Pulmonary Function & Spirometry – EKG 117 (Week 5, Chapter 51)

Pulmonology & Respiratory System

• Pulmonology = medical specialty devoted to the study, diagnosis, & treatment of diseases of the respiratory system.
• Respiratory system anatomy (conducting & gas-exchange structures):
  • Trachea → Bronchial tubes → Lungs → Alveoli.

Primary Physiologic Functions

• Transport O_2 from lungs to all body cells via bloodstream.
• Remove cellular waste products (primarily CO2 + H2O) via bloodstream to lungs for exhalation.

Role of the Medical Assistant (MA) in Pulmonary Care

• Perform &/or assist with Pulmonary Function Tests (PFTs).
• Purposes:
  • Evaluate lung volume & capacity.
  • Help diagnose suspected obstructive or restrictive processes.
  • Assess effectiveness of medications & other therapies.
• Indications for PFT referral: asthma, chronic bronchitis, emphysema, COPD, cystic fibrosis, annual physicals, pre-employment exams.

Categorization of Pulmonary Disorders

• Common symptoms: coughing, wheezing, cyanosis, rales, stridor, rhonchus, hemoptysis.
• Chronic obstructive conditions: asthma, chronic bronchitis, emphysema, COPD, cystic fibrosis.
• Infectious conditions: pneumonia, influenza, tuberculosis, pleuritis.
• Mechanical injuries: pulmonary emboli, collapsed lung, pneumothorax, hemothorax.

Types of Pulmonary Function Tests (PFTs)

• Spirometry (core focus of Week 5).
• Arterial Blood Gases (ABGs).
• Lung volume determination.
• Pulse oximetry.
• Diffusion capacity testing.
• Cardiopulmonary exercise tests.

Spirometry – Fundamentals

• Non-invasive; uses mouthpiece & tubing → computerized recorder.
• Measures:
  • Elasticity/compliance of lungs.
  • Ventilatory ability (forced exhalation performance).
  • Strength/endurance of respiratory muscles.
• Results automatically compared with predicted values based on height, weight, age, race, sex, & current clinical status.

Lung Volumes (single subdivisions of air)

• Tidal Volume (TV or V_T): ≈ 500\,\text{mL} inhaled/exhaled during quiet breathing.
• Inspiratory Reserve Volume (IRV): additional volume that can be inhaled beyond normal inspiration (≈ 3100\,\text{mL} in healthy adult).
• Expiratory Reserve Volume (ERV): additional volume that can be forcibly exhaled after normal expiration (≈ 1200\,\text{mL}).
• Residual Volume (RV): air remaining in lungs after maximal expiration (≈ 1200\,\text{mL}); prevents alveolar collapse.

Lung Capacities (combinations of volumes)

• Vital Capacity (VC): maximal volume that can be ventilated in a single breath.
  • Formula: VC = IRV + TV + ERV (≈ 4800\,\text{mL}).
  • Reduced in restrictive disorders (pulmonary fibrosis, scoliosis, etc.); usually normal in purely obstructive disorders.
• Total Lung Capacity (TLC): volume in lungs at peak inspiration.
  • TLC = TV + IRV + ERV + RV (≈ 6000\,\text{mL}).
• Inspiratory Capacity (IC): IC = TV + IRV — amount that can be inhaled after normal expiration.
• Functional Residual Capacity (FRC): FRC = ERV + RV — air remaining after normal expiration.

Forced Vital Capacity (FVC) & Flow-Volume Metrics

• FVC = maximum gas volume the patient can exhale as forcefully & rapidly as possible following one maximal inhalation.
• Commonly equal to Slow Vital Capacity (SVC) in healthy lungs.
• Decreased primarily in obstructive lung disease due to air trapping.
• FEV_1 = volume (or % of VC) expelled in first second of forced exhalation.
  • Healthy ratio: \ge 75\%.
  • COPD/asthma: may drop <70\%.
• Clinicians often track FEV_1/FVC ratio for obstruction severity.

Interpretation Benchmarks

• Healthy lungs: up to 90\% of FVC exhaled in 1 s.
• COPD: ratio often <70\%.

Patient Preparation – Spirometry

• No smoking for ≥ 4–6 h pre-test.
• No large meal for ≥ 4–6 h.
• Hold bronchodilators/nebulizers for ≥ 6 h unless physician orders otherwise.
• Record accurate height & weight for predicted calculations.
• Remove ill-fitting dentures; loosen tight clothing/ties/girdles/belts/bras.
• Positioning: seated preferred (flat feet, legs uncrossed, chin slightly elevated) to prevent dizziness; standing acceptable if more comfortable (chair nearby).
• Demonstrate maneuver in simple language; repeat acceptable test at least 3 times to ensure reproducibility.

