scholarly journals Effects of hypoxic hypoxia on O2 uptake and heart rate kinetics during heavy exercise

1996 ◽  
Vol 81 (6) ◽  
pp. 2500-2508 ◽  
Author(s):  
Marielle Engelen ◽  
Janos Porszasz ◽  
Marshall Riley ◽  
Karlman Wasserman ◽  
Kazuhira Maehara ◽  
...  
Keyword(s):  
Heart Rate ◽  
Time Constant ◽  
Slow Component ◽  
Hypoxic Hypoxia ◽  
Baseline Heart Rate ◽  
Heavy Exercise ◽  
Rate Kinetics ◽  
Lactic Acidosis Threshold ◽  
Kinetics Of ◽  
Heart Rate Kinetics

Engelen, Marielle, Janos Porszasz, Marshall Riley, Karlman Wasserman, Kazuhira Maehara, and Thomas J. Barstow. Effects of hypoxic hypoxia on O2 uptake and heart rate kinetics during heavy exercise. J. Appl. Physiol. 81(6): 2500–2508, 1996.—It is unclear whether hypoxia alters the kinetics of O2 uptake (V˙o 2) during heavy exercise [above the lactic acidosis threshold (LAT)] and how these alterations might be linked to the rise in blood lactate. Eight healthy volunteers performed transitions from unloaded cycling to the same absolute heavy work rate for 8 min while breathing one of three inspired O2 concentrations: 21% (room air), 15% (mild hypoxia), and 12% (moderate hypoxia). Breathing 12% O2 slowed the time constant but did not affect the amplitude of the primary rise inV˙o 2 (period of first 2–3 min of exercise) and had no significant effect on either the time constant or the amplitude of the slowV˙o 2 component (beginning 2–3 min into exercise). Baseline heart rate was elevated in proportion to the severity of the hypoxia, but the amplitude and kinetics of increase during exercise and in recovery were unaffected by level of inspired O2. We conclude that the predominant effect of hypoxia during heavy exercise is on the early energetics as a slowed time constant forV˙o 2 and an additional anaerobic contribution. However, the sum total of the processes representing the slow component ofV˙o 2 is unaffected.

V˙o 2 and heart rate kinetics in cycling: transitions from an elevated baseline

2001 ◽  
Vol 90 (6) ◽  
pp. 2081-2087 ◽  
Author(s):  
S. E. Bearden ◽  
R. J. Moffatt
Keyword(s):  
Heart Rate ◽  
Base Excess ◽  
Slow Component ◽  
Lactate Concentration ◽  
Fast Component ◽  
Square Wave ◽  
Mean Response Time ◽  
Rate Kinetics ◽  
Component Amplitude ◽  
Heart Rate Kinetics

The purpose of this study was to examine oxygen consumption (V˙o 2) and heart rate kinetics during moderate and repeated bouts of heavy square-wave cycling from an exercising baseline. Eight healthy, male volunteers performed square-wave bouts of leg ergometry above and below the gas exchange threshold separated by recovery cycling at 35%V˙o 2 peak.V˙o 2 and heart rate kinetics were modeled, after removal of phase I data by use of a biphasic on-kinetics and monoexponential off-kinetics model. Fingertip capillary blood was sampled 45 s before each transition for base excess, HCO[Formula: see text] and lactate concentration, and pH. Base excess and HCO[Formula: see text] concentration were significantly lower, whereas lactate concentration and pH were not different before the second bout. The results confirm earlier reports of a smaller mean response time in the second heavy bout. This was the result of a significantly greater fast-component amplitude and smaller slow-component amplitude with invariant fast-component time constant. A role for local oxygen delivery limitation in heavy exercise transitions with unloaded but not moderate baselines is presented.

