Chapter 13

Concept Overview

Gas Exchange represents processes that facilitate and impair the transport of oxygen to tissues and carbon dioxide from tissues. It is interrelated with perfusion, intracranial regulation, metabolism, mobility, tissue integrity, sleep, and nutrition.

  • Clinical Case Example: John Armstrong

    • 59-year-old male, smoked a pack of cigarettes daily for 41 years.

    • COPD pathology: Obstructed bronchi increase breathing effort; destruction of alveoli impairs diffusion and leads to air trapping.

    • Findings: Hypoxemia, dyspnea (shortness of breath), activity intolerance, weight loss/malnutrition, and orthopnea (needs 3 pillows or sleeps in a recliner).

Anatomy and Physiology

  • Purpose: Supply oxygen to cells and remove carbon dioxide through ventilation and diffusion.

  • Ventilation: Moving gases in and out of the lungs (inspiration and expiration).

  • Diffusion: Movement of gases from higher to lower concentration across the alveolar-capillary membrane.

  • Transportation: The cardiovascular system transports gases between alveoli and cells via erythrocytes.

Internal Thorax

  • Mediastinum: Middle of the chest; contains heart, aorta arch, superior vena cava, lower esophagus, and trachea.

  • Pleural Cavities: Contain the lungs; lined by parietal pleura (chest wall/diaphragm) and visceral pleura (lungs).

  • Lung Lobes: Right lung has 3 lobes; Left lung has 2 lobes.

  • Extension: Apex extends 1.5 in (4 cm) above the first rib; base expands to T12 during deep inspiration and rises to T9 on expiration.

External Thorax

  • Thoracic Cage: 11 thoracic vertebrae, 12 pairs of ribs, and the sternum.

    • Ribs 1-7: Connect to sternum via costal cartilages.

    • Ribs 8-10: Connect to superior ribs.

    • Ribs 11-12: Floating ribs.

  • Sternum Components: Manubrium, body, and xiphoid process (17 cm long).

  • Intercostal Space (ICS): Named after the rib above it.

Topographic Markers

  • Anterior: Suprasternal notch, Angle of Louis (manubriosternal junction), Midsternal line, Costal angle (\le 90^{\circ}), Clavicles, Midclavicular lines.

  • Lateral: Anterior axillary lines, Posterior axillary lines, Midaxillary lines.

  • Posterior: Vertebra prominens (C7), Vertebral line, Scapular lines.

Mechanics of Breathing

  • Primary Muscles: Diaphragm and intercostal muscles.

    • Inspiration: Diaphragm contracts/descends, intercostals push chest outward, decreasing intrathoracic pressure (negative pressure).

    • Expiration: Muscle relaxation increases pressure, expelling air.

  • Accessory Muscles: Sternocleidomastoid, scalenus, pectoralis minor, etc.

  • Upper Airway: Nose, pharynx, larynx, trachea (10 cm long). Functions: conductive, protective, warming, filtering, and humidifying.

  • Lower Airway: Right/left main-stem bronchi (trachea splits at T4/T5), bronchioles, and alveoli.

Health History

  • Present Health Status: Assess chronic illnesses (heart/renal disease), allergies, dyspnea during activities, orthopnea, medications (including inhalers and OTC/herbal supplements like ginseng), and oxygen use.

  • Past Health History: Previous lung problems, injuries, or surgeries.

  • Family History: Genetic links for lung disease.

  • Personal/Psychosocial History:

    • Tobacco Use: Documented in pack-years (packs/day \times years).

    • Infectious Disease Exposure: Screening for TB, influenza, or COVID-19.

    • Home Environment: Air pollution, allergens (pets, mold, dust mites), hazards (lead, carbon monoxide).

    • Occupational Environment: Exposure to chemicals, dust, asbestos, or vapors.

    • Travel History: Exposure to uncommon diseases (e.g., histoplasmosis, SARS).

Problem-Based History (OLD CARTS)
Cough

  • Acute: < 3 weeks (infections, asthma, embolism).

  • Chronic: > 8 weeks (GERD, ACE inhibitors like captopril).

  • Sputum Characteristics:

    • White/Clear: Colds, viral infections.

    • Yellow/Green: Bacterial infections.

    • Black: Smoke/coal dust.

    • Rust: TB, pneumococcal pneumonia.

    • Pink/Frothy: Pulmonary edema.

    • Hemoptysis: Blood in sputum.

Shortness of Breath (Dyspnea)

  • Dyspnea on Exertion (DOE): Occurs during activity.

  • Orthopnea: Difficulty breathing when lying flat.

  • Paroxysmal Nocturnal Dyspnea: Awakening at night with suffocation feeling.

  • Documentation: Record "word dyspnea" (e.g., "three-word dyspnea" if the patient breathes after every 3 words).

Chest Pain with Breathing

  • Pleuritic Chest Pain: Sharp, stabbing pain during inspiration.

  • Splinting: Patient reduces movement on the affected side to minimize pain.

Physical Examination
Routine Techniques

  1. Inspect Appearance/Posture: Observe for respiratory distress (nasal flaring, retractions, use of accessory muscles).

    • Tripod Position: Leaning forward, suggests COPD/asthma.

    • Pursed-lip Breathing: Slows exhalation in COPD.

  2. Count Respirations: Normal rate 12-20 breaths/min (eupnea).

    • Men: Abdominal breathing; Women: Thoracic breathing.

  3. Measure Oxygen Saturation: Normal SaO_2 is 95\%-100\%. < 90\% is abnormal.

  4. Inspect Skin/Nails: Check for cyanosis, pallor, or clubbing (chronic hypoxia).

  5. Inspect Thorax: Check for barrel chest (1:1 AP to lateral ratio), scoliosis, or other deformities.

  6. Auscultation:

    • Vesicular: Low pitch, soft; heard over peripheral lung fields.

    • Bronchovesicular: Moderate pitch; heard over main bronchi.

    • Bronchial: High pitch, loud; heard over trachea.

    • Adventitious Sounds: Crackles (fluid), Wheezes (narrowed airways), Rhonchi (obstruction/mucus), Pleural friction rub (inflammation).

Special Circumstances

  • Palpate for Expansion: Thumbs at T9/T10; should move apart symmetrically.

  • Vocal (Tactile) Fremitus: Palpable vibrations while saying "ninety-nine." Increased in consolidation (pneumonia); decreased in obstruction.

  • Tracheal Position: Should be midline and movable.

  • Percussion: Normal tone is resonant.

    • Hyperresonance: Overinflation (emphysema).

    • Dullness: Consolidation (pneumonia, effusion, atelectasis).

  • Diaphragmatic Excursion: Normal is 3-5 cm (7-8 cm in athletes).

Common Respiratory Conditions

  • Acute Bronchitis: Mucous membrane inflammation; rhonchi and wheezing present.

  • Pneumonia: Infection of terminal bronchioles; viral (nonproductive) or bacterial (productive).

  • Tuberculosis (TB): Infectious bacteria (Mycobacterium tuberculosis); night sweats, weight loss, fever.

  • Asthma: Hyperreactive airway; bronchoconstriction and audible wheezes.

  • Emphysema: Alveolar wall destruction; barrel chest and nail clubbing.

  • Chronic Bronchitis: Productive cough for 3 months over 2 successive years; cyanosis and clubbing.

  • Pneumothorax: Air in pleural space causing lung collapse; absent breath sounds over the affected area.

  • Hemothorax: Blood in pleural space.

  • Atelectasis: Collapsed alveoli due to pressure or hypoventilation.

  • Lung Cancer: Malignant cell growth; persistent cough and hemoptysis.