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# Vent/Diff DS

### Alveolar ventilation and diffusion- 1/11/2013- CJ

Purpose of ventilation To keep diffusion going (maintain O2 and CO2 partial pressure gradients) and to help maintain blood pH
Total ventilation definition The rate at which air is brought into and out of the lungs per minute
Tidal volume definition The volume of air brought in with each breath
Respiratory frequency How many times air is brought in each minute
Typical tidal volume value 500 ml
Typical breathing frequency value 15 breaths for minute
Two sources of work for the lung Elastic work and frictional work
Optimal tidal volumes and breathing frequencies occur when Elastic work and Frictional work are lowest, producing the lowest amount of total work (500ml and 15 breaths per minute)
Define dead space Airways that conduct air but do no gas exchange (ventilation but no perfusion)
Define alveolar ventilation Amount of tidal gas reaching the alveoli per minute (vTidal volume-volume of dead space times respiratory rate)
Alveolar ventilation depends on Dead space volume and respiratory frequency
Alveolar ventilation equation (Vt-Vd) x n Vt= Tidal volume Vd= Dead space volume n= Respiratory frequency
Alveolar ventilation can be increased by (2 things) Increasing the tidal volume or the respiratory frequency
Most effective way to change alveolar ventilation Increasing tidal volume (more efficient)
An arterial Pco2 value under 40 reveals Hyperventilation
An arterial Pco2 value over 40 reveals Hypoventilation
Hypoxemia with an elevated arterial Pco2 is diagnostic of Hypoventilation
In a healthy person, what is the ratio of physiologic to anatomic dead space Equal
In diseased lungs, what is the relative ratio of physiologic to anatomic dead space? Physiologic dead space is greater than the anatomic dead space
Dead space causes wasted ventilation that can be estimated by measuring Peco2 (mixed expired gas). The more diluted Peco2 is, the more dead space there is.
The bohr equation can be used to calculate Dead space
The Bohr equation Vd/Vt= (Paco2-Peco2)/(Paco2)
Normal Paco2 value 40 mmHg
Normal Peco2 value 30 mmHg
Normal Vt (Tidal volume) value 500 ml
Normal Vd/Vt value .2-.35
Ventilation is higher at the ____ than the ____ Higher at the base than the apex
Ventilation is not uniform in the upright lung due to Gravity
Hypoventilation causes ___ partial pressure gradients in the lung Reduced, which leads to hypoxemia
Ventilation ______ down the lung, from the apex to the base Increases
Which is more compliant, base or apex of the lung? Base
Intraplueral pressure is less at ___ lung volumes Higher
Intrapleural pressure is _____ at the lung base less negative (greater)
Ficks law Diffusion of gas= (Area x Partial pressure difference x D)/ (Thickness of barrier) D= Solubility/√MolecularWeight
An increase in surface area who do what to diffusion rate Increase
A decrease in Solubility of the gas would do what to diffusion rate Decrease
An increase in barrier thickness would do what to diffusion rate Decrease
A heavier gas would do what to diffusion rate Decrease
Increasing the partial pressure difference would do what to diffusion rate Increase
Why is CO less effected by the change in the blood-gas barrier Because it is more soluble
Slowed diffusion rarely causes hypoxia on its on because of Spare capacity
Why is impaired diffusion typically only a problem in exercise but not at rest Space capacity can be saved from exercise or impaired diffusion but there is not enough to equilibrate both exercise AND impaired diffusion
Only about ___ of the capillary is used for diffusion in a normal patient 1/3
Diffusion impairment is only problematic when combined with Exercise or alveolar hypoxia
Perfusion-limited gas exchange is seen when the total amount of gas transported across the barrier is limited by blood flow, such that equilibrium is reached between the partial pressures of the gas in the alveoli and in the pulmonary capillaries. The rate of gas exchange can be increased by increasing blood flow. O2 and CO2
Diffusion-limited gas exchange is seen when the total amount of gas transported across the barrier is limited by the diffusion process, so diffusion will continue along the full length of the capillary. The rate of gas exchange is increased by increasing its partial pressure in the alveoli.
Diffusion-Limited gas exchange is typically seen Only with O2 during strenuous exercise, at high altitude, and in pathologic conditions such as emphysema and pulmonary fibrosis.
Normal Venous Pco2 value 46 mmHg
Created by: mcasto