Ventilation and Perfusion Overview
84 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of alveolar ventilation?

  • To cool the lungs
  • To increase heart rate
  • To assist in the process of digestion
  • To remove carbon dioxide and deliver oxygen to the blood (correct)

What is anatomic dead space in the respiratory system?

  • The parts of the respiratory system filled with air but lacking alveoli such as the trachea and nose (correct)
  • The total dead space including both functional and anatomical components
  • Alveoli that do not participate in gas exchange
  • The volume of air exhaled in a single breath

What contributes to physiologic dead space being greater than anatomic dead space?

  • Decreased air pressure in the environment
  • Excessive ventilation rates
  • Overactive gas exchange in alveoli
  • Insufficient perfusion to parts of the lungs (correct)

What does dead space ventilation refer to?

<p>Ventilation that does not participate in gas exchange (D)</p> Signup and view all the answers

Which part of the lung is primarily responsible for contributing to physiologic dead space?

<p>The apex of the lungs (D)</p> Signup and view all the answers

What defines functional dead space?

<p>Alveoli that should exchange gas but do not due to dysfunction (A)</p> Signup and view all the answers

How is ventilation calculated?

<p>By multiplying the volume of air per breath by the respiratory rate (D)</p> Signup and view all the answers

What happens to the physiologic dead space in many diseases?

<p>It increases (C)</p> Signup and view all the answers

What effect does decreasing dead space have on expired carbon dioxide concentration?

<p>It approaches the arterial concentration. (B)</p> Signup and view all the answers

What effect does increasing the number of non-gas exchanging alveoli have on physiologic dead space?

<p>It increases physiologic dead space. (B)</p> Signup and view all the answers

What happens to expired carbon dioxide concentration when dead space reaches 100%?

<p>It becomes zero. (B)</p> Signup and view all the answers

Why does the presence of dead space not typically cause hypoxemia?

<p>Oxygen saturation remains at 100%. (C)</p> Signup and view all the answers

Which of the following parameters is NOT needed to calculate physiologic dead space using Bohr's method?

<p>Concentration of oxygen in inspired air (D)</p> Signup and view all the answers

What condition can lead to elevated carbon dioxide levels in the blood due to dead space?

<p>Hypercapnia (B)</p> Signup and view all the answers

In Bohr's method, how is the dead space volume (VD) calculated?

<p>VD = VT * (PACO2 - PECO2) / PACO2 (D)</p> Signup and view all the answers

What is the relationship between total ventilation and dead space?

<p>Alveolar ventilation is total ventilation minus dead space. (D)</p> Signup and view all the answers

What would happen to expired CO2 levels if the lungs were entirely made up of non-functional alveoli?

<p>Expired CO2 would be zero. (B)</p> Signup and view all the answers

Which of the following describes total ventilation?

<p>Volume per minute moving in and out of the lungs. (C)</p> Signup and view all the answers

What is one major problem identified with increased dead space?

<p>It reduces the body's ability to remove carbon dioxide. (C)</p> Signup and view all the answers

How does increased dead space affect the concentration of CO2 in the blood?

<p>CO2 concentration increases. (D)</p> Signup and view all the answers

During normal physiological conditions, what would the expired CO2 be if working alveoli were present?

<p>Equal to the alveolar CO2 concentration. (B)</p> Signup and view all the answers

What happens to CO2 concentration in the body as dead space increases?

<p>It increases unless compensated by respiratory rate. (A)</p> Signup and view all the answers

What happens in the alveolus that becomes dead space when perfusion is obstructed?

<p>No gas exchange occurs. (B)</p> Signup and view all the answers

What happens to the arterial CO2 concentration as dead space increases?

<p>It increases due to reduced gas exchange. (C)</p> Signup and view all the answers

Which condition would lead to an expired CO2 concentration of 40 mmHg?

<p>A perfect system with no dead space. (B)</p> Signup and view all the answers

How is alveolar ventilation calculated?

<p>Total ventilation minus dead space. (D)</p> Signup and view all the answers

What occurs in the lung when both alveoli are functioning despite an increase in dead space?

<p>Blood oxygen saturation remains unchanged. (A)</p> Signup and view all the answers

Which partial pressure symbol indicates the venous CO2 concentration?

<p>PVCO2 (B)</p> Signup and view all the answers

What occurs to the expired concentration of carbon dioxide as gas exchange decreases?

