DSA 2: Respiratory Adaptations Flashcards
How do you calculate alveolar oxygen levels?
Alveolar O2 (PAO2) = Inspired Oxygen - Oxygen consumed
How do you calculate inspired oxygen?
PiO2= (Patm - 47 mm Hg)x FiO2
How do you calculate oxygen consumed?
Oxygen Consumed = [PaCO2/RQ]
What is the normal respiratory quotient?
0.8
What respiratory quotient for those who are using an IV glucose solution?
1
What respiratory quotient for those who are hypoglycemic?
0.7
What is the proper way to calculate alveolar oxygen levels?
Alveolar O2 (PAO2) = [(Patm - 47 mm Hg)x FiO2] - [PaCO2/RQ]
Under normal/ideal conditions, the alveolar oxygen and the arterial oxygen should be at ______.
Equilibrium
-consider <12 mm Hg normal
If alveolar oxygen and the arterial oxygen are not in equilibrium, what does that mean?
Diffusion Impairment
- COPD
- Pneumonia
- Interstitial Fibrosis
What is the V/Q ratio?
Balance between:
Ventilation: bringing oxygen into alveoli and removing CO2 from the alveoli
Perfusion: removing O2 from the alveoli and adding CO2
What happens when V/Q ratio is decreased?
- Alveolar (and therefore arterial) levels of oxygen will decrease
- CO2 levels will increase
What happens when V/Q ratio is increased?
- Alveolar (and therefore arterial) levels of oxygen will increase
- CO2 levels will decrease
During hypoventilation, what happens to the alveolar/arterial gradient?
Stays the same
- Hypoventilation has nothing to do with the alveolar barrier itself
- A-a O2 gradient only increases when the process of gas exchange is impaired somehow - meaning that what happens at the alveolar barrier is impaired.
When we stand up, do we see a higher or lower V/Q ratio?
Lower: more blood reaches base of lung while less air reaches there
What is a physiological shunt?
Blood travelled to the lungs, it didn’t get any oxygen
What is an anatomical shunt?
Blood physically doesn’t enter the lungs
What is hypoxic vasoconstriction?
Low V/Q ratio:
- blood coming into the area will be directed to other parts of the lung.
- decreasing the perfusion of the hypoxic region will raise the V/Q ratio and bring the arterial blood gases closer to what we expect
What is bronchoconstriction?
High V/Q ratio:
- bronchi will constrict slightly to increase the resistance and decrease the amount of ventilation coming into an area that is not well perfused (although it won’t shut it down entirely).
- limits the amount of alveolar dead space that occurs and minimizes the ‘wasted’ work that occurs with alveolar dead space.
What is hypoxia?
Inadequate oxygen available for use by the tissues
What is hypoxemia?
Low oxygen content in the blood
What is hypoxic hypoxia?
PaO2 is below normal because:
- alveolar PO2 is reduced (e.g environmental reasons such as altitude)
- blood is unable to equilibrate fully with the alveolar air (e.g. as would occur in lung diseases with diffusion impairments such as emphysema or fibrosis)
What is anemic hypoxia?
Lungs are in perfect working condition, but the oxygen carrying capacity of the blood has been reduced.
- Carbon Monoxide: it binds to the Hb with high affinity, preventing oxygen from binding and reducing the oxygen carrying-capacity of blood
- Tissues do not get sufficient oxygen to maintain their metabolic needs because the blood is not carrying it.
What is circulatory hypoxia?
Lungs are fine and the blood can carry sufficient oxygen, but the tissue is not receiving sufficient oxygen
-Heart cannot pump the blood to the tissue (or arteries
blocked)
-Sickle cell anemia: cells sickle in the blood vessels and block them. (also produces an anemic hypoxia)
What is histotoxic hypoxia?
Lungs, blood, and circulatory system are all fine but tissue cells are poisoned and cannot use oxygen
- Cyanide: poisons systems that utilize oxygen to create energy and preventing them from using the oxygen
- Plenty of oxygen there but cells experience a lack of oxygen
What is direct stimulus for central chemoreceptors?
Hydrogen ions in CSF
Information about what blood gas is sent to the brain from central chemoreceptors?
Carbon Dioxide
If someone is suffering with a disease involving diffusion impairment, would the alveolar ventilation be greater or lesser compared to a healthy individual?
Greater: need more air to maintain oxygen levels
In early lung disease, do we see low or high levels of arterial oxygen?
Normal or low
In early lung disease, do we see low or high levels of arterial carbon dioxide?
Low
How do central chemoreceptors deal with lower levels of carbon dioxide?
Current Situation: PaCO2 and hydrogen levels are low, leading to an increase in pH (less hydrogen available)
Goal: Decrease pH
How: Choroid plexus will pump out hydrogen to CSF and pump bicarbonate back to blood
How does the body compensate for hypercapnia?
Due to excessive carbon dioxide in the blood, there is an acidification of CSF
-Choroid plexus shunts bicarbonate to CSF to neutralize hydrogen ions
With increasing altitude, barometric pressure ____.
With increasing altitude, barometric pressure decreases.
At higher altitudes, what are some immediate reactions the body has?
1) Response to hypoxia: peripheral chemoreceptors increase firing rate to increase ventilation
2) Increase in arterial oxygen means decrease in arterial carbon dioxide
3) Response to hypocapnia: central chemoreceptors increase firing rate
How does the body acclimate to higher altitudes?
1) Choroid plexus is more basic than normal: pumps more hydrogen and less bicarbonate, allowing peripheral chemoreceptors to increase ventilation
2) Release of erythropoietin: stimulation of RBC production to increase oxygen carrying capacity
3) Increase size and number of mitochondria: body can be more efficient with oxygen use
Why does altitude sickness occur?
Cerebral circulation in response to hypoxia
- Cerebral blood vessels will dilate to bring more blood into the area
- Increase in the perfusion pressure and therefore increased filtration
- Increased net filtration from the cerebral capillaries leads to mild cerebral edema, particularly if the autoregulatory mechanisms do not cause vasoconstriction
- Can cause headache, irritability, insomnia, etc
Why can pulmonary edemas be seen with altitude sickness?
Result of an increase in pulmonary vascular permeability
For every 10 meters below the water surface (sea water) you go, the barometric pressure increases by how much?
1 atm
How do you calculate total barometric pressure?
Total barometric pressure = (Pressure due to water) + (Pressure due to air)
*always remember 1 atm pressure from air
Why is too much oxygen content dangerous?
In excess, oxygen can be toxic due to formation of superoxide anion (O2-) and peroxide (H2O2).
-highly reactive species and are toxic to cells
How can high oxygen content be used to treat someone?
Carbon monoxide poisoning and injuries resulting in or related to decreased perfusion
-can increase oxygen levels in patient
What happens if there is too much nitrogen our system?
Nitrogen narcosis: similar effects of alcohol
Decompression sickness: in a quick ascent, nitrogen does not have time to reach lungs and instead stuck in body, which can be quite painful
