Alveolar Arterial Gradient Calculator

The Alveolar Arterial (A-a) Gradient is a measure used in medicine, particularly in pulmonology and critical care, to understand the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen. This gradient is often used to assess whether the body is properly oxygenating the blood in the lungs. This tutorial provides an in-depth look at the A-a Gradient, its calculations, intriguing facts, and relevance in different fields, with real-life examples and notable contributors to its development.

Alveolar Arterial Gradient Calculator
Patients Age
Fraction of Inspired Oxygen(FiO2) %
Atmospheric Pressure(Patm) mmHg
Water vapor pressure(PH2O) mmHg
Partial pressure of arterial CO2(PaCO2) mmHg
Respiratory quotient (RQ)
Partial pressure of arterial O2(PaO2)
Alveolar Arterial Gradient Calculator Results
A-a Gradient mmHg
Estimated Normal Gradient mmHg

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Interestingly, the A-a Gradient increases with age. Under normal conditions, the gradient should be less than 10-15 mmHg. However, an elevated A-a Gradient suggests that there may be a problem with oxygen transfer between the alveoli and the blood.

The formula for calculating the A-a Gradient is as follows:

A-a Gradient = PAO2 - PaO2


PAO2 (Alveolar O2) = FiO2 (PB - PH2O) - (PaCO2 / R)

And FiO2 is the fraction of inspired oxygen, PB is the barometric pressure, PH2O is the water vapor pressure, PaCO2 is the arterial CO2 pressure, and R is the respiratory quotient.

Beyond healthcare, this concept is relevant in biomedical research, sports science, and any other field concerned with human physiological performance, such as high-altitude mountaineering and professional sports, where efficient oxygen utilization is paramount.

A real-life example could be a patient in an intensive care unit with respiratory distress. The A-a gradient can help determine whether the patient's lungs are effectively oxygenating the blood, thus informing the need for interventions like supplemental oxygen or ventilation support.

A significant contributor to our understanding of oxygen transport and utilization, including concepts like the A-a gradient, is Dr. John B. West. He extensively researched the effects of extreme altitude on human physiology, leading to advancements in critical care and pulmonary medicine.

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Please note that the Alveolar Arterial Gradient Calculator is provided for your personal use and designed to provide information and information relating to the calculations only. The Alveolar Arterial Gradient Calculator should not be used for you to self-diagnose conditions, self-medicate or alter any existing medication that you are currently prescribed by your Doctor. If the Alveolar Arterial Gradient Calculator produces a calculation which causes you concern, please consult your Doctor for support, advice and further information.