Measurement Of Respiratory Quotient Research Articles

Validation of an alternative technique for RQ estimation in anesthetized pigs

BackgroundRespiratory quotient (RQ) is an important variable when assessing metabolic status in intensive care patients. However, analysis of RQ requires cumbersome technical equipment. The aim of the current study was to examine a simplified blood gas-based method of RQ assessment, using Douglas bag measurement of RQ (Douglas-RQ) as reference in a laboratory porcine model under metabolic steady state. In addition, we aimed at establishing reference values for RQ in the same population, thereby generating data to facilitate further research.MethodsRQ was measured in 11 mechanically ventilated pigs under metabolic steady state using Douglas-RQ and CO-oximetry blood gas analysis of pulmonary artery and systemic carbon dioxide and oxygen content. The CO-oximetry data were used to calculate RQ (blood gas RQ). Paired recordings with both methods were made once in the morning and once in the afternoon and values obtained were analyzed for potential significant differences.ResultsThe average Douglas-RQ, for all data points over the whole day, was 0.97 (95%CI 0.95–0.99). The corresponding blood gas RQ was 0.95 (95%CI 0.87–1.02). There was no statistically significant difference in RQ values obtained using Douglas-RQ or blood gas RQ for all data over the whole day (P = 0.43). Bias was − 0.02 (95% limits of agreement ± 0.3). Douglas-RQ decreased during the day 1.00 (95%CI 0.97–1.03) vs 0.95 (95%CI 0.92–0.98) P < 0.001, whereas the decrease was not significant for blood gas RQ 1.02 (95%CI 0.89–1.16 vs 0.87 (0.80–0.94) P = 0.11.ConclusionRQ values obtained with blood gas analysis did not differ statistically, compared to gold standard Douglas bag RQ measurement, showing low bias but relatively large limits of agreement, when analyzed for the whole day. This indicates that a simplified blood gas-based method for RQ estimations may be used as an alternative to gold standard expired gas analysis on a group level, even if individual values may differ. In addition, RQ estimated with Douglas bag analysis of exhaled air, was 0.97 in anesthetized non-fasted pigs and decreased during prolonged anesthesia.

Continuous and repeat metabolic measurements compared between post-cardiothoracic surgery and critical care patients

ObjectiveUsing a system, which accuracy is equivalent to the gold standard Douglas Bag (DB) technique for measuring oxygen consumption (VO2), carbon dioxide generation (VCO2), and respiratory quotient (RQ), we aimed to continuously measure these metabolic indicators and compare the values between post-cardiothoracic surgery and critical care patients.MethodsThis was a prospective, observational study conducted at a suburban, quaternary care teaching hospital. Age 18 years or older patients who underwent mechanical ventilation were enrolled.ResultsWe included 4 post-surgery and 6 critical care patients. Of those, 3 critical care patients died. The longest measurement reached to 12 h and 15 min and 50 cycles of repeat measurements were performed. VO2 of the post-surgery patients were 234 ± 14, 262 ± 27, 212 ± 16, and 192 ± 20 mL/min, and those of critical care patients were 122 ± 20, 189 ± 9, 191 ± 7, 191 ± 24, 212 ± 12, and 135 ± 21 mL/min, respectively. The value of VO2 was more variable in the post-surgery patients and the range of each patient was 44, 126, 71, and 67, respectively. SOFA scores were higher in non-survivors and there were negative correlations of RQ with SOFA.ConclusionsWe developed an accurate system that enables continuous and repeat measurements of VO2, VCO2, and RQ. Critical care patients may have less activity in metabolism represented by less variable values of VO2 and VCO2 over time as compared to those of post-cardiothoracic surgery patients. Additionally, an alteration of these values may mean a systemic distinction of the metabolism of critically ill patients.

Venous Minus Arterial Carbon Dioxide Gradients in the Monitoring of Tissue Perfusion and Oxygenation: A Narrative Review.

