Generally, normal oxygen levels in humans range from 95 to 100 percent, and less than 90 percent is considered low, according to Mayo Clinic. A low blood oxygen level, called hypoxemia, can cause shortness of breath. Arterial blood samples or readings from a pulse oximeter reveal blood oxygen levels.
Causes of hypoxemia include chronic obstructive pulmonary disease, blocked air passages, pneumonia, sleep apnea and narcotics, notes Mayo Clinic. Individuals with COPD benefit from oxygen treatments using equipment delivery systems such as liquid oxygen devices, oxygen concentrators and oxygen-gas cylinders, according to WebMD. By increasing the amount of oxygen that flows through the bloodstream and the lungs, the treatments improve a person's breathing capacity.