Respiratory Gas Exchange Measurements Research Articles

194 Evaluation of a method to optimize diets of individual dairy cows to maximize income over feed cost

Abstract Recent optimization methods have demonstrated the potential to maximize marginal profits in beef (Marques et al., 2020) and dairy (Campos et al., 2023) by optimizing diet formulation. These methods present an opportunity to explore how diets could be optimized for individual dairy cows, such as in a closed-loop precision feeding system. Therefore, our objectives were to 1) compare individual income over feed costs (IOFC), calculated with observed dry matter intake (DMI), milk yield (MY), milk protein and milk fat, with a predicted IOFC for the same diet and cows using the NASEM (2021) model, and 2) optimize the inclusion rate of ingredients in the diet to maximize predicted IOFC. Previously, 20 multiparous (lactation 2 through 4) and 9 primiparous cows, ranging from 22 to 472 d in milk (DIM), were housed in a free-stall pen at the Ontario Dairy Research Centre (Canada) equipped with sensors to record DMI, body weight (BW; walk-over-weight) and body condition score (BCS; DeLavel 3D camera), in addition to daily MY, weekly milk component tests, and 4 X/d respiratory gas exchange measurements (GreenFeed, C-Lock Inc, USA) for estimation of daily energy flows (Kedzierski, 2020). Weekly means for each cow were used to evaluate IOFC in this study (n = 116). Each IOFC was calculated as milk revenue minus total feed cost. Milk revenue was calculated from milk fat, protein and other solids, consistent with pricing on Canadian dairy farms. The observed IOFC was calculated using the observed MY, milk components and DMI, and the same diet formulation and costs for all cows, whereas the predicted IOFC estimated these values using the NASEM (2021) model with all available observed animal inputs (e.g., BW, BCS, DIM). However, the observed DMI and MY had to be provided initially for the model, as the DMI prediction equation requires a target MY, but the prediction of MY requires DMI. Final predicted DMI and MY values were used in the calculation of predicted IOFC. The differential evolution algorithm from the ‘SciPy’ package (v 1.11.4) in python (v 3.12.0) was used to maximize IOFC by adjusting the inclusion of wheat straw, alfalfa silage, corn silage and high moisture corn grain, while fixing minerals to their original proportions. Overall, the concordance correlation coefficient (CCC) indicated moderate agreement (0.62) between the predicted IOFC and observed IOFC and good agreement (0.99) between the predicted IOFC and the optimized IOFC, suggesting the optimization method was able to select diets to meet a similar objective. Results indicate that a strategy is needed to minimize the residual error between predicted and observed values for individual cows, such as algebraic reparameterization of the NASEM model, before using an optimization method to automatically formulate diets.

Estimation of physiological exercise thresholds based on dynamical correlation properties of heart rate variability.

Aerobic and anaerobic thresholds of the three-zone exercise model are often used to evaluate the exercise intensity and optimize the training load. Conventionally, these thresholds are derived from the respiratory gas exchange or blood lactate concentration measurements. Here, we introduce and validate a computational method based on the RR interval (RRI) dynamics of the heart rate (HR) measurement, which enables a simple, yet reasonably accurate estimation of both metabolic thresholds. The method utilizes a newly developed dynamical detrended fluctuation analysis (DDFA) to assess the real-time changes in the dynamical correlations of the RR intervals during exercise. The training intensity is shown to be in direct correspondence with the time- and scale-dependent changes in the DDFA scaling exponent. These changes are further used in the definition of an individual measure to estimate the aerobic and anaerobic threshold. The results for 15 volunteers who participated in a cyclo-ergometer test are compared to the benchmark lactate thresholds, as well as to the ventilatory threshods and alternative HR-based estimates based on the maximal HR and the conventional detrended fluctuation analysis (DFA). Our method provides the best overall agreement with the lactate thresholds and provides a promising, cost-effective alternative to conventional protocols, which could be easily integrated in wearable devices. However, detailed statistical analysis reveals the particular strengths and weaknessess of each method with respect to the agreement and consistency with the thresholds-thus underlining the need for further studies with more data.

Redirected Attention and Impaired Recognition Memory during Exhaustive Cycling Has Implications for Information Processing Models of Effort-Regulation.

