Bicycle Handlebar Width Does Not Affect Spirometry, Ventilation, or Gas Exchange

Bicycle fit may affect comfort, aerodynamics, efficiency, ventilation, and power generation. Handlebars determine how the rider interacts with the bicycle. A wide range of handlebar widths are commercially available, but it is unclear if the resultant position affects lung function, ventilation, gas exchange, or efficiency. PURPOSE We aimed to measure the effects of handlebar widths on ventilation, gas exchange, spirometry, and comfort during moderate constant power exercise. METHODS Twenty-four recreationally active adults completed the study (32 ± 5 yrs., 175 ± 9 cm, 74 ± 12 kg, 8 women, 16 men). Participants completed three moderate constant power bouts of exercise on a cycle ergometer (Lode Excalibur PFM) while using handlebars set equivalent to, or ± 4cm in width to the participant shoulder width. We used a one-way RMANOVA to compare the three handlebar widths. RESULTS There was no difference in gas exchange and ventilation between the three handlebar widths: V̇O2 (F[2, 23] = 0.99, p = 0.38), V̇CO2 (F[1.47, 23] = 0.39, p = 0.62), V̇E (F[2, 23] = 0.53, p = 0.59], VT (F[2, 23] = 0.44, p = 0.65], fBr (F[2, 23] = 0.17, p = 0.84], PetO2(F[2, 23] = 0.45, p = 0.64), PetCO2 (F[2, 23] = 0.25, p=0.78]. Similarly, there were no differences in inspiratory capacity during the bout (F[1.49, 22] = 1.34, p = 0.27) or any spirometry variables immediately following exercise: FVC (F[1.43, 22] = 0.88, p = 0.39], FEV1 (F[2, 22] = 0.30, p = 0.74], FEV1/FVC (F[2, 22] = 0.18, p = 0.84], PEF (F[2, 22] = 0.14, p = 0.87]. There was no difference in the overall comfort (F[2, 23] = 0.90, p = 0.41] or shoulder discomfort (F [2, 23] = 0.90, p = 0.42). CONCLUSIONS Bicycle handlebar widths within 4 cm shoulder width do not result in changes to ventilation, gas exchange, efficiency, spirometry, or comfort during moderate power cycling exercise. Within the limits of rider preference, comfort, and safety, handlebar width can be adjusted substantially for aerodynamic purposes without affecting rider physiology

Diaphragm Force and Mitochondrial Function Ex Vivo Following GSNOR Inhibition In Vivo Preceding Mechanical Ventilation

During mechanical ventilation (MV), force developed by the diaphragm is decreased over time much faster than locomotor muscles. This is known as ventilator-induced diaphragm dysfunction (VIDD), and VIDD may be accelerated by intramyofiber oxidative stress. An important free radical used for the treatment of acute respiratory distress syndrome (ARDS) is nitric oxide (NO) which can diffuse to diaphragm myofibers during treatment. However, little is known whether NO or NO by-products such as S-nitrosothiols (RSNO), can accelerate or prevent VIDD. PURPOSE: To investigate whether inhibiting S-nitrosoglutathione reductase (GSNORi) during MV could affect ex vivo diaphragm force and mitochondrial respiration. METHODS: Male (C57BL6J) mice (n=27) were anesthetized and subjected to MV for 2, 4, or 6h, and non-MV mice (0 h) were used as controls. Alternatively, mice were treated with PBS/10% DMSO (n=6) or 25 µg SPL-334 (GSNORi, n=6) or 25 µg SPL-334 + 1.7 mg isosorbide dinitrate (ISDN; n=6), and then subjected to MV for 2 h. After MV, mice were euthanized, and diaphragm strips were used for force or for mitochondrial oxidative phosphorylation and reactive oxygen species generation measurements. RESULTS: Peak tetanic force was decreased by MV starting at 4 h (30 ± 2 N/cm2 vs 26 ± 1 N/cm2 vs 23 ± 2 N/cm2 vs 18 ± 4 N/cm2, for 0 vs 2 vs 4 vs 6h MV, P=0.0097 one-way ANOVA). Peak force was not different between DMSO vs GSNORi (P=0.3834). Leak respiration (Mann-Whitney p=0.26; CI95 7, 45 vs 10, 68 pmol/s/mg), coupled-phosphorylating mitochondrial respiration (Mann-Whitney p=0.91; CI95 121, 180 vs 107, 215 pmol/s/mg), and H2O2 flux in any of the respiratory states (e.g. coupled-phosphorylating Mann-Whitney p=0.26; CI95 30, 245 vs 4, 543 fmol/s/mg), were not different between DMSO vs GSNORi. CONCLUSION: VIDD was developed at 4 hours MV, but GSNORi treatment for 2 h did not produce any changes to VIDD and to mitochondrial function. These data suggest that if exogenous NO is not provided, inhibiting GSNOR in vivo alone does not affect diaphragm function ex vivo. Support: SDSU 2023 SEED Grant (to L.N.

