BCSE Practice Exam 2026 – Complete Study Resource

The normal alveolar-arterial (Aa) gradient typically falls within the range of 5 to 15 mmHg in healthy individuals, with many references citing around 10 mmHg as a standard value. This gradient is a measure of the difference between the oxygen concentration in the alveoli and that in the arterial blood, which reflects the efficiency of gas exchange in the lungs.

A gradient of around 10 mmHg indicates that oxygen transfer from the alveoli into the bloodstream is functioning well, and that the individual does not have significant ventilation-perfusion mismatches or diffusion impairments. An increasing Aa gradient can suggest problems such as shunting, diffusion defects, or hypoventilation, which can lead to insufficient oxygenation.

While values can vary with age and other physiological factors, a gradient of approximately 10 mmHg is widely recognized in clinical practice and textbooks as being indicative of normal lung function.