CPET: MVV, Breathing Reserve, Contraindications

Cardiopulmonary Exercise Test (CPET)

• CPET is a maximal exercise test with gas exchange measurements.
• It's used to assess cardiorespiratory fitness (CRF) or functional/exercise capacity.
• CPET, also called a Metabolic Test or CPX, evaluates the integrated responses of pulmonary, cardiovascular, and skeletal muscle systems.
• The test involves measuring respiratory oxygen uptake, carbon dioxide production, and ventilatory measures at rest and during symptom-limited exercise.
• CPET aids in determining the cause of unexplained shortness of breath (SOB) or dyspnea (cardiac vs. pulmonary limitation to exercise).
• It's used to assess surgical risk, peri-surgical/postsurgical complication risk, and the severity of respiratory diseases.
• CPET helps assess the prognosis for various diseases and guides treatment for heart failure patients, especially those with end-stage CHF needing a transplant.

Peak Exercise Capacity (pVO2, VO2max)

• pVO2/VO2max measures the cardiovascular system's maximum ability to deliver oxygen to exercising skeletal muscle and the muscle's efficiency in extracting oxygen from the blood.
• This is a key indicator for exercise tolerance.

Chain of O2 Delivery During Exercise

• Exercise capacity is related to the cardiovascular (CV) system's ability to deliver oxygen to muscles and the lungs' ability to clear carbon dioxide from the blood.
• During steady-state conditions, oxygen uptake (VO2) and carbon dioxide output (VCO2) match overall production/utilization within cells.

Physiology of Exercise

• Exercise tolerance depends on:
  • Pulmonary gas exchange
  • Cardiovascular performance
  • Skeletal muscle metabolism

Fick Equation

• The Fick equation states that oxygen uptake (VO2) equals cardiac output (stroke volume x heart rate) multiplied by the arterial-venous oxygen difference (arterial minus mixed venous oxygen content).
• At maximal exercise, the equation is expressed as VO2max = (SVmax x HRmax) x (CaOmax - CvOmax).
• This shows the maximum ability to take in, transport, and use oxygen.
• VO2max defines functional aerobic capacity.

CPET Parameters

• VO2 (volume of O2 consumed): Measured in mL/min (absolute) or mL/kg/min (relative) for intersubject comparisons.
• Respiratory Exchange Ratio (RER) or Respiratory Quotient (RQ): Calculated as VCO2 / VO2. RER gives an indication of the main macronutrient (carbohydrate, fat or protein) being metabolized for energy.
  • At rest, RER is typically 0.82-0.85 (mixed diet).
  • RER >1.0 indicates anaerobic metabolism (lactic acid buildup).
  • RER increases as CO2 production rises faster than oxygen consumption.
• Anaerobic Threshold (AT) or Ventilatory Threshold (VT), Lactate Threshold (LT): The highest exercise level/oxygen consumption that can be sustainably maintained without metabolic acidosis (lactic acid buildup).
  • Normally occurs between 40-80% of VO2max(40-60% in average individuals, 80% in well-trained athletes).
  • Indicates a point where the body shifts from aerobic to anaerobic energy production.
• Expiratory Volume (VE) (Minute Ventilation): Total amount of air in and out of lungs per minute (Tidal volume x breathing frequency).
• Respiratory Rate (RR) or Ventilatory Frequency (Vf): Number of breaths per minute.
• Tidal Volume (Vt): The volume of air moved in or out of the lungs per breath.

Exercise Responses During CPET

• VO2 and heart rate (HR) rise linearly in relation to work rate.
• VCO2 and minute ventilation (VE) rise in relation to work rate up to the anaerobic threshold (AT).
• VE may rise exponentially at the end of a true maximal test.
• RER = 1, intersection of VO2 and VCO2 graphs, marks true maximal test point.

Determining Anaerobic Threshold (AT) in CPET

• AT is the point where CO2 production rises disproportionately to oxygen consumption (V-Slope Method).
• RER starts to rise sharply after AT, approaching 1.0.
• End-tidal partial pressure of oxygen (PETO2) and VE/VO2 (ventilatory equivalent of oxygen) are used for confirming AT points.

CPET Normal Values (Example)

• Normal values depend on various factors (age, weight, size).
• At rest and maximum exercise values are listed in the provided data.

CPET Protocols - Treadmill vs Bike

• Treadmill tests are often more familiar but decreasing treadmill rail holding can reduce metabolic cost.
• Bike tests may be safer or have a lower metabolic cost but can be unfamiliar or have inherent inaccuracies.