<p>It approaches zero. (B)</p> Signup and view all the answers

What is the primary principle of pulmonary physiology regarding expired CO2 as dead space increases?

<p>Expired CO2 decreases as dead space increases. (C)</p> Signup and view all the answers

What causes the dilution of expired CO2 in healthy individuals?

<p>Mixing of dead space air with alveolar air. (D)</p> Signup and view all the answers

In the scenario of dead space, which alveolus continues to adequately oxygenate blood?

<p>The right alveolus. (D)</p> Signup and view all the answers

Which condition reflects a physiological dead space that is entirely composed of non-performing alveoli?

<p>Complete absence of gas exchange. (B)</p> Signup and view all the answers

What must patients often do to compensate for the effects of dead space?

<p>Increase their respiratory rate. (D)</p> Signup and view all the answers

What is hypercapnia primarily caused by?

<p>Increased carbon dioxide production (B), Decreased respiratory rate (D)</p> Signup and view all the answers

What physiological response occurs when elevated carbon dioxide levels are sensed by the body?

<p>Increased respiratory rate (B)</p> Signup and view all the answers

Which variable is NOT included in the modified alveolar ventilation equation?

<p>Partial pressure of oxygen (C)</p> Signup and view all the answers

What occurs when there is an increase in dead space volume?

<p>Increase in PACO2 if total ventilation remains the same (B)</p> Signup and view all the answers

In what situation would hypercarbia NOT typically occur?

<p>During intense exercise (A)</p> Signup and view all the answers

Which factor primarily helps reduce elevated CO2 concentrations in the lungs?

<p>Increased alveolar ventilation (C)</p> Signup and view all the answers

What is the most common respiratory exchange ratio (R) value assumed for an average person?

<p>0.8 (A)</p> Signup and view all the answers

Which of the following statements regarding alveolar oxygen concentration is true?

<p>Inspiration of oxygen with a higher percentage than normal raises alveolar oxygen. (D)</p> Signup and view all the answers

What happens to PACO2 if both dead space increases and total ventilation is not adjusted?

<p>PACO2 increases (B)</p> Signup and view all the answers

What role does the respiratory exchange ratio (R) play in determining alveolar gas concentrations?

<p>It influences the balance between oxygen consumption and carbon dioxide production. (B)</p> Signup and view all the answers

Which condition would most likely lead to hypoventilation?

<p>Severe asthma exacerbation (A)</p> Signup and view all the answers

What is a key factor that prevents hypercapnia during exercise?

<p>Increased respiratory rate (B)</p> Signup and view all the answers

What is the most likely outcome if a patient cannot increase their ventilatory rate despite increased CO2 production?

<p>Development of respiratory acidosis (B)</p> Signup and view all the answers

What happens to alveolar oxygenation when PACO2 increases?

<p>It decreases. (D)</p> Signup and view all the answers

What principle is critical for understanding the relationship between ventilation and CO2 concentration?

<p>CO2 levels can rise if ventilation does not compensate for increased production. (D)</p> Signup and view all the answers

What is the normal value of PAO2 when PACO2 is 40?

<p>100 (C)</p> Signup and view all the answers

How does hypoventilation affect carbon dioxide levels?

<p>It raises carbon dioxide levels. (D)</p> Signup and view all the answers

Which zone of the lungs has the highest perfusion?

<p>Zone Three (A)</p> Signup and view all the answers

What is the typical ventilation to perfusion (VQ) ratio for the entire lung?

<p>0.8 (C)</p> Signup and view all the answers

What primarily causes the uneven distribution of blood flow in the lungs?

<p>Gravity. (D)</p> Signup and view all the answers

What results from high CO2 levels in the lungs?

<p>Decreased alveolar oxygenation. (B)</p> Signup and view all the answers

Which statement about gas exchange in the lungs is true?

<p>The VQ ratio should be balanced for effective gas exchange. (A)</p> Signup and view all the answers

What effect does the apex of the lungs have on ventilation?

<p>Ventilation is lowest at the apex. (B)</p> Signup and view all the answers

What occurs to PAO2 when PACO2 rises significantly to 80?

<p>It decreases to approximately 50. (D)</p> Signup and view all the answers

What is primarily affected when ventilation is reduced due to lung compression?

<p>Alveolar oxygen levels. (A)</p> Signup and view all the answers

What does a high ventilation with low blood flow indicate?

