63,107 research outputs found
Confidence intervals estimator of the kinetic parameters: do its reliability depend on the assembling method of the oxygen uptakes?
No full textGas 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 Asymptotic Standard Errors; ASEs). We tested, for two different assembling procedures, whether the range of values identified by the ASE actually correspond to the 95% Confidence Interval. Ten O2 uptake responses were acquired on 10 healthy volunteers performing a square-wave moderate-intensity exercise. Kinetic parameters were estimated running the non-linear regression with a mono-exponential model on an increasingly greater number of responses (Nr, from 1 to 10), assembled together using the “stacking” and the “1-s-bins” procedures. Kinetic values obtained assembling together the 10 repetitions were assumed as “true” values. The time constant was not affected by Nr or by the assembling procedure (ANOVA; p>0.54 and p>0.16, respectively). The corresponding ASE decreased according to Nr (ANOVA; p=0.000), being significantly smaller for the “1-s-bins” procedure compared to the “stacking” one (ANOVA; p<0.001). Excluding 20s at the start of the fitting window, the range of values identified with the ASE provided by the “1-s-bins” and the “stacking” procedures included the “true” value in 85% and in 95% of cases, respectively. The “stacking” procedure should be preferred since it yielded ASEs for the time constant that provided a range of values satisfying the statistical meaning of the width of the Confidence Intervals, at the given degree of probability
The 1-s interpolation of breath-by-breath O2 uptake data to determine kinetic parameters: the misleading procedure
No full textThe algorithm used for the calculation of gas exchange affects the estimation of O2 uptake kinetics at the onset of moderate-intensity exercise
No full textAbstract: 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 0.07). 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. New Findings: What is the central question of this study? Is the kinetics of breath-by-breath gas exchange at the start of a square-wave moderate intensity exercise faster when accounting for the changes in lung gas stores? What is the main finding and its importance? Accounting for the changes in lung gas stores, the time constant of the (Formula presented.) kinetics changed less when the data pertaining to the initial period were progressively removed; time delays and mean response times were faster. Consequently, using different gas exchange calculation algorithms, the physiological phenomena occurring at the beginning of moderate-intensity exercise are characterized differently
Interchangeability between two breath-by-breath O2 uptake calculation algorithms in asthmatic and healthy volunteers
No full textIntroduction: 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 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
Mitochondrial coupling in humans: assessment of the P/O2 ratio at the onset of calf exercise
No full textCoupling of oxidation to ATP synthesis (P/O2 ratio) is a critical step in the conversion of carbon substrates to fuel (ATP) for cellular activity. The ability to quantitatively assess mitochondrial coupling in vivo can be a valuable tool for basic research and clinical purposes. At the onset of a square wave moderate
exercise, the ratio between absolute amount of phosphocreatine
split and O2 deficit (corrected for the amount of O2 released from the body O2 stores and in the absence of lactate production), is the mirror image of the P/O2 ratio. To calculate this value, cardiac output Q'; whole bodyO2 uptake V'O2;O2 deficit O2def and high-energy phosphates concentration (by 31P-NMR spectroscopy) in the calf muscles were measured on nine healthy volunteers at rest and during moderate intensity plantar flexion exercise (3.44 ± 0.73 W per unit active muscle mass). _Q and _V O2 increased (from 4.68 ± 1.56 to 5.83 ± 1.59 l min–1 and from 0.28 ± 0.05 to 0.48 ± 0.09 l min–1, respectively), while phosphocreatine (PCr) concentration decreased significantly
(22 ± 6%) from rest to steady-state exercise. For each volunteer, ‘‘gross’’ O2def was corrected for the individual
changes in the venous blood O2 stores (representing 49.9 +- 9.5% of the gross O2def) yielding the ‘‘net’’ O2def. Resting PCr concentration was estimated from the appropriate spectroscopy data. The so calculated P/O2 ratio amounted on average to 4.24 ± 0.13 and was, in all nine subjects, very close to the literature values obtained directly on intact skeletal muscle. This unfolds the prospect of a non-invasive tool to quantitatively study mitochondrial coupling in vivo
Mithocondrial coupling in humans: assessment of the P/O2 ratio at the onset of calf exercise
