What is perfusion in the lungs?
What is perfusion in the lungs?
Perfusion refers to the blood flow to tissues and organs. Alveoli are perfused by capillaries so the diffusion of oxygen and carbon dioxide can take place.
What is meant by drug clearance?
Drug clearance is defined as the volume of plasma cleared of a drug over a specified time period. [1] Thus, the unit of measurement for drug clearance is volume/time. Another equation can calculate clearance.
What’s the difference between clearance and the rate of drug elimination?
Clearance is defined as ‘the volume of blood cleared of drug per unit time’. It is the proportionality constant between plasma drug concentration and elimination rate. Drug elimination rate is defined as ‘the amount of drug cleared from the blood per unit time’
What does oral clearance mean?
Oral clearance (CL/F) is an important pharmacokinetic parameter and plays an important role in the selection of a safe and tolerable dose for first-in-human studies.
What does perfusion limited mean?
Perfusion-limited Gas Exchange describes the scenario in which the rate at which gas is transported away from functioning alveoli and into tissues is principally limited by the rate of blood flow through the pulmonary capillaries and thus across the alveolar membrane.
Why is lung perfusion important?
Most bronchioles and large airways are part of the conducting zone of the lung, which delivers gas to sites of gas exchange in alveoli. Gas exchange occurs in the lungs between alveolar air and the blood of the pulmonary capillaries. For effective gas exchange to occur, alveoli must be ventilated and perfused.
Why is drug clearance important?
Most drugs are given continuously. Clearance, the parameter which relates rate of elimination to drug concentration, is important because it defines the rate of administration required to maintain a plateau drug concentration.
What can affect the clearance of a drug?
Drug clearance is influenced by age and by disease, with a reduction in drug clearance being associated with an increase in the half-life of the drug, and an increase in clearance being associated with a decrease in the half-life of the drug.
What affects drug clearance?
What do you mean by clearance?
Definition of clearance 1 : an act or process of clearing: such as. a : the removal of buildings from an area (such as a city slum) b : the act of clearing a ship at the customhouse also : the papers showing that a ship has cleared. c : the offsetting of checks and other claims among banks through a clearinghouse.
What is the difference between diffusion limited and perfusion limited?
Diffusion-limited gas exchange (left) is characterized by incomplete equilibration. In this scenario, the rate of gas diffusion across the alveolar membrane limits its transport away from the lung. In contrast, perfusion-limited gas exchange (right) is characterized by complete equilibration.
Is o2 perfusion limited?
Normally, oxygen is a perfusion-limited gas, which allows us to markedly increase the rate of its uptake by varying the pulmonary blood flow. However, in the cases, oxygen exchange can become a diffusion-limited affair.
How does pneumonia affect perfusion?
When alveoli are totally filled with inflammatory exudate, there may be no ventilation to these regions, and extreme ventilation-perfusion inequality (i.e., shunt) results. Pneumonia commonly results in ventilation-perfusion mismatch (with or without shunting) and hypoxemia.
How does COPD affect perfusion?
Decreased V/Q Ratio Lung diseases like COPD or asthma can impair airflow with little effect on pulmonary blood flow, resulting in low ventilation and nearly normal perfusion. This is described as a decreased V/Q ratio because the ventilation is more severely affected than the perfusion.
What does drug clearance depend on?
Each substance has a specific clearance that depends on how the substance is handled by the nephron. Clearance is a function of 1) glomerular filtration, 2) secretion from the peritubular capillaries to the nephron, and 3) reabsorption from the nephron back to the peritubular capillaries.
What determines clearance?
Clearance is the parameter that determines total systemic exposure to drug, which is simply the ratio of dose/clearance. Total body clearance is the sum of all processes by which drugs are removed from the body or inactivated, primarily renal excretion and metabolism.
What is an example of clearance?
Clearance means space between, or authorization, or items on sale. An example of a clearance is a pathway through the woods. An example of clearance is a document allowing a person into a government building. An example of clearance is a regularly priced $50 t-shirt up for sale at $10.
What is diffusion limitation in the lungs?
Diffusion-limited uptake The amount of carbon monoxide taken up in the pulmonary circulation depends on the diffusion characteristics of the alveolar-capillary membrane, not the amount of pulmonary capillary blood flow. The uptake of carbon monoxide is said to be diffusion limited.
What is meant by perfusion limited gas exchange?
Perfusion-limited Gas Exchange describes the scenario in which the rate at which gas is transported away from functioning alveoli and into tissues is principally limited by the rate of blood flow through the pulmonary capillaries and thus across the alveolar membrane.
How does the rate of blood perfusion affect diffusion?
The rate of blood perfusion determines the amount of time blood flow is available for diffusion to take place. Under normal, resting circumstances, a red blood cell spends about 0.75 seconds in the pulmonary capillary. The physiology of two gases highlights these principles: carbon monoxide (CO) and nitrous oxide (N 2 O).
Why is nitrous oxide transfer described as perfusion limited?
The amount of nitrous oxide taken up in the pulmonary capillaries depends entirely on the rate of pulmonary blood flow, not on the diffusion characteristics of the alveolar-capillary membrane. Hence, nitrous oxide transfer is described as perfusion limited.
Is oxygen absorption perfusion limited?
Therefore, oxygen absorption is normally perfusion limited. However, in a variety of disease states, equilibration of alveolar and blood partial pressures of oxygen may be delayed relative to red blood cell capillary transit time, with resultant diffusion limitation, as well. Figure 6.