Pulmonary Function Tests

Flow Volume Loops, before and after bronchodilator

Flow volume loops (FVL) are critical in pulmonary function testing, providing a graphical representation of airflow versus volume over time. Below are the key aspects of FVL, both before and after bronchodilator administration:

Before Bronchodilator:

1. Measurement of Vital Capacities: Includes vital capacity (VC) and forced vital capacity (FVC).
2. Measurement of Flows: Measures include forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), and forced expiratory flow (FEF25-75%).
3. Diagnostic Indications: Used to assess obstructive patterns (e.g., asthma, COPD) and restrictive patterns (e.g., fibrosis, neuromuscular disorders).
4. Graphical Representation: The spirogram displays volume-time and flow-volume curves, essential for assessing patient effort and the quality of the test.
5. Obstructive Disease Evaluation: Identifies reductions in FEV1 and the FEV1/FVC ratio, indicative of airway obstruction.
6. Restrictive Disease Evaluation: Identifies reductions in VC and FVC without significant changes in flows, suggesting a restrictive pattern.

After Bronchodilator:

1. Assessment of Reversibility: Bronchodilators are administered to evaluate the reversibility of airflow obstruction.
2. Improvements in Measurements: Post-bronchodilator improvements in FEV1, FVC, and other flow rates are key indicators of reversible airway obstruction.
3. Confirmation of Diagnosis: Significant improvement post-bronchodilator supports a diagnosis of asthma; minimal change may indicate COPD or other non-reversible obstructive lung disease.
4. Changes in Flow-Volume Loop: The loop may show increased flows at all lung volumes, indicating reduced airway resistance.

Additional Considerations:

• Measurement of Additional Parameters: Forced inspiratory vital capacity (FIVC) and inspiratory flow rates like peak inspiratory flow (PIF) and FIF50% can also be assessed.
• Assessment of Large vs. Small Airway Function: Detailed analysis of flow rates at different lung volumes helps pinpoint the location and nature of airway obstruction.

Flow volume loops provide comprehensive information critical for diagnosing and managing pulmonary conditions, enhanced by bronchodilator testing to differentiate between reversible and non-reversible airway obstructions.

Indications for FVL

Diagnostic

• To evaluate symptoms, signs, or abnormal laboratory tests
• To measure the effect of disease on pulmonary function
• To screen individuals at risk of having pulmonary disease
• To assess preoperative risk
• To assess prognosis
• To assess health status before enrolment in strenuous physical activity programs Monitoring
• To assess therapeutic intervention
• To describe the course of diseases affecting lung function
• To monitor those exposed to injurious agents
• To monitor for adverse reactions to drugs with known pulmonary toxicity Disability/Impairment Evaluations
• To assess patients as part of a rehabilitation program
• To assess risks as part of an insurance evaluation
• To assess individuals for legal reasons Public Health
• Epidemiological surveys
• Derivation of reference equations
• Clinical research

Contraindications of FVL

• The following conditions may pose a relative danger to the patient or affect the validity of performance of spirometry:
• Haemoptysis of unknown origin
• Recent pneumothorax
• Unstable cardiovascular status
• Thoracic, abdominal, or cerebral aneurysms
• Recent eye surgery
• Presence of an acute disease that might interfere with test performance (e.g., nausea, or vomiting, chest or abdominal pain)
• Recent surgery of thorax or abdomen

Lung Volumes (Body Plethysmography)

• Lung Capacities:
  • Functional Residual Capacity (FRC): Volume of gas in the lungs at the end of a normal exhalation.
  • Total Lung Capacity (TLC): Maximum volume of gas in the lungs after a full inhalation.
  • Vital Capacity (VC): Maximum volume of air expelled from the lungs after a full inhalation.
  • Inspiratory Capacity (IC): Maximum amount of air that can be inhaled from the end of a normal exhalation.
• Subdivisions of Lung Volumes:
  • Inspiratory Reserve Volume (IRV): Additional air that can be inhaled after a normal inhalation.
  • Expiratory Reserve Volume (ERV): Additional air that can be exhaled after a normal exhalation.
  • Tidal Volume (TV): Air volume moved during a normal breath.
  • Residual Volume (RV): Air volume remaining in the lungs after a maximal exhalation.
• Additional Definitions:
  • Thoracic Gas Volume (TGV): Not recommended for use; replaced by specific terms like FRCpleth.
• Capacity Calculations:
  • FRC: Calculated by adding ERV and RV.
  • TLC: Can be derived by adding FRC and IC, or VC and RV.
  • VC: Composed of TV, IRV, and ERV.
• Clinical Relevance:
  • Increase in FRC: Common with aging and in obstructive lung diseases (e.g., asthma, chronic bronchitis, emphysema).
  • Decrease in FRC: Seen in restrictive lung diseases (e.g., interstitial lung disease, pneumonectomy).
  • TLC Variations: Normal or increased in obstructive conditions; reduced in restrictive diseases and neuromuscular disorders.
  • VC Changes: Maintained or reduced depending on the nature of the lung disease; often diminished in both obstructive and restrictive lung diseases.
  • RV Changes: Typically elevated in obstructive lung diseases; reduced in restrictive conditions.
• Diagnostic Applications:
  • Assessment of Restrictive Ventilatory Defect: Diagnosing reduced lung volumes.
  • Hyperinflation and Abnormal Distensibility: Notable in emphysema.
  • Differentiating Airflow Limitation: Helps distinguish between types of lung diseases with similar expiratory patterns.

