Respiratory Physiology Review

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Questions and Answers

What does alveolar ventilation specifically refer to?

The volume of air that reaches the alveoli available for gas exchange. (correct)

The volume of air that does not participate in gas exchange.

The total volume of air inhaled in a minute.

The volume of air trapped in the conducting airways.

How is dead space ventilation defined?

The volume of air that is fully exchanged with blood.

The volume of air that is absorbed by the lung tissue.

The volume of air that enters the alveoli for gas exchange.

The volume of air that remains in the conducting airways or is ventilated but not perfused. (correct)

What is the formula to calculate alveolar ventilation?

AV = TV - VD x RR

AV = (TV - VD) + RR

AV = (TV - VD) x RR (correct)

AV = TV + VD x RR

What is the relationship between alveolar ventilation and PaCO2?

They are inversely proportional; increased ventilation decreases PaCO2. Signup and view all the answers

Which of the following statements is true regarding physiological dead space?

It refers to air ventilated but not perfused in the lungs. Signup and view all the answers

What does tidal volume (TV) specifically refer to?

The amount of air inhaled or exhaled in a normal breath. Signup and view all the answers

How is inspiratory reserve volume (IRV) characterized?

It is the additional air that can be inhaled after a normal inhalation. Signup and view all the answers

What additional volume does expiratory reserve volume (ERV) represent?

The volume of air that can be exhaled after a normal exhalation. Signup and view all the answers

Which method is used to measure tidal volume, inspiratory reserve volume, and expiratory reserve volume?

Spirometry Signup and view all the answers

What is the significance of effective ventilation in the context of CO2 in the blood?

It reduces the concentration of CO2 in the alveoli. Signup and view all the answers

What is the relationship between residual volume (RV) and total lung capacity (TLC)?

TLC is calculated using RV. Signup and view all the answers

Which statement correctly describes vital capacity (VC)?

VC is the maximum air exhaled after maximum inhalation. Signup and view all the answers

How is lung compliance defined?

It is related to the change in lung volume per unit change in pressure. Signup and view all the answers

What components are included in the calculation of Total Lung Capacity (TLC)?

TV, IRV, ERV, and RV. Signup and view all the answers

Which technique can be used to measure the residual volume (RV) in the lungs?

Gas dilution techniques. Signup and view all the answers

What does decreased compliance in the lungs indicate?

The lungs are stiffer and require more pressure to inflate. Signup and view all the answers

Which disease is characterized by decreased compliance due to lung tissue scarring?

Pulmonary fibrosis Signup and view all the answers

How does surface tension affect alveoli within the lungs?

It causes alveoli to collapse due to inward pulling forces. Signup and view all the answers

What is the function of surfactant in the alveoli?

To reduce surface tension and enhance lung compliance. Signup and view all the answers

What does increased compliance indicate about the lungs?

The lungs can hold more air than normal but may struggle to expel it. Signup and view all the answers

What is the main function of surfactant produced by Type II cells in the alveoli?

To reduce surface tension and prevent alveolar collapse Signup and view all the answers

What is a consequence of insufficient development of Type II cells in premature humans?

Collapse of alveoli making ventilation difficult Signup and view all the answers

Which factor does NOT affect the rate of gas diffusion at the air-blood barrier?

Chemical structure of the gases involved Signup and view all the answers

What effect does pulmonary edema have on gas diffusion?

Hinders diffusion by thickening the air-blood barrier Signup and view all the answers

Why do gases like CO2 diffuse more readily than gases like O2?

CO2 is more soluble in blood than O2 Signup and view all the answers

What percentage of oxygen is transported in the blood bound to hemoglobin?

98.5% Signup and view all the answers

How does increased temperature affect hemoglobin's affinity for oxygen?

Decreases affinity Signup and view all the answers

Which form accounts for the majority of carbon dioxide transportation in the blood?

As bicarbonate ions Signup and view all the answers

A low ventilation/perfusion (V/Q) ratio is an indication of what condition?

