Calculated Oxygen Consumption Research Articles

The role of multimodality imaging in aortic valve assessment: A review

Aortic stenosis (AS) is one of the most prevalent valvular diseases. Doppler echocardiography is the most common imaging modality for the assessment of AS severity. Cardiac catheterization is also used when there are discrepancies between clinical and echocardiographic data. However, there exist many pitfalls in the assessment of the flow rate and pressure gradient by both imaging strategies. Doppler echocardiography assumes a circular left ventricular outflow tract (LVOT) and a flat velocity profile through the LVOT and does not account for pressure recovery. While cardiac catheterization accounts for pressure recovery, the formulas used to calculate oxygen consumption needed for cardiac output are also a source of inaccuracy in assessing the aortic valve area (AVA). Therefore, less flow-dependent modalities can be used to assess AS severity. Those methods can be divided into non-invasive such as 3-dimensional and resting flow rate assessment of AVA, invasive such as valvular resistance and valvulo-arterial impedance, and surrogate markers like the degree of aortic valve calcification, the degree of cardiac damage, and the delay between left ventricular and aortic systolic pressure peaks. Multimodality imaging, specifically dobutamine stress echocardiography and non-contrast cardiac computed tomography (CT) can also be used to assess the severity of moderate AS with discordant criteria on Doppler echocardiography. Finally, cinefluoroscopy, cardiac CT, cardiac magnetic resonance, and nuclear imaging can be used to assess prosthetic aortic valves when valve dysfunction is suspected or when there is discordance between the echocardiographic assessment and the patient's clinical status.

Calculation of hemodynamics by the Fick method in pulmonary hypertension associated with congenital heart defects

In December, 2021 at the IXth All-Russian Congress «Pulmonary Hypertension – 2021» the first Eurasian guidelines for the diagnosis and treatment of pulmonary hypertension associated with congenital heart disease (CHD) in adults were approved. In this review, the expert group presents the basic principles of calculating hemodynamics according to Fick for the systemic and pulmonary circulation. The method is indispensable for congenital heart defects. Theoretical and practical aspects of calculating hemodynamics with arteriovenous, venoarterial and bidirectional shunting are considered. The calculation of the cardiac index of each of the circles of blood circulation is performed on the basis of oxygen consumption, the oxygen capacity of the blood and the oxygen arteriovenous difference of each of the circles of blood circulation. Formulas are given for calculating the cardiac index of the systemic and pulmonary circulation, the cardiac index of effective blood flow, arteriovenous and venoarterial shunt, pulmonary and peripheral vascular resistance, as well as the classical table and the LaFarge and Miettinen formula for the calculated oxygen consumption depending on gender, age and heart rate. The review is illustrated with three clinical examples. Calculation of hemodynamics according to Fick should be started after getting acquainted with the anatomy and clinic of congenital heart disease: diagnosis, typical hemodynamic disorders, number and possible direction of shunts, saturation by pulse oximeter on the arms and legs; a purely mechanistic approach that does not take into account the clinical picture can reduce the information content and reliability of the method. The Fick method is somewhat limited by the impossibility of catheterization of the left atrium with an intact interatrial septum. Inaccuracies that are possible when assessing absolute indicators by the indirect Fick method are leveled when calculating their relative values, and the values are identical in reliability to the direct method. The Fick method, due to the obviously high error, is not advisable to use if there is another source of pulmonary blood flow besides the pulmonary artery system, as well as with a low arteriovenous difference in circulatory circles.

Discordance Between Measured vs Calculated Oxygen Consumption in Adults With Congenital Heart Disease: Limitations and Clinical Implications.

