Low oxygen in the blood is medically termed hypoxia and symptoms include:
•Shortness of breath (dyspnea)
•Increased blood pressure
•Rapid heart rate (tachycardia)
•A bluish discoloration of the skin, lips and/or nail beds (cyanosis)
Does your friend have any of the above listed symptoms?
There can be chronic obstructive pulmonary disease (COPD), is a lung disease that causes a blockage or narrowing of the airways, the tubes in your lungs that air flows through. This results in a decrease in the flow of air, both in and out of your lungs. The disease has a slow, progressive course and is irreversible. Need to rule out or treat...its a serious medical condition.
•Breathlessness with any type of activity
•Increase in sputum production
•Frequent chest infections
Does your friend have any of shown symptoms? I had hypoxia, and it was heart related. When it is heart related hypoxia results from blood backing up into the lungs and inhibits the lung's ability to obtain enough oxygen. This results in excessive dry coughing and a feeling of not getting enough air to breath and choking sensation.
Unfortunately you know too little information for anyone to give a response. Usually when Oxygen saturation is that low it's caused by a Lung problem, pneumonia or fluid in the lungs. A ventilating machine can push air into the lungs at a greater pressure than the patient can and gives them a huge chance of recovery. When a patient is laying down and relaxed, the heart doesn't have to work very hard at all to get enough oxygen to the brain and this is why I think its more likely the lungs. Are you sure its the heart?