Respiratory Exchange Ratio Values Research Articles

Myoglobin deficiency impairs maximal oxygen uptake and exercise performance: a lesson from Mb-/- mice.

Myoglobin (Mb) plays an important role at rest and during exercise as a reservoir of oxygen and has been suggested to regulate NO• bioavailability under hypoxic/acidic conditions. However, its ultimate role during exercise is still a subject of debate. We aimed to study the effect of Mb deficiency on maximal oxygen uptake ( ) and exercise performance in myoglobin knockout mice (Mb-/- ) when compared to control mice (Mb+/+ ). Furthermore, we also studied NO• bioavailability, assessed as nitrite (NO2 - ) and nitrate (NO3 - ) in the heart, locomotory muscle and in plasma, at rest and during exercise at exhaustion both in Mb-/- and in Mb+/+ mice. The mice performed maximal running incremental exercise on a treadmill with whole-body gas exchange measurements. The Mb-/- mice had lower body mass, heart and hind limb muscle mass (P<0.001). Mb-/- mice had significantly reduced maximal running performance (P<0.001). expressed in mlmin-1 in Mb-/ - mice was 37% lower than in Mb+/+ mice (P<0.001) and 13% lower when expressed in mlmin-1 kg body mass-1 (P=0.001). Additionally, Mb-/- mice had significantly lower plasma, heart and locomotory muscle NO2 - levels at rest. During exercise NO2 - increased significantly in the heart and locomotory muscles of Mb-/- and Mb+/+ mice, whereas no significant changes in NO2 - were found in plasma. Our study showed that, contrary to recent suggestions, Mb deficiency significantly impairs and maximal running performance in mice. KEY POINTS: Myoglobin knockout mice (Mb-/- ) possess lower maximal oxygen uptake ( ) and poorer maximal running performance than control mice (Mb+/+ ). Respiratory exchange ratio values at high running velocities in Mb-/- mice are higher than in control mice suggesting a shift in substrate utilization towards glucose metabolism in Mb-/- mice at the same running velocities. Lack of myoglobin lowers basal systemic and muscle NO• bioavailability, but does not affect exercise-induced NO2 - changes in plasma, heart and locomotory muscles. The present study demonstrates that myoglobin is of vital importance for and maximal running performance as well as explains why previous studies have failed to prove such a role of myoglobin when using the Mb-/- mouse model.

Signal-correction errors in the EasyOne Pro LAB multiple-breath washout device significantly impact outcomes in children and adults.

Multiple-breath washout (MBW) is an established technique to assess functional residual capacity (FRC) and ventilation inhomogeneity in the lung. Indirect calculation of nitrogen concentration requires accurate measurement of gas concentrations. To investigate the accuracy of the CO2 concentration and molar mass (MM) values used for the indirect calculation of nitrogen concentration in a commercial MBW device [EasyOne Pro LAB (EOPL), ndd Medizintechnik AG, Switzerland] and its impact on outcomes. We used high-precision gas mixtures to evaluate CO2 and MM sensor output in vivo and in vitro. We developed updated algorithms to correct observed errors and assessed the impact on MBW outcomes and FRC measurement accuracy compared with body plethysmography. The respiratory exchange ratio (RER)-based adjustment of the measured CO2 signal used in the EOPL led to an overestimated CO2 signal (range -0.1% to 1.0%). In addition, an uncorrected dependence on humidity was identified. These combined effects resulted in an overestimation of expired nitrogen concentrations (range -0.7% to 2.6%), and consequently MBW outcomes. Corrected algorithms reduced the mean (SD) cumulative expired volume by 15.8% (9.7%), FRC by 6.6% (3.0%), and lung clearance index by 9.9% (7.6%). Differences in FRC between the EOPL and body plethysmography further increased. Inadequate signal correction causes RER- and humidity-dependent expired nitrogen concentration errors and overestimation of test outcomes. Updated algorithms reduce average signal error, however, RER values far from the population average still cause measurement errors. Despite improved signal accuracy, the updated algorithm increased the difference in FRC between the EOPL and body plethysmography.NEW & NOTEWORTHY We investigated the accuracy of the molar mass (MM) and CO2 sensors of a commercial multiple-breath washout device (ndd Medizintechnik AG, Switzerland). We identified humidity and respiratory exchange ratio-dependent errors that in most measurements resulted in an overestimation of expired nitrogen concentrations, and consequently, MBW results. Functional residual capacity and lung clearance index decreased by 6.6% and 9.9%, respectively. Despite improved signal accuracy, the difference in FRC between the EOPL and body plethysmography increased.