According to Fick's principle, the total uptake of (or release of) a substance by tissues is the product of blood flow and the difference between the arterial and the venous concentration of the substance. Therefore, the mixed or central venous minus arterial CO2 content difference depends on cardiac output (CO). Assuming a linear relationship between CO2 content and partial pressure, central or mixed venous minus arterial PCO2 differences (Pcv-aCO2 and Pmv-aCO2) are directly related to CO. Nevertheless, this relationship is affected by alterations in the CO2Hb dissociation curve induced by metabolic acidosis, hemodilution, the Haldane effect, and changes in CO2 production (VCO2). In addition, Pcv-aCO2 and Pmv-aCO2 are not interchangeable. Despite these confounders, CO is a main determinant of Pcv-aCO2. Since in a study performed in septic shock patients, Pmv-aCO2 was correlated with changes in sublingual microcirculation but not with those in CO, it has been proposed as a monitor for microcirculation. The respiratory quotient (RQ)-RQ = VCO2/O2 consumption-sharply increases in anaerobic situations induced by exercise or critical reductions in O2 transport. This results from anaerobic VCO2 secondary to bicarbonate buffering of anaerobically generated protons. The measurement of RQ requires expired gas analysis by a metabolic cart, which is not usually available. Thus, some studies have suggested that the ratio of Pcv-aCO2 to arterial minus central venous O2 content (Pcv-aCO2/Ca-cvO2) might be a surrogate for RQ and tissue oxygenation. In this review, we analyze the physiologic determinants of Pcv-aCO2 and Pcv-aCO2/Ca-cvO2 and their potential usefulness and limitations for the monitoring of critically ill patients. We discuss compelling evidence showing that they are misleading surrogates for tissue perfusion and oxygenation, mainly because they are systemic variables that fail to track regional changes. In addition, they are strongly dependent on changes in the CO2Hb dissociation curve, regardless of changes in systemic and microvascular perfusion and oxygenation.

Beneficial effects of SGLT2 inhibitor on metabolic inflexibility and visceral fat amount in animal model of obese type 2 diabetes

BackgroundObesity and type 2 diabetes mellitus (T2DM) are often accompanied with a disrupted diurnal rhythm of eating and sustained anabolic state, leading to metabolic inflexibility. In the present study, we plan to investigate effects of a sodium glucose co-transporter 2 (SGLT2) inhibitor, canagliflozin (CANA), on such a metabolic inflexibility, especially on fat metabolism, in the obese type 2 diabetic rats. Materials and methodsFive-week-old male SDT (Spontaneously Diabetic Torii) fatty rats as a model of obesity and T2DM and Sprague-Dawley (SD) rats were treated by either CANA (10 mg/kg) or saline (vehicle) orally for 14 days. Then, after the measurement of respiratory quotient (RQ) and visceral and subcutaneous fat volumes, rats were euthanized and blood and tissue samples were collected. ResultsThe treatment by CANA significantly enhanced β-ketone concentration in the blood during light period in the SDT fatty rats with no effect on blood glucose concentration. The CANA treatment significantly reduced visceral fat volume in the SDT fatty rats. A diurnal rhythm of RQ was severely disrupted and persistently high throughout the day in the vehicle-treated SDT fatty rats. By the administration of CANA clearly restored the disrupted diurnal rhythm of RQ with a revival of the nadir during light period. Quantitative real-time RT-PCR revealed a significant increase of AMP-activated protein kinase and decrease of acetyl-CoA carboxylase-1 expression in the liver, and a significant increase of hormone sensitive lipase and uncoupling protein-2 expression in the white adipose tissue by the treatment of CANA in the SDT fatty rats. ConclusionCANA as a SGLT2i reduced visceral fat amount via the enhancement of fat oxidation during the light period, leading to an amelioration of metabolic inflexibility in an obese diabetic model. A novel mechanism of CANA prompts the possibility that this new class of anti-diabetic agent could be a promising anti-obesity agent as well.

Effect of Dietary Strategies on Respiratory Quotient and Its Association with Clinical Parameters and Organ Fat Loss: A Randomized Controlled Trial.

