Estimate of mean tissue O2 consumption at onset of exercise in males

1987 ◽  
Vol 63 (4) ◽  
pp. 1578-1585 ◽  
Author(s):  
M. D. Inman ◽  
R. L. Hughson ◽  
K. H. Weisiger ◽  
G. D. Swanson
Keyword(s):  
Mathematical Model ◽  
Cardiac Output ◽  
Time Delay ◽  
Impedance Cardiography ◽  
Work Rate ◽  
Rate Of Change ◽  
O2 Consumption ◽  
Weighted Mean ◽  
Mean Response Time ◽  
The Mean

A mathematical model has been developed that permitted the calculation of the flow-weighted mean tissue O2 consumption (VO2T) at the onset of a step increase in work rate. From breath-by-breath measurements of alveolar O2 consumption (VO2A) and cardiac output (Q) by impedance cardiography and assumptions about the site of depletion of O2 stores, the rate of change in O2 stores (VO2s) was determined. The sum of VO2A + VO2s = VO2T. Six very fit males performed six repetitions of each of two step increases in work rate. STlo was a transition from rest to 100-W cycling; SThi was a transition from 100- to 200-W cycling. For each work rate transition, the responses of VO2A and Q were averaged over the six repetitions of each subject and the model was solved to yield VO2T. The responses of VO2A, VO2T, and Q after the increase in work rate were fit with a monoexponential function. This function included a time constant and time delay, the sum of which gave the mean response time (MRT). In the STlo test, the MRT of VO2A (24.9 +/- 1.1 s, mean +/- SE) was longer than that of VO2T (15.3 +/- 1.3 s) and of Q (16.5 +/- 6.5 s) (P less than 0.05). The MRT of VO2T and Q did not differ significantly. Also for SThi, the MRT of VO2A (34.4 +/- 3.3 s) was significantly longer than that of VO2T (30.0 +/- 3.4 s) (P less than 0.05). The MRT of VO2T and Q (30.3 +/- 5.5 s) were not significantly different at this work rate either.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of extracellular Po 2 on the fall in intracellular Po 2 in contracting single myocytes

2003 ◽  
Vol 94 (5) ◽  
pp. 1964-1970 ◽  
Author(s):  
Casey A. Kindig ◽  
Richard A. Howlett ◽  
Michael C. Hogan
Keyword(s):  
Skeletal Muscle ◽  
Time Delay ◽  
Time Constant ◽  
Initial Rate ◽  
Metabolic Response ◽  
Rate Of Change ◽  
Phosphorescence Quenching ◽  
Mean Response Time ◽  
The Mean ◽  
Lumbrical Muscles

The purpose of this investigation was to study the effects of altered extracellular Po 2 (Pe O2 ) on the intracellular Po 2(Pi O2 ) response to contractions in single skeletal muscle cells. Single myocytes ( n = 12) were dissected from lumbrical muscles of adult female Xenopus laevis and injected with 0.5 mM Pd- meso-tetra(4-carboxyphenyl)porphine for assessment of Pi O2 via phosphorescence quenching. At a Pe O2 of ∼20 (low), ∼40 (moderate), and ∼60 (high) Torr, tetanic contractions were induced at a frequency of 0.67 Hz for ∼2 min with a 5-min recovery between bouts (blocked order design). The Pi O2 response to contractions was characterized by a time delay followed by a monoexponential decline to steady-state (SS) values. The fall in Pi O2 to SS values was significantly greater at each progressively greater Pe O2 (all P < 0.05). The mean response time (time delay + time constant) was significantly faster in the low (35.2 ± 5.1 s; P < 0.05 vs. high) and moderate (43.3 ± 6.4 s; P < 0.05 vs. high) compared with high Pe O2 (61.8 ± 9.4 s) and was correlated positively ( r = 0.965) with the net fall in Pi O2 . However, the initial rate of change of Pi O2 (calculated as net fall in Pi O2 /time constant) was not different ( P > 0.05) among Pe O2 trials. These latter data suggest that, over the range of 20–60 Torr, Pe O2 does not play a deterministic role in setting the initial metabolic response to contractions in isolated frog myocytes. Additionally, these results suggest that oxidative phosphorylation in these myoglobin-free myocytes may be compromised by Pe O2 at values nearing 60 Torr.

