Ventilation Flashcards
What does ventilation refer to?
The amount of air entering and leaving the lungs per minute.
What is alveolar ventilation?
The amount of air exchanging with blood - Air actually getting to the alveoli
How is CO2 concentration in alveolar gas related to ventilation?
They are inversely related.
What is anatomic dead space?
The amount of a breath not reaching alveoli
What is the physiologic dead space?
The amount of a breath not exchanging with blood (measured by ratio of CO2 in expired air vs. arteries)
What regions of the lung are ventilated better?
The lower regions are ventilated better than the upper regions.
What does ventilation describe?
How gas (oxygen) gets to the alveoli
What is one of four general causes of reduced oxygen in the blood (hypoxia)?
A reduction in ventilation
What are six things that can cause a reduction in ventilation?
- Drugs (opiates)
- Brain damage
- Breathholding
- Pneumothorax
- Nerve damage
- Muscle damage
What is Tidal Volume? What is it’s average value?
The amount of air inspired and expired in routine breathing.
About 500 ml.
What is total lung volume usually about?
4000 mL
What is total lung capacity usually about?
7000 mL
What is vital capacity? What is it’s value?
The maximum volume of air that can be exhaled after a maximum inspiration. [The largest breath you can take!]
About 6000 mL.
What is residual volume? What is it’s value?
The amount remaining in the lungs after a maximal expiration.
About 1500 mL.
What is Functional Residual Capacity? What is it’s value?
The amount remaining in the lungs after a typical exhalation.
About 2500 mL.
How can you measure Functional Residual Capacity?
You can’t measure this directly, BUT you can calculate it!
What can you measure/calculate with the Gas Dilution Technique?
- Functional residual volumes
- Tidal volumes
- Vital Capacity
What other technique can be used to measure Lung Volume?
Plethysmograph
How does a plethysmograph measure?
It measures pressure in a box of fixed volume surrounding an individual.
-You have to measure change in pressure in the mouth along with change in volume in the box.
What two equations should you know with the plethysmograph?
- P1V1 = P2V2
2. Change in volume = V2-V1
What is Total Ventilation?
The amount of air entering and leaving the lung each minute.
How is Total Ventilation usually calculated? What is it’s usual value?
Volume*bpm = Total Ventilation
500 mL*15bpm = 7500 mL/min
How much of each breath with Total Ventilation usually reaches the alveoli?
350 mL
How much of each breath remains in the anatomic dead space with Total Ventilation?
150 mL
How do we calculate Alveolar ventilation? What is it’s usual value?
Volume reaching alveoli*bpm = Alveolar ventilation
350 mL*15bpm = 5250 mL/min
How can you calculate Alveolar ventilation?
Take the amount of CO2 in the exhaled air divided by the fractional concentration of CO2 in the expired air.
What is the equation used to calculate Alveolar ventilation?
VA = VCO2/PCO2*K VCO2 = amount of CO2 produced/minute K = constant around 1000 PCO2 = about 40
How can (Anatomic) Dead Space Volume be measured?
By breathing pure O2.
How is (Anatomic) Dead Space Volume calculated using a graph?
- Expired gas is plotted vs. N2 in expired gas
- N2 concentration increases with expiration until it reaches a peak [The peak represents pure alveolar gas]
- One can calculate dead space by finding the midpoint (half-maximal) N2 concentration such that the volume above and below this point are equal –> this represents the volume of anatomic dead space
What does the midpoint (half maximal) N2 concentration tell us?
It measures the midpoint in the transition from dead space to alveolar ventilation.
How can Physiological Dead Space be calculated?
By taking the fraction of CO2 in expired gas and comparing it to alveolar gas.
What is the Bohr Equation? What is it used to measure?
Vd/VT = (PACO2 - PECO2)/PACO2
Physiological Dead Space = Vd
Tidal volume = VT
PACO2 = arterial Pco2
What machine is used to measure vital capacity?
Spirometer
What does vital capacity depend on that varies between people?
Depends on size (women tend to have smaller vital capacities)
What happens when you hard exhale?
This crushes the small airways/alveoli
What causes the breath sounds heard upon expiration in asthma?
They have a lot more resistance in the lung so exhaling and crushing the alveoli takes more time
What are some obstructive lung diseases? What happens to the alveoli in these disease?
Alveoli gets crushed.
-COPD, emphysema, bronchitis, asthma
What volume cannot be measured by a spirometer?
Residual volume
What can change your residual volume?
Some diseases
What do you call the additional air you can exhale after your regular exhaled breath?
Expiratory reserve volume
What is the functional residual volume/capacity?
What’s remaining in the lungs after a “normal” exhale. Usually 2/2.5 L.
What test can you use to measure Functional Residual Capacity?
Helium gas dilution technique
What determines functional residual volume?
The natural resting state of the chest. Where lung contracting and chest expanding is exactly balanced. This makes it require very little energy to breathe.
How does the Helium gas dilution technique work?
- Usually 5L of helium at 10% is given to the person to breathe into until it equilibrates.
- Helium is not taken up by blood, but gets diluted in the lungs
- This is diluted based on the volume of the lungs
- As you dilute the helium, you can measure this dilution (concentration) and the amount of helium released and use it to measure lung volume.
What diseases have very large residual volumes? How much volume is this?
COPD (barrel-chested)
5-6 L
What principle is the gas dilution technique based upon?
Fick’s Principle
What is the most effective way of determining residual volume?
Plethysmograph
Do you measure residual volume directly or indirectly?
Indirectly
What is the average alveolar ventilation?
5L/min
What happens to your pCO2 if you increase alveolar ventilation (VA)?
pCO2 drops rapidly!!
The faster you breathe, the lower your. .
pCO2!
What does a low pCO2 and high respiration indicate?
Respiratory alkalosis –> can present with panic attacks
What causes low pCO2 with a high RR?
You produce CO2 and it gets diluted by the air you breathe. If you breathe a lot of air in and out, it gets diluted. If you don’t breathe much, it’s more concentrated. (this is IMP and relevant to alkalosis and acidosis)
What percentage of a normal breath is alveolar ventilation?
30%
What will the PO2 be in better perfused regions of the lung?
Lower
-PO2 reflects the amount of oxygen gas dissolved in the blood