The relation between changes in respiratory quotient (RQ) following dietary interventions and clinical parameters and body fat pools remains unknown. In this randomized controlled trial, participants with moderate abdominal obesity or/and dyslipidemia (n = 159) were randomly assigned to a Mediterranean/low carbohydrate (MED/LC, n = 80) or a low fat (LF, n = 79) isocaloric weight loss diet and completed a metabolic assessment. Changes in RQ (measured by indirect calorimeter), adipose-tissue pools (MRI), and clinical measurements were assessed at baseline and after 6 months of intervention. An elevated RQ at baseline was significantly associated with increased visceral adipose tissue, hepatic fat, higher levels of insulin and homeostatic insulin resistance. After 6 months, body weight had decreased similarly between the diet groups (−6 ± 6 kg). However, the MED/LC diet, which greatly improved metabolic health, decreased RQ significantly more than the LF diet (−0.022 ± 0.007 vs. −0.002 ± 0.008, p = 0.005). Total cholesterol and diastolic blood pressure were independently associated with RQ changes (p = 0.045). RQ was positively associated with increased superficial subcutaneous-adipose-tissue but decreased renal sinus, pancreatic, and intramuscular fats after adjusting for confounders. Fasting RQ may reflect differences in metabolic characteristics between subjects affecting their potential individual response to the diet.

Lipid Oxidation Assessed by Indirect Calorimetry Predicts Metabolic Syndrome and Type 2 Diabetes.

Purpose: Diabetes has been linked to an impaired ability to oxidize fatty acids. Fat oxidation can be assessed clinically by a respiratory quotient measurement during fasting. We hypothesized that a respiratory quotient might predict metabolic syndrome and type 2 diabetes onset.Methods: In this longitudinal study we used an existing database of 233 individuals who had complete nutritional and biochemical data at baseline and after 12-month follow-up. All participants underwent an indirect calorimetry to measure the respiratory quotient. We excluded participants with diabetes, metabolic syndrome, chronic diseases, and those who had changed food habits in the previous 3 months. Only 88 subjects met the inclusion criteria.Results: Two individuals developed type 2 diabetes and 10 metabolic syndrome after 1 year. Participants in the high respiratory quotient group (>0.91) had a higher incidence of metabolic syndrome/diabetes than those in the low quotient group (25 vs. 8% p = 0.04). In this group, mean basal respiratory quotient was 0.97 ± 0.04. In the high respiratory quotient group, Kaplan-Meier curves showed a greater probability of having metabolic syndrome/diabetes than those in the low respiratoryquotient group (log Rank χ2-test = 8.44; p = 0.004). A multivariable Cox proportional hazards model demonstrated that energy expenditure and weight increase did not predict metabolic syndrome/diabetes [HR (95% CI) = 1 (0.996–1.005), p = 0.86 and 3.9 (0.407–38.061), p = 0.23, respectively).Conclusions: A greater probability of metabolic syndrome/diabetes was found in individuals with a basal respiratory quotient of >0.91 than in those with a respiratoryquotient of ≤ 0.91 after 1 year. In the short-term anthropometric measurements and their variation overtime were not correlated with metabolic syndrome/diabetes.

Melatonin Relations With Respiratory Quotient Weaken on Acute Exposure to High Altitude.

High altitude (HA) exposure may affect human health and performance by involving the body timing system. Daily variations of melatonin may disrupt by HA exposure, thereby possibly affecting its relations with a metabolic parameter like the respiratory quotient (RQ). Sea level (SL) volunteers (7 women and 7 men, 21.0 ± 2.04 y) were examined for daily changes in salivary melatonin concentration (SMC). Sampling was successively done at SL (Antofagasta, Chile) and, on acute HA exposure, at nearby Caspana (3,270 m asl). Saliva was collected in special vials (Salimetrics Oral Swab, United Kingdom) at sunny noon (SMCD) and in the absence of blue light at midnight (SMCN). The samples were obtained after rinsing the mouth with tap water and were analyzed for SMC by immunoassay (ELISA kit; IBL International, Germany). RQ measurements (n = 12) were realized with a portable breath to breath metabolic system (OxiconTM Mobile, Germany), between 8:00 PM and 10:00 PM, once at either location. At SL, SMCD, and SMCN values (mean ± SD) were, respectively, 2.14 ± 1.30 and 11.6 ± 13.9 pg/ml (p < 0.05). Corresponding values at HA were 8.83 ± 12.6 and 13.7 ± 16.7 pg/ml (n.s.). RQ was 0.78 ± 0.07 and 0.89 ± 0.08, respectively, at SL and HA (p < 0.05). Differences between SMCN and SMCD (SMCN–SMCD) strongly correlate with the corresponding RQ values at SL (r = -0.74) and less tight at HA (r = -0.37). Similarly, mean daily SMC values (SMC) tightly correlate with RQ at SL (r = -0.79) and weaker at HA (r = -0.31). SMCN–SMCD, as well as, SMC values at SL, on the other hand, respectively, correlate with the corresponding values at HA (r = 0.71 and r = 0.85). Acute exposure to HA appears to loosen relations of SMC with RQ. A personal profile in daily SMC variation, on the other hand, tends to be conserved at HA.

