Normative Peak Cardiopulmonary Exercise Test Responses in Canadian Adults Aged ≥40 Years.

BACKGROUND: Up-to-date normative reference sets for cardiopulmonary exercise testing (CPET) are important to aid in the accurate interpretation of CPET in clinical or research settings. RESEARCH QUESTION: This study aimed to (1) develop and externally validate a contemporary reference set for peak CPET responses in Canadian adults identified with population-based sampling; and (2) evaluate previously recommended reference equations for predicting peak CPET responses. STUDY DESIGN AND METHODS: Participants were healthy adults who were ≥40 years old from the Canadian Cohort Obstructive Lung Disease who completed an incremental cycle CPET. Prediction models for peak CPET responses were estimated from readily available participant characteristics (age, sex, height, body mass) with the use of quantile regression. External validation was performed with a second convenience sample of healthy adults. Peak CPET parameters that were measured and predicted in the validation cohort were assessed for equivalence (two one-sided tests of equivalence for paired-samples and level of agreement (Bland-Altman analyses). Two one-sided tests of equivalence for paired samples assessed differences between responses in the derivation cohort using previously recommended reference equations. RESULTS: Normative reference ranges (5th-95th percentiles) for 28 peak CPET parameters and prediction models for 8 peak CPET parameters were based on 173 participants (47% male) who were 64 ± 10 years old. In the validation cohort (n = 84), peak CPET responses that were predicted with the newly generated models were equivalent to the measured values. Peak cardiac parameters predicted by the previously recommended reference equations by Jones and colleagues and Hansen and colleagues were significantly higher. INTERPRETATION: This study provides reference ranges and prediction models for peak cardiac, ventilatory, operating lung volume, gas exchange, and symptom responses to incremental CPET and presents the most comprehensive reference set to date in Canadian adults who were ≥40 years old to be identified with population-based sampling.

Validity of maximal oxygen consumption prediction equations in young Saudi females.

OBJECTIVES: To determine the applicability of Jones, Hansen, and Wasserman predictive equations for maximal oxygen consumption (VO2max) in Saudi females.  Methods: This cross-sectional study was conducted at Imam Abdulrahman Bin Faisal University, Dammam, Kingdom of Saudi Arabia, between March and May 2017. Maximal oxygen consumption was measured directly through the COSMED system for cardiopulmonary exercise testing in 102 girls with normal body mass index (19-25 years old). Maximal oxygen consumption was indirectly predicted by Jones, Hansen, and Wasserman equations. Paired t-test, Pearson correlation, and Bland-Altman plot were used for comparison, correlation, and agreement analysis. Results: The difference between the mean and standard deviation (±SD) VO2max values of the direct measurement (27.39±4.06 ml/kg-1/min-1), and the Jones (35.19±2.12 ml/kg-1/min-1), Hansen (33.64±0.24 ml/kg-1/min-1), and Wasserman (35.20±0.17 ml/kg-1/min-1) equations, was statistically significant (p less than 0.001). Bland-Altman plot analysis suggested a lack of agreement between direct and predicted VO2max. Pearson correlation failed to reveal any correlation between direct VO2max and VO2max calculated with any of the 3 equations. Conclusion: Jones, Hansen, and Wasserman equations for prediction of VO2max cannot be justified in the studied population. For the better prediction of VO2max, either these equations should be modified, or a new equation should be developed for the Saudi population.

Applying current normative data to prognosis in heart failure: The Fitness Registry and the Importance of Exercise National Database (FRIEND).

INTRODUCTION: Percent of predicted peak VO2 (ppVO2) is considered a standard measure for establishing disease severity, however, there are known limitations to traditional normative values. This study sought to compare ppVO2 from the newly derived "Fitness Registry and the Importance of Exercise: a National Database" (FRIEND) registry equation to conventional prediction equations in a clinical cohort of patients undergoing cardiopulmonary exercise testing (CPX). METHODS AND RESULTS: We selected 1094 patients referred for evaluation of heart failure (HF) symptoms who underwent CPX. ppVO2 was calculated using the FRIEND, Wasserman/Hansen and Jones equations. Participants were followed for a median of 4.5 years [Interquartile range 3.5-6.0] for the composite endpoint of death, advanced HF therapy, or acute decompensated HF requiring hospital admission. Mean age was 48 ±â€¯15 years and 62% were female. The FRIEND registry equation predicted the lowest ppVO2 (measured/predicted; 71 ±â€¯31%), compared to the Wasserman/Hansen (74 ±â€¯29%) and Jones equations (83 ±â€¯33%) (p < 0.001). All expressions of peak VO2 were significant as univariate predictors of outcome with no significant differences between equations on pairwise analysis of receiver operating characteristic curves. When compared at a similar threshold of ppVO2 the event rate was significantly lower in the FRIEND registry equation versus the currently used Wasserman and Jones equations. CONCLUSION: The use of the newly derived FRIEND registry equation predicts HF outcomes; however, it appears to predict a higher predicted VO2; the clinical implication being a lower threshold of percent predicted peak VO2 should be considered when risk stratifying patients with HF.