Perfusion exceeding ventilation Signup and view all the answers

What factors can decrease hemoglobin's affinity for oxygen and increase its release in tissues?

Low pH and high CO2 levels Signup and view all the answers

What condition is associated with a high ventilation/perfusion (V/Q) ratio?

Pulmonary embolism Signup and view all the answers

Which of the following best describes hypoxemia?

Below-normal level of oxygen in the blood Signup and view all the answers

Which of the following causes can lead to hypoxemia?

Decreased breathing rate or depth Signup and view all the answers

Which phenomenon is a result of ventilation-perfusion mismatch?

Reduced oxygen levels in blood Signup and view all the answers

Which of the following conditions may result in a ventilation-perfusion mismatch?

Pulmonary embolism Signup and view all the answers

What is hypercapnia?

An elevated level of carbon dioxide in the blood Signup and view all the answers

What is the most frequent cause of hypercapnia?

Hypoventilation Signup and view all the answers

How does mammalian respiration primarily differ from avian respiration?

Avian respiration facilitates continuous airflow Signup and view all the answers

Which statement best describes the gas exchange process in mammals?

Gas exchange occurs in alveoli with tidal flow Signup and view all the answers

What role does the diaphragm play in mammalian respiration?

It aids in the tidal flow of air and gas exchange Signup and view all the answers

What is a unique anatomical adaptation of the avian respiratory system that allows continuous airflow through the lungs?

Air sacs Signup and view all the answers

Which of the following describes the primary site of gas exchange in birds?

Parabronchi Signup and view all the answers

What type of airflow is generated in the larger airways and branch points of the respiratory system?

Turbulent flow Signup and view all the answers

Why can parabronchi in the avian respiratory system become sites of infection?

Because of their extensive surface area Signup and view all the answers

How does airflow in smaller airways differ from airflow in larger airways?

It is laminar Signup and view all the answers

What occurs to the velocity of air as it transitions from the trachea to the alveoli?

Velocity decreases due to increased cross-sectional area. Signup and view all the answers

Which gas is more soluble in tissue fluid?

Carbon Dioxide Signup and view all the answers

Which parameter does NOT influence gas diffusion across the air-blood barrier?

Color of the gas molecules Signup and view all the answers

Which gas has a greater partial pressure gradient at the air-blood barrier?

Oxygen Signup and view all the answers

The rate of gas transfer across the air-blood barrier is dependent on what factor?

Surface area and thickness of the barrier Signup and view all the answers

In which condition does gas equilibration not occur effectively due to a thicker air-blood barrier?

Pulmonary fibrosis Signup and view all the answers

What change occurs to the partial pressure of oxygen in blood passing through the alveolar capillaries?

It increases from 40 mmHg to 100 mmHg Signup and view all the answers

How does the partial pressure of carbon dioxide change in the blood as it circulates through the alveoli?

It decreases from 46 mmHg to 40 mmHg Signup and view all the answers

What is the partial pressure gradient for oxygen at the air-blood barrier?

60 mmHg Signup and view all the answers

Why might diffusion be slower in cases of pulmonary edema?

The thickness of the air-blood barrier increases Signup and view all the answers

What does a right shift in the Hb-O2 dissociation curve indicate about hemoglobin's affinity for oxygen?

Hemoglobin affinity for oxygen decreases and more oxygen is unloaded to the tissues. Signup and view all the answers

How does hemoglobin affinity for oxygen change among mammals of different sizes?

Smaller species have right shifted curves facilitating oxygen delivery. Signup and view all the answers

What is the partial pressure gradient for CO2 at the air-blood barrier?

6 mmHg Signup and view all the answers

What effect does a left shift in the Hb-O2 dissociation curve have on oxygen delivery to tissues?

Decreases oxygen delivery as hemoglobin affinity for oxygen increases. Signup and view all the answers

What physiological adaptation is observed in smaller mammal species regarding oxygen delivery?

Right shifted Hb-O2 dissociation curve facilitating increased oxygen delivery. Signup and view all the answers

What is the primary method by which carbon dioxide is transported from the blood into the alveolar space?

