Respiratory Physiology Quiz

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Questions and Answers

What is the result of a V/Q ratio of infinity?

Wasted ventilation (correct)

Venous admixture

Ideal V/Q ratio

Underventilation

What allows for full oxygenation of blood in the lungs, even during exercise?

Increased diffusion capacity for O2

Nearly ideal V/Q ratio in the upper lungs (correct)

Increased blood pressure

Increased surface area of capillaries

During strenuous exercise, what happens to the diffusing capacity for oxygen?

It remains constant at 21 ml/min/mm Hg

It increases to 65 ml/min/mm Hg (correct)

It increases to 100 ml/min/mm Hg

It decreases to 10 ml/min/mm Hg

What happens to the PO2 in the pulmonary blood during oxygen uptake?

It rises to equal the alveolar pressure Signup and view all the answers

How does gravity affect venous return and systemic blood volume?

Gravity decreases venous return and systemic blood volume Signup and view all the answers

What is a characteristic of the V/Q distribution throughout the normal lung?

It is heterogeneous Signup and view all the answers

What is a factor that contributes to the safety factor in the uptake of O2 by pulmonary blood?

The time of exposure in the capillaries Signup and view all the answers

What is the diffusing capacity for CO2 during exercise?

1200 to 1300 ml/min/mm Hg Signup and view all the answers

In which zone is blood flow the highest?

Zone 3 Signup and view all the answers

What is the approximate rate of oxygen diffusing through the respiratory membrane each minute during quiet breathing?

230 ml/min Signup and view all the answers

What is the approximate PO2 of blood pumped into the aorta?

95 mm Hg Signup and view all the answers

What is the minimum pressure required for full support of cellular metabolism?

1-3 mm Hg Signup and view all the answers

What is the effect of CO2 content on airflow?

Increases airflow Signup and view all the answers

What is the relationship between ventilation and perfusion in the lungs?

V/Q = 1 Signup and view all the answers

What is the term for the blood that bypasses gas exchange areas in the lungs?

Shunt flow Signup and view all the answers

What is a common cause of respiratory acidosis due to impaired gas exchange?

Severe kyphoscoliosis Signup and view all the answers

Which of the following is a sign of respiratory acidosis?

Cardiac dysrhythmias Signup and view all the answers

What is the term for abnormally slow and shallow breathing, leading to respiratory acidosis?

Hypoventilation Signup and view all the answers

Which of the following is a cause of respiratory alkalosis?

Hypoxemia Signup and view all the answers

What is a neurological abnormality that may occur in respiratory acidosis?

All of the above Signup and view all the answers

Which of the following is a cause of impaired respiratory control leading to respiratory acidosis?

Respiratory depressant drugs Signup and view all the answers

What is a sign of respiratory alkalosis?

Increased neuromuscular excitability Signup and view all the answers

Which of the following is a cause of respiratory acidosis due to impaired neuromuscular function?

Guillain–Barré syndrome Signup and view all the answers

What is the term for the state of acidosis resulting from high CO2 levels in the blood?

Respiratory acidosis Signup and view all the answers

Which of the following is a cause of respiratory acidosis due to impaired gas exchange?

Bacterial pneumonia Signup and view all the answers

Study Notes

Ventilation/Perfusion

Ventilation (Vo) and perfusion (Q) are mismatched in extreme cases, resulting in either wasted ventilation (V/Q = ∞) or venous admixture (V/Q = 0)
The V/Q distribution throughout the normal lung is not homogeneous, with some units being overventilated and others underventilated

Uptake of O2 by Pulmonary Blood

PO2 rises to equal alveolar pressure by the time blood has moved 1/3rd of the distance through the capillary, ensuring a safety factor
During exercise, diffusion capacity for O2 increases almost 3-folds due to increased surface area of capillaries participating in diffusion and nearly ideal V/Q ratio in the upper lungs

