V̇o2, V̇co2, and RQ in a respiratory chamber: accurate estimation based on a new mathematical model using the Kalman-Bucy method

Closed-loop control of air supply to whole-room indirect calorimeters to improve accuracy and standardize measurements during 24-hour dynamic metabolic studies

OBJECTIVE

The aim of this study was to test proportional-integral-derivative (PID) control of air inflow rate in a whole-room indirect calorimeter to improve accuracy in measuring oxygen (O₂ ) consumption ( V ̇ O 2 ) and carbon dioxide (CO₂ ) production ( V ̇ CO 2 ).

METHODS

A precision gas blender infused nitrogen (N₂ ) and CO₂ into the calorimeter over 24 hours based on static and dynamic infusion profiles mimicking V ̇ O 2 and V ̇ CO 2 patterns during resting and non-resting conditions. Constant (60 L/min) versus time-variant flow set by a PID controller based on the CO₂ concentration was compared based on errors between measured versus expected values for V ̇ O 2 , V ̇ CO 2 , respiratory exchange ratio, and metabolic rate.

RESULTS

Compared with constant inflow, the PID controller allowed both a faster rise time and long-term maintenance of a stable CO₂ concentration inside the calorimeter, resulting in more accurate V ̇ CO 2 estimates (mean hourly error, PID: -0.9%, 60 L/min = -2.3%, p < 0.05) during static infusions. During dynamic infusions mimicking exercise sessions, the PID controller achieved smaller errors for V ̇ CO 2 (mean: -0.6% vs. -2.7%, p = 0.02) and respiratory exchange ratio (mean: 0.5% vs. -3.1%, p = 0.02) compared with constant inflow conditions, with similar V ̇ O 2 (p = 0.97) and metabolic rate (p = 0.76) errors.

CONCLUSIONS

PID control in a whole-room indirect calorimeter system leads to more accurate measurements of substrate oxidation during dynamic metabolic studies.

Advances in Nutritional Epigenetics-A Fresh Perspective for an Old Idea. Lessons Learned, Limitations, and Future Directions

Nutritional epigenetics is a rapidly expanding field of research, and the natural modulation of the genome is a non-invasive, sustainable, and personalized alternative to gene-editing for chronic disease management. Genetic differences and epigenetic inflexibility resulting in abnormal gene expression, differential or aberrant methylation patterns account for the vast majority of diseases. The expanding understanding of biological evolution and the environmental influence on epigenetics and natural selection requires relearning of once thought to be well-understood concepts. This research explores the potential for natural modulation by the less understood epigenetic modifications such as ubiquitination, nitrosylation, glycosylation, phosphorylation, and serotonylation concluding that the under-appreciated acetylation and mitochondrial dependant downstream epigenetic post-translational modifications may be the pinnacle of the epigenomic hierarchy, essential for optimal health, including sustainable cellular energy production. With an emphasis on lessons learned, this conceptional exploration provides a fresh perspective on methylation, demonstrating how increases in environmental methane drive an evolutionary down regulation of endogenous methyl groups synthesis and demonstrates how epigenetic mechanisms are cell-specific, making supplementation with methyl cofactors throughout differentiation unpredictable. Interference with the epigenomic hierarchy may result in epigenetic inflexibility, symptom relief and disease concomitantly and may be responsible for the increased incidence of neurological disease such as autism spectrum disorder.

Improving temporal accuracy of human metabolic chambers for dynamic metabolic studies

Metabolic chambers are powerful tools for assessing human energy expenditure, providing flexibility and comfort for the subjects in a near free-living environment. However, the flexibility offered by the large living room size creates challenges in the assessment of dynamic human metabolic signals-such as those generated during high-intensity interval training and short-term involuntary physical activities-with sufficient temporal accuracy. Therefore, this paper presents methods to improve the temporal accuracy of metabolic chambers. The proposed methods include 1) adopting a shortest possible step size, here one minute, to compute the finite derivative terms for the metabolic rate calculation, and 2) applying a robust noise reduction method-total variation denoising-to minimize the large noise generated by the short derivative term whilst preserving the transient edges of the dynamic metabolic signals. Validated against 24-hour gas infusion tests, the proposed method reconstructs dynamic metabolic signals with the best temporal accuracy among state-of-the-art approaches, achieving a root mean square error of 0.27 kcal/min (18.8 J/s), while maintaining a low cumulative error in 24-hour total energy expenditure of less than 45 kcal/day (188280 J/day). When applied to a human exercise session, the proposed methods also show the best performance in terms of recovering the dynamics of exercise energy expenditure. Overall, the proposed methods improve the temporal resolution of the chamber system, enabling metabolic studies involving dynamic signals such as short interval exercises to carry out the metabolic chambers.

