Hypoxemia is:

A. Bronchodilators are medications specifically designed to relax the muscles around the airways, making it easier to breathe by increasing airflow. They are commonly used in conditions like asthma and chronic obstructive pulmonary disease (COPD).
B. Doxycycline is an antibiotic used to treat bacterial infections. It has no direct effect on airway muscles or airflow.
C. ACE inhibitors are used primarily to treat high blood pressure and heart failure. They do not act on the airways and are not used to improve airflow.
D. Anti-androgen therapy is used to reduce levels of male hormones, typically in the treatment of prostate cancer or hormone-sensitive conditions. It has no role in bronchodilation or respiratory therapy.

A. Inability to breathe without dyspnea unless sitting upright refers to a postural issue that might be seen in certain respiratory conditions but does not describe Cheyne-Stokes respirations.
B. Shallow breathing alternating with periods of apnea is not characteristic of Cheyne-Stokes respirations. While apnea does occur, the breathing pattern is more varied in depth.
C. Cheyne-Stokes respirations are characterized by a periodic pattern where the depth of breathing alternates between very deep and very shallow breaths, followed by periods of apnea. This is often seen in end-of-life care and is associated with respiratory distress or certain neurological conditions.
D. Rapid respirations that are unusually deep and regular are more consistent with Kussmaul respirations, which are typically seen in conditions like metabolic acidosis, not Cheyne-Stokes.