Effects of Grape Syrup Intake on Metabolic Rate and Substrate Oxidation During and After Sprint Intermittent Exercise

Background: Regarding sports drinks' role in substrate oxidation, the present study investigated the effect of grape syrup intake on metabolic rate and substrate oxidation after sprint intermittent exercise in active male students. Methods: In a double-blind, placebo-controlled, crossover study, 12 active male college students (body mass = 62.77 ± 9.05 kg; height = 173 ± 6.78 cm; BMI = 21 ± 2.5 kg/m2) were divided into two groups and performed two separate exercise sessions after grape syrup (1.1 mL/kg. body weight) or placebo intake. In the exercise session, subjects performed four 30-second Wingate tests (75 g / kg body weight) with a 5‐minute rest period. Energy expenditure (EE), respiratory exchange ratio (RER), fat oxidation (FO), heart rate (HR), and oxygen intake (VO2) were assessed 5 minutes before, during, and 30 minutes after exercise. Statistical analysis was performed using mixed-model ANOVA with repeated measures. Results: The results showed only between-group differences in respiratory exchange ratio (P = 0.04). However, the effect of time was significant between different situations (before, during, and after SIE) on all variables (P &lt; 0.05). No time-group interaction effect was also observed in investigated variables (P &gt; 0.05). The effect of different measurement times showed that in the post-SIE period, RER and fat oxidation rate values respectively decreased and increased compared to pre-SIE (P &lt; 0.05) in both situations. Conclusions: The grape syrup intake improved metabolic rate and substrate oxidation during the recovery period after SIE, comparable to the placebo-containing synthetic carbohydrates. Therefore, it is recommended to use this herbal supplement as a substitute for a carbohydrate drink during SIE. However, more research is needed in this case.

Investigating the effects of thermoneutral housing on skeletal and cardiac muscle function in D2 mdx mice

Since its discovery, the mdx mouse has been the foundation for research on Duchenne muscular dystrophy (DMD) and its potential therapies. Although, nearly all studies using mdx mice as an experimental model have been conducted under “standard” lab conditions using room (22C) instead of thermoneutral (TN, 30C) temperature housing. Room temperature (RT) is a mild cold stress to mice, causing metabolic adaptations that can confound experimental results, limiting their interpretation and translation to humans. This study investigated the effects of housing temperature on whole-body metabolism and skeletal and cardiac muscle function in the mdx mouse. To this end, 20 D2 mdx mice (age 5 weeks, n = 10 per group) were housed at RT and TN for 10 weeks. Metabolic cage analysis demonstrated that TN housed mdx mice displayed significantly decreased VO2 consumption and reduced food intake that was likely due to lowered daily energy expenditure. TN housed mice also had significantly lower respiratory exchange ratio values, indicative of increased fat metabolism. However, there were no differences in body mass or composition (i.e., % lean and fat mass). Treadmill-to-fatigue experiments revealed no differences in exercise performance. Furthermore, ex vivo muscle contractility analysis displayed no differences in extensor digitorum longus or soleus specific force generation between TN and RT housed mice. Analysis of cardiac structure/function demonstrated that TN housed mdx mice exhibited a reduction in cardiac output, which we attributed to diastolic dysfunction. While ejection fraction and fractional shortening were not different among the two groups, TN housing led to a significant reduction in end diastolic volume (EDV) and left ventricle internal diameter (diastole, LVID;d), as well as increased relative wall thickness (diastole, RWT;d) compared to RT housed mice. Though isovolumic relaxation time was prolonged in TN-housed mice, this did not reach statistical significance. Taken together, our results demonstrate that TN housing had minimal effects on skeletal muscle contractility, but did lead to signs of diastolic dysfunction in young mdx mice. Future studies will examine the effects of TN housing in aged mdx mice, when systolic dysfunction occurs, as well as any influence of TN housing on the efficacy of potential muscle wasting therapeutics. Overall, our results support the growing literature that highlights the importance of selecting the appropriate housing temperature when studying metabolism or muscle wasting conditions in mice. NSERC This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Metabolic impact of feeding prior to a 60-min bout of moderate-intensity exercise in females in a fasted state.