<p>Inefficient gas exchange. (A)</p> Signup and view all the answers

Why is the change in perfusion greater than the change in ventilation from base to apex?

<p>Because of gravity. (C)</p> Signup and view all the answers

Where in the lungs is the VQ ratio the lowest?

<p>At the base (A)</p> Signup and view all the answers

What is the VQ ratio at the apex of the lung?

<p>3.0 (A)</p> Signup and view all the answers

How does blood flow and ventilation compare at the base of the lung?

<p>Highest blood flow, highest ventilation (A)</p> Signup and view all the answers

What is the normal PAO2 range in blood leaving the base of the lungs?

<p>90 to 100 (D)</p> Signup and view all the answers

What happens to the VQ ratio as you move from the base to the apex of the lungs?

<p>It increases (C)</p> Signup and view all the answers

What is a consequence of having a high VQ ratio at the apex?

<p>Reduced blood flow (B)</p> Signup and view all the answers

Which zone of the lung has the lowest blood flow and lowest ventilation?

<p>Zone one (D)</p> Signup and view all the answers

What drives the pulmonary blood flow primarily?

<p>Pressure difference between arteries and veins (C)</p> Signup and view all the answers

How does alveolar pressure impact blood flow in zone two?

<p>It compresses the veins but allows arterial flow (B)</p> Signup and view all the answers

What is the PAO2 in the apex of the lung?

<p>130 (D)</p> Signup and view all the answers

Which bacteria is known to develop infections at the apex of the lung due to high PAO2?

<p>Tuberculosis (A)</p> Signup and view all the answers

What occurs in zone two of the lung?

<p>Pulsatile blood flow only occurs when arterial pressure is at its highest. (B)</p> Signup and view all the answers

In zone three of the lungs, what is true about the pressures?

<p>Arterial and venous pressure are both higher than alveolar pressure (A)</p> Signup and view all the answers

Why is the ventilation at the apex not utilized effectively?

<p>Minimal blood flow (B)</p> Signup and view all the answers

What happens at the apex of the lung when alveolar pressure is greater than arterial pressure?

<p>Blood flow is completely hindered. (B)</p> Signup and view all the answers

What is the consequence of a slight fall in arterial pressure in zone one?

<p>Capillary compression occurs. (A)</p> Signup and view all the answers

How does exercise affect the ventilation-perfusion (VQ) ratio in the lungs?

<p>The VQ ratio approaches one. (D)</p> Signup and view all the answers

What happens to arterial oxygen and carbon dioxide content during exercise?

<p>They remain unchanged. (B)</p> Signup and view all the answers

What is observed in venous blood during exercise?

<p>Decreased oxygen and increased carbon dioxide. (A)</p> Signup and view all the answers

In which zone is there the least blood flow?

<p>Apex of the lung. (A)</p> Signup and view all the answers

Why does zone one become dead space in certain conditions?

<p>Decreased arterial pressure leading to capillary compression. (C)</p> Signup and view all the answers

Which statement best describes blood flow dynamics in the lungs?

<p>Blood flow is dependent on the pressure relationship between arteries and alveoli. (A)</p> Signup and view all the answers

What is the characteristic of the alveolar pressure throughout the lungs?

<p>It remains constant throughout the lung. (D)</p> Signup and view all the answers

Flashcards

Ventilation

The movement of air into and out of the lungs.

Alveolar Ventilation

The part of ventilation that involves gas exchange in the alveoli.

Dead Space Ventilation

Ventilation that doesn't participate in gas exchange.

Anatomic Dead Space

Dead space due to the conducting airways (like nose and trachea).

Signup and view all the flashcards

Functional Dead Space

Alveoli that do not exchange gas properly.

Signup and view all the flashcards

Physiologic Dead Space

The total dead space in the lungs (anatomic + functional).

Signup and view all the flashcards

Respiratory Rate

The number of breaths per minute.

Signup and view all the flashcards

Causes of increased physiologic dead space

Insufficient perfusion to parts of the lungs, especially the apex, and certain diseases.

Signup and view all the flashcards

Bohr's Method

A method to calculate physiological dead space volume using tidal volume, exhaled CO2 concentration, and arterial CO2 concentration.

Signup and view all the flashcards

Tidal Volume (VT)

The volume of air inhaled and exhaled during a normal breath.

Signup and view all the flashcards

Exhaled CO2 Concentration

The concentration of carbon dioxide in the air exhaled from the lungs.