Diffusion of CO2 in solution from plasma Signup and view all the answers

How does the relationship between CO2 partial pressure and its content in the bloodstream compare to that of oxygen?

CO2 relationship is linear within life-relevant partial pressure ranges Signup and view all the answers

What happens to bicarbonate in the plasma when it diffuses into red blood cells?

It reacts with H+ to form carbonic acid Signup and view all the answers

What is the final step for carbon dioxide before it is exhaled from the alveolar space?

Exhalation through the respiratory tract Signup and view all the answers

Which of the following statements accurately describes the transport of CO2 in the bloodstream?

More is carried as bicarbonate than as dissolved CO2 Signup and view all the answers

What is indicated by a normal A-a gradient of 4-6 mmHg?

Gas exchange is maximal Signup and view all the answers

How is the Alveolar-arterial gradient used in clinical practice?

To distinguish causes of hypoxemia Signup and view all the answers

If the A-a gradient is elevated, what is likely true about the patient's condition?

VQ mismatching is likely a significant cause of hypoxemia Signup and view all the answers

What occurs during normal ventilation and perfusion matching?

Partial pressures of gas in blood match those in alveolar gas Signup and view all the answers

What happens to the gas exchange process during ventilation-perfusion mismatch?

Gas exchange becomes impaired Signup and view all the answers

What does an A-a gradient over 10 mmHg indicate?

Compromised gas exchange Signup and view all the answers

How does mild V/Q mismatching affect oxygen and CO2 levels?

Oxygen drops to hypoxemic levels while CO2 remains normal. Signup and view all the answers

What is the reason that breathing higher than normal oxygen levels does not benefit a normal patient?

O2 is driven into solution instead of loading onto Hb. Signup and view all the answers

Who would benefit from breathing oxygen-enriched air?

A patient with mild to moderate V/Q mismatch in hypoxic range Signup and view all the answers

What might occur with severe A/Q mismatch in terms of CO2 levels?

CO2 levels remain normal due to hyperventilation. Signup and view all the answers

What is the primary reason a patient with severe V/Q mismatch does not benefit from breathing enriched oxygen?

Oxygen does not reach the gas exchange regions due to poor ventilation. Signup and view all the answers

Which group of animals is characterized by a completely separate pulmonary and systemic circulation?

Mammals Signup and view all the answers

What is the minimum arterial blood oxygen partial pressure (PO2) recommended for adequate oxygenation?

85 mmHg Signup and view all the answers

Which method can be used to measure blood oxygen saturation in a patient?

Both arterial sample and pulse oximeter Signup and view all the answers

At what level of SpO2 is significant hypoxemia indicated?

90% Signup and view all the answers

Study Notes

Alveolar Ventilation

Represents the volume of fresh air reaching the alveoli each minute for gas exchange.
Calculated using the formula: AV = (TV - VD) x RR, where AV is alveolar ventilation, TV is tidal volume, VD is dead space volume, and RR is respiratory rate.

Dead Space Ventilation

Consists of air volume that doesn't participate in gas exchange.
Includes anatomical dead space (air in conducting airways) and physiological dead space (ventilated but not perfused areas).

Relationship Between Alveolar Ventilation and PaCO2

Alveolar ventilation is inversely proportional to PaCO2 levels in the bloodstream; if alveolar ventilation rises, PaCO2 decreases, and vice versa.

Ventilation and Gas Exchange

Effective ventilation is crucial for removing carbon dioxide (CO2) from the alveoli, which helps maintain lower CO2 concentrations in the bloodstream.

Tidal Volume (TV)

Tidal Volume refers to the volume of air inhaled or exhaled during a normal breath.
It is a key measurement in assessing respiratory function and can be accurately measured using spirometry.

Inspiratory Reserve Volume (IRV)

Inspiratory Reserve Volume represents the additional amount of air that can be inhaled following a normal inhalation.
This volume indicates the lungs' capacity for increased airflow and is measurable via spirometry.

