Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans

High-intensity exercise (> or =90% of maximal O(2) uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means +/- SD; maximal O(2) uptake = 53.5 +/- 5.2 ml.kg(-1).min(-1)) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pga(tw)) and quadriceps twitch force (Q(tw)), respectively. The reduction in Pga(tw) was not different after resistive breathing vs. after CON-EX (-27 +/- 5 vs. -26 +/- 6%; P = 0.127). Exercise time was reduced by 33 +/- 10% in EMF-EX vs. CON-EX (6.85 +/- 2.88 vs. 9.90 +/- 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (-28 +/- 9 vs. -12 +/- 5% for Pga(tw), P = 0.001; -28 +/- 7 vs. -14 +/- 6% for Q(tw), P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX (P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort

Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans

High-intensity exercise (> or =90% of maximal O(2) uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means +/- SD; maximal O(2) uptake = 53.5 +/- 5.2 ml.kg(-1).min(-1)) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pga(tw)) and quadriceps twitch force (Q(tw)), respectively. The reduction in Pga(tw) was not different after resistive breathing vs. after CON-EX (-27 +/- 5 vs. -26 +/- 6%; P = 0.127). Exercise time was reduced by 33 +/- 10% in EMF-EX vs. CON-EX (6.85 +/- 2.88 vs. 9.90 +/- 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (-28 +/- 9 vs. -12 +/- 5% for Pga(tw), P = 0.001; -28 +/- 7 vs. -14 +/- 6% for Q(tw), P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX (P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort

Exercise-induced abdominal muscle fatigue in healthy humans

Exercise-induced abdominal muscle fatigue in healthy humans. J Appl Physiol 100: 1554–1562, 2006. First published January 19, 2006; doi:10.1152/japplphysiol.01389.2005.—The abdominal muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. We investigated whether the abdominal muscles fatigue in response to dynamic lower limb exercise using such techniques. Eleven male subjects [peak oxygen uptake (V˙ O2 peak) 50.0 1.9 (SE) ml kg 1 min 1] cycled at 90% V˙ O2 peak to exhaustion (14.2 4.2 min). Abdominal muscle function was assessed before and up to 30 min after exercise by measuring the changes in gastric pressure (Pga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1–25 Hz. Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean 25 4%; P 0.001) that persisted up to 30 min postexercise ( 12 4%; P 0.001). These reductions were unlikely due to changes in membrane excitability because amplitude, duration, and area of the rectus abdominis M wave were unaffected. Declines in the Pga response to maximal voluntary expiratory efforts occurred after exercise (158 13 before vs. 145 10 cmH2O after exercise; P 0.005). Voluntary activation, assessed using twitch interpolation, did not change (67 6 before vs. 64 2% after exercise; P 0.20), and electromyographic activity of the rectus abdominis and external oblique increased during these volitional maneuvers. These data provide new evidence that the abdominal muscles fatigue after sustained, high-intensity exercise and that the fatigue is primarily due to peripheral mechanisms

Intelligent modelling of bioprocesses: A comparison of structured and unstructured approaches

This contribution moves in the direction of answering some general questions about the most effective and useful ways of modelling bioprocesses. We investigate the characteristics of models that are good at extrapolating. We trained 3 fully predictive models with different representational structures (diff eqns, inheritance of rates, network of reactions) on Saccharopolyspora erythraea shake flask fermentation data using genetic programming. The models were then tested on unseen data outside the range of the training data and the resulting performances compared. It was found that constrained models with mathematical forms analogous to internal mass balancing and stoichiometric were superior to flexible unconstrained models even though no A priori knowledge of this fermentation was used

Outer zone electrons

Spatial and temporal behavior of high energy trapped electrons in outer zone of magnetospher

Submaximal exercise pulmonary gas exchange in left heart disease patients with different forms of pulmonary hypertension.

