Gas exchange in lungs lecture 3

The thickness of the membrane separating the alveoli and capillaries is inversely proportional to the diffusion of gas. A thinner barrier allows faster gas exchange.

Carbon dioxide diffuses across the alveolar-capillary membrane faster than oxygen.

The diffusion coefficient is a measure of how easily a gas diffuses through a membrane. It is influenced by factors like surface area, temperature, and pressure difference.

The equation D = (KA × A × (P1 - P2)) / (T × V) describes the diffusion coefficient (D) in terms of various factors like solubility, surface area, pressure difference, temperature, and volume.

A test used to measure the lungs' ability to transfer gas from the alveoli into the blood. It involves breathing in a single breath of a gas mixture containing carbon monoxide (CO) and helium (He).

Carbon monoxide (CO) is used as a tracer in the DLCO test because it binds strongly to hemoglobin, similar to oxygen, but it is not metabolized by the body, allowing for accurate measurements.

Helium (He) is used to measure the alveolar volume in the DLCO test. Its inert nature allows for accurate measurement of the volume of air in the lungs.

A reduced DLCO value indicates impaired diffusion of gas into the blood, which could be caused by various factors like pulmonary fibrosis or emphysema.

An increased DLCO value suggests a more efficient diffusion of gas from the alveoli into the blood, indicating healthy lung function.

Gas exchange is limited by the rate of diffusion, meaning the gas doesn't completely equilibrate between the alveoli and blood. This often happens when the diffusion barrier is thick or the diffusion coefficient is low.

Gas exchange reaches equilibrium quickly, so the rate is limited only by the blood flow to the lungs. Increasing cardiovascular output can enhance this type of gas exchange.

In diffusion-limited gas exchange, the thickness of the diffusion barrier is the limiting factor. A thicker barrier slows down gas diffusion.

In perfusion-limited gas exchange, the rate of gas exchange is determined by the blood flow. The more blood flowing through the lungs, the faster the gas exchange.

The partial pressure at which 50% of the hemoglobin molecules are bound by oxygen. It reflects the affinity of hemoglobin for oxygen.

An increased P50 indicates a decreased affinity of hemoglobin for oxygen. The hemoglobin needs a higher partial pressure of oxygen to achieve 50% saturation.

A decreased P50 indicates an increased affinity of hemoglobin for oxygen. Hemoglobin binds more readily to oxygen, even at lower partial pressures.

Carbon dioxide is transported in the blood predominantly as bicarbonate (HCO3-), but also as dissolved CO2 and carbaminohemoglobin.

Carbon monoxide (CO) has a much stronger affinity for hemoglobin than oxygen, binding 240 times more readily, making it extremely dangerous.

The oxygen-hemoglobin dissociation curve depicts the relationship between the partial pressure of oxygen and the percentage saturation of hemoglobin with oxygen. It has a sigmoid shape.

During hyperventilation, you breathe faster and deeper, leading to lower carbon dioxide in the alveoli and increased oxygen.

Hypoventilation involves slow and shallow breathing, leading to higher carbon dioxide and lower oxygen in the alveoli.

Hyperventilation increases the oxygen content in the blood due to increased oxygen uptake in the lungs.

Hypoventilation reduces the oxygen content in the blood because of reduced oxygen uptake.

Impaired diffusion results in reduced oxygen diffusion from the alveoli to the blood, while carbon dioxide diffusion remains relatively normal. This can lead to low blood oxygen levels.

Impaired diffusion can be compensated by increasing the pulmonary blood flow, enhancing delivery of oxygenated blood to the tissues.

Increasing the surface area for diffusion in the lungs can help improve gas exchange in impaired diffusion. This could involve mechanisms like alveolar expansion or angiogenesis.

The diffusion of CO2 is actually increased in impaired diffusion, but this is mainly due to the increased partial pressure of CO2 in the blood due to the reduced oxygen diffusion.