scholarly journals Establishing the V̇o2 versus constant-work-rate relationship from ramp-incremental exercise: simple strategies for an unsolved problem

2019 ◽  
Vol 127 (6) ◽  
pp. 1519-1527 ◽  
Author(s):  
Danilo Iannetta ◽  
Rafael de Almeida Azevedo ◽  
Daniel A. Keir ◽  
Juan M. Murias
Keyword(s):  
Lactate Threshold ◽  
Unsolved Problem ◽  
Critical Power ◽  
Work Rate ◽  
Incremental Exercise ◽  
Mean Response Time ◽  
Constant Work Rate ◽  
Ramp Exercise ◽  
The Mean ◽  
Highly Correlated

The dissociation between constant work rate of O2 uptake (V̇o2) and ramp V̇o2 at a given work rate might be mitigated during slowly increasing ramp protocols. This study characterized the V̇o2 dynamics in response to five different ramp protocols and constant-work-rate trials at the maximal metabolic steady state (MMSS) to characterize 1) the V̇o2 gain (G) in the moderate, heavy, and severe domains, 2) the mean response time of V̇o2 (MRT), and 3) the work rates at lactate threshold (LT) and respiratory compensation point (RCP). Eleven young individuals performed five ramp tests (5, 10, 15, 25, and 30 W/min), four to five time-to-exhaustions for critical power estimation, and two to three constant-work-rate trials for confirmation of the work rate at MMSS. G was greatest during the slowest ramp and progressively decreased with increasing ramp slopes (from ~12 to ~8 ml·min−1·W−1, P < 0.05). The MRT was smallest during the slowest ramp slopes and progressively increased with faster ramp slopes (1 ± 1, 2 ± 1, 5 ± 3, and 10 ± 4, 15 ± 6 W, P < 0.05). After “left shifting” the ramp V̇o2 by the MRT, the work rate at LT was constant regardless of the ramp slope (~150 W, P > 0.05). The work rate at MMSS was 215 ± 55 W and was similar and highly correlated with the work rate at RCP during the 5 W/min ramp ( P > 0.05, r = 0.99; Lin’s concordance coefficient = 0.99; bias = −3 W; root mean square error = 6 W). Findings showed that the dynamics of V̇o2 (i.e., G) during ramp exercise explain the apparent dichotomy existing with constant-work-rate exercise. When these dynamics are appropriately “resolved”, LT is constant regardless of the ramp slope of choice, and RCP and MMSS display minimal variations between each other. NEW & NOTEWORTHY This study demonstrates that the dynamics of V̇o2 during ramp-incremental exercise are dependent on the characteristics of the increments in work rate, such that during slow-incrementing ramp protocols the magnitude of the dissociation between ramp V̇o2 and constant V̇o2 at a given work rate is reduced. Accurately accounting for these dynamics ensures correct characterizations of the V̇o2 kinetics at ramp onset and allows appropriate comparisons between ramp and constant-work-rate exercise-derived indexes of exercise intensity.

Response time of cardiac mitochondrial oxygen consumption to heart rate steps

1991 ◽  
Vol 260 (2) ◽  
pp. H613-H625 ◽  
Author(s):  
J. H. Van Beek ◽  
N. Westerhof
Keyword(s):  
Heart Rate ◽  
Response Time ◽  
Time Course ◽  
Mean Transit Time ◽  
Impulse Response Function ◽  
Heart Tissue ◽  
Experimental Information ◽  
O2 Consumption ◽  
Mean Response Time ◽  
The Mean

We investigated the time course of cardiac mitochondrial O2 consumption following steps in heart rate in 16 isolated rabbit hearts perfused with Tyrode solution. The time course was characterized by the mean response time, i.e., the first statistical moment (mean time) of the impulse response function. Like the mean transit time for an indicator, it provides an important characteristic of the response time course. The venous O2 content transients during steps in heart rate were measured and corrected for O2 diffusion and vascular transport using a mathematical model with experimental information derived from O2 washout following steps in arterial O2 concentration or perfusion flow. We deduce from these washout experiments that the effective O2 solubility in heart tissue is 86 +/- 13% (mean +/- SE) of solubility in water. The measured venous mean response time following a step in heart rate at 37 degrees C was 17.6 +/- 1.1 s. The mean response time of cardiac mitochondrial O2 consumption to changes in heart rate after correction for O2 transport was 7.7 +/- 0.7 s.