Signup and view all the flashcards

Arterial CO2 Concentration (PACO2)

The concentration of carbon dioxide in the arterial blood.

Signup and view all the flashcards

Dead Space Volume (VD)

The volume of air in the lungs that doesn't take part in gas exchange.

Signup and view all the flashcards

Alveolar Partial Pressure (PA)

The partial pressure of a gas in the alveoli (air sacs of the lungs).

Signup and view all the flashcards

Arterial Partial Pressure (Pa)

The partial pressure of a gas in the arterial blood.

Signup and view all the flashcards

Venous CO2 Concentration (PVCO2)

The concentration of carbon dioxide in the venous blood.

Signup and view all the flashcards

Expired Air

The air that is breathed out of the lungs.

Signup and view all the flashcards

Equilibrium

A state where the pressures of CO2 are equal in the alveoli and the arterial blood.

Signup and view all the flashcards

Normal PACO2

40mmHg

Signup and view all the flashcards

Venous CO2 Pressure

46mmHg

Signup and view all the flashcards

Expired CO2 < Alveolar CO2

Dead space causes a lower expired CO2 concentration because of dilution from the non-functional area.

Signup and view all the flashcards

Complete Dead Space

Entirely non-functional lungs, no gas exchange occurs.

Signup and view all the flashcards

Bohr's Equation

An equation that relates the expired carbon dioxide concentration to the arterial carbon dioxide concentration and the amount of dead space in the lungs. It helps us understand how dead space affects gas exchange.

Signup and view all the flashcards

Dead space

The space in the lungs that isn't involved in gas exchange. This space is essentially 'dead' for gas exchange because it's either not perfused by blood or is poorly ventilated.

Signup and view all the flashcards

How does decreased dead space affect expired CO2?

Decreasing dead space allows more gas exchange, leading to an increase in expired CO2 concentration, as more CO2 is removed from the body.

Signup and view all the flashcards

How does increased dead space affect expired CO2?

Increasing dead space reduces gas exchange, causing a decrease in expired CO2 concentration, as less CO2 is removed from the body.

Signup and view all the flashcards

Dead space and oxygenation

While increased dead space doesn't directly cause hypoxemia (low blood oxygen), it can lead to hypercapnia (high blood CO2) by reducing CO2 removal.

Signup and view all the flashcards

Total ventilation

The total amount of air moved in and out of the lungs with each breath.

Signup and view all the flashcards

Alveolar ventilation equation

A formula used to predict the level of carbon dioxide in the alveoli based on total ventilation and dead space.

Signup and view all the flashcards

What's the relationship between total ventilation and alveolar ventilation?

Alveolar ventilation is equal to total ventilation minus the dead space.

Signup and view all the flashcards

Hypercapnia

A condition characterized by high levels of carbon dioxide in the blood.

Signup and view all the flashcards

How does dead space lead to hypercapnia?

Increased dead space reduces CO2 removal, leading to its accumulation in the blood and causing hypercapnia unless the patient increases their breathing rate.

Signup and view all the flashcards

Why might patients compensate for increased dead space?

Patients might increase their respiratory rate to compensate for increased dead space and keep their CO2 levels from rising.

Signup and view all the flashcards

Hypoxemia

A condition characterized by low levels of oxygen in the blood.

Signup and view all the flashcards

Does dead space directly cause hypoxemia?

No, dead space itself shouldn't cause hypoxemia. However, certain diseases that cause dead space might also cause other pulmonary problems that lead to hypoxemia.

Signup and view all the flashcards

Respiratory Acidosis

A condition where the blood becomes acidic due to an increase in CO2 levels.

Signup and view all the flashcards

What is the body's response to elevated CO2?

The body increases its respiratory rate to blow off excess CO2.

Signup and view all the flashcards

What factors influence alveolar CO2 concentration?

Increased CO2 production, decreased alveolar ventilation (hypoventilation), and increased dead space ventilation can all elevate alveolar CO2.

Signup and view all the flashcards

Why doesn't exercise usually lead to hypercapnia?

During exercise, increased CO2 production is balanced by an increase in the respiratory rate, preventing CO2 buildup.

Signup and view all the flashcards

How does dead space volume affect PACO2?

An increase in dead space volume decreases the denominator in the alveolar ventilation equation, leading to a potential rise in PACO2.

Signup and view all the flashcards

Can dead space always cause hypercapnia?