Oxygen consumption (VO2) is frequently estimated using derived formulas for ease of use. We performed a prospective study to assess the correlation and limits of agreement between measured and assumed VO2 (mL/min) in adults with congenital heart disease (CHD). Consecutive adults with CHD who have undergone cardiac catheterization at Mayo Clinic Rochester from January 2018 to December 2019 were retrospectively enrolled in the study. Expired gas analysis was performed to measure VO2. We estimated VO2 using LaFarge (VO2L), Dehmer (VO2D), and Bergstra (VO2B) formulas. Bland-Altman and linear-regression analyses were used to assess the correlation between measured and calculated VO2. We enrolled 84 patients with a mean age of 43 ± 12 years; 66% were men. Linear correlation analysis showed a moderate correlation of VO2L and VO2B with VO2M (r = 0.58; P<.001 and r = 0.44; P<.01, respectively) and good correlation of VO2D with VO2M (r = 0.79; P<.001). The large spread of limits of agreement assessed using Bland-Altman analysis demonstrates poor agreement of VO2L and VO2B with VO2M (bias, -58; 95% confidence interval [CI], -258 to 48) and bias, 38; 95% CI, -91 to 167, respectively). The limits of agreement for VO2D have a large spread, demonstrating a low degree of agreement with VO2M (bias, 13; 95% CI, -64 to 89). VO2L predominantly misclassified patients as low cardiac index and VO2D and VO2B misclassified patients as normal/ high cardiac index. In adults with CHD, assumed VO2 will lead to a significant error while assessing invasive intracardiac hemodynamics.

Research on coal spontaneous combustion period based on pure oxygen adiabatic oxidation experiment

Spontaneous combustion period is an important characteristic parameter of coal spontaneous combustion. It must be understood to prevent and control coal fire disasters in a coal mine. Fresh coal samples were then collected from the Bulianta Coal Mine in the Shenfu-Dongsheng Coalfield for mini combustion furnace experiments. We then analyzed the changing rules of coal temperature, O2 and CO during spontaneous combustion of coal under pure oxygen adiabatic conditions. A method for calculating oxygen consumption rate during spontaneous combustion of coal under those conditions was then proposed. Based on the Arrhenius law, heat loss rate (RPD) function during coal spontaneous combustion was developed. The coal temperature and oxygen concentration during spontaneous combustion oxidation process of coal in air accurately were calculated from a pure oxygen insulation experiment. When RPDair = 0, 0.2, 0.4, 0.6, and 0.8, the coal spontaneous combustion periods of Bulianta were 15.12, 18.94, 25.25, 37.87, and 75.74 days, respectively. The spontaneous combustion period of Bulianta coal, which was measured using 2-t experimental furnace for coal spontaneous combustion, was 16.66 days. The temperature change curve for spontaneous ignition experiment is similar to the adiabatic condition (RPDair = 0). This demonstrates that the coal spontaneous combustion period calculation method in air using pure oxygen adiabatic experiment is valid.

Critical COVID-19 patient evacuation on an amphibious assault ship: feasibility and safety. A case series

IntroductionAn amphibious assault ship was deployed on 22 March in Corsica to carry out medical evacuation of 12 critical patients infected with COVID-19. The ship has on-board hospital capacity and...

Reproducibility of Different Methodologies to Calculate Oxygen Consumption and Oxygen Cost During Walking in Chronic Stroke Survivors

Objective: The most common methods to calculate energy costs are based on measured oxygen uptake during walking a standardized distance or time. Unfortunately, it is unclear which method is most reliable to determine energy cost of walking in stroke survivors. The objective of this study was to evaluate the 3 most commonly used methods for calculating oxygen consumption and -cost by assessing test-retest reliability and measurement error in community dwelling chronic stroke survivors during a 6 Minute Walk Test. Methods: In this secondary analysis of a longitudinal study, reproducibility of the outcome of walking distance, walking speed, oxygen consumption and oxygen cost from 3 methods (Kendall's tau, assumed steady-state and total walking time oxygen consumption) were determined using Intraclass Correlation Coefficient, Standard Error of Measurement and Smallest Detectable Change. Results:20 from the 31 participants successfully performed the 6 minute walk test-retest within a timeframe of 1 month. Within the 2 tests the reproducibility of walking distance and walking speed was high. The 3 methods to determine reproducibility for oxygen cost and oxygen consumption were considered good (Kendall's tau), good (assumed steady-state) and excellent (total walking time). Conclusions: The method using oxygen consumption and -cost over the total walking time resulted in the highest reproducibility considering the Intraclass Correlation Coefficient, its 95% Confidence Interval, and smaller absolute differences.