The metabolic impact of pre-exercise feeding of protein or carbohydrate on fat oxidation and energy expenditure rates, especially, in females, is poorly understood. Recreationally active females (n = 15, 32 ± 10 years, 164.8 ± 5.6 cm, 63.5 ± 9.3 kg, 23.4 ± 3.2 kg/m2) completed four testing sessions in a randomized, double-blind, crossover fashion after fasting overnight. Participants ingested isovolumetric and isoenergetic solutions containing either 25 g of whey protein, casein protein, carbohydrate (CHO), or a non-caloric placebo (PLA). Participants then completed 60 min of treadmill exercise at 15% below ventilatory threshold 30 min after ingestion. Respiratory exchange ratio (RER) was evaluated throughout exercise and resting energy expenditure (REE) was assessed pre-exercise, and 0-, 60-, and 120-min post-exercise. A significant condition x time interaction was observed for RER (p = 0.008) during exercise, with CHO exhibiting higher RER values (vs. PLA) at four time points. A significant main effect for condition was observed for carbohydrate (p = 0.001) and fat (p = 0.02) oxidation rates during exercise, with fat oxidation rates being higher in PLA vs. CHO (p = 0.01). When total fat oxidized was calculated across the entire exercise bout, a significant main effect for condition was observed (p = 0.01), with PLA being greater than CHO (p = 0.04). A significant condition x time interaction (p = 0.02) was found for both absolute and normalized REE, with casein and whey protein having significantly higher values than CHO (p < 0.05) immediately post-exercise. When compared to a fasted control (PLA), consuming CHO, but not protein, decreased total fat oxidation prior to a 60-min bout of moderate-intensity exercise in females.

Specific Incremental Test for Aerobic Fitness in Trail Running: IncremenTrail.

Trail running (TR) is performed in a natural environment, including various ranges of slopes where maximal oxygen consumption is a major contributor to performance. The aim of this study is to investigate the validity of tests performed in uphill conditions named the "IncremenTrail" (IncT), based on the incremental ascending speed (AS) to evaluate trail runners' cardiorespiratory parameters. IncT protocol included a constant gradient slope set at 25% during the whole test; the starting speed was 500 m·h-1 (25% slope and 2.06 km·h-1) and increased by 100 m·h-1 every minute (0.41 km·h-1). Twenty trail runner specialists performed the IncT and a supramaximal exercise bout to exhaustion with intensity set at 105% of maximal AS (Tlim). Oxygen consumption, breathing frequency, ventilation, respiratory exchange ratio (RER), and heart rate were continuously recorded during the exercises. The blood lactate concentration and rate of perceived exertion were collected at the end of the exercises. During the IncT test, 16 athletes (80%) reached a plateau of maximal oxygen uptake (65.5 ± 7.6 mL·kg-1·min-1), 19 athletes (95%) reached RER values over 1.10 (1.12 ± 0.02) and all the athletes achieved blood lactate concentration over 8.0 mmol·L-1 (17.1 ± 3.5 mmol·L-1) and a maximal heart rate ≥90% of the theoretical maximum (185 ± 11 bpm). Maximal values were not significantly different between IncT and Tlim. In addition, ventilatory thresholds could be determined for all runners with an associated AS. IncT provided a suitable protocol to evaluate trail runners' cardiorespiratory limitations and allowed us to obtain specific intensities based on the ascending speed useful for training purposes in specific conditions.

Middle-Aged Lpaatδ-Deficient Mice Have Altered Metabolic Measures.

Lysophosphatidic acid acyltransferases/acylglycerophosphate acyltransferases (LPAATs/AGPATs) are a group of homologous enzymes that catalyze the formation of phosphatidic acid (PA) from lysophosphatidic acid. We have previously reported that LPAATδ/AGPAT4 localizes to mitochondria, suggesting a potential role in energy metabolism. However, in prior studies of young Lpaatδ-deficient mice (age 9-12 weeks old), we found no differences in body weights, food intakes, activity levels, respiratory gas exchange, or energy expenditure compared to their wildtype (Wt) littermates. To test whether Lpaatδ-/- mice may develop differences in metabolic measures with advancing age, we recorded body weights and food intakes, and used metabolic chambers to assess ambulatory and locomotor activity levels, oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER), and total energy expenditure (heat). Fourteen-month-old Lpaatδ-/- mice had significantly lower mean body weights compared to Wt littermate controls (44.6 ± 1.08 g vs. 53.5 ± 0.42 g, respectively), but no significant differences in food intake or activity levels. This phenotypic difference was accompanied by significantly elevated 24 h daily, and 12 h light and dark photoperiod average VO2 (~20% higher) and VCO2 (~30% higher) measures, as well as higher RER and total energy expenditure (heat) values compared to Wt control littermates. Thus, an age-related metabolic phenotype is evident in Lpaatδ-/- mice. Future studies should examine the role of the lipid-modifying enzyme LPAATδ across the lifespan for greater insight into its role in normal and pathophysiology.

