Diagnostic and Prognostic Value of Lactate Threshold and pH - Threshold Determination during Cardiopulmonary Testing in Patients with Chronic Heart Failure

Abstract

Objective: lactate threshold and pH-threshold determination during cardiopulmonary testing (CPET) and evaluate their diagnostic and prognostic value in patients with chronic heart failure. Methods: The study included 58 HF patients with NYHA class II-IV, who have performed CPET on treadmill using equipment «Oxycon PRO», Jaeger, Germany. Individual exercise test protocol (ramp protocol) was created for every participant. The cubital venous catheter was installed in all subjects before exercise test. Blood samples were taken at baseline and at 1-minute intervals during test. PH, lactate and HCO3- concentration were estimated using analyzer i-STAT, cartridge CG4 (Abbot, USA). Lactate threshold (LT) and pH-threshold (pH-T) were determined by changes in pH and lactate levels in correlation with dynamics of oxygen uptake (VO2), carbon dioxide output (VCO2), minute ventilation (VE), ventilatory equivalent of carbon dioxide (VE/VCO2), respiratory exchange ratio (RER). Respiratory compensation point (RCP) was determined, when ventilation dramatically increase relative VE/VCO2. Results: In HF patients with NYHA class II level of physical performance was significantly higher than in patients NYHA class III and IV. However, during exercise in all HF patients were observed similar physiological stages and compensatory mechanisms of regulation of homeostasis, but with varying of exercise intensity. In HF patient with NYHA class IV, exercise was stopped before reaching of RCP in connection with the development shortness of breath, weakness, tiredness, fatigue in the legs 8-9/10 Borg scale. Among HF patients with NYHA class III RCP reached 12 (36%) of people, among patients with class II - 14 (82%). The 95% confidence intervals (CI) for the VO2 peak, RCP, pH-T and LT in II, III and IV NYHA class are follows: in HF patients with NYHA class II - 17.4 to 18.2, 16.3 to 17.2, 14.7 to 15.3 and 9.7 to 10.1; NYHA class III - 13.5 to 14.3, 12.2 to 12.8, 11.4 to 11.8 and 8.2 to 8.6; NYHA class IV - 8.6 to 10.6 for VO2 peak, 8.1 to 9.7 for VO2 pH-T, 5.7 to 7.5 for VO2 LT. HF NYHA class correlated with VO2 LT, VO2 pH-T and VO2 RCP, r=-0.7, p<0.01, r=-0.5, p<0.01 and r=-0.4, p<0.01, respectively. Patients were observed in the average 21.4 of +/ - 1.5 months (6-48). For the specified period in the study group died 15 HF patients (25%) with III-IV FC. We observed the following correlations: the survival and VO2 LT - r=0.8, p<0.05; survival and VO2 рН-T - r=0.5, p<0.05; survival and VO2 RCP - r=0.2, p<0.07. Conclusion: In HF patients with NYHA class II-IV significant diagnostic and prognostic markers are content VO2 at lactate threshold and pH-threshold, especially at the lactate threshold.