An innovative method to calculate oxygen consumption rate

Based on heat and mass transfer characteristics of spontaneous combustion of coal, Arrhenius equation and the Ranz-Marshall correlation, a novel approach was proposed in this paper to estimate oxygen consumption rate of self-ignition of coal at high temperature. Compared with the conventional methods, this approach involves not only kinetic properties of self-ignition of coal and temperature, but also the ambient air flow characteristics and diameter of coal particle. To testify the proposed approach, oxygen consumption rates at high temperature were measured by the programmable isothermal oven experiments. Comparisons between experimental and theoretical results indicate that the rates of oxygen depletion calculated by the proposed approach agree well with those measured from laboratory-scale experiments, which further validates the proposed approach.

Extracellular Flux Assays to Determine Oxidative Phosphorylation and Glycolysis in Chronic Lymphocytic Leukemia Cells.

Extracellular flux assays are conducted using seahorse XF96 analyzer. They are used to calculate oxygen consumption rate which is to determine mitochondrial oxidative phosphorylation and extracellular acidification rate which is a measure of glycolysis. Collectively, these assays are used to assess the metabolic phenotype of a cell. Up to four drugs can be loaded and tested in the XF cartridges used in the assay and their effect on cells could be determined. While adherent cell lines are easy to use for this assay, suspension cultures or primary cells are difficult to use. In the following sections, we describe the methodology for this assay for CLL cells in suspension cultures and CLL-stroma cocultures.

Impact of atrial fibrillation on rest and exercise haemodynamics in heart failure with mid‐range and preserved ejection fraction

Heart failure with preserved (HFpEF) and mid-range ejection fraction (HFmrEF) are becoming the most prevalent forms of heart failure. Patients with HFpEF/HFmrEF in atrial fibrillation (AF) have poorer survival and quality of life, but the mechanism underpinning this is unknown. We sought to investigate the influence of AF on the haemodynamic profile of HFpEF/HFmrEF patients at rest and during exercise. We invasively measured central haemodynamics at rest and during symptom-limited supine bicycle exercise in HFpEF/HFmrEF patients, 35 in sinus rhythm and 20 in AF with matched left ventricular ejection fraction. At rest, AF patients had significantly increased pulmonary capillary wedge pressure, lower cardiac index and reduced left ventricular stroke work index, despite similar resting heart rate. Under resting conditions, calculated oxygen consumption and systemic arteriovenous oxygen gradient were not different between the two groups. During supine cycling at similar levels of workload, AF patients exhibited a reduced capacity to increase their oxygen consumption and this was accompanied by a persistently impaired cardiac index and left ventricular stroke work index. The adverse interaction of AF and HFpEF/HFmrEF may be accounted for by an adverse impact on left ventricular systolic function and peripheral oxygen kinetics.

Event-Associated Oxygen Consumption Rate Increases ca. Five-Fold When Interictal Activity Transforms into Seizure-Like Events In Vitro.

Neuronal injury due to seizures may result from a mismatch of energy demand and adenosine triphosphate (ATP) synthesis. However, ATP demand and oxygen consumption rates have not been accurately determined, yet, for different patterns of epileptic activity, such as interictal and ictal events. We studied interictal-like and seizure-like epileptiform activity induced by the GABAA antagonist bicuculline alone, and with co-application of the M-current blocker XE-991, in rat hippocampal slices. Metabolic changes were investigated based on recording partial oxygen pressure, extracellular potassium concentration, and intracellular flavine adenine dinucleotide (FAD) redox potential. Recorded data were used to calculate oxygen consumption and relative ATP consumption rates, cellular ATP depletion, and changes in FAD/FADH2 ratio by applying a reactive-diffusion and a two compartment metabolic model. Oxygen-consumption rates were ca. five times higher during seizure activity than interictal activity. Additionally, ATP consumption was higher during seizure activity (~94% above control) than interictal activity (~15% above control). Modeling of FAD transients based on partial pressure of oxygen recordings confirmed increased energy demand during both seizure and interictal activity and predicted actual FAD autofluorescence recordings, thereby validating the model. Quantifying metabolic alterations during epileptiform activity has translational relevance as it may help to understand the contribution of energy supply and demand mismatches to seizure-induced injury.