Comparison of two noninvasive techniques for estimating cardiac output during exercise

1986 ◽  
Vol 61 (1) ◽  
pp. 155-159 ◽  
Author(s):  
D. D. Hatcher ◽  
O. D. Srb
Keyword(s):  
Cardiac Output ◽  
Large Range ◽  
Impedance Plethysmography ◽  
Cycle Ergometer ◽  
O2 Consumption ◽  
Noninvasive Techniques ◽  
Transthoracic Impedance ◽  
The Mean ◽  
The Difference ◽  
Male Subjects

This study presents the comparison of two different noninvasive techniques for the estimation of cardiac output (Q). The two techniques used were transthoracic impedance plethysmography (Z) and the indirect Fick CO2 rebreathing (RB) method. Paired estimates of Q were made on 60 different male subjects at rest and during graded increments of work on a cycle ergometer. The mean resting Q as measured by the Z technique (COZ) was 7.46 +/- 0.35 and 5.96 +/- 0.43 l/min using the RB (CORB) technique. At 200 W the mean COZ was 18.67 +/- 0.72 l/min and the CORB was 23.73 +/- 0.84 l/min. Both the techniques were linearly correlated (R) with O2 consumption; i.e., RZ = 0.752, RRB = 0.855. The difference between these two R values is statistically significant (P less than 0.001). A linear relationship was found between the Z and RB techniques at all work loads (R = 0.75). This study suggests that both techniques are equally as reliable over a large range of work loads, with the Z technique being the simplest and most efficient to implement. It was also found that lung volume had no effect on the calculated COZ.

V˙co 2 andV˙e kinetics during moderate- and heavyintensity exercise after acetazolamide administration

1999 ◽  
Vol 86 (5) ◽  
pp. 1534-1543 ◽  
Author(s):  
Barry W. Scheuermann ◽  
John M. Kowalchuk ◽  
Donald H. Paterson ◽  
David A. Cunningham
Keyword(s):  
Carbonic Anhydrase ◽  
Ventilatory Threshold ◽  
Exponential Model ◽  
Work Rate ◽  
Model Fit ◽  
Mean Response Time ◽  
Carbonic Anhydrase Inhibition ◽  
Nonsteady State ◽  
The Mean ◽  
The Difference

The effect of carbonic anhydrase inhibition with acetazolamide (Acz) on CO2 output (V˙co 2) and ventilation (V˙e) kinetics was examined during moderate- and heavy-intensity exercise. Seven men [24 ± 1 (SE) yr] performed cycling exercise during control (Con) and Acz (10 mg/kg body wt iv) sessions. Each subject performed step transitions (6 min) in work rate from 0 to 100 W [below ventilatory threshold (<V˙eT)] and to an O2 uptake corresponding to ∼50% of the difference between the work rate atV˙eT and peak O2 uptake [above ventilatory threshold (>V˙eT)].V˙e and gas exchange were measured breath by breath. The time constant (τ) was determined for exercise <V˙eT by using a single-exponential model (fit between 20 s and end-exercise); the mean response time (MRT) was determined for exercise >V˙eT by using a three-component model (fit from the start of exercise).V˙co 2 kinetics were slower in Acz (<V˙eT, τ = 45 ± 6 s; >V˙eT, MRT = 75 ± 10 s) than Con (<V˙eT, τ = 34 ± 6 s; >V˙eT, MRT = 54 ± 7 s). During <V˙eT exercise,V˙e kinetics were slower in Acz (τ = 48 ± 6 s) than Con (τ = 34 ± 6 s), but >V˙eT kinetics were faster in Acz (MRT = 85 ± 17 s) than Con (MRT = 106 ± 16 s). Carbonic anhydrase inhibition slowedV˙co 2 kinetics during both moderate- and heavy-intensity exercise, demonstrating impaired CO2 elimination in the nonsteady state of exercise. The slowedV˙e kinetics in Acz during exercise <V˙eT is consistent with a mechanism coupling V˙e kinetics with the flow of CO2 to the lungs.