Expiratory Reserve Volume (ERV)

Expiratory Reserve Volume signifies the extra air that can be exhaled after a normal exhalation.
Understanding this volume provides insights into lung function and efficiency, also measurable with spirometry.

Lung Volumes and Capacities

Residual Volume (RV): The air remaining in the lungs after maximal exhalation, ensuring the alveoli do not collapse.
Measurement Methods: Can be determined using gas dilution techniques or body plethysmography.
Total Lung Capacity (TLC): Represents the total volume of air the lungs can hold after maximal inhalation.
Calculation: TLC = Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV) + Residual Volume (RV).
Vital Capacity (VC): The maximum amount of air that can be forcibly exhaled after taking the deepest possible breath.
Calculation: VC = Inspiratory Reserve Volume (IRV) + Tidal Volume (TV) + Expiratory Reserve Volume (ERV).

Lung Function Dynamics

Lung Compliance: Indicates the lung's ability to stretch and expand in response to pressure changes.
Definition: Lung compliance is quantified as the change in lung volume (ΔV) per unit change in pressure (ΔP), expressed as C = ΔV/ΔP.

Decreased Compliance

Refers to stiffer lungs that require greater pressure to achieve a specific volume of air.
Example of a disease: Pulmonary Fibrosis
- Condition characterized by scarring and stiffening of lung tissue.
- Reduces lung elasticity, making it difficult to fully expand the lungs.

Increased Compliance

Indicates overly distensible lungs that can hold more air than normal but struggle to expel it effectively.
Example of a disease: Emphysema
- Condition involving destruction of alveolar walls.
- Loss of elastic recoil results in difficulty exhaling air from the lungs.

Surface Tension and Alveoli

Defined as the cohesive force exerted by liquid molecules at the air-liquid interface within the alveoli.
Creates a tendency for alveoli to collapse, a condition known as atelectasis.
The liquid lining alveoli pulls inward due to surface tension, potentially leading to lung complications.
Surfactant, produced by Type II alveolar cells, plays a crucial role in:
- Reducing surface tension to prevent alveolar collapse.
- Improving lung compliance and facilitating easier breathing.

Type II Cells in Premature Humans and Large Animals

Type II cells are underdeveloped in premature humans and large animals.
Insufficient surfactant production leads to alveolar collapse.
Collapse of alveoli impairs ventilation, making breathing difficult.

Role of Surfactant in Alveoli Stabilization

Surfactant is a phospholipid produced by Type II cells.
It coats alveoli to stabilize them by reducing surface tension.
This mechanism prevents alveoli from collapsing, facilitating efficient gas exchange.

Factors Affecting Gas Diffusion at the Air-Blood Barrier

Partial Pressure Gradient: A greater difference in pressure enhances gas diffusion.
Surface Area: Increased surface area improves gas exchange efficiency.
Barrier Thickness: Thinner barriers promote faster diffusion; thickened barriers (e.g., due to pulmonary edema) hinder diffusion rates.
Gas Solubility: Gases that are more soluble in blood, such as CO2, diffuse more readily than less soluble gases like O2.

Oxygen Transport in Blood

Approximately 98.5% of oxygen is transported bound to hemoglobin, while only about 1.5% is dissolved in plasma.

Hemoglobin Affinity and Oxygen Delivery

Hemoglobin's affinity for oxygen can be altered by temperature, CO2 levels, and pH (known as the Bohr effect).
A decrease in hemoglobin affinity, often due to increased temperature, higher CO2, or increased acidity, promotes greater oxygen release to tissues with higher metabolic activity.

Carbon Dioxide Transport Mechanisms

About 7-10% of carbon dioxide is dissolved in plasma.
Approximately 20-23% of carbon dioxide binds to hemoglobin.
About 70% of carbon dioxide is transported as bicarbonate ions, formed from CO2 in red blood cells through the action of carbonic anhydrase.

Low Ventilation/Perfusion (V/Q) Ratio

A low V/Q ratio signifies that blood flow is greater than airflow in the lungs.
Conditions such as pneumonia or asthma can cause a low V/Q ratio due to fluid accumulation or airflow obstruction in the alveoli.

