Gas Exchange Flashcards
anatomy of the pulmonary interface
- THIN endothelial cytoplasm of the T1P
- THIN basal lamina (connective tissue between the cells)
- THIN endothelial cytoplasm of the capillary
physiology of the pulmonary interface
propertities of diffusion
gas exchange is a passive process of diffusion
gas goes from high to low concentrations
diffusion is proportional to
- pressure gradient
- cross-section involved
- soluable gas
diffusion is inversely proportional to
- the distance in which it must travel
explain how the partial pressures of gases change depending on their location during ventilation
atmosphere: PPO2 = 21% (160)
alveoli: immediately will equilibriate with the arterial pressure (as it passes by in the capillary)
brings oxygen to the tissues and takes the co2
venous PP will be higher in CO2 and lower in O2 and deliver the CO2 out
what is aedquacy of ventilation
how does the breathing (respirations) match up to the metabolic need for gases
** defined in terms of CO2**
define hypoventilation & hyperventilation
hypoventiliation: increase in CO2 production in which the alveolar ventilation cannot keep up –> PaCO2 increased
hyperventilation: alveolar ventilation is increased in comparison to the CO2 production –> PaCO2 decreased
** carbon dioxide diffuses at a much faster rate than oxygen does **
what is diffusion capactiy and how is it influenced
the ability of the pulmonary interface to exchange gases over a set amount of time
** this value can change depending on demand for gas exchange**
influenced by…
- ventilation changes
- thickness of the membrane where diffusion occurs
- changes in circulatory renewal (cant get RBC there –> cannot diffuse gases)
clinical examples of…
- changes in ventilation that will effect diffusion capacity
-environmental pressure (sea level vs. Vail)
- obstruction in the airway (FB)
- bronchoconstriction (asthma)
clinical examples of…
- changes in membrane thickness that will effect diffusion capacity
- added secretions in the alveolar surface (pneumonia, pulmonary edema)
- reductions in the overall respiratory surface (emphysema, TB)
clinical examples of…
- changes in circulatory renewal that will effect diffusion capacity
- circulatory failure (HF)
- pulmonary emboli (blocks the flow)
define the ventilation/perfusion ratio
Va/Q
the relationship between the rate that the alveoli is ventilating gas in relation to the flow of the blood through the lungs
– better match = better perfusion and exchange of gas to the blood
what is often the probelm with ventilation/perfusion ratios
** not poor oxygen**
a mismatch between the perfusion of blood and the ventilation of gas from the alveoli
- poor ventilation: a lack of the air getting to the pulmonary interface –> the PERFUSION is okay (blood still got there) but no gas exhcange could occur –> results in shunting of blood ( deO2 blood) to the heart
** cannot be fixed by increasing O2** - poor perfusion: a lack of blood flow getting to the alveoli –> the VENTILATION is okay but there is no blood to exchange the gas with
** can be fixed by increasing O2 because it will flow to other areas and oxygenate the blood**
approximate values for Va/Q
(vary by lung region?)
Va/Q varies by region of the lung
- average: ventilation 4.5L/min & perfusion 5L/min == Va/Q = .9
why might the Va/Q be low?
- poor ventilation (most commonly)
- ** ex. (3.0/5 =.6 instead of .9)**
- excessive blood flow
what is shunting
movement of unoxygenated blood through the capillaries back to the heart
happens when there is a LOW Va/Q because there is improper ventliation –> cannot exchange gas to the blood
leads to a hypoxemic state
why might the Va/Q be high?
what is the result or possible negative outcome?
- high ventilation
- poor perfusion (most common)
** blood not getting to the interface**
results in….
- increases oxygen tension in the alveoli (no one to pass the O2 to!)
- can create environment for infections to occur (TB, bacterial infections, etc.)