Exam 2: 25 Feb Pulmonary Gas Exchange And Vascular Resistance Flashcards
What is the role of gravity in lung perfusion?
What is gravity dependence?
- Gravity affects blood flow in the lungs, with higher blood flow in areas where gravity has the greatest effect.
- Gravity dependence describes the relationship between gravity and blood flow in the lungs, where dependent regions receive the highest blood flow.
Just note that in an upright patient, West’s Perfusion Zone 4 dictates that the most bottom areas of the lung suffer some perfusion loss D/T compression against the diaphragm.
What are the typical blood flow zones in healthy lungs?
Healthy lungs typically exhibit zone two and zone three blood flow, with no widespread zone one (no perfusion) unless pathological.
What happens to pleural pressure and alveolar pressure during inspiration?
During inspiration, pleural pressure decreases (becomes more negative), causing alveolar pressure to become negative and air to flow into the lungs.
Describe the elastic recoil pressure.
Elastic recoil pressure, or transpulmonary pressure, is the force that fills the lung with air, balancing pleural pressure and alveolar pressure.
What factors influence pulmonary vascular resistance?
Factors include lung volume, gravity, cardiac output, and active influences like catecholamines.
How does lung volume affect pulmonary vascular resistance?
Lung volume affects resistance, with FRC having the lowest resistance and larger vessels being distended at higher volumes.
What is the effect of increased cardiac output on pulmonary vascular resistance?
Increased cardiac output decreases pulmonary vascular resistance by distending blood vessels and recruiting more pathways.
List the passive influences that increase pulmonary vascular resistance. What about passive decrease?
Increases PVR:
* Lung volume (increase/decrease either above/below FRC)
* Increased Interstitial pressure
* Increased blood viscosity
* Positive Pressure Ventilation
Decreases PVR:
* Increase in pulm. artery pressure (weird right?)
* Gravity-dependent bloodflow
List the active influences that increase pulmonary vascular resistance.
List the active influences that decrease pulmonary vascular resistance.
What is the composition of atmospheric gases? How does this correlate with the partial pressures if 1 ATM is 760mmHg?
Atmospheric gases consist of approximately 79% (600.3mmHg) nitrogen and 21% (159mmHg) oxygen, 0.04% (0.3mmHg) carbon dioxide, with negligible amounts of other gases.
Using normal atmospheric gas percentages, what are the partial pressures of these gases in our lungs? What effect does humidification play?
% listed in picture
Our body always humidifies the incoming air with 47.0mmHg worth of H2O. This effectively displaces some of the gas partial pressures within our lungs.
What is the partial pressure of water vapor in humidified air?
The partial pressure of water vapor in humidified air is 47 millimeters of mercury.
What are the average (equilibrium) alveolar gas pressures in a healthy lung?
- PA O2 : 100mmHg (104mmHg is perfect)
- PA CO2 : 40mmHg
- PA N2 : 569mmHg (doesn’t change much with respiration)
- PA H2O : 47mmHg (something that we will consider a constant throughout the program because we cannot change it)
How does fresh air intake affect gas exchange in the lungs?
Fresh air intake maintains stable gas conditions in the lungs, allowing for continuous gas exchange. Without FRC, ABG would havecrazy peaks and valleys.
Fill in the blank: The pressure in a healthy lung at the start of the respiratory cycle is ______.
zero
True or False: Alveolar nitrogen levels change significantly during gas exchange.
False
What is the expected alveolar nitrogen level in healthy lungs?
Alveolar nitrogen remains nearly constant due to minimal absorption or release.
Explain the continuous nature of gas exchange in the lungs.
Gas exchange is continuous as blood moves through the lungs, unloading CO2 and absorbing oxygen.
What is the relationship between pleural pressure and alveolar pressure during expiration?
During expiration, pleural pressure increases and alveolar pressure becomes positive.
What is the formula for calculating alveolar pressure?
Alveolar pressure = pleural pressure + elastic recoil pressure (AKA transpulmonary pressure).
What happens to pulmonary vascular resistance with reduced cardiac output?
Reduced cardiac output increases pulmonary vascular resistance, posing challenges for the right heart.
Fill in the blank: At sea level, atmospheric pressure is ______ millimeters of mercury.
760
How is the partial pressure of a specific gas calculated?
Partial pressure is calculated by multiplying the gas’s concentration by atmospheric pressure.
What are the components of pulmonary vascular resistance?
- Extra alveolar blood vessels
- Alveolar blood vessels
What is the effect of humidity on the partial pressure of oxygen?