Evaluation Of Valid VO2max Criteria For Graded Exercise Testing In Cancer Survivors

INTRO: Using a metabolic cart (met cart) to obtain an individual's maximal oxygen consumption (VO2max) is considered the gold standard method of measurement. An accurate VO2max value is important in every population for individualized exercise prescriptions (ExRx), but specifically within the cancer population due to treatment status. Certain criteria must be met for a value to be considered a true VO2max. Utilizing gas analysis to track the changing respiratory exchange ratio (RER) and achieving >1.10 is the best criteria to determine if true max was obtained. Other maximal criteria such as 85% of heart rate max (HR) using the Tanaka formula and rate of perceived exertion (RPE) of >7 on the Modified Borg Scale also have the potential to be used as maximal criteria eliminating the need for a met cart. It is unknown if HR and RPE can be used independently as valid termination criteria in the cancer population during VO2max assessments. PURPOSE: To evaluate the frequency of achieving VO2max as determined by RER and alternate maximal criteria using HR and RER in a sample of cancer survivors. METHODS: Forty cancer survivors participated in the study. Subjects performed one GXT per week for three weeks using gas analysis. RER, HR, and RPE values were recorded. A total of 111 GXTs were used for data analysis. A Cochran’s Q test was used to determine if there were differences in the frequency of successful achievement of RER, HR, and RPE maximal criteria during the GXTs. RESULTS: Maximal criteria was successfully met in 95, 89, and 102 GXTs when evaluating RER, HR, and RPE, respectively. No significant differences occurred in the achievement of max between RER, HR, and RPE criteria (p < 0.061). CONCLUSION: The findings from this data set suggest that HR and RPE may be valid and suitable criteria for termination of a GXT if obtaining an RER value is not feasible or clinically practical. Cancer survivors experience toxicities such as skin irritation, muscular impairments, balance issues, peripheral neuropathy, and/or cancer related fatigue, making use of a met cart and mask potential impediments to maximal performance. Elimination of the met cart may allow the individual to advance further into a GXT leading to more accurate VO2max values and thus more accurate ExRx in the cancer population.

Effect of a High Fat Diet vs. High Carbohydrate Diets With Different Glycemic Indices on Metabolic Parameters in Male Endurance Athletes: A Pilot Trial.

Consuming low glycemic carbohydrates leads to an increased muscle fat utilization and preservation of intramuscular glycogen, which is associated with improved flexibility to metabolize either carbohydrates or fats during endurance exercise. The purpose of this trial was to investigate the effect of a 4-week high fat low carbohydrate (HFLC-G: ≥65% high glycemic carbohydrates per day; n = 9) vs. high carbohydrate low glycemic (LGI-G: ≥65% low glycemic carbohydrates daily; n = 10) or high glycemic (HGI-G: ≥65% fat, ≤ 50 g carbohydrates daily; n = 9) diet on fat and carbohydrate metabolism at rest and during exercise in 28 male athletes. Changes in metabolic parameters under resting conditions and during cycle ergometry (submaximal and with incremental workload) from pre- to post-intervention were determined by lactate diagnostics and measurements of the respiratory exchange ratio (RER). Additionally, body composition and perceptual responses to the diets [visual analog scale (VAS)] were measured. A significance level of α = 0.05 was considered. HFLC-G was associated with markedly decreased lactate concentrations during the submaximal (−0.553 ± 0.783 mmol/l, p = 0.067) and incremental cycle test [−5.00 ± 5.71 (mmol/l) × min; p = 0.030] and reduced RER values at rest (−0.058 ± 0.108; p = 0.146) during the submaximal (−0.078 ± 0.046; p = 0.001) and incremental cycle test (−1.64 ± 0.700 RER × minutes; p < 0.001). In the HFLC-G, fat mass (p < 0.001) decreased. In LGI-G lactate, concentrations decreased in the incremental cycle test [−6.56 ± 6.65 (mmol/l) × min; p = 0.012]. In the LGI-G, fat mass (p < 0.01) and VAS values decreased, indicating improved levels of gastrointestinal conditions and perception of effort during training. The main findings in the HGI-G were increased RER (0.047 ± 0.076; p = 0.117) and lactate concentrations (0.170 ± 0.206 mmol/l, p = 0.038) at rest. Although the impact on fat oxidation in the LGI-G was not as pronounced as following the HFLC diet, the adaptations in the LGI-G were consistent with an improved metabolic flexibility and additional benefits regarding exercise performance in male athletes.