Preliminary observations in systemic oxygen consumption during targeted temperature management after cardiac arrest

AimLimited data suggests low oxygen consumption (VO2), driven by mitochondrial injury, is associated with mortality after cardiac arrest. Due to the challenges of measurement in the critically ill, post-arrest metabolism remains poorly characterized. We monitored VO2, carbon dioxide production (VCO2) and the respiratory quotient (RQ) in post-arrest patients and explored associations with outcome. MethodsUsing a gas exchange monitor, we measured continuous VO2 and VCO2 in post- arrest patients treated with targeted temperature management. We used area under the curve and medians over time to evaluate the association between VO2, VCO2, RQ and the VO2:lactate ratio with survival. ResultsIn 17 patients, VO2 in the first 12 h after return of spontaneous circulation (ROSC) was associated with survival (median in survivors 3.35 mL/kg/min [2.98,3.88] vs. non-survivors 2.61 mL/kg/min [2.21,2.94], p = .039). This did not persist over 24 h. The VO2:lactate ratio was associated with survival (median in survivors 1.4 [IQR: 1.1,1.7] vs. non-survivors 0.8 [IQR: 0.6,1.2] p < 0.001). Median RQ was 0.66 (IQR 0.63,0.70) and 71% of RQ measurements were <0.7. Patients with initial RQ < 0.7 had 17% survival versus 64% with initial RQ > 0.7 (p = .131). VCO2 was not associated with survival. ConclusionsThere was a significant association between VO2 and mortality in the first 12 h after ROSC, but not over 24 h. Lower VO2: lactate ratio was associated with mortality. A large percentage of patients had RQs below physiologic norms. Further research is needed to explore whether these parameters could have true prognostic value or be a potential treatment target.

Congruent validity and inter-day reliability of two breath by breath metabolic carts to measure resting metabolic rate in young adults

Background & aimsAchieving high inter-day reliability is a key factor to analyze the magnitude of change in RMR, for instance after an intervention. The aims of this study were: i) to determine the congruent validity of RMR and respiratory quotient (RQ) with two breath by breath commercially available metabolic carts [CCM Express (CCM) and Ultima CardiO2 (MGU)]; and ii) to analyze the inter-day reliability of RMR and RQ measurements. Methods & resultsSeventeen young adults participated in the study. RMR measurements were performed during two consecutive 30-min periods, on two consecutive days with both metabolic carts. The 5-min period that met the steady state criteria [Coefficient of variance (CV) < 10% for VO2, VCO2, and VE, and CV<5% for RQ] and with the lowest CV average was included in further analysis. RMR values were higher with the MGU than with the CCM on both days (two-way ANOVA, P = 0.021), however, no differences were found on RQ values obtained by both metabolic carts (P = 0.642). Absolute inter-day RMR differences obtained with the MGU were higher than those obtained with the CCM (219 ± 185 vs. 158 ± 154 kcal/day, respectively, P = 0.002; 18.3 ± 17.2% vs. 13.5 ± 15.3%, respectively, P = 0.046). We observed a significant positive association of absolute inter-day differences in RMR obtained with both metabolic carts (β = 0.717; R2 = 0.743; P < 0.001). ConclusionsThe CCM metabolic cart provides lower RMR values and seems more reliable than the MGU in our sample of young adults. Our findings also suggest that a great part of inter-day variability is explained by the individuals.

