Pulmonary Phys- Trachte Flashcards
How do gases move across the blood-gas interface?
Diffuse!!!
Goes from high pressure to low pressure!
What 2 things does gas movement across a barrier depend on?
Cross sectional area
Thickness
What makes up the anatomical dead space?
Trachea to terminal bronchioles
(longer neck = increased dead space!)
NOTE* intubation can also increase dead space
What does compliant mean in terms of the lungs? What would increase it? decrease it?
Change in lung volume for a given change in pressure (stiffness)
- Compliance is decreased in pulmonary fibrosis, pneumonia, pulmonary edema
- Compliance is increased in emphysema, normal aging
What is the role of surfactant?
reduces surface tension and prevents alveolar collapse
**probably represents a key factor allowing for terrestrial life
What are the 4 general causes of reduced oxygen in the blood?
- reduction in ventilation
- Drugs (opiates)
- brain damage
- breath holding
What is tidal volume?
The amount of air inspired and expired in each breath
Usually around 500 mls
What is vital capacity?
the maximum volume of air that can be exhaled after a maximum inspiration
Usually about 6,000 ml
What is residual volume?
the amount of remaining in the lungs after a maximal expiration (never able to get rid of it, unless your lung collapses).
In a maximal expiration you are blowing out your expiratory reserve volume.
Usually about (1,500 mL)
What is functional residual capacity?
the amount of air remaining after a typical exhalation
expiratory reserve volume + residual volume
What does smoking paralyze in the lungs?
mucous-ciliary elevator
What is the volume amount remaining after a typical exhalation?
2500 mL (residual volume + expiratory reserve volume)
Function residual Volume = expiratory reserve volume + residual volume
How do you measure the functional residual capacity?
Helium gas dilution technique
What is total ventilation?
the amount of air entering and leaving the lung each MINUTE
Tidal volume x respirations per minute
What happens to functional residual capacity in obstructive diseases?
It goes UP!
How do you determine the volume of dead space?
Fowler’s single breath N2 washout
Which part of the lungs are ventilated better?
Lower regions of the lung are ventilated better than upper regions
What is the driving force of diffusion?
PRESSURE difference
Is CO a diffusion or perfusion limited?
Diffusion limited!
Only the diffusion barrier is creating resistance to flow of air, RBC affinity is so great that little rise in the blood partial pressure of carbon monoxide with tie in the capillary
Is O2 a diffusion or perfusion limited process?
Perfusion limited!
It is going to equilibrate and stop moving across barrier unless blood flow increases
What 3 gases are Perfusion Limited?
Nitrous Oxide
Oxygen
Carbon Dioxide
What would you use to measure diffusion capacity?
Use carbon monoxide because it is NOT perfusion limited
What happens to compliance in a pneumothorax?
GOES DOWN
What is LaPlaces Law?
Tension = (Pressure x radius)/2
If you increase ventilation, the concentration of what alveolar gas will decrease?
CO2
Why are lower regions of the lungs ventilated better?
More of a negative pressure
NE, 5HT, and histamine do what to pulmonary vessels?
Contract–increase resistance
Acetylcholine, isoproterenol, and prostacyclin do what to pulmonary vessels?
Relax–decrease resistance
What does the respiratory quotient tell you?
How do you figure it out?
What type of fuel you are burning
CO2/O2
Describe the 3 zones of perfusion of pulmonary blood flow.
Zone 1: Alveolar pressure>arterial pressure>venous pressure.
This is the alveolar dead space!! Lung apex
Zone 2: Arterial pressure>Alveolar pressure>venous pressure
Zone 3: Arterial pressure >venous pressure>alveolar pressure….Flow is dependent on the arterial-venous pressure dfference! This is the normal situation in the circulatory system. Occurs in midregions and base of lung.
Describe the mechanism of constriction of blood vessels perfusing hypoxic regions of the lungs.
The inhibition of voltage gated K channels depolarizes the membrane…An increase in intracellular calcium occurs…Vasoconstricion.
why is there less fluid leakage in the lungs than in systemic circulation?
Lower hydrostatic pressure in the capillaries! Good thing
If the gradient for CO2 to move into the alveoli is much smaller than the gradient for oxygen to enter the blood, why do we have equal amounts moving across the alveoli?
CO2 is more permeable!
What is the equation for Alveolar PO2?WE NEED TO KNOW THIS!
Alveolar PO2 = PIO2 - [PACO2/R]
PIO2 is inspired air PO2
PACO2 is alveolar PCO2
R is respiratory quotient (1 if carbohydrates, 0.7 if fat)
Can 100 % O2 correct the hypoxemia resulting from a shunt?
NOOOOOO
If the PO2 is 150 and the PCO2 is 0 in the alveoli, what are you thinking?
NO PERFUSION
Still ventilated
If the PO2 is 40 and the PCO2 is 46 in the alveoli, what are you thinking?
There is perfusion but no ventilation!
What part of the lung has a higher ventilation/perfusion ratio?
