The most likely culprit in this scenario is the respiratory system. Low blood oxygen levels can indicate that the lungs are not efficiently exchanging oxygen and carbon dioxide, leading to inadequate oxygen levels in the bloodstream. This could be caused by conditions such as asthma, chronic obstructive pulmonary disease (COPD), pneumonia, or respiratory muscle weakness. Additional tests and evaluations would be needed to determine the specific cause of the low blood oxygen levels and appropriate treatment.
