Long-term Reproducibility of Respiratory Gas Exchange Measurements during Exercise in Patients: METHODS

28 Feb
2011

Ritient Population

Sixteen successive outpatients with chronic, stable, cardiac failure were selected on the basis of their having had, in addition to their first test that was not included in the analysis, at least four exercise tests during a period of time that exceeded three months. In addition, there had to be at least five patients in each of the following functional exercise classes: A, B, and C. Functional class was determined at entry into the study according to the patients maximal Vos (Vo2max): functional class A, Vo2max >20 ml/min/kg; class В, 16 to 20 ml/min/kg; and class C, 10 to 16 ml/min/kg.2 As can be seen in Table 1 there were six class A, five class B, and five class С patients. The range in age was 51 to 75 years (61 ± 7 years) and 14 were male.

The spectrum of heart disease included idiopathic dilated cardi­omyopathy (six patients), ischemic cardiomyopathy and coronary heart disease as evidenced by clinical history or serum enzyme changes during a previously known myocardial infarction or by angiography (four patients), chronic aortic and mitral incompetence (three patients), chronic aortic incompetence (one patient), and chronic systemic hypertension (two patients).

Table 1 —Patient Population

Study

Patient No. and

Period.

No. of

Class/Age, y/Sex

Etiology

mo

Tests

1A/51/M

ICM

22

5

2A/55/M

HT

10

8

3A/56/M

ICM

10

5

4A/61/M

AR,MR

5

4

5A/58/M

IHD

10

4

6A/54/F

ICM

13

6

7B/58/M

HT

13

5

8B/63/M

IHD

10

4

9B/68/M

AR,MR

8

5

10B/71/M

AR,MR

16

7

11B/58/M

IHD

9

4

12C/57/M

ICM

3

5

13C/67/M

IHD

8

6

14C/67/F

ICM

4

7

15C/75/M

ICM

4

5

16C/52/M

AR

4

6

All patients were in sinus rhythm and remained clinically stable during the study period that varied from 3 to 22 months (9 ±5 months). Also, their New York Heart Association functional class did not change and there were no significant changes in medications. The number of exercise tests per patient ranged from 4 to 8 (5 ± 1).

Protocol

Exercise tests were performed using a programmable treadmill and incremental work schedule, where every two minutes either treadmill speed, grade, or both was varied (Table 2). The patients were exercised to exhaustion and Vo2max. Heart rate, gas exchange, and ventilation (ie, tidal volume [Vt] and respiratory rate) were measured, and Vo2 and Vco, were calculated on a breath-by-breath basis throughout the test. In addition, BP was obtained during the last minute of each stage.

Table 2—Exercise Protocol

Speed,

Grade,

Stage

mph

percent

1

1.0

0.0

2

1.5

0.0

3

2.0

3.5

4

2.0

7.0

5

2.0

10.5

6

3.0

7.5

7

3.0

10.0

8

3.0

12.5

9

3.0

15.0

10

3.4

14.0

Following each test the anaerobic threshold (AT) and Vo2max were determined from the results of the test as follows: AT was taken to be the Vo2 at which Vco2 and Ve began to increase at a greater rate than Vo2, and end-tidal 02 began to increase relative to an invariant end-tidal C02. The Vo2max was considered to be attained when following an increment in work equivalent to 2 to 3 ml/min/kg, 02 uptake increased by <1 ml/min/kg. Since the necessary variables were continuously being updated and displayed as the test progressed, it was possible to immediately verify that AT was attained and to determine that the patient was achieving Vo2max.

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