Model based leak correction of real-time RQ measurement for dynamic controlled atmosphere storage

A method was developed to correct real-time measurements of the respiratory quotient (RQ) of pome fruit for gas leakage of a cool room. The method is based on a general leakage model that was simplified by performing sensitivity analysis of the contribution of the pressure driven and concentration driven gas transport terms. The analysis showed that pressure driven leakage was dominant over diffusive leakage. The methodology was validated successfully using an empty storage container at 0.4kPa O2 and 1.3kPa CO2. A sensitivity analysis using virtual storage experiments showed that the error of the RQ estimates with leak correction was 0%, while without leak correction they increased to above 700%. Finally, the validated model was successfully implemented in an automated RQ-DCA control system using ‘Braeburn’ apple fruit (Malus×domestica ‘Braeburn’ 2x). RQ estimates without leakage correction were heavily biased when leakage of atmospheric air into the storage container occurred and would lead to erroneous control of the storage atmosphere composition. With the developed leakage correction, RQ measurements were found to be accurate during decreasing as well as increasing atmospheric air pressure.

Relative validity of an indirect calorimetry device for measuring resting energy expenditure and respiratory quotient.

Resting energy expenditure (REE) and respiratory quotient (RQ) are important for optimal nutritional care. The purpose of this study was to assess the accuracy and repeatability of an indirect calorimetry device (IIM-IC-100) in the measurement of REE and RQ in healthy Chinese adults. A total of 38 healthy adults (19 male and 19 female) aged 18-52 years (25±6 years) were enrolled in this study. REE and RQ were measured by IIM-IC-100 and by VO2000, alternately and in duplicate. There was a highly significant correlation between IIM-IC-100 REE and VO2000 REE (r=0.906, p<0.001), with mean IIM-IC-100 REE significantly higher than that of VO2000 (1475±269 vs 1394±313 kcal/d, p=0.002). Bland- Altman analysis revealed that the mean difference between IIM-IC-100 REE and VO2000 REE was 81.3 kcal/d, with limits of agreement of -185 to +347 kcal/d. There was no significant difference in RQ between the two devices. No significant differences were observed between the repeated measurements for both devices. Intrasubject coefficients of variation (CVs) of REE were smaller for IIM-IC-100 (5.8%) than for VO2000 (10.5%), while CVs of RQ were similar for IIM-IC-100 (7.2%) and VO2000 (6.9%). These preliminary data indicated that the IIM-IC-100 showed promise as an accurate and precise tool in the assessment of REE and RQ in healthy Chinese adults.

The impact of measurement of respiratory quotient by indirect calorimetry on the achievement of nitrogen balance in patients with severe traumatic brain injury.

This study evaluated the impact of IC on the optimization of nutritional support and the achievement of +NB in patients with TBI. 27 patients (GCS≤8), treated with a 5-day multimodality monitoring and goal-directed therapy protocol, received enteral nutrition on day 1 followed by IC on days 3 and 5 and assessment of NB on day 7. In the first cohort (n=11), no adjustment in kcal was made. In the second cohort (n=16), nutrition was targeted to an RQ of 0.83 by day 3. The first cohort was analyzed with respect to NB status; the second cohort was compared to patients with (-) and +NB of the first cohort. Data (mean±SD) were analyzed with unpaired t test, and Chi square and Fisher exact tests. 4/11(36%) patients in the first cohort had +NB. The predicted mortality by TRISS, substrate utilization, and RQ was significantly lower compared to the second cohort. The mortality predicted by the CrasH model did not differ between the two cohorts. A RQ of 0.74 was associated with the preferential use of fat and protein and -NB, whereas a RQ of 0.84 favored utilization of carbohydrates and +NB. All patients whose kcal intake was adjusted based on the RQ on day 3 reached a +NB by day 7. An increase in kcal ≥25% in patients with a RQ<0.83 on day 3 improves substrate utilization, decreases protein utilization and optimizes the achievement of +NB by day 7.

A novel type of dynamic controlled atmosphere storage based on the respiratory quotient (RQ-DCA)