CHANGES IN METABOLIC EFFICIENCY IN SKILLED ATHLETES DURING INTENSE EXERCISE

The body’s predominant choice of substrates and the rate of their oxidation in the working muscle are largely influenced by physical activity intensity. The higher the intensity of work, the more important role in energy supply processes are played by carbohydrates. It is suggested that the ability to most effectively use fat as an energy substrate at rest and during exercise allows athletes to save carbohydrates to perform high-intensity work. This study investigated the efficiency of metabolism in skilled athletes at rest and during the exercise of increasing intensity. 99 body composition assessments (via bioelectrical impedance) and 99 incremental exercise tests using a gas analysis system were performed in 90 male national- and international-level athletes (age 16-35 y.o.) of sports related to endurance and combat sports. The respiratory exchange ratio in skilled athletes at rest significantly correlates with the values of respiratory exchange ratio when reaching the anaerobic threshold ((r = 0.52, р ≤ 0,05)) and respiratory exchange ratio when reaching the maximum oxygen consumption ((r = 0.52, р ≤ 0,05)) and with the maximum oxygen consumption (r = -0.26, р ≤ 0,05). The oobtained data shows that efficient resting metabolism creates the preconditions for more efficient use of energy substrates during intense muscle activity. The respiratory exchange ratio is an informative indicator of the efficiency of metabolism, which can be used in the complex control of the functional condition of the athlete.

Performance and Recovery of Well-Trained Younger and Older Athletes during Different HIIT Protocols.

Due to physiological and morphological differences, younger and older athletes may recover differently from training loads. High-intensity interval training (HIIT) protocols are useful for studying the progression of recovery. It was the objective of this study to determine age differences in performance and recovery following different HIIT protocols. Methods: 12 younger (24.5 ± 3.7 years) and 12 older (47.3 ± 8.6 years) well-trained cyclists and triathletes took part in this study. Between the age groups there were no significant differences in relative peak power to fat-free mass, maximal heart rate (HR), training volume, and VO2max-percentiles (%). Participants performed different HIIT protocols consisting of 4 × 30 s Wingate tests with different active rest intervals (1, 3, or 10 min). Peak and average power, lactate, HR, respiratory exchange ratio (RER), subjective rating of perceived exertion (RPE), and recovery (Total Quality Recovery scale, TQR) were assessed. Results: During the different HIIT protocols, metabolic, cardiovascular, and subjective recovery were similar between the two groups. No significant differences were found in average lactate concentration, peak and average power, fatigue (%), %HRmax, RER, RPE, and TQR values between the groups (p > 0.05). Conclusion: The findings of this study indicate that recovery following HIIT does not differ between the two age groups. Furthermore, older and younger participants displayed similar lactate kinetics after the intermittent exercise protocols.

Correlation of maximal respiratory exchange ratio with anaerobic power and maximal oxygen uptake in anaerobic trained athletes

Background and Study Aim. The respiratory exchange ratio (RER) is the ratio of the amount of carbon dioxide produced (VCO2) to the amount of oxygen uptake (VO2) is important. It indirectly informs about the predominant metabolic pathway to provide the energy needed during exercise. The relationship of maximal RER with aerobic and anaerobic capacity in athletes remains unclear. The purpose of this study was to investigate the relationship between maximal RER and anaerobic power and maximal oxygen uptake (VO2max) in anaerobic trained athletes.&#x0D; Material and Methods. Thirteen male alpine skiers (age 18.1 ± 3.1 years) competing in national and international competitions participated in the study. Athletes first performed an incremental treadmill run test to determine their VO2max (ml/kg/min), maximal RER (VCO2 / VO2) and maximal running speed (km/h). After 48 hours, the athletes performed the Wingate anaerobic test to determine peak power, mean power, minimum power, and fatigue index. Pearson correlation coefficients were used to examine the relations between variables.&#x0D; Results. Maximal RER was positively correlated with peak power (r = 0.587, p &lt; 0.035), mean power (r = 0.656, p &lt; 0.015) and minimum power (r = 0.674, p &lt; 0.012). Maximal RER did not significantly correlate with fatigue index (p &gt; 0.05). Maximal RER was negatively correlated with the VO2max (r = – 0.705, p &lt; 0.007) and maximal running speed (r = – 0.687, p &lt; 0.01).&#x0D; Conclusions. Maximal RER may be useful for evaluating anaerobic capacity in anaerobic-trained athletes. Measuring the maximal RER values of athletes during incremental exercise may provide information about physiological adaptations in response to physical training.