No full textCoupling of oxidation to ATP synthesis (P/O2 ratio) is a critical step in the conversion of carbon substrates to fuel (ATP) for cellular activity. The ability to quantitatively assess mitochondrial coupling in vivo can be a valuable tool for basic research and clinical purposes. At the onset of a square wave moderate exercise, the ratio between absolute amount of phosphocreatine split and O2 deficit (corrected for the amount of O2 released from the body O2 stores and in the absence of lactate production), is the mirror image of the P/O2 ratio. To calculate this value, cardiac output (Q), whole body O2 uptake (VO2), O2 deficit (O2(def)) and high-energy phosphates concentration (by 31P-NMR spectroscopy) in the calf muscles were measured on nine healthy volunteers at rest and during moderate intensity plantar flexion exercise (3.44 +/- 0.73 W per unit active muscle mass). Q and VO2 increased (from 4.68 +/- 1.56 to 5.83 +/- 1.59 l min(-1) and from 0.28 +/- 0.05 to 0.48 +/- 0.09 l min(-1), respectively), while phosphocreatine (PCr) concentration decreased significantly (22 +/- 6%) from rest to steady-state exercise. For each volunteer, "gross" O2(def) was corrected for the individual changes in the venous blood O2 stores (representing 49.9 +/- 9.5% of the gross O2(def)) yielding the "net" O2(def). Resting PCr concentration was estimated from the appropriate spectroscopy data. The so calculated P/O2 ratio amounted on average to 4.24 +/- 0.13 and was, in all nine subjects, very close to the literature values obtained directly on intact skeletal muscle. This unfolds the prospect of a non-invasive tool to quantitatively study mitochondrial coupling in vivo
Management of exercise-induced glycaemic imbalances in type 1 diabetes
No full textRegular moderate-intensity exercise is strongly recommended for its beneficial effects in all people. In patients with type 1 diabetes, however, the exercise-associated glycemic imbalances remain an unresolved clinical challenge. Current guidelines require an in-depth understanding of the glycemic responses to exercise and each patient has to discover, by trial-and-error, his/her own strategy, several attempts being usually required to gain sufficient experience. Consequently, fear of hypoglycemia remains the strongest barrier to physical activity. This paper explores the potential strategies that may be employed to minimize the risk of exercise related glycemic imbalances. Moreover, a newly developed algorithm (ECRES, Exercise Carbohydrate Requirement Estimating Software) is described, which estimates on a patient-and situation-specific basis the glucose supplement required by the patient to maintain safe blood glucose levels. The algorithm was tested on 27 patients who performed three 1-hr constant intensity walks (each starting at a different time interval following insulin injection). Results showed that in 70.4% of the trials, independent of the time of day, the algorithm provided a satisfactory estimate of the carbohydrates needed by patients to complete the exercise with a glucose level within safe thresholds (i.e. 3.9 - 10 mmol·L -1). Despite the algorithm requires further experimental testing to be applied by the majority of patients, these results indicate its potential usefulness as a tool for preventing immediate exercise-induced glycemic imbalances (i.e. during exercise) in type 1 diabetic patients, in particular for spontaneous activities not planned in advance, thus allowing all insulin-dependent patients to safely enjoy the benefits of exercise
Modeling of glycogen resynthesis according to insulin concentration: Towards a system for prevention of late-onset exercise-induced hypoglycemia in Type 1 diabetes patients
No full textOne of the major barriers for physical activity in type 1 diabetes (T1D) patients is the risk of exercise-induced hypoglycemia, in particular the late-onset one. The identification of the relation between glycogen resynthesis rate after an exercise and insulin concentration would allow the development of new predictive models. The aim of the present work was thus to investigate this relation in T1D patients. We recruited 8 T1D subjects which underwent two 24-h observational experimental sessions: complete rest and a 3-hours treadmill walk. Glucose and insulin concentrations were measured throughout the two sessions. Comparing the data collected in the two sessions, the net glucose uptake was calculated; positive values were suggestive of glycogen repletion while negative values suggested liver glycogen breakdown. A significant correlation (r=0.742, p<0.001) was observed between insulin concentration and net glucose uptake, with the negative values corresponding to time periods showing the lowest insulin concentrations. In conclusion, the present study preliminarily assessed the impact of insulin concentration on the risk of late onset hypoglycemia, which is the first step towards a comprehensive and personalized system for prevention of exercise-induced hypoglycemia in Type 1 diabetes patients
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