ABSTRACT
BACKGROUND: Increased end-tidal oxygen (ET-O(2)) and decreased end-tidal carbon dioxide (ET-CO(2)) gas tensions are noninvasively measurable correlates of ventilatory inefficiency, leading to increased ventilatory requirements relative to gas exchange among patients with chronic heart failure (CHF). We investigated the prognostic value of ET-O(2) and ET-CO(2) as predictors of CHF mortality. METHODS: We measured resting ET-O(2) and ET-CO(2) electrochemically in 134 patients with symptomatic CHF in the supine position. We used Kaplan-Meier analysis, Cox proportional hazard models, and receiver operating characteristic curves to test our hypothesis. RESULTS: At a median follow-up of 16.5 months, 32 patients had died. ET-O(2) levels were increased (P = .001) and ET-CO(2) levels decreased (P = .002) with increased New York Heart Association class (I-IV). Survivors showed lower ET-O(2) (121 vs 118 mm Hg; P = .021) and higher ET-CO(2) (33.2 vs 32.1 mm Hg; P = .032) levels than nonsurvivors. Patients with ET-O(2) values ≥121 mm Hg and/or ET-CO(2) values <31 mm Hg had an increased risk of death with hazard ratios of 2.93 (95% confidence interval [CI], 1.43-6.01) and 2.47 (95% CI, 1.23-4.97), respectively. Kaplan-Meier estimates for follow-up mortality with ET-O(2) ≥121 mm Hg and/or ET-CO(2) <31 mm Hg were 83.8% (vs 60.1%; P = .0014) and 80.3% (vs 60.2%; P = .0061), respectively. Areas under the receiver operating characteristic curves for prediction of death with ET-O(2) and ET-CO(2) were both significant and similar to that of echocardiographic left ventricular function. CONCLUSIONS: In CHF, high levels of ET-O(2) and low levels of ET-CO(2) are associated with increased mortality. We suggest that the measurements may be useful prognostic markers for risk stratification.
Subject(s)
Heart Failure/physiopathology , Pulmonary Alveoli/physiopathology , Aged , Carbon Dioxide/analysis , Chronic Disease , Echocardiography , Female , Forced Expiratory Volume , Heart Failure/etiology , Heart Failure/mortality , Humans , Male , Middle Aged , Myocardial Ischemia/diagnostic imaging , Myocardial Ischemia/physiopathology , Oxygen/analysis , Prognosis , Proportional Hazards Models , Supine Position , Tidal Volume/physiology , Ventricular Dysfunction, Left/physiopathologyABSTRACT
BACKGROUND: Impairment of ventilatory efficiency in congestive heart failure (CHF) correlates well with symptomatology and contributes importantly to dyspnea. METHODS AND RESULTS: We investigated 142 CHF patients (mean NYHA class, 2.6; mean maximum oxygen consumption [VO(2)max], 15.3 mL O(2) x kg(-1) x min(-1); mean left ventricular ejection fraction [LVEF], 27%). Patients were compared with 101 healthy control subjects. Cardiopulmonary exercise testing was performed, and ventilatory efficiency was defined as the slope of the linear relationship of V(CO(2)) and ventilation (VE). Results are presented in percent of age- and sex-adjusted mean values. Forty-four events (37 deaths and 7 instances of heart transplantation, cardiomyoplasty, or left ventricular assist device implantation) occurred. Among VO(2)max, NYHA class, LVEF, total lung capacity, and age, the most powerful predictor of event-free survival was the VE versus V(CO(2)) slope; patients with a slope 130% (54.7%; P<0.001). CONCLUSIONS: The VE versus V(CO(2)) slope is an excellent prognostic parameter. It is easier to obtain than parameters of maximal exercise capacity and is of higher prognostic importance than VO(2)max.
Subject(s)
Heart Failure/physiopathology , Respiration , Adult , Aged , Exercise Test , Female , Follow-Up Studies , Heart Failure/blood , Humans , Lung/physiopathology , Male , Middle Aged , Multivariate Analysis , Oxygen/blood , Physical Endurance , Prognosis , Proportional Hazards Models , Survival AnalysisABSTRACT
Cardiopulmonary exercise testing (CPX) is a non-invasive method of recording quantitative data from gas exchange and ventilation for the evaluation of oxidative metabolism at rest and during exercise. Determination of oxygen uptake (VO2) and carbon dioxide output (VCO2) describes the activity of anaerobic vs aerobic metabolism. An incremental exercise test measuring gas exchange, ventilation and lactate release was performed in healthy volunteers and in patients suffering from mitochondrial disorders. At rest as well as during exercise patients with mitochondrial disorders differ from healthy subjects with regard to gas exchange and ventilation parameters. During exercise, the decreased oxygen utilization of skeletal muscle and early activation of anaerobic metabolism in these patients are mirrored by a reduced anaerobic threshold, reduced maximal oxygen uptake and reduced oxygen pulse. Our study shows that CPX is a sensitive and practical clinical screening method of investigating mitochondrial disorders.
Subject(s)
Exercise Test , Mitochondrial Encephalomyopathies/diagnosis , Mitochondrial Myopathies/diagnosis , Spirometry , Adolescent , Adult , Anaerobic Threshold/physiology , Diagnosis, Differential , Female , Humans , Lactic Acid/blood , Male , Middle Aged , Mitochondrial Encephalomyopathies/genetics , Mitochondrial Myopathies/genetics , Oxygen/blood , Predictive Value of Tests , Reference ValuesABSTRACT
The ventilatory equivalent for CO2 defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16-75 years, measuring ventilation and gas exchange at rest (n = 64) and on exercise (modified Naughton protocol, n = 101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output (VE:VCO2), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output (VE vs VCO2 slope), oxygen uptake at the anaerobic threshold and at maximum (VO2AT, VO2max, respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [VE:VCO2 50.5 (SD 8.8) vs 57.6 (SD 12.6) P < 0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: (VE vs VCO2 slope = 0.13 x age + 19.9; women: VE vs VCO2 slope = 0.12 x age + 24.4). The VO2AT and VO2max were 23 (SD 5) and 39 (SD 7) ml O2 x kg x min(-1) in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The VO2AT was reached at 58 (SD 9)% VO2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults.