Feasibility, Methodology, and Interpretation of Broad-Scale Assessment of Cardiorespiratory Fitness in a Large Community-Based Sample

Cardiorespiratory fitness (CRF) is intricately related to health status. The optimal approach for CRF quantification is through assessment of peak oxygen uptake (VO2), but such measurements have been largely confined to small referral populations. Here we describe protocols and methodological considerations for peak VO2 assessment and determination of volitional effort in a large community-based sample. Maximum incremental ramp cycle ergometry cardiopulmonary exercise testing (CPET) was performed by Framingham Heart Study participants at a routine study visit (2016 to 2019). Of 3,486 individuals presenting for a multicomponent study visit, 3,116 (89%) completed CPET. The sample was middle-aged (54 ± 9 years), with 53% women, body mass index 28.3 ± 5.6 kg/m2, 48% with hypertension, 6% smokers, and 8% with diabetes. Exercise duration was 12.0 ± 2.1 minutes (limits 3.7to20.5). No major cardiovascular events occurred. A total of 98%, 96%, 90%, 76%, and 57% of the sample reached peak respiratory exchange ratio (RER) values of ≥1.0, ≥1.05, ≥1.10, ≥1.15, and ≥1.20, respectively (mean peak RER=1.21 ± 0.10). With rising peak RER values up to ≈1.10, steep changes were observed for percent predicted peak VO2, VO2 at the ventilatory threshold/peak VO2, heart rate response, and Borg (subjective dyspnea) scores. More shallow changes for effort dependent CPET variables were observed with higher achieved RER values. In conclusion, measurement of peak VO2 is feasible and safe in a large sample of middle-aged, community-dwelling individuals with heterogeneous cardiovascular risk profiles. Peak RER ≥1.10 was achievable by the majority of middle-aged adults and RER values beyond this threshold did not necessarily correspond to higher peak VO2 values.

A Handheld Metabolic Device (Lumen) to Measure Fuel Utilization in Healthy Young Adults: Device Validation Study

BackgroundMetabolic carts measure the carbon dioxide (CO2) produced and oxygen consumed by an individual when breathing to assess metabolic fuel usage (carbohydrates versus fats). However, these systems are expensive, time-consuming, and only available in health care laboratory settings. A small handheld device capable of determining metabolic fuel usage via CO2 from exhaled air has been developed.ObjectiveThe aim of this study is to evaluate the validity of a novel handheld device (Lumen) for measuring metabolic fuel utilization in healthy young adults.MethodsMetabolic fuel usage was assessed in healthy participants (n=33; mean age 23.1 years, SD 3.9 years) via respiratory exchange ratio (RER) values obtained from a metabolic cart as well as % CO2 from the Lumen device. Measurements were performed at rest in two conditions: fasting, and after consuming 150 grams of glucose, in order to determine changes in metabolic fuel usage. Reduced major axis regression and simple linear regression were performed to test for agreement between RER and Lumen % CO2.ResultsBoth RER and Lumen % CO2 significantly increased after glucose intake (P<.001 for both) compared with fasting conditions, by 0.089 and 0.28, respectively. Regression analyses revealed an agreement between the two measurements (F1,63=18.54; P<.001).ConclusionsThis study shows the validity of Lumen for detecting changes in metabolic fuel utilization in a comparable manner with a laboratory standard metabolic cart, providing the ability for real-time metabolic information for users under any circumstances.

Physiological and metabolic characteristics of novel double-mutant female mice with targeted disruption of both growth hormone-releasing hormone and growth hormone receptor.

Mice with disruptions of growth hormone‐releasing hormone (GHRH) or growth hormone receptor (GHR) exhibit similar phenotypes of prolonged lifespan and delayed age‐related diseases. However, these two models respond differently to calorie restriction indicating that they might carry different and/or independent mechanisms for improved longevity and healthspan. In order to elucidate these mechanisms, we generated GHRH and GHR double‐knockout mice (D‐KO). In the present study, we focused specifically on the characteristics of female D‐KO mice. The D‐KO mice have reduced body weight and enhanced insulin sensitivity compared to wild‐type (WT) controls. Growth retardation in D‐KO mice is accompanied by decreased GH expression in pituitary, decreased circulating IGF‐1, increased high‐molecular‐weight (HMW) adiponectin, and leptin hormones compared to WT controls. Generalized linear model‐based regression analysis, which controls for body weight differences between D‐KO and WT groups, shows that D‐KO mice have decreased lean mass, bone mineral density, and bone mineral content, but increased adiposity. Indirect calorimetry markers including oxygen consumption, carbon dioxide production, and energy expenditure were significantly lower in D‐KO mice relative to the controls. In comparison with WT mice, the D‐KO mice displayed reduced respiratory exchange ratio (RER) values only during the light cycle, suggesting a circadian‐related metabolic shift toward fat utilization. Interestingly, to date survival data suggest extended lifespan in D‐KO female mice.

Effects of conventional and sugar-free energy drinks intake in runners: a double-blind, randomized, placebo-controlled crossover clinical trial.