Twenty male participants performed two laboratory ramped cycling tests beginning at 50 W and increasing by 0.25 W/s until volitional exhaustion. Ratings of perceived exertion, heart rate and respiratory gas exchange measures were recorded during the first test. During the second test, participants listened to a list of spoken words presented through headphones at a rate of one word every 4 s. Afterwards, their recognition memory for the word pool was measured. Recognition memory performance was found to have strong negative correlations with perceived exertion (p < 0.0001), percentage of peak power output (p < 0.0001), percentage of heart rate reserve (p < 0.0001), and percentage of peak oxygen uptake (p < 0.0001). The results show that, as the physiological and psychophysiological stress of cycling intensified, recognition memory performance deteriorated. This might be due to impairment of memory encoding of the spoken words as they were presented, or because of a diversion of attention away from the headphones, perhaps towards internal physiological sensations as interoceptive sources of attentional load increase with exercise intensity. Information processing models of pacing and performance need to recognise that an athlete's capacity to attend to and process external information is not constant, but changes with exercise intensity.

Responses to exercise in systemicsclerosis-associated interstitial lung disease.

Pulmonary complications in systemic sclerosis (SSc) significantly increase morbidity and mortality. Our aim was to determine the factors limiting exercise capacity in SSc patients with and without interstitial lung disease (ILD), and to identify and quantify abnormalities during exercise that might assist in clinical assessment of this complication. Fifteen patients with SSc and ILD(SSc-ILD) were compared with 10 patients with SSc without ILD and 9age- and sex-matched normal volunteers. Subjects performed symptom-limited incremental treadmill exercise with online measurement of respiratory gas exchange, arterial blood gas sampling and measurement of neurohormones in venous blood. Patients with SSc-ILD had lower exercise capacity than SSc patients without ILD or normal subjects (peak oxygen consumption (PV̇O2 ) (17.1 [4.2] vs. 22.0 [4.7] and 23.0 [5.4] ml kg-1 min-1 , respectively, mean [SD], p < 0.01 ANOVA), but PV̇O2 did not correlate with static pulmonary function measurements. Ventilatory equivalent for CO2 (V̇E/V̇CO2 ; nadir) was higher in SSc-ILD patients than the other two groups (36.6 [8.0] vs. 29.9 [4.4] and 30.0 [2.5], p < 0.005) as were peak exercise dead-space tidal volume ratio (0.44 [0.06] vs. 0.26 [0.09] and 0.26 [0.05], p < 0.001) and peak exercise alveolar-arterial difference (28.9 [16.9] vs. 18.8 [14.0] and 11.5 [6.9] mmHg, p < 0.05). Atrial natriuretic peptide was elevated in both SSc patient groups. SSc-ILD results in lower exercise capacity than SSc without ILD, and abnormalities of gas exchange are seen. The possible use of cardiopulmonary exercise testing to identify disease and quantify impairment in SSc-ILD merits further study.

The Lognormal Lung: A new approach to quantifying lung inhomogeneity in COPD.

Early diagnosis and disease phenotyping in COPD are currently limited by the use of spirometry, which may remain normal despite significant small-airways disease and which may not fully capture a patient's underlying pathophysiology. In this study we explored the use of a new non-invasive technique that assesses gas-exchange inhomogeneity in patients with COPD of varying disease severity (according to GOLD Stage), compared with age-matched healthy controls. The technique, which combines highly accurate measurement of respiratory gas exchange using a bespoke molecular flow sensor and a mechanistic mathematical model of the lung, provides new indices of lung function: the parameters σCL, σCd, and σVD represent the standard deviations of distributions for alveolar compliance, anatomical deadspace and vascular conductance relative to lung volume, respectively. It also provides parameter estimates for total anatomical deadspace and functional residual capacity (FRC). We demonstrate that these parameters are robust and sensitive, and that they can distinguish between healthy individuals and those with mild-moderate COPD (stage 1-2), as well as distinguish between mild-moderate COPD (stage 1-2) and more severe (stage 3-4) COPD. In particular, σCL, a measure of unevenness in lung inflation/deflation, could represent a more sensitive non-invasive marker of early or mild COPD. In addition, by providing a multi-dimensional assessment of lung physiology, this technique may also give insight into the underlying pathophysiological phenotype for individual patients. These preliminary results warrant further investigation in larger clinical research studies, including interventional trials.