Indications for Lung Volumes

• Establish or confirm a diagnosis of a restrictive ventilatory defect
• To distinguish between obstructive and restrictive process
• Assess response to therapeutic intervention E.g. lobectomy, chemotherapy, transplantation.
• Evaluation of pulmonary disability
• Aid in the interpretation of other lung function tests
• Preoperative assessment
• Quantify the amount of non-ventilated lung

Contraindication for Lung Volumes

• Severe claustrophobia (body plethysmogaphy performed in booth)
• The presence of acute disease that might affect test performance i.e. any condition causing pain on inspiration e.g. pleurisy
• The presence of any abnormality that might affect test performance e.g. mouth deformities causing leakage of air around the mouthpiece or a cracked rib causing pain
• Any mental or physical condition that affects the ability of the patient to cooperate and follow instructions

Gas Transfer

• Purpose: Evaluates the transfer of gases from the air spaces of the lungs to the blood in the pulmonary capillaries.
• Test Substance: Uses carbon monoxide (CO), a gas that binds strongly to hemoglobin, providing a measure of lung function related to gas transfer.
• Methodology:
  • Inhalation: Patient breathes in a test gas containing 0.3% CO, 0.3% CH4 (or 10% He in some setups), 21% oxygen (O2), and the balance nitrogen (N2).
  • Breath-Hold: The test gas is held in the lungs for about 10 seconds to allow gas exchange.
  • Exhalation: The patient exhales sufficiently to clear the mechanical and anatomical dead space and then collects a sample for analysis.
• Measurement: The disappearance rate of CO is assessed by comparing the concentrations of CO in the inspired and expired air. This is expressed as mL CO/min/mmHg, factoring in the driving pressure across the alveolar-capillary membrane.

• Increases in DLCO occur in:
  • Polycythemia
  • Pulmonary haemorrhage
  • Diseases associated with increased pulmonary blood flow
  • Exercise
  • Asthma
  • Mueller manoeuvre
• Decreases in DLCO occur in:
  • Emphysema
  • Parenchymal lung diseases (e.g., interstitial pulmonary fibrosis)
  • Pulmonary involvement in systemic diseases
  • Cardiovascular diseases
  • Pulmonary embolism
  • Anemia
  • Haemoglobin binding changes (e.g., increased COHb)
  • Valsalva manoeuvre

Indications for Gas Transfer

• Evaluation and follow-up diseases which involve lung parenchyma (e.g., those associated with dusts, drug reactions, or sarcoidosis)
• Evaluation and follow-up of emphysema
• Differentiating among chronic bronchitis, emphysema and asthma
• Evaluation of pulmonary involvement in systemic disease
• Evaluation of cardiovascular diseases
• Prediction of arterial desaturation during exercise in some patients with lung disease
• Evaluation and quantification of impairment and disability associated with interstitial lung diseases and emphysema
• Evaluation of the pulmonary effects of chemotherapy agents or other drugs known to induce pulmonary dysfunction
• Evaluation of pulmonary haemorrhage
• As an early indication of certain pulmonary infections that cause diffuse pneumocystis (e.g., pneumocystis pneumonia)

Contraindications

• The presence of acute disease that might affect test performance i.e. any condition causing pain on inspiration e.g. pleurisy
• The presence of any abnormality that might affect test performance e.g. mouth deformities causing leakage of air around the mouthpiece or a cracked rib causing pain
• Any mental or physical condition that affects the ability of the patient to cooperate and follow instructions

Bronchial Provocation Test (BPT)

• Purpose: To demonstrate variable airways obstruction and assess airway hyper-responsiveness (AHR), commonly used to confirm a diagnosis of asthma.
• Key Index: Forced Expiratory Volume in one second (FEV1).
  • Significant Change: An increase in FEV1 of >12% and 200 ml post-bronchodilator indicates reversible airway obstruction.
  • Hyper-responsiveness: A significant decrease in FEV1 during the test indicates bronchial hyper-responsiveness.
  • Indications for BPT
    • Assessment of Airway Hyper-responsiveness (AHR)

Types of Bronchial Provocation Tests:

