Practicals (lent and easter)

Question 1

What are possible explanations for increasing spirometer volume?

Answer 1

1. Leak in the spirometer, so air is sucked into the apparatus.
2. Forgetting to wear nose-clip.

Question 2

Why was the response to hypoxia (low PO₂) not induced during hypoxia experiment (air w. CO₂ absorber)?

Answer 2

Hyperventilation only induced by the PCRs when PO₂ < 60mmHg, which was never reached in the experiment.

Question 3

What experimental precautions should have been taken during the breathing experiments?

Answer 3

1. Subjects should be breathing normally and not controlling breathing.
2. Subjects should not be able to see the monitor.
3. Subjects (and experimenters) should not know the gas mixture. This is called double blinding.
4. Data for breathing rate/tidal volume should have been averaged over same time window.
5. Volume of gas in the spirometer at the beginning of each experiment should be the same.

Question 4

Why are estimates for tidal volume expected to be underestimates if gas used was pure O₂ and a CO₂ absorber was in circuit?

Answer 4

Volume of CO₂ in expired gas will be absorbed, so measured experatory volume would be smaller than actual volume.

Question 5

What is different about a spirometry tidal volume measurment compared to lung tidal volume measurment?

Answer 5

• The lowest point in spirometry trace is inspiration while the highest point is expiration.

Question 6

How is oxygen debt calculated?

Answer 6

Question 7

How are volumes converted between atmospheric temperature pressure saturated (ATPS) and standard temperature pressure dry (STPD)?

Answer 7

Where:

A = Atmospheric temperature

S = Saturated water pressure

T = Atmospheric temperature (in °C)

Question 8

What evidence is there for feedforward control of ventilation during exercise?

Answer 8

Ventilation rate immediately increases at the beginning of exercise. This response is too quick for it to be mediated by feedback control via increased PCO₂.

Question 9

What is the role of feedback during excercise?

Answer 9

Fine-tuning. Matching of ventilation rate exactly to rate of O₂ consumption.

Question 10

What causes the oxygen debt?

Answer 10

• Metabolic inertia
• At the onset of exercise, the rate of O₂ supply to mitochondria is insufficient to supply the muscles with enough energy.
• Phosphocreatine and lactate fermentation used to make up for ATP deficit.

Question 11

What are the processes occuring during oxygen debt repayment?

Answer 11

1. Restoration of PCr and ATP supply in muscles.
2. Metabolising lactate produced by exercise.
3. Restoring myoglobin O₂ supply.

Question 12

Why is oxygen debt repayment greater than oxygen debt?

Answer 12

1. Extra O2 consumption by heart muscle due to faster heart rate.
2. Extra O2 consumption by respiratory muscle due to elevated ventilation rate.
3. Increased body temperature due to exercise results in increased rate of metabolism.
4. Restoring ionic concentration gradients.

Question 13

What is the BMR for males and females?

Answer 13

• Male: 65-75 W
• Female: 55-65 W

Question 14

What is the equation for calculating incremental efficiency?

Answer 14

Incremental efficiency = 0.3 x (Y₁ - Y₂)/(X₁ - X₂)

Where:

Y = Rate of work against resistance

X = Rate of O₂ consumption

Question 15

What is the conversion between mmHg and KPa?

Answer 15

1 mmHg = ~0.13 kPa

Question 16

How are the alveolar gas partial pressures calculated using end-expiratory gas %ages?

Answer 16

P_gas = (A-47) x %gas/100

Question 17

What type of diagram is a Davenport diagram?

Answer 17

Nomogram

Question 18

Why are 3 breaths taken in and out quickly during the P_VCO2 experiment?

Answer 18

To replace dead-space air with air from the Douglas bag, ensuring that all air entering the lungs during actual measurment is from the Douglas bag and contains the same gas percentages.

Question 19

What are the possible sources of errors when measuring the cardiac output?

Answer 19

1. The gas analyser may not have been calibrated properly.
2. The gas in the Douglas bag may not have been well mixed.
3. The extrapolation may not have been accurate when finding the value of P_VCO2.
4. The subject may have been hyper-/hypoventilating during any experiment.

Question 20

What are the possible experimental errors associated with blood glucose experiments?

Answer 20

1. Some subjects may not have consumed all the food.
2. Some subjects may not have washed their hands after eating, resulting in higher blood glucose measurments.
3. Some subjects may not have fasted for >5 hours prior to experiment.

Question 21

What are the possible reasons for obtaining RQ value outside normal physiological range (0.7-1.0)?

Answer 21

1. Hyperventilation would give RQ greater than 1.0.
2. If gas breathed in was gas in the tube, this would skew the results, giving RQ greater than it would be.
3. Errors in the gas analyser.
4. The RQ calculation itself is slightly flawed.

Question 22

Why does blood glucose never reach theoretical maximum predicted for each food item?

Answer 22

1. Glucose is absorbed from the gut slowly instead of instantaneously.
2. Some glucose is stored in the liver and never makes it into the systemic circulation.
3. Glucose may diffuse freely from plasma into ECF.
4. Tissues are stimulated to take up glucose from the blood on secretion of insulin.