Lab 4 - Respiratory Flashcards
How does the design of the H-P tube ensure that the sample of gas removed represents alveolar gas?
Long and thing tube = minimal diffusion (Fick’s Law)
Collection is near the mouth
What could account for the difference between expected partial pressure values and those from the samples?
Technical error
Experimental error
Subject error
What happened to alveolar gases after breath hold?
Build up of CO2
Decrease in O2
What happened to alveolar gases after a deep inspiration?
Decrease in PCO2 and increase in PO2
What is the effect of Hyperventilation on alveolar gases?
(Hyperventilation is fast and deep breathing causing an increase of alveolar gas turn over).
Causes increase in PO2 and decrease in PCO2.
How did deep inspiration affect the duration of the breath-hold?
Can hold breath for longer
How does hyperventilation alter pH/H+?
Equilibrium shifts to the left as there is a decrease in CO2.
Meaning decrease in H+ and increased pH (more alkaline).
How did hyperventilation affect the duration of breath hold?
Hold breath for longer
Why is there greater consistency between PCO2 than PO2 at the end of each breath hold?
Because our body has a greater sensitivity to CO2.
Can you hold your breath for longer with a higher or lower PACO2?
Lower PCO2 = hold you breath for longer
What is CaO2?
Arterial oxygen content
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?
Because there is only a small change in CaO2, due to the shape of the O2- Hb dissociation curve
Will a small change in PaCO2 cause a change in ventilation or make you break your breath hold?
yes - because it will cause a relatively large increase in CaO2 due to the share of the Co2 blood saturation curve
What does your breath hold tell you about the relative importance of arterial PO2 and arterial PCO2 in the control of normal breathing?
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
What is the main drive of ventilation?
H+ ions in the cerebrospinal fluid which stimulates central chemoreceptors
What causes FVC to be less than VC in pathological conditions?
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
What must happen to Ptp in order for lung volume to increase?
Ptp must increase / become more positive
What happens to transpulmonary pressure during inspiration?
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
What is a peak flow meter?
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.
What other variables influences expected value on peak flow meter?
Age, sex and height
What are the key differences between human lungs and the lung model?
Huge inter pleural space
Rigid walls
pleural space not filled with fluid
Model is one compartment whereas the lungs are millions of alveolar compartments
What is the longest breath hod recorded with inspiring 21% O2 before the breath hold?
12 minutes
What is the longest breath hold recorded after inspiring 100% O2 for 30 minutes?
24.5 minutes
what is the primary cause of blackouts while free diving?
Cerebral hypoxia (not enough oxygen in the brain)
How does drowning occur?
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
Explain how free diving drowning occurs?
- Before you dive you hyperventilate (increasing in O2 and decreasing in CO2)
- 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.
- Hyperventilation induced CO2 depletion means no breath reflex is stimulated and O2 now too low to stay conscious = Unconsciousness.
- Once unsoncisous a reflex breath occurs even though your still underwater = breath in water = drown.
Why are free divers more likely to black out as they ascend from a deep dive?
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
What are the equations used to calculate the partial pressure of alveolar gases in mmHg under the temperature and humidity conditions of the body?
PAO2 = FAO2 x (PB - 47)
PACO2 = FACO2 x (PB - 47)
47 is the value for PH20 at 37 degrees C.
What is normal PAO2 range?
98-108 mmHg
What is normal PACO2 range?
36-42 mmHg
