Trachte: Ventilation Flashcards
What is ventilation?
how oxygen gets to the alveoli
What causes hypoxia?
A reduction in ventilation
What are three causes of hypoxia?
- Drugs (opiates)
- Brain damage
- Breath holding
What is tidal volume?
The amount of air inspired and expired in routine breathing
How much air is normally expired/inspired (tidal volume)?
500 ml
What is total long volume?
4000 ml
What is total lung capacity?
7000 ml
What is the vital capacity?
The maximum volume of air that can be exhaled after a maximum inspiration
What is vital capacity usually equal to?
6000 ml
What is the residual volume?
The amount remaining in the lungs after a maximal expiration
What is the residual volume usually equal to?
1500 ml
What is the functional residual capacity?
Amount remaining after a typical exhalation
What is the normal functional residual capacity?
2500 ml
How do you measure the functional residual capacity?
You can’t measure it directly but you can calculate it using:
a gas dilution technique
Plethysmograph
What is a gas dilution technique?
Take a spirometer w/ a known amt of helium. Ask the pt to breathe starting from the functional residual capacity (volume of air left in the lung after a normal breath out). Measure the new helium concentration once the He settles into the lungs.
Calculate FRC using FRC = ((C1xv1)/C2) - V1
What is a plethysmograph?
Measure pressure in a box of fixed volume surrounding an individual.
P1 x V1 = P2 x V2
Change in volume = V2- V1
What is total ventilation?
Amount of air entering and leaving the lung each minute
What is typical ventilation/minute?
500 ml x 15 breaths/min = 7500 ml/min
How much of each breath reaches the alveoli?
350 ml of each breath
How much of each breath remains in the anatomic dead space?
150 ml
What is typical alveolar ventilation?
350 ml x 15 b/min = 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
Va = VCO2/PCO2 x K
What happens if there is an increase in alveolar ventilation?
If Va increases and VCO2 stays the same, then PCO2 HAS TO BE lowered.
How do you measure dead space volume?
By breathing pure O2!
The expired gas is plotted vs N2 in expired gas. The N2 concentration increases with expiration until it reaches a peak.
How do you calculate dead space?
By finding the MIDPOINT N2 concentration such that the volume above and below this point are EQUAL.
THE MIDPOINT represents the VOLUME of the anatomic dead space.
The MIDPOINT represents the midpoint in the transition from dead space to alveolar ventilation.
How do you calculate physiological dead space?
By taking the fraction of CO2 in expired gas and comparing it to alveolar gas
What is the Bohr equation?
Used to calculate physiological dead space
Vd/VT= (PAco2- PEco2)/ PAco2
What are regional differences in ventilation?
LOWER portions of the lung are ventilated BETTER than the apical regions
