Effects of exercise-induced arterial hypoxemia on limb muscle fatigue and performance

1. Reductions in arterial O2 saturation (−5% to −10% SaO2 below rest) occur over time during sustained heavy-intensity exercise in a normoxic environment, caused primarily by the effects of acid pH and increased temperature on the position of the HbO2 dissociation curve. 2. We prevented the desaturation incurred during exercise at ∼90% √O2 MAX via increased fraction of inspired O2 (FiO2) (0.23 to 0.29) and showed that exercise time to exhaustion was increased. 3. We used supramaximal magnetic stimulation (1–100 Hz) of the femoral nerve to test for quadriceps fatigue. We used mildly hyperoxic inspirates (FiO2 0.23 to 0.29) to prevent O2 desaturation. We then compared the amount of quadriceps fatigue incurred following cycling exercise at SaO2 91% vs 98% with each trial carried out at identical work rates and for equal durations. 4. Preventing the normal exercise-induced O2 desaturation prevented about one-half the amount of exercise-induced quadriceps fatigue; plasma lactate and effort perception were also reduced. In a subset of less fit subjects who showed only minimal arterial hypoxaemia during sustained exercise (SaO2 ∼95%), breathing a mildly hypoxic inspirate (FiO2 0.17; SaO2 ∼88%) exacerbated the quadriceps fatigue. 5. We conclude that the normal exercise-induced O2 desaturation during heavy-intensity endurance exercise contributes significantly to exercise performance limitation in part because of its effect on locomotor muscle fatigue

Effect of exercise-induced arterial hypoxemia on quadriceps muscle fatigue in healthy humans

The effect of exercise-induced arterial hypoxemia (EIAH) on quadriceps muscle fatigue was assessed in 11 male endurance-trained subjects [peak O2 uptake (V̇o2 peak) = 56.4 ± 2.8 ml·kg−1·min−1; mean ± SE]. Subjects exercised on a cycle ergometer at ≥90% V̇o2 peak to exhaustion (13.2 ± 0.8 min), during which time arterial O2 saturation (SaO2) fell from 97.7 ± 0.1% at rest to 91.9 ± 0.9% (range 84–94%) at end exercise, primarily because of changes in blood pH (7.183 ± 0.017) and body temperature (38.9 ± 0.2°C). On a separate occasion, subjects repeated the exercise, for the same duration and at the same power output as before, but breathed gas mixtures [inspired O2 fraction (FiO2) = 0.25–0.31] that prevented EIAH (SaO2 = 97–99%). Quadriceps muscle fatigue was assessed via supramaximal paired magnetic stimuli of the femoral nerve (1–100 Hz). Immediately after exercise at FiO2 0.21, the mean force response across 1–100 Hz decreased 33 ± 5% compared with only 15 ± 5% when EIAH was prevented (P < 0.05). In a subgroup of four less fit subjects, who showed minimal EIAH at FiO2 0.21 (SaO2 = 95.3 ± 0.7%), the decrease in evoked force was exacerbated by 35% (P < 0.05) in response to further desaturation induced via FiO2 0.17 (SaO2 = 87.8 ± 0.5%) for the same duration and intensity of exercise. We conclude that the arterial O2 desaturation that occurs in fit subjects during high-intensity exercise in normoxia (−6 ± 1% ΔSaO2 from rest) contributes significantly toward quadriceps muscle fatigue via a peripheral mechanism

Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans

Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans. Am J Physiol Regul Integr Comp Physiol 292: R598–R606, 2007. First published September 7, 2006; doi:10.1152/ajpregu.00269.2006.—We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean SE maximum O2 uptake (V˙ O2 max) 56.5 2.7 ml kg 1 min 1] cycled at 90% V˙ O2 max to exhaustion in normoxia [NORM-EXH; inspired O2 fraction (FIO2) 0.21, arterial O2 saturation (SpO2) 93 1%] and hypoxia (HYPOX-EXH; FIO2 0.13, SpO2 76 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; SpO2 96 1%). Quadriceps twitch force, in response to supramaximal single (nonpotentiated and potentiated 1 Hz) and paired magnetic stimuli of the femoral nerve (10–100 Hz), was assessed pre- and at 2.5, 35, and 70 min postexercise. Hypoxia exacerbated exercise-induced peripheral fatigue, as evidenced by a greater decrease in potentiated twitch force in HYPOX-EXH vs. NORM-CTRL ( 39 4 vs. 24 3%, P 0.01). Time to exhaustion was reduced by more than two-thirds in HYPOX-EXH vs. NORM-EXH (4.2 0.5 vs. 13.4 0.8 min, P 0.01); however, peripheral fatigue was not different in HYPOX-EXH vs. NORM-EXH ( 34 4 vs. 39 4%, P 0.05). Blood lactate concentration and perceptions of limb discomfort were higher throughout HYPOX-EXH vs. NORM-CTRL but were not different at end-exercise in HYPOX-EXH vs. NORM-EXH. We conclude that severe hypoxia exacerbates peripheral fatigue of limb locomotor muscles and that this effect may contribute, in part, to the early termination of exercise

Effects of arterial oxygen content on peripheral locomotor muscle fatigue

The effect of arterial O2 content (Ca(O2)) on quadriceps fatigue was assessed in healthy, trained male athletes. On separate days, eight participants completed three constant-workload trials on a bicycle ergometer at fixed workloads (314 +/- 13 W). The first trial was performed while the subjects breathed a hypoxic gas mixture [inspired O2 fraction (Fi(O2)) = 0.15, Hb saturation = 81.6%, Ca(O2) = 18.2 ml O2/dl blood; Hypo] until exhaustion (4.5 +/- 0.4 min). The remaining two trials were randomized and time matched with Hypo. The second and third trials were performed while the subjects breathed a normoxic (Fi(O2) = 0.21, Hb saturation = 95.0%, Ca(O2) = 21.3 ml O2/dl blood; Norm) and a hyperoxic (Fi(O2) = 1.0, Hb saturation = 100%, Ca(O2) = 23.8 ml O2/dl blood; Hyper) gas mixture, respectively. Quadriceps muscle fatigue was assessed via magnetic femoral nerve stimulation (1-100 Hz) before and 2.5 min after exercise. Myoelectrical activity of the vastus lateralis was obtained from surface electrodes throughout exercise. Immediately after exercise, the mean force response across 1-100 Hz decreased from preexercise values (P < 0.01) by -26 +/- 2, -17 +/- 2, and -13 +/- 2% for Hypo, Norm, and Hyper, respectively; each of the decrements differed significantly (P < 0.05). Integrated electromyogram increased significantly throughout exercise (P < 0.01) by 23 +/- 3, 10 +/- 1, and 6 +/- 1% for Hypo, Norm, and Hyper, respectively; each of the increments differed significantly (P < 0.05). Mean power frequency fell more (P < 0.05) during Hypo (-15 +/- 2%); the difference between Norm (-7 +/- 1%) and Hyper (-6 +/- 1%) was not significant (P = 0.32). We conclude that deltaCa(O2) during strenuous systemic exercise at equal workloads and durations affects the rate of locomotor muscle fatigue development

Repeat exercise normalizes the gas-exchange impairment induced by a previous exercise bout in asthmatic subjects

