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7.2.5Unit 6: Practical Skills in Biology II

Calculation of Cardiac Output — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 27 of 48 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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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.
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Part 1 of 5The Cardiac Output Equation

Cardiac output
  • Cardiac output The volume of blood pumped out of one ventricle in one minute, measured in cm³ min⁻¹.
Heart rate
  • Heart rate The number of cardiac cycles per minute, in beats per minute.
Stroke volume
  • Stroke volume The volume of blood ejected from the left ventricle during one cardiac cycle, in cm³.
Formula
  • Formula Cardiac output = heart rate × stroke volume, which can be rearranged to find either of the other values.
Typical value
  • Typical value An adult at rest has a cardiac output of about 4.7 dm³ min⁻¹, and trained people often have higher values.

Part 2 of 5Control of Heart Rate

1
Baroreceptors detect changes in blood pressure, and chemoreceptors detect changes in blood pH and the carbon dioxide and oxygen levels.
2
Receptors send impulses to the cardiovascular control centre in the medulla oblongata.
3
For low blood pressure or exercise, impulses pass along sympathetic neurones, which release noradrenaline onto the sinoatrial node and increase its firing rate.
4
For high blood pressure or high oxygen levels, impulses pass along parasympathetic neurones, which release acetylcholine and slow the sinoatrial node.
5
As the factor returns toward normal, receptor signals fall and the heart rate returns to its resting level.

Part 3 of 5Breathing During Exercise

Breathing During Exercise
Stimulus
  • Stimulus Greater respiration raises blood CO₂, which forms carbonic acid, releases H⁺ and lowers blood pH.
Detection
  • Detection Chemoreceptors in the medulla, aortic bodies and carotid bodies respond to the lower pH.
Response
  • Response The medulla sends more frequent impulses to the diaphragm and intercostal muscles, increasing breathing rate and depth.
Outcome
  • Outcome More oxygen enters the blood and more CO₂ is removed, so pH returns toward normal.

Part 4 of 5Worked Example

Question

  • One cardiac cycle lasts 0.80 s and the stroke volume is 70 cm³.
  • Calculate the cardiac output in dm³ min⁻¹.

  1. Heart rate = 60 ÷ 0.80 = 75 beats per minute.
  2. Cardiac output = 75 × 70 = 5250 cm³ min⁻¹.
  3. Convert5250 ÷ 1000 = 5.25 dm³ min⁻¹.

Answer 5.25 dm³ min⁻¹.

Part 5 of 5Exam Checklist & Tips

7.2.5 – Key Points for the Exam

  • Cardiac output Volume of blood pumped by a ventricle per minute.
  • Stroke volume Volume of blood ejected from the ventricle in each beat.
  • Medulla oblongata The part of the brainstem that houses the cardiovascular and ventilation control centres.
  • Chemoreceptor A receptor that responds to changes in the chemical composition of blood.
  • Baroreceptor A receptor that responds to changes in blood pressure.

Common Mistakes

  • Mixing the units of cm³ and dm³ without converting; 1 dm³ equals 1000 cm³.
  • Using the length of a cycle in seconds directly as the heart rate; convert to beats per minute.
  • Stating that parasympathetic neurones speed up the heart.
  • Giving the stimulus for faster breathing as low oxygen rather than a fall in pH from raised CO₂.

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