Assessment of respiratory compensation phase during graded exercise in patients with chronic heart failure

The VE-VO2 relationship during graded exercise has an inflection point beyond the ventilatory anaerobic threshold (VAT) termed the respiratory compensation point (RCP). Metabolic variables analyzed at the level of VAT and RCP may contribute to the better understanding of such limiting symptoms in chronic heart failure (CHF) patients as dyspnea and early fatigue. The AIM of the present study was to analyze the RCP during symptom limited ramp exercise testing in CHF patients.

Forty six CHF patients (II and III NYHA functional class; age = 51 +/- 9 years, LVEF% = 35% +/- 6%; mean +/- SD) and 20 matched controls performed graded cardiopulmonary exercise test on a cycle ergometer.

The duration and productivity of RCP (delta(x) = peak(x) - VAT(x)) in patients were significantly (p < 0.001) reduced compared to healthy subjects: delta duration = 3.0 +/- 1.2 vs 4.3 +/- 1.5 min, delta watts = 24.3 +/- 11.5 vs. 39.4 +/- 11.5, delta VO2/kg (ml.kg-1 x min-1) = 3.8 +/- 1.3 vs 8.8 +/- 2.3. An important characteristic of this phase was the higher subjective cost of physical effort assessed by Borg scale and Watts/Borg ratio (Borg peak = 9.9 +/- 0.4 vs. 6.0 +/- 1.2; p < 0.001, Watts/Borg peak = 9.2 +/- 2.3 vs 23.9 +/- 6.4, p < 0.001). The relative hyperventilation of patients on the basis of the watt exercise can be seen in the values of derivative index V (ml x min-1 x watt-1) 478 +/- 59 vs 568 +/- 118; (p < 0.001) in controls and patients, respectively.

The impaired efficiency of oxygen delivery systems in patients with CHF is what causes the appearance of early limiting symptoms. Duration and productivity of respiratory compensation phase in CHF patients are considerably reduced compared to controls.