Vet Phys - Respiratory 5/6

What is the average PO2 of the gaseous O2 in the alveolus?

104 mmHg

What is the average $\text{PO}_2$ of venous blood entering the arterial end of the pulmonary capillary?

40 mmHg

What is the initial pressure difference for oxygen at the arterial end of the pulmonary capillary?

64 mmHg

How quickly does P_O2 rise as blood travels through the pulmonary capillary?

There is a rapid rise in P_O2 before blood has moved 1/3 of the way through the capillary

How does normal blood transit time in the pulmonary capillary compare to the time required for full oxygenation?

Blood stays in the capillary 3 times longer than needed

How does strenuous exercise affect oxygen demand and capillary transit time?

Oxygen uptake can require up to 20 times the normal amount of oxygen, while increased cardiac output reduces the time blood remains in the capillary

What safety factors provide the bandwidth to ensure full blood oxygenation during strenuous exercise?

Recruitment of capillaries in Zones 1 and 2 (which increases surface area), capillary distension, and built-in safety margins

How much blood passes through the alveolar capillaries?

98%

What is shunt flow?

When blood bypasses the gas exchange areas

What is the P_O2 of shunt blood?

40 mmHg

What is venous admixture?

the theoretical amount of deoxygenated mixed venous blood that must mix with ideal end-capillary pulmonary blood to account for the lower oxygen levels found in systemic arterial blood

What pressure does venous admixture of blood cause P_O2 to fall to?

95 mmHg

What are the key P_O2 pressure levels during oxygen diffusion in peripheral tissues?

• Arterial: 95 mmHg

• Venous: 40 mmHg1

• Interstitial Fluid: 40 mmHg

• Tissue: 23 mmHg

What primary factor drives an increase in interstitial P_O2

Increased blood flow.

How much of an increase in blood flow is required to raise interstitial P_O2 from 40 mmHg to 60 mmHg?

A 400x increase in blood flow.

What effect does a decrease in blood flow have on interstitial PO2?

Interstitial PO2 decreases.

How does increasing tissue metabolism impact interstitial PO2?

It increases oxygen consumption, thereby decreasing interstitial PO2

Why is there variability in intracellular PO2 across different tissues?

Due to considerable variability in the distance between capillaries and tissues.

What is the normal range and average value for intracellular PO2?

• Range: 5 – 40 mmHg

• Average: 23 mmHg

What minimum intracellular PO2 level is required for full support of cellular chemical processes?

Only 1 – 3 mmHg.

What is the relationship between cellular O2 consumption and CO2 diffusion in the gas exchange chain?

Virtually all O₂ consumed by cells becomes CO_2, which diffuses in the opposite direction at each point in the gas exchange chain

How does the diffusion rate of CO2 compare to O2, and what is the physiological implication?

CO2 diffuses about 20x faster than O2, meaning a much smaller pressure gradient is required to drive its diffusion.

What are the key PCO2 values throughout the gas exchange pathway?

• Intracellular P_CO2 = 46 mmHg

• Interstitial P_CO2 = 45 mmHg

• P_CO2 leaving capillary = 45 mmHg

• P_CO2 leaving lung = 40 mmHg

Is there a safety margin for carbon dioxide exchange during extreme physiological demands?

Yes, a safety factor exists for CO2 diffusion as well.

How do tissue capillary blood flow and tissue metabolism affect tissue PCO2 relative to their effect on tissue PO2?

They affect PCO2 in ways exactly opposite to their effect on tissue PO2

What effect does a 25% decrease in blood flow have on tissue PCO2?

results in 15 mmHg elevation of P_CO2

What happens to tissue PCO2 when blood flow is increased 6-fold?

reduces P_CO2 to 40 mmHg

How does a 10-fold increase in metabolic rate impact interstitial PCO2?

it elevates interstitial P_CO2 at all rates of blood flow

What percentage of oxygen is transported by chemical combination with hemoglobin in RBCs under normal conditions?

97%

What is the primary function of erythrocytes (RBCs)?

To transport hemoglobin (though some animals and invertebrates use free dissolved hemoglobin).

What is the molecular structure of hemoglobin and the oxidation state of its iron?