Comparison of oxygen uptake kinetics during knee extension and cycle exercise

2005 ◽  
Vol 288 (1) ◽  
pp. R212-R220 ◽  
Author(s):  
Shunsaku Koga ◽  
David C. Poole ◽  
Tomoyuki Shiojiri ◽  
Narihiko Kondo ◽  
Yoshiyuki Fukuba ◽  
...  
Keyword(s):  
Blood Flow ◽  
Time Constant ◽  
Phase Ii ◽  
Slow Component ◽  
Muscle Blood Flow ◽  
Knee Extension ◽  
Primary Component ◽  
Heavy Exercise ◽  
Muscle Energetics ◽  
Kinetics Of

The knee extension exercise (KE) model engenders different muscle and fiber recruitment patterns, blood flow, and energetic responses compared with conventional cycle ergometry (CE). This investigation had two aims: 1) to test the hypothesis that upright two-leg KE and CE in the same subjects would yield fundamentally different pulmonary O2 uptake (pV̇o2) kinetics and 2) to characterize the muscle blood flow, muscle V̇o2 (mV̇o2), and pV̇o2 kinetics during KE to investigate the rate-limiting factor(s) of pV̇o2 on kinetics and muscle energetics and their mechanistic bases after the onset of heavy exercise. Six subjects performed KE and CE transitions from unloaded to moderate [< ventilatory threshold (VT)] and heavy (>VT) exercise. In addition to pV̇o2 during CE and KE, simultaneous pulsed and echo Doppler methods, combined with blood sampling from the femoral vein, were used to quantify the precise temporal profiles of femoral artery blood flow (LBF) and mV̇o2 at the onset of KE. First, the gain (amplitude/work rate) of the primary component of pV̇o2 for both moderate and heavy exercise was higher during KE (∼12 ml·W−1·min−1) compared with CE (∼10), but the time constants for the primary component did not differ. Furthermore, the mean response time (MRT) and the contribution of the slow component to the overall response for heavy KE were significantly greater than for CE. Second, the time constant for the primary component of mV̇o2 during heavy KE [25.8 ± 9.0 s (SD)] was not significantly different from that of the phase II pV̇o2. Moreover, the slow component of pV̇o2 evident for the heavy KE reflected the gradual increase in mV̇o2. The initial LBF kinetics after onset of KE were significantly faster than the phase II pV̇o2 kinetics (moderate: time constant LBF = 8.0 ± 3.5 s, pV̇o2 = 32.7 ± 5.6 s, P < 0.05; heavy: LBF = 9.7 ± 2.0 s, pV̇o2 = 29.9 ± 7.9 s, P < 0.05). The MRT of LBF was also significantly faster than that of pV̇o2. These data demonstrate that the energetics (as gain) for KE are greater than for CE, but the kinetics of adjustment (as time constant for the primary component) are similar. Furthermore, the kinetics of muscle blood flow during KE are faster than those of pV̇o2, consistent with an intramuscular limitation to V̇o2 kinetics, i.e., a microvascular O2 delivery-to-O2 requirement mismatch or oxidative enzyme inertia.

Kinetics of oxygen uptake during supine and upright heavy exercise

1999 ◽  
Vol 87 (1) ◽  
pp. 253-260 ◽  
Author(s):  
Shunsaku Koga ◽  
Tomoyuki Shiojiri ◽  
Manabu Shibasaki ◽  
Narihiko Kondo ◽  
Yoshiyuki Fukuba ◽  
...  
Keyword(s):  
Heart Rate ◽  
Oxygen Uptake ◽  
Supine Position ◽  
Slow Component ◽  
Fast Component ◽  
Heavy Exercise ◽  
The Difference ◽  
Early Rise ◽  
Kinetics Of ◽  
State Increase

