Pulmonary 5 Flashcards
How is gas transferred across the blood brain barrier?
Via diffusion
What are the 3 factors that facilitate diffusion in the respiratory system?
- Large Surface Area
- Short Distances
- Gases with advantageous diffusion properties
What is Fick’s Law?
Vgas = Area * Diffusion constant * Difference in Partial Pressure / THICKNESS
The amount of gas transferred through the capillaries is proportional to what? What is it indirectly proportional to?
Area, Diffusion constant, and difference in partial pressure
Indirectly proportional to THICKNESS
What is graham’s law? What is the solubility of O2 and CO2 and how is this important for the rate of diffusion?
Rate of Diffusion = Solubility coefficient of the gas/ (molecular weight)^1/2
O2 = 1 CO2 = 22
Rate of diffusion of CO2 is twice as fast than the rate of diffusion of O2
What gasses are perfusion limited? What does this mean?
N2O and O2
- their partial pressures have equilibrated with alveolar pressure before exiting the capillary
(once it hits the threshold, the concentration does not change)
What gas is diffusion limited? What does this mean?
CO
-partial pressure of CO does not reach equilibrium with alveolar pressure (can continuously increase)
What is O2 and CO2 uptake usually? Perfusion or Diffusion limited? When does this change
Perfusion limited
- changes at LOW ALVEOLAR PO2 such as in high altitude
- severe exercise can lead to diffusion impairment oxygen transfer in healthy people
Is Cardiac output different in the systemic & pulmonary circuit?
NO, same since it is in series
- resistance to flow through the lungs is VERY low so the pulmonary driving pressure is 6 mmHg as compared to 87 mmHg in the systemic system
The following describe which structure?
- Only Arteries with deoxygenated blood
- Thin wall
- 7x more compliant
- Easily Distensible
- Low Pressure Circulation
PULMONARY ARTERIES
During inspiration, what occurs to alveolar & extra-alveolar vessels?
Alveolar are compressed
Extra-alveolar are pulled open
What 4 factors influence lung perfusion?
- Gravity
- Pulmonary Vascular Resistance
- Alveolar Pressure
- Arterial-Venous pressure gradient
How does the lung respond to an increase in vascular pressure?
Decreases pulmonary vascular resistance
- Capillary Recruitment
- Capillary Distension
When would Capillary Recruitment & Capillary Distension occur?
During increased Cardiac Output
Why does the change in total pulmonary vascular resistance form a U shape?
There is a tradeoff between the increase in resistance in alveolar pressure & decrease in resistance in extra-alveolar vessels (and opposite for expiration) which forms a curve
What are two reasons for more blood in the base of the lung( similar to the movement of airflow)
- Gravity
2. shape of lung - forming a triangular base that allows more blood to be stored
Describe the 3 zones of the lung. What is the waterfall zone? Which zone only exists under abnormal conditions? Which zone only depends on the arterial/capillary and venous pressures?
Zone 1 - exists only under abnormal conditions
“no flow zone” - no blood can reach this because the Right Ventricle cannot pump that strongly
exists under:
1. Positive Pressure Ventilation (PA high)
2. Hypotension/Shock (Pa low)
PA>Pa>Pv
Zone 2 - Water Fall zone - blood falls down through the capillaries since the pulmonary venous pressure is below atmospheric pressure Pa>PA>Pv
- Alveolar Pressure controls the flow (not venous/arterial gradient)
“compressive flow” since alveolar pressure compresses the capillaries and collapses them slightly
Zone 3 : Normal Zone at the base of the lung –> both pulmonary arterial and venous pressure are above atmospheric pressure & ALVEOLAR pressure has NO AFFECT on the vascular resistance
What are 2 controls of pulmonary perfusion?
- Hypoxic Vasoconstriction
2. Local Vasoconstrictors/Vasodilators
What occurs to the flow of blood under Hypoxic Vasoconstriction? What determines this?
Determined by PO2 in ALVEOLAR gas (not by arterial PO2)
- shifts blood from hypoxic areas to well-perfused areas
What creates the lung fluid balance?
Hydrostatic & Oncotic Pressures
- STARLING FORCES!
What happens if the plasma water that is filtered from systemic capillaries cannot be picked up by lymphatics?
Engorgement of the pleural space resulting in pleural effusions at the expense of loss of lung volume
- Interstitial Lung Edema
THEN - Alveolar Lung Edema
What is O2 and Co2 usually limited by? When does this change?
Perfusion Limited
- Becomes diffusion limited under extreme conditions
1. Alveolar Hypoxia
2. Exercise
3. Thickening of blood-gas barrier
What would occur if the erythrocyte spend less than 0.25 seconds in the capillary bed?
Diffusion Limitation of CO2 and O2 (instead of perfusion limitation)
What are two conditions when PVR increases?