Abstract 16772: Aerobic Capacity (VO 2peak ) in Congenital Heart Disease: Prognostic Implications

Introduction: Cardiopulmonary exercise testing provides information about functional capacity via direct measurement of respiratory gas exchange. Whether peak oxygen consumption during exercise (VO 2peak ) is predictive of outcomes in patients with congenital heart disease is controversial. Hypothesis: VO 2peak has prognostic implications for death, left ventricular assist device (LVAD) placement, and cardiac transplant in adult patients with congenital cardiac diseases. Methods: Congenital heart disease patients were selected from a registry of cardiac patients who completed a VO 2peak exercise test at Washington University School of Medicine between May 1993 and October 2012. Diagnoses were verified by chart review and classified according to American Heart Association guidelines. Outcome data were verified via medical record, Social Security Death Index, or phone interview. A Cox proportional-hazard regression analysis was used to investigate the association between patient survival time and one or more predictor variables. Survival time was defined as the time elapsed between VO 2peak test and the earliest outcome of death, heart transplant, or LVAD placement. Results: The sample included 149 patients (49% women, mean ± SD age of 33.4 ± 11.5 years and body mass index of 25.7 ± 5.4 kg/m 2 ). Mean follow-up time was 11.8 ± 3.2 years. Mean VO 2peak was 23.0 ± 7.3 mL/kg/min for men and 20.0 ± 6.4 mL/kg/min for women. Age was comparable between men and women in the sample. In the univariate analysis, higher VO 2peak was associated with longer event-free survival time (HR 0.91, 95% CI 0.85-0.98, p= 0.01). In the multivariable analysis, higher VO 2peak was shown to be protective, independent of age and sex (HR 0.90, 95% CI 0.83-0.97, p=0.004). Conclusions: Among patients with congenital cardiac disease, higher VO 2peak independently predicted longer event-free survival. VO 2peak is a valuable clinical prognostic tool for patients with congenital cardiac disease.

The use of stoichiometric bioenergetics to elucidate metabolic energy substrate use and specific dynamic action in cultured juvenile spiny lobsters (Sagmariasus verreauxi) of different nutritional status

Simultaneous measurements of nitrogenous (ammonia and urea) excretion and respiratory gas (O2 and CO2) exchange provide a non-destructive stoichiometric bioenergetic approach to elucidate metabolic energy substrate use which has rarely been used with aquatic ectotherms due to previous difficulties in measuring total CO2 excretion. This study examined metabolic energy substrate use and specific dynamic action (SDA) in cultured spiny lobster, Sagmariasus verreauxi, of different nutritional status. SDA magnitude calculated by stoichiometry was compared to a traditional composite oxycalorific coefficient approach. Protein synthesis can account for a large part of SDA in aquatic ectotherms. This study used a protein synthesis inhibitor cycloheximide to investigate the contribution of cycloheximide-sensitive protein synthesis to SDA and the effect of cycloheximide on nitrogenous and CO2 excretion. Lobsters were subjected to five treatments: 2-day fasted juveniles sham injected with saline (FS treatment); 2-day fasted juveniles injected with cycloheximide (FC treatment); 10-day starved juveniles injected with cycloheximide (SC treatment); post-prandial juveniles fed squid Nototodarus sloanii (FED treatment) and; post-prandial juveniles injected with cycloheximide (FEDC treatment). Protein was the primary energy substrate (65% of oxygen consumption) for 2-day fasted juveniles, with lipid accounting for the remainder (35%). After 10-day starvation lipid became the main substrate, indicating lipid oxidation increased with extended fasting. Following feeding, protein contribution remained above 50%, while lipid (0–43%) and carbohydrate (0–37%) provided significant energy at different time periods, indicating besides protein appropriate proportions of non-protein ingredients are also essential to lobsters. SDA magnitude in FED and FEDC treatments estimated by the traditional approach was 10.5 and 0.4 J g−1, respectively, indicating S. verreauxi expended 96% of post-prandial energy on protein synthesis and that decapod protein synthesis can account for one of the highest proportions of SDA in aquatic ectotherms. SDA magnitude in the FED treatment evaluated by stoichiometry (12.6 J g−1) was comparable to the traditional approach. Interestingly, stoichiometry was not applicable in the FEDC treatment as the respiratory quotient exceeded the theoretical maximum under aerobic conditions. Cycloheximide did not affect CO2 excretion among all treatments or nitrogenous excretion among unfed treatments, while the post-treatment total nitrogenous excretion reduced in fed lobsters. The combined measurement of substrate use and SDA potentially helps optimize the feed to achieve sustainable aquaculture. However, more research is required to decipher limitations and the applicability of stoichiometry for crustaceans.

