Dyspnea Physiology Flashcards
What structures are in the conducting zone?
Trachea, bronchi, bronchioles, terminal bronchioles
Zones 0 - 16
What structures are in the transitional and respiratory zones?
Respiratory bronchioles, alveolar ducts, alveolar sacs
Zones 17 - 23
Where does gas exchange occur in the lungs?
Alveoli - capillaries run in the wall of alveoli
What is Tidal Volume?
The volume of air moved into or out of the lungs during normal, quiet respiration
What is the difference between anatomic dead space and physiologic dead space?
Anatomic dead space - volume of conducting airways (~150 cc)
Physiologic dead space - volume of gas that does not eliminate CO2
Approximately the same in normal subjects, but physiologic dead space is increased in patients with lung disease
What is Fowler’s method to measure anatomic dead space?
Nitrogen washout (or Fowler’s method) is a test for measuring anatomic dead space in the lung during a respiratory cycle, as well as some parameters related to the closure of airways.
22 yr old diabetic male arrives in the ER with a 3 day history of nausea, vomiting, and diarrhea, with very high blood sugar
Respiratory parameters:
Vt = 900 ml (normal ~ 500)
RR = 16 bpm (normal 12-16)
SpO2 = 100%
What is his minute ventilation? Why is he breathing like this?
Minute ventilation (Ve):
= Vt x RR = 0.9 x 12 = 14.4 L/min
He is breathing like this because he has diabetic keto-acidosis. Ketones that are produced are buffered by the body resulting in excess CO2 that he has to breath out.
As the VCO2 increases, ventilation increases in response to keep the PaCO2 constant.
How do we calculate alveolar ventilation (Va)?
Va = (Vt - Vd) x RR
What is the relationship between alveolar ventilation (Va) and PaCO2?
As the partial pressure of CO2 in the lungs increases, the alveolar ventilation decreases, meaning less L/min is exchanged at the alveoli.
What is Fick’s Law?
V(gas) ~ A/T x D x (P1 - P2)
The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure (P1-P2), proportional to the area of the membrane (A) and inversely proportional to the thickness of the membrane (T).
What are the determining factors in pulmonary blood flow?
- Gravity
- Hypoxic vasoconstriction
- Lung volume
How does gravity impact the blood flow to the three zones of the lungs?
(top = zone 1, middle = zone 2, bottom = zone 3)
The blood flow is greatest at the bases, and very minimal at the top of the lungs
What is hypoxic vasoconstriction?
It is a mechanism by which blood ends up in the better ventilated portions of the lungs.
Low alveolar PO2 –> local vasoconstriction –> blood doesnt move into poorly ventilated areas, and is diverted to well ventilated areas
How does lung volume impact the blood flow to the lung?
Alveolar capillaries are exposed to alveolar pressure and are compressed when this increases. Extra-alveolar vessels are exposed to less alveolar pressure and are pulled open on inspiration.
