When is diffusion rate important for a patient

Diffusion of a gas occurs when there is a net movement of molecules from an area in which that particular gas exerts a high partial pressure to an area in which it exerts a lower partial pressure. During bulk flow, gas movement results from differences in total pressure, and molecules of different gases move together along the total pressure gradient.

During diffusion, different gases move according to their own individual partial pressure gradients. Gas transfer during diffusion occurs by random molecular movement. It is therefore dependent on temperature because molecular movement increases at higher temperatures. In a static situation, diffusion continues until no partial pressure differences exist for any gases in the 2 areas; in the lungs, oxygen and carbon dioxide continuously enter and leave the alveoli, and so such an equilibrium does not take place.

Oxygen is brought into the alveoli by bulk flow through the conducting airways. When air flows through the conducting airways during inspiration, the linear velocity of the bulk flow decreases as the air approaches the alveoli. This is because the total cross-sectional area increases dramatically in the distal portions of the tracheobronchial tree, as was seen in Figure 1—2. The linear velocity of bulk flow through a tube is equal to the flow divided by the cross sectional area:.

By the time the air reaches the alveoli, bulk flow probably ceases, and further gas movement occurs by diffusion. Oxygen then moves through the gas phase in the alveoli according to its own partial pressure gradient.

The distance from the alveolar duct to the alveolar-capillary interface is usually less than 1 mm. Diffusion in the alveolar gas phase is believed to be greatly assisted by the pulsations of the heart and blood flow, which are transmitted to the alveoli and increase molecular motion. Oxygen then diffuses through the alveolar-capillary interface. It must first, therefore, move from the gas phase to the Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'.

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Factors affecting the rate of diffusion If a crystal of a coloured chemical, eg potassium manganate VII , is placed in water, the particles spread out and mix with the water particles. The potassium manganate VII is the solute. The water is the solvent. The potassium manganate VII has dissolved.

The mixture that results is the solution. The rate of diffusion The rate of diffusion can be affected by a number of factors: Factor Reason The concentration gradient The greater the difference in concentration, the quicker the rate of diffusion. The temperature The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly.

The surface area of the cell membrane separating the different regions The greater the surface area, the faster the rate of diffusion. Diffusion, surface area and volume For a bacterium , substances diffuse into and out of the bacterial cell across its surface.

If a person has a condition that affects blood flow to the lungs or they have damaged lung tissue, their lungs will not be able to diffuse gas as well. As a result, they may have a lower or higher lung diffusing capacity measurement than expected. They will often order other pulmonary function tests to help with the diagnosis, such as spirometry and lung volume tests.

When a person has a lung diffusion test to monitor an existing condition, the doctor will compare their results to previous tests to see if the condition has improved, worsened, or stabilized. Based on the results, a doctor may continue or change current treatments. They may use the test to diagnose conditions or to assess how well lung-related treatments are working.

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When do doctors use the test? Preparing for the test.