Classical experiments in whole-body metabolism: open-circuit respirometry-diluted flow chamber, hood, or facemask systems

For over two centuries, scientists have measured gas exchange in animals and humans and linked this to energy expenditure of the body. The aim of this review is to provide a comprehensive overview of open-circuit diluted flow indirect calorimetry and to help researchers to make the optimal choice for a certain system and its application. A historical perspective shows that 'open circuit diluted flow' is a technique first used in the 19th century and applicable today for room calorimeters, ventilated hood systems, and facemasks. Room calorimeters are a classic example of an open-circuit diluted flow system. The broadly applied ventilated hood calorimeters follow the same principle and can be classified as a derivative of these room calorimeters. The basic principle is that the subject breathes freely in a passing airflow that is fully captured and analyzed. Oxygen and CO2 concentrations are measured in inlet ambient air and captured outlet air. The airflow, which is adapted depending on the application (e.g., rest versus exercise), is measured. For a room indirect calorimeter, the dilution in the large room volume is also taken into account, and this is the most complex application of this type of calorimeter. Validity of the systems can be tested by alcohol burns, gas infusions and by performing repeated measurements on subjects. Using the latter, the smallest CV (%) was found for repeated VO2max tests (1.2%) with an SD of approximately 1 kJ min-1. The smallest SD was found for sleeping metabolic rate (0.11 kJ min-1) with a CV (%) of 2.4%.

Codonopsis lanceolata Water Extract Increases Hepatic Insulin Sensitivity in Rats with Experimentally-Induced Type 2 Diabetes

We examined the mechanisms and efficacy of Codonopsis lanceolata water extract (CLW) for treating type 2 diabetic (T2DM) symptoms. Partial pancreatectomized (Px) rats, a non-obese T2DM model, were provided high fat diets containing cellulose (control), 0.3% (CLW-L) or 1% CLW (CLW-H) for eight weeks. The positive control group was provided with rosiglitazone (20 mg/kg bw/day). The control group had lower epididymal fat masses than the CLW and the positive control groups, possibly due to urinary glucose loss, although CPT-1 and SIRT-1 expression was higher in the CLW group. CLW-H significantly reduced serum glucose levels and urinary glucose loss compared to the untreated control. The improvement of glucose utilization was associated with a higher fat mass in the CLW-H and positive control groups. Glucose-stimulated insulin secretion was higher in the untreated control than other groups and CLW tightly regulated insulin secretion as much as the positive control, and it was much tighter than the untreated control. Glucose infusion rates were higher during the hyperinsulinemic euglycemic clamp in the CLW and positive controls than the untreated control, and liver glucose outputs were lower during basal and hyperinsulinemic conditions in the CLW and positive control groups than the untreated control group. The increased hepatic insulin sensitivity was associated with enhanced insulin signaling in CLW (pAkt➔pGSK-1β). In conclusion, CLW consumption effectively alleviated diabetic symptoms by improving insulin sensitivity, potentiating hepatic insulin signaling and tightly regulating the insulin secretion capacity in non-obese T2DM rats.

