Pulmonary Physiology Flashcards
What are the stages of respiration for oxygen?
- ventilation 2. pulmonary gas exchange 3. gas transports 4. peripheral gas exchange
Contrast the gas exchange system and the conductive system.
Conductive: continues until terminal bronchioles, anatomical dead space, roughly 150 mL Gas exchange: repiratory bronchioles starts, alveolar exchange, roughly 2.5-3 L
Describe Fick’s Law of Diffusion.
D = (A/T)*D*(P1-P2) Diffusion constant = solubility/sqrt(MW)
What is the air fraction of oxygen in room air?
21%
How much of the pressure in the trachea is due to water vapor that needs to be subtracted out?
47 mmHg
Contrast elasticity and compliance.
Elasticity is the ability to return to original shape and compliance is the ability to change shape. (Think of a rubber band!) They are inverses of each other. Compliance = 1/elasticity = change in V/change in P
What equation is used to calculate alveolar O2?
Palv O2 = (760-47) X FiO2 – PalvCO2/0.8 You have to subtract out the partial pressure of carbon dioxide that is present at this level of the exchange. The 0.8 is the gas exchange ratio between CO2 and O2.
What are the four lung volumes?
Tidal volume, residual volume, inspiratory reserve volume, expiratory reserve volume
What are the four lung capacities?
Total lung capacity, functional reserve capacity, vital capacity, inspiratory capcity
If you breathed in 500 mL of air, how much air is in the gas exchange system? How much is in the conductive system?
150 ml in conductive 350 ml in gas exchange
Which lung volumes and capacities cannot be measured by spirometry?
residual volume, FRC, and TLC
What is the equation for minute ventilation?
VE = RR x TV Normally 7500/min
Describe the relationships between alveolar minute ventilation and blood flow?
They are usually a 1:1 ratio
Contrast anatomic dead space and physiologic dead space.
Anatomic dead space is the conducting zone. In physiologic dead space, there are alveoli but they are not functioning properly and therefore functionally is considered dead space.
What is the relationship between PaCO2 and minute ventilation? How is this related to adjusting ventilators?
VeCO2 x 0.862/ (1-Vd/VT) = Ve x PaCO2 = constant (in a steady state) If you adjust the respiratory rate, then the PaCO2 and Ve have an inverse relationship. If you adjust the tidal volume, this is a more difficult relationship to govern.
Fowler method
Used to measure anatomical dead space. Patient inhales 100% O2, when nitrogen or carbon dioxide starts to appear on expiration, then they know that have reached the physiologic area.
Bohr method
Collect patient breathe and measure expired CO2 to infer the physiologic dead space.
What does it mean for a gas to be perfusion limited?
This means that the gas diffuses readily accross the membrane, but what limits it is how much blood and how quickly it can perfuse that area. For example, N20.
What does it mean for a gas to be diffusion limited?
The gas does not easily cross diffuse accross the barrier and so it is limited by how quickly it can perfuse rather than by perfusion. For example, CO. Because CO gets bound up by hemoglobin, there is always a gradient (P1-P2), so what determines the amount of gets through is how fast it can diffuse, not perfusion.
Explain oxygen in terms of perfusion limited and diffusion limited.
Oxygen is considered both perfusion and diffusion limited. Intiially, oxygen is more limited by perfusion, but later on it is limitted by diffusion. (0 to 0.25 then 0.25 to 0.75)
How would oxygen limitation change with fibrosis?
This would shift oxygen to be more limited in terms of diffusion because of the increased of thickness in the alveolar membrane per Fick’s Law of Diffusion.
How do we measure a patient’s diffusion capability?
We use CO because it is a gas that is diffusion dependent and Fick’s Law of diffusion. We dervie that DL (transfer factor) = Vgas/PACO.
What are the five physiologic causes of hypoxemia?
Low PaO2
- Low inspired O2
- Hypoventilation
- Diffusion limitations
- Shunt
- V/Q imbalance
Describe hypoxemia caused by low PiO2.
This results in lower oxygenation and can be corrected by putting the patient on 100% oxygen.
Describe hypoxemia caused by hypoventilation.
The lungs are not properly filled with oxygen and there is a build up of CO2 in the arteries. The treatment is to put someone on 100% oxygen.
Describe hypoxemia due to diffusion limitations.
This can result from a thickening of the blood gas barrier. This can be treated by putting the patient on 100% O2.
Describe hypoxemia due to a shunt.
There is perfusion but no ventilation. V/Q = O
You cannot fix this with 100% oxygen.
What is are examples of two shunts?
Bronchial circulation and Thebesian circulation
What causes the a-A gradient?
Anatomical shunts
Describe V/Q imbalance.
V/Q is normally 1.
