Open-circuit respirometry: real-time, laboratory-based systems

The algorithm used for the calculation of gas exchange affects the estimation of O2 uptake kinetics at the onset of moderate-intensity exercise

At the start of a moderate-intensity square-wave exercise, after a short delay, breath-by-breath O2 uptake at the mouth is approximated to a mono-exponential function, whose time constant is considered matched to that of the O2 uptake of the working muscles. We compared the kinetic parameters obtained from the breath-by-breath gas exchange data yielded by the 'Independent-breath' algorithm (IND), which accounts for the changes in lung gas stores, with those obtained with the classical 'Expiration-only' algorithm (EXP). The two algorithms were applied on the same flow and gas fraction traces acquired on 10 healthy volunteers, performing 10 times the same moderate-intensity exercise transition. Repeated O2 uptake responses were stacked together and the kinetic parameters of a mono-exponential function were estimated by non-linear regression, removing the data pertaining to 1-s progressively longer initial periods (ΔTr ). Independently of ΔTr , the mean response time (time constant + time delay) obtained for the IND data was faster compared to the EXP data (∼43 s vs. ∼47 s, P < 0.001), essentially because of shorter time delays. Between ΔTr  = 16 s and ΔTr  = 29s, the time constants of the IND data decreased (30.7 s vs. 28.0 s, P < 0.05; drop = 10%), but less than those of the EXP data (32.2 s vs. 26.2 s, P < 0.001; drop = 23%); with the same ΔTr , the time constants of the two algorithms' data were not different (P > 0.07). The different decrease in the time constant, together with the different mean response time, suggests that the data yielded by the two algorithms provide a different picture of the phenomena occurring at the beginning of the exercise.

Accuracy of respiratory gas variables, substrate, and energy use from 15 CPET systems during simulated and human exercise

PURPOSE

Various systems are available for cardiopulmonary exercise testing (CPET), but their accuracy remains largely unexplored. We evaluate the accuracy of 15 popular CPET systems to assess respiratory variables, substrate use, and energy expenditure during simulated exercise. Cross-comparisons were also performed during human cycling experiments (i.e., verification of simulation findings), and between-session reliability was assessed for a subset of systems.

METHODS

A metabolic simulator was used to simulate breath-by-breath gas exchange, and the values measured by each system (minute ventilation [V̇E], breathing frequency [BF], oxygen uptake [V̇O2 ], carbon dioxide production [V̇CO2 ], respiratory exchange ratio [RER], energy from carbs and fats, and total energy expenditure) were compared to the simulated values to assess the accuracy. The following manufacturers (system) were assessed: COSMED (Quark CPET, K5), Cortex (MetaLyzer 3B, MetaMax 3B), Vyaire (Vyntus CPX, Oxycon Pro), Maastricht Instruments (Omnical), MGC Diagnostics (Ergocard Clinical, Ergocard Pro, Ultima), Ganshorn/Schiller (PowerCube Ergo), Geratherm (Ergostik), VO2master (VO2masterPro), PNOĒ (PNOĒ), and Calibre Biometrics (Calibre).

RESULTS

Absolute percentage errors during the simulations ranged from 1.15%-44.3% for V̇E, 1.05-3.79% for BF, 1.10%-13.3% for V̇O2 , 1.07%-18.3% for V̇CO2 , 0.62%-14.8% for RER, 5.52%-99.0% for Kcal from carbs, 5.13%-133% for Kcal from fats, and 0.59%-12.1% for total energy expenditure. Between-session variation ranged from 0.86%-21.0% for V̇O2 and 1.14%-20.2% for V̇CO2 , respectively.

CONCLUSION

The error of respiratory gas variables, substrate, and energy use differed substantially between systems, with only a few systems demonstrating a consistent acceptable error. We extensively discuss the implications of our findings for clinicians, researchers and other CPET users.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 1: Foundational principles and theories of regulation