Disadvantages of Automated Respiratory Gas Exchange Analyzers.

The use of automated gas exchange analysis systems in exercise studies is common throughout the industrialized world and are frequently used in sports medicine laboratories for the measurement of maximal oxygen uptake (VO2max), as an integrative parameter that allows the physical condition to be assessed, in spite of its limitations. Actually, the fundamental principles behind the measurement of respiratory gas exchange (RGE) have not changed for a century. It was used a manual Douglas bag method together with separate chemical analyses. The need for faster and more efficient techniques, has conditioned the traditional procedures and determined the emergence of automated systems. However, the validity and reliability of all these different systems is not well known. The common features associates with these systems, also have disadvantages that must be evaluated at the time of the acquisition of an automated equipment: (1) regular quality control checks, which entails other added economic costs, (2) the validity and reliability of the results, which it is necessary to verify, and (3) the user does not know the equations that determine the values of oxygen consumption and carbon dioxide production. This work aims to clarify the disadvantages of these automated systems. At maximum intensities, the variation of VO2max or VO2peak can be very significant in athletes and even more relevant in sick people undergoing a training program. Therefore, considerable care is needed when comparing RGE data with automated systems.New and NoteworthyActually, stress tests are more conveniently performed with automated systems. It is necessary to examine the validity and reliability of automated respiratory gas exchange systems. The algorithms incorporated in the software, apart from being a “mystery,” show differences with respect to the data provided.

Sex-Related Differences in the Maximal Lactate Steady State.

The maximal lactate steady state (MLSS) is one of the factors that differentiates performance in aerobic events. The purpose of this study was to investigate the sex differences in oxygen consumption (VO2), heart rate (HR), and the respiratory exchange ratio (RER) at the MLSS in well-trained distance runners. Twenty-two (12 female, 10 male) well-trained distance runners (23 ± 5.0 years) performed multiple 30-min steady-state runs to determine their MLSS, during which blood lactate and respiratory gas exchange measures were taken. To interpret the MLSS intensity as a training tool, runners completed a time-to-exhaustion (TTE) run at their MLSS. The relative intensity at which the MLSS occurred was identical between males and females according to both oxygen consumption (83 ± 5 %O2max) and heart rate (89 ± 7 %HRmax). However, female runners displayed a significantly lower RER at MLSS compared to male runners (p < 0.0001; 0.84 ± 0.02 vs. 0.88 ± 0.04, respectively). There was not a significant difference in TTE at MLSS between males (79 ± 17 min) and females (80 ± 25 min). Due to the observed difference in the RER at the MLSS, it is suggested that RER derived estimates of MLSS be sex-specific. While the RER data suggest that the MLSS represents different metabolic intensities for males and females, the relative training load of MLSS appears to be similar in males and female runners.

Effect of sodium bicarbonate on prolonged running performance: A randomized, double-blind, cross-over study.

