8 - Cardiopulmonary Testing

cardiopulmonary exercise testing (CPET)

pulmonary function testing that evaluates heart and lung function under conditions of increased metabolic demand

indications for CPET

• dyspnea with exertion

• pain (especially angina)

• fatigue

• exercise-induced bronchospasm

• arterial desaturation

parameters that CPET can detect

• exercise tolerance

• limits of heart/lungs

• max/safe workload for daily exercise

• level of disability for rehab

• oxygen needs with exercise and titration

• outcome measure following surgical or medical issue (rehab)

ensuring patient safety for CPET

• exam by provider

• identify any contraindications (ECG, resting BP, ABG)

• signed consent

• trained staff

• physical setting

absolute contraindications for CPET

• acute MI (3-5 days)

• uncontrolled angina/dysrhythmias/CHF/asthma/HTN

• syncope

• active endo-/myo-/pericarditis

• systematic severe aortic stenosis

• symptomatic severe aortic stenosis

• acute PE/pulmonary infarct

• DVT

• S_pO₂ < 85% on room air

• respiratory failure

• mental impairment

relative contraindications for CPET

• left main coronary stenosis

• moderate stenotic valvular disease

• untreated HTN (>200/>120)

• high degree heart block

• cardiomyopathy

• pregnancy

• electrolyte impairment

• orthopedic impairment

progressive multistage tests

CPET protocol that assesses effects of increasing workloads

• cardiopulmonary variables, gas exchange, and ventilation measured

steady state tests

CPET protocol that assesses function during constant metabolic demand

• tests effectiveness of therapy or medications

• similar test used to assess exercise-induced bronchospasm

steps of progressive multistage (incremental) exercise test

1. determine maximum measurements

   • VO₂ max, ventilation, HR, symptom limit

2. start at baseline at predetermined intervals

3. increase workload every 1-6 minutes

4. measurements done in last 20-30 seconds of each interval

   • BP, ABGs, C.O.

   • computerized, continuous

5. total time: 8-10 minutes after warmup

steady state

HR unchanged for 1 minute at given workload

normal capacities for 6-minute walk

• females: ≥ 350 m

• males: ≥ 450 m

steps for 6-minute walk

1. resting assessment

2. standing assessment

3. instruct patient

4. start test

   • walk as far as possible in 6 minutes on 100 ft track

   • rests allowed, but time continues

5. encourage patient throughout test

6. stop after 6 minutes

7. reassess patient

8. record total distance, O₂ levels and mode, and range of perceived exertion (RPE) [level of dyspnea]

methods of exercise workload

main methods

• treadmill

• cycle ergometer

other methods

• arm ergometer

• steps

• free running/walking

treadmill for CPETs

• change slope/speed

• easy to obtain maximal levels of exercise

• workload impacts

  • patient weight

  • walking pattern/stride

  • handrails

• VO₂ max 7-10% higher than cycle ergometer

cycle ergometer for CPETs

• alter pedaling resistance/speed

• workload independent of weight

• easier monitoring

• ramp test (easy transition to increasing workloads)

work

• formula: force × distance

• unit: kilopond-meter (kpm)

power

• formula: work ÷ unit of time

• units: kilopond-meter/minute (kpm/min), watts

units for energy

• VO₂ (L)

• mL/min in STPD

• metabolic equivalents (METs)

  • 1 MET = 3.5 mL/min/kg O₂

non-invasive monitoring for CPETs

• ECG/BP

• ventilation

• exhaled gases (mass spectroscopy is gold standard)

• oximetry

• volume

• CO₂

invasive monitoring for CPETs

• ABGs

• mixed venous blood gases

• CO₂

ECG for CPETs

• electrodes designed for exercise testing

• continuous monitoring

  • resting vs exercise

  • ST segment changes/PVCs

• max HR = 220 − age

CV response to exercise

• 5× increase of C.O.