Twenty-one subjects with asthma underwent treadmill exercise to exhaustion at a workload that elicited approximately 90% of each subject's maximal O2 uptake (EX1). After EX1, 12 subjects experienced significant exercise-induced bronchospasm [(EIB+), %decrease in forced expiratory volume in 1.0 s = -24.0 +/- 11.5%; pulmonary resistance at rest vs. postexercise = 3.2 +/- 1.5 vs. 8.1 +/- 4.5 cmH2O.l(-1).s(-1)] and nine did not (EIB-). The alveolar-to-arterial Po2 difference (A-aDo2) was widened from rest (9.1 +/- 6.7 Torr) to 23.1 +/- 10.4 and 18.1 +/- 9.1 Torr at 35 min after EX1 in subjects with and without EIB, respectively (P < 0.05). Arterial Po2 (PaO2) was reduced in both groups during recovery (EIB+, -16.0 +/- -13.0 Torr vs. baseline; EIB-, -11.0 +/- 9.4 Torr vs. baseline, P < or = 0.05). Forty minutes after EX1, a second exercise bout was completed at maximal O2 uptake. During the second exercise bout, pulmonary resistance decreased to baseline levels in the EIB+ group and the A-aDo2 and PaO2 returned to match the values seen during EX1 in both groups. Sputum histamine (34.6 +/- 25.9 vs. 61.2 +/- 42.0 ng/ml, pre- vs. postexercise) and urinary 9alpha,11beta-prostaglandin F2 (74.5 +/- 38.6 vs. 164.6 +/- 84.2 ng/mmol creatinine, pre- vs. postexercise) were increased after exercise only in the EIB+ group (P < 0.05), and postexercise sputum histamine was significantly correlated with the exercise PaO2 and A-aDo2 in the EIB+ subjects. Thus exercise causes gas-exchange impairment during the postexercise period in asthmatic subjects independent of decreases in forced expiratory flow rates after the exercise; however, a subsequent exercise bout normalizes this impairment secondary in part to a fast acting, robust exercise-induced bronchodilatory response

Gas exchange during exercise in habitually active asthmatic subjects

We determined the relations among gas exchange, breathing mechanics, and airway inflammation during moderate- to maximum-intensity exercise in asthmatic subjects. Twenty-one habitually active (48.2 +/- 7.0 ml.kg(-1).min(-1) maximal O2 uptake) mildly to moderately asthmatic subjects (94 +/- 13% predicted forced expiratory volume in 1.0 s) performed treadmill exercise to exhaustion (11.2 +/- 0.15 min) at approximately 90% of maximal O2 uptake. Arterial O2 saturation decreased to < or =94% during the exercise in 8 of 21 subjects, in large part as a result of a decrease in arterial Po2 (PaO2): from 93.0 +/- 7.7 to 79.7 +/- 4.0 Torr. A widened alveolar-to-arterial Po2 difference and the magnitude of the ventilatory response contributed approximately equally to the decrease in PaO2 during exercise. Airflow limitation and airway inflammation at baseline did not correlate with exercise gas exchange, but an exercise-induced increase in sputum histamine levels correlated with exercise Pa(O2) (negatively) and alveolar-to-arterial Po2 difference (positively). Mean pulmonary resistance was high during exercise (3.4 +/- 1.2 cmH2O.l(-1).s) and did not increase throughout exercise. Expiratory flow limitation occurred in 19 of 21 subjects, averaging 43 +/- 35% of tidal volume near end exercise, and end-expiratory lung volume rose progressively to 0.25 +/- 0.47 liter greater than resting end-expiratory lung volume at exhaustion. These mechanical constraints to ventilation contributed to a heterogeneous and frequently insufficient ventilatory response; arterial Pco2 was 30-47 Torr at end exercise. Thus pulmonary gas exchange is impaired during high-intensity exercise in a significant number of habitually active asthmatic subjects because of high airway resistance and, possibly, a deleterious effect of exercise-induced airway inflammation on gas exchange efficiency

Pyrosequencing of Mytilus galloprovincialis cDNAs: tissue-specific expression patterns.

BACKGROUND: Mytilus species are important in marine ecology and in environmental quality assessment, yet their molecular biology is poorly understood. Molecular aspects of their reproduction, hybridisation between species, mitochondrial inheritance, skewed sex ratios of offspring and adaptation to climatic and pollution factors are priority areas. METHODOLOGY/PRINCIPAL FINDINGS: To start to address this situation, expressed genetic transcripts from M. galloprovincialis were pyrosequenced. Transcripts were isolated from the digestive gland, foot, gill and mantle of both male and female mussels. In total, 175,547 sequences were obtained and for foot and mantle, 90% of the sequences could be assembled into contiguous fragments but this reduced to 75% for the digestive gland and gill. Transcripts relating to protein metabolism and respiration dominated including ribosomal proteins, cytochrome oxidases and NADH dehydrogenase subunits. Tissue specific variation was identified in transcripts associated with mitochondrial energy metabolism, with the digestive gland and gill having the greatest transcript abundance. Using fragment recruitment it was also possible to identify sites of potential small RNAs involved in mitochondrial transcriptional regulation. Sex ratios based on Vitelline Envelop Receptor for Lysin and Vitelline Coat Lysin transcript abundances, indicated that an equal sex distribution was maintained. Taxonomic profiling of the M. galloprovincialis tissues highlighted an abundant microbial flora associated with the digestive gland. Profiling of the tissues for genes involved in intermediary metabolism demonstrated that the gill and digestive gland were more similar to each other than to the other two tissues, and specifically the foot transcriptome was most dissimilar. CONCLUSIONS: Pyrosequencing has provided extensive genomic information for M. galloprovincialis and generated novel observations on expression of different tissues, mitochondria and associated microorganisms. It will also facilitate the much needed production of an oligonucleotide microarray for the organism

