Ventilation Flashcards
What is Boyle’s Law (P-V)?
Volume is inversely proportional to pressure
What is Charles’ Law (T-V)?
Volume is directly proportional to temperature
What is Gay-Lussac’s Law (P-T)?
Pressure is directly proportional to temperature
What is the normal PaO2 in blood?
~100 mmHg
How is the PaO2 calculated?
PaO2 = PiO2 (inspired) - PaCO2/R
R - respiratory quotient = excreted CO2/O2 taken up
What is alveolar CO2 related to?
It is inversely related to ventilation and is directly related to CO2 production
What is the partial pressure of O2 in air?
160 mmHg
If the partial pressure of O2 in air is 160, why is it only 100 in blood?
The humidification of the air by the upper airway causes the dilution of the gases due to the water vapor that was added.
If ventilation is cut in half what will happen to the PaCO2?
It will double
Where does the most ventilation occur in the lung?
In the lower regions. As you go up the lung, there is less and less ventilation
Why is inspired air preferentially shunted to the base of the lung?
- The lung has a triangular structure with the base being the widest part of it so there are more alveoli at the base than at the apex
- At FRC the base of the lung is more compliant than the apex so airflow causes a greater volume change in the base
What does the rate of alveolar filling depend on?
Resistance
Compliance
What happens to the rate of alveolar filling when resistance is increased?
The rate will decrease
What happens to the rate of alveolar filling when the compliance is decreased.
The rate will increase, but the alveoli is stiffer and fills up less than normal
What is a nitrogen washout test?
Patients inhale 100% O2 from RV and then exhale slowly where N2 % is measured.
What is the 1st part on the single-breath nitrogen washout test?
N2% is at 0% initially as the dead spaces filled with 100% O2 empty first.
What is the 2nd part on the single-breath nitrogen washout test?
N2% rapidly increases as the alveolar regions are being emptied
What is the 3rd part on the single-breath nitrogen washout test?
There is a plateau as there is an equal emptying of the alveolar regions in the lungs
What is the 4th part on the single-breath nitrogen washout test?
There is a second increase in the N2% because of the slowly emptying alveoli
What is the first air to reach the deep alveoli?
It is the “dirty” air from the previous exhalation
What can be used to determine the anatomical dead space?
Fowler’s Method
Describe Fowler’s Method.
The nitrogen washout test is used and by plotting the expired volume VS N2% and a curve is drawn that will show the volume of the dead space.
What is anatomical dead space?
It is the dead space where gas exchange is not possible, like in the conducting pathways of the mouth and trachea.
What is physiological dead space?
It is the total volume that does not participate in gas exchange and is equal to:
Anatomical Dead Space + Alveoli Ventilated but not Perfused
What is the equation for the dead space?
Vd = Vt * (PaCO2-PeCO2)/PaCO2
What is the normal ratio for Vd/Vt?
0.2-0.35
What is Vd normally?
150 mL
As tidal volume increases, what happens to the dead space ventilation?
It decreases
In order to increase alveolar ventilation, what is the most effective method?
Increasing the tidal volume is more effective that increasing the respiratory rate