High Ventilation/Perfusion (V/Q) Ratio

A high V/Q ratio signifies that ventilation (airflow) surpasses blood flow in the lungs.
Commonly observed in conditions such as pulmonary embolism that obstructs blood flow to ventilated regions of the lungs.
A high V/Q ratio can lead to inefficient gas exchange and contribute to hypoxemia.

Hypoxemia

Defined as an abnormally low level of oxygen in the blood, posing risks to organ function and overall health.
Causes of hypoxemia include:
- Hypoventilation: Reduced breathing rate or depth results in insufficient oxygen intake.
- Ventilation-perfusion mismatch: Conditions like pneumonia and pulmonary embolism disrupt balanced airflow and blood flow to the lungs.
- Diffusion impairment: Conditions such as pulmonary fibrosis hinder the transfer of oxygen from the alveoli to the bloodstream.
- Low inspired oxygen: High altitudes lead to decreased oxygen availability in the atmosphere.
- Venous admixture (right-to-left shunt): Situations where deoxygenated blood bypasses the lungs, preventing proper gas exchange.

Hypercapnia

Defined as an elevated level of carbon dioxide (CO2) in the blood.
Most frequent cause is hypoventilation, characterized by insufficient ventilation leading to inadequate CO2 removal.
Accumulation of CO2 in the bloodstream can have significant physiological effects.

Differences in Mammalian and Avian Respiration

Mammalian respiration uses a tidal flow mechanism, where air enters and exits the lungs, involving gas exchange primarily at alveoli.
The diaphragm plays a crucial role in mammalian respiration, aiding in inhalation and exhalation.
In contrast, avian respiration employs a unidirectional air flow through the lungs, enhanced by dedicated air sacs.
This unidirectional flow allows for more efficient gas exchange, ensuring constant oxygen supply.
Avian respiratory systems are generally more efficient than mammalian systems due to their unique anatomical structure.

Avian Respiratory System Adaptations

Air sacs allow continuous airflow through bird lungs, improving respiratory efficiency.
Parabronchi serve as gas exchange sites; their complex structure increases the surface area for oxygen absorption, making them prone to infections.

Airflow Characteristics

Larger airways experience turbulent airflow, which can produce audible sounds during auscultation.
Smaller airways feature laminar flow, resulting in minimal sound production.

Airflow Dynamics

As air moves from upper airways to alveoli, its velocity decreases.
Decrease in velocity occurs due to increasing cross-sectional area in the trachea and lower branches.
In alveoli, air molecules predominantly move by diffusion rather than bulk flow.

Gas Solubility

Carbon dioxide (CO2) is more soluble than oxygen (O2) in tissue fluids.

Factors Affecting Gas Diffusion

Gas transfer volume across the air-blood barrier is affected by:
- Surface area available for diffusion.
- Thickness of the air-blood barrier, which inversely impacts transfer rate.
- Diffusivity of the gas, influenced by its solubility in tissue fluid and molecular weight (MW).
- Partial pressure gradient (P1 - P2) which drives diffusion.

Partial Pressure Gradient

Oxygen has a greater partial pressure gradient at the air-blood barrier compared to carbon dioxide.

Conditions Preventing Complete Gas Equilibration

Complete gas equilibration is hindered in pulmonary fibrosis and pulmonary edema.
In these conditions, the air-blood barrier becomes thicker, which impedes the diffusion of gases.
Slower diffusion rates result in reduced efficiency of gas exchange in the lungs.

Gas Levels in Alveolar Capillaries

Blood in the capillaries of the alveolar region experiences rapid gas equilibration, taking approximately 0.7 seconds.
Oxygen partial pressure increases from 40 mmHg to 100 mmHg during gas exchange.
Carbon dioxide levels decrease from 46 mmHg to 40 mmHg as blood circulates through the alveoli.

Oxygen Partial Pressure Gradient

The partial pressure gradient for oxygen at the air-blood barrier is 60 mmHg.
This gradient facilitates the movement of oxygen from the alveoli into the blood, driving effective gas exchange.