Peak Flow Meter (PFM)

• Assesses Peak Expiratory Flow Rate (PEFR) – fastest airflow (L/s or L/min) produced after maximal inspiration.
• Instructions: seal lips around mouthpiece & blow hard & fast once; repeat per protocol; document best of 3.
• Patients keep home diary → detects response to meds & early exacerbations.
• Higher PEFR post-medication = desirable therapeutic effect.

Pediatric PFT Considerations

• Graphics reminder: children require size-appropriate mouthpieces & coaching; engage with games or incentives for maximal effort.

Pulse Oximetry

• Measures arterial oxygen saturation (SpO₂) non-invasively via photoplethysmography.
• Normal: 95\%!! - !100\%.
• <70\% = life-threatening; warrants immediate intervention.
• Remove nail polish/artificial nails for accurate readings.

Breath (Adventitious) Sounds – Definitions & Clinical Correlates

• Stridor – harsh, high-pitched, loudest during inspiration; indicates upper airway obstruction (e.g., croup, laryngeal edema).
• Stertor – coarse “snoring” noise during inspiration; often from oropharyngeal obstruction.
• Crackles (Rales) – fine/coarse popping resembling crumpling tissue; fluid in airways: pulmonary edema, CHF, pneumonia, asthma.
• Rhonchi – low-pitched rattling/whistling in throat or larger airways; common in chronic bronchitis, COPD, CF, pneumonia.
• Wheezes – musical/high-pitched, from narrowed lower airways (asthma, COPD).
• Cheyne–Stokes – cyclic crescendo–decrescendo respirations with apnea; seen in brain injury, stroke, tumors.

Vital-Sign Reference Questions

• Normal adult RR: ~12!\text{–}!20\,\text{breaths/min}; HR: 60!\text{–}!100\,\text{bpm}.
• Pediatrics: RR & HR vary by age – generally higher (e.g., infant RR 30!\text{–}!60, HR 100!\text{–}!160).
• Medical term for difficulty breathing = Dyspnea.

Scope-of-Practice / Ethics

• MAs may perform the test, document that it was done, and hand data to physician.
• Interpretation & communication of diagnostic meaning must be done by the physician – providing results directly to patient is outside MA scope.

Practice-Question Key Points (Condensed)

• Stridor = high-pitched, shrill inspiratory noise.
• Rhonchi = rattling, whistling, low-pitched throat sounds.
• Wheezes = high-pitched sounds from narrowed airways.
• Cheyne-Stokes = irregular hyper/hypopnea with apnea pauses.
• FVC = maximum forced exhaled volume post-full inhalation.
• TLC = total volume lungs hold at peak inspiration.
• TV = volume in & out during normal breathing.
• RV = amount left after full exhalation (not measurable by simple spirometry).
• VC measures maximum ventilatable volume in one breath.
• TLC includes TV, IRV, ERV, RV — does not include FVC as a separate component.
• Peak-flow meter protocol statements are true (keep diary, monitor med response, etc.).
• Patient instructions recap: no smoking, no large meal, withhold bronchodilators, follow physician guidance on meds.

Key Equations & Numerical Benchmarks

• VC = IRV + TV + ERV.
• TLC = VC + RV.
• Healthy FEV_1 \ge 75\% of VC; in healthy adults up to 90\% may be expelled in 1 s.
• Typical adult volumes:
  • TV \approx 500\,\text{mL}
  • IRV \approx 3100\,\text{mL}
  • ERV \approx 1200\,\text{mL}
  • RV \approx 1200\,\text{mL}
  • VC \approx 4800\,\text{mL}
  • TLC \approx 6000\,\text{mL}.

Practical & Safety Considerations

• Perform tests in seated position where possible (dizziness risk).
• Repeat spirometry maneuver ≥ 3 acceptable, reproducible times.
• Keep chair nearby if standing.
• Document patient’s physical condition (e.g., recent respiratory infection) which may affect results.

Real-World Relevance & Clinical Significance

• Objective PFT data guide medication titration (e.g., inhaled bronchodilators, steroids).
• Early detection of declining PEFR allows intervention before severe asthma attack.
• Pulse-oximetry screening identifies silent hypoxemia (e.g., COVID-19, pneumonia).
• Accurate breath-sound recognition enhances triage & timely airway management.

Summary Reminders for Exam

• Memorize normal volumes/capacities & their formulas.
• Understand difference between obstructive vs. restrictive patterns on spirometry (ratio vs. absolute volumes).
• Recall pre-test patient instructions & MA scope-of-practice boundaries.
• Be able to identify & define adventitious lung sounds and their pathologic associations.
• Practice interpreting basic spirometry values (FVC, FEV₁, ratios).