This contribution is the first of a four-part, historical series encompassing foundational principles, mechanistic hypotheses and supported facts concerning human thermoregulation during athletic and occupational pursuits, as understood 100 years ago and now. Herein, the emphasis is upon the physical and physiological principles underlying thermoregulation, the goal of which is thermal homeostasis (homeothermy). As one of many homeostatic processes affected by exercise, thermoregulation shares, and competes for, physiological resources. The impact of that sharing is revealed through the physiological measurements that we take (Part 2), in the physiological responses to the thermal stresses to which we are exposed (Part 3) and in the adaptations that increase our tolerance to those stresses (Part 4). Exercising muscles impose our most-powerful heat stress, and the physiological avenues for redistributing heat, and for balancing heat exchange with the environment, must adhere to the laws of physics. The first principles of internal and external heat exchange were established before 1900, yet their full significance is not always recognised. Those physiological processes are governed by a thermoregulatory centre, which employs feedback and feedforward control, and which functions as far more than a thermostat with a set-point, as once was thought. The hypothalamus, today established firmly as the neural seat of thermoregulation, does not regulate deep-body temperature alone, but an integrated temperature to which thermoreceptors from all over the body contribute, including the skin and probably the muscles. No work factor needs to be invoked to explain how body temperature is stabilised during exercise.

Current definitions of the breathing cycle in alveolar breath-by-breath gas exchange analysis

Identification of the breathing cycle forms the basis of any breath-by-breath gas exchange analysis. Classically, the breathing cycle is defined as the time interval between the beginning of two consecutive inspiration phases. Based on this definition, several research groups have developed algorithms designed to estimate the volume and rate of gas transferred across the alveolar membrane ("alveolar gas exchange"); however, most algorithms require measurement of lung volume at the beginning of the ith breath (VLi-1; i.e., the end-expiratory lung volume of the preceding ith breath). The main limitation of these algorithms is that direct measurement of VLi-1 is challenging and often unavailable. Two solutions avoid the requirement to measure VLi-1 by redefining the breathing cycle. One method defines the breathing cycle as the time between two equal fractional concentrations of lung expired oxygen (Fo2) (or carbon dioxide; Fco2), typically in the alveolar phase, whereas the other uses the time between equal values of the Fo2/Fn2 (or Fco2/Fn2) ratios [i.e., the ratio of fractional concentrations of lung expired O2 (or CO2) and nitrogen (N2)]. Thus, these methods identify the breathing cycle by analyzing the gas fraction traces rather than the gas flow signal. In this review, we define the traditional approach and two alternative definitions of the human breathing cycle and present the rationale for redefining this term. We also explore the strengths and limitations of the available approaches and provide implications for future studies.

Exercise Physiology and Cardiopulmonary Exercise Testing

Aerobic, or endurance, exercise is an energy requiring process supported primarily by energy from oxidative adenosine triphosphate synthesis. The consumption of oxygen and production of carbon dioxide in muscle cells are dynamically linked to oxygen uptake (V̇O2) and carbon dioxide output (V̇CO2) at the lung by integrated functions of cardiovascular, pulmonary, hematologic, and neurohumoral systems. Maximum oxygen uptake (V̇O2max) is the standard expression of aerobic capacity and a predictor of outcomes in diverse populations. While commonly limited in young fit individuals by the capacity to deliver oxygen to exercising muscle, (V̇O2max) may become limited by impairment within any of the multiple systems supporting cellular or atmospheric gas exchange. In the range of available power outputs, endurance exercise can be partitioned into different intensity domains representing distinct metabolic profiles and tolerances for sustained activity. Estimates of both V̇O2max and the lactate threshold, which marks the upper limit of moderate-intensity exercise, can be determined from measures of gas exchange from respired breath during whole-body exercise. Cardiopulmonary exercise testing (CPET) includes measurement of V̇O2 and V̇CO2 along with heart rate and other variables reflecting cardiac and pulmonary responses to exercise. Clinical CPET is conducted for persons with known medical conditions to quantify impairment, contribute to prognostic assessments, and help discriminate among proximal causes of symptoms or limitations for an individual. CPET is also conducted in persons without known disease as part of the diagnostic evaluation of unexplained symptoms. Although CPET quantifies a limited sample of the complex functions and interactions underlying exercise performance, both its specific and global findings are uniquely valuable. Some specific findings can aid in individualized diagnosis and treatment decisions. At the same time, CPET provides a holistic summary of an individual's exercise function, including effects not only of the primary diagnosis, but also of secondary and coexisting conditions.

