Questions: V/Q mismatch and oxygen in the blood Flashcards
Remember the patient from Session 2 ith coal miners lung? (Reminder: A 65-year-old retired coal miner is diagnosed with Diffuse Lung Fibrosis caused by coal dust (pneumoconiosis). Analysis of his arterial blood reveals a pO2 of 8.0 kPa. The pCO2 is in the normal range at 5.3kPa
Why is his pO2 low while his pCO2 is in the normal
range?
in diffuse fibrosis, the intersititum becomes thickened, therefore disrupting diffusioj of O2 across the membrane.
Howevere CO2 is 20x more soluble than O2, so can keep with the adequate gas exchange
A woman decides to climb Mount Kilimanjaro;she exercises in her home city of Leicester by participating in local triathlons. She arrives in Dar es Salaam, the capital of Tanzania and feels well, however, as she ascends Mount Kilimanjaro she notes increasing breathlessness whilst climbing (dyspnoea on exertion). A recent sign saying how far she has climbed states that at this elevation the atmospheric pressure is 60 kPa, whereas where she arrived in Dar es Salaam it was 101 kPa.
- 1 Assuming a water vapour pressure of 6.2O8 kPa, and normal levels of oxygen (20.9% of air), what would the partial pressure of oxygen be in this persons
* trachea when she was in Dar es Salaam?
101 ( atmospheric pressure in Dar es Salaam) - 6.208 (water vapour pressure)= 94.792
therefore 20.9% of 94.792= 0.209x 94.792
pO2 in trachea= 19.81
Assuming a water vapour pressure of 6.28 kPa, and normal levels of oxygen (20.9% of air), what would the partial pressure of oxygen be in this persons trachea when she was on Kilimanjaro at the level of the sign?
60kPa- 6.28= 53.72
53.72 x 0.209= 11.22 pO2
Why do you think this person had dyspnoea on exertion as she climbed Mount Kilimanjaro?
chemoreceptors in the carotid bodies and aortic sinuses detect hypoxaemia and send signals back to the resp cnetre in the medulla to increase breathing minute rate
Whenapersongoesdeepseadivingtheirbodyis no longer exposed to atmospheric pressure but rather to water pressure; because water is much denser than air, it exerts a much greater compressive force on the body. Consequently, the air being breathed in (provided from the air tanks) is at a higher pressure whilst the diver is underwater.
The gas in the scuba divers tank will typically be air and thus will have the same percentages of oxygen, nitrogen and carbon dioxide as in the air: 21% oxygen, 78% nitrogen and 1% CO2 and other inert gases.
4.1 What happens to the amount of nitrogen dissolved in a divers blood if the pressure doubles from 100 kPa to 200 kPa (as happens after diving 10 meters)?
amount dissolved= partial pressure x solubility coefficient of gas
therefore it will double
A 24-year-old man is noted to be hyperventilating (increased rate and depth of respiration) during a panic attack.
what is likely to happen to his aolveolar pO2 and pCO2?
pO2 increase
- increased oxygen minute rate.
- increased o2 conc gradient
- max O2 pp- highe rO2 in capillaries
pCO2 decrease
- ‘blowing off CO2’
A 30-year-old man was found in a semiconscious
A narcotic overdose is suspected. His breathing is slow and shallow. What is likely to have happened to his alveolar pO2 and pCO2?
decreased pO2
increased pCO2
What will happen to the total content of oxygen in the blood if a normal individual breathes air at twice the normal atmospheric pressure?
only increase by a tiny bit
amount of O2 dissolved at normal atmospheric pressure= solubility coeffient (0.1) x (pO2 (13.3)= 0.313
Can you think of a pathological process that causes V/Q mismatch by decreasing perfusion, but not affecting ventilation? How would you express that V:Q ratio?
pulmonary embolism
V/Q >1
Can you think of a pathological condition that causes V/Q mismatch by decreasing ventilation relative to perfusion?
- asthma
- aspiration
- mucus plus
SHUNT
A 28-year-old man has a severe pneumonia affecting the left lung (left upper and lower lobes). The diagram below represents the alveolar units affected by pneumonia on the left side and the normal alveolar units on the right. Since an acute inflammatory exudate fills the alveoli of the left lung, ventilation of these alveoli is reduced.
The PaO2 & PaCO2 of the alveolar air on each sides and blood draining the two sides is shown in the following image and table.
The blood returning from both lungs mixes in the left atrium.
Assume that equal amounts of blood are being drained from the lung two sides.
Using the oxygen-Hb dissociation curve work out the oxygen content and pO2 of the mixed blood (Note: Both % O2 saturation & the corresponding O2 content are shown on two separate scales on the vertical axis).
A 28-year-old man has a severe pneumonia affecting the left lung (left upper and lower lobes). The diagram below represents the alveolar units affected by pneumonia on the left side and the normal alveolar units on the right. Since an acute inflammatory exudate fills the alveoli of the left lung, ventilation of these alveoli is reduced.
The PaO2 & PaCO2 of the alveolar air on each sides and blood draining the two sides is shown in the following image and table.
The blood returning from both lungs mixes in the left atrium.
Assume that equal amounts of blood are being drained from the lung two sides.
What is the oxygen content in blood after it mixes?
The paO2 of blood after it mixes?
PP is not linear (cant just divide the two pps by each other)- need to add total O2 content and use the graph