JOURNAL ARTICLECopyright © 2015 Elsevier Inc. All rights reserved.BACKGROUND: We determined whether pulmonary gas exchange indices during submaximal exercise are different in heart-failure (HF) patients with combined post- and pre-capillary pulmonary hypertension (PPC-PH) vs. HF patients with isolated post-capillary PH (IPC-PH) or no-PH. METHODS & RESULTS: Pulmonary hemodynamics and pulmonary gas exchange were assessed during rest and submaximal exercise in 39 HF patients undergoing right-heart catheterization. Post-hemodynamic evaluation, patients were classified as having no-PH (n=11), IPC-PH (n=12) or PPC-PH (n=16). At an equivalent oxygen consumption, end-tidal CO2 (PETCO2) and arterial oxygen saturation (SaO2) were greater in no-PH and IPC-PH vs. PPC-PH patients (36.1±3.2 vs. 31.7±4.5 vs. 26.2±4.7 mmHg and 97±2 vs. 96 ±3 vs. 91±1%, respectively). Conversely, dead-space ventilation (VD/VT) and the ventilatory equivalent for carbon dioxide (V̇E/V̇CO2 ratio) were lower in no-PH and IPC-PH vs. PPC-PH patients (0.37±0.05 vs. 0.38±0.04 vs. 0.47±0.03 and 38±5 vs. 42±8 vs. 51±8, respectively). The exercise-induced change in VD/VT, V̇E/V̇CO2 ratio and PETCO2 correlated significantly with the change in mean pulmonary arterial pressure, diastolic pressure difference and transpulmonary pressure gradient in PPC-PH patients only. CONCLUSION: Noninvasive pulmonary gas exchange indices during submaximal exercise are different in HF patients with combined post-and pre-capillary PH compared to patients with isolated post-capillary PH or no-PH.NIHAmerican Heart Associatio

Association of Cognitive Performance with Time at Altitude, Sleep Quality, and Acute Mountain Sickness Symptoms

Objective It is well documented that cognitive performance may be altered with ascent to altitude, but the association of various cognitive performance tests with symptoms of acute mountain sickness (AMS) is not well understood. Our objective was to assess and compare cognitive performance during a high-altitude expedition using several tests and to report the association of each test with AMS, headache, and quality of sleep. Methods During an expedition to Mount Everest, 3 cognitive tests (Stroop, Trail Making, and the real-time cognitive assessment tool, an in-house developed motor accuracy test) were used along with a questionnaire to assess health and AMS. Eight team members were assessed pre-expedition, postexpedition, and at several time points during the expedition. Results There were no significant differences (P >.05) found among scores taken at 3 time points at base camp and the postexpedition scores for all 3 tests. Changes in the Stroop test scores were significantly associated with the odds of AMS (P <.05). The logistic regression results show that the percent change from baseline for Stroop score (β = −5.637; P = .032) and Stroop attempts (β = −5.269; P = .049) are significantly associated with the odds of meeting the criteria for AMS. Conclusions No significant changes were found in overall cognitive performance at altitude, but a significant relationship was found between symptoms of AMS and performance in certain cognitive tests. This research shows the need for more investigation of objective physiologic assessments to associate with self-perceived metrics of AMS to gauge effect on cognitive performance

Respiratory Muscle Weakness in Patients with Heart Failure: Time to Make It a Standard Clinical Marker and a Need for Novel Therapeutic Interventions?

Dysfunction of the respiratory muscles (particularly the diaphragm) can compromise ventilation, pulmonary gas exchange, and oxygen delivery to the tissues. This is especially true for patients with heart failure (HF), where a loss in respiratory muscle strength and endurance capacity is common.¹‾⁴ Inspiratory muscle weakness in HF causes heightened breathlessness, exertional intolerance, and reduces health-related quality-of-life.⁵‾⁷ The clinical importance of respiratory muscle weakness has also been clearly demonstrated

At risk of being risky: The relationship between "brain age" under emotional states and risk preference.

Developmental differences regarding decision making are often reported in the absence of emotional stimuli and without context, failing to explain why some individuals are more likely to have a greater inclination toward risk. The current study (N=212; 10-25y) examined the influence of emotional context on underlying functional brain connectivity over development and its impact on risk preference. Using functional imaging data in a neutral brain-state we first identify the "brain age" of a given individual then validate it with an independent measure of cortical thickness. We then show, on average, that "brain age" across the group during the teen years has the propensity to look younger in emotional contexts. Further, we show this phenotype (i.e. a younger brain age in emotional contexts) relates to a group mean difference in risk perception - a pattern exemplified greatest in young-adults (ages 18-21). The results are suggestive of a specified functional brain phenotype that relates to being at "risk to be risky.