A novel type of dynamic controlled atmosphere storage (RQ-DCA) was developed to control O2 and CO2 partial pressures in storage containers for apple fruit automatically, based on measurements of the stored fruit respiratory quotient (RQ). ‘Granny Smith’ apples were stored under RQ-DCA and the effect on fruit quality immediately after storage as well as during subsequent shelf life was investigated and compared to the effect of regular CA and regular CA storage with 1-MCP (SmartFreshSM) treatment. The RQ-DCA system managed to control O2 and CO2 partial pressures in the storage container in an autonomous way. During RQ-DCA storage, the RQ breakpoint was found to vary between 0.25kPa and 0.4kPa O2. However, difficulties to obtain a reliable RQ measurement were observed at very low oxygen levels due to reduced fruit respiration and when the pressure of the storage container increases due to increased atmosphere pressure due to leakiness of the storage container. Superficial scald was found to be controlled almost completely during storage with RQ-DCA and the effect remained visible during up to 14 days of shelf life. Magness-Taylor firmness and skin color (hue angle) were found to be significantly higher after RQ-DCA storage compared to conventional CA storage and were comparable to these of fruit stored with regular CA after 1-MCP treatment up to 7 days of shelf life at 18°C. In-fruit ethanol concentrations were found to be very low (<0.028gL−1), indicating the RQ-DCA system managed to store the fruit close to the anaerobic compensation point but the fruit metabolism did not shift from aerobic respiration to fermentation.

Non-invasive Measurements of Energy Expenditure and Respiratory Quotient by Respiratory Mass Spectrometry in Children on Extracorporeal Membrane Oxygenation-A Pilot Study.

Extracorporeal membrane oxygenation (ECMO) provides temporary life-saving support for pediatric patients with severe cardiac failure, but causes metabolic disturbances and altered nutritional requirements. However, few studies have addressed the optimal energy supply to meet the demand of these children, largely due to technical difficulties with their invasive nature. We have adapted respiratory mass spectrometry to continuously measure O2 consumption and CO2 production in the gas exchange across the ECMO oxygenator, as well as that across the ventilator. This study aimed to assess energy expenditure (EE) and respiratory quotient (RQ) in children on ECMO. Five children (aged 0.3 to 36 months, median 20) were studied between Day 1 and Day 6 on ECMO. EE and RQ were measured in sequential fashion at the child's native lungs and ECMO oxygenator using respiratory mass spectrometry. Measurements were collected at 4-h intervals, with the means in 24 h representing the values of each day. Each child's caloric and protein intakes were recorded for each day. Between ECMO Days 1 and 6, there was a small but significant increase in EE from 40 to 46 kcal/kg/day (P = 0.03). In comparison, the caloric intake significantly increased by twice as much as EE from 30 to 61 kcal/kg/day (P = 0.017). As a result, RQ significantly increased from 0.6 to 1.0 (P < 0.0001). Protein intake significantly increased during ECMO Days 1 to 6 from 0.5 to 1.5 g/kg/day (P = 0.04). Respiratory mass spectrometry is feasible to provide a unique and safe technique to measure EE and RQ in patients on ECMO. Without this knowledge, inadequate feeding may occur. Further studies are warranted in a larger patient population to provide better information to guide clinical practice in this special group of critically ill children.

The effects of respiratory muscle strengthening exercise using a sling on the amount of respiration.

[Purpose] The purpose of this study was to present aerobic exercise that can be performed together with respiratory muscle strength training and examine whether the vital capacity of individuals can be enhanced when respiratory muscle strength training is conducted together with aerobic exercise. [Subjects and Methods] The subjects were 10 male students and 8 female students. The sling exercise method was used to conduct three types of training to strengthen the muscles around the shoulder joints. A maximal respiratory quotient measurement device was used to measure the vital capacity of the subjects five times. [Results] There was a significant difference in each respiratory training time point compared with before the performance of respiratory training. [Conclusion] This study presented respiratory muscle strength training using a sling as a training method for respiratory training.

An Exploratory Study of Respiratory Quotient Calibration and Association with Postmenopausal Breast Cancer

The respiratory quotient (RQ), defined as the ratio of carbon dioxide exhaled to oxygen uptake, reflects substrate utilization when energy is expended. Fat and alcohol have RQ values of approximately 0.7, compared with 1.0 for carbohydrate, and approximately 0.8 for protein. Here, the association between RQ and postmenopausal breast cancer risk is studied. Paired RQ measurements were obtained, separated by approximately 6 months, for women in the reliability subset of a Women's Health Initiative (WHI) Nutrition and Physical Activity Assessment Study. Linear regression of the average of the paired log RQ assessments on a corresponding log food quotient (FQ) average and other study subject characteristics, including age, body mass index, race, and education, yielded calibration equations for predicting RQ. Calibration equations, using any of food frequency, food record, or dietary recall data, explained an appreciable fraction of measured log RQ variation, and these were used to compute calibrated RQ estimates throughout WHI cohorts. Calibrated RQ estimates using 4-day food record (4DFR) data related inversely (P = 0.004) to (invasive) breast cancer risk in the WHI Dietary Modification trial comparison group, and corresponding RQ estimates using food-frequency data related inversely (P = 0.002) to breast cancer incidence in this cohort combined with the larger WHI observational study. Although preliminary, these analyses suggest a substantially higher postmenopausal breast cancer risk among women having relatively low RQ. RQ elevation could provide a novel target for breast cancer risk reduction.