Apex
Relate surfactant to the Law of Laplace
P= 2T/r
P= collapsing pressure T= surface tension r= radius
Alveoli have a tendency to collapse on expiration as radius decreases - surfactant decreases alveolar surface tension and prevents collapse
It also reduces variation in distending pressures amongst spheres of varying sizes. (prevents small spheres from emptying into larger spheres)
What are two examples of when O2 might become diffusion limited rather than perfusion limited?
- Pulmonary disease states (may have thick diffusion barrier, and so O2 does not become saturated before RBC reaches end of capillary)
- Breathing low PO2 (like at high altitudes) = pressure gradient becomes smaller and results in less diffusion
Is Oxygen still perfusion-limited during exercise?
Yes! Normally O2 saturates 1/3 of the way through the capillary (0.25 sec)
During exercise, blood flow increases dramatically, but saturation still happens before RBC traverses the capillary
During what point in respiration is resistance the lowest?
Resistance is lowest at functional residual capacity
What happens to arteriolar resistance in the lungs as blood oxygen content decreases?
Arteriolar resistance increases as blood oxygen content decreases
What are two causes of hypoxemia when there is a normal A-a gradient?
- Alveolar hypoventilation (may be from suppressed central respiratory drive like sedation, or in disease with decreased inspiratory capacity like myasthenia gravis or obesity)
- Inspiration of air with low PO2 (high altitudes!)
What happens to pO2 and pCO2 in arterial blood during exercise?
Stays the same!!!
Partial pressures change in venous blood (increased pCO2, and decreased pO2)
However there is increased O2 consumption, and increased delivery to tissues! But partial pressure stays the same
In controlling ventilation, what to central chemoreceptors primarily respond to? why?
Respond to increased PaCO2
H+ cannot cross BBB, CO2 diffuses and is converted to bicarb and H+ by CA.
In controlling ventilation, what do peripheral chemoreceptors primarily respond to?
Sense arterial PaO2, and are stimulated by hypoxemia
**also stimulated by hypercapnia but not as important as central chemoreceptors in that regard
In controlling ventilation, what do receptors in the lung respond to primarily?
Pulmonary stretch receptors! (Herring-Breuer Reflex) YOGA!
And irritant receptors
What is the most relevant for day-to-day control of ventilation according to Trachte?
CO2!!! (1 mmHg increased in PCO2, leads to a 2-3 L increase in ventilation if PO2 is held constant)
Except for two conditions: O2 is important in altitude adaptions and COPD.
Why are the lungs less likely to experience edema compared to other circulations?
Low hydrostatic pressure!!
What are some of the metabolic functions of the lungs?
-ACE
-Inactivates bradykinin (through ace)
NOTE* this is why you get a cough with an ACE inhibitor
-Removes serotonin from circulation
-Metabolizes and synthesizes prostaglandins and leukotrienes
What is an important role of PGE in pulmonary/systemic circulation?
Keeps ductus arteriosis open in fetal circulation
To close - give indomethacin (COX inhibitor)
What are some non-ventilation functions of the lungs?
Reservoir for blood- when we lay down blood drains from the legs to the lungs
Filters blood - thrombi from periphery cannot get to brain!
What 3 things in general would cause an increased A-a gradient?
V/Q mismatch
Shunt
Diffusion limitations
What are two things can damage the extremely thin walls of pulmonary vessels?
Increased capillary pressure
Increased alveolar pressure
What three things could make oxygen a diffusion limited gas, rather than perfusion limited gas?
High altitudes: decreased pressure gradient
Emphysema: decreased diffusion surface area
Fibrosis: thickened diffusion barrier
What is the fick equation to determine pulmonary blood flow?
Pulmonary blood flow = VO2 consumed/ (CAO2-CVO2)
What is the mechanism for causing hypoxic pulmonary vasoconstriction? Does it involve nerves?
No! Does NOT involve nerves
Uses voltage gated K channels - hyper polarize membrane - increases Ca+ concentration - vasoconstriction
Why is cough a common side effect of ACE inhibitor drugs?
ACE in the lung normally inactivates bradykinin
With an ACE inhibitor there is a higher concentrated of activated bradykinin leading to cough
Which has more affinity for hemoglobin… O2 or CO? How do you treat someone with CO poisoning?
CO has greater affinity! Treat with hyperbaric oxygen
How does decreased pH affect the oxygen association curve?
Shifts right- less affinity for O2
How does increased CO2 affect the oxygen association curve? (Bohr effect)
Shifts right- less affinity for O2
How does increased temperature affect the oxygen association curve?
Shifts right- less affinity for O2
How does increased 2, 3 BPG affect the oxygen association curve?
Shifts right- less affinity for O2
How will emphysema affect compliance of the lungs?
It will increase!
Fibrosis would decrease compliance
Is intrapleural pressure higher at the base or the apex of the lung?
Intrapleural pressure is higher at the apex
Weight of lung pressing against chest wall