Humidity reduces (displaces) the partial pressure of oxygen in humidified air from 159 to 149 mmHg.
What happens to smaller blood vessels during increased lung volume?
Increased volume stretches the capillaries, increasing vascular resistance.
What are the normal expected values for inspired and humidified alveolar gas components?
Normal values include alveolar PA O2 at 104mmHg and PA CO2 at 40 mmHg.
PA N2 levels remain fairly consistent with atmospheric amount of 569mmHg (body doesn’t really use any atmospheric nitrogen so we can pretty much disregard it)
What is the role of catecholamines in pulmonary vascular resistance?
Catecholamines can actively influence pulmonary vascular resistance by causing vasodilation or vasoconstriction.
What happens to alveolar pressure during inspiration?
Alveolar pressure becomes negative during inspiration due to a higher force acting to stretch the lung open.
What is the relationship between alveolar pressure, pleural pressure, and recoil pressure?
Alveolar pressure = Pleural pressure + Recoil pressure.
What does a negative alveolar pressure indicate? Which direction is air movement?
It indicates that the inward recoil force is outweighed by the force acting to expand the lung.
- Air will be moving into the lung.
At the end of inspiration, what is the alveolar pressure?
Alveolar pressure returns to zero.
This is D/T the inward movement of air creating a higher recoil pressure that equalizes with the intrapleural pressure.
What happens to pleural pressure at the end of inspiration?
Pleural pressure remains negative. (specifically -7.5cmH2O)
Pleural pressure should always remain negative as this is the force counteracting the elastic recoil pressure of the alveoli. When it becomes more negative or we introduce positive pressure ventilation, the alveoli expands with air.
What is the effect of increased lung volume on recoil pressure?
Increased lung volume leads to increased recoil pressure.
- As the alveoli fill with air they stretch. This stretch creates more recoil pressure (like a rubber band, the harder you pull it back, the harder it snaps your friend’s arm when you let go)
What does transpulmonary pressure represent?
Transpulmonary pressure represents the pressure available to fill the lung with air. It is synonomous with elastic recoil.
What are the two most important passive influences on pulmonary vascular resistance?
- Lung volume
- Gravity
What happens to pulmonary vascular resistance when lung volume increases above FRC? What about when it decreases below FRC?
Pulmonary vascular resistance increases in both cases.
What is the lowest possible lung volume called? What is the amount of this volume?
Residual volume (RV). 1.5L
- You cannot physically exhale this volume
At what lung volume is pulmonary vascular resistance at its lowest?
At functional residual capacity (FRC).
What is the highest lung volume a healthy adult can achieve? What is that volume?
Total lung capacity (TLC). 6.0L
- Do not confuse with vital capacity which is the largest working volume (4.5L)
What is the relationship between transpulmonary pressure and lung volume?
When transpulmonary pressure increases, lung volume increases.
- This is a counter-intuitive idea because the positive transpulmonary pressure is working to counteract the increase in volume. In action, TP (AKA Elastic Recoil) allows for expiration without using energy.
What is the effect of positive pressure ventilation on transpulmonary pressure?
It increases transpulmonary pressure.
- Because this is an unnatural ventilatory pattern, it also increases (makes more positive) intrapleural pressure. This can be dangerous to extra-alveolar vessels becuase they rely on the negative pull of the intrapleural pressure to keep adequate bloodflow.
What does a positive alveolar pressure indicate during expiration?
It indicates that the alveolar pressure is greater than the outside atmospheric pressure.
What is the term for the tendency of the lung to collapse on itself?
Elastic recoil (transpulmonary pressure).
True or False: Alveolar pressure must equal atmospheric pressure during expiration.
True.
What happens to the pleural pressure during expiration?
Pleural pressure increases towards zero.
What does a decrease in pleural pressure lead to during expiration?
It reduces the outward pull on the lung tissue.
- Think pneumothorax, where air leaks into the pleural space, causing a loss of negative pressure and the lungs collapse.
- The alveoli succumb to elastic recoil (transpulmonary pressure)
What is the significance of the relationship between lung volume and pulmonary vascular resistance?
It indicates that the lowest pulmonary vascular resistance occurs at FRC, which is important for efficient heart function.
What is the significance of FRC in relation to pulmonary vascular resistance?
FRC is the point where pulmonary vascular resistance (PVR) is at its lowest.
How does increasing lung volume affect pulmonary vascular resistance?
Increasing lung volume leads to an increase in pulmonary vascular resistance.
What are the two general components that make up total pulmonary vascular resistance?
