Flashcards in Ventilation Deck (11):
Volume of air per unit time moved into or out of the lungs.
How is it measured?
Measured by collecting expired volume for a fixed time
What is a typical value for minute ventilation?
7.5 L/min (BTPS)
What is the equation for minute ventilation?
VE= VT • f
(Tidal Volume times respiratory frequency)
What is the difference between anatomic dead space and physiological dead space?
Anatomic dead space is the volume of the lung that is not involved in gas exchange (this includes the mouth, larynx, pharynx, trachea, and bronchi).
Physiological dead space is anatomic dead space plus alveolar dead space (alveoli with no gas exchange)
Fowler's method of measuring anatomic dead space:
Expired N2 concentration is analyzed following a single breath of 100% oxygen
When is gas exchange optimal?
Only when individual regions are ventilated in proportion to their capillary blood flow
What are "dead-space-like" and "shunt-like" regions in the lungs?
"dead-space-like": well ventilated but poorly perfused.
"shunt-like": well perfused but poorly ventilated
True or false:
In the upright position of a healthy individual physiological dead space is only slightly greater than anatomical dead space because alveolar dead space is negligible and so ventilation and perfusion are relatively homogeneous
Supine, not upright
The Bohr equation is used to measure physiological dead space knowing:
1. That all CO2 comes from alveolar gas not dead space
2. Arterial PCO2 is almost always equal to alveolar PCO2
3. There is conservation of mass
What is the Bohr equation?
(Vd/VE) = (Vd/VT) = (PaCO2 - PECO2)/PaCO2