Lab 4 - Respiratory

Question 1

How does the design of the H-P tube ensure that the sample of gas removed represents alveolar gas?

Answer 1

Long and thing tube = minimal diffusion (Fick’s Law)

Collection is near the mouth

Question 2

What could account for the difference between expected partial pressure values and those from the samples?

Answer 2

Technical error
Experimental error
Subject error

Question 3

What happened to alveolar gases after breath hold?

Answer 3

Build up of CO2
Decrease in O2

Question 4

What happened to alveolar gases after a deep inspiration?

Answer 4

Decrease in PCO2 and increase in PO2

Question 5

What is the effect of Hyperventilation on alveolar gases?

Answer 5

(Hyperventilation is fast and deep breathing causing an increase of alveolar gas turn over).

Causes increase in PO2 and decrease in PCO2.

Question 6

How did deep inspiration affect the duration of the breath-hold?

Answer 6

Can hold breath for longer

Question 7

How does hyperventilation alter pH/H+?

Answer 7

Equilibrium shifts to the left as there is a decrease in CO2.

Meaning decrease in H+ and increased pH (more alkaline).

Question 8

How did hyperventilation affect the duration of breath hold?

Answer 8

Hold breath for longer

Question 9

Why is there greater consistency between PCO2 than PO2 at the end of each breath hold?

Answer 9

Because our body has a greater sensitivity to CO2.

Question 10

Can you hold your breath for longer with a higher or lower PACO2?

Answer 10

Lower PCO2 = hold you breath for longer

Question 11

What is CaO2?

Answer 11

Arterial oxygen content

Question 12

What allows us to be able to have a large decrease in PaO2 before a change in ventilation is stimulated or you need to break your breath hold?

Answer 12

Because there is only a small change in CaO2, due to the shape of the O2- Hb dissociation curve

Question 13

Will a small change in PaCO2 cause a change in ventilation or make you break your breath hold?

Answer 13

yes - because it will cause a relatively large increase in CaO2 due to the share of the Co2 blood saturation curve

Question 14

What does your breath hold tell you about the relative importance of arterial PO2 and arterial PCO2 in the control of normal breathing?

Answer 14

Demonstrates that CO2 is the primary modulator of normal restful ventilation - because it produces H+ ions in the cerebrospinal fluid which stimulates central chemoreceptors and this is the main drive for ventilation

Question 15

What is the main drive of ventilation?

Answer 15

H+ ions in the cerebrospinal fluid which stimulates central chemoreceptors

Question 16

What causes FVC to be less than VC in pathological conditions?

Answer 16

Air getting trapped in a portion of the airway that is compressed or collapsed meaning that less air is able to be breathed out so FVC less than VC

Question 17

What must happen to Ptp in order for lung volume to increase?

Answer 17

Ptp must increase / become more positive

Question 18

What happens to transpulmonary pressure during inspiration?

Answer 18

The alveolar pressure becomes slightly more negative/subatmospheric which tends to decrease the Ptp

The intrapleural pressure becomes much more negative/subatmospheric which tends to have a large increase on transpulmonary pressure

The decrease in the intrapleural pressure is larger leading to an increase in the transpulomnary pressure

Question 19

What is a peak flow meter?

Answer 19

Lung function test - the one you blow into.

Can be used to detect obstructive lung disorders such as asthma as narrowing of the airways reduces the rate at which air can be exhaled.

Question 20

What other variables influences expected value on peak flow meter?

Answer 20

Age, sex and height

Question 21

What are the key differences between human lungs and the lung model?

Answer 21

Huge inter pleural space
Rigid walls
pleural space not filled with fluid
Model is one compartment whereas the lungs are millions of alveolar compartments

Question 22

What is the longest breath hod recorded with inspiring 21% O2 before the breath hold?

Answer 22

12 minutes

Question 23

What is the longest breath hold recorded after inspiring 100% O2 for 30 minutes?

Answer 23

24.5 minutes

Question 24

what is the primary cause of blackouts while free diving?

Answer 24

Cerebral hypoxia (not enough oxygen in the brain)

Question 25

How does drowning occur?

Answer 25

Once O2 in blood stream is used up your brain starts to be effected and you become unconscious - you’ll end up ingesting water and you will drown

Question 26

Explain how free diving drowning occurs?

Answer 26

1. Before you dive you hyperventilate (increasing in O2 and decreasing in CO2)
2. Once you dive you stop ventilation = O2 drops during breath hold and CO2 increases but due to hyperventilation induced CO2 depletion chemorecptor threshold of CO2 is not met despite how low O2 is.
3. Hyperventilation induced CO2 depletion means no breath reflex is stimulated and O2 now too low to stay conscious = Unconsciousness.
4. Once unsoncisous a reflex breath occurs even though your still underwater = breath in water = drown.

Question 27

Why are free divers more likely to black out as they ascend from a deep dive?

Answer 27

Because the partial pressure of oxygen rapidly decreases as you ascend therefore there is less driving force for O2 to being to Hb = PO2 drops too low to sustain consciousness = blackout

Question 28

What are the equations used to calculate the partial pressure of alveolar gases in mmHg under the temperature and humidity conditions of the body?

Answer 28

PAO2 = FAO2 x (PB - 47)
PACO2 = FACO2 x (PB - 47)

47 is the value for PH20 at 37 degrees C.

Question 29

What is normal PAO2 range?

Answer 29

98-108 mmHg

Question 30

What is normal PACO2 range?

Answer 30

36-42 mmHg