Respiratory Cycle and Lung Volumes Flashcards
______ ______ = volume inspired or expired with each normal breath
Tidal volume
How do you calculate minute ventilation rate?
Tidal volume x breaths/min
How do you calculate minute alveolar ventilation rate?
(Tidal volume - dead space) x breaths/min
Describe the relationship of air flow to the pressure difference between the mouth and the alveoli
Air flow is driven by and is directly proportional to the pressure difference between the mouth and the alveoli
What is the relationship of alveolar pressure and atmospheric pressure at rest?
Alveolar pressure = atmospheric pressure
[because the lung pressures are expressed relative to atmospheric pressure, the alveolar pressure is said to be 0]
What is the relative value of intrapleural pressure at rest?
Negative
[opposing forces of the lungs trying to collapse and the chest wall trying to expand creates a negative pressure in the intrapleural space between them]
A balloon catheter placed in the esophagus would measure what type of pressure?
Intrapleural pressure
What lung capacity value represents lung volume at rest (prior to inspiration)?
Functional residual capacity
During inspiration, inspiratory muscles contract and cause the volume of the thorax to increase. As the lung volume increases, what happens to alveolar pressure? What is the result?
Decreases to less than atmospheric pressure (becomes negative)
Pressure gradient between atm and alveoli now causes air to flow into the lungs; air flow will continue until the pressure gradient dissipates
What changes occur to intrapleural pressure during inspiration?
Becomes more negative because the elastic recoil strength of the lungs increases as lung volume increases
Changes in intrapleural pressure during inspiration are used to measure the dynamic _______ of the lungs
Compliance
How is lung volume calculated at the peak of inspiration?
Functional reserve capacity + one tidal volume
What changes occur with alveolar pressure during expiration? What does this lead to?
Alveolar pressure becomes greater than atm (becomes positive) because alveolar gas is compressed by the elastic forces of the lung
Since alveolar pressure is now higher than atmospheric pressure, the pressure gradient is reversed and air will flow out of the lungs
What changes occur with intrapleural pressure during normal, passive expiration?
Intrapleural pressure returns to its resting value during a normal passive expiration
What occurs with intrapleural pressure during forced expiration?
Intrapleural pressure becomes more positive, which compresses the airways and makes expiration more difficult [this occurs in COPD patients]
How might a COPD patient compensate for the collapse of the airways that occurs with forced expiration?
They exhale slowly with pursed lips
What is the most important muscle of inspiration? How does it work?
Diaphragm
When the diaphragm contracts, the abdominal contents are pushed down and the ribs are lifted upward and outward, increasing the volume of the thoracic cavity
What muscles of inspiration are not used during normal, quiet breathing? When are they used?
External intercostals
Accessory muscles
Used during exercise and in diseases causing respiratory distress
Expiration is normally a passive process, so expiratory muscles are only used during exercise or when airway resistance is increased due to things like asthma.
What are considered the expiratory muscles?
Abdominal muscles
Internal intercostal mm.
Abdominal muscles may be used in forced expiration, what is their action?
Compress the abdominal cavity, push the diaphragm up, and push air out of the lungs
Internal intercostals may be used in forced expiration, what is their action?
Pull the ribs down and in
Using a capital A, such as with partial pressure of oxygen: PAO2, what does the “A” indicate?
Alveolar gas
Using a lowercase “a” such as with partial pressure of oxygen: PaO2, what does the “a” indicate?
Arterial gas
What do we expect the relationship to be between the partial pressure of alveolar gas (PAO2) and the partial pressure of arterial gas (PaO2)?
They should be the same
What relationship is described by Boyle’s Law?
Pressure of a gas is inversely proportional to its volume
[P1V1 = P2V2]
Based on Boyle’s Law, an increase in lung volume corresponds with a _______ in pressure, and air will _____ the lung.
Decrease; enter
What kind of muscle(s) are/is the inspiratory muscles?
A. Smooth muscle
B. Skeletal muscle
C. Cardiac muscle
D. A and B
B. Skeletal muscle
What units are utilized in the measurement of pressures in respiratory physiology?
A. mm Hg
B. cm Hg
C. mm H2O
D. cm H2O
D. cm H2O
[note that we normalize atmospheric pressure to 0 cm H2O]
What is the intrapleural pressure at rest? How does it change during inspiration?
About -5 cm H2O
During inspiration, volume increases and intrapleural presure decreases to near -8 cm H2O
As the thoracic cavity increases in size during inspiration, alveolar pressure (pressure within the alveoli) _________, which causes air to ______ the lungs
Decreases; enter
At rest, alveolar pressure = _____ cm H2O
At the end of inspiration, alveolar pressure = ____ cm H2O
This is due to _______ in alveolar size
0
-1
Increase
As the thoracic cavity increases in size with inspiration, pleural pressure (pressure within the pleural spaces _________
Decreases
[starts negative, gets more negative]
T/F: transpulmonary pressure should always be negative
False: The transpulmonary pressure should always be positive because the pleural pressure should always be negative, so subtracting a negative will give you a positive.
How is transpulmonary pressure calculated?
Transpulmonary pressure = alveolar pressure - pleural pressure