With anatomical dead space, V/Q = infinity. This is normal.
Contrast anatomic and physiologic dead space.
Anatomic dead space is normal areas that lack gas exchange. Physiologic dead space is equal to the amount of anatomic dead space plus pathologic dead space.
Explain how shunts and and mucus block affect the V/Q ratio.
If there is a block of the airway, the V/Q ratio will go towards zero. If there is an embolism, then the V/Q ratio will go towards infinity.
Why will the V/Q ratio for the lung as a whole never be above 1?
The pulmonary circulation is very effective at matching high blood flow to areas of high ventilation. Usually the pathologies will result in lower V/Q ratios. Under normal conditions, V/Q can be corrected by putting someone on 100% oxygen.
Contrast diffusion at the top and bottom of the lungs.
Bottom > Top
The alveoli at the top of the lung are normally open but purely perfused. The opposite is true at the bottom of th elung, but with inhalation, these alveoli open.
The best V/Q ratio is at rib 3 with a V/Q of 1.
Describe Westing Zones.
Zone 1: top of lung; alveolar pressure > vascular pressure
Zone 2: middle of lung; alveolar pressure = vascular pressure
Zone 3: bottom of lung: alveolar pressure < vascular pressure
Explain the five cuases of hypoxemia, the A-a gradient, and the treatment.
How much oxygen can be carried by hemoglobin?
1.34 ml O2/ g Hb
How do you calculate oxygen delivery?
DO2 = CaO2 x CO x 10
How do you calculate oxygen consumption? (VO2)
VO2 = CO x (CaO2-CvO2) x 10
How do you calculate oxygen content?
CaO2 = (HbxSaO2X1.34) + (PaO2 x 0.003)
Extraction ratio
The fraciton of O2 delivered in the blood that is consumed by tissue; maximal is 66%
What is the capacity of oxygen?
Maximal saturation of hemoglobin, the most oxygen that can be carried.
Describe the relationship between extraction fraction and hemorrage.
If there is blood loss, the body can extract up to 66% of oxygen from the blood supply before there is a feeling of oxygen loss.
Describe the relationship between sepsis and extraction ratio.
When the body is fighting an infection, more oxygen is required. As long as DO2 is above 1000 ml/min, the body can compensate. But in septic shock, it falls below this. This is why lactic acid is a hallmark of septic shock. In order to account for this, you need to increase delivery and reduce consumption.
Describe the Hb binding curve.
This curve is sigmoidal due to the way in which it becomes easier for oxygen to bind to Hb after the first oxygen has bound.
What would cause a right or left shift in the Hb curve?
Right shift causes advantagous because it unloads more oxygen. It is caused by pH drop, more CO2, temperature increase, DPG. (Exercise)
Left shift of Hb is bad because it makes it harder to unload oxygen (Carbon monoxide poisioning) Causes by the opposite as above.
What is the concentration of oxygen and carbon dioxide in the interstitial fluid?
40 mmHg O2 and 45 mmHg CO2
What percentage of CO2 is carried by Hb, bicarbonate, or dissolved?
10% dissolved
30% Hb
60% bicarbonate
Haldane effect
Deoxygenation of blood increases it ability to carry CO2.
In RBC, carbonic anhydrase converts CO2 to bicarbonate.
CO2 + H2O → H2CO3 → H+ + HCO3−
Because deoxygenated Hb will readily uptake H, it shifts this equation to the right resulting in increased production of HCO3 and carrying capacity for bicarbonate in the blood.
What factors cause a right shift in the Hb saturation curve?
“CADET”
CO2, academia, DPG, exercise, temperature
What makes a left shift caused by carbon monoxide a double whammy for the Hb saturation curve?
First of all CO binds with a much higher affinity than oxygen to Hb. Secondly, this causes a leftward shift of the Hb saturation curve meaning that oxygen does not unload as easily into the tissues.
How is CO poisioning treated?
Put patient in a hyperbolic chamer with 100% O2.
What are the partial pressures of the interstitium for CO2 and O2?
CO2: 40 mmHg
O2: 45 mmHg
How is CO2 carried in the blood?
dissolved 10%
Hb 30%
bicarbonate 60%
What organs are responsible for acid/base balance?
Lungs & kidneys
Describe the speed of metabolic v. respiratory compensation for acid base imbalance.
Metabolic = slow
Respiratory = fast
What are the normal values of the following: physiologic pH, PaCO2, and PaO2?
PaCO2 = 40 mmHg
pH = 7.4
PaO2 = 95 mmHg
Henderson-Hasselbach equation
pH = 6.1 + log(HCO3/0.03PCO2)
Acidemia/Alkalemia
Blood pH below/above 7.4
Acidosis/Alkalosis
Disorder dealing with lowered/elevated pH
What are the initial changes in HCO3 and CO2 levels related to the four different acid base balance issues?
