Respiratory Physiology Chapter 5

Study Notes

Dead Space vs Shunt

Dead space: area where ventilation occurs without perfusion.
Shunt: area where perfusion occurs without ventilation.

Ventilation-Perfusion Imbalance

Imbalance impairs overall gas exchange, leading to hypoxemia.

Primary Lung Function

Lungs primarily facilitate gas exchange, particularly oxygen and carbon dioxide.

Causes of Hypoxemia

Factors include hypoventilation, diffusion limitation, shunt, and V/Q mismatch.

V/Q Mismatch

Most common cause of hypoxemia in patients with respiratory disease.

Alveolar PO2 Determinants

Alveolar PO2 (PAO2) is determined by oxygen removal by blood and replenishment by ventilation.

Tissue PCO2 Increase

Impaired pulmonary gas exchange results in an increase in tissue PCO2.

Atmospheric PO2 and PCO2

Normal atmospheric PO2: 150 mmHg; PCO2: 0 mmHg.

PO2 Distribution

Different organs receive varying amounts of PO2.

PO2 Gradient

PO2 decreases from the atmosphere to mitochondria as gas is utilized.

Hypoxemia Levels

Normal: 80-100 mmHg
Mild: 60-79 mmHg
Moderate: 40-59 mmHg
Severe: less than 40 mmHg

Hypoventilation

Occurs when ventilation is insufficient to clear CO2, leading to increased arterial PCO2.
Common in obstructive lung diseases.

Hypoventilation Effects

Causes an increase in arterial PCO2, decrease in PO2 unless supplemental oxygen is given.
Hypoxemia can be reversed by administering oxygen.

Diffusion Limitation

Occurs when gas exchange is hindered due to thickened or damaged alveolar-capillary membranes.
Classic sign is hypoxemia during exercise, but not at rest.

Shunt Effects

Blood enters the arterial system without going through ventilated lung areas, contributing to hypoxemia.
Does not increase arterial PCO2 due to chemoreceptor responses.

Summary on Shunt

Hypoxemia does not improve with 100% oxygen due to bypassed alveoli not being exposed to higher oxygen levels.

V/Q Mismatch Consequences

Causes hypoxemia and hypercapnia (CO2 retention).

V/Q Inequality in Patients

Patients with V/Q inequality, such as COPD, can have normal PCO2 due to compensatory increased ventilatory drive.

V/Q Definition

V/Q indicates how well alveolar ventilation compares to pulmonary capillary perfusion.

Normal V/Q Ratio

Normal V/Q ratio is 0.8, indicating optimal gas exchange with matched ventilation and perfusion.

Shunt Characteristics

V/Q equals 0: no ventilation, but perfusion occurs. Results in decreased O2 and increased CO2.

Dead Space Characteristics

V/Q is greater than 1: ventilation occurs without perfusion. Results in increased O2 and decreased CO2.

Factors Affecting V/Q

Ventilation and perfusion vary throughout the lungs due to gravity and other factors. Higher V/Q at the lung apex, lower at the base.

Importance of V/Q

V/Q is critical for determining gas exchange efficacy in lung units. Mismatches reduce overall gas exchange efficiency.

Diseases Decreasing V/Q

Conditions causing decreased V/Q include chronic bronchitis, asthma, pulmonary embolism, and pneumonia.

Diseases Increasing V/Q

Conditions resulting in increased V/Q include emphysema and pulmonary hypertension.

Summary of V/Q Mismatch

Responds to 100% O2, with increased A-a gradient; causes include COPD, pulmonary fibrosis, and pneumonia.

Hypoxemia and A-a Difference

Hypoventilation: no A-a difference, good O2 response.
Diffusion limitation: increased A-a, good O2 response.
Shunt: increased A-a, modest O2 response.
V/Q inequality: increased A-a, good O2 response.

Symptoms of V/Q Mismatch

Common symptoms include fatigue, headache, dizziness, shortness of breath (SOB), rapid breathing, confusion, and cyanosis.

Measuring V/Q Mismatch

V/Q scans assess ventilation and perfusion in the lungs using x-ray technology to identify mismatches.

Description

This flashcard quiz focuses on the ventilation-perfusion relationships from Chapter 5 of Respiratory Physiology. It covers key concepts like dead space, shunt, gas exchange, and the causes of hypoxemia. Test your understanding of these critical topics in respiratory function.

Respiratory Physiology Chapter 5

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Questions and Answers

What is the difference between dead space and shunt?

The imbalance of ventilation-perfusion impairs overall gas exchange.

What is the primary function of the lungs?

What are the potential causes of hypoxemia?

What determines alveolar PO2 (PAO2)?

Impaired pulmonary gas exchange causes __________ in tissue PCO2.

What are the normal PO2 and PCO2 in the air?

Hypoxemia is characterized by an abnormally low PO2 in arterial blood.

Hypoventilation causes which of the following?

What is V/Q mismatch?

Normal V/Q ratio is __________.

What causes an increase in V/Q?

What are symptoms of V/Q mismatch?

How is V/Q mismatch measured?