliosis, compensate by breathing faster but more shallowly because they lack the muscle strength to stretch a stiff rib cage. They may also have smaller lung volumes that further reduce respiratory muscle efficiency and drastically increase the work of breathing. This can lead to underventilation and respiratory failure.