• Structure: 4 Heme chains (each composed of iron + 4 pyrrole rings)

• Iron Oxidation State: Ferrous state (Fe²⁺)

What crucial enzyme is contained within red blood cells for gas transport and pH regulation?

carbonic anhydrase.

What are the physical dimensions and structural properties of a normal RBC?

• Average Diameter: 7.8 µm

• Thickness: 2.3 µm (tapering to 1 µm in the center)

• Deformability: Highly deformable to pass through narrow capillaries

What is the nature of the chemical bond between oxygen and hemoglobin?

Oxygen binds loosely and reversibly to heme in hemoglobin.

How does the partial pressure of oxygen (P_O2) regulate oxygen binding and release from hemoglobin?

• High P_O2: Oxygen binds to heme (e.g., in pulmonary capillaries).

• Low P_O2: Oxygen is released from heme (e.g., in tissue capillaries).

What are the average hemoglobin percent saturation values leaving the lungs versus returning from tissues?

• Leaving lungs (arterial): Averages 97% saturation

• Returning from tissues (venous): Averages 75% saturation

How much oxygen can 1 gram of pure hemoglobin bind?

1.34 mL of O2 per 1 gram of hemoglobin.

Assuming a normal concentration of 15 grams of hemoglobin per 100 mL of blood, what is the total oxygen-carrying capacity at 100% saturation?

20 mL of O2 per 100 mL of blood (also expressed as 20 volume percent / 20 vol%).

What are the key oxygen parameters (PO2, % saturation, and O2 content) for systemic arterial vs. venous blood at rest?

• Arterial Blood: PO2 = 95 mmHg | 97% saturation | 19.4 mL O2 / 100 mL blood

• Venous Blood: PO2 = 40 mmHg | 75% saturation | 14.4 mL O2 / 100 mL blood

How much oxygen is delivered to tissues per 100 mL of blood flow under normal resting conditions?

About 5 mL’s of O2 are transported from the lungs to the tissue by each 100 mL of blood flow (19.4 mL − 14.4 mL).

How do oxygen parameters change in active muscle tissue during exercise?

• Muscle interstitial fluid PO2 falls from 40 mmHg to 15 mmHg

• Blood PO2 & Saturation: 15 mmHg | 25% saturation (4.4 mL O2 / 100 mL blood)

What does O2 transport look like in extreme cases of exercise?

•Under extreme cases, about 15 mL’s (3x of normal) of O2 are transported from the lungs to the tissue by each 100 mL of blood flow

How can total oxygen delivery to tissues increase up to 20-fold in trained athletes during strenuous exercise?

In trained athletes/animals, CO can increase 6-7x, meaning that O2 transport can increase up to 20x to the tissues

What is the Utilization Coefficient, and what are its normal resting vs. maximal exercise values?

• Definition: The percentage of blood/hemoglobin that gives up its O2 as it passes through tissue capillaries.

• Normal Rest: ~25%

• Extreme Exercise: 75% – 85%

What four key factors cause the oxygen-hemoglobin dissociation curve to shift to the right and downard?

1. increased H+ (Bohr effect)

2. CO2

3. blood temperature

4. BPG

What is BPG?

2,3-Bisphosphoglycerate (2,3-BPG) is a molecule in red blood cells that lowers hemoglobin's affinity for oxygen, helping release oxygen to body tissues that need it. [1, 2]

What causes upregulated BPG?

• high altitude

• chronic hypoxia/anemia

• pregnancy

What does a rightward shift in the curve mean?

Relatively more oxygen is off-loaded given the same PO2

What 4 things happen in a shift to the right of the curve?

1. increase H ions

2. increased CO2

3. increased temp

4. increased BPG

How do physiological conditions in exercising muscle compare to the lungs in terms of curve shifting?

• Exercising Muscle: Increased H+, CO2, and temperature shift the curve to the right, enhancing O2 delivery to working tissues.

• Lungs: Cooling, lower CO2, and higher pH keep the curve suited for high O2 affinity and loading.

What other function does hemoglobin have?

It’s a tissue oxygen buffer system, stabilizes PO2 in the tissues

How does hemoglobin set an upper limit of ~40 mmHg on normal tissue PO2?