This study evaluated the effects of two types of energy drinks (ED) intake in trained runners. A double-blind randomized placebo-controlled clinical trial was conducted over 6 weeks. Participants and beverages were allocated by randomization. Twelve men 23±2.6 years, 177±3.4 cm, 74.4±5.5 kg, VO<inf>2max</inf>=59.8±5.5 mL·(kg.min)-1] ingested either a conventional energy drink containing carbohydrates and 3 mg·kg-1 of caffeine, (ED1), a sugar-free energy drink 3 mg·kg-1 of caffeine (ED2), or a carbohydrate-containing, decaffeinated placebo (PL) 40-minutes before an exercise protocol. Sprint time, rate of perceived exertion (RPE), respiratory exchange ratio (RER), blood pressure (BP), heart rate and plasmatic glucose were evaluated during the experimental protocol. Performance improved after consuming both ED (P<0.004 ED1 and P=0.001 ED2) with lower RPE (P<0.05 for ED1 and P<0.05 for ED2) compared to PL. Consumption of ED2 decreased RER values at 0-5 minutes and 40-45 minutes (P<0.001), and ED1 increased systolic BP (P<0.05) during exercise compared to PL. There were no differences in the evaluated parameters between EDs (P>0.05). Consumption of conventional or sugar free ED represents a valid ergogenic strategy to improve acute performance with reduction of RPE. However, intake of a conventional ED warrants caution, mainly because the effects on systolic BP.

Impact of peak respiratory exchange ratio on the prognostic power of symptoms-limited exercise testing using Bruce protocol in patients with Fontan physiology.

We evaluated the impact of peak respiratory exchange ratio on the prognostic values of cardiopulmonary exercise variables during symptoms-limited incremental exercise tests in patients with Fontan physiology. Retrospective single-centre chart review study of Fontan patients who underwent exercise testing using the Bruce protocol between 2014 and 2018 and follow-up. A total of 34 patients (age > 18 years) had a Borg score of ≥7 on the Borg 10-point scale, but only 50% of patients achieved a peak respiratory exchange ratio of ≥ 1.10 (maximal test). Peak oxygen consumption, percent-predicted peak oxygen consumption, and peak oxygen consumption at the ventilatory threshold was reduced significantly in patients with a peak respiratory exchange ratio of < 1.10. Peak oxygen consumption and percent-predicted peak oxygen consumption was positively correlated with peak respiratory exchange ratio values (r = 0.356, p = 0.039). After a median follow-up of 21 months, cardiac-related events occurred in 16 (47%) patients, with no proportional differences in patients due to their respiratory exchange ratio (odds ratio, 0.62; 95% CI: 0.18-2.58; p = 0.492). Multivariate Cox proportional hazard analysis showed percent-predicted peak oxygen consumption, peak heart rate, and the oxygen uptake efficient slope were highly related to the occurrence of events in patients only with a peak respiratory exchange ratio of ≥ 1.10. The value of peak cardiopulmonary exercise variables is limited for the determination of prognosis and assessment of interventions in Fontan patients with sub-maximal effort. Our findings deserve further research and clinical application.

Breath holding as an example of extreme hypoventilation: experimental testing of a new model describing alveolar gas pathways.

What is the central question of this study? We modelled the alveolar pathway during breath holding on the hypothesis that it follows a hypoventilation loop on the O2 -CO2 diagram. What is the main finding and its importance? Validation of the model was possible within the range of alveolar gas compositions compatible with consciousness. Within this range, the experimental data were compatible with the proposed model. The model and its characteristics might allow predictions of alveolar gas composition whenever the alveolar ventilation goes to zero; for example, static and dynamic breath holding at the surface or during ventilation/intubation failure in anaesthesia. According to the hypothesis that alveolar partial pressures of O2 and CO2 during breath holding (BH) should vary following a hypoventilation loop, we modelled the alveolar gas pathways during BH on the O2 -CO2 diagram and tested it experimentally during ambient air and pure oxygen breathing. In air, the model was constructed using the inspired and alveolar partial pressures of O2 ( and , respectively) and CO2 ( and , respectively) and the steady-state values of the pre-BH respiratory exchange ratio (RER). In pure oxygen, the model respected the constraint of . To test this, 12 subjects performed several BHs of increasing duration and one maximal BH at rest and during exercise (30W cycling supine), while breathing air or pure oxygen. We measured gas flows, and before and at the end of all BHs. Measured data were fitted through the model. In air, =150±1mmHg and =0.3±0.0mmHg, both at rest and at 30W. Before BH, steady-state RER was 0.83±0.16 at rest and 0.77±0.14 at 30W; =107±7mmHg at rest and 102±8mmHg at 30W; and =36±4mmHg at rest and 38±3mmHg at 30W. By model fitting, we computed the RER during the early phase of BH: 0.10 [95% confidence interval (95% CI) =0.08-0.12] at rest and 0.13 (95% CI=0.11-0.15) at 30W. In oxygen, model fitting provided : 692 (95% CI=688-696) mmHg at rest and 693 (95% CI=689-698) mmHg at 30W. The experimental data are compatible with the proposed model, within its physiological range.

