Respiratory System 7: Respiratory System Conditions and Measurements

Respiratory System Conditions

Obstructive and Restrictive Respiratory Conditions

• Obstructive Conditions:

  • Characterized by difficulty in getting air out of the lungs.

  • Examples: Asthma, narrowed airways, masses in the airways, damaged or diseased airways, and loss of lung tissue elasticity.

  • Reduced airflow during exhalation due to obstructions.

  • Accessory muscles are needed to force air out, which can cause bronchioles to collapse and trap air.

  • Normal Expiration:

    • Passive process relying on the inward recoil of the lungs and surface tension of alveolar water.

  • In obstructive conditions, the obstruction prevents passive exhalation.

  • Accessory muscles must be used to create more pressure to force air out.

  • Forcing exhalation can cause small airways to collapse, trapping air in the alveoli, reducing FVC and FEV1.

• Restrictive Conditions:

  • Characterized by difficulty in getting air into the lungs due to decreased lung capacity.

  • Caused by issues affecting the ability to inflate the lungs, such as problems with the diaphragm, intercostal muscles, rib movement, pleural membrane integrity, or lung tissue compliance.

  • Examples: pneumothorax, mobility issues.

  • Restrictive conditions impair the ability to inflate the lungs and bring air in.

  • Lung measurement values are reduced due to the inability to fully inhale or exhale.

• Factors Affecting Airway Integrity

  • Damaged airways are more prone to collapse during forced exhalation due to loss of elasticity and water surface tension.

  • Asthma: Narrowed airways due to smooth muscle activation make it difficult to exhale.

• Factors Affecting Lung Movement

  • Diaphragm and external intercostal muscle function.

  • Rib movement.

  • Pleural membrane integrity and intrapleural space pressure.

  • Lung tissue compliance and elasticity.

  • Appropriate function of muscles, bones, joints, and pleural membranes.

Ventilation

• Ventilation: The amount of air that can be moved in and out of the lungs for gas exchange over time.

• Factors increasing ventilation:

  • Respiratory rate.

  • Lung inflation (using accessory respiratory muscles).

Peak Flow Measurement

• Measures the maximum flow rate of air that can be exhaled.

• Procedure: Breathe out as hard and fast as possible through a device that measures peak flow.

• Factors affecting peak flow:

  • Age: Peak flow increases with age, then decreases.

  • Height: Taller individuals tend to have larger thoracic cavities and lung capacity.

  • Genetics, gender, and physiology.

• Low peak flow indicates a potential obstructive respiratory condition.

Forced Vital Capacity (FVC)

• FVC: The total volume of air that can be exhaled after a maximal inhalation.

  • Measured in liters.

  • Reflects the ability to both inhale and exhale.

Forced Expiratory Volume in One Second (FEV1)

• FEV1: The volume of air that can be exhaled in the first second of a forced exhalation after a maximal inhalation.

  • Measured in litres.

• FEV1/FVC Ratio:

  • In healthy individuals, FEV1 should be approximately 70-80% of FVC.

  • $\frac{FEV1}{FVC} \approx 0.7 - 0.8$

  • Example Calculation:

    • If FVC = 5 liters, then FEV1 should ideally be around 4 liters (80% of 5 liters).

    • To calculate without a calculator, convert to a fraction with a denominator of 100. E.g. $\frac{4}{5} = \frac{8}{10} = \frac{80}{100} = 80\%$

• Clinical Significance:

  • Low FEV1 indicates a problem with airflow out of the lungs (obstructive condition).

  • Low FVC indicates a problem with the total volume of air that can be moved in and out (can be either obstructive or restrictive).

Interpreting FVC and FEV1 Measurements

Pneumothorax

• A condition in which air leaks into the space between the lung and chest wall, causing the lung to collapse.

• Consider whether pneumothorax is a restrictive or obstructive condition based on its effect on lung function and measurement values.