- Extra alveolar blood vessels
- Alveolar blood vessels
What are extra alveolar blood vessels?
Large pulmonary blood vessels, such as pulmonary arteries and veins.
What are alveolar blood vessels?
Smaller blood vessels, specifically pulmonary capillaries, attached to the alveoli.
What role do pulmonary capillaries play?
Gas exchange occurs at the level of the pulmonary capillaries.
How does pleural pressure influence larger blood vessels?
Negative pleural pressure keeps larger blood vessels open and affects their diameter.
What happens to vascular resistance as pleural pressure becomes more positive?
Vascular resistance in larger blood vessels increases.
What is the relationship between lung volume and extra alveolar vascular resistance?
Extra alveolar vascular resistance decreases as lung volume increases.
What occurs to alveolar blood vessels as lung volume increases?
Alveolar blood vessels become longer (and get compressed), resulting in increased pulmonary vascular resistance.
At what lung volume is total pulmonary vascular resistance lowest?
At functional residual capacity (FRC).
How does positive pressure ventilation affect pulmonary vascular resistance?
It alters the dynamics of vascular resistance, potentially increasing it.
What is the effect of low lung volumes on alveolar vascular resistance?
Alveolar vascular resistance is low at low lung volumes.
Fill in the blank: Total pulmonary vascular resistance is the sum of _______.
[alveolar vascular resistance and extra alveolar vascular resistance]
True or False: Increasing lung volume typically decreases alveolar vascular resistance.
False.
Increasing lung volume will stretch alveolar capillaries and slightly compress them which both add to resistance.
What happens to the diameter of capillaries at low lung volumes?
Capillaries are wider and shorter.
What happens to the diameter of capillaries at high lung volumes?
Capillaries are narrower and longer.
What is the general behavior of extra alveolar blood vessels during normal breathing?
They experience lower resistance as lung volume increases due to negative pleural pressure.
What is the role of the negative pleural pressure in the lungs?
It holds the lungs open and influences vascular pressures in larger blood vessels.
What is the relationship between the length of capillaries and pulmonary vascular resistance?
Longer capillaries result in higher pulmonary vascular resistance.
What physical changes occur in blood vessels during forced expiration?
Positive pleural pressure compresses larger blood vessels (extra-alveolar), increasing resistance.
Describe the effect of lung volume on the pulmonary vascular resistance profile.
Pulmonary vascular resistance is lowest at FRC and increases with deviations from this volume.
What are the pulmonary capillaries embedded in?
The walls of the alveoli
This proximity to air facilitates gas exchange.
What is a characteristic of healthy lungs in terms of moisture?
Healthy lungs should be dry
Excess water in the lungs can hinder gas exchange.
What happens to pulmonary vascular resistance when right heart cardiac output increases?
Pulmonary vascular resistance typically decreases
This is counterintuitive compared to the systemic circuit.
What is the term for the widening of blood vessels due to increased blood flow?
What is the process of utilizing additional blood pathways in the lungs called?
- Distension
- Recruitment
Distension lowers pulmonary vascular resistance while recruitment occurs when cardiac output increases. The decrease in vascular resistance D/T increased CO is a special function of the lungs to accomadate more blood oxygenation during stress.
What are the regions of the lung with continuous flow referred to as?
Zone 3
Zone 2 is pulsatile flow, while Zone 1 is a non-perfused area.
True or False: Healthy lungs have large continuous areas that are unused.
False
Healthy lungs have spotty alveoli that are not always used.
What happens to pulmonary vascular resistance when right heart cardiac output decreases?
Pulmonary vascular resistance increases
This can lead to a vicious cycle of worsening cardiac output.
List two passive factors that can change pulmonary vascular resistance. Don’t worry, there are plenty to choose from.
- Gravity from body position changes
- Lung volume
These are the 2 most important factors.
What effect does increased blood viscosity have on pulmonary vascular resistance?
Increases pulmonary vascular resistance
Thicker blood makes it harder to move through the circuit.
What is the atmospheric pressure at sea level in millimeters of mercury?
760 millimeters of mercury
This is equivalent to 1 atm.
What happens to atmospheric pressure as altitude increases?
Atmospheric pressure decreases
This is due to less atmosphere above.
Fill in the blank: The weight of the atmosphere above us contributes to _______.
atmospheric pressure
What is the physiological effect of sympathetic stimulation on pulmonary blood vessels?
Increases pulmonary vascular resistance.
This is the effect on the vasculature, not the bronchial smooth muscle.
This effect is due to vasoconstriction.