Effects of short-term continuous Montmorency tart cherry juice supplementation in participants with metabolic syndrome.

Metabolic Syndrome (MetS) augments the incidence of cardiovascular disease by two-fold and type II diabetes mellitus by five-fold. Montmorency tart cherries are rich in phytochemicals shown to improve biomarkers related to cardio-metabolic health in humans. This study aimed to examine cardio-metabolic responses after 7-days Montmorency tart cherry juice (MTCJ) supplementation and also acute on short-term supplementation responses to a single bolus, in humans with MetS. In a randomised, single-blind, placebo-controlled, crossover trial, 12 participants with MetS (50 ± 10years; 6M/6F), consumed MTCJ or placebo (PLA) for 7days. Blood-based and functional cardio-metabolic biomarkers were measured pre- and post-supplementation, and acute responses measured pre-bolus and up to 5h post-bolus on the 7th day. 24-h ambulatory systolic (P = 0.016), diastolic (P = 0.009) blood pressure and mean arterial pressure (P = 0.041) were significantly lower after 7-days MTCJ supplementation compared to PLA. Glucose (P = 0.038), total cholesterol (P = 0.036), LDL (P = 0.023) concentrations, total cholesterol:HDL ratio (P = 0.004) and respiratory exchange ratio values (P = 0.009) were significantly lower after 6-days MTCJ consumption compared to PLA. This study revealed for the first time in humans that MTCJ significantly improved 24-h BP, fasting glucose, total cholesterol and total cholesterol:HDL ratio, and also lowered resting respiratory exchange ratio compared to a control group. Responses demonstrated clinically relevant improvements on aspects of cardio-metabolic function, emphasising the potential efficacy of MTCJ in preventing further cardio-metabolic dysregulation in participants with MetS. Registered at clinicaltrials.gov (NCT03619941).

Effects Of Short-term Continuous Montmorency Tart Cherry Juice Supplementation In Participants With Metabolic Syndrome

PURPOSE: The prevention of cardiovascular disease (CVD) and type II diabetes mellitus (T2D) would be a major step in retarding rising global prevalence and incidence rates. Metabolic Syndrome (MetS) augments the incidence of CVD by 2-fold and T2D by 5-fold. Montmorency tart cherries are rich in phytochemicals and have previously been shown to improve cardio-metabolic biomarkers in humans. This study aimed to examine cardio-metabolic responses after 7 days Montmorency tart cherry juice (MTCJ) supplementation and also acute responses to a single-bolus, in humans with MetS. METHODS: In a randomised, single-blind, placebo-controlled, crossover trial, twelve participants with MetS (50 ±10 y; 6M/6F), consumed MTCJ or placebo (PLA) for 7 days. Blood-based (serum glucose, insulin, lipid profile) and functional (cardiac haemodynamics, arterial stiffness and resting metabolic rate) cardio-metabolic biomarkers were measured pre- and post-supplementation, and acute responses measured pre-bolus and up to 5 hours post-bolus on the 7th day. Comparisons were made by two-way, repeated measures ANOVA design. RESULTS: 24-hour ambulatory systolic (PLA vs. MTCJ, 2±1 vs. -5±1 mmHg, P = 0.016), diastolic (2±1 vs. -2±1 mmHg , P = 0.009) blood pressure and mean arterial pressure (3±1 vs. -2±0 mmHg, P = 0.041) were significantly lower after 7 days MTCJ supplementation compared to PLA. Findings also showed a significant reduction in glucose (0.03±0.07 vs. -0.50±0.00 mmol.L-1, P = 0.038), total cholesterol (0.04±0.06 vs. -0.40±0.07 mmol.L-1, P = 0.036), LDL (0.26±0.09 vs. -0.36±0.14 mmol.L-1, P = 0.023) concentrations and total cholesterol:HDL ratio (0.13±0.00 vs. 0.02±0.00, P = 0.004) with concomitant lower resting respiratory exchange ratio values (0.01±0.02 vs. -0.03±0.00, P = 0.009) after 6 days MTCJ consumption compared to PLA. CONCLUSIONS: This study revealed for the first time MTCJ to significantly improve 24-hour BP, fasting glucose, total cholesterol and total cholesterol:HDL ratio, and also lower resting respiratory exchange ratio compared to a control in any human population. Responses demonstrated clinically relevant improvements on aspects of cardio-metabolic function, emphasising the potential efficacy of MTCJ in preventing further cardio-metabolic dysregulation in an ‘at risk’ population.