The effect of carbon dioxide on growth and energy metabolism in pikeperch (Sander lucioperca)

Pikeperch (Sander lucioperca) is a popular fish for human consumption and decreasing wild catches increase the demand for aquaculture production. Limited knowledge of the species' requirements under intense recirculating aquaculture system (RAS) culture conditions has motivated this study to focus on the effect of elevated carbon dioxide (CO2) levels on pikeperch metabolism. The trial was conducted in a recirculating aquaculture respirometer system with pikeperch (average body weight 251.9g) and three hypercapnia regimes over 58 feeding days. Food grade CO2 gas was gradually added to the medium (15mgL−1) and high (30mgL−1) treatments while no gas was added to the low treatment (hence 4mgL−1). Fish were fed daily for 10min with a commercial diet (ALLER Metabolica). O2, T, pH, CO2 were measured individually for each tank and logged every 2h to calculate oxygen consumption rates of each treatment. Total Ammonia-Nitrogen was measured monthly for individual tanks and used to calculate TAN excretion. Results showed a linear decrease of 6% in final body weight with increasing CO2 levels between the low and the high CO2 treatment. Feed intake was linearly increased after four weeks of the experiment from 0.97±0.07% in the low CO2 treatment to 0.86±0.03% in the high CO2 treatment but the effect faded after eight weeks, indicating a habituation to the hypercapnia conditions. High levels of CO2 were associated with reductions in haematocrit and metabolic oxygen consumption. The results suggest that adult pikeperch can survive carbon dioxide concentrations of up to 30mgL−1 when other water quality parameters are in acceptable levels but will be affected in metabolism already at moderate CO2 levels of 15mgL−1.

High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells.

A high-resolution oxygraph is a device for measuring cellular oxygen consumption in a closed-chamber system with very high resolution and sensitivity in biological samples (intact and permeabilized cells, tissues or isolated mitochondria). The high-resolution oxygraph device is equipped with two chambers and uses polarographic oxygen sensors to measure oxygen concentration and calculate oxygen consumption within each chamber. Oxygen consumption rates are calculated using software and expressed as picomoles per second per number of cells. Each high-resolution oxygraph chamber contains a stopper with injection ports, which makes it ideal for substrate-uncoupler-inhibitor titrations or detergent titration protocols for determining effective and optimum concentrations for plasma membrane permeabilization. The technique can be applied to measure respiration in a wide range of cell types and also provides information on mitochondrial quality and integrity, and maximal mitochondrial respiratory electron transport system capacity.

Modelling of Scanning Electrochemical Microscopy at Redox Competition Mode Using Diffusion and Reaction Equations

Scanning electrochemical microscopy (SECM) is an advanced electrochemical method, which is based on electrochemical scanning of electrochemical system surface by an ultramicroelectrode. Due to very high complexity of such systems the evaluation of data collected by this electrochemical method is a challenging task, which could be partly solved by mathematical modeling of processes that are influencing the signal of SECM. Several attempts to describe these processes mathematically have been performed for both feedback and generation-collection SECM modes. However, mathematical models for the redox competition SECM mode still were not elaborated due to high complexity of this problem. Therefore in this research work we have developed a mathematical model for the evaluation of enzyme − glucose oxidase (GOx) − modified surface by SECM, which was acting at redox competition mode. The rates of (i) GOx catalyzed processes, (ii) electrode reactions and (iii) diffusion were taken into account by proposed mathematical model. Using this model, it is possible to calculate oxygen consumption rate, to evaluate enzymatic reaction kinetics, and to determine diffusion coefficients of oxygen diffusion in the SECM-based systems.