Prevalence and side preference for tooth grinding in twins

The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.Background: Estimates of the prevalence of tooth grinding in children range considerably, reflecting different methods of recording. The main aims of this study were to determine the prevalence of tooth grinding in monozygotic (MZ) and dizygotic (DZ) twin pairs by assessing wear faceting on the primary canines, and to compare the faceting on the right and left to determine whether children have a side preference for grinding. Methods: The sample consisted of 116 MZ twin pairs and 124 dizygous DZ twin pairs, all participants in an ongoing study of dento-facial development at the dental schools in Adelaide and Melbourne. Evidence of wear faceting on primary maxillary and mandibular canine tips was recorded from dental casts, and the side with the larger wear facet recorded. Types of occlusal relationship, handedness, zygosity and gender were also recorded, and associations between variables analysed statistically. Results: Canine tip wear facets were found in 100 per cent of the sample, and grinding was lateralized in 59 per cent of children. MZ twin pairs showed a higher discordance for grinding side preference than DZ twin pairs (33.8 per cent compared with 16.8 per cent), providing evidence of a mirror-imaging effect for grinding side preference. There was no strong evidence that individuals had the same preference for grinding side and handedness, although right-handers (RH) showed a preference for a grinding side more often than non-righthanders (NRH) (63.6 per cent compared with 51.2 per cent), consistent with previous findings that RHs display more cerebral lateralization than NRHs. Conclusions: Tooth grinding appears to be a universal phenomenon in children and is commonly expressed more on one side than the other. The significantly higher discordance for grinding side preference in MZ twin pairs compared with DZ twin pairs may reflect a mirror-imaging effect in the former. However, at present we have no evidence to suggest that handedness and preferred tooth grinding side are associated.K V Dooland, G C Townsend, J A Kaidoni

Vaccination with DNA plasmids expressing Gn coupled to C3d or alphavirus replicons expressing Gn protects mice against rift valley fever virus

Background: Rift Valley fever (RVF) is an arthropod-borne viral zoonosis. Rift Valley fever virus (RVFV) is an important biological threat with the potential to spread to new susceptible areas. In addition, it is a potential biowarfare agent. Methodology/Principal Findings: We developed two potential vaccines, DNA plasmids and alphavirus replicons, expressing the Gn glycoprotein of RVFV alone or fused to three copies of complement protein, C3d. Each vaccine was administered to mice in an all DNA, all replicon, or a DNA prime/replicon boost strategy and both the humoral and cellular responses were assessed. DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited high titer neutralizing antibodies that were similar to titers elicited by the live-attenuated MP12 virus. Mice vaccinated with an inactivated form of MP12 did elicit high titer antibodies, but these antibodies were unable to neutralize RVFV infection. However, only vaccine strategies incorporating alphavirus replicons elicited cellular responses to Gn. Both vaccines strategies completely prevented weight loss and morbidity and protected against lethal RVFV challenge. Passive transfer of antisera from vaccinated mice into naïve mice showed that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited antibodies that protected mice as well as sera from mice immunized with MP12. Conclusion/Significance: These results show that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn administered alone or in a DNA prime/replicon boost strategy are effective RVFV vaccines. These vaccine strategies provide safer alternatives to using live-attenuated RVFV vaccines for human use. © 2010 Bhardwaj et al