Abstract
Introduction. The relation between minute ventilation (VE) and carbon dioxide production (VCO2) can be characterised by the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO2 (VEqCO2). We hypothesised that the time taken to achieve the lowest VEqCO2 (time to VEqCO2 nadir) may be a prognostic marker in patients with chronic heart failure (CHF). Methods. Patients and healthy controls underwent a symptom-limited, cardiopulmonary exercise test (CPET) on a treadmill to volitional exhaustion. Results. 423 patients with CHF (mean age 63 ± 12 years; 80% males) and 78 healthy controls (62% males; age 61 ± 11 years) were recruited. Time to VEqCO2 nadir was shorter in patients than controls (327 ± 204 s versus 514 ± 187 s; P = 0.0001). Univariable predictors of all-cause mortality included peak oxygen uptake (X 2 = 53.0), VEqCO2 nadir (X 2 = 47.9), and time to VEqCO2 nadir (X 2 = 24.0). In an adjusted Cox multivariable proportional hazards model, peak oxygen uptake (X 2 = 16.7) and VEqCO2 nadir (X 2 = 17.9) were the most significant independent predictors of all-cause mortality. Conclusion. The time to VEqCO2 nadir was shorter in patients with CHF than in normal subjects and was a predictor of subsequent mortality.
Highlights
The relation between minute ventilation (VE) and carbon dioxide production (VCO2) can be characterised by the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO2 (VEqCO2)
We hypothesised that the time taken to reach VEqCO2 nadir would be shorter in patients with chronic heart failure (CHF) compared to healthy controls and may be an important prognostic indicator
423 patients with CHF were included in the study
Summary
The relation between minute ventilation (VE) and carbon dioxide production (VCO2) can be characterised by the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO2 (VEqCO2). In patients with chronic heart failure (CHF), the normal linear relation between ventilation (VE) and carbon dioxide production (VCO2) is maintained, but the slope of the relation is greater than normal, so that, for a given volume of carbon dioxide production, the ventilatory response is greater [2,3,4,5,6]. Another way of characterising the relation between minute ventilation and carbon dioxide production is the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO2 (VEqCO2). We hypothesised that the time taken to reach VEqCO2 nadir would be shorter in patients with CHF compared to healthy controls and may be an important prognostic indicator
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