The influence of metabolic and circulatory heterogeneity on the expression of pulmonary oxygen uptake kinetics in humans

Keir, Daniel A.; Robertson, Taylor C.; Benson, Alan P.; Rossiter, Harry B.; Kowalchuk, John M.

doi:10.1113/ep085338

Cited by 39 publications

(30 citation statements)

References 35 publications

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“…However, it is becoming clearer (Hughson, ; Keir et al . ) that models that consider the complex interaction between O 2 delivery and utilization are more appropriate to study aerobic system dynamics. In fact, we showed that the overall

p {\overset{V}{true}}_{O_{2}}

dynamic is composed of a complex interaction between multiple‐order systems.…”

Section: Discussionmentioning

confidence: 99%

“…; Keir et al . ), absolute and relative standard error (SE and %SE, respectively) and the statistical significance level ( P ) of the estimated parameters.…”

Section: Methodsmentioning

confidence: 99%

“…; Keir et al . ) between the monotonic exercise transitions (25 ↔ 100 W), with identical system dynamics between on‐ and off‐transitions (Hoffmann et al . ); thus:

false[(a_{0} + a) t f false] - false[\sum_{t = 0}^{t f} a_{0} + a (1 - e^{- t / M R T}) false] = false(normalp {\dot{V}}_{normalO 2} (t f) false) - false(normalp {\dot{V}}_{normalO 2} (t f) - a_{0} false) \times false(1 - e^{- t / M R T} false)

, where

t f

is the length of the PRBS unit.…”

Section: Methodsmentioning

confidence: 99%

“…Previous studies (Hughson & Morrissey, ; Keir et al . ; Wilcox et al . ) have shown that the apparent first‐order

p {\overset{V}{true}}_{O_{2}}

dynamics to a

\overset{W}{true}

increase can be the resultant of the complex interaction between the static and dynamic aerobic system gains that are directly influenced by the O 2 delivery–utilization balance.…”

Section: Introductionmentioning

confidence: 99%

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Linear and non‐linear contributions to oxygen transport and utilization during moderate random exercise in humans

Beltrame

Hughson

2017

Experimental Physiology

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What is the central question of this study? The pulmonary oxygen uptake (pV̇O2) data used to study the muscle aerobic system dynamics during moderate-exercise transitions is classically described as a mono-exponential function controlled by a complex interaction of the oxygen delivery-utilization balance. This elevated complexity complicates the acquisition of relevant information regarding aerobic system dynamics based on pV̇O2 data during a varying exercise stimulus. What is the main finding and its importance? The elevated complexity of pV̇O2 dynamics is a consequence of a multiple-order interaction between muscle oxygen uptake and circulatory distortion. Our findings challenge the use of a first-order function to study the influences of the oxygen delivery-utilization balance over the pV̇O2 dynamics. The assumption of aerobic system linearity implies that the pulmonary oxygen uptake (pV̇O2) dynamics during exercise transitions present a first-order characteristic. The main objective of this study was to test the linearity of the oxygen delivery-utilization balance during random moderate exercise. The cardiac output (Q̇) and deoxygenated haemoglobin concentration ([HHb]) were measured to infer the central and local O availability, respectively. Thirteen healthy men performed two consecutive pseudorandom binary sequence cycling exercises followed by an incremental protocol. The system input and the outputs pV̇O2, [HHb] and Q̇ were submitted to frequency-domain analysis. The linearity of the variables was tested by computing the ability of the response at a specific frequency to predict the response at another frequency. The predictability levels were assessed by the coefficient of determination. In a first-order system, a participant who presents faster dynamics at a specific frequency should also present faster dynamics at any other frequency. All experimentally obtained variables (pV̇O2, [HHb] and Q̇) presented a certainly degree of non-linearity. The local O availability, evaluated by the ratio pV̇O2/[HHb], presented the most irregular behaviour. The overall [HHb] kinetics were faster than pV̇O2 and Q̇ kinetics. In conclusion, the oxygen delivery-utilization balance behaved as a non-linear phenomenon. Therefore, the elevated complexity of the pulmonary oxygen uptake dynamics is governed by a complex multiple-order interaction between the oxygen delivery and utilization systems.

