Physiology: oxygen uptake is a flow–content balance
A lower extraction fraction can coexist with greater total oxygen uptake if flow rises enough. A mixed sample also conceals regional differences. Keep flow, content and fractional extraction separate before interpreting a change.
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Scope and responsibility
An invented steady oxygen-transport balance for textbook learning. The free Calgary book is exercise physiology, not a full medical course. Costanzo gives a concise organ-system spine; the selected Guyton and Hall edition gives broader explanation. The numbers are not patient data, reference ranges, diagnosis or treatment advice.
Choose your starting point
I need free exercise-specific reading
Use the open exercise-physiology text for circulation, pulmonary physiology and metabolic measurement.
I need a concise medical course
Choose Costanzo for cellular foundations and organ-system mechanisms.
I need a fuller explanation
Use Guyton and Hall to expand the concise route, retaining the selected fourteenth edition.
Compare the three books
Open Textbook of Exercise Physiology
Brian R. MacIntosh (editor)
Free exercise-specific anchor
- Choose it when
- You know basic anatomy, units and graphs and want integrated exercise physiology.
- Use another route when
- You need a complete medical curriculum covering every organ system.
- Selected reading
- Pulmonary Physiology, Circulatory Physiology and Measurement of Metabolic Rates.
- Limits and trade-offs
- Open chapters connect oxygen delivery and exercise, but their specialized scope does not replace a medical spine.
Try before choosing
Multiply 5 L/min by a content difference of 50 mL O2/L.
Check your work: Uptake is 250 mL O2/min; liters cancel.
Costanzo Physiology
Linda S. Costanzo · Edition: 8 · 2026
Concise organ-system spine
- Choose it when
- You can study mechanisms from compact text, diagrams and quantitative relations.
- Use another route when
- You require a large reference with every explanatory detail.
- Selected reading
- Cellular foundations, cardiovascular physiology and respiratory physiology in the eighth edition.
- Limits and trade-offs
- Concise organization supports a first pass but may need expanded explanation; its 2026 release and 2027 copyright are different fields.
Try before choosing
Compare uptake and extraction for the two states in the main case.
Check your work: State B has greater uptake but smaller extraction fraction.
Guyton and Hall Textbook of Medical Physiology
John E. Hall; Michael E. Hall · Edition: 14 · 2020
Expanded systems reference
- Choose it when
- You want circulation and respiratory transport explained in more connected detail.
- Use another route when
- You need a short review or assume the selected edition is the latest.
- Selected reading
- Blood flow, circulation and oxygen transport across the corresponding organ-system discussions.
- Limits and trade-offs
- Breadth adds explanatory context and reading load; the selected fourteenth edition is retained rather than silently upgraded.
Try before choosing
Mix venous contents from beds with flows 2 and 8 L/min.
Check your work: Use a flow-weighted average, not the arithmetic mean of two samples.
Check your preparation
What is oxygen content?
Amount of oxygen per blood volume, here mL O2/L. It is not oxygen partial pressure or saturation percentage.
What is conserved at steady state?
For the stated compartment, oxygen uptake is Q(Ca−Cv), with matching inflow/outflow and no storage accumulation.
How is fractional extraction defined?
E=(Ca−Cv)/Ca for Ca>0. It is dimensionless and does not alone determine total uptake.
A six-step study plan
Steps completed: 0 / 6
These are your own study marks, not an assessment. They are not sent to this site.
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Define the variables
Selected reading: Circulation and transport.
What to do: Make a unit table for Q,Ca,Cv,uptake and E.
Check your work: Content, pressure and saturation are not substituted for one another.
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Calculate state A
Selected reading: Steady balance.
What to do: Compute delivery, uptake and extraction.
Check your work: Delivery 1000, uptake 250 mL/min, E=0.25.
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Calculate state B
Selected reading: Integrated transport.
What to do: Repeat and compare each quantity separately.
Check your work: Delivery 2000, uptake 400, E=0.20.
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Explain the apparent reversal
Selected reading: Flow–content relations.
What to do: Give an algebraic reason for greater uptake with smaller fraction.
Check your work: Uptake=QCaE; the rise in Q more than offsets the lower E.
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Resolve parallel mixing
Selected reading: Regional circulation and the follow-up.
What to do: Sum bed oxygen fluxes before dividing by total flow.
Check your work: Mixed Cv=160 and total uptake 400.
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Test identifiability
Selected reading: Your two bed models.
What to do: Construct a different regional allocation with the same mixed sample.
Check your work: Whole-system measurements need not identify regional uptake.
Worked exercise
Greater uptake with a smaller extraction fraction
In an invented steady model, state A has Q=5 L/min,Ca=200,Cv=150 mL O2/L. State B has Q=10 L/min,Ca=200,Cv=160 mL O2/L. Compare total uptake and extraction fraction.
Assumptions
Steady state, matched inflow/outflow, contents measured at the boundaries of the same modeled system, no oxygen storage change. These are exact educational values, not clinical observations.
- For A, uptake Q(Ca−Cv)=5·50=250 mL O2/min. Extraction E=50/200=0.25; delivery QCa=1000 mL O2/min.
- For B, uptake=10·40=400 mL O2/min. E=40/200=0.20; delivery=2000 mL O2/min.
- Uptake=delivery·E. Doubling delivery while extraction changes by a factor 0.8 increases uptake by a factor 1.6.
Answer and interpretation
Uptake increases from 250 to 400 mL O2/min while fractional extraction falls from 25% to 20%.
Test the result
Cv alone would suggest a smaller content difference, but not a smaller total uptake without flow. Units L/min times mL/L correctly give mL/min.
Change an assumption
A mixed sample hides regional allocation
Model state B as two parallel beds with common Ca=200 mL O2/L: Q1=2,Q2=8 L/min and Cv1=100,Cv2=175 mL O2/L. Find mixed Cv and uptake. Can the same whole-system result arise from another regional allocation?
- Venous oxygen flux is 2·100+8·175=1600 mL/min. Divide by total flow 10 to get mixed Cv=160 mL/L.
- Bed uptakes are 2·(200−100)=200 and 8·(200−175)=200 mL/min, summing to 400. An unweighted content mean 137.5 would wrongly predict 625.
- Alternatively set both regional venous contents to 160 with the same flows. Uptakes become 80 and 320 mL/min, still totaling 400, and mixed Cv remains 160.
Answer and interpretation
The mixed content is 160 mL O2/L and total uptake 400 mL O2/min. Regional uptake can be (200,200) or (80,320); it is not identified by the mixed result.
Test the result
In both models the sum of outgoing oxygen fluxes is 1600 mL/min and incoming flux is 2000. This is a transport-identifiability example, not evidence about any patient or exercise prescription.
Common mistakes
Content is pressure
Content, saturation and partial pressure are different quantities.
Extraction fraction is total uptake
Flow and arterial content are also required.
Equal-weight mixing
Conserved oxygen fluxes require flow weights.
Before moving on
- Compute uptake with consistent units.
- Explain a changed fraction without reversing the total conclusion.
- Demonstrate regional nonidentifiability constructively.
Sources and edition checks
Sources checked:
- Calgary: open exercise-physiology text
The free text contains pulmonary, circulatory and metabolic-measurement chapters, with exercise-specific scope.
- Elsevier: available eighth edition
The selected eighth edition was released in 2026 despite its 2027 copyright notice.
- Elsevier: selected fourteenth-edition catalogue
The publisher catalogue identifies the selected fourteenth edition and 2020 release; no later edition is substituted.
These are proposed study activities, not official course assignments or a claim that every book has been read cover to cover.