A longer tube would not allow breathing when snorkelling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher. The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.[4] The pressure difference across the tissues in the lungs, between the blood capillaries and air spaces would increase the risk of pulmonary edema.[citation needed]