Determining the best percent-predicted equation for estimated VO2 peak by a 1-km moderate perceptually-regulated treadmill walk to predict mortality in outpatients with cardiovascular disease.

OBJECTIVES: To determine the prognostic ability of established percent-predicted equations of peak oxygen consumption (%PRED) estimated by a moderate submaximal walking test in a large cohort of outpatients with cardiovascular disease (CVD). DESIGN: Population-based prospective study. METHODS: A total of 1442 male patients aged 25-85 years at baseline, underwent a moderate perceptually-regulated (11-13 on the 6-20 Borg scale) treadmill walk (1k-TWT) for peak oxygen consumption estimation (VO2 peak). %PRED was derived from ACSM, Ades et al, Morris et al, and the Wasserman/Hansen equations, and their prognostic performance was assessed. Overall mortality was the end point. Participants were divided into quartiles of %PRED, and mortality risk was estimated using a Cox regression model. RESULTS: During a median 8.2year follow-up, 167 all-cause deaths occurred. The Wasserman/Hansen equation provided the highest prognostic value. Mortality rate was lower across increasing quartiles of %PRED. Compared to the first quartile, after adjustment for confounders, the mortality risk decreased for the second, third, and fourth quartiles, with HRs of 0.75 (95% CI 0.44-1.29, p=0.29), 0.67 (95% CI 0.38-1.18, p=0.17), and 0.37 (95% CI 0.10-0.78, p=0.009), respectively (p for trend <0.0001). Each 1% increase in %PRED conferred a 4% improvement in survival. CONCLUSIONS: The percent-predicted VO2 peak determined by Wasserman/Hansen equations applied to the 1k-TWT is inversely and significantly related to survival in cardiac outpatients. The 1k-TWT is a simple and useful tool for stratifying mortality risk in patients participating in secondary prevention programs.

Bayesian model comparison in nonlinear BOLD fMRI hemodynamics.

Nonlinear hemodynamic models express the BOLD (blood oxygenation level dependent) signal as a nonlinear, parametric functional of the temporal sequence of local neural activity. Several models have been proposed for both the neural activity and the hemodynamics. We compare two such combined models: the original balloon model with a square-pulse neural model (Friston, Mechelli, Turner, & Price, 2000) and an extended balloon model with a more sophisticated neural model (Buxton, Uludag, Dubowitz, & Liu, 2004). We learn the parameters of both models using a Bayesian approach, where the distribution of the parameters conditioned on the data is estimated using Markov chain Monte Carlo techniques. Using a split-half resampling procedure (Strother, Anderson, & Hansen, 2002), we compare the generalization abilities of the models as well as their reproducibility, for both synthetic and real data, recorded from two different visual stimulation paradigms. The results show that the simple model is the better one for these data.

Glycolytic sequence and respiration of Debaryomyces hansenii as compared to Saccharomyces cerevisiae.

The fermentation and respiration activities of Debaryomyces hansenii were compared with those of Saccharomyces cerevisiae grown to stationary phase with high respiratory activity. It was found that: (a) glucose consumption, fermentation and respiration were lower than for S. cerevisiae; (b) fasting produced a much smaller decrease of respiration; (c) glucose consumed and not transformed to ethanol was higher; (d) in S. cerevisiae, full oxygenation prevented ethanol production but this effect was reversed by CCCP, whereas D. hansenii still showed some ethanol production under aerobiosis, which was moderately increased by CCCP. ATP levels were similar in the two yeasts. Levels of glycolytic intermediaries after glucose addition, and enzyme activities, indicated that the main difference and limiting step to explain the lower fermentation of D. hansenii is phosphofructokinase activity. Respiration and fermentation, which are lower in D. hansenii, compete for the re-oxidation of reduced nicotinamide adenine nucleotides; this competition, in turn, seems to play a role in defining the fermentation rates of the two yeasts. The effect of CCCP on glucose consumption and ethanol production also indicates a role of ADP in both the Pasteur and Crabtree effects in S. cerevisiae but not in D. hansenii. D. hansenii shows an alternative oxidase, which in our experiments did not appear to be coupled to the production of ATP.

Xylose metabolism in Debaryomyces hansenii UFV-170. Effect of the specific oxygen uptake rate.

