Alveolar Ventilation Flashcards
What is alveolar ventilation?
The exchange of gas between the alveoli and the external environment.
What are the four standard lung volumes?
Tidal Volume (Vt)
Residual Volume (RV)
Expiratory Reserve Volume (ERV)
Inspiratory Reserve Volume (IRV)
What are the four standard lung capacities
Functional Residual Capacity (FRC)
Inspiratory Capacity (IC)
Total Lung Capacity (TLC)
Vital Capacity (VC)
What is the tidal volume (Vt)?
The volume of air entering or leaving the note or mouth per breath
Usually 500ml per breath
What is inspiratory capacity (IC)?
IRV + TV
The volume of air that is inhaled into the lungs during maximal effort that begins at the end of a normal tidal expiration (the FRC)
Usually around 3.0L
What is the functional residual capacity (FRC)?
ERV + RV
The volume of gas remaining in the lungs at the end of a normal tidal expiration
Determined by:
a. inward recoil of lung
b. outward recoil of the chest wall when there is no contraction of inspiration and expiration muscles
Usually around 3.0L
What is total lung capacity (TLC)?
The volume of air in the lungs after a maximal inspiratory effort Determined by: a. inward recoil of lungs b. inward recoil of chest wall c. inspiratory muscles
Usually around 6.0L
What is vital capacity (VC)?
IRV + Vt + ERV
The volume of air expelled from the lungs during maximal forced expiration starting after a maximal forced inspiration
What is the residual volume (RV)?
The volume of gas remaining in the lungs after maximal forced expiration
Usually around 1.5L
What is the expiratory reserve volume (ERV)?
The volume of gas that is expelled from the lungs during a maximal forced expiration
Usually around 1.5L
What is inspiratory reserve volume (IRV)
The volume of gas that is inspired into the lungs during a maximal forced inspiration starting at the end of normal tidal inspiration
How do things with volume and capacity change with diseases?
Obstructive disease - huge residual volume, much larger overall TLC
Restrictive disease - everything is compressed especially RV and TV
How does a water filled spirometer measure gas volumes?
What can it measure?
What can it not measure?
Patient breathes in and out of a mouthpiece and a tube connected to the spirometer, a bell is suspended in a volume of water and as the air inside the spirometer increases the bell rises
Can Measure: Vt, ERV, and IRV
Cannot measure: RV (part of FRC), FRC (part of TLC), or TLC
Patient must be awake, alert, and cooperative… may throw off “normal” numbers cause they’re trying hard or have been coached by attorney (bastards)
What does a pulmonary function test measure?
What are some types of pulmonary function tests?
Important tool in diagnosing and measuring patient progress.
Types: Water filled spirometer Nitrogen Washout Helium Dilution Body Plethysmograph
What is the nitrogen washout and how does it work?
Cheap and easy method to measure TLC, RV, and FRC - can be used on unconscious patient
Patient inhales some N2 and begins to exhale, then 100% O2 (this will be in anatomical dead space and blown out first) it should be down to 2% after 7 minutes.
Multiply total volume expired by %N2 to get Original volume of N2 in lungs
Nitrogen constitutes about 80% of the initial lung volume, so multiplying the initial nitrogen volume by 1.25 will give you the total initial volume
If a person has high resistance airways then it could take forever to blow it all off
What is the Helium dilution test?
Person breathes in and out a known amount of helium, he keeps breathing until the amount in the apparatus and the amount in his lungs have equalized
The test is then stopped at the end of normal tidal volume which should give us his FRC
Total amount of Helium and start = total amount at end
Concentration of helium x Initial Spirometer Volume = Final Concentration of Helium x (Final Spirometer Volume + FRC) Fhei x Vsp = Fhef (Vspf + VLf)
can be used on unconscious patient
What is the body plethysmography?
Best but the most expensive - measure FRC
Uses Boyle’s law: Pressure x volume is constant at constant temperature
Sit in airtight box and breath out through a tube and the box measures pressure, pressure in his mouth is equal to pressure in alveoli
At the end of a normal tidal expiration a shutter closes the tubing and the patient breathes against a closed airway and the chest expands and the pressure measured increases because the volume inside the box decreases equal to the amount of chest volume increase
The advantage is that it includes trapped gas
Whats the difference between alveoli ventilation and minute ventilation
Minute ventilation is the air going into and out of the mouth, including anatomical dead space
Alveoli ventilation is air going into or out of the alveoli
What can cause alveoli dead space?
Pulmonary embolism
Positive pressure ventilation
Compression of pulmonary vessels
Bad right ventricle
How does age affect lung volume?
Aging decreases elastic recoil
Decrease of inward recoil of lung will cause small gradual increase in FRC
Larger increase in RV
above 55, closing capacity will be greater than the FRC
Arteriole PO2, diffusion capacity, decrease linearly
What makes up expired CO2?
CO2 from dead space and CO2 from alveoli
Whats the alveolar air equation?
Alveolar O2= inspired O2 x (barometric pressure – water vapor pressure) - (alveolar CO2/ (CO2 out/O2 in))
Barometric pressure= 760mmHg; Water vapor pressure= 47mmHg
Expired O2= air at end of airways that’s been heated. Partial pressure= 47, so the PO2 at the end of the airways= barometric pressure (760)- 47 (water vapor pressure) x FiO2 (.21)- alveolar PCO2/ respiratory exchange ratio
Gives you an alveolar PCO2 of 99
**Tells you what the alveolar PCO2 ought to be under those circumstances (not what it is!)
Using the Xenon gas test, where does the air go?
More goes into lower alveoli, then mid, then upper
