L29. Physiology - Gas Exchange II

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Questions and Answers

What volume of atmospheric air is typically inspired during each breath?

800 ml

150 ml

500 ml (correct)

350 ml

What is the partial pressure of carbon dioxide at the level of the alveoli at the end of expiration?

42 mmHg (correct)

97 mmHg

103 mmHg

38 mmHg

How much stale air remains in the conducting zone at the end of expiration?

500 ml

150 ml (correct)

200 ml

350 ml

What process is responsible for the movement of gases between the alveoli and capillary blood?

Simple diffusion Signup and view all the answers

What is the partial pressure of oxygen at the level of the alveoli at the end of inspiration?

103 mmHg Signup and view all the answers

What type of breathing occurs when expired gas contains air from both the atmosphere and the stale air?

Mixed breathing Signup and view all the answers

What factor optimizes gas diffusion in the alveolar capillary bed?

Large surface area Signup and view all the answers

During normal breathing, how much of the total inspired air reaches the alveoli?

350 ml Signup and view all the answers

What is the primary significance of an elevated alveolar to arterial PO2 difference, (A-a) DO2?

Indicates inadequate diffusion of gases at the alveolar-capillary membrane. Signup and view all the answers

Which factor is NOT a determinant of the diffusion of oxygen and carbon dioxide across the alveolar membrane?

Temperature of the gas Signup and view all the answers

In which lung zone does pulmonary blood flow typically exceed alveolar pressure?

Zone III Signup and view all the answers

What is the effect of vasoconstriction on vascular compliance and pulmonary vascular resistance?

It decreases vascular compliance and increases pulmonary vascular resistance. Signup and view all the answers

What characterizes physiological shunting in pulmonary physiology?

Blood moving through lung areas with mismatched ventilation and perfusion. Signup and view all the answers

Which factor is least likely to impact net fluid outflow from capillaries?

Hydrostatic pressure in the venous system. Signup and view all the answers

How does hyperventilation primarily affect partial pressure of carbon dioxide (PCO2) in the blood?

Decreases PCO2 through excess carbon dioxide elimination. Signup and view all the answers

How does hypoventilation affect arterial levels of oxygen and carbon dioxide?

It decreases arterial oxygen and increases carbon dioxide. Signup and view all the answers

What is the typical pH level of arterial blood under normal conditions?

7.4 Signup and view all the answers

Which condition would likely lead to an increase in hydrostatic pressure and subsequently cause pulmonary edema?

Left-sided heart failure Signup and view all the answers

Which component would contribute to the outward net pressure in capillary fluid exchange?

Capillary hydrostatic pressure. Signup and view all the answers

What best describes the average ventilation/perfusion (V/Q) ratio in a healthy lung?

Ideal V/Q ratio of 1:1 across all lung segments. Signup and view all the answers

What happens to arterial blood pH if carbon dioxide levels increase without ventilation change?

pH decreases, becoming more acidic. Signup and view all the answers

What effect does altered gravity have on the distribution of ventilation and perfusion in the lung?

It causes a gradient where perfusion is higher in the lower lung zones. Signup and view all the answers

What role does ventilation play in acid-base balance in the bloodstream?

It acutely alters pH in arterial blood. Signup and view all the answers

Which condition is associated with increased interstitial fluid hydrostatic pressure affecting fluid exchange?

Acute respiratory distress syndrome. Signup and view all the answers

What happens to the PCO2 value when the alveoli are inadequately perfused with blood?

It approaches zero. Signup and view all the answers

How does gravity affect blood flow distribution in the lungs?

Blood flow is highest near the base of the lung. Signup and view all the answers

What is the primary effect of variations in ventilation and perfusion at different lung levels?

They change the V/Q ratio and consequently affect PO2 and PCO2. Signup and view all the answers

As one moves from the apex to the base of the lung, how does the V/Q ratio change?

It decreases consistently. Signup and view all the answers

What compensatory mechanisms exist in the lungs to correct V/Q mismatches?

Local compensatory mechanisms adjust to pathological V/Q mismatches. Signup and view all the answers

What effect does a lower V/Q ratio at the base of the lung have on gas concentration?

It decreases PO2 and increases PCO2. Signup and view all the answers

When ventilation is greater at the base of the lungs compared to the apex, what can be inferred?

Base ventilated regions are more effective in gas exchange. Signup and view all the answers

How does inadequate blood perfusion in the alveoli affect alveolar gas levels?

Alveolar PO2 increases due to atmospheric gas equilibrium. Signup and view all the answers

What happens to the V/Q ratio when one lung is completely obstructed?

The V/Q ratio decreases to zero. Signup and view all the answers

How does the body respond to decreased ventilation in one lung?

It constricts pulmonary vessels around the obstructed lung. Signup and view all the answers

What is the expected change in the partial pressure of carbon dioxide in an obstructed lung?

It increases towards mixed venous levels. Signup and view all the answers

What occurs when one lung is adequately ventilated but not perfused?