Oxygen uptake kinetics from ramp work tests: variability of single test values

1986 ◽  
Vol 61 (1) ◽  
pp. 373-376 ◽  
Author(s):  
R. L. Hughson ◽  
M. D. Inman
Keyword(s):  
Ventilatory Threshold ◽  
Oxygen Uptake Kinetics ◽  
Work Rate ◽  
Base Line ◽  
Exercise Tests ◽  
Kinetics Parameters ◽  
Mean Response Time ◽  
Vo2 Kinetics ◽  
The Mean ◽  
The Individual

The variability in the estimation of the mean response time (MRT) of O2 uptake (VO2) kinetics from single ramp work rate exercise tests was examined in six repetitions by five fit subjects. Work rate increased at 50 W/min from a base line of 25 W to a work rate of 120% ventilatory threshold. Breath-by-breath data were analyzed by linear regression from 2 min after the onset of the ramp to the 120% work rate. Individual subjects showed approximately twofold differences in estimates of MRT; the coefficient of variation from individuals ranged from 18.5 to 29.3%. The MRT obtained as the mean from the individual repetitions did not differ from the MRT obtained from pooled within-subject data. Analysis of variance on the individual MRT estimates showed 53.9% of the variability was attributable to the slope of the regression, whereas only 2.4% could be attributed to baseline VO2. It was concluded that several repetitions of the ramp work rate tests should be pooled prior to estimation of kinetics parameters.

Batch Crystallization with Crystals Attrition

1993 ◽  
Vol 58 (8) ◽  
pp. 1855-1860 ◽  
Author(s):  
Jaroslav Nývlt ◽  
Stanislav Žáček
Keyword(s):  
Mathematical Model ◽  
Calcium Sulfate ◽  
Crystal Size ◽  
Theoretical Description ◽  
Secondary Nucleation ◽  
Batch Crystallization ◽  
Batch Time ◽  
The Mean

The dependence of the mean crystal size of the products from batch crystallizers on the batch time occasionally exhibits a maximum, which can be explained by secondary nucleation due to the attrition of crystals. A kinetic equatation of nucleation, comprising a term for crystal attrition, can be used for the theoretical description of such behaviour. A mathematical model of a batch crystallizer with crystal attrition has been verified on the calcium sulfate precipitation.

scholarly journals Development of Perceptual Inhibition in Adolescents—a Critical Period?

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 457
Author(s):  
Isabel María Introzzi ◽  
María Marta Richard’s ◽  
Yesica Aydmune ◽  
Eliana Vanesa Zamora ◽  
Florencia Stelzer ◽  
...  
Keyword(s):  
Response Time ◽  
Executive Functions ◽  
Critical Period ◽  
Search Task ◽  
Probability Distributions ◽  
Linear Trajectory ◽  
Gaussian Functions ◽  
Mean Response Time ◽  
The Mean ◽  
One Year

Recent studies suggest that the developmental curves in adolescence, related to the development of executive functions, could be fitted to a non-linear trajectory of development with progressions and retrogressions. Therefore, the present study proposes to analyze the pattern of development in Perceptual Inhibition (PI), considering all stages of adolescence (early, middle, and late) in intervals of one year. To this aim, we worked with a sample of 275 participants between 10 and 25 years, who performed a joint visual and search task (to measure PI). We have fitted ex-Gaussian functions to the probability distributions of the mean response time across the sample and performed a covariance analysis (ANCOVA). The results showed that the 10- to 13-year-old groups performed similarly in the task and differ from the 14- to 19-year-old participants. We found significant differences between the older group and all the rest of the groups. We discuss the important changes that can be observed in relation to the nonlinear trajectory of development that would show the PI during adolescence.

Sign in / Sign up

Export Citation Format

Share Document