It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinetics would be altered by body posture during heavy exercise [i.e., above the lactate threshold (LT)]. Nine subjects performed transitions from unloaded cycling to work rates representing moderate (below the estimated LT) and heavy exercise (V˙o 2 equal to 50% of the difference between LT and peakV˙o 2) under conditions of upright and supine positions. During moderate exercise, the steady-state increase in V˙o 2was similar in the two positions, butV˙o 2 kinetics were slower in the supine position. During heavy exercise, the rate of adjustment ofV˙o 2 to the 6-min value was also slower in the supine position but was characterized by a significant reduction in the amplitude of the fast component ofV˙o 2, without a significant slowing of the phase 2 time constant. However, the amplitude of the slow component was significantly increased, such that the end-exerciseV˙o 2 was the same in the two positions. The changes inV˙o 2 kinetics for the supine vs. upright position were paralleled by a blunted response of heart rate at 2 min into exercise during supine compared with upright heavy exercise. Thus the supine position was associated with not only a greater amplitude of the slow component forV˙o 2 but also, concomitantly, with a reduced amplitude of the fast component; this latter effect may be due, at least in part, to an attenuated early rise in heart rate in the supine position.

Kinetics of oxygen uptake at the onset of exercise near or above peak oxygen uptake

2000 ◽  
Vol 88 (5) ◽  
pp. 1812-1819 ◽  
Author(s):  
R. L. Hughson ◽  
D. D. O'Leary ◽  
A. C. Betik ◽  
H. Hebestreit
Keyword(s):  
Oxygen Uptake ◽  
Cardiovascular System ◽  
Time Constant ◽  
Exponential Model ◽  
Peak Oxygen Uptake ◽  
Phase 2 ◽  
Heavy Exercise ◽  
The Difference ◽  
Kinetics Of ◽  
Model Phase

We tested the hypothesis that kinetics of O2 uptake (V˙o 2) measured in the transition to exercise near or above peakV˙o 2(V˙o 2 peak) would be slower than those for subventilatory threshold exercise. Eight healthy young men exercised at ∼57, ∼96, and ∼125%V˙o 2 peak. Data were fit by a two- or three-component exponential model and with a semilogarithmic transformation that tested the difference between required V˙o 2 and measuredV˙o 2. With the exponential model, phase 2 kinetics appeared to be faster at 125% V˙o 2 peak[time constant (τ2) = 16.3 ± 8.8 (SE) s] than at 57%V˙o 2 peak(τ2 = 29.4 ± 4.0 s) but were not different from that at 96%V˙o 2 peakexercise (τ2 = 22.1 ± 2.1 s).V˙o 2 at the completion of phase 2 was 77 and 80%V˙o 2 peak in tests predicted to require 96 and 125%V˙o 2 peak. WhenV˙o 2 kinetics were calculated with the semilogarithmic model, the estimated τ2 at 96%V˙o 2 peak (49.7 ± 5.1 s) and 125%V˙o 2 peak (40.2 ± 5.1 s) were slower than with the exponential model. These results are consistent with our hypothesis and with a model in which the cardiovascular system is compromised during very heavy exercise.

Effect of heliox on heart rate kinetics and dynamic hyperinflation during high-intensity exercise in COPD

2010 ◽  
Vol 111 (2) ◽  
pp. 225-234 ◽  
Author(s):  
Pierantonio Laveneziana ◽  
Gabriele Valli ◽  
Paolo Onorati ◽  
Patrizia Paoletti ◽  
Alessandro Maria Ferrazza ◽  
...  
Keyword(s):  
Heart Rate ◽  
High Intensity ◽  
High Intensity Exercise ◽  
Dynamic Hyperinflation ◽  
Rate Kinetics ◽  
Heart Rate Kinetics

Muscle Metaboreflex Modulation of Heart Rate Kinetics During the Transition to Low-Moderate and High-Moderate Exercise Intensities

2017 ◽  
Vol 49 (5S) ◽  
pp. 725
Author(s):  
Natasha G. Boyes ◽  
Josie T.J. Fries ◽  
Stephanie Fusnik ◽  
Paul J. Fadel ◽  
Corey R. Tomczak
Keyword(s):  
Heart Rate ◽  
Moderate Exercise ◽  
Muscle Metaboreflex ◽  
Rate Kinetics ◽  
Heart Rate Kinetics
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