Notational Analysis and Physiological and Metabolic Responses of Male Junior Badminton Match Play

We examined the game characteristics of badminton and the physiological and metabolic responses in highly trained male junior players. Players from a Badminton England accredited Performance Centre (n = 10, age: 14.0 ± 1.2 y, height: 1.69 ± 0.06 m, body mass: 59.1 ± 5.0 kg) completed a 20-m shuttle run test (V˙O_2max: 64 ± 7 mL·kg^-1·min^-1) and a simulated ability-matched competitive singles badminton game consisting of two 12-min games with a 2-min break wearing the COSMED K5 metabolic system with notational analysis. In five games, 427 points were contested with a rally time of 5.7 ± 3.7 s, a rest time of 11.2 ± 5.9 s, shots per rally of 5.6 ± 3.6, work density of 0.50 ± 0.21, an effective playing time of 32.3 ± 8.4%, and shots frequency of 1.04 ± 0.29. During badminton play, heart rate was 151 ± 12 b·min^-1 (82 ± 10% of maximum heart rate), oxygen uptake was 39.2 ± 3.9 mL·kg^-1·min^-1 (62 ± 7% of V˙O_2max), and energy expenditure was 11.2 ± 1.1 kcal·min^-1 with a post-game blood lactate of 3.33 ± 0.83 mmol·L^-1. Compared to adult badminton play, the physiological responses of junior badminton are lower and may be due to the shorter rally durations. Male junior badminton players should be exposed to training methodologies which include rally durations in excess of what they encounter during match play so as to develop greater consistency. Our observations on game characteristics and physiological responses during junior badminton can be used to inform training practice.

The Effect of a Hydroxytyrosol-Rich, Olive-Derived Phytocomplex on Aerobic Exercise and Acute Recovery

There is current scientific interest in naturally sourced phenolic compounds and their potential benefits to health, as well as the effective role polyphenols may provide in an exercise setting. This study investigated the chronic effects of supplementation with a biodynamic and organic olive fruit water phytocomplex (OliPhenolia® [OliP]), rich in hydroxytyrosol (HT), on submaximal and exhaustive exercise performance and respiratory markers of recovery. Twenty-nine recreationally active participants (42 ± 2 yrs; 71.1 ± 2.1 kg; 1.76 ± 0.02 m) consumed 2 × 28 mL∙d−1 of OliP or a taste- and appearance-matched placebo (PL) over 16 consecutive days. Participants completed a demanding, aerobic exercise protocol at ~75% maximal oxygen uptake (V˙O2max) for 65 min 24 h before sub- and maximal performance exercise tests prior to and following the 16-day consumption period. OliP reduced the time constant (τ) (p = 0.005) at the onset of exercise, running economy (p = 0.015) at lactate threshold 1 (LT1), as well as the rating of perceived exertion (p = 0.003) at lactate turnpoint (LT2). Additionally, OliP led to modest improvements in acute recovery based upon a shorter time to achieve 50% of the end of exercise V˙O2 value (p = 0.02). Whilst OliP increased time to exhaustion (+4.1 ± 1.8%), this was not significantly different to PL (p > 0.05). Phenolic compounds present in OliP, including HT and related metabolites, may provide benefits for aerobic exercise and acute recovery in recreationally active individuals. Further research is needed to determine whether dose-response or adjunct use of OliP alongside longer-term training programs can further modulate exercise-associated adaptations in recreationally active individuals, or indeed support athletic performance.

The formula for calculating the predicted value of cardiorespiratory endurance using a foot rest-based cardiorespiratory exercise device

This study developed a formula for calculating the predicted VO2 max value using a prototype model of foot-based cardiorespiratory exercise. Forty sedentary workers (20 men and 20 women) were enrolled via consecutive sampling. They underwent direct measurement of VO2 max using spiroergometry as the gold standard; the predicted VO2 max value was calculated using a prototype model of foot-based cardiorespiratory exercise, which was performed on consecutive days. Multivariate linear regression analysis was used to formulate the equation for the predicted VO2 max value by including potential contributing variables: gender, body height, body weight and heart rate. Bland-Altman test was used for assessing the agreement level for the predicted VO2 max value. The equation for the predicted VO2 max value was formulated as 3.2 + 0.15 optimal exercise heart rate -5.5 sexes (0 for men, 1 for women). The agreement level for the formula was acceptable in all measurement result ranges. The formula developed in this study can be used to measure the predicted VO2 max value with an acceptable agreement level.

Recovery Off-Kinetics Following Exhaustive Upper Body Exercise in Spinal Cord Injury

Background

People with spinal cord injury (SCI) present with impaired autonomic control when the lesion is above T6. This could lead to delayed cardiorespiratory recovery following vigorous physical activity.