- Low Volumes
2. High volumes
What type of gas transfer is the following:
- N20
- O2 & CO2
- CO
(diffusion limited, perfusion limited, both)
- N20 - Perfusion limited
- O2 & CO2 usually perfusion limited, but during exercise/high altitude it is diffusion limited
- CO Diffusion limited
What is perfusion limited transfer of gas? Does equilibrium occur? How can one increase the Partial Pressure of a gas that is perfusion limited?
Perfusion limited gas transfer means that the gas reaches Equilibrium fairly quickly (before passing through 1/3 of the capillary bed)
- the only way to increase partial pressure of N2O that has reached equilibrium, would be to increase the FLOW OF BLOOD
- insoluble gases that do not chemically combine with proteins are Perfusion Limited because their partial pressure can build up
What is Diffusion limited transfer of gas? Does equilibrium occur? How can one increase the Partial Pressure of a gas that is perfusion limited?
Diffusion limited transfer of SOLUBLE gas that have a high affinity for hemoglobin
- Little or NO increase in partial pressure so equilibrium is NOT reached for CO (linear increase)
- transfer only depends on
the diffusion properties of the gas
When is the exchange of CO2 and O2 diffusion limited?
Heavy Exercise at High Altitude
- the transit time of erythrocytes is very short (fast) so system cannot reach equilibrium for the gas (O2 or CO2)
- high altitudes usually form a lower pressure gradient for O2/CO2 exchange and so gas transfer is slower
What is the equation for Pulmonary Vascular Resistance? PVR
PVR = Pressure Change / Flow (Q)
When pressure in the system increases, how does it change to reach baseline values?
Decrease pulmonary vascular resistance!
- by recruiting capillaries and by distention of perfused capillaries
What demarcates the upper boundary between zones 1 and 2?
What demarcates the LOWER boundary between zones 2 and 3?
Pulmonary Artery Pressure
Pulmonary VEIN pressure!
What are 2 ways that the Pa can be lower than the PA in zone 1?
- Low cardiac output
2. Hypotension
Which zone is based off the pressure gradient of alveolar pressure and NOT venous pressure?
Zone 2
Which zone are Pulmonary Arterial & Venous pressures SUBATMOSPHERIC?
Zone 1!
The PO2 in arteries determined Hypoxic Vasoconstriction.
True or False?
FALSE
- determined by PO2 in ALVEOLAR gas
What are 3 situations that change O2 diffusion from perfusion limited o DIFFUSION limited?
- Alveolar Hypoxia
- Exercise
- Thickening of blood-gas barrier (fibrosis)
When the erythrocyte spends less than 0.25 in the capillary bed, what happens to gas exchange of CO2 and O2?
Changes from Perfusion limited to DIFFUSION LIMITATION
If capillary pressure is less than alveolar pressure and the capillaries collapse and blood flow stops, which zone does this represent?
ZONE 1
What is the amount of blood volume in the alveolar capillary network under resting conditions? During exercise?
Total blood volume is 70 mL
- increases to 150-200 mL during exercise
- Capilalry recruitment
- Distension
How is the Pulmonary Vascular Resistance different from Autoregulation?
OPPOSITE of auto regulation
- As pressure INCREASES, the vascular resistance DECREASES due to recruitment and distention
(most of PVR lies in the capillaries)
Where is most of the Pulmonary Vascular Resistance located?
CAPILLARIES
What is the function of the perivascular sheath in the pulmonary vessel?
As you INHALE the whole lung expands and radial forces of the perivascular sheath pull the vessels apart
- diameter increases so FLOW increases & resistance decreases
(high lung volumes, blood resistance decreases)
When is PVR lowest?
at FRC! - intermediate point
u-shaped graph of alveolar & extra-alveolar resistance
When is PVR the highest?
at VERY LOW and VERY HIGH volumes
When does the difference in flow between the apex and base become less?
DURING EXERCISE!
When is Hypoxic Vasoconstriction important?
During BIRTH
- the first breath there is a dramatic decrease in PVR
- increase in pulmonary blood flow
What are a few pulmonary vasoconstrictors?
- ThromboxaneA2
- α1-adrenergic receptor agonists
- Angiotensin
- Leukotriens
- Neuropeptides
- Serotonin
- Endothelin
- Histamine
- Prostaglandins
- High CO2
High CO2 causes constriction or dilation?
Vasoconstriction!
What are a few pulmonary vasodilators?
- Prostacyclin
- B1-adrenergic receptor agonists
- Nitric oxide (NO)
- Acetylcholine
- Bradykinin
- Dopamine
When are the effects of vasoconstrictors/dilators most important?
PATHOLOGICAL CONDITIONS!
- not important under normal circumstances
PVR is low, and falls even lower when?
During an increase in Cardiac Output!