BackgroundThe ability to sustain intense exercise seems to be partially limited by the body’s capability to counteract decreases in both intra- and extracellular pH. While the influence of an enhanced buffering capacity via sodium bicarbonate (BICA) on short-term, high-intensity exercise performance has been repeatedly investigated, studies on prolonged endurance performances are comparatively rare, especially for running. The aim of the following study was to assess the ergogenic effects of an oral BICA substitution upon exhaustive intensive endurance running performance.MethodIn a double-blind randomized cross-over study, 18 trained runners (VO2peak: 61.2 ± 6.4 ml•min-1•kg-1) performed two exhaustive graded exercise tests and two constant load tests (30 main at 95% individual anaerobic threshold (IAT) followed by 110% IAT until exhaustion) after ingestion of either sodium bicarbonate (BICA) (0.3 g/kg) or placebo (4 g NaCl) diluted in 700 ml of water. Time to exhaustion (TTE) in the constant load test was defined as the main outcome measure. Throughout each test respiratory gas exchange measurements were conducted as well as determinations of heart rate, blood gases and blood lactate concentration.ResultsTTE in the constant load test did not differ significantly between BICA and placebo conditions (BICA: 39.6 ± 5.6 min, placebo: 39.3 ± 5.6 min; p = 0.78). While pH in the placebo test dropped to a slightly acidotic value two minutes after cessation of exercise (7.34 ± 0.05) the value in the BICA trial remained within the normal range (7.41 ± 0.06) (p < 0.001). In contrast, maximum running speed (Vmax) in the exhaustive graded exercise test was significantly higher with BICA (17.4 ± 1.0 km/h) compared to placebo (17.1 ± 1.0 km/h) (p = 0.009). The numerical difference in maximum oxygen consumption (VO2peak) failed to reach statistical significance (BICA: 61.2 ± 6.4 ml•min-1•kg-1, placebo: 59.8 ± 6.4 ml•min-1•kg-1; p = 0.31). Maximum blood lactate was significantly higher with BICA compared to the corresponding placebo test (BICA: 11.1 ± 2.3 mmol/l, placebo: 8.9 ± 3.0 mmol/l; p < 0.001). At the end of exercise, an acidotic pH value was found in both exhaustive graded exercise tests (p = 0.002). BICA caused gastrointestinal side effects in 15 patients.ConclusionMaximal performance was enhanced significantly after BICA administration. The ergogenic effect of BICA in the exhaustive graded exercise test can most likely be attributed to an increased anaerobic glycolysis that is reflected by an accumulation of lactate. However, TTE in prolonged high-intensity running was not improved. Even at the end of exercise no severe metabolic acidosis was found. Metabolic acidification as one of the dominant factors causing muscular fatigue should therefore be reconsidered.Trial registrationGerman Clinical Trials Register (DRKS) DRKS00011284.

Cardiopulmonary Exercise Testing in Pediatrics.

Aerobic fitness is an important determinant of overall health. Higher aerobic fitness has been associated with many health benefits. Because myocardial ischemia is rare in children, indications for exercise testing differ in children compared with adults. Pediatric exercise testing is imperative to unravel the physiological mechanisms of reduced aerobic fitness and to evaluate intervention effects in children and adolescents with a chronic disease or disability. Cardiopulmonary exercise testing includes the measurement of respiratory gas exchange and is the gold standard for determining aerobic fitness, as well as for examining the integrated physiological responses to exercise in pediatric medicine. As the physiological responses to exercise change during growth and development, appropriate pediatric reference values are essential for an adequate interpretation of the cardiopulmonary exercise test.

Left Ventricular Assist Device as a Bridge to Recovery for Patients With Advanced Heart Failure

BackgroundLeft ventricular assist devices (LVADs) have been used as an effective therapeutic option in patients with advanced heart failure, either as a bridge to transplantation, as destination therapy, or in some patients, as a bridge to recovery. ObjectivesThis study evaluated whether patients undergoing an LVAD bridge-to-recovery protocol can achieve cardiac and physical functional capacities equivalent to those of healthy controls. MethodsFifty-eight male patients—18 implanted with a continuous-flow LVAD, 16 patients with LVAD explanted (recovered patients), and 24 heart transplant candidates (HTx)—and 97 healthy controls performed a maximal graded cardiopulmonary exercise test with continuous measurements of respiratory gas exchange and noninvasive (rebreathing) hemodynamic data. Cardiac function was represented by peak exercise cardiac power output (mean arterial blood pressure × cardiac output) and functional capacity by peak exercise O2 consumption. ResultsAll patients demonstrated a significant exertional effort as demonstrated with the mean peak exercise respiratory exchange ratio >1.10. Peak exercise cardiac power output was significantly higher in healthy controls and explanted LVAD patients compared with other patients (healthy 5.35 ± 0.95 W; explanted 3.45 ± 0.72 W; LVAD implanted 2.37 ± 0.68 W; and HTx 1.31 ± 0.31 W; p < 0.05), as was peak O2 consumption (healthy 36.4 ± 10.3 ml/kg/min; explanted 29.8 ± 5.9 ml/kg/min; implanted 20.5 ± 4.3 ml/kg/min; and HTx 12.0 ± 2.2 ml/kg/min; p < 0.05). In the LVAD explanted group, 38% of the patients achieved peak cardiac power output and 69% achieved peak O2 consumption within the ranges of healthy controls. ConclusionsThe authors have shown that a substantial number of patients who recovered sufficiently to allow explantation of their LVAD can even achieve cardiac and physical functional capacities nearly equivalent to those of healthy controls.