The new yeast Debaryomyces hansenii UFV-170 was tested in this work in batch experiments under variable oxygenation conditions. To get additional information on its fermentative metabolism, a stoichiometric network was proposed and checked through a bioenergetic study performed using the experimental data of product and substrate concentrations. The yeast metabolism resulted to be practically inactive under strict oxygen-limited conditions (qO2 = 12.0 mmol(O2) C-mol(DM)(-1) h(-1)), as expected by the impossibility of regenerating NADH2+. Significant fractions of the carbon source were addressed to both respiration and biomass growth under excess oxygen levels (qO2 > or = 55.0 mmol(O2) C-mol(DM)(-1) h(-1)), thus affecting xylitol yield (Y(P/S) = 0.41-0.52 g g(-1)). Semi-aerobic conditions (qO2 = 26.8 mmol(O2) C-mol(DM)(-1) h(-1)) were able to ensure the best xylitol production performance (Pmax = 76.6 g L(-1)), minimizing the fractions of the carbon source addressed either to respiration or biomass production and increasing Y(P/S) up to 0.73 g g(-1). An average P/O ratio of about 1.0 mol(ATP) mol(O)(-1) allowed estimation of the main kinetic-bioenergetic parameters of the biosystem. The overall ATP requirements of biomass were found to be particularly high and dependent on the oxygen availability in the medium as well as on the physiological state of the culture. Under semi-aerobic and aerobic conditions, they varied in the ranges 13.5-15.4 and 9.74-10.2 mol(ATP) C-mol(DM)(-1), respectively, whereas during the best semi-aerobic bioconversion they progressively increased from 5.68 to 24.7 mol(ATP) C-mol(DM)(-1). After a starting phase of adaptation to the medium, the cell achieved a phase of decelerated growth during which its excellent xylose-to-xylitol capacity kept almost constant after 112 h up to the end of the run.

Carbon material and bioenergetic balances of xylitol production from corncobs by Debaryomyces hansenii.

The effect of oxygenation on xylitol production by the yeast Debaryomyces hansenii has been investigated in this work using the liquors from corncob hydrolysis as the fermentation medium. The concentrations of consumed substrates (glucose, xylose, arabinose, acetate and oxygen) and formed products (xylitol, arabitol, ethanol, biomass and carbon dioxide) have been used, together with those previously obtained varying the hydrolysis technique, the level of adaptation of the microorganism, the sterilization procedure and the initial substrate and biomass concentrations, in carbon material balances to evaluate the percentages of xylose consumed by the yeast for the reduction to xylitol, alcohol fermentation, respiration and cell growth. The highest xylitol concentration (71 g/L) and volumetric productivity (1.5 g/L.h) were obtained semiaerobically using detoxified hydrolyzate produced by autohydrolysis-posthydrolysis, at starting levels of xylose (S(0)) and biomass (X(0)) of about 100 g/L and 12 g(DM)/L, respectively. No less than 80% xylose was addressed to xylitol production under these conditions. The experimental data collected in this work at variable oxygen levels allowed estimating a P/O ratio of 1.16 mol(ATP)/mol(O). The overall ATP requirements for biomass production and maintenance demonstrated to remarkably increase with X(0) and for S(0) >or= 130 g/L and to reach minimum values (1.9-2.1 mol(ATP)/C-mol(DM)) just under semiaerobic conditions favoring xylitol accumulation.

Physiological behaviour of Hanseniaspora guilliermondii in aerobic glucose-limited continuous cultures.

The physiology of Hanseniaspora guilliermondii was studied under aerobic glucose-limited conditions using the accelerostat procedure (continuous acceleration of dilution rate) and classical chemostat cultures. By both cultivation techniques this yeast was found to be Crabtree-positive. Up to a dilution rate of 0.25 h(-1), glucose was completely metabolised into biomass, glycerol and carbon dioxide. Above this value, an increase in the dilution rate was accompanied by the production of other metabolites like ethanol, acetic and malic acids. Biomass yield during the purely oxidative growth was 0.49 g g(-1) and decreased to 0.26 g g(-1) for D=0.34 h(-1). A maximal specific ethanol production rate of 1.36 mmol g(-1) h(-1) and a maximal ethanol yield of 0.05 g g(-1) were achieved at D=0.34 h(-1).

Effect of temperature on oxygen stores during aerobic diving in the freshwater turtle Mauremys caspica leprosa.

Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15 degrees, 25 degrees, and 35 degrees C) and during the thermal transient (30 degrees-15 degrees C) induced by immersion in cold water. The term "aerobic dive limit" has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15 degrees C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30 degrees-15 degrees C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.