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All 12 Flashcards — Measuring lung volumes
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Question
What is a spirometer?
Answer
An instrument that **measures the air a person breathes in and out**, recording it as a **trace** of lung volume against time.
Question
Define tidal volume (TV).
Answer
The volume of air in **one normal, resting breath** — the height of one small wave on the trace.
Question
Define vital capacity (VC).
Answer
The **largest volume of air moved in one breath**: IRV + TV + ERV (deepest breath in to fullest breath out).
Question
Define residual volume (RV).
Answer
Air that **always stays in the lungs** and cannot be breathed out — so it never appears on the trace.
Question
How do you read vital capacity off a trace?
Answer
Measure the volume from the **top of the deepest breath in** to the **bottom of the fullest breath out**.
Question
How do you find the ventilation rate from a trace?
Answer
**Count the complete waves (breaths) in one minute.**
Question
What is the function of the one-way valves in a spirometer?
Answer
They keep **inhaled and exhaled air on separate tubes** so the two airstreams do not mix.
Question
What does the soda lime do in a spirometer?
Answer
It **absorbs the carbon dioxide breathed out**, so the person re-breathes air without a CO₂ build-up.
Question
Why does the resting baseline slope downward over time?
Answer
**Oxygen is used up in respiration** and the **CO₂ is absorbed by the soda lime (not replaced)**, so the total gas in the closed circuit falls.
Question
During inspiration, does the spirometer pen rise or fall?
Answer
It **rises** — air is drawn out of the chamber, the drum sinks and the pen goes up.
Question
How does the trace change during exercise?
Answer
The waves become **taller (larger tidal volume)** and **closer together (faster rate)**, raising the air inhaled per minute.
Question
How does total lung capacity relate to vital capacity?
Answer
**Total lung capacity = vital capacity + residual volume** — the residual volume can never be breathed out.
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Topic 2.6 hub
Gas exchange
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