No, increasing the total ventilation rate can offset the rise in dead space, preventing CO2 buildup.

Signup and view all the flashcards

Alveolar Gas Equation

An equation that relates the oxygen level in the alveoli to the partial pressure of oxygen in inspired air, alveolar CO2 concentration, and the respiratory exchange ratio.

Signup and view all the flashcards

What does PIO2 represent?

The partial pressure of oxygen in inspired air. This is usually 150 mmHg at sea level.

Signup and view all the flashcards

What is the respiratory exchange ratio (R)?

The ratio of CO2 produced for every oxygen molecule consumed. It's usually around 0.8.

Signup and view all the flashcards

How does PIO2 affect alveolar oxygen tension?

An increase in PIO2 raises the alveolar oxygen tension. It's like adding more oxygen to the alveoli.

Signup and view all the flashcards

What does PACO2 represent?

The partial pressure of carbon dioxide in the alveoli.

Signup and view all the flashcards

How does the alveolar gas equation help us understand oxygen levels?

It explains how changes in inspired oxygen, alveolar CO2, and the respiratory exchange ratio can affect alveolar oxygen levels.

Signup and view all the flashcards

Why does hypercapnia decrease PAO2?

As the partial pressure of carbon dioxide in the alveoli (PACO2) increases, the alveolar oxygen pressure (PAO2) decreases due to the competition for space and the shift in the equilibrium.

Signup and view all the flashcards

How does hypoventilation affect oxygen and carbon dioxide?

Hypoventilation leads to increased PACO2 (hypercapnia) and decreased PAO2 (hypoxemia) due to inadequate removal of carbon dioxide and oxygen uptake.

Signup and view all the flashcards

How does gravity affect lung perfusion?

Gravity causes uneven blood flow distribution in the lungs: highest at the base and lowest at the apex, due to the energy required to pump blood against gravity.

Signup and view all the flashcards

What are the three zones of lung perfusion?

Lungs are divided into three zones based on blood flow: Zone 1 (apex, lowest flow), Zone 2 (middle, moderate flow), and Zone 3 (base, highest flow).

Signup and view all the flashcards

How does gravity affect lung ventilation?

Gravity also affects ventilation, leading to higher ventilation at the base and lower ventilation at the apex due to compression of air spaces at the base during expiration.

Signup and view all the flashcards

Ventilation vs. Perfusion variation

The change in perfusion from the base to the apex is much greater than the change in ventilation. This means perfusion is more affected by gravity than ventilation.

Signup and view all the flashcards

Ventilation/Perfusion Ratio (VQ ratio)

The ratio of alveolar ventilation to pulmonary blood flow; it reflects the efficiency of gas exchange in the lungs.

Signup and view all the flashcards

What is a normal VQ ratio?

A normal VQ ratio for the entire lung is about 0.8, which indicates a good balance between ventilation and perfusion, leading to normal blood gas values.

Signup and view all the flashcards

Effects of abnormal VQ ratio

If ventilation and perfusion become imbalanced, the VQ ratio deviates from normal, leading to abnormal blood gas values and potential respiratory problems.

Signup and view all the flashcards

Why is VQ ratio important?

The VQ ratio is crucial for efficient gas exchange because it determines the amount of oxygen that can be transferred from the alveoli to the blood.

Signup and view all the flashcards

Base of the lung: ventilation and perfusion

The base of the lung has the highest blood flow and ventilation, but the variation in blood flow from apex to base is much greater than the variation in ventilation.

Signup and view all the flashcards

Apex of the lung: ventilation and perfusion

The apex of the lung has the lowest blood flow and ventilation due to gravity, with a greater decrease in blood flow compared to ventilation.

Signup and view all the flashcards

What causes VQ mismatch?

Conditions like pneumonia, pulmonary embolism, or asthma can disrupt ventilation and perfusion, leading to a mismatch between the two and impairing gas exchange.

Signup and view all the flashcards

What is a shunt?

A shunt is a condition where blood flows through the lungs without participating in gas exchange, reducing the oxygen content of the blood.

Signup and view all the flashcards

What is dead space?

Dead space refers to areas in the lungs where ventilation occurs but no gas exchange takes place, effectively wasting ventilation.

Signup and view all the flashcards

VQ Ratio

The ratio of ventilation (airflow) to perfusion (blood flow) in the lungs.

Signup and view all the flashcards

Lowest VQ Ratio

Found at the base of the lungs, indicating more blood flow than ventilation, resulting in some blood flow 'wasted' since it doesn't get enough oxygen.