Evaluation of a rapid determination of fasting heat production and respiratory quotient in Holstein steers using the washed rumen technique1

The objective of this study was to validate use of the washed rumen (WR) technique for rapid measurement of fasting heat production (HP) and respiratory quotient (RQ). Sixteen Holstein steers were divided into 2 groups of 8 for a comparison of measurements made during feeding (both groups; 16 steers) and fasting (8 steers; BW = 237 ± 17 kg) and using the WR model (8 steers; BW = 322 ± 30 kg). Steers were maintained in a controlled temperature (21°C) environment and treated as follows: 10 d diet adaptation, 1 d measurement of respiratory gases at 1.5 × NEm (Fed state; all steers d 11), 1 d measurement of respiratory gases under fasting conditions (Fasted; 8 steers d 12) or using the WR technique (8 steers d 12), and 7 d to monitor the reestablishment of intake. Steers were offered alfalfa cubes top-dressed with a mineral premix at 1.5 × NEm. Using an indwelling probe, core temperature (CT) and heart rate (HR) were monitored continuously during the days respiratory gases were measured. For fasting measurements using the WR technique, the reticulorumen was washed and refilled with ruminal buffer (NaCl = 96, NaHCO3 = 24, KHCO3 = 30, K2HPO4 = 2, CaCl2 = 1.5, and MgCl2 = 1.5 mmol/kg of buffer) with Cr-EDTA aerated with 75% N2 and 25% CO2 before introduction to the rumen. Mean hourly CT, RQ, and daily HP between Fasted steers and WR steers were decreased for the WR steers on average from 8 to 24 h after removal of rumen contents (P = 0.049, P < 0.001, and P = 0.076, respectively). Fitting RQ data obtained during fasting to a 1-phase decay equation showed that plateau was achieved at 0.756 ± 0.003 and 0.719 ± 0.003 and time to plateau was 9 and 8 h for Fasted and WR steers, respectively. Mean RQ after WR were 0.778, 0.732, and 0.726 (SEM = 0.003) for time segments 0 to 8 h, 9 to 16 h, and 17 to 24 h, respectively. Mean fasting HP after WR was 18.8, 16.8, and 16.5 (SEM = 0.51) kJ/(h • kg(0.75)) for time segments 0 to 8 h, 9 to 16 h, and 17 to 24 h, respectively. There were no significant differences in RQ and fasting HP (P = 0.23 and P = 0.81, respectively) between the time segment of 9 to 16 h and 17 to 24 h after rumen washing. In contrast, both RQ and HP differed (P = 0.090 and P = 0.081, respectively) across these same time segments for the Fasted group. Therefore, an accurate measurement of fasting HP can be obtained using a shorter-term measurement with the WR technique. This approach provides an alternative to the traditional 48 h fasting time or measurements made during the third and fourth day after starvation.

Clinical usefulness of non‐protein respiratory quotient measurement in non‐alcoholic fatty liver disease

Little is known about the effects of non-alcoholic fatty liver disease (NAFLD) on energy metabolism, although this disease is associated with metabolic syndrome. We measured non-protein respiratory quotient (npRQ) using indirect calorimetry, which reflects glucose oxidation, and compared this value with histological disease severity in NAFLD patients. Subjects were 32 patients who were diagnosed with NAFLD histopathologically. Subjects underwent body composition analysis and indirect calorimetry, and npRQ was calculated. An oral glucose tolerance test was performed, and plasma glucose area under the curve (AUC glucose) was calculated. There were no differences in body mass index, body fat percentage or visceral fat area among fibrosis stage groups. As fibrosis progressed, npRQ significantly decreased (stage 0, 0.895 ± 0.068; stage 1, 0.869 ± 0.067; stage 2, 0.808 ± 0.046; stage 3, 0.798 ± 0.026; P < 0.005). Glucose intolerance worsened and insulin resistance increased with fibrosis stage. npRQ was negatively correlated with AUC glucose (R = -0.6308, P < 0.001), Homeostasis Model of Assessment - Insulin Resistance (R = -0.5045, P < 0.005), fasting glucose (R = -0.4585, P < 0.01) and insulin levels (R = -0.4431, P < 0.05), suggesting that decreased npRQ may reflect impaired glucose tolerance due to insulin resistance, which was associated with fibrosis progression. Estimation of fibrosis stage using npRQ was as accurate as several previously established scoring systems using receiver-operator curve analysis. npRQ was significantly decreased in patients with advanced NAFLD. Our data suggest that measurement of npRQ is useful for the estimation of disease severity in NAFLD patients.