The V/Q ratio approaches infinity. Signup and view all the answers

What effect does an increased V/Q ratio have on the bronchial smooth muscle in an unperfused lung?

It causes bronchial smooth muscle constriction. Signup and view all the answers

What is the likely arterial blood gas consequence when an individual inhales 100% oxygen with a V/Q mismatch?

The alveolar-arterial difference will be reduced or eliminated. Signup and view all the answers

How does reduced perfusion affect surfactant production in the unperfused lung?

Surfactant production decreases. Signup and view all the answers

What compensation occurs when the body detects a high V/Q ratio in a lung?

Decreased ventilation in the affected lung. Signup and view all the answers

Study Notes

Normal Blood Gas Values

Typical Values:
Alveolar PO2: 100 mmHg
Alveolar PCO2: 40 mmHg
Arterial PO2: 95 mmHg
Arterial PCO2: 40 mmHg
Mixed Venous PO2: 40 mmHg
Mixed Venous PCO2: 46 mmHg

Alveolar to Arterial PO2 Difference (A-a) DO2

Calculation: Arterial PO2 subtracted from Alveolar PO2
Normal Value: Less than 10 mmHg
Elevated (A-a) DO2 Significance: Indicates a problem with gas exchange in the lungs:
- Diffusion impairment
- Shunt
- Ventilation/perfusion mismatch
- Hypoventilation

Factors Affecting Gas Diffusion Between Alveoli and Capillaries

Solubility: Higher solubility means faster diffusion.
Gas Molecular Weight: Lighter gases diffuse faster.
Cross-Sectional Area: Larger surface area means increased diffusion.
Membrane Thickness: Thinner membrane allows faster diffusion.

Diseases Affecting Gas Diffusion

Emphysema: Destroys alveoli, reducing surface area for gas exchange.
Fibrotic Lung Disease: Thickens alveolar walls, slowing diffusion.
Pulmonary Edema: Fluid in the alveoli interferes with gas exchange.

Pulmonary Edema Development

Increased Hydrostatic Pressure: Left-sided heart failure increases pressure in pulmonary capillaries, forcing fluid into alveoli.
Increased Permeability: Inflammation or injury allows fluid to leak from capillaries into alveoli.
Impaired Lymphatic Drainage: Impaired lymphatic system prevents proper fluid removal from interstitial space.

Shunts

Right-to-Left Shunts: Blood bypasses the lungs without oxygenation.
Anatomic Shunts: Blood flow through congenital heart defects avoids pulmonary circulation.
Physiological Shunts: Blood flow through poorly ventilated lung regions.
Physiological Dead Space: Alveoli ventilated but not perfused.

Ventilation/Perfusion (V/Q) Ratio

V/Q Ratio: Ratio of ventilation to perfusion in a specific alveoli-capillary unit.
Normal Average V/Q: 0.8 (Slightly higher at the apex of the lungs)
Impact of Gravity on V/Q:
- Base of Lungs: Higher blood flow, slightly lower ventilation, lower V/Q.
- Apex of Lungs: Lower blood flow, slightly higher ventilation, higher V/Q.

Lung Zones (Upright Person)

Zone 1: Apex of the lung. Alveolar pressure is higher than pulmonary arterial pressure, limiting blood flow.
Zone 2: Middle of the lung. Pulmonary arterial pressure is higher than alveolar pressure, but lower than venous pressure. Blood flow increases.
Zone 3: Base of the lung. Pulmonary arterial pressure is higher than both alveolar and venous pressures. Blood flow is highest.

Hypoventilation and Hyperventilation

Hypoventilation: Lowers arterial PO2 and elevates arterial PCO2.
Hyperventilation: Elevates arterial PO2 and lowers arterial PCO2.

Ventilation/Perfusion Mismatch

Non-Uniform V/Q: Variations in ventilation and perfusion can occur even in healthy lung tissue.
V/Q Mismatch Effects: Can cause hypoxemia (low blood PO2) and hypercapnia (high blood PCO2).

Compensatory Mechanisms for V/Q Mismatch

Obstructed Lung: Unventilated lung reduces V/Q to zero, leading to shunt. Pulmonary vasoconstriction diverts blood to ventilated lung.
Non-Perfused Lung: V/Q approaches infinity. Ventilation decreases in the non-perfused lung to compensate, diverting airflow to the perfused lung.

Diagnosing V/Q Mismatch

100% Oxygen Inhalation: Helps differentiate between a shunt and a ventilation/perfusion ratio mismatch.
Shunt: Increased arterial PO2, but not to normal levels.
V/Q Mismatch: Arterial PO2 will approach normal with 100% oxygen.

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Description

Test your knowledge on normal blood gas values and the factors influencing gas diffusion. This quiz covers essential parameters like alveolar and arterial PO2, PCO2, and the significance of A-a DO2 differences in diagnosing respiratory issues. Additionally, learn about diseases that can affect gas diffusion.