Lung Mechanics: Factors Affecting Airway Resistance

Questions and Answers

What is the primary determinant of airway resistance?

Elastic resistance of the lung

Surface tension forces at the alveolar air-fluid interface

Radius of the airway (correct)

Compliance of the chest wall

Which of the following would increase lung compliance?

Production of surfactant (correct)

Increase in surface tension forces

Increase in elastic resistance of the lung

Decrease in chest wall stiffness

A patient with airflow obstruction would likely have a decreased:

FEV1/FVC ratio

Peak expiratory flow rate

FVC

All of the above (correct)

Dynamic compression of airways occurs during:

Exhalation Signup and view all the answers

Which of the following is NOT a symptom of increased work of breathing?

Chest pain Signup and view all the answers

Spirometry is a test of lung function that measures:

Lung volumes and airflow rates Signup and view all the answers

What is the relationship between flow and pressure difference according to Darcy's Law?

Flow is directly proportional to pressure difference Signup and view all the answers

Which of the following is NOT a factor that determines resistance to flow?

Surface area of tube Signup and view all the answers

What happens to flow rate if the radius of a tube is halved, assuming the same pressure gradient?

Flow rate decreases to 1/16th Signup and view all the answers

What is the main site of airway resistance in the respiratory system?

Medium-sized bronchi Signup and view all the answers

What is the equivalent of voltage in the context of flow through tubes?

Pressure gradient Signup and view all the answers

What is the relationship between resistance to flow and the length of a tube?

Resistance is directly proportional to length Signup and view all the answers

What is the site of highest individual airway resistance?

Smaller distal airways Signup and view all the answers

According to Darcy's Law, what is the relationship between flow and resistance to flow?

Flow is inversely proportional to resistance to flow Signup and view all the answers

What is the primary mechanism by which high intrapleural pressures cause dynamic compression of airways during forced expiration?

External compression of airways by the increased pleural pressure Signup and view all the answers

What is the main site of maximum airway resistance in the lungs?

Generation 3 or 4 bronchi Signup and view all the answers

What is the effect of dynamic compression of airways on expiratory airflow in normal people?

Limits expiratory airflow at low lung volumes Signup and view all the answers

What is the unit of measurement for lung compliance?

mL/cmH2O Signup and view all the answers

What is the primary determinant of elastic resistance in the lungs?

Lung tissue elasticity Signup and view all the answers

What is the role of neural inspiratory activity in regulating airway diameter?

Increases airway diameter through stimulation of inhibitory NANC Signup and view all the answers

What is the primary mechanism by which adrenaline (in blood) affects airway diameter?

Causes bronchodilation through stimulation of inhibitory NANC Signup and view all the answers

What is the effect of high RAW on expiratory airflow in people with lung disease?

Decreases expiratory airflow rate Signup and view all the answers

What is the primary factor affecting airway diameter during forced expiration?

Intrapleural pressure Signup and view all the answers

What is the term used to describe the effort-independent nature of expiratory airflow at low lung volumes?

Flow limitation Signup and view all the answers

In a patient with lung fibrosis, which of the following is true?

Lung recoil is increased, leading to a decreased FRC Signup and view all the answers

What is the characteristic feature of the flow-volume loop in obstructive airway disease of smaller airways?

Concave appearance of forced expiratory curve Signup and view all the answers

During respiratory muscle weakness, which of the following is true regarding FRC?

FRC is normal since the inward recoil of the lungs balances the outward recoil of the chest wall Signup and view all the answers

What is the effect of emphysema on lung compliance?

Increases lung compliance Signup and view all the answers

Which of the following would lead to an increased FEV1/FVC ratio?

Increased lung compliance Signup and view all the answers

What is the relationship between FEV1 and FVC in restrictive disease?

FEV1 is decreased, FVC is decreased Signup and view all the answers

Surfactant plays a crucial role in reducing which of the following at the alveolar air-fluid interface?

Surface tension forces Signup and view all the answers

What is the effect of lung stiffness on FRC?

Decreases FRC Signup and view all the answers

A patient with emphysema would likely have which of the following?

Barrel chest due to decreased lung recoil Signup and view all the answers

What is the feature of the flow-volume loop in normal individuals?

Linear appearance of forced expiratory curve Signup and view all the answers

Which of the following would be affected by changes in stiffness of the lungs?

Lung volumes, including FRC Signup and view all the answers

What is the effect of lung fibrosis on lung compliance?

Decreases lung compliance Signup and view all the answers

What is the characteristic feature of the flow-volume loop in restrictive lung disease?

Reduced peak flow rates Signup and view all the answers

What is the effect of asthma on lung compliance?

Has no effect on lung compliance Signup and view all the answers

Study Notes

Lung Mechanics 2

Factors Affecting Airway Resistance

Two main sources of resistance to breathing: elastic resistance of the lung and airway resistance
Airway resistance is affected by two main factors:
- Factors within the airways (bronchial smooth muscle tone, inflammation of epithelium with hypertrophy of glands and secretions)
- Pressure across the airway wall (negative intrapleural pressure in normal breathing, positive intrapleural pressure in forced expiration)
Medium-sized bronchi (around generation 3-5) contribute most to airway resistance

Dynamic Compression of Airways

Occurs when airway pressure falls below pleural pressure during a forced expiration
Airways most likely to collapse are bronchi around generation 3 or 4
Causes limitation of expiratory airflow at low lung volumes (effort-independent airflow)
In lungs with high airway resistance, it causes marked limitation of airflow, leading to slow expiration, low peak expiratory flow rate, air trapping, and expiratory wheezes

Lung Compliance

Elastic resistance of the lung, usually measured as compliance (stretchiness)
Compliance = change in lung volume / change in transpulmonary pressure
Healthy lungs have high compliance (easy to expand), while stiff lungs have low compliance (hard to expand)
Lung fibrosis (scarred/stiff) has low compliance, while emphysema (tissue destruction/floppy) has high compliance
Asthma does not usually affect compliance

Measuring Lung Compliance

Transmural pressure gradient = alveolar pressure - intrapleural pressure
Intrapleural pressure measured with an oesophageal balloon, volume measured with a spirometer
Subject breathes in from RV to TLC in steps to measure compliance

Simple Tests of Lung Function

Spirometry: measures lung function and detects airflow obstruction
FEV1 (forced expiratory volume in 1 second): measures airflow obstruction
FVC (forced vital capacity): measures lung size and detects restrictive lung disease
FEV1/FVC ratio: detects airflow obstruction (normal > 0.7)
Peak expiratory flow rate: measures airflow obstruction and detects small airway disease

Effects of Chest Wall & Pulmonary Restriction and Airflow Obstruction

Chest wall and pulmonary restriction: decrease FEV1, FVC, and peak expiratory flow rate
Airflow obstruction: decrease FEV1, FEV1/FVC ratio, and peak expiratory flow rate, while FVC may be normal or decreased

Surface Tension Forces and Surfactant

Surface tension forces at the alveolar air-fluid interface important for lung expansion and stability
Surfactant: a complex mixture of lipids and proteins produced by type II alveolar cells, reduces surface tension and facilitates lung expansion

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Description

This quiz covers the main sources of resistance to breathing, including elastic resistance and airway resistance, and the factors that affect airway resistance, such as bronchial smooth muscle tone and intrapleural pressure. Learn about the mechanisms that influence airway resistance in normal breathing and forced expiration.