Algorithm to improve accuracy of energy expended in a room calorimeter

The whole-room indirect calorimeter is considered as important equipment for human energy expenditure measurement, but noise reduction in the system remains a challenge. A selective filtering method (SFM) was designed to improve the accuracy of the computation of O₂ consumption rate ([Formula: see text]) and CO₂ production rate ([Formula: see text]), based on two facts: (1) the rapid changes of [Formula: see text], [Formula: see text] and respiratory quotient (RQ) in human should be accompanied by physical activity; (2) the oxygen consumption and the carbon dioxide production should not be negative because living humans do not generate oxygen, nor consume carbon dioxide. The performance of SFM was compared with the moving average method, the central difference method and the wavelet de-noising method. The range of [Formula: see text] and [Formula: see text] in the empty room (the background noise) is reduced from -130.00-146.00 ml/min to -26.00-24.00 ml/min, and from -20.50-12.50 ml/min to -3.99-4.19 ml/min, by SFM. The background noise was added to simulated rectangular and sinusoidal signals that were used to evaluate the four methods over different time periods (64, 32, 16 and 8 min). The highest signal-to-noise ratio and the lowest deviation were achieved by SFM. Abnormal metabolic rates and RQs were corrected and compensated with measurement accuracy of 98.51 ± 0.3 % for 24-h alcohol burning tests. The results of the study showed that SFM can significantly improve [Formula: see text] and [Formula: see text] measurements.

Measuring the short-term substrate utilization response to high-carbohydrate and high-fat meals in the whole-body indirect calorimeter

The paper demonstrates that minute‐to‐minute metabolic response to meals with different macronutrient content can be measured and discerned in the whole‐body indirect calorimeter. The ability to discriminate between high‐carbohydrate and high‐fat meals is achieved by applying a modified regularization technique with additional constraints imposed on oxygen consumption rate. These additional constraints reduce the differences in accuracy between the oxygen and carbon dioxide analyzers. The modified technique was applied to 63 calorimeter sessions that were each 24 h long. The data were collected from 16 healthy volunteers (eight males, eight females, aged 22–35 years). Each volunteer performed four 24‐h long calorimeter sessions. At each session, they received one of four treatment combinations involving exercise (high or low intensity) and diet (a high‐fat or high‐carbohydrate shake for lunch). One volunteer did not complete all four assignments, which brought the total number of sessions to 63 instead of 64. During the 24‐h stay in the calorimeter, subjects wore a continuous glucose monitoring system, which was used as a benchmark for subject's postprandial glycemic response. The minute‐by‐minute respiratory exchange ratio (RER) data showed excellent agreement with concurrent subcutaneous glucose concentrations in postprandial state. The averaged minute‐to‐minute RER response to the high‐carbohydrate shake was significantly different from the response to high‐fat shake. Also, postprandial RER slopes were significantly different for two dietary treatments. The results show that whole‐body respiration calorimeters can be utilized as tools to study short‐term kinetics of substrate oxidation in humans.

Estimation of Instantaneous Gas Exchange in Flow-Through Respirometry Systems: A Modern Revision of Bartholomew's Z-Transform Method

Flow-through respirometry systems provide accurate measurement of gas exchange over long periods of time. However, these systems have limitations in tracking rapid changes. When an animal infuses a metabolic gas into the respirometry chamber in a short burst, diffusion and airflow in the chamber gradually alter the original signal before it arrives at the gas analyzer. For single or multiple bursts, the recorded signal is smeared or mixed, which may result in dramatically altered recordings compared to the emitted signal. Recovering the original metabolic signal is a difficult task because of the inherent ill conditioning problem. Here, we present two new methods to recover the fast dynamics of metabolic patterns from recorded data. We first re-derive the equations of the well-known Z-transform method (ZT method) to show the source of imprecision in this method. Then, we develop a new model of analysis for respirometry systems based on the experimentally determined impulse response, which is the response of the system to a very short unit input. As a result, we present a major modification of the ZT method (dubbed the ‘EZT method’) by using a new model for the impulse response, enhancing its precision to recover the true metabolic signals. The second method, the generalized Z-transform (GZT) method, was then developed by generalizing the EZT method; it can be applied to any flow-through respirometry system with any arbitrary impulse response. Experiments verified that the accuracy of recovering the true metabolic signals is significantly improved by the new methods. These new methods can be used more broadly for input estimation in variety of physiological systems.