Glucose oxidation and nonoxidative glucose disposal during prolonged fasts of the northern elephant seal pup (Mirounga angustirostris)

Elephant seal weanlings demonstrate rates of endogenous glucose production (EGP) during protracted fasts that are higher than predicted on the basis of mass and time fasting. To determine the nonoxidative and oxidative fate of endogenously synthesized glucose, substrate oxidation, metabolic rate, glycolysis, and EGP were measured in fasting weanlings. Eight weanlings were sampled at 14 days of fasting, and a separate group of nine weanlings was sampled at 49 days of fasting. Metabolic rate was determined via flow-through respirometry, and substrate-specific oxidation was determined from the respiratory quotient and urinary nitrogen measurements. The rate of glucose disposal (Glu((R)(d))) was determined through a primed, constant infusion of [3-(3)H]glucose, and glycolysis was determined from the rate of appearance of (3)H in the body water pool. Glu((R)(d)) was 1.41 ± 0.27 and 0.95 ± 0.21 mmol/min in the early and late fasting groups, respectively. Nearly all EGP went through glycolysis, but the percentage of Glu((R)(d)) oxidized to meet the daily metabolic demand was only 24.1 ± 4.4% and 16.7 ± 5.9% between the early and late fasting groups. Glucose oxidation was consistently less than 10% of the metabolic rate in both groups. This suggests that high rates of EGP do not support substrate provisions for glucose-demanding tissues. It is hypothesized that rates of EGP may be ancillary to the upregulation of the tricarboxylic acid cycle to meet high rates of lipid oxidation while mitigating ketosis.

Comparison of seasonal variation in the fasting respiratory quotient of young Japanese, Polish and Thai women in relation to seasonal change in their percent body fat

BackgroundFrom the viewpoint of human physiological adaptability, we previously investigated seasonal variation in the amount of unabsorbed dietary carbohydrates from the intestine after breakfast in Japanese, Polish and Thai participants. In this investigation we found that there were significant seasonal variations in the amount of unabsorbed dietary carbohydrates in Japanese and Polish participants, while we could not find significant seasonal variation in Thai participants. These facts prompted us to examine seasonal variations in the respiratory quotient after an overnight fast (an indicator of the ratio of carbohydrate and fat oxidized after the last meal) with female university students living in Osaka (Japan), Poznan (Poland) and Chiang Mai (Thailand).MethodsWe enrolled 30, 33 and 32 paid participants in Japan, Poland and Thailand, respectively, and measurements were taken over the course of one full year. Fasting respiratory quotient was measured with the participants in their postabsorptive state (after 12 hours or more fasting before respiratory quotient measurement). Respiratory quotient measurements were carried out by means of indirect calorimetry using the mixing chamber method. The percent body fat was measured using an electric bioelectrical impedance analysis scale. Food intake of the participants in Osaka and Poznan were carried out by the Food Frequency Questionnaire method.ResultsThere were different seasonal variations in the fasting respiratory quotient values in the three different populations; with a significant seasonal variation in the fasting respiratory quotient values in Japanese participants, while those in Polish and Thai participants were non-significant. We found that there were significant seasonal changes in the percent body fat in the three populations but we could not find any significant correlation between the fasting respiratory quotient values and the percent body fat.ConclusionsThere were different seasonal variations in the fasting respiratory quotient values in the three different populations. There were significant seasonal changes in the percent body fat in the three populations but no significant correlation between the fasting respiratory quotient values and the percent body fat.