Respiratory Physiology II Flashcards
State the alveolar gas equation
What is the A-a gradient?
The difference between the oxygen content in the alveoli (A) and the oxygen content in the blood (a)
There are five causes of hypoxemia. Which ones are associated with changes in the A-a gradient?
A-a gradient is normal in hypoxic mixture and hypoventilation
A-a is increased by diffusion limitation, V/Q mismatch, and shunt
Hypoxemia is defined as a PaO2 < ______
80
How do you go about determining the A-a gradient?
You use the alveolar gas equation to calculate A and draw a blood gas to determine a
When breathing room air, what is a normal A-a gradient?
< 15 mmHg
What are some scenarios that increase the A-a gradient?
Age
Vasodilators (reduce the lungs ability to perform hypoxic vasoconstriction)
Right to left shunt (atelectasis, pneumonia, bronchial intubation, intracardiac defect)
Diffusion limitation (anything that thickens the alveolocapillary membrane)
How can you calculate the degree of shunting?
You can estimate that shunt (the amount of blood moving through without undergoing gas exchange)
increases 1% for every 20mmHg increase in the A-a gradient
What’s the difference between lung volumes and lung capacities?
Capacities are the combination of two or more volumes
INSPIRATORY RESERVE VOLUME
DEFINITION
NORMAL VALUE
Volume of gas that can be forcibly inhaled after a tidal inhalation
3000ml
TIDAL VOLUME
DEFINITION
NORMAL VALUE
volume of gas that enters and exits the lungs during tidal breathing
500ml
EXPIRATORY RESERVE VOLUME
DEFINITION
NORMAL VALUE
volume of gas that can be forcibly exhaled after a tidal exhalation
1100ml
RESIDUAL VOLUME
DEFINITION
NORMAL VALUE
volume of gas that remains after a forced exhalation
gas that CANNOT be exhaled
1200ml
CLOSING VOLUME
DEFINITION
NORMAL VALUE
volume above residual volume when the airways start to collapse
Conveyed as a percentage of the total lung capacity
for young people it’s around 30%
Old people around 55%
TOTAL LUNG CAPACITY
DEFINITION
NORMAL VALUE
IRV + TV + ERV + RV
5,800ml
VITAL CAPACITY
DEFINITION
NORMAL VALUE
IRV + TV + ERV
4,500 ml
INSPIRATORY CAPACITY
DEFINITION
NORMAL VALUE
IRV + TV
3500mL
FUNCTIONAL RESIDUAL CAPACITY
DEFINITION
NORMAL VALUE
RV + ERV
volume of the lung at end-expiration
2300 mL
CLOSING CAPACITY
DEFINITION
NORMAL VALUE
absolute volume of gas contained in the lungs when the small airways close
RV + CV
Variable
What are the weight-based calculations for Vt, VC, and FRC?
Vt: 6-8 ml/kg
VC: 65-75 ml/kg
FRC: 35 ml/kg
BASED ON IBW NOT ACTUAL WEIGHT
How do lung volumes differ in females?
25% smaller
Lung volumes are _____ when sitting and ____ when supine
larger
smaller
Patients with obstructive lung disease have increased:
residual volume
closing capacity
total lung capacity
Spirometry cannot measure ______
residual volume
so it also can’t measure total lung capacity or FRC
also can’t measure closing volume or capacity
Functional Residual Capacity is:
the volume of air in the lungs at the end of expiration
At the point of FRC, the lungs are in a state of:
static equilibrium
The inward elastic recoil is exactly equal to the outward elastic recoil
_______ is the volume of air that prevents hypoxemia during apnea
FRC
How can we determine how long a patient can remain apneic before becoming hypoxemic?
FRC / VO2
Conditions that reduce the FRC tend to reduce _____ or _____
Outward lung expansion
Lung compliance
What are some causes of decreased FRC in the OR?
What factors increase closing volume?
What’s the difference between CaO2 and DO2?
CaO2 is the carrying capacity of the blood
DO2 is the delivery of oxygen to tissues per minute
Most oxygen forms a reversible bond with hemoglobin. The remainder dissolves into the blood according to _______ law
Henry’s
How can you calculate the carrying capacity of the blood?
What is this number?
What is this number?
_____ is the driving mechanism of DO2
Cardiac Output
What is the equation for DO2?
What is the calculation for VO2?
Fick’s Equation!
What causes a decreased p50?
What causes increased p50?
Most hemoglobinopathies effect the oxyhemoglobin dissociation curve by causing a shift to the:
Left
What is the Bohr Effect?
An increase in PaCO2 and a decrease in pH cause hemoglobin to release oxygen
What is 2,3 - DPG?
It’s a by-product of RBC glycolysis
THINK: RBCs are in glycolysis when there isn’t enough oxygen
DPG causes a right shift, making it easier for oxygen to be released
It makes sense that in chronic hypoxic states, 2,3-DPG is VITAL to adapting
Why is it significant that banked blood is low in 2,3-DPG?
Banked blood is shifted to the left. It will not released oxygen as easily, reducing DO2
Why is fetal blood always shifted to the left?
Because HgB F does not have 2,3-DPG
Where is ATP stored in the body?
It isn’t! ATP cannot be stored, so the supply must be continuously replenished
What is the byproduct of glycolysis?
What happens after glucose is broken down into pyruvic acid?
The primary purpose of the Kreb’s cycle is to:
Produce large amounts of H+ ions in the form of NADH
In oxidative phosphorylation, _____ is the final electron accepter
Oxygen
What are the end products of oxidative phosphorylation?
34 ATP
Water
What is the Hamburger shift?
The shifting of Cl- into venous blood cells to keep the cell electrically neutral after bicarb is transferred to the plasma
What is carbonic anhydrase?
Where is it found?
Facilitates formation of carbonic acid out of water and CO2
It is present inside of erythrocytes, NOT in the plasma
Why is venous hematocrit always higher than arterial hematocrit?
When Cl ions shift into the cells, water moves osmotically with them
Venous erythrocytes are always a little larger, and therefore take up a greater percentage of the blood volume
Solubility of CO2 and O2 is a function of ______ law
Henry’s
In the presence of oxygenated hemoglobin, the CO2 dissociation curve shifts to the _____
Right
Blood has less affinity for CO2 and it is therefore “released”
In the presence of deoxygenated Hgb, the CO2 dissociation curves shifts to the ______
left
When there’s not as much O2, the blood “loves” CO2