• ↑BP

  • healthy: SBP 120 → 200-250

  • a-line for continuous monitoring

• cool down to avoid hypotension

• stop test when SBP > 250 or no rise is seen

when to stop CPET

• monitor failure

• ST depression/elevation

• T-wave inversion

• significant Q wave

• sustained SVT

• increased multifocal PVCs

• second-/third-degree heart block

• exercise-induced bundle branch block

• angina

• diaphoresis

• pallor

• BP >250/>120 (or SBP drop > 10)

• no change in BP

• lightheadedness, mental confusion, HA

• cyanosis

• nausea and vomiting

• muscle cramping

ventilation during CPET

• equipment

• pneumotachometer

• gas analyzers

• valves (low resistance, low V_D)

ventilation during CPET

• data collected

• volume (L)

• temperature at measuring device (convert to BTPS)

• time of collection

• RR

• F_eCO₂

• F_eO₂

ventilation during CPET

• ventilatory response

• V_E increases to meet VO₂ and VCO₂

• ↑V_T first, then ↑RR

ventilation during CPET

• gas exchange

• V_D/V_T not used

• V_T increases, V_D decreases by ~30% during exercise

• P_aO₂ remains normal with regular exercise

ventilation during CPET

• parameters

• V_E

• V_T

• RR (f)

• VO₂

• VCO₂

• respiratory exchange ratio

minute ventilation (V_E) during CPET

• normal ranges

  • average: <100 L/min

  • athletes: >200 L/min

• increases with work in response to increased O₂ demand

maximal minute ventilation (V_Emax)

minute ventilation at highest exercise level reached/measured (L/min)

formula for ventilatory capacity

__ = V_Emax ÷ MVV

maximal voluntary ventilation (MVV)

maximum volume patient can breathe per unit of time (12 seconds)

• breathe as fast and as deep as possible for 12 seconds

• MVV × 5 = MVV/min

• affected by muscle strength, C_L and C_CW, R_aw, patient effort

• performed during spirometry

• estimation: FEV₁ × 40

ventilatory reserve

difference between MVV and V_Emax

formula:

__ = [1 − (V_Emax ÷ MVV)] × 100

ranges:

• normal: 20-40%

• pulmonary disease: <20%

V_T and RR (f) during CPET

watch patient’s breathing pattern during CPET

• ↑RR and ↓V_T → increased air trapping and SOB

• ↓RR and ↑V_T → SOB

• little change in V_T and ↑RR → restrictive disease

VO₂ during CPET

oxygen consumption

• normal value at rest: 0.25 L/min

• calculation:

__ = F_iO₂ − F_eO₂

VO₂max

VO₂ at highest level of work attainable

• 60-80% predicted = moderate impairment

• <50% predicted = severe impairment

VCO₂ during CPET

carbon dioxide production

• reflects metabolism

• formula:

__ = (F_eCO₂ − 0.0003) × V_E

• concentration based on rate of removal from lungs by inflation:

F_ACO₂ = __ ÷ V_A

• normal value: 0.20 L/min

• athletic value: 5 L/min

respiratory exchange ratio (RER)

__ = VCO₂ ÷ VO₂

• normal value: 0.8

• during anaerobic metabolism, VCO₂ close to/exceeds VO₂

anaerobic threshold (AT)

point during exercise at which energy demand > energy supply by aerobic metabolism

1. lactic acid produced

2. HCO₃^- buffers acid

3. ↑CO₂

4. ↑V_E to maintain pH

ventilatory threshold

assessment of V_E and CO₂ during exercise to detect anaerobic metabolism

anaerobic threshold for various patient populations

• normal

  • AT 60-70% of VO₂max

  • AT < 40% = abnormally low

• cardiac

  • AT reached at lower workloads due to limited heart function and C.O.

• pulmonary

  • may not reach AT due to ventilation limits

O₂ pulse for CPET

Fick equation:

__ = VO₂ ÷ HR

uses HR, SV, VO₂, C_aO₂, C_vO₂

ABGs during exercise

• P_aO₂ relatively stable

  • P_AO₂ increases, P_(A-a)O₂ widens

• P_aCO₂ constant at low/moderate workloads

  • with severe obstruction, V_A won’t match increasing VCO₂ → ↑CO₂ and respiratory acidosis

cardiac output (C.O.) during activity

normal values:

• rest: 4-6 L/min

• exercise: 25-35 L/min

non-invasive monitoring

• pulse wave transit time

• Doppler (ultrasound)

• pulse wave analysis

invasive monitoring

• arterial waveform

• Fick equation (VCO₂ ÷ C_(a-v)O₂)

• thermodilution

interpreting CPET results

• quality of test

  • HR_max > 85-90% predicted

• CV response

  • ECG, BP, C.O., O₂ pulse, symptoms

• ventilatory response

  • ventilatory capacity, ventilatory reserve, breathing kinetics

• gas exchange

  • S_pO₂, P_aO₂, P_(A-a)O₂, V_D/V_T, P_aCO₂

• metabolic/O₂ uptake

  • AT, VO₂max, VO₂