1. Mannitol Test (Aridol):
   • Method: Indirect osmotic bronchial challenge.
   • Criterion for Positive Test: A fall in FEV1 of 15% from baseline or an incremental fall of 10% in FEV1 between consecutive Mannitol doses.
   • Use: Considered the gold standard for identifying bronchial hyperresponsiveness in asthma diagnosis.
2. Hypertonic Saline Challenge:
   • Method: Inhalation of 4.5% saline via an ultrasonic nebuliser, starting at 1 minute and doubling exposure up to 8 minutes.
   • Criterion for Termination: Either a 15% decrease in FEV1, completion of 15-18 g of saline, or maximum exposure time reached.
   • Use: Commonly used for SCUBA diving medical clearance due to its capacity to identify subtle hyper-responsiveness.
3. Histamine Challenge:
   • Method: Direct pharmacological challenge using increasing concentrations of histamine.
   • Features: Rapid metabolism of histamine minimizes cumulative effects, allowing frequent dosage increments.
   • Limitation: Less commonly used now due to the availability of other agents that offer more controlled testing environments.

Each of these tests measures the sensitivity of the airways to various stimuli and helps in diagnosing asthma by evaluating the responsiveness of the bronchial tubes.

Cardiopulmonary Exercise Test (CPET)

• Purpose: To assess cardiovascular and pulmonary function during incremental exercise.
• Components:
  • Electrocardiogram (ECG): Monitors heart activity.
  • Blood Pressure Measurement: Assesses cardiovascular response.
  • Power Output: Evaluates physical work capacity.
  • Exhaled Gas Analysis: Measures volumes of oxygen (O2) and carbon dioxide (CO2) breathed in and out, assessing respiratory and metabolic function.
• Clinical Relevance:
  • Diagnostics: Helps in the diagnosis of conditions affecting the heart and lungs.
  • Evaluation of Treatment: Assists in assessing the effectiveness of interventions.
  • Fitness Assessment: Determines fitness level and physical capacity.
  • Research Tool: Used in studies of exercise physiology and health.
• Physiological Basis:
  • Cellular Respiration: Utilizes carbohydrates, fats, and glycogen through aerobic and anaerobic pathways.
  • Oxygen Consumption (VO2): Increases proportionally with exercise intensity; crucial for assessing metabolic efficiency.
  • CO2 Production (VCO2): Evaluated to understand metabolic and respiratory function during exercise.
  • Minute Ventilation (VE): Measures the total volume of air inhaled or exhaled per minute.
• Utility in Clinical Settings:
  • Considered when there are unresolved questions after initial evaluations like physical exams, chest radiographs, pulmonary function tests, and ECGs.
  • Maximal O2 Consumption (VO2max): Key indicator of aerobic capacity and cardiorespiratory fitness; identification of limits provides insight into potential cardiovascular or pulmonary impairments.
• System Responses:
  • Integrated Response: Cardiovascular, pulmonary, and muscular responses must coordinate to meet increased demands during exercise.
  • Limitation Identification: CPET can pinpoint which system(s) may be limiting further increases in exercise capacity, aiding in targeted medical interventions.

• Indications for CPET
  • Determination of the exercise capacity
  • Determination of the cause of a cardiopulmonary limitation to exercise
  • Identification of abnormal cardiopulmonary responses to exercise
  • Exercise prescription and monitoring response to exercise for training and rehabilitation
  • Evaluation of results of therapeutic intervention
  • Pre-operative evaluation
  • Impairment/disability evaluation
  • Selection of patients for cardiac transplantation
  • Evaluating unexplained dyspnea when initial cardiopulmonary testing is nondiagnostic

6-Minute Walk Test (6MWT)

• Purpose: To assess the functional capacity and endurance in patients with respiratory and cardiopulmonary conditions.
• Method:
  • Test Description: Patients walk as far as possible for 6 minutes on a flat, hard surface.
  • Measurement: Distance covered in six minutes (6MWD) is recorded.
• Key Features:
  • Non-Maximal: Patients do not need to reach their maximum exercise capacity; they set their own pace.
  • Equipment: No specialized exercise equipment is necessary.
  • System Involvement: Evaluates the integrated response of all bodily systems involved in exercise but does not isolate specific organ functions.
• Clinical Uses:
  • Treatment Response: Often used to measure the effectiveness of therapeutic interventions in severe cardiopulmonary diseases by comparing pre- and post-treatment 6MWD.
  • Functional Status Assessment: Commonly used to evaluate the functional status of patients with Chronic Obstructive Pulmonary Disease (COPD).
• Oxygen Assessment:
  • Oxygen Desaturation Monitoring: If oxygen saturation drops below 88%, the test is sometimes repeated with supplemental oxygen to evaluate the need for long-term home oxygen therapy.
  • MASS Benefits Assessment: Helps determine eligibility for mobility aids and support services based on functional limitations.

