Alveolar ventilation Flashcards
What is meant by minute ventilation?
Total volume of air moved into the respiratory tract per minute
What is the calculation for minute ventilation?
Respiratory rate x tidal volume
What is the average respiratory rate?
15 breaths/min
What is the average minute ventilation?
0.5L x 15 = 7.5L/min
What is meant by alveolar ventilation?
Volume of air moved into the respiratory part of the respiratory tract per minute
What is the calculaton for alveolar ventilation?
Respiratory rate x (tidal volume - anatomical dead space)
How can a person change their minute/alveolar ventilation?
Changing their respiratory rate
Changing their depth of breathing to change the tidal volume
What is dead space?
Volume of air in the respiratory tract that is not used in gas exchange
What are the types of dead space?
Anatomical dead space
Alveolar dead space
Physiological dead space
What is anatomical dead space?
Volume of air in the conducting part of the respiratory tract
What is the average anatomical dead space?
0.15L out of 0.5L tidal volume
What is the disadvantage of anatomical dead space?
The air in the upper respiratory tract, conducting part is expired before the air in the alveoli
What is alveolar dead space?
Volume of air in alveoli that are only partially functional or non-functional because of poor or absent blood flow through adjacent pulmonary capillaries
What is physiological dead space?
Anatomical dead space + alveolar dead space
What is the average physiological dead space? Why?
Approximately 0.15L
Because alveolar dead space is very small since most alveoli are fully functional
What is the average alveolar ventilation?
15 x (0.5L-0.15L) = 15 x 0.35L = 5.25L/min
What is the most important factor of resistance in a tube?
Radius of tube
How does resistance in a tube relate to the radius of the tube?
It is inversely proportional to the radius of the tube
so if the radius increases, the resistance decreases significantly
Is there more resistance in the trachea or in a bronchi/bronchiole? Why?
Bronchi/bronchiole has higher resistance
because it has a smaller radius
which increases the resistance significantly
Is there more resistance in the trachea or all of the bronchioles?
Trachea has higher resistance
because there is only one trachea but there are many bronchioles
connected to each other in parallel
reduces the overall resistance of the bronchioles
Is there more resistance in the airways during inspiration or expiration? Why?
Expiration has higher resistance
because during inspiration, the airways are pulled open, increasing their radius, decreasing resistance significantly
whereas during expiration, the airways narrow by elastic recoil, decreasing their radius, increasing resistance significantly
How does air flow change during expiration? Why?
Decreases from the beginning to the end of expiration
because the airways narrow by elastic recoil, reducing their radius, increasing resistance against air flow significantly
Where in the tracheobronchial tree do pathological increases in resistance to air flow mostly occur? Why?
The smaller bronchioles
because they have a smaller lumen so they are more easily occluded
What are some examples of pathological causes of increased resistance to air flow in the smaller bronchioles?
Increased mucus
Hypertrophy of smooth muscle in the walls of the airways
Oedema
Loss of radial traction
What is radial traction?
Connective tissue surrounding respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli
that hold those airways open
How do all of the pathological causes increase resistance to air flow in the smaller bronchioles?
Reduce radius of bronchioles, which increases resistance significantly
