Confidence intervals estimator of the kinetic parameters: do its reliability depend on the assembling method of the oxygen uptakes?

Gas exchange data acquired repeatedly under the same exercise conditions are assembled together to improve the kinetic parameters of breath-by-breath oxygen uptake. The latter are provided by the non-linear regression procedure, together with the corresponding estimators of the width of the Confidence Intervals (i.e.

The algorithm used for the calculation of gas exchange affects the estimation of O 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 O uptake at the mouth is approximated to a mono-exponential function, whose time constant is considered matched to that of the O 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.

Influence of the fitting window on the O uptake kinetics at the onset of moderate intensity exercise.

The O uptake (V̇o) data at the onset of an exercise are usually fitted with a mono-exponential function, after removal of the data pertaining to a conventional initial time period (ΔTr) lasting ∼20 s. We performed a thorough quantitative analysis on the effects of removing data pertaining to different ΔTr, aiming at identifying an objective method to establish the appropriate ΔTr. Breath-by-breath O uptake responses, acquired from 25 healthy adults performing a step moderate-intensity exercise, and 10 simulated biexponential responses, were analyzed.

Interchangeability between two breath-by-breath O 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 O 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'O) was calculated with the two algorithms under comparison.

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.

Comparison of different breath-by-breath gas exchange algorithms using a gas exchange simulation system.

Background: Mechanical Gas Exchange Simulation Systems (GESS) have never been used to compare different breath-by-breath oxygen uptake calculation algorithms.

Methods: Oxygen uptakes were calculated for each GESS cycle by the "Expiration-only" algorithm (estimating inspiratory volume from the expiratory one), and by two "alveolar" algorithms (both processing inspiratory and expiratory flows and designed to account for the changes in lung gas stores). The volume of oxygen stored in the GESS from one cycle to the subsequent one was either maintained constant or increased/decreased by changing the pumped gas volumes.

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.

Calculation algorithms for breath-by-breath alveolar gas exchange: the unknowns!

Purpose: Several papers (algorithm papers) describe computational algorithms that assess alveolar breath-by-breath gas exchange by accounting for changes in lung gas stores. It is unclear, however, if the effects of the latter are actually considered in literature. We evaluated dissemination of algorithm papers and the relevant provided information.

Assessing breath-by-breath alveolar gas exchange: is the contiguity in time of breaths mandatory?

Purpose: A new algorithm is illustrated for the determination of breath-by-breath alveolar gas exchange that neglects the contiguity in time of breaths, i.e. it allows the breaths to be partially superimposed or disjoined in time.

Calculation algorithms alter the breath-by-breath gas exchange values when abrupt changes in ventilation occur.

The automatic metabolic units calculate breath-by-breath gas exchange from the expiratory data only, applying an algorithm ('expiration-only' algorithm) that neglects the changes in the lung gas stores. These last are theoretically taken into account by a recently proposed algorithm, based on an alternative view of the respiratory cycle ('alternative respiratory cycle' algorithm). The performance of the two algorithms was investigated where changes in the lung gas stores were induced by abrupt increases in ventilation above the physiological demand.

Influence of phosphagen concentration on phosphocreatine breakdown kinetics. Data from human gastrocnemius muscle.

At the onset of a square-wave exercise of moderate intensity, in the absence of any detectable lactate production, the hydrolysis of phosphocreatine (PCr) fills the gap between energy requirement and energy yield by oxidative pathways, thus representing a readily available source of energy for the muscle. We verified experimentally the relationships between high-energy phosphates and/or their changes and the time constant of PCr concentration ([PCr]) kinetics in humans (tau(PCr)). High-energy phosphate concentration (by (31)P-NMR spectroscopy) in the calf muscles were measured during three repetitions of the rest-to-work transition of moderate aerobic square-wave exercise on nine healthy volunteers, while resting [PCr] was estimated from the appropriate spectroscopy data.

Vastus lateralis O2 desaturation in response to fast and short maximal contraction.

Purpose: The purpose of this study was to investigate, in heavy-resistance strength-trained (N = 10) and untrained (N = 10) subjects, the vastus lateralis muscle oxyhemoglobin (O2Hb) desaturation time course in response to a brief, maximal, voluntary isometric contraction.

Methods: The two groups were not statistically different physically. Mean (+/- SD) age, height, and body mass of all the subjects were 28.

Functional activity mapping of the mesial hemispheric wall during anticipation of pain.

The relative contributions of autonomic arousal and of cognitive processing to cortical activity during anticipation of pain, and the role of changes in thalamic outflow, are still largely unknown. To address these issues, we investigated with functional magnetic resonance imaging (fMRI) the activity of the contralateral mesial hemispheric wall in 56 healthy volunteers while they expected the stimulation of one foot, which could be either painful or innocuous. The waiting period was characterized by emotional arousal, a moderate rise in heart rate, and by increases in mean fMRI signals in the medial thalamus, mid- and posterior cingulate cortex, and in the putative foot area of the primary somatosensory and motor cortex.