Transport of O2 in Arterial Blood

98% of blood that enters the left atrium becomes oxygenated, with a PO2 of 104 mm Hg
2% of blood, from bronchial circulation, bypasses gas exchange areas, resulting in a PO2 of 40 mm Hg (like venous blood), known as venous admixture of blood
The combined blood in the pulmonary veins has a PO2 of 95 mm Hg

Diffusion of O2 and CO2

1-3 mmHg of pressure is enough for full support of cellular metabolism, with a safety factor of 23 mm Hg
Diffusion of CO2 from tissue fluid into peripheral capillaries and from pulmonary blood into the alveolus occurs efficiently

Control of Ventilation and Perfusion

O2 content affects blood flow, while CO2 content affects airflow
V/Q ratio increases with increased pulmonary blood flow and alveolar ventilation

Diffusing Capacity

Diffusing capacity for oxygen: 21 ml/min/mm Hg, with a mean oxygen ∆P during quiet breathing of 11 mm Hg
During strenuous exercise, diffusing capacity increases to 65 ml/min/mm Hg due to opening up of dormant pulmonary capillaries and extradilation of already open capillaries
Diffusing capacity for CO2: 20 times that of O2, with values of 400-450 ml/min/mm Hg at rest and 1200-1300 ml/min/mm Hg during exercise

Gravity Effects

Gravity affects venous return, cardiac output, and systemic blood volume distribution
Gravity has a greater effect on pulmonary circulation than systemic circulation due to lower vascular pressures
There are three zones of blood flow in the lung, depending on pulmonary arterial, venous, and alveolar pressures.

Acid-Base Balance: Role of the Lungs

Acid-base balance refers to the regulation of free hydrogen-ion (H+) concentration in the body fluids.

Sources of Acidity

CO2 + H2O → H2CO3 → H+ + HCO3- (source of acidity)

Regulation of H+ Balance

The Henderson-Hasselbalch equation is used to calculate how changes in CO2 and HCO3− affect pH.
pH = [HCO3-] controlled by kidney function / [CO2] controlled by lung function.

Defense Mechanisms against Changes in [H+]

Three lines of defense operate to maintain [H+] at a nearly constant level (pH 7.4):
Chemical buffer systems
Respiratory mechanism of pH control
Renal mechanism of pH control

Respiratory Mechanism of pH Control

Ventilation can compensate for pH disturbances.
Increased H+ concentration stimulates respiration, which increases alveolar ventilation and decreases H+ concentration.

Relationship between Respiration and pH

High concentrations of hydrogen trigger hyperventilation.
Respiratory system is a negative feedback mechanism.
In hypoventilation, we have increased CO2 levels.

Respiratory Acid-Base Regulation

Acts at a moderate speed.
Activated when chemical buffer systems alone are unable to minimize pH deviations.
Requires a few minutes to be initiated.
Respiratory system serves as the second line of defense.

Respiratory Compensation

Peripheric chemoreceptors and central chemoreceptors are involved in respiratory compensation.

Respiratory Acidosis

Causes:
Impaired gas exchange
Type B chronic obstructive pulmonary disease (COPD)
Bacterial pneumonia
Severe asthma episode
Pulmonary edema
Acute (adult) respiratory distress syndrome
Impaired neuromuscular function
Chest injury or surgery (pain limits ventilation)
Hypokalemic respiratory muscle weakness
Severe kyphoscoliosis
Respiratory muscle fatigue
Impaired respiratory control (brainstem)
Respiratory depressant drugs (opioids, barbiturates)
Signs and symptoms:
Headache
Tachycardia
Cardiac dysrhythmias
Neurologic abnormalities
Blurred vision
Tremors
Vertigo
Disorientation
Lethargy
Somnolence

Respiratory Alkalosis

Causes:
Hypoxemia
Signs and symptoms:
Increased neuromuscular excitability

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Description

Test your understanding of ventilation and perfusion, including the uptake of oxygen by pulmonary blood and the effects of exercise.