Respiratory acidosis: High CO2
Respiratory alkalosis: Low CO2
Metabolic acidosis: Low HCO3
Metabolic alkalosis: High HCO3
How do you determine whether respiratory acidosis is acute or chronic?
Acute respiratory acidosis:
A change in PaCO2 by 10 = change in pH by 0.08 in the opposite direction
For example, if the CO2 is elevated from 40 to 60 mmHg, then the pH would be lowered from 7.4 to 7.24. For acute respiratory acidosis, the HCO3 value will remain the same because not enough time has passed for it to compensate.
Chronic respiratory acidosis:
A change in PaCO2 by 10 = change by 0.3 to 0.5 units
Summarize the expected pH, PaCO2, and HCO3 for a patient with the six forms of acidosis/alkalosis.
“ROME”
Respiratory Opposite Metabolic Equal
Respiratory Increase pH decrease CO2 alkalosis
Metabolic Increase PH increase HCO3 increases alklaosis
Contrast metabolic alkalosis and metabolic acidosis.
Metabolic acidosis results from the decrease in HCO3, which leads to a lower pH. The body immediately responds by hyperventalating lowering PaCO2.
Metabolic alkalosis results from the increase of HCO3, which leads to a higher pH. The body immediately responds by hypoventalating increasing PaCO2.
Davenport Diagrams
These diagrams illustrate the mechanisms of compensation for alkalosis and acidosis either renal or respiratory.
What factors alter compliance of a lung?
Collagen fibers can create stiffness in the lung. Elastin fibers contribute to increased elasticity. Cellularity of the interstitium can cause stiffer lungs. Vascular distention can also lead to further lung stiffness.
Sarcoidosis
Collection of inflamed granulomas, in particular in the lung, that create stiffness in the lung, reducing their compliance.
Interstitial fibrosis
Restrictive lung issue that makes the lungs stiff and less compliant.
Laplace’s Law
P = 2T/R
P is the recoil pressure of the alveolus, T is the surface tension, and R is the radius of the alveolus.
How does surfactant help prevent atelectasis?
Surfactant produced by type II pneuocytes helps to reduce the surface tension, thus reducing the recoil pressure of alveoli (Leplace’s Law).
What is the normal ratio of lectithin:sphingomyelin ratio of surfactant?
2:1
Lung Hysteresis
There is a difference between the compliance of the lung with inhalation and expiration. Inhalation will always require more energy because of the need to recruit alveoli.
Transpulmonary pressure
Palv-Ppl (alveolar and pleural pressures)
This pressure graident propels the gas to the terminal bronchioles and expands the lungs and chest wall.
Thoracic cavity pressure
Patmos - Ppl = 0 - Ppl
Contrast active and passive inflation.
Active inflation: Atmos is zero, Ppl is O, and negative Ppl creates a positive transmural pressure that allows the lungs to expand
Passive inflation: manual expansion of the lung (ventilator) with gas pushed into the lungs with a zero pleural pressure creating the positive transmural pressure we need to inspire
What limits compliance?
The chest wall limits exhilation (sets the residual volume) and the lung limits inhalation (sets total lung capacity).
How does the FRC relate to the compliance curve?
The compliance curve is the mean between the compliance of the chest wall and the lungs. When these work together, the resting airway pressure is 0, at FRC. This is also where the steepest part of the compliance curve occurs.
How would a stiffer, less compliant lung change the combined compliance curve for the lung/chest wall?
A stiffer lung would flatter the curve, resulting in a flatter curve that would shift to the right.
Why would we add PEEP (positive end-expiratory pressure) to patients on a ventilator?
Ensures that the ventilator stops at a set number to keep the alveoli open at a compliant level of the curve to return our patient at FRC.
Contrast a sucking blowing wound and sucking wound?
A sucking blowing wound allows air in a pneumothorax to enter and escape. However, a tension pneumothorax would result in positive pleural pressure and the lung to collapse.
Specific compliance
One lung is less compliant than both lungs together
Peak pressure
Pressure needed to get the air into the thorax (dynamic compliance)
Plateau pressure
Pressure required to hold the air in the thorax (static compliance)
How do you calculate static and dynamic compliance?
C dynamic = TV/(Peak-Peep)
C static = TV/(Plateau-Peep)
Compare the values for static and dynamic compliance.
Static will always be greater than dynamic because peak pressure has to overcome elastic resistance of the chest wall and airway resistance.
How do you calculate airway resistance?
Raw = (Peak-Plateau)/Flow
What can causes peak pressure to increase?
Descreased compliance, increased resistance, larger TV, or higher flow
What can affect plateau pressure?
Compliance and tidal volume