Other Measurements (O2 Saturation)

• Pulse oximetry is used to measure oxygen saturation in red blood cells.
• It measures the percentage of oxygen-saturated hemoglobin.
• Limitations include: poor circulation, dark skin, and artificial nails can reduce accuracy. Movement can also impact measurements.
• Normal resting SpO2 values are generally 95% or higher. A drop of more than 3-5 percentage points during exercise is abnormal, requiring oxygen therapy support.

CPET Pre-test Instructions

• Similar to standard exercise tests (GXTs)
• Medications are taken as usual
• Comfortable clothing/footwear is worn
• Avoid heavy meals 2 hrs prior or provide light snack
• Avoid caffeine 2 hrs prior.
• Stop smoking or intensive sports/exercise in the 2 hours to an hour prior.

Test Preparation and Instructions

• Review patient medical history and assess for contraindications.
• Establish if the patient is clinically stable on the day of the test, if there have been any recent medical procedures or hospital visits.
• Ensure patient consent.
• Demonstrate the testing modality (treadmill or bike).
• Adjust equipment (mask, mouthpiece, headgear etc.).
• Site-specific protocols and pre-existing patient limitations are crucial considerations.

CPET Contraindications

• Absolute: Acute myocardial infarction (within 2 days), ongoing unstable angina, uncontrolled cardiac arrhythmias, active endocarditis, symptomatic severe aortic stenosis, decompensated heart failure, acute pulmonary embolism/infarction/deep vein thrombosis, acute myocarditis/pericarditis/aortic dissection, physical disability that prevents safe enough adequate testing.
• Relative: Known obstructive left main coronary stenosis, moderate to severe aortic stenosis(with uncertain relationship to symptoms), tachycardia arrhythmias with uncontrolled heart rates, acquired advanced/complete heart block, recent stroke or transient ischemia, mental impairment limiting cooperation, resting hypertension (systolic >200 mmHg, or diastolic >110mmHg), and uncorrected medical conditions (significant anemia, electrolyte imbalance, hyperthyroidism)

CPET Procedure - Calibration

• Gas calibration verifies 02 and CO2 analyzer accuracy; usually performed prior to each test using ambient air and calibrated reference gasses.
• Flowmeter calibration ensures the airflow device accurately measures air volumes. This is often done during the morning and afternoon, though this might vary depending on the equipment in use.

CPET - Gas Analysis (Mask, Mouthpiece)

• Assess advantages/disadvantages of using a mask vs. mouthpiece for gas analysis.
• Consider patient comfort, including dentures, anxiety, claustrophobia, and gag reflex.
• Ensure proper seal and calibration with a leak test.

Test Procedure Key Points

• Identify the test's goal.
• Describe the maximal effort requirement.
• Obtain reports of perceived exertion (RPE).
• Gather symptom reports and communicate using hand signals (modified Borg or 4-point scale).
• Emphasize maintaining a tight seal with the mouthpiece.
• Explain treadmill procedures; avoid treadmill rails (for balance if needed, support patient with hands against side rail).
• Ensure patient safety

General Indications for Termination of an Exercise Test

• ST elevation (≥1 mm) in leads (without pre-existing Q-waves), prior MI.
• Drop in systolic blood pressure (≥10 mmHg) despite workload increase, with ischemia signs.
• Moderate to severe angina
• Central nervous system symptoms (ataxia, dizziness).
• Signs of poor perfusion (cyanosis).
• Sustained ventricular tachycardia or arrhythmias interfering with cardiac output maintenance.
• Technical monitoring difficulties
• Patient's request to stop.
• Marked ST displacement (≥2mm).
• Drop in systolic blood pressure (≥10mmHg) despite increase in exercise
• Increasing chest pains.
• Fatigue, shortness of breath, wheezing, leg cramps or claudication.
• Specific arrhythmias (multifocal ectopy, ventricular triplets, supraventricular tachycardia, bradyarrhythmias).
• Exaggerated hypertensive response (>250 mmHg systolic, or >115 mmHg diastolic).
• Development of (undifferentiated) bundle branch block from ventricular tachycardia.
• SpO2 ≤80%

Test Prep: Explanation of Test ("Spiel")

• This describes the process of administering a CPET to patients. It includes directions for collecting patient data and monitoring procedures in the context of the procedure.

Test Prep and Instructions (Additional)

• Spirometry: Spirometry measures lung function values before CPET.
• Data Entry and Demographics: Ensure accurate recording of subject demographics (age, weight, height, ethnicity).
• Test Modality Selection (treadmill vs. bike): consider site specific needs and patient limitations to determine testing protocol.
• Protocol Selection: Choosing the right protocol (e.g., Bruce, Naughton) based on patient history, age, limitations, and ensure tests reach target end point (8-12 min max). (site- specific information)