The 6MWT is valued for its simplicity and the practical insights it offers into a patient’s physical capabilities and response to medical interventions.

• Indications for 6MWT
  • Functional status for those with moderate to severe cardiopulmonary disease
  • Response to medical or surgical intervention for patients with cardiopulmonary disease
  • To assess suitability for certain medications such as for treatment of PAH
  • To assess for suitability for home oxygen (MASS evaluation)
  • Pre-operative risk assessment
  • Assessment as part of pulmonary rehabilitation
• Contraindications for 6MWT
  • Unstable angina and myocardial infarction during previous month
  • Heart rate at rest above 120
  • Blood pressure above 180/100

Respiratory Muscle Strength Testing

• Purpose: To quantify the strength of respiratory muscles, specifically the muscles involved in breathing in (inspiratory muscles) and breathing out (expiratory muscles).
• Tests Involved:
  • Maximum Inspiratory Pressure (MIP or PImax): Assesses the maximum pressure that can be generated by the inspiratory muscles, primarily the diaphragm. This is a critical measure in conditions like neuromuscular disorders and respiratory muscle weakness.
  • Maximum Expiratory Pressure (MEP or PEmax): Measures the maximum pressure exerted during expiration, which involves abdominal and intercostal muscles. This is important for assessing conditions that impair expiratory force, such as COPD or asthma.
• Procedure: Patients breathe against a closed system with a mouthpiece, and pressures are measured. These values are compared to normal reference values based on age, gender, and body size.

Hypoxic Altitude Simulation Test (HAST)

• Purpose: To evaluate how well patients with respiratory conditions can tolerate lower oxygen environments, similar to those experienced at high altitudes, particularly in airplane cabins.
• Procedure:
  • Patients breathe a gas mixture that simulates the oxygen content at a specific altitude (typically equivalent to 15% O2, similar to 2438 meters or 8000 feet).
  • Monitoring includes measurement of oxygen saturation, heart rate, and symptoms.
• Clinical Importance: It is crucial for assessing the risk of hypoxemia and guiding recommendations for supplemental oxygen during flights, especially in patients with chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, or other severe respiratory ailments.
• Indications for HAST
  • Patients wishing to fly by commercial airliner likely to develop PaO2 <55mmHg under in-flight conditions (COPD, other lung disease or cardiovascular disease resulting in PaO2 <72mmHg under sea-level, room air conditions)
  • Pre-existing requirements for oxygen
  • Other subjects with medical conditions at risk may include
  • Obstructive sleep apnoea
  • Parenchymal lung disease
  • PaO2 of 60-70 mmHg

Overnight Oximetry

• Purpose: To detect episodes of decreased oxygenation during sleep, indicative of sleep apnea.
• Test Details:
  • Pulse Oximetry: A sensor placed on the finger measures the blood’s oxygen saturation continuously throughout the night.
  • Apnoea-Hypopnea Index (AHI): Calculates the number of apnea (complete stop in breathing) and hypopnea (reduced breathing) episodes per hour of sleep.
• Clinical Use: Screening for obstructive sleep apnea (OSA) in patients who exhibit symptoms such as excessive daytime sleepiness, loud snoring, or observed episodes of stopped breathing during sleep. A high AHI indicates a need for further assessment via polysomnography.
• Indications for Overnight Oximetry
  • As a pre-curser to performing an overnight sleep study
  • For those who have demonstrated oxygen saturations below 88% at rest
  • Symptoms of disordered sleeping

Fractional Exhaled Nitric Oxide (FeNO)

• Purpose: To measure the concentration of nitric oxide in the exhaled breath, which is a marker of eosinophilic airway inflammation and can guide asthma management.
• Procedure:
  • Patients exhale into a device that measures the level of nitric oxide at a standardized exhalation flow rate.
  • Elevated FeNO levels indicate eosinophilic inflammation, commonly associated with allergic asthma.
• Clinical Relevance:
  • Asthma Diagnosis: Helps in diagnosing asthma in patients with respiratory symptoms.
  • Monitoring Response to Treatment: Used to evaluate the effectiveness of anti-inflammatory treatment, particularly inhaled corticosteroids (ICS).
  • Treatment Decisions: High FeNO levels may suggest the need for initiation or escalation of ICS therapy, while low levels may support the decision to reduce or discontinue ICS.
• Advantages:
  • Simple, non-invasive, and provides immediate results.
  • Particularly useful in settings where other diagnostic modalities (like spirometry) might be challenging to perform due to severe airflow limitation.

• Indications for FeNO
  • To diagnose the presence of eosinophilic airway inflammation
  • To assess the likely responsiveness to an inhaled cortico-steroid
  • To monitor airway inflammation in those with asthma