Respiratory System Overview

Introduction

• An adequate volume of air must pass through the lungs to maintain gas exchange to the tissues
• At rest, a normal person breathes ~500 mL of air per breath at a frequency of 12-16 times per minute, resulting in a ventilation of 6 to 8 L/min
• The alveolar surface area (~70 m2) enables efficient blood-gas diffusion within the thoracic cavity

Symptoms

• Dyspnea:
  • Subjective feeling of shortness of breath
  • Classified as air hunger, increased effort or work of breathing, or chest tightness
  • Upper airway obstruction can be caused by foreign bodies, tumors, edema (e.g., anaphylaxis), and stenosis
  • Acute: minutes to days (laryngeal edema, acute asthma)
  • Subacute: Days to weeks
  • Chronic: Months to years (Chronic obstructive lung disease, chronic bronchiolitis)

Symptoms

• Orthopnea:
  • Shortness of breath in the recumbent position
  • Often measured by the number of pillows or the angle of elevation needed to relieve dyspnea
  • Caused by increased venous return and central intravascular volume in the recumbent position
• Paroxysmal nocturnal dyspnea (PND):
  • Waking from sleep with dyspnea
  • Similar to orthopnea but doesn't occur immediately after lying down
• Platypnea:
  • Shortness of breath in the upright position

Symptoms

• Cough:
  • Protective mechanism for clearing the airway
  • Can be a symptom of lung disease, but not useful for differential diagnosis
  • Acute cough (<3 weeks): Usually due to acute viral infection of the respiratory tract
  • Subacute cough (3-8 weeks):
  • Chronic cough (>8 weeks): Common causes in nonsmokers include postnasal drip, gastroesophageal reflux, and asthma

Symptoms

• Sputum:
  • Suggests airway disease
  • Yellow or green indicates presence of leukocytes (neutrophils or eosinophils)
• Hemoptysis:
  • Can originate from airways, pulmonary parenchyma, or vasculature
  • Most often due to airway diseases (e.g., bronchitis)
• Chest pain:
  • Usually originates from parietal pleura involvement
  • Pain can be worse on inspiration (pleuritic pain)

Diagnostic Procedures

• Chest X-ray:
  • Standard views: posteroanterior (PA) and lateral
  • PA: X-ray beam passes from back to front
  • Lateral: Patient’s side against the film, beam directed through the patient

Diagnostic Procedures

• Computed Tomography (CT):
  • Narrow beam of X-rays passes through the patient and detected by a rotating sensor
  • High-resolution CT: individual image thickness reduced to 1-2 mm
  • Advantages:
    • Distinguishes between densities
    • Accurate size assessment of lesions
    • Distinguishes vascular from nonvascular structures
    • Helical CT technology for faster scans, improved contrast enhancement, and thinner collimation
    • Image obtained during single breath-holding maneuver for less motion artifact