Objectives

To characterize and compare gas exchange off-kinetics following exhaustive exercise in individuals with SCI and an apparently healthy control group.

Methods

Participants were 19 individuals with SCI who presented with the inability to voluntarily lift their legs against gravity (age, 44.6 ± 14.2 years; AIS A, n = 5; AIS B, n = 7; AIS C, n = 7; paraplegia, n = 14; tetraplegia, n = 5) and 10 healthy comparisons (COM; age, 30.5 ± 5.3 years). All participants performed an arm ergometer cardiopulmonary exercise test (aCPET) to volitional exhaustion followed by a 10-minute passive recovery. O₂ uptake (V̇o₂ ) and CO₂ output (V̇co₂ ) off-kinetics was examined using a mono-exponential model in which tau off (τ_off ) and mean response time (MRT) were determined. The off-kinetics transition constant (Kt_off ) was calculated as ΔV̇o₂ /MRT. Student t tests were used to compare SCI versus COM group means.

Results

COM had a significantly higher relative peak V̇o₂ compared to SCI (1.70 ± 0.55 L/min vs 1.19 ± 0.51 L/min, p = .019). No difference was observed for τ_off between the groups, however Kt_off for both V̇o₂ and V̇co₂ was significantly lower in the SCI compared to the COM group.

Conclusion

A reduced Kt_off during recovery may suggest inefficiencies in replenishing muscle ATP stores and lactate clearance in these participants with SCI. These findings may contribute to the observed lower cardiorespiratory fitness and greater fatigability typically reported in individuals with SCI.

Interchangeability between two breath-by-breath O2 uptake calculation algorithms in asthmatic and healthy volunteers

INTRODUCTION

The interchangeability analysis has been recently proposed to objectively assess whether a newly developed measurement tool can substitute the older ones; this analysis assumes that the measures yielded by the compared tools should differ less than a maximum acceptable value. We aimed to assess the interchangeability rate (IR) of the breath-by-breath O₂ uptake data calculated with the "Independent breath" (IND) and the "Expiration-only" (EXP) algorithms.

METHODS

Oxygen, carbon dioxide fractions, and ventilatory flow were recorded continuously over 26 min in 18 asthmatic and 20 well-matched healthy volunteers at rest, during cycling, and recovery; oxygen uptake (V'O₂) was calculated with the two algorithms under comparison. Coefficients of variation (CVs) of all the steady-state condition were modeled as a function of the average V'O₂ values and IR was calculated accordingly.

RESULTS

CVs were significantly greater in the asthmatic volunteers (F = 5.97, p < 0.05), being lower for IND compared to EXP (F > 7.04, p < 0.02). CVs decreased as a function of the reciprocal of the square root of the average V'O₂. The IR, calculated on the basis of this relationship, was not significantly different in the two groups of volunteers (F = 0.77, p = 0.385); taking as reference method the IND, or EXP algorithms, the IR values were significantly different (F = 58.6, p < 0.001), amounting to 97.4 ± 2.2% or to 98.2 ± 1.7%, respectively.

CONCLUSION

The relative noise of V'O₂ was greater in the asthmatic volunteers compared to the healthy ones and was lower for IND compared to EXP. The interchangeability analysis suggested that IND might be a better substitute for EXP than the opposite.

Quantifying the effects of four weeks of low-volume high-intensity sprint interval training on V̇O2max through assessment of hemodynamics

BACKGROUND

Sprint interval training is a popular workout modality. Studies have eluded to a positive effect on maximal oxygen uptake, however little is known about the mechanistic basis of this adaptation. Therefore, the purpose of this study was to determine the effects of a short-term high-intensity sprint interval training (SIT) intervention on V̇O2max through quantification of both the respiratory and hemodynamic responses.

METHODS

Thirty-six physically active participants undertook 4 weeks of either cycling-based SIT (8×20 s at 170% P-V̇O2max with 10 s recovery) or continuous exercise training (CET) (30 min at 70% P-V̇O2max) 3 times per week. V̇O2max, blood-based markers and hemodynamic responses were assessed pre and post the intervention period. V̇O2max was assessed using breath-by-breath open circuit spirometry, while hemodynamic responses were monitored using thoracic impedance cardiography.

RESULTS

V̇O2max exhibited a non-significant 4.1% increase (ES=0.24) for SIT with 7.0% P=0.007 (ES=0.40) increase for CET. Hemodynamic responses (maximal cardiac output, maximal stroke volume) displayed non-significant responses for CET and SIT while a-vO2dif-max increased from 15.8±4.8 to 18.3±2.9 mL/100 mL) (P=0.02) (ES=0.63) in SIT.

