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The ventilatory efficiency for carbon dioxide output ( V ˙ CO2) during exercise, as measured by the minute ventilation vs. V ˙ CO2 slope ( V ˙ E vs. V ˙ CO2 slope), is a powerful prognostic index in patients with chronic heart failure (CHF). This measurement is higher in women than in men, and it increases with age. This study aimed to investigate the usefulness of the predicted value of the percentage V ˙ E vs. V ˙ CO2 slope (% V ˙ E vs. V ˙ CO2 slope) as a prognostic index in patients with CHF. A total of 320 patients with CHF and a left ventricular ejection fraction (LVEF) < 45% (male, 85.6%; mean age, 64.6 years) who underwent symptom-limited cardiopulmonary exercise tests using a cycle ergometer were included in the study. The % V ˙ E vs. V ˙ CO2 was calculated using predictive formulae based on age and sex. Cardiovascular-related death was defined as the primary endpoint. The mean follow-up duration was 7.5 ± 3.3 years. Of 101 patients who died during the study period, 75 experienced cardiovascular-related deaths. The average V ˙ E vs. V ˙ CO2 slope was 32.8 ± 8.0, and the average % V ˙ E vs. V ˙ CO2 slope was 119.6 ± 28.2%. The cumulative incidence of cardiovascular-related death after 10 years of follow-up were 44.7% (95% CI 34.4–54.6%) in patients with % V ˙ E vs. V ˙ CO2 slope > 120 and 15.0% (95% CI 9.4–21.8%) in patients with % V ˙ E vs. V ˙ CO2 slope ≤ 120. The multivariate Cox regression analysis indicated that a % V ˙ E vs. V ˙ CO2 slope > 120 was an independent predictor of cardiovascular-related death (adjusted hazard ratio, 3.24; 95% confidence interval 1.65–6.67; p < 0.01). The % V ˙ E vs. V ˙ CO2 slope can be used for risk stratification in patients with CHF and an LVEF < 45%. [ABSTRACT FROM AUTHOR]

We examined the oxygen uptake (VO2) and carbon dioxide output (VCO2) during completion of a circuit developed for testing fire fighters and related performance time to laboratory measures of fitness. Twenty-two healthy university students (ten women) were trained in the tasks then performed the circuit as quickly as possible. Breath-by-breath gas exchange and heart rate were continuously measured with a portable system. Median circuit time was 6:13 (min:s, 25-75% = 5:46-6:42) for men and 7:25 (25-75% = 6:49-10:21) for 8 women finishers (P = 0.023), and VO2 averaged 68 and 64% VO2max for the men and women during the circuit. Both men and women had high respiratory exchange ratios (>1.0) suggesting marked anaerobic energy contribution. Physiological variables associated with circuit time were assessed by backward stepwise regression yielding a significant model that included only peak work rate during arm cranking exercise as a function of circuit completion time across men and women combined (P < 0.001). For men, but especially for women, the time required for the simulated victim drag (68.2 kg mannequin) was positively correlated with total time to complete the other circuit elements (r = 0.51, r = 0.96 respectively). The simple correlation between circuit time and VO2max (mL/kg/min) revealed poor relationships for men (r = -0.37, P > 0.05) and women (r = 0.20, P > 0.05). These data demonstrated that upper body fitness as reflected by peak work rate during arm cranking correlated with total circuit time for the men and women in our population sample. [ABSTRACT FROM AUTHOR]

The purpose of the study was to characterise statistically the inherent fluctuations in breath-by-breath measurements of pulmonary gas exchange (oxygen uptake and carbon dioxide output, VO2 and VCO2, respectively) and pulmonary ventilation (VE) in patients with chronic obstructive pulmonary disease (COPD) and to compare them with those of healthy control subjects. Thirty subjects with COPD [mean (SD): 67 (6) years old; forced expiratory volume in 1 min, FEV1 1.25( 0.18) l; 42 (6)% predicted FEV1] and 12 healthy subjects [31 (3) years old; FEV1 3.62 (0.54) l; 99 (8)% predicted FEV1] performed exercise tests on a cycle ergometer at a constant work rate of moderate intensity. Steady-state exercise values for VO2, VCO2 and VE were 905 (96) ml·min–1, 847(90) ml·min–1 and 23 (3) l·min–1, respectively for the COPD patients and 1239(89) ml·min–1, 1191(84) ml·min–1 and 37(3) l·min–1, respectively, for the healthy controls. The breath-by-breath fluctuations were well characterised by a Gaussian density-probability function with breath-to-breath autocorrelations that were not significantly different from 0, up to four subsequent breaths. Its magnitude varied among variables, but was independent of the signal amplitude for the same subject and variable. With ratios of amplitude of fluctuation:signal of around 10%, typical of the patients studied, the resolution of time constants and amplitude were ≅9 s and ≅100 ml·min–1, respectively for VO2 or VCO2 with one repetition. [ABSTRACT FROM AUTHOR]