Name a dilator of pulmonary blood vessels. There are also a lot of these!
Nitric oxide
What is the effect of positive pressure ventilation on pulmonary vascular resistance?
Increases pulmonary vascular resistance
It compresses structures within the chest.
What is the effect of prostacyclin on pulmonary blood vessels?
It tends to relax blood vessels
Prostacyclin analogs were studied as inhaled treatments for pulmonary hypertension.
What is the primary function of gravity in relation to atmospheric pressure?
It retains the atmosphere
Gravity holds the gas close to the Earth’s surface.
What happens to atmospheric pressure as altitude increases?
Atmospheric pressure decreases as altitude increases.
What is the atmospheric pressure at sea level in millimeters of mercury?
760 millimeters of mercury.
What two factors are needed to get gas into the body?
Gas and pressure.
What is the concentration of nitrogen in the atmosphere?
About 79%.
What is the concentration of oxygen in the atmosphere?
About 21%.
What is the status of CO2 concentration in the atmosphere for most purposes?
Negligible.
0.04%
What is the abbreviation for concentration?
Brackets [ ] or capital F for fractional concentration.
How is partial pressure of a gas calculated?
Total gas pressure multiplied by the concentration of that gas.
What is the partial pressure of nitrogen at sea level?
600.3mmHg
What is the partial pressure of oxygen in dry atmospheric air at sea level?
159.0mmHg
How does altitude affect the concentration of oxygen in the atmosphere?
Concentration remains approximately 21% regardless of altitude.
- Partial pressures, however, decrease as you increase your altitude which can affect oxygenation.
What happens to the partial pressure of gases when water vapor is added?
The partial pressures of other gases are reduced.
What is the partial pressure of water vapor at 37 degrees Celsius?
47mmHg
- This will be the exact number used for the program
What is the formula for calculating the partial pressure of oxygen in humidified air?
Fractional concentration of oxygen multiplied by (barometric pressure - partial pressure of water vapor).
Fill in the blank: The total pressure of gases in the atmosphere at sea level is _______.
760 millimeters of mercury.
What does the symbol P Io2 represent?
Partial pressure of oxygen in humidified gas.
What happens to the partial pressure of oxygen as air is humidified in the lungs?
It decreases due to the presence of water vapor.
How much of the fresh air actually reaches the alveoli for gas exchange?
350 cc.
The last 150cc of inspired air or first 150cc of expired air is considered anatomical deadspace becuase it is not used in ventilating the lungs.
True or False: The concentration of gases in the atmosphere changes significantly at high altitudes.
False.
What is the typical alveolar PO2 after gas exchange?
About 100 mmHg
- The more correct number is 104mmHg, however the 100mmHg takes into account the mixing of pulmonary vasculature venous blood mixing with the rest of the blood entering the left atrium.
This is an average value after fresh air has been mixed with pre-existing gases and gas exchange has occurred.
What is the average alveolar PCO2 level?
About 40 mmHg
This represents the normal partial pressure of CO2 in a healthy lung.
What happens to oxygen levels in pulmonary venous blood after passing through the lungs?
PO2 increases from 40 mmHg to 100 mmHg
This increase occurs as oxygen is absorbed into the blood.
What is the change in PCO2 levels as blood moves through the pulmonary capillaries?
PCO2 decreases from 45 mmHg to 40 mmHg
This decrease occurs as CO2 is unloaded into the alveoli.
Why does the change in oxygen PO2 have a larger magnitude compared to CO2 PCO2?
Oxygen is less soluble than CO2 and has a storage place on hemoglobin
The solubility and binding properties of these gases explain the differences in their partial pressure changes.
What is the significance of the abbreviation PAO2?
It refers to alveolar PO2
Understanding this abbreviation is crucial for interpreting questions about alveolar gas pressures.
What is the average partial pressure of nitrogen in alveolar gas?
Close to inspired nitrogen levels (564mmHg vs. 600.3mmHg). Some is displaced by water vapor pressure.
Nitrogen levels do not change significantly during respiration.
What is the average partial pressure of water vapor in alveolar gas?
About 47 mmHg
This reflects the presence of water vapor in the lungs.
True or False: Gas exchange occurs only during inhalation.
False
Gas exchange is a continuous process that occurs as blood moves through the lungs.
Fill in the blank: The average alveolar PO2 is approximately _______.
100 mmHg
What occurs continuously in the lungs as fresh air is brought in?
Oxygen is absorbed and CO2 is unloaded
This process helps maintain stable gas pressures in the lungs.