Development of a new clinically applicable device for embryo evaluation which measures embryo oxygen consumption

Does a new system-the chip-sensing embryo respiration monitoring system (CERMs)-enable evaluation of embryo viability for potential application in a clinical IVF setting? The system enabled the oxygen consumption rate of spheroids, bovine embryos and frozen-thawed human embryos to be measured, and this rate corresponded to the developmental potential of embryos. To date, no reliable and clinically suitable objective evaluation methods for embryos are available, which circumvent the differences in inter-observer subjective view. Existing systems such as the scanning electrochemical microscopy (SECM) technique, which enables the measurement of oxygen consumption rate in embryos, need improvement in usability before they can be applied to a clinical setting. This is a prospective original research study. The feasibility of measuring the oxygen consumption rate was assessed using CERMs for 9 spheroids, 9 bovine embryos and 30 redundant frozen-thawed human embryos. The endpoints for the study were whether CERMs could detect a dissolved oxygen gradient with high sensitivity, had comparable accuracy to the SECM measuring system with improved usability, and could predict the development of an embryo to a blastocyst by measuring the oxygen consumption rate. The relationship between the oxygen consumption rate and standard morphological evaluation was also examined. We developed a new CERMs, which enables the oxygen consumption rate to be measured automatically using an electrochemical method. The device was initially used for measuring a dissolved oxygen concentration gradient in order to calculate oxygen consumption rate using nine spheroids. Next, we evaluated data correlation between the CERMs and the SECM measuring systems using nine bovine embryos. Finally, the oxygen consumption rates of 30 human embryos, which were frozen-thawed on 2nd day after fertilization, were measured by CERMs at 6, 24, 48, 72 and 96 h after thawing with standard morphological evaluation. Furthermore, the developed blastocysts were scored using the blastocyst quality score (BQS), and the correlation with oxygen consumption rate was also assessed. The device enabled the oxygen consumption rate of an embryo to be measured automatically within a minute. The oxygen concentration gradient profile showed excellent linearity in a distance-dependent change. A close correlation in the oxygen consumption rates of bovine embryos was observed between the SECM measuring system and CERMs, with a determination coefficient of 0.8203 (P =0.0008). Oxygen consumption rates of human embryos that have reached the blastocyst stage were significantly higher than those of arrested embryos at 48, 72 and 96 h after thawing (P =0.039, 0.004 and 0.049, respectively). Thus, in vitro development of frozen-thawed human embryos to the blastocyst stage would be predicted at 48 hafter thawing (day 4) by measuring the oxygen consumption using CERMs. Although a positive linear relationship between BQS and the oxygen consumption rate was observed [the determination coefficient was R(2)=0.6537 (P =0.008)], two blastocysts exhibited low oxygen consumption rates considering their relatively high BQS. This suggests that morphology and metabolism in human embryos might not correlate consistently. Transfer of the embryo and pregnancy evaluation was not performed. Thus, a correlation between oxygen consumption and the in vivo viability of embryos remains unknown. Clinical trials, including embryo transfer, would be desirable to determine a threshold value to elect clinically relevant, quality embryos for transfer. We utilized frozen-thawed human embryos in this study. The effect of these manipulations on the respiratory activity of the embryo is also unknown. Selection of quality embryos, especially in a single embryo transfer cycle, by CERMs may have an impact on obtaining better clinical outcomes, albeit with clinical trials being required. Furthermore, the early determination of quality embryos by CERMs may enable the omission of long-term in vitro embryo culture to the blastocyst stage. CERMs is scalable technology that can be integrated into incubators and/or other embryo evaluation systems, such as the time-lapse systems, due to its chip-based architecture. Thus, CERMS would enable automatic measurement of oxygen consumption, under 5% CO2, in the near future, in order to reduce oxidative stress from exposure to atmospheric air. This study was supported by grants from the Health and Labor Sciences Research Grant (H24-Hisaichiiki-Shitei-016). The authors have no conflicts of interest. Not applicable.

An Interventional Study to assess the effect of Aerobic Training on Physiological Cost Index in Normal Individuals at a Tertiary Care Hospital, Mumbai

