Interpreting the Results of Cardiopulmonary Exercise Tests

Abstract

Once the data collection portion of the cardiopulmonary exercise test has been completed, the final task is to interpret the results of the test. This section of the primer provides general information regarding test interpretation as well as suggestions for the content and format of the final report. It also reviews one of the key components of test interpretation—identification of the ventilatory threshold.

Appendix: Sample Cardiopulmonary Exercise Test Report

Cardiopulmonary Stress Test Interpretation

Date of Study: 9/21/10

Referring Provider:

Test Performed By:

Indications for Testing: 50-year-old woman with dyspnea on exertion of unclear etiology

Diagnoses:

Dyspnea on exertion

Cough

Age: 50

Height: 165 cm

Weight: 81.7 kg

BMI: 30

Pulmonary Function Testing

Spirometry: FEV₁ 2.91 l (105% predicted), FVC 3.44 l (101% ­predicted), FEV₁/FVC 0.85

Post-bronchodilator Spirometry: Not performed

Maximum Voluntary Ventilation: 131 l/minute

Postexercise spirometry: The FEV₁ remained between 2.77 and 2.91 l at testing performed every 3 minute postexercise up until 20 minute had elapsed. The contour of the inspiratory limb of the flow volume loops during the postexercise testing was irregular but did not show evidence of flattening consistent with an upper airway obstruction.

Interpretation: Normal spirometry. No evidence of airflow obstruction following exercise.

Pulmonary Stress Test, Complex

Exercise Protocol: The risks and benefits of progressive maximal cardiopulmonary exercise testing and arterial line placement were explained to the patient. After obtaining consent, an arterial line was placed on the first attempt in the left wrist in a sterile manner using a modified Seldinger technique. Upon placement of the catheter, the patient was placed on the exercise bicycle and was without symptoms. She was exercised on the cycle ergometer to a symptom-limited ­maximum with progressively increasing workload at 15-W/minute increments. Continuous oxygen saturation, ECG, and expired gas analysis were performed. Serial blood pressures were obtained. Arterial blood gas samples were obtained prior to the start of exercise and every 2 minute during the exercise test. The patient reached a maximum of 118 W and appeared to give a good effort. She was sweating at the end of the test.

Reason For Stopping Exercise: Leg fatigue. The patient did not develop any coughing similar to what she describes when she is having difficulty with exercise at home or at work.

Results

Summary Data

Measurement	Rest	Max exercise	Predicted max	% Predicted
Work (W)	0	118	129	91
$\rm \dot{V}{\text{O}}_{2}$(ml/minute)	242	1,458	1,620	90
$\rm\dot{V}{\rm{O}}_{2}/\text{kg}$(ml/kg/minute)	3.0	17.8	19.8	90
Heart rate (bpm)	81	153	169	91
O2 pulse (ml O2/beat)	3	10	10	99
Blood pressure (mmHg)	98/60	162/90
Ventilation (l/minute)	8.4	65.9	116	50% of MVV
				57% of FEV1  ×  40
Respiratory rate (bpm)	9	31
Tidal volume (l)	0.88	2.11
O2 saturation (%)	100	100
${\text{PETCO}}_{2}$(mmHg)	35	35a

1. ^a ${\text{PETCO}}_{2}$ reached 44 at the ventilatory threshold before falling to 35 at the end of the study

Maximum oxygen consumption: The patient’s $\rm\dot{V}{\rm{O}}_{2\mathrm{max}}$ was 1,458 ml/minute, which represented 90% of her predicted maximum. When normalized for her body weight of 81 kg, her $\rm\dot{V}{\rm{O}}_{2\mathrm{max}}$ was 17.8 ml/kg/minute which was 90% of her predicted maximum. When normalized for her IBW of only 57 kg given her height of 165 cm, her $\rm\dot{V}{\rm{O}}_{2\mathrm{max}}$ was 25.7 ml/kg/minute. She achieved a maximum work rate of 118 W, which was 91% of her predicted maximum.

Cardiac response: The resting ECG showed a sinus rhythm with a normal rate, normal axis, and intervals. No ischemic changes were noted at maximum exercise. Her heart rate was 81 beats per minute at rest and rose to 153 beats per minute at maximum exercise, which was 91% of her age-predicted maximum. The O₂ pulse rose from 3 ml/beat at rest to 10 ml/beat at maximum exercise, which was 99% of her predicted maximum. Blood pressure rose from 98/60 at rest to 162/90 at maximum exercise. A ventilatory threshold was observed at a $\rm \dot{V}{\text{O}}_{2}$ of roughly 840 ml/minute, which was about 57% of her $\rm\dot{V}{\rm{O}}_{2\mathrm{max}}$.

Ventilatory response: The patient’s resting ventilation was 8.4 l/minute and increased to 65.9 l/minute at maximum exercise, representing only 50% of her MVV and 57% of her FEV₁  ×  40. The respiratory rate rose from 9 at rest to 31 at maximum exercise while tidal volume increased from 0.88 to 2.11 l over the course of the test. The patient’s ventilatory equivalents for CO₂ were elevated in the mid-30 range while sitting at rest and subsequently declined to the upper 20-range midway through exercise before rising again over the last half of the test. The ventilatory equivalents for O₂ were in the low 30s at rest and then declined into the 20s once exercise began before rising again in the later half of the test.

Gas exchange: The patient’s oxygen saturation was 98–100% at rest and 96% at maximal exercise. Her arterial blood gas results were as follows:

Time point	pH	${\rm PaC{O}_{2}}$	${\rm Pa{O}_{2}}$	(A  − a)ΔO2	Lactate	Vd/Vt
Rest	7.42	39	100	9	0.8	0.36
Max exercise	7.42	30	125	3	8.3	0.10

Impression/Summary

The patient achieved a $\rm\dot{V}{\rm{O}}_{2\mathrm{max}}$, normalized for her actual body weight, of 17.8 ml/kg/minute, which was 90% of her predicted maximum. The pattern on this test was consistent with a cardiac pattern of limitation. At maximum exercise, she had a large ventilatory reserve, there was no evidence of hypoxemia, and a clear ventilatory threshold was present as indicated by a rise in her ventilatory equivalents and end-tidal oxygen, drop in her arterial carbon dioxide at end-exercise, and development of a lactic acidosis. There was no evidence of chronotropic limitation. The patient’s dead-space fraction decreased appropriately at maximum exercise making it unlikely that she has a pulmonary vascular/interstitial lung disease pattern of limitation. She had no ­evidence of ventilatory limitation, as evidenced by the fact that her ventilation at peak exercise was only 50% of her MVV and her arterial CO₂ fell at end-exercise. Her postexercise spirometry did not show any decrements in FEV₁ or FVC compared to her pre-exercise spirometry and there was no evidence of flattening of the inspiratory limb of the flow volume loops on these maneuvers.