For the standard 5 mL of O2 per 100 mL of blood to be released from hemoglobin, tissue PO2 must drop to ~40 mmHg. If tissue PO2 were higher, hemoglobin would not unload the needed oxygen

What is required for the normal 5mL of O2 / 100 mL of blood flow?

PO2 must fall to about 40 mmHG

What two factors allow large amounts of extra oxygen (up to 20x) to be delivered during heavy exercise with minimal drop in tissue PO2?

• The steep slope of the oxygen-hemoglobin dissociation curve (where a tiny drop in PO2 releases vast amounts of O2)

• The increase in tissue blood flow caused by decreased PO2

Why is the steep portion of the hemoglobin–O₂ dissociation curve physiologically important?

A small decrease in PO₂ causes large amounts of O₂ to be released from hemoglobin. This allows hemoglobin to automatically deliver oxygen to tissues and maintain tissue PO₂ within a relatively narrow range of about 15–40 mm Hg.

What is the normal alveolar PO₂, and how can it change in different environments?

• Normal alveolar PO₂ ≈ 104 mm Hg

• At high altitude, alveolar PO₂ may fall to less than half this value.

• In compressed air environments (deep-sea diving, pressurized chambers), alveolar PO₂ may rise to up to 10 times normal.

What happens to hemoglobin saturation when alveolar PO₂ falls to 60 mm Hg?

• At alveolar PO₂ = 60 mm Hg, arterial hemoglobin is still about 89% saturated with O₂.

• This is only 8% below the normal saturation of 97%.

• Demonstrates the safety margin provided by the plateau of the O₂–hemoglobin dissociation curve.

What happens to hemoglobin saturation when alveolar PO₂ rises to 500 mm Hg?

the maximum O2 saturation of hemoglobin can never rise above 100%, which is only 3% above the normal level of 97%.

How does hemoglobin act as an "oxygen buffer" for the tissues?

Even when alveolar PO₂ varies widely (from ~60 to >500 mm Hg), the PO₂ in peripheral tissues changes very little.

This demonstrates the oxygen-buffering function of hemoglobin, which helps maintain a relatively stable oxygen supply to tissues despite large fluctuations in alveolar oxygen levels.

In a normal resting pulmonary capillary, how long will it take for the blood to be saturated with oxygen?

a. 33% 

b. 50 %

c. 75%

d. All the way through

a. 33%

What is typical venous PO2 in a dog?

a. 104 mmHg

b. 95 mmHg

c. 40 mmHg

d. 15 mmHg

c. 40 mmHg

CO2 does not need the partial pressure differences of O2 because it diffuse faster

a. True

b.False

c. Capillary osmotic pressure

d. A and B

a. True

What is the effect of increased blood flow on PCO2 in interstitial fluid?

a. Increases it 

b. Decreases it

c. Doesn’t change it

d. Not enough information given

b. Decreases it

Why does the systemic PO2 average 95 mmHg and not the 104 mmHg of atmospheric air?

a. Diffusion distance is too small 

b. Surface area is too large

c. Blood flow is too slow thru capillaries

d. Systemic blood is a venous admixture

d. Systemic blood is a venous admixture

What are the function(s) of RBC’s?

a. Transport hemoglobin

b. Enzymatic action of carbonic anhydrase

c. Serve as immune cells

d. A and B

d. A and B

Given a PO2 of 40 mmHg, what would oxygen saturation be?

a. 90%

b. 75%

c. 20%

d. None of the above

b. 75%

An animal is heavily exercising but cannot increase their blood flow to those muscles. Assuming everything else is healthy, which statement is correct? 

a. Oxygen delivery would decrease without increased blood flow 

b. Hemoglobin saturation would remain the same

c. The fall in interstitial PO2 would cause increased offloading of oxygen from hemoglobin

d. All of the above

c. The fall in interstitial PO2 would cause increased offloading of oxygen from hemoglobin

What are the force(s) that cause a rightward and downward shift of the hemoglobin/oxygen dissociation curve?

a. Increased H+

b. Increased BPG

c. Increased CO2

d. Decreased Temperature

A, B, and C

True or false? Hemoglobin does not act a buffer, which we can derive as the variation in alveolar PO2 is mimicked in the PO2 of the tissues.

False