Signup and view all the flashcards

Highest VQ Ratio

Found at the apex (top) of the lungs, indicating less blood flow relative to ventilation, meaning some ventilation is 'wasted' due to limited blood to exchange gases.

Signup and view all the flashcards

Alveolar Pressure (PA)

The pressure inside the alveoli (air sacs) of the lungs; can affect blood flow by squeezing capillaries.

Signup and view all the flashcards

Blood Flow in Zone 1 of the Lung

Occurs when PA is higher than both arterial (PA) and venous (PV) pressures; results in very little blood flow due to capillary collapse.

Signup and view all the flashcards

Blood Flow in Zone 2 of the Lung

Occurs when PA is higher than PV, but lower than PA; intermittent blood flow due to the pulsing arterial pressure.

Signup and view all the flashcards

Blood Flow in Zone 3 of the Lung

Occurs when PA is lower than both PA and PV; continuous blood flow, as PA is not high enough to collapse capillaries.

Signup and view all the flashcards

Cause of Cavitary Tuberculosis

Tuberculosis bacteria thrive in oxygen-rich environments like the apex of the lungs due to high VQ ratio, resulting in cavitary lesions.

Signup and view all the flashcards

PAO2

Alveolar partial pressure of oxygen, reflecting the amount of oxygen in the alveoli.

Signup and view all the flashcards

PACO2

Arterial partial pressure of carbon dioxide, representing the amount of carbon dioxide in the blood.

Signup and view all the flashcards

Causes of Dead Space

Can be caused by inadequate perfusion (blood flow) to alveoli, leading to ineffective gas exchange, or from anatomical structures like the trachea that don't participate in gas exchange.

Signup and view all the flashcards

Zone 2

The middle zone of the lung where blood flow is pulsatile, meaning it only occurs during peak arterial pressure.

Signup and view all the flashcards

Zone 1

The apex of the lung where alveolar pressure is equal to or greater than arterial pressure, leading to minimal or no blood flow.

Signup and view all the flashcards

Zone 1: Dead Space

When arterial pressure falls in Zone 1, capillary compression occurs, leading to a ventilated area that is not perfused, thus becoming dead space.

Signup and view all the flashcards

Exercise: VQ Ratio

During exercise, the VQ ratio (ventilation/perfusion) for the whole lung approaches 1, meaning ventilation and perfusion are more evenly matched.

Signup and view all the flashcards

Exercise: Arterial Blood Gases

Despite increased oxygen demand and CO2 production during exercise, arterial blood gas levels remain relatively unchanged.

Signup and view all the flashcards

Exercise: Venous Blood Gases

During exercise, venous blood gases show significant changes: lower oxygen and higher carbon dioxide due to increased tissue metabolism.

Signup and view all the flashcards

Exercise: Lung Adaptation

Increased ventilation and perfusion during exercise allow the lungs to compensate for the increased CO2 production and oxygen demand.

Signup and view all the flashcards

Hemorrhage/Shock: Zone 1

A decrease in arterial pressure during hemorrhage or shock can lead to Zone 1 becoming dead space because of capillary compression.

Signup and view all the flashcards

Pulmonary Capillary Pressure (PV)

The pressure inside the pulmonary capillaries, which is influenced by heart function and other factors.

Signup and view all the flashcards

Study Notes

Ventilation and Perfusion

  • Ventilation: Movement of air in and out of the lungs. Measured in cubic centimeters per breath (CCS) and breaths per minute (respiratory rate).
  • Alveolar Ventilation: Air used for gas exchange. Removes CO2 and delivers O2 to the blood.
  • Dead Space Ventilation: Air that does not participate in gas exchange.
    • Anatomic Dead Space: Due to conducting airways (e.g., nose, trachea) that lack alveoli.
    • Functional Dead Space: Alveoli that should exchange gas but do not due to issues in the system.
    • Physiological Dead Space: Total dead space, including anatomic and functional. Often higher than anatomic due to insufficient perfusion, especially in the apex of the lungs.

