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Respiratory Phys 4
WVSOM -- Ventilation and Diffusion
| Question | Answer |
|---|---|
| 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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