On the accuracy of instantaneous gas exchange rates, energy expenditure and respiratory quotient calculations obtained from indirect whole room calorimetry

This paper analyzes the accuracy of metabolic rate calculations performed in the whole room indirect calorimeter using the molar balance equations. The equations are treated from the point of view of cause-effect relationship where the gaseous exchange rates representing the unknown causes need to be inferred from a known, noisy effect-gaseous concentrations. Two methods of such inference are analyzed. The first method is based on the previously published regularized deconvolution of the molar balance equation and the second one, proposed in this paper, relies on regularized differentiation of gaseous concentrations. It is found that both methods produce similar results for the absolute values of metabolic variables and their accuracy. The uncertainty for O2 consumption rate is found to be 7% and for CO2 production--3.2%. The uncertainties in gaseous exchange rates do not depend on the absolute values of O2 consumption and CO2 production. In contrast, the absolute uncertainty in respiratory quotient is a function of the gaseous exchange rates and varies from 9.4% during the night to 2.3% during moderate exercise. The uncertainty in energy expenditure was found to be 5.9% and independent of the level of gaseous exchange. For both methods, closed form analytical formulas for confidence intervals are provided allowing quantification of uncertainty for four major metabolic variables in real world studies.

Genes involved in mitochondrial biogenesis/function are induced in response to bilio-pancreatic diversion in morbidly obese individuals with normal glucose tolerance but not in type 2 diabetic patients

AIMS/HYPOTHESIS

The mechanisms allowing normalisation of insulin sensitivity and reversal of type 2 diabetes after bilio-pancreatic diversion (BPD) have not been elucidated. We studied whether the expression of genes relevant to mitochondrial biogenesis/function is induced in response to BPD and whether the response differs between morbidly obese patients with normal glucose tolerance (NGT) and patients with type 2 diabetes.

METHODS

The effect of stable weight reduction after BPD on metabolic variables and expression of nuclear genes encoding for mitochondrial proteins or regulators of mitochondrial function was investigated in skeletal muscle. Insulin sensitivity was assessed by euglycaemic-hyperinsulinaemic clamp and substrate oxidation by indirect calorimetry.

RESULTS

Both NGT and type 2 diabetic patients showed a net improvement of insulin sensitivity, with the latter also showing blood glucose normalisation. NGT patients had a large increase in glucose oxidation and substantial reduction in lipid oxidation. In contrast, type 2 diabetic patients had a blunted response to BPD in terms of glucose oxidation. NGT patients showed increased expression of genes encoding mitofusin 2, porin or citrate synthase; no significant changes were detected in diabetic patients. The expression of genes regulating mitochondrial activity (PGC-1beta [also known as PPARGC1B], PGC-1alpha [also known as PPARGC1A], PPARdelta [also known as PPARD], SIRT1) was induced only in NGT patients.

CONCLUSIONS/INTERPRETATION

These findings indicate that weight loss after BPD exerts a beneficial effect on insulin sensitivity via mechanisms that are independent of the expression of genes involved in mitochondrial biogenesis/activity. Furthermore, the observation that gene expression is not altered with weight loss in type 2 diabetic patients while it is induced in NGT patients suggests a heritable component.

Algorithm for transient response of whole body indirect calorimeter: deconvolution with a regularization parameter

A whole body indirect calorimeter provides accurate measurement of energy expenditure over long periods of time, but it has limitations to assess its dynamic changes. The present study aimed to improve algorithms to compute O2 consumption and CO2 production by adopting a stochastic deconvolution method, which controls the relative weight of fidelity to the data and smoothness of the estimates. The performance of the new algorithm was compared with that of other algorithms (moving average, trends identification, Kalman filter, and Kalman smoothing) against validation tests in which energy metabolism was evaluated every 1 min. First, an in silico simulation study, rectangular or sinusoidal inputs of gradually decreasing periods (64, 32, 16, and 8 min) were applied, and samples collected from the output were corrupted with superimposed noise. Second, CO2 was infused into a chamber in gradually decreasing intervals and the CO2 production rate was estimated by algorithms. In terms of recovery, mean square error, and correlation to the known input signal in the validation tests, deconvolution performed better than the other algorithms. Finally, as a case study, the time course of energy metabolism during sleep, the stages of which were assessed by a standard polysomnogram, was measured in a whole body indirect calorimeter. Analysis of covariance revealed an association of energy expenditure with sleep stage, and energy expenditure computed by deconvolution and Kalman smoothing was more closely associated with sleep stages than that based on trends identification and the Kalman filter. The new algorithm significantly improved the transient response of the whole body indirect calorimeter.