Bohr's Method

  • Used to measure physiological dead space volume (VD)
  • Requires three parameters:
    • Tidal volume (VT): Volume of air inhaled or exhaled in one breath
    • Exhaled CO2 concentration: CO2 concentration in exhaled air
    • Arterial CO2 concentration (PACO2): CO2 concentration in arterial blood (from blood gas analysis)
  • Bohr's equation: VD/VT = (PACO2 - exhaled CO2)/PACO2
  • Nomenclature:
    • PA (capital): Alveolar partial pressure (e.g., PAO2, PACO2)
    • Pa (lowercase): Arterial partial pressure (e.g., PaO2, PaCO2)

Gas Exchange (Alveoli & Capillaries)

  • Blood enters pulmonary capillaries with high CO2 (PvCO2).
  • Blood flows through capillaries, CO2 diffuses into alveoli, and equilibrium with alveolar CO2 (PACO2) is achieved.
  • Arterial CO2 concentration (PACO2) equals the alveolar CO2 concentration.
  • Inspired air has no CO2.

Dead Space and Expired CO2

  • In a healthy system with 100% working alveoli, expired CO2 concentration (PECO2) would equal PACO2.
  • In reality, dead space exists, and PECO2 is lower than PACO2 (e.g., 30 or 20 instead of 40) because dead space dilutes exhaled CO2.

Elevated CO2 (Hypercapnia/Hypercarbia)

  • Increased CO2 levels lead to respiratory acidosis.
  • The body compensates by raising respiratory rate to increase alveolar ventilation.
  • Hypercapnia results from:
    • Increased CO2 production
    • Decreased alveolar ventilation (hypoventilation)
    • Increased dead space

Alveolar Ventilation Equation

  • Predicts alveolar CO2 level
  • Equation: PACO2 = VCO2 × K / Alveolar Ventilation
  • Increased CO2 production raises alveolar CO2. Increased ventilation lowers alveolar CO2.
  • Increase in dead space will result in raising PACO2.

Alveolar Gas Equation

  • Predicts alveolar O2 (PAO2)
  • Equation: PAO2 = PIO2 - (PACO2/R)
  • Increased inspired oxygen (PIO2) raises PAO2. Alveolar CO2 (PACO2) lowers PAO2.
  • Respiratory exchange ratio (R) varies with diet and metabolism (0.8 is typical).
  • High PACO2 corresponds to low PAO2 resulting in hypoxemia in the case of under-ventilation.

Pulmonary Blood Flow (Perfusion)

  • Blood flow is uneven in upright position due to gravity:
    • Highest at the base, lowest at the apex.
  • Lung zones:
    • Zone 3 (base): Highest blood flow.
    • Zone 1 (apex): Lowest blood flow.
    • Zone 2 (middle): Pulsatile blood flow (driven by pulsatile arterial pressure).

Ventilation-Perfusion (VQ) Ratio

  • VQ ratio: Alveolar ventilation / pulmonary blood flow
  • Normal VQ ratio for entire lung: ~0.8
  • VQ ratio varies from base to apex:
    • Low VQ ratio at the base (high blood flow, less change in ventilation).
    • High VQ ratio at the apex (low blood flow, less change in ventilation)

Exercise

  • Exercise increases oxygen demand and cardiac output increasing both ventilation and perfusion.
  • Arterial blood gas values remain mostly normal during exercise.
  • Venous blood shows significant changes with increased CO2 and decreased oxygen.

Other Important Factors

  • Zone 1 (apex), where alveolar pressure may be equal or greater than arterial pressure.
  • Compression of pulmonary capillaries can occur leading to dead space if arterial pressure drops.
  • Variations in the VQ ratio are important for Step 1 questions.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Description

This quiz covers key concepts related to ventilation and perfusion, focusing on definitions and measurement methods, including Bohr's method for assessing physiological dead space volume. Understand the different types of ventilation, including alveolar and dead space ventilation, and their significance in respiratory physiology.

More Like This

Respiratory System: Ventilation and Gas Exchange
21 questions

Respiratory System: Ventilation and Gas Exchange

LovelyNeodymium2535 avatar
LovelyNeodymium2535
Respiratory System Physiology Quiz
88 questions

Respiratory System Physiology Quiz

StainlessCosecant avatar
StainlessCosecant
Physiology Chapter 4: Respiratory System
48 questions

Physiology Chapter 4: Respiratory System

JubilantDiopside1201 avatar
JubilantDiopside1201
Physiology of Ventilation and Gas Exchange
47 questions

Physiology of Ventilation and Gas Exchange

AbundantSanDiego4803 avatar
AbundantSanDiego4803
Use Quizgecko on...
Browser
Open
Browser
Browser