Respiratory Changes in Response to Cognitive Load: A Systematic Review

When people focus attention or carry out a demanding task, their breathing changes. But which parameters of respiration vary exactly and can respiration reliably be used as an index of cognitive load? These questions are addressed in the present systematic review of empirical studies investigating respiratory behavior in response to cognitive load. Most reviewed studies were restricted to time and volume parameters while less established, yet meaningful parameters such as respiratory variability have rarely been investigated. The available results show that respiratory behavior generally reflects cognitive processing and that distinct parameters differ in sensitivity: While mentally demanding episodes are clearly marked by faster breathing and higher minute ventilation, respiratory amplitude appears to remain rather stable. The present findings further indicate that total variability in respiratory rate is not systematically affected by cognitive load whereas the correlated fraction decreases. In addition, we found that cognitive load may lead to overbreathing as indicated by decreased end-tidal CO2 but is also accompanied by elevated oxygen consumption and CO2 release. However, additional research is needed to validate the findings on respiratory variability and gas exchange measures. We conclude by outlining recommendations for future research to increase the current understanding of respiration under cognitive load.

Sampling and analyzing alveolar exhaled breath condensate in mechanically ventilated patients: a feasibility study

Recent studies in spontaneously breathing subjects indicate the possibility of obtaining the alveolar fraction of exhaled breath condensate (aEBC). In critically ill mechanically ventilated patients, in whom microbial colonization of the upper airways is constant, collection of aEBC could considerably add to the ability of monitoring alveolar inflammation. We designed this study to test the feasibility of collecting aEBC in mechanically ventilated critically ill patients through a dedicated apparatus, i.e. a CO2 valve combined with a condenser placed in the expiratory limb of the ventilator circuit. We also aimed to assess the adequacy of the samples obtained by measuring different markers of oxidative stress and inflammation.We enrolled 40 mechanically ventilated patients, 20 with and 20 without acute respiratory distress syndrome (ARDS). Measurements of respiratory mechanics, gas exchange and hemodynamics were obtained with a standard ventilator circuit after 30 min of aEBC collection and after inserting the dedicated collecting apparatus. Data showed that intrinsic positive end-expiratory pressure, peak and plateau pressure, static compliance and airway resistance (Raw) were similar before and after adding the collecting apparatus in both ARDS and controls. Similarly, gas exchange and hemodynamic variables did not change and 30 min collection provided a median aEBC volume of 2.100 and 2.300 ml for ARDS and controls, respectively. aEBC pH showed a trend toward a slight reduction in the ARDS group of patients, as opposed to controls (7.83 (7.62–8.03) versus 7.98 (7.87–8.12), respectively, p = 0.055)). H2O2 was higher in patients with ARDS, compared to controls (0.09 (0.06–0.12) μM versus 0.03 (0.01–0.09) μM, p = 0.043), while no difference was found in proteins content, 8-isoprostane, 4-hydroxy-2-nonhenal.In conclusion, we demonstrate, in patients receiving controlled mechanical ventilation, that aEBC collection is feasible without detrimental effects on ventilator functioning, respiratory mechanics and gas exchange. In addition, we show that the sample obtained is appropriate for compounds analysis.

Prediction Of Maximal Mets And Ventilatory Threshold Using 6-minute Walk Test Distance And The Rating Of Perceived Exertion

The 6-minute walk test (6MWT) is a commonly used outcome measure in clinical exercise programs. The utility of predicting aerobic capacity (maxMETs) from the 6MWT is limited, however, due to biomechanical limitations related to maximal walking speed. This limitation also makes it difficult to prescribe training workloads from 6MWT performance. The latest exercise prescription guidelines suggest that threshold-based training may be superior to range-based training in clinical populations. It was hypothesized that the addition of the Rating of Perceived Exertion (RPE) to 6MWT distance could enhance the prediction of maximal METs from the 6MWT and increase its utility as a prescriptive tool. PURPOSE: To develop equations to predict maxMETs and ventilatory threshold ([email protected]) from 6MWT distance and terminal RPE. METHODS: Twenty-nine subjects between 40-76 years of age completed a treadmill VO2max test with direct measurement of respiratory gas exchange to identify maxMETs and [email protected] On a separate day subjects completed a 6MWT. At the conclusion of the 6MWT subjects rated their effort using the 6-20 Borg Scale. MaxMETs and [email protected] were predicted from 6MWT distance (m) and RPE using stepwise regression. The accuracy of the equations were determined using multiple correlation (R), R2, standard error of estimate (SEE), and coefficient of variation (CV). RESULTS: The resultant equations were: MaxMETs=6.428+.013 (6MWT distance)-.398 (RPE); R=.71, R2=.50, SEE=1.3, CV=13% [email protected] = 3.165 + .01 (6MWT distance) - .18 (RPE); R=.59, R2=.35, SEE=1.1, CV=15% CONCLUSION: It was found that maxMETs could be predicted with reasonable accuracy using 6MWT distance and RPE. [email protected] VT was not quite as robust, but the SEE of estimate was within 1.1 METs. These data suggest that the addition of RPE to 6MWT distance may aid in identifying both maximal and sustainable exercise workloads.