Prolactin and insulin ultradian secretion and adipose tissue lipoprotein lipase expression in severely obese women after bariatric surgery

BACKGROUND

Hyperprolactinemia is associated with obesity. Furthermore, in human adipose tissue cultured in vitro, prolactin (PRL) inhibited lipoprotein lipase (LPL) activity via functional PRL receptors.

OBJECTIVE

To study PRL and insulin ultradian rhythm and subcutaneous adipose tissue LPL mRNA and protein expressions in severely obese women before and after malabsorptive bariatric surgery.

METHODS AND PROCEDURES

Seven severely obese, fertile women were studied twice, once before and the second time 1 year after bilio-pancreatic diversion (BPD), when the weight was stable for at least 3 months. Metabolizable energy intake and 24-h energy expenditure (EE) were measured. Fourier and PULSEFIT analyses were applied to 24-h hormonal time-series to study daily fluctuations and hormonal clearance. Insulin sensitivity was assessed by euglycemic-hyperinsulinemic clamp. Quantitative-competitive reverse transcriptase-PCR and western blot analysis were used to measure LPL gene expression.

RESULTS

Spontaneous 24-h PRL secretion was significantly reduced after BPD (mean-daily release, 128.4 +/- 28.1 microg/l vs. 67.2 +/- 9.2 microg/l distribution volume (Vd/l.24 h), P = 0.02); insulin secretion also was significantly reduced (499.9 +/- 204.0 microg/Vd/l.24 h vs. 85.6 +/- 21.0 microg/Vd/l.24 h, P = 0.0001). Metabolizable energy/kg(FFM) did not change significantly after BPD. Twenty-four-hour EE, but not 24-h EE/FFM, was significantly decreased after BPD (P < 0.05). Insulin sensitivity significantly (P < 0.0001) increased after BPD from 21.41 +/- 1.92 to 68.62 +/- 5.03 micromol/kg(FFM)/min. LPL mRNA concentration (from 42.63 +/- 4.21% to 19.00 +/- 2.74% of cyclophilin mRNA, P = 0.001) as well as LPL protein level (from 8.94 +/- 2.73 to 3.16 +/- 1.05 as ratios of protein of interest vs. housekeeping protein, P = 0.038) significantly decreased after BPD. The major determinant of PRL secretion was insulin secretion, whereas the best predictors of LPL expression were insulin and PRL secretion rates.

DISCUSSION

The restriction of lipid metabolizable energy rather than weight loss seems to be responsible for both reduction in PRL circulating levels and normalization of its secretion rhythm after bariatric surgery. Furthermore, the reduced adipose tissue LPL expression, being significantly correlated with the decrease in insulin and PRL, suggests a role of hyperinsulinemia and hyperprolactinemia in inducing and sustaining obesity.

Estimation of Respiratory Gas Exchange: A Comparative Study of Linear and Nonlinear Model-Based Estimation Techniques

Monitoring of respiratory gas exchange in humans is an important task in order to establish the physical condition of the patient and to control important physiological indices. In a previous work, we proposed an approximated linear dynamical model of gas exchange within a controlled volume, to be used as a basis for Kalman filtering technique in order to improve the accuracy of the estimates. In this paper, we propose an alternative nonlinear dynamical model of the same phenomenon and suggest the use of a nonlinear estimation technique. A simulation study demonstrates that operative conditions exist where the latter results are more accurate than the estimates based on the linear model. A set of controlled experiments are also designed in order to create situations in which the above difference is significant. In the paper it is evidenced that, in different operative conditions, the analysis both of simulated and experimental data, give systematically the same indications about the choice of the filtering method. The conclusive result of this paper is that a nonlinear model, and the corresponding nonlinear estimation technique, turn out to be convenient when the operative volume and the accuracy of the instrumentation of the experimental set up are both low (operative volumes of about ten liters and flows measurements errors with variances not less than 1 [liter/min]2). It should be also remarked that the proposed model-based estimation techniques, both linear and nonlinear, are highly superior to conventional methods used in medical practice. The present study provides insights and guidelines that can also be useful when dealing with similar gas exchange estimation problems in many other different application areas.

Ultradian ghrelin pulsatility is disrupted in morbidly obese subjects after weight loss induced by malabsorptive bariatric surgery

BACKGROUND

Suppression of ghrelin production after Roux-en-Y gastric bypass that suggested its contribution to appetite reduction has been reported.

