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Respiratory Phys 4

WVSOM -- Ventilation and Diffusion

Where is the main site of airway resistance in the lung? medium sized bronchi
How is airway resistance affect by lung volume? resistance decreases with increase in lung volume
What limits airflow during a forced expiration? the transairway pressure becomes negative
What is diffusion? it is the movement of the gas across the blood barrier
What is ventilation? process by moving gas into and out of the lung
What is perfusion? means by which O2 is delivered to the cells and CO2 from the cell
What is the purpose of ventilation? to maintain O2 and CO2 partial pressure gradients
What does total ventilation depend on? tidal volume and respiratory frequency. Total ventilation = Tidal Volume X Frequency
Why does not all inspired air reach the alveoli? dead space
What is dead space? about 150 ml of 500ml stays in the trachea and bronceholes. Only 350 ml gets to the alveoli
How do you calculate alveolar ventilation? Tidal volume – Dead space volume X frequency; (500-150) X 15
What can increase alveolar ventilation? increase in tidal volume or increase in respiratory rate
What is usually the most effective way to increase alveolar ventilation? increase in tidal volume
How is arterial Pco2 proportional to alveolar ventilation? inversely proportional
What is hypoventilation? hypoxemia with an elevated arterial Pco2
A patient’s arterial Pco2 is 40mmHg and he doubles his alveolar ventilation rate voluntarily. His arterial Pco2 becomes? 20mmHg
What is anatomic dead space? volume of conducting airways
What is physiologic dead space? volume of airways not involved in gas exchange
What is physiologic and anatomic dead space like under normal conditions? they are equal
In disease, how are physiologic and anatomic deadspace? physiologic > Anatomic
How do you calculate physiologic dead space? PaCO2 – PeCO2 / PaCO2
What is normal PaCO2? 40mmHG
What is normal PeCO2? 30mmHG
What is normal tidal volume? 500 ml
What is ventilation/perfusion inequality? ventilation but NOT perfusion…they aren’t matched
How do you measure dead space? by measuring expired CO2 and arterial CO2
Is ventilation uniform in the upright lung? Why? No, because of gravity. The lower zones have more ventilation than the upper zones.
What is intrapleural pressure at the lung base? less negative
What law does diffusion obey when moving across the blood-gas barrier? Fick’s Law
What circumstances would reduce the rate of oxygen diffusion into the pulmonary blood? surface area, partial pressure gradient and thickness
What kind of capacity does the lung have for diffusion? huge reserve capacity. Only needs a third of the distance of the lung for gas exchange.
Why is the huge reserve in the lung important? need more reserve for excersize where it will take the whole distance
How long is an RBC capillary time when at rest? 3/4 second
What is the RBC capillary time in exercise? 1/4 second
When is diffusion impairment problematic? when combined with exercise or alveolar hypoxia
Why is CO2 less affected by the thickening of the blood-gas barrier? CO2 diffuses more easily because it has a greater solubility
Created by: tjamrose



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