Background: In patients with chronic heart failure (CHF) augmented exercise ventilation is related to functional severity and increased mortality. Nevertheless, the optimal approach to the assessment of ventilatory response to controlled exercise has not been established.
Aim: The study was carried out to evaluate the clinical application of the measurement of ventilatory response to the early phase of exercise in the non-selected group of patients with CHF.
Material and methods: We investigated 180 consecutive patients with CHF (155 men, age: 59 +/- 11 years, left ventricle ejection fraction: 31 +/- 7%; NYHA class I/II/III/IV: 13/90/60/17). All patients underwent the cardiopulmonary exercise testing (CPX) with RER > 1.0 (mean peak oxygen consumption [peakVO2]: 15.5 +/- 4.8 ml/kg/min). Ventilatory response to exercise was assessed: 1) during the whole exercise--expressed as a correlation coefficient of linear regression describing the relationship between minute ventilation (VE) and carbon dioxide production (VCO2) during the whole exercise (VE-VCO2 100%); 2) during the early phase of exercise--expressed as VE-VCO2 derived from VE and VCO2 during first 180 seconds of exercise (VE-VCO2 180 s).
Results: Ventilatory responses to early and maximal exercise were significantly augmented in CHF patients (VE-VCO2 100% -36.1 +/- 9.8, VE-VCO2 180% -34.4 +/- 10.3; p < 0.0001 vs values in the reference group without CHF). Ventilatory responses to early and whole exercise were strongly interrelated (r = 0.88, p < 0.0001). Indices of exercise ventilation correlated with the severity of CHF expressed as NYHA class (for VE-VCO2 100% and VE-VCO2 180 s -r = 0.52 and r = 0.51) and peak VO2 (for VE-VCO2 100% and VE-VCO2 180 s, r = -0.49 and r = -0.47, respectively) (p < 0.0001 for all correlations). Among echocardiographic parameters only right ventricular systolic pressure correlated with indices of exercise ventilation (for VE-VCO2 100% -r = 0.45, p = 0.001; for VE-VCO2 180 s -r = 0.35, p = 0.01). The reproducibility of indices of exercise ventilation was assessed in 19 CHF patients (another CPX during 2-9 days), and variability coefficients reached 7.8% for VE-VCO2 100% and 8.5% for VE-VCO2 180 s.
Conclusions: Indices of ventilatory response to both early and maximal exercise can significantly differentiate the CHF patients with regard to their exercise capacity, are highly reproducible, and may therefore constitute useful parameters carrying an important clinical message. The assessment of ventilatory response during the early stage of exercise seems to be of a particular significance in CHF patients who are unable to perform the maximal exercise effort, as diagnostic data obtained during first 180 seconds of exercise are in accordance to those derived from the standard maximal CPX.