OBJECTIVE

Because biliopancreatic diversion (BPD) does not affect appetite, we compared ghrelin production and 24-h pulsatility between healthy control subjects and obese subjects before and after BPD.

DESIGN

A computerized algorithm identified peak heights, clearance rate, and peak frequency of ghrelin over 24 h. Twenty-four-hour energy expenditure was measured in the calorimetric chamber, and energy intakes were computed. Insulin sensitivity was measured with a euglycemic-hyperinsulinemic clamp.

RESULTS

Mean (+/-SD) 24-h plasma ghrelin concentrations were significantly (P < 0.0001) higher in control than in obese subjects (338.17 +/- 22.09 and 164.47 +/- 29.19 microg/L, respectively), but they increased to 204.64 +/- 28.51 microg/L in the obese subjects after BPD (P < 0.01). The pulsatility index was 0.098 +/- 0.016 and 0.041 +/- 0.014 microg . L(-1) . min(-1) in control and obese subjects, respectively (P < 0.01), and decreased to 0.025 +/- 0.007 microg . l(-1) . min(-1) after BPD (P < 0.05). Energy intakes before and after BFP did not differ significantly. Although metabolizable energy after BPD was 40% of the energy intake, that (per kg fat-free mass) after BPD did not different significantly from that before BPD.

CONCLUSIONS

Weight loss induced by malabsorptive bariatric surgery is associated with greater ghrelin concentrations, which, however, remain consistently lower than those in control subjects, whereas ghrelin pulsatility is subverted. Higher ghrelin concentrations may contribute to the high calorie intakes observed in post-BPD subjects. The lack of normal pulsatility may explain the new impulse of these subjects to eat very frequently.

Leptin pulsatility in formerly obese women

Plasma leptin and growth hormone (GH) profile and pulsatility have been studied in morbidly obese subjects before and 14 months after bilio-pancreatic diversion (BPD), a bariatric technique producing massive lipid malabsorption. The maximum leptin diurnal variation (acrophase) decreased (10.27+/-1.70 vs. 22.60+/-2.79 ng x ml(-1); P=0.001), while its pulsatility index (PI) increased (1.084+/-0.005 vs. 1.050+/-0.004 ng x ml(-1) x min(-1); P=0.02) after BPD. Plasma GH acrophase increased (P=0.0001) from 0.91+/-0.20 to 4.58+/-0.80 microg x l(-1) x min(-1) after BPD as well as GH PI (1.70+/-0.13 vs. 1.20+/-0.04 microg x l(-1) x min(-1); P=0.024). Whole-body glucose uptake (M), assessed by euglycemic-hyperinsulinemic clamp, almost doubled after BPD (from 0.274+/-0.022 to 0.573+/-0.027 mmol x kgFFM(-1) x min(-1); P<0.0001), while 24 h lipid oxidation was significantly (P<0.0001) reduced (131.94+/-35.58 vs. 44.56+/-15.10 g). However, the average lipid oxidation was 97.2+/-3.1% (P<0.01) of the metabolizable lipid intake after the bariatric operation, while it was 69.2+/-8.5% before. After the operation, skeletal muscle ACC2 mRNA decreased (P<0.0001) from 452.82+/-76.35 to 182.45+/-40.69% of cyclophilin mRNA as did the malonyl-CoA (from 0.28+/-0.02 to 0.16+/-0.01 nmol x g(-1); P<0.0001). Leptin changes negatively correlated with M changes (R2=0.69, P<0.001). In a stepwise regression (R2=0.87, P=0.0055), only changes in 24 h free fatty acids (B=0.105+/-0.018, P=0.002) and glucose/insulin ratio (B=0.247+/-0.081, P=0.029) were the best predictors of leptin variations. In conclusion, the reversion of insulin resistance after BPD might allow reversal of leptin resistance, restoration of leptin pulsatility, and consequent inhibition of ACC2 mRNA expression, translating to a reduced synthesis of malonyl-CoA, which, in turn, results in increased fatty acid oxidation. Finally, since leptin inhibits GH secretion, a reduction of circulating leptin levels might have produced an increase in GH secretion, as observed in our series.