Respiratory Gas Analysis in Patients with Chronic Heart Failure

Abstract

Traditionally, the clinical severity of chronic heart failure has been assessed by clinical symptoms and was graded according to the criteria of the New York Heart Association (NYHA). These criteria are by their nature subjective with a low reproducibility [16]. In order to detect any change in the functional state of patients with heart failure, e.g. improvement over time with specific treatment, it appears crucial to apply an objective, reproducible, and sensitive method. Except for advanced, severe chronic heart failure, symptoms occur with physical activity only. Therefore, exercise testing with determination of variables unaffected by patient motivation and the supervising physician, should be useful in the assessment of functional capacity of patients with chronic heart failure (Table 1). It is important to recognize that the determination of LV-function, although of major prognostic value, correlates poorly with functional classes [2, 12, 14, 18, 34]. Thus, among patients with similar degrees of LV-dysfunction, clinical symptoms may vary considerably and normal exercise capacity may be almost preserved despite substantial LV-dysfunction. Two patients with identical cardiac lesions will have different symptoms during exercise if the peripheral circulation of one adapts to the exercise better than that of the other. Heart failure during exercise occurs when the peripheral circulation does not adequately adjust to an inadequate cardiac output to keep pace with the metabolic requirements of the exercising muscle. Thus, although the primary defect is due to myocardial failure, the symptoms are not solely dependent on the behavior of the heart. Similarly, exercise hemodynamics do not relate closely to exercise capacity in patients with chronic heart failure; in addition, it remains an invasive procedure which cannot be repeated unlimitedly.