Background : It is difficult to calculate oxygen consumption clinically due to expensive equipments required to measure it. Physiological cost index is one the indirect ways of calculate energy expenditure. Aim : To study the effect of aerobic training program on the physiological cost index (PCI) in normal healthy individuals. Study Design : This was an intervention based study conducted on 20 students of K.J.Somaiya college of physiotherapy, Mumbai.DURATION: 4 weeks. Study Procedure : A sub maximal 6 minute walk test was performed and the distance walked, walking speed and vitals were recorded pre training and post training. The physiological cost index for each subject was calculated. All the 20 subjects underwent an aerobic training program in the form of aerobic cycling. Training was imparted 3 times a week, for 4 consecutive weeks. Statistical Analysis : Paired't' test was used to analyse the data. Results : The average PCI value in normal healthy individuals, reduced from 0.37 beats/min to 0.30 beats/min, after 4 weeks of aerobic training, which was found to be statistically significant (p < 0.05). the average values of the difference in heart rates reduced from 34.1 beats/min to 28.1 beats/min. post 4 weeks of aerobic training, which was also found to be statistically significant (p value=0.05). The average value of difference in speed increased from 92.58 mts/min to 93.98 mts/min after 4 weeks of aerobic training, which was found to be statistically insignificant Conclusion : There is significant reduction in physiological cost index after 4 weeks of aerobic training in normal healthy individuals.

Winter Energetics of Female Indiana Bats Myotis sodalis

Understanding physiological limits and environmental optima is critical to developing protection strategies for endangered and threatened species. One theory to explain the decline in endangered Indiana bat Myotis sodalis populations involves increasing cave temperatures in winter hibernacula. Altered cave temperatures can raise metabolism and cause more arousals in torpid bats, both of which use more fat reserves. In addition, fluctuations in cave temperatures may cause additional arousals. Our objectives were to quantify the effect of temperature and fluctuations thereof on torpid metabolism and arousal frequency in this species. Female Indiana bats (n=36) were collected from caves just before hibernation, maintained in an environmental chamber that simulated hibernacula conditions, and had skin temperature recorded every 30 min throughout the winter. One environmental chamber containing bats (n=12) was sequentially set at 8°, 6°, and 4°C over the winter. The second chamber containing bats (n=12) experienced the same mean temperatures, but temperature fluctuated ±2°C on a regular basis. Torpor bouts were longest at 4°C and were not affected by temperature fluctuations. However, the temperature fluctuations appeared to cause longer arousals. Other bats (n=12) were individually placed in metabolic chambers to calculate oxygen consumption during torpor and during arousals. Torpid metabolism was affected by temperature; at 9°C, it was higher than at 7° or 5°C. Metabolism during arousals was not different among temperature treatments, but rates were almost 200 times higher than torpid metabolic rates. We calculated a winter energy budget and, from the energetic perspective, determined an optimum hibernation temperature (3°-6°C) for female Indiana bats. These findings suggest that hibernacula that provide these conditions deserve extra protection, although other factors in addition to energetics may play a role in temperature preferences.

Estimated time change of dissolved oxygen and carbon dioxide concentrations in the interstitial water of red sea bream, Pagrus major, egg aggregation

Morphogenesis is most active during fish embryonic development with increased susceptibility to environmental stressors. In order to elucidate the causalities of malformations in fishes that produce buoyant eggs, this study estimated the time change of dissolved oxygen (DO) and carbon dioxide (DCD) concentrations in the interstitial water of red sea bream, Pagrus major, egg aggregation. Since direct measurement of DO and DCD concentrations is not possible by current methodologies, we measured those in one liter water containing approximately 500,000 eggs for their estimation. Calculated oxygen consumption and carbon dioxide excretion rates from observed data were 1.32×10−6 and 2.16×10−7mg/ind/min, respectively. Volumetric method with these numeric values estimated that DO decreases below 10% saturation within 21s and DCD increases to more than 135mg/L within 60min in the interstitial water of egg aggregation. These results suggest that hypoxia and hypercapnia may become teratogenic within a short time in the aquaculture practices of egg collection, treatment, and transportation where eggs aggregate at the water surface in containers or rearing tanks, or in the wild when eggs are exposed to red tide in the open sea.