CONCLUSIONS

V̇O2max is a function of maximal cardiac output and a-vO2dif-max, so for a meaningful change to occur in cardiorespiratory fitness, there must be a concomitant increase in O2 delivery. This study demonstrates that a low volume SIT intervention evokes peripherally mediated responses (a-vO2dif) and anaerobic substrate utilization rather than O2 delivery components. Future works should address the time course of the responses and when assessing V̇O2max-based responses that due attention be given to the hemodynamic responses as means of quantification of the response.

Accuracy of the Cosmed K5 portable calorimeter

PURPOSE

The purpose of this study was to assess the accuracy of the Cosmed K5 portable metabolic system dynamic mixing chamber (MC) and breath-by-breath (BxB) modes against the criterion Douglas bag (DB) method.

METHODS

Fifteen participants (mean age±SD, 30.6±7.4 yrs) had their metabolic variables measured at rest and during cycling at 50, 100, 150, 200, and 250W. During each stage, participants were connected to the first respiratory gas collection method (randomized) for the first four minutes to reach steady state, followed by 3-min (or 5-min for DB) collection periods for the resting condition, and 2-min collection periods for all cycling intensities. Collection periods for the second and third methods were preceded by a washout of 1-3 min. Repeated measures ANOVAs were used to compare metabolic variables measured by each method, for seated rest and each cycling work rate.

RESULTS

For ventilation (VE) and oxygen uptake (VO2), the K5 MC and BxB modes were within 2.1 l/min (VE) and 0.08 l/min (VO2) of the DB (p≥0.05). Compared to DB values, carbon dioxide production (VCO2) was significantly underestimated by the K5 BxB mode at work rates ≥150W by 0.12-0.31 l/min (p<0.05). K5 MC and BxB respiratory exchange ratio values were significantly lower than DB at cycling work rates ≥100W by 0.03-0.08 (p<0.05).

CONCLUSION

Compared to the DB method, the K5 MC and BxB modes are acceptable for measuring VE and VO2 across a wide range of cycling intensities. Both K5 modes provided comparable values to each other.

Breath-by-breath oxygen uptake during running: Effects of different calculation algorithms

NEW FINDINGS

What is the central question of this study? Breath-by-breath gas exchange analysis during treadmill exercise can be disturbed by different breathing patterns depending on cadence, and the flow sensor might be subjected to variable mechanical stress. It is still unclear whether the outcomes of the gas exchange algorithms can be affected by running at different speeds. What is the main finding and its importance? Practically, the three investigated breath-by-breath algorithms ('Wessel', 'expiration-only' and 'independent breath') provided similar average gas exchange values for steady-state conditions. The 'independent breath' algorithm showed the lowest breath-by-breath fluctuations in the gas exchange data compared with the other investigated algorithms, both at steady state and during incremental exercise.

ABSTRACT

Recently, a new breath-by-breath gas exchange calculation algorithm (called 'independent breath') was proposed. In the present work, we aimed to compare the breath-by-breath O₂ uptake ( V ̇ O 2 ) values assessed in healthy subjects undergoing a running protocol, as calculated applying the 'independent breath' algorithm or two other commonly used algorithms. The traces of respiratory flow, O₂ and CO₂ fractions, used by the calculation algorithms, were acquired at the mouth on 17 volunteers at rest, during running on a treadmill at 6.5 and 9.5 km h^-1 , and thereafter up to volitional fatigue. Within-subject averages and standard deviations of breath-by-breath V ̇ O 2 were calculated for steady-state conditions; the V ̇ O 2 data of the incremental phase were analysed by means of linear regression, and their root mean square was assumed to be an index of the breath-by-breath fluctuations. The average values obtained with the different algorithms were significantly different (P < 0.001); nevertheless, from a practical point of view the difference could be considered 'small' in all the investigated conditions (effect size <0.3). The standard deviations were significantly lower for the 'independent breath' algorithm (post hoc contrasts, P < 0.001), and the slopes of the relationships with the corresponding data yielded by the other algorithms were <0.70. The root mean squares of the linear regressions calculated for the incremental phase were also significantly lower for the 'independent breath' algorithm, and the slopes of the regression lines with the corresponding values obtained with the other algorithms were <0.84. In conclusion, the 'independent breath' algorithm yielded the least breath-by-breath O₂ uptake fluctuation, both during steady-state exercise and during incremental running.

