Exam 3, L1 Flashcards
(31 cards)
What is dead space in healthy lungs primarily composed of?
Air in the upper airways and conducting zones — called anatomical dead space.
How much of a normal 500 mL tidal breath reaches the alveoli?
About 350 mL.
How much is anatomical dead space in a healthy adult?
Approximately 150 mL.
Is the transition from dead space to alveolar air a hard boundary?
No — there is a transitional zone where some mixing and limited gas exchange occur.
What is the formula for calculating partial pressure of a gas?
P_gas = F_gas × P_total
What values are used for total pressure in the lungs?
Either 760 mmHg (dry air) or 713 mmHg (humidified, subtracting 47 mmHg for water vapor).
How do you calculate the concentration of a gas in the lungs?
F_gas = P_gas / P_total
Why is nitrogen concentration lower in alveolar air than in dry air?
Because water vapor displaces nitrogen, reducing it from 80% to about 75%.
What does Fowler’s test measure?
Anatomical dead space using nitrogen content during expiration after a 100% O₂ breath.
What does the initial exhaled air contain in Fowler’s test?
0% nitrogen — it comes from anatomical dead space.
What is the midpoint of the transitional nitrogen slope used for?
To calculate dead space volume — typically around 150 mL in a healthy adult.
What is the goal of the nitrogen washout test?
To evaluate ventilation evenness by observing how quickly nitrogen is exhaled while breathing 100% O₂.
What is the expected end-point nitrogen concentration?
Around 2.5% in exhaled air.
What time is considered abnormal for nitrogen washout?
> 7 minutes to reach 2.5% indicates uneven ventilation or large lung volume.
What are causes of prolonged washout times?
COPD, large lungs, or poor ventilation distribution.
What does a flow-volume loop plot?
Airflow (y-axis) vs. lung volume (x-axis) during forced inspiration and expiration.
What does the top half of the loop represent?
Forced expiration from total lung capacity (TLC) to residual volume (RV).
What does the bottom half of the loop represent?
Forced inspiration from RV to TLC.
What is the shape of a normal flow-volume loop?
An upside-down ice cream cone — quick peak flow followed by tapering expiration.
What is effort dependence?
Early in expiration, airflow is influenced by how hard you push.
What is effort independence?
Later in expiration, airflow becomes limited by airway dynamics, not effort.
What causes effort-independent flow?
Airway compression from high pleural pressure exceeding airway pressure.
What changes in obstructive disease on the flow-volume loop?
Reduced peak flow, scooped-out shape, and increased residual volume.
What causes the “scooped” appearance in obstructive loops?
Small airway collapse and poor elastic recoil during forced expiration.