Assessment of energy balance of Indian farm women in relation to their nutritional profile in lean and peak agricultural seasons

In India, the farm women are not only involved in household activities but also contribute in various farm operations, animal husbandry. The objective was to assess nutritional profile of the farmwomen and their occupational health problems, to compare the physiological workload in lean and peak seasons and to find out relationship between physiological workload and nutritional intake. The study was conducted on a sample of 90 farmwomen. Energy Intake was calculated using physiological fuel values of carbohydrate, fat and protein. Energy Expenditure Rate (EER), Total Energy Expenditure (TEE) and Energy Balance were calculated. The physiological workload was assessed using sub-maximal workload technique. The results revealed that all the respondents of all categories were, more or less, performing all the agriculture, allied and household activities. In all the agriculture activities physiological hazards such as body pain and fatigue were dominant. Dietary, nutritional and energy intake was lower for heavy workers, from all landholding and BMI categories. HR and OCR were in linear relationship in all BMI categories. Physical work capacity increased with good nutritional status and decreased with age. Regression equations were suggested for calculating oxygen consumption (y) at their known heart rate (x) during various agriculture operations.

A new approach for flow-through respirometry measurements in humans

Indirect whole room calorimetry is commonly used in studies of human metabolism. These calorimeters can be configured as either push or pull systems. A major obstacle to accurately calculating gas exchange rates in a pull system is that the excurrent flow rate is increased above the incurrent flow rate, because the organism produces water vapor, which also dilutes the concentrations of respiratory gases in the excurrent sample. A common approach to this problem is to dry the excurrent gases prior to measurement, but if drying is incomplete, large errors in the calculated oxygen consumption will result. The other major potential source of error is fluctuations in the concentration of O(2) and CO(2) in the incurrent airstream. We describe a novel approach to measuring gas exchange using a pull-type whole room indirect calorimeter. Relative humidity and temperature of the incurrent and excurrent airstreams are measured continuously using high-precision, relative humidity and temperature sensors, permitting accurate measurement of water vapor pressure. The excurrent flow rates are then adjusted to eliminate the flow contribution from water vapor, and respiratory gas concentrations are adjusted to eliminate the effect of water vapor dilution. In addition, a novel switching approach is used that permits constant, uninterrupted measurement of the excurrent airstream while allowing frequent measurements of the incurrent airstream. To demonstrate the accuracy of this approach, we present the results of validation trials compared with our existing system and metabolic carts, as well as the results of standard propane combustion tests.

A study of passive weight-bearing lower limb exercise effects on local muscles and whole body oxidative metabolism: a comparison with simulated horse riding, bicycle, and walking exercise

BackgroundWe have developed an exercise machine prototype for increasing exercise intensity by means of passively exercising lower limb muscles. The purpose of the present study was to compare the passive exercise intensity of our newly-developed machine with the intensities of different types of exercises. We also attempted to measure muscle activity to study how these forms of exercise affected individual parts of the body.MethodsSubjects were 14 healthy men with the following demographics: age 30 years, height 171.5 cm, weight 68.3 kg. They performed 4 types of exercise: Passive weight-bearing lower limb exercise (PWLLE), Simulated horse riding exercise (SHRE), Bicycle exercise, and Walking exercise, as described below at an interval of one week or longer. Oxygen uptake, blood pressure, heart rate, and electromyogram (EMG) were measured or recorded during exercise. At rest prior to exercise and immediately after the end of each exercise intensity, the oxygenated hemoglobin levels of the lower limb muscles were measured by near-infrared spectroscopy to calculate the rate of decline. This rate of decline was obtained immediately after exercise as well as at rest to calculate oxygen consumption of the lower limb muscles as expressed as a ratio of a post-exercise rate of decline to a resting one.ResultsThe heart rate and oxygen uptake observed in PWLLE during maximal intensity were comparable to that of a 20-watt bicycle exercise or 2 km/hr walking exercise. Maximal intensity PWLLE was found to provoke muscle activity comparable to an 80-watt bicycle or 6 km/hr walking exercise. As was the case with the EMG results, during maximal intensity PWLLE, the rectus femoris muscle consumed oxygen in amounts identical to that of an 80-watt bicycle or a 6 km/hr walking exercise.ConclusionPassive weight-bearing lower limb exercise using our trial machine could provide approximately 3 MET of exercise and the thigh exhibited muscle activity equivalent to that of 80-watt bicycle or 6 km/hr walking exercise. Namely, given the same oxygen uptake, PWLLE exceeded bicycle or walking exercise in muscle activity, thus PWLLE is believed to strengthen muscle power while reducing the load imposed on the cardiopulmonary system.