The effect of feeding on CO2 production and energy expenditure in ponies measured by indirect calorimetry and the 13C-bicarbonate technique

Energy expenditure (EE) can be estimated based on respiratory gas exchange measurements, traditionally done in respiration chambers by indirect calorimetry (IC). However, the 13C-bicarbonate technique (13C-BT) might be an alternative minimal invasive method for estimation of CO2 production and EE in the field. In this study, four Shetland ponies were used to explore the effect of feeding on CO2 production and EE measured simultaneously by IC and 13C-BT. The ponies were individually housed in respiration chambers and received either a single oral or intravenous (IV) bolus dose of 13C-labelled sodium bicarbonate (NaH13CO3). The ponies were fed haylage 3 h before (T−3), simultaneously with (T0) or 3 h after (T+3) administration of 13C-bicarbonate. The CO2 produced and O2 consumed by the ponies were measured for 6 h with both administration routes of 13C-bicarbonate at the three different feeding times. Feeding time affected the CO2 production (P<0.001) and O2 consumption (P<0.001), but not the respiratory quotient (RQ) measured by IC. The recovery factor (RF) of 13C in breath CO2 was affected by feeding time (P<0.01) and three different RF were used in the calculation of CO2 production measured by 13C-BT. An average RQ was used for the calculations of EE. There was no difference between IC and 13C-BT for estimation of CO2 production. An effect of feeding time (P<0.001) on the estimated EE was found, with higher EE when feed was offered (T0 and T+3) compared with when no feed was available (T−3) during measurements. In conclusion, this study showed that feeding time affects the RF and measurements of CO2 production and EE. This should be considered when the 13C-BT is used in the field. IV administration of 13C-bicarbonate is recommended in future studies with horses to avoid complex 13C enrichment-time curves with maxima and shoulders as observed in several experiments with oral administration of 13C-bicarbonate.

Caffeine With and Without Sugar: Individual Differences in Physiological Responses During Rest

Background: The consumption of caffeine with and without sugar is endemic, but little is known about variation in individual physiological responses at rest. We have previously shown that the ingestion of caffeine with sugar increased the rate of carbon dioxide production more than when sugar alone was consumed. Objective: The aim of this study was to determine the effect of the ingestion of caffeine, sugar, and caffeine with sugar on carbon dioxide production and heart rate. Methods: In a crossover three-treatment design, 12 participants reported fasting on three separate days. Treatments were 1.33 mg/kg body weight caffeine only, 0.4 g/kg body weight sugar only, and caffeine with sugar. Breath-by-breath measurements of respiratory gas exchange and heart rate were recorded for 30 min before and after treatments. Data visualization techniques were used to examine the patterns of response. Results: Carbon dioxide production increased or remained the same with all three treatments. Caffeine alone slowed the...

Exercise tolerance in obese vs. lean adolescents: a systematic review and meta-analysis.

To prescribe feasible and medically safe exercise interventions for obese adolescents, it remains to be determined whether exercise tolerance is altered and whether anomalous cardiopulmonary responses during maximal exercise testing are present. Studies that examined cardiopulmonary responses to maximal exercise testing in obese adolescents were searched: cardiopulmonary exercise tests with respiratory gas exchange measurements of peak oxygen uptake (VO2peak) were performed and comparisons between obese and lean adolescents were made. Study quality was assessed using a standardized item list. By meta-analyses VO2peak, peak cycling power output (Wpeak) and peak heart rate (HRpeak) were compared between groups. Nine articles were selected (333 obese vs. 145 lean adolescents). VO2peak (L min(-1)), HRpeak and Wpeak were not different between groups (P ≥ 0.10), while a trend was found for a reduced VO2peak (mL min(-1) kg(-1) lean tissue mass) (P=0.07) in obese vs. lean adolescents. It remained uncertain whether anomalous cardiopulmonary responses occur during maximal exercise testing in obese adolescents. In conclusion, a trend was found for lowered VO2peak (mL min(-1)kg(-1) lean tissue mass) in obese vs. lean adolescents. Whether cardiopulmonary anomalies during maximal exercise testing would occur in obese adolescents remains uncertain. Studies are therefore warranted to examine the cardiopulmonary response during maximal exercise testing in obese adolescents.

