23 Questions
What is the major cause of non-uniform distribution of inspired air in the lungs?
Body position
During eupnea, which region of the lung is subjected to a greater distending pressure?
Apical region
What is the typical change in intra-alveolar pressure (IPP) from apical to basilar regions during inspiration?
$0.5$ cm H2O increase per cm from apical to basilar regions
After a forced expiration to residual volume (RV), where does dynamic compression occur?
Smaller airways of the basilar region
Which type of alveoli are less compliant and typically hold most alveolar air at functional residual capacity (FRC)?
Apical (non-dependent) alveoli
What is the effect of an increase in physiologic dead space on alveolar ventilation?
Alveolar ventilation decreases due to less air reaching perfused alveoli.
How does the Bohr equation help in determining physiologic dead space?
By comparing the partial pressure of CO2 in the blood and exhaled air.
In a circle system, where does dead space begin according to the text?
At the Y-piece where inspired and expired gas mix.
What happens to alveolar air with each tidal breath of fresh air, based on the information provided?
Approximately 500 ml of new air is delivered to the alveoli.
Which component of alveolar air has the highest partial pressure?
Nitrogen
What happens to PACO2 and PaCO2 if alveolar ventilation is doubled in healthy individuals?
They are reduced by one-half
According to the alveolar air equation, what happens to PACO2 as alveolar ventilation increases?
It decreases
What does the Alveolar Gas (Air) Equation help in calculating for a healthy person?
Partial pressure of inspired oxygen
What is the maximum value of PAO2 that can be achieved by breathing air at sea level?
149 mmHg
What is the primary reason for airway closure in the dependent lung at higher lung volumes in emphysema and advanced age?
Loss of alveolar elastic recoil
During the second breath of a breathing test, where does most of the oxygen enter after inhalation up to TLC?
Upper alveoli
What makes up the gas left in the lungs after a forced expiration to residual volume?
80% nitrogen
Which phase of expired gas measurement during the second breath involves a mixture of dead space and alveolar gas?
Phase II
What contributes to the increased static lung compliance and decreased chest wall compliance seen with aging?
Loss of alveolar elastic recoil
What is the primary function of tidal volume in respiration?
To move air into (or out of) the lungs with each respiration
If a seated person breathes in from residual volume, where would most of the inhaled gas be found after accounting for dead space?
In alveoli in upper portions of the lung
In the context of regional ventilation differences, what role does alveolar elastic recoil play?
Preventing dynamic compression in smaller airways
How does closing volume impact regional ventilation differences in the lungs?
It causes unequal closing pressures in different lung regions
Study Notes
Regional Distribution of Alveolar Ventilation
- Lower alveoli receive more ventilation/unit volume due to gravity, body position, mechanical advantage, and pulmonary abnormalities
- Dependent areas of the lung receive a greater volume of fresh air per breath
- Gravity is the major cause of regional differences in ventilation/unit volume, producing unequal stretching and expansion
- Apical region is gravity non-dependent, more distended, and has a more negative IPP
- Basilar region is gravity dependent, less distended, and has a less negative IPP
- IPP increases by 0.5 cm H2O for each cm from apical to basilar regions
Explanation for Differences in Regional Ventilation During Eupnea
- IPP is more negative in upper regions of the lung compared to lower regions
- Alveoli in upper regions are subjected to a greater distending pressure, resulting in greater volume and ventilation
- Compliance of apical alveoli is lower, while basilar alveoli are more compliant
- Apical alveoli have a higher FRC, while basilar alveoli have a higher IRV
Differences in Regional Ventilation After a Forced Expiration to the RV
- After a forced expiration to RV, dynamic compression occurs in the smaller airways of the basilar region
- Inspiration from low lung volumes initially goes to the upper alveoli, and later to the dependent alveoli
- Airways of the basilar dependent alveoli begin to open and fill later in the inspiration
Closing Volume
- Closing volume is the volume at which airway closure begins to occur
- Normally, it is around 10% of VC in young adults
- Loss of alveolar elastic recoil (from age or pathology) results in decreased traction on small airways, leading to airway closure in the dependent lung even at higher lung volumes
Alveolar and Physiologic Dead Space
- Alveolar dead space is the volume of alveolar air not equilibrating with pulmonary capillary blood
- Physiologic dead space is the volume of all inhaled air not exchanging with pulmonary capillary blood
- Physiologic dead space = Anatomic dead space + Alveolar dead space
Bohr Equation
- The Bohr equation determines physiologic dead space (alveolar + anatomic DS)
- It compares the partial pressure of CO2 in the blood (PaCO2) vs the exhaled CO2 (PeCO2)
- The greater the difference between these values, the greater the amount of dead space
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