2.6.4Additional lessons
Measuring Lung Volumes: Skills — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 30 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Using a Spirometer
1
The subject breathes through a mouthpiece connected to a chamber whose lid moves up and down with each breath.
2
The movement of the lid is recorded by a pen on a revolving drum or by a computer that draws a trace.
3
Soda lime in the circuit absorbs the carbon dioxide breathed out, so the fall in trace level shows oxygen used.
4
The trace is calibrated so that vertical distance represents volume, usually in dm³ or cm³.
5
Each breath produces one peak and trough, so counting peaks over time gives the ventilation rate.
Section 2 of 5Lung Volumes
Tidal volume
- Tidal volume The volume of air breathed in or out in one normal breath at rest.
Inspiratory reserve volume
- Inspiratory reserve volume The extra air that can be breathed in after a normal inspiration.
Expiratory reserve volume
- Expiratory reserve volume The extra air that can be breathed out after a normal expiration.
Vital capacity
- Vital capacity The largest volume that can be exhaled after the deepest possible inhalation, VC = TV + IRV + ERV.
Residual volume
- Residual volume The air left in the lungs after the strongest exhalation, which cannot be measured by a spirometer.
| Quantity | Typical use | Where read on trace |
|---|---|---|
| Tidal volume | Resting breath size | Height between peak and trough of a normal breath |
| Vital capacity | Maximum breath size | Height from deepest inhalation to deepest exhalation |
| Ventilation rate | Breaths per minute | Count peaks per minute |
Section 3 of 5Interpreting Results
Interpreting Results
Exercise
- Exercise During exercise, both tidal volume and ventilation rate increase, so peaks are taller and closer together.
Fitness and size
- Fitness and size Vital capacity varies with age, sex, height and fitness, so comparisons need the same type of subject.
Reliability
- Reliability Repeat measurements and take a mean to reduce the effect of anomalies.
Safety
- Safety Use a clean mouthpiece, sterilise the equipment between users and avoid the subject feeling dizzy.
Section 4 of 5Worked Example
Question
- A spirometer trace shows tidal volume 0.5 dm³, inspiratory reserve volume 3.0 dm³ and expiratory reserve volume 1.1 dm³.
- The subject takes 14 breaths per minute.
- Calculate vital capacity and minute ventilation.
- Vital capacity = TV + IRV + ERV = 0.5 + 3.0 + 1.1 = 4.6 dm³.
- Minute ventilation = ventilation rate × tidal volume = 14 × 0.5.
- 14 × 0.5 = 7.0 dm³ per minute.
Answer Vital capacity is 4.6 dm³ and minute ventilation is 7.0 dm³ per minute.
Section 5 of 5Exam Checklist & Tips
2.6.4 – Key Points for the Exam
- Spirometer A device used to record the volume and rate of breathing.
- Tidal volume The volume of one resting breath.
- Vital capacity The maximum volume of air that can be breathed out after a maximal inhalation.
- Residual volume The air that remains in the lungs after maximum exhalation.
Common Mistakes
- Including residual volume in the vital capacity calculation, when it is not part of it.
- Reading ventilation rate from the height of the trace rather than the number of peaks.
- Forgetting to state the units, such as dm³ or cm³.
- Saying that a spirometer measures the air in the lungs completely, when it cannot measure residual volume.
Last updated:
\n