Performance Related Factors Are the Main Determinants of the von Willebrand Factor Response to Exhaustive Physical Exercise

BackgroundPhysical stress triggers the endothelium to release von Willebrand Factor (VWF) from the Weibel Palade bodies. Since VWF is a risk factor for arterial thrombosis, it is of great interest to discover determinants of VWF response to physical stress. We aimed to determine the main mediators of the VWF increase by exhaustive physical exercise.Methods105 healthy individuals (18–35 years) were included in this study. Each participant performed an incremental exhaustive exercise test on a cycle ergometer. Respiratory gas exchange measurements were obtained while cardiac function was continuously monitored. Blood was collected at baseline and directly after exhaustion. VWF antigen (VWF:Ag) levels, VWF collagen binding (VWF:CB) levels, ADAMTS13 activity and common variations in Syntaxin Binding Protein-5 (STXBP5, rs1039084 and rs9399599), Syntaxin-2 (STX2, rs7978987) and VWF (promoter, rs7965413) were determined.ResultsThe median VWF:Ag level at baseline was 0.94 IU/mL [IQR 0.8–1.1] and increased with 47% [IQR 25–73] after exhaustive exercise to a median maximum VWF:Ag of 1.38 IU/mL [IQR 1.1–1.8] (p<0.0001). VWF:CB levels and ADAMTS13 activity both also increased after exhaustive exercise (median increase 43% and 12%, both p<0.0001). The strongest determinants of the VWF:Ag level increase are performance related (p<0.0001). We observed a gender difference in VWF:Ag response to exercise (females 1.2 IU/mL; males 1.7 IU/mL, p = 0.001), which was associated by a difference in performance. Genetic variations in STXBP5, STX2 and the VWF promoter were not associated with VWF:Ag levels at baseline nor with the VWF:Ag increase.ConclusionsVWF:Ag levels strongly increase upon exhaustive exercise and this increase is strongly determined by physical fitness level and the intensity of the exercise, while there is no clear effect of genetic variation in STXBP5, STX2 and the VWF promoter.

Relationship Between the Talk Test and Ventilatory Thresholds in Well-Trained Cyclists

The aim of this study was to extend the range of populations where the Talk Test (TT) might be used as a marker of physiologic thresholds. Eighteen highly trained cyclists underwent 2 incremental tests. One test included measurement of respiratory gas exchange to determine the ventilatory (VT) and respiratory compensation thresholds (RCTs). On a separate day, a TT was performed using the same exercise protocol. During TT, subjects read a standard paragraph at the end of each stage. The first stage at which the cyclists could not talk comfortably and could definitely not talk were referred to as the equivocal (EQ) and the negative stages (NEG), respectively. There were no significant differences in workload, heart rate, lactate, and rating of perceived exertion between VT (3.7 ± 0.4 W kg, 150 ± 10 b min, 1.6 ± 0.3 mm L, and 4.1 ± 1.4, respectively) vs. EQ (3.6 ± 0.4 W kg, 148 ± 12 b min, 1.3 ± 0.5 mm L, and 3.8 ± 1.2, respectively) and RCT (5.3 ± 0.4 W kg, 177 ± 7 b min, 4.0 ± 0.9 mm L, and 7.2 ± 1.0, respectively) vs. NEG (5.3 ± 0.5 W kg, 176 ± 10 b min, 4.2 ± 1.3 mm L, and 6.8 ± 1.5, respectively). We found significant relationships (p < 0.01) between VT and EQ and RCT and NEG for workload (r = 0.86 and 0.94, respectively), heart rate (r = 0.79 and 0.92, respectively), and rating of perceived exertion (r = 0.79 and 0.88, respectively). In conclusion, the present study showed that the EQ and NEG stages of TT can be used as a simple and practical surrogate of the VT and RCT in highly trained cyclists.