The Diffusion of Pulmonary Gases

Flashcards covering key concepts from Chapter 4, 'The Diffusion of Pulmonary Gases,' including Dalton's Law, partial pressures, gas gradients, the Ideal Alveolar Gas Equation, Fick's Law, and perfusion-limited gas flow.

Dalton's Law of Partial Pressures

States that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted independently by each gas in the mixture. The partial pressure of each gas is directly proportional to its percentage in the gas mixture.

Atmospheric Oxygen Partial Pressure (PO2) at Sea Level

Approximately 159.6 mmHg, calculated as 0.21 (21%) multiplied by normal barometric pressure (760 mmHg).

Effect of Altitude on Atmospheric Gases

As altitude increases, atmospheric pressure and the partial pressure exerted by each gas decrease, while the concentration (percentage) of atmospheric gases remains the same.

Effect of Descent Below Sea Level on Atmospheric Gases

Atmospheric pressure increases by 1 atmosphere (760 mmHg) for each 33 feet of descent below sea level, leading to an increase in the partial pressure exerted by each gas.

Pressure Gradient (Ventilation)

The movement of a mass of gas (e.g., air) from an area of high pressure to an area of low pressure, responsible for moving air in and out of the lungs.

Gas Diffusion Gradient

The movement of individual gas molecules from an area of high partial pressure (high concentration) to an area of low partial pressure (low concentration), independent of other gases.

Ideal Alveolar Gas Equation

A formula used clinically to compute alveolar oxygen tension (PAO2), considering barometric pressure, water vapor pressure, inspired oxygen fraction (FIO2), and arterial carbon dioxide partial pressure (PaCO2).

Fick's Law of Gas Diffusion

Describes the rate of gas diffusion across a membrane, influenced by the surface area, the difference in partial pressures, and inversely by the thickness of the membrane.

Fick's Law: Area (A) Component

Relates to the alveolar surface area; a decrease (e.g., from alveolar collapse or fluid) reduces oxygen's ability to enter pulmonary capillary blood.

Fick's Law: P1-P2 (Partial Pressure Difference) Component

Relates to the difference in partial pressures; a decreased alveolar oxygen pressure (PAO2), e.g., from high altitudes or hypoventilation, reduces oxygen diffusion into capillary blood.

Fick's Law: Thickness (T) Component

Relates to the alveolar tissue thickness; an increase (e.g., from alveolar fibrosis or edema) reduces the movement of oxygen across alveolar-capillary membranes.

Perfusion Limited Gas Flow

A condition where the transfer of gas across the alveolar wall is primarily a function of the amount of blood that flows past the alveoli.

Dalton's Law of Partial Pressures

States that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted independently by each gas in the mixture.

Partial Pressure

The pressure exerted by each individual gas in a mixture, directly proportional to its percentage in the total gas mixture.

Effect of Altitude on Partial Pressure

As altitude increases, atmospheric pressure decreases, and thus the partial pressure of each gas (e.g., P_O2) decreases, while the concentration percentage remains constant.

Pressure Gradient (Gas Movement)

The bulk movement of an entire mixture of gases from an area of high total pressure to an area of low total pressure, responsible for moving air in and out of lungs.

Gas Diffusion (Diffusion Gradient)

The movement of individual gas molecules from an area of their own high partial pressure to an area of their own low partial pressure, independently of other gases.

Ideal Alveolar Gas Equation

P_AO2 = [P_B - P_H2O] F_IO2 - P_aCO2 (1.25), a clinically used equation to compute the alveolar oxygen tension (P_AO2).

Fick's Law of Gas Diffusion

Describes that the rate of gas diffusion across the alveolar-capillary membrane is directly proportional to surface area and partial pressure gradient, and inversely proportional to membrane thickness.

Perfusion-Limited Gas Flow

A scenario where the transfer of gas across the alveolar wall is primarily dependent on the amount of blood flow (perfusion) passing the alveoli, with nitrous oxide (N_2O) being an example.

Dalton's Law of Partial Pressures

States that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted independently by each gas in the mixture.

Partial Pressure

The pressure exerted by each individual gas in a mixture, directly proportional to its percentage concentration in the total gas mixture.

Atmospheric Partial Pressure of Oxygen (P{O2})

Calculated by multiplying the barometric pressure (P_B) by the fractional concentration of oxygen (e.g., 0.21).

Effect of Altitude on Partial Pressure

As altitude increases, atmospheric pressure decreases, leading to a decrease in the partial pressure of each gas, while the percentage concentration of gases remains constant.

Effect of Depth (Underwater) on Partial Pressure

Atmospheric pressure increases by 1 atmosphere (760 mmHg) for every 33 feet of descent, causing a proportional increase in the partial pressure of each gas.

Pressure Gradient (Bulk Flow)

The movement of an entire mixture of gases from an area of high total pressure to an area of low total pressure, responsible for air movement into and out of the lungs.

Gas Diffusion (Diffusion Gradient)

The movement of individual gas molecules from an area of their own high partial pressure to an area of their own low partial pressure, independently of other gases.

Alveolar Gas Equation

P{AO2} = [PB - P{H2O}] F{IO2} - P{aCO2} (1.25), used to compute the alveolar oxygen tension (P{AO_2}).

Fick's Law of Gas Diffusion

Describes that the rate of gas diffusion across the alveolar-capillary membrane is directly proportional to the surface area (A) and the partial pressure gradient (P1 - P2), and inversely proportional to the thickness (T) of the membrane.

Perfusion-Limited Gas Flow

A scenario where the transfer of gas across the alveolar wall is primarily dependent on the amount of blood flow (perfusion) passing the alveoli, rather than the rate of diffusion across the membrane (e.g., Nitrous oxide (N_2O)).

Dalton's Law of Partial Pressures

States that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted independently by each gas in the mixture.

Partial Pressure

The pressure exerted by each individual gas in a mixture, directly proportional to its percentage concentration in the total gas mixture.

Atmospheric Partial Pressure of Oxygen (P{O2})

Calculated by multiplying the barometric pressure (P_B) by the fractional concentration of oxygen (e.g., 0.21).

Effect of Altitude on Partial Pressure

As altitude increases, atmospheric pressure decreases, leading to a decrease in the partial pressure of each gas, while the percentage concentration of gases remains constant.

Effect of Depth (Underwater) on Partial Pressure

Atmospheric pressure increases by 1 atmosphere (760 mmHg) for every 33 feet of descent, causing a proportional increase in the partial pressure of each gas.

Pressure Gradient (Bulk Flow)

The movement of an entire mixture of gases from an area of high total pressure to an area of low total pressure, responsible for air movement into and out of the lungs.

Gas Diffusion (Diffusion Gradient)

The movement of individual gas molecules from an area of their own high partial pressure to an area of their own low partial pressure, independently of other gases.

Alveolar Gas Equation

P{AO2} = [PB - P{H2O}] F{IO2} - P{aCO2} (1.25), used to compute the alveolar oxygen tension (P{AO_2}).

Fick's Law of Gas Diffusion

Describes that the rate of gas diffusion across the alveolar-capillary membrane is directly proportional to the surface area (A) and the partial pressure gradient (P1 - P2), and inversely proportional to the thickness (T) of the membrane.

Perfusion-Limited Gas Flow

A scenario where the transfer of gas across the alveolar wall is primarily dependent on the amount of blood flow (perfusion) passing the alveoli, rather than the rate of diffusion across the membrane (e.g., Nitrous oxide (N_2O)).