Wearable oxygen uptake and energy expenditure monitors

Obesity is a major health issue in both developed and developing countries. The balance between energy intake and exercise is important, and measurements of both energy intake and energy expenditure are required. Many studies have attempted to monitor energy intake via wearable technology, but no standard methods have yet been developed for this purpose. This is in marked contrast to the long history of measurement and estimation of energy expenditure. Indirect calorimetry is commonly used in the laboratory. Energy expenditure associated with daily activity is the most important measure, although a number of alternative measures have also been proposed. This mini-review discusses the current status of energy expenditure measurement.

Validity of Wrist-Worn Activity Trackers for Estimating VO2max and Energy Expenditure

Activity trackers are a simple and mostly low-priced method to capture physiological parameters. Despite the high number of wrist-worn devices, there is a lack of scientific validation. The purpose of this study was to assess whether the activity trackers represent a valid alternative to gold-standard methods in terms of estimating energy expenditure (EE) and maximum oxygen uptake (VO_2max). Twenty-four healthy subjects participated in this study. In total, five commercially available wrist-worn devices were tested with regard to their validity of EE and/or VO_2max. Estimated values were compared with indirect calorimetry. Validity of the activity trackers was determined by paired sample t-tests, mean absolute percentage errors (MAPE), Intraclass Correlation Coefficient, and Bland-Altman plots. Within the tested devices, differences in scattering in VO_2max and EE could be observed. This results in a MAPE > 10% for all evaluations, except for the VO_2max-estimation of the Garmin Forerunner 920XT (7.3%). The latter significantly underestimates the VO_2max (t(23) = –2.37, p = 0.027), whereas the Garmin Vivosmart HR significantly overestimates the EE (t(23) = 2.44, p = 0.023). The tested devices did not show valid results concerning the estimation of VO_2max and EE. Hence, the current wrist-worn activity trackers are most likely not accurate enough to be used for neither purposes in sports, nor in health care applications.

The "independent breath" algorithm: assessment of oxygen uptake during exercise

PURPOSE

Reduction of noise of breath-by-breath gas-exchange data is crucial to improve measurements. A recently described algorithm ("independent breath"), that neglects the contiguity in time of breaths, was tested.

METHODS

Oxygen, carbon dioxide fractions, and ventilatory flow were recorded continuously over 26 min in 20 healthy volunteers at rest, during unloaded and moderate intensity cycling and subsequent recovery; oxygen uptake ([Formula: see text]) was calculated with the "independent breath" algorithm (IND) and, for comparison, with three other "classical" algorithms. Average [Formula: see text] and standard deviations were calculated for steady-state conditions; non-linear regression was run throughout the [Formula: see text] data of the transient phases (ON and OFF), using a mono-exponential function.

RESULTS

Comparisons of the different algorithms showed that they yielded similar average [Formula: see text] at steady state (p = NS). The standard deviations were significantly lower for IND (post hoc contrasts, p < 0.001), with the slope of the relationship with the corresponding data obtained from "classical" algorithms being < 0.69. For both transients, the overall kinetics (evaluated as time delay + time constant) was significantly faster for IND (post hoc contrasts, p < 0.001). For the ON transient, the asymptotic standard errors of the kinetic parameters were significantly lower for IND, with the slope of the regression line with the corresponding values obtained from the "classical" algorithms being < 0.60.

CONCLUSION

The "independent breath" algorithm provided consistent average O₂ uptake values while reducing the overall noise of about 30%, which might result in the halving of the required number of repeated trials needed to assess the kinetic parameters of the ON transient.

Reply to Garcia-Tabar et al.: Quality control of open-circuit respirometry: real-time, laboratory-based systems. Let us spread "good practice"

PURPOSE

This article is in response to the Letter of Garcia-Tabar et al. [Eur J Appl Physiol (in press), 2018] relating to the issue of post-test sensor calibration 'verification'. This issue is poorly addressed in contemporary patient-related position statements on cardiopulmonary exercise testing (CPET).

METHODS

Post-test sensor calibration verification approaches were compared.

RESULT

The potential impact on data quality of changing sensor calibration during the course of an exercise test was described.

CONCLUSION

It is recommended that post-test sensor calibration verification be incorporated into existing CPET 'best practice'.