USMLE Step 1 Respiratory Physiology Review 60 12 Partial Pressures

# USMLE Step 1 Respiratory Physiology Review 60 12 Partial Pressures

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### Begin 60 12 Partial Pressures Transcription

Moving now to gas transport. In order to understand oxygen and carbon dioxide transport in the blood, we have to talk about partial pressure because partial pressure is what gets the gases into the blood in the first place.

The partial pressure of each gas in a mixture of gases is the pressure it would exert if the other gases weren’t present. This is a restatement of whose law?

•  Dalton’s Law.

How is the partial pressure of a particular gas in a mixture calculated?

•  Multiply the total pressure of the mixture times percent concentration of the gas.

What percent of the atmosphere is oxygen?

• The atmosphere is 21% oxygen.

What is atmospheric pressure at sea level?

• Atmospheric pressure at sea level is 760 millimeters of Mercury (mm Hg).

How do you calculate the PO2 or partial pressure of oxygen in ambient air at sea level?

•  You multiply the total pressure, which is 760 mm Hg, by the fractional concentration of oxygen, which is 21%.

What is the resulting partial pressure of oxygen for ambient air?

Another word for partial pressure is tension. Ambient air is about 79% nitrogen. What is the nitrogen tension in the ambient air at sea level?

What is carbon dioxide tension in ambient air?

• The partial pressure of carbon dioxide in ambient air is basically zero.

Student doctor please pause the tape and summarize what has been discussed about partial pressure.

• Dalton’s law states that the partial pressure of each gas in a mixture of gases equals the pressure it would exert if the other gases weren’t present. To calculate the partial pressure of a particular gas in a mixture, multiple total pressure of the mixture times percent concentration of the gas. The atmosphere is 21% oxygen. Atmospheric pressure at sea level  is 760 mm Hg. To calculate the partial pressure of oxygen in ambient air at sea level you multiply the total pressure, which is 760 mm Hg, by the fractional concentration of oxygen, which is 21%. The resulting PO2, or partial pressure of oxygen, for ambient air is 160 mm Hg. Another word for partial pressure is tension. Ambient air is about 79% nitrogen. Nitrogen tension in ambient air at sea level is about 600 mm Hg. The partial pressure of carbon dioxide in the ambient air is basically zero.

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