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p {\overset{V}{true}}_{O_{2}}

dynamic is composed of a complex interaction between multiple‐order systems.…”

Section: Discussionmentioning

confidence: 99%

“…; Keir et al . ), absolute and relative standard error (SE and %SE, respectively) and the statistical significance level ( P ) of the estimated parameters.…”

Section: Methodsmentioning

confidence: 99%

“…; Keir et al . ) between the monotonic exercise transitions (25 ↔ 100 W), with identical system dynamics between on‐ and off‐transitions (Hoffmann et al . ); thus:

false[(a_{0} + a) t f false] - false[\sum_{t = 0}^{t f} a_{0} + a (1 - e^{- t / M R T}) false] = false(normalp {\dot{V}}_{normalO 2} (t f) false) - false(normalp {\dot{V}}_{normalO 2} (t f) - a_{0} false) \times false(1 - e^{- t / M R T} false)

, where

t f

is the length of the PRBS unit.…”

Section: Methodsmentioning

confidence: 99%

“…Previous studies (Hughson & Morrissey, ; Keir et al . ; Wilcox et al . ) have shown that the apparent first‐order

p {\overset{V}{true}}_{O_{2}}

dynamics to a

\overset{W}{true}

increase can be the resultant of the complex interaction between the static and dynamic aerobic system gains that are directly influenced by the O 2 delivery–utilization balance.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Linear and non‐linear contributions to oxygen transport and utilization during moderate random exercise in humans

Beltrame

Hughson

2017

Experimental Physiology

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show abstract

“…The mean response time ( MRT ) was calculated by adding t and TD (Macdonald et al, 1997). The quality of the fitting was assured by the analysis of squared error, coefficient of determination ( r 2 ), 95% confidence interval band ( CI 95 ) of the model (Fawkner et al, 2002; Keir et al, 2016) and the significance level ( p -value) of the estimated parameters. The comparison between MNG and τ, both derived from measured

\overset{V}{true} O_{2}

data, has the purpose to experimentally support the expected correlation between both parameters (further demonstrated by computer simulations).…”

Section: Methodsmentioning

confidence: 99%

Mean Normalized Gain: A New Method for the Assessment of the Aerobic System Temporal Dynamics during Randomly Varying Exercise in Humans

Beltrame

Hughson

2017

Front. Physiol.

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The temporal dynamics of the oxygen uptake (trueV˙O2) during moderate exercise has classically been related to physical fitness and a slower trueV˙O2 dynamics was associated with deterioration of physical health. However, methods that better characterize the aerobic system temporal dynamics remain challenging. The purpose of this study was to develop a new method (named mean normalized gain, MNG) to systematically characterize the trueV˙O2 temporal dynamics. Eight healthy, young adults (28 ± 6 years old, 175 ± 7 cm and 79 ± 13 kg) performed multiple pseudorandom binary sequence cycling protocols on different days and time of the day. The MNG was calculated as the normalized amplitude of the trueV˙O2 signal in frequency-domain. The MNG was validated considering the time constant τ obtained from time-domain analysis as reference. The intra-subject consistency of the MNG was checked by testing the same participant on different days and times of the day. The MNG and τ were strongly negatively correlated (r = −0.86 and p = 0.005). The MNG measured on different days and periods of the day was similar between conditions. Calculations for the MNG have inherent filtering characteristics enhancing reliability for the evaluation of the aerobic system temporal dynamics. In conclusion, the present study successfully validated the use of the MNG for aerobic system analysis and as a potential complementary tool to assess changes in physical fitness.

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Association between $$\dot{\text{V}}$$O2 kinetics and $$\dot{\text{V}}$$O2max in groups differing in fitness status

2021

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The influence of metabolic and circulatory heterogeneity on the expression of pulmonary oxygen uptake kinetics in humans

Abstract: What is the main finding and its importance? 31Here we demonstrate how a first-order system can respond with non-first-order response 32

Cited by 39 publications

References 35 publications

Linear and non‐linear contributions to oxygen transport and utilization during moderate random exercise in humans

Linear and non‐linear contributions to oxygen transport and utilization during moderate random exercise in humans

Mean Normalized Gain: A New Method for the Assessment of the Aerobic System Temporal Dynamics during Randomly Varying Exercise in Humans

Association between $$\dot{\text{V}}$$O2 kinetics and $$\dot{\text{V}}$$O2max in groups differing in fitness status

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