To be clinically useful as indices reflective of altered physiological function consequent to interventions in patients with chronic obstructive pulmonary disease (COPD), the time constant (τ) and steady-state amplitude of the kinetic responses for oxygen uptake (VO2) carbon dioxide output (VCO2) ventilation (VE) and heart rate (HR) have to be appropriately differentiable and reproducible. We therefore assessed the reproducibility of τ and steady state amplitude values in 41 patients with severe COPD [mean (SD)] [forced expiratory volume in 1 s=41 (7)% predicted], aged 64 (5) years. Of the total, 6 of the patients (15%) did not produce breath-by-breath data of sufficient quality to warrant kinetic analysis. The remaining 35 patients completed two moderate-intensity 10 mm square-wave exercise tests separated by 2 h, both before and after an endurance training programme. Tests were conducted on an electromagnetically-braked cycle ergometer at an exercise intensity corresponding to 80% of the estimated lactate threshold (θLa) or 50% of peak oxygen uptake if °La was insufficiently differentiable. Breath-by-breath measurements of VO2, VCO2, VE and HR were averaged into 10 s bins and the on-transient response kinetics were estimated using a mono-exponential model. Analysing the pre-training and the post-training test 1 and test 2 comparisons together, the test 1-test 2 differences were not significantly different from 0 for either τ or A. The standard deviation of the test 1-test 2 differences allowed us to define the magnitude of change that would reach statistical significance. For τ, this averaged some 8, 10, 11 and 8 s, for VO2, VCO2, VE and HR, respectively, for a one-tailed paired-comparisons test (i.e. appropriate for assessing hypothesised improvements resulting from an intervention); for a two-tailed comparison, the differences were approximately 2 s greater. The corresponding one-tailed values for A were 100 ml·min-1, 95 ml·min-1, 2.5 1 mm-1 and 4 beats·min-1, respectively; the two-tailed values were 10%-15% greater. We therefore conclude that both τ and A for moderate-intensity exercise can be reproducibly estimated in patients with COPD when the data set provides a sufficiently large amplitude of response and sufficiently low sample variability to allow appropriate parameter estimation. [ABSTRACT FROM AUTHOR]

A self-calibrating fully automatic instrument for the measurement of oxygen consumption, carbon dioxide production and the respiratory quotient of mechanically ventilated patients has been developed. The instrument is based on commercially available conventional oxygen and carbon dioxide gas analysers and a domestic natural gas volumetric flow meter. The distribution of the different gas flows, i.e. calibration gases, the inspiratory mixture sample and the expiratory mixture sample, are controlled by in inexpensive microprocessor, which also performs the necessary calculations. The accuracy of the instrument has been validated by bench tests. The present prototype has been in use for over 3000 h without major failures. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to determine whether the linear relationship between CO2 output ( V˙CO2) and pulmonary ventilation ( V˙E) is altered during incremental cycling performed after exercise-induced metabolic acidosis. Ten untrained, female subjects performed two incremental cycling tests (15 W · min−1 up to 165 W) on separate days. One incremental exercise test was conducted without prior exercise, whereas the other test was preceded by a 1-min bout of maximal cycling. The ventilatory equivalent for O2 ( V˙E/ V˙O2) was only elevated above control values at 15–60 W during incremental cycling performed after high-intensity exercise. In contrast, the ventilatory equivalent for CO2 ( V˙E/ V˙CO2) was significantly increased above control levels at nearly every work stage of incremental work (all except 165 W). Hyperventilation relative to V˙CO2 was confirmed by the significantly lower end-tidal CO2 tension ( PETCO2) obtained throughout the incremental cycling that was performed after high-intensity exercise (except at 165 W). V˙E and V˙CO2 were significantly correlated under both treatment conditions ( r > 0.99; P < 0.001). Moreover, both the slope and y-intercept of the linear regression were found to be significantly elevated during the incremental cycling performed after high-intensity cycling compared to control conditions ( P < 0.01). The increase in the slope of the V˙E- V˙CO2 relationship during incremental exercise performed under these conditions does not represent an uncoupling of V˙E from V˙CO2, but could be accounted for by the significantly lower PETCO2 observed during exercise. [ABSTRACT FROM AUTHOR]

An estimated average CO2 output from Etna's summit craters in the range of 13±3 Mt/a has recently been determined from the measured SO2 output and measured CO2/SO2 molar ratios. To this amount the CO2 output emitted diffusely from the soil (≈ 1 Mt/a) and the amount of CO2 dissolved in Etna's aquifers (≈ 0.25 Mt/a) must be added. Data on the solubility of CO2 in Etnean magmas at high temperature and pressure allow the volume of magma involved in the release of such an amount of this gas to be estimated. This volume of magma (≈ 0.7 km3/a) is approximately 20 times greater than the volume of magma erupted annually during the period 1971–1995. On the basis of C-isotopic data of CO2 collected in the Etna area and of new hypotheses on the source of Mediterranean magmas, significant contributions of CO2 from non-magmatic sources to the total output from Etna are unlikely. Such large outputs of CO2 and also of SO2 from Etna could be due to an anomalously shallow asthenosphere beneath the volcano that allows a continuous escape of gases toward the surface, even without migration of magma. [ABSTRACT FROM AUTHOR]

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