Skeletal myofiber VEGF deficiency leads to mitochondrial, structural and contractile alterations in mouse diaphragm

Diaphragm dysfunction accompanies cardiopulmonary disease and impaired oxygen delivery. Vascular endothelial growth factor (VEGF) regulates oxygen delivery through angiogenesis, capillary maintenance, and contraction-induced perfusion. We hypothesized that myofiber-specific VEGF deficiency contributes to diaphragm weakness and fatigability. Diaphragm protein expression, capillarity and fiber morphology, mitochondrial respiration and hydrogen peroxide (H2O2) generation, and contractile function were compared between adult mice with conditional gene ablation of skeletal myofiber VEGF (SkmVEGF-/-; n=12) and littermate controls (n=13). Diaphragm VEGF protein was ~50 % lower in SkmVEGF-/- than littermate controls (1.45±0.65 vs. 3.04±1.41 pg/total protein; P=0.001). This was accompanied by an ~15% impairment in maximal isometric specific force (F[1,23] = 15.01, P=0.001) and a trend for improved fatigue resistance (P=0.053). Mean fiber cross-sectional area and type I fiber cross-sectional area were lower in SkmVEGF-/- by ~40 % and ~25% (P0.05). However mitochondrial-derived reactive oxygen species (ROS) flux was lower in SkmVEGF-/- (P=0.0003). In conclusion, myofiber-specific VEGF gene deletion resulted in a lower capillary-to-fiber ratio, type I fiber atrophy, actin loss, and contractile dysfunction in the diaphragm. In contrast, mitochondrial respiratory function was preserved alongside lower ROS generation, which may play a compensatory role to preserve fatigue resistance in the diaphragm

Skeletal muscle ATP turnover by 31P magnetic resonance spectroscopy during moderate and heavy bilateral knee-extension

During constant-power high-intensity exercise, the expected increase in oxygen uptake (V̇O2) is supplemented by a V̇O2 slow component (V̇O2 sc ), reflecting reduced work efficiency, predominantly within the locomotor muscles. The intracellular source of inefficiency is postulated to be an increase in the ATP cost of power production (an increase in P/W). To test this hypothesis, we measured intramuscular ATP turnover with (31)P magnetic resonance spectroscopy (MRS) and whole-body V̇O2 during moderate (MOD) and heavy (HVY) bilateral knee-extension exercise in healthy participants (n = 14). Unlocalized (31)P spectra were collected from the quadriceps throughout using a dual-tuned ((1)H and (31)P) surface coil with a simple pulse-and-acquire sequence. Total ATP turnover rate (ATPtot) was estimated at exercise cessation from direct measurements of the dynamics of phosphocreatine (PCr) and proton handling. Between 3 and 8 min during MOD, there was no discernable V̇O2 sc (mean ± SD, 0.06 ± 0.12 l min(-1)) or change in [PCr] (30 ± 8 vs. 32 ± 7 mm) or ATPtot (24 ± 14 vs. 17 ± 14 mm min(-1); each P = n.s.). During HVY, the V̇O2 sc was 0.37 ± 0.16 l min(-1) (22 ± 8%), [PCr] decreased (19 ± 7 vs. 18 ± 7 mm, or 12 ± 15%; P < 0.05) and ATPtot increased (38 ± 16 vs. 44 ± 14 mm min(-1), or 26 ± 30%; P < 0.05) between 3 and 8 min. However, the increase in ATPtot (ΔATPtot) was not correlated with the V̇O2 sc during HVY (r(2) = 0.06; P = n.s.). This lack of relationship between ΔATPtot and V̇O2 sc , together with a steepening of the [PCr]-V̇O2 relationship in HVY, suggests that reduced work efficiency during heavy exercise arises from both contractile (P/W) and mitochondrial sources (the O2 cost of ATP resynthesis; P/O)

Skeletal muscle power and fatigue at the tolerable limit of ramp-incremental exercise in COPD

Muscle fatigue (a reduced power for a given activation) is common following exercise in COPD. Whether muscle fatigue, and reduced maximal voluntary locomotor power, are sufficient to limit whole-body exercise in COPD is unknown. We hypothesized in COPD: 1) exercise is terminated with a locomotor muscle power reserve; 2) reduction in maximal locomotor power is related to ventilatory limitation; and 3) muscle fatigue at intolerance is less than age-matched controls. We used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power at the limit of incremental exercise ('performance fatigue') in 13 COPD (FEV1 49±17 %pred) and 12 controls. By establishing the baseline relationship between muscle activity and isokinetic power, we apportioned performance fatigue into the reduction in muscle activation and muscle fatigue. Peak isokinetic power at intolerance was ~130% of peak incremental power in controls (274±73 vs 212±84W, p<0.05), but ~260% in COPD (187±141 vs 72±34W, p<0.05) - greater than controls (p<0.05). Muscle fatigue as a fraction of baseline peak isokinetic power was not different in COPD vs controls (0.11±0.20 vs 0.19±0.11). Baseline to intolerance, the median frequency of maximal isokinetic muscle activity was unchanged in COPD but reduced in controls (+4.3±11.6 vs -5.5±7.6%, p<0.05). Performance fatigue as a fraction of peak incremental power was greater in COPD vs controls and related to resting (FEV1/FVC) and peak exercise (V̇E/MVV) pulmonary function (r2=0.47, r2=0.55, p<0.05). COPD patients are more fatigable than controls, but this fatigue is insufficient to constrain locomotor power and define exercise intolerance

Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705

We present Spitzer observations of the dwarf starburst galaxy NGC 1705 obtained as part of SINGS. The galaxy morphology is very different shortward and longward of ~5 microns: short-wavelength imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer-wavelength data reveals warm dust emission arising from two off-nuclear regions offset by ~250 pc from the SSC. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times lower than the Milky Way average). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed H Alpha emission; these photons are unassociated with the SSC (though a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 micron band in the eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse 8 micron emission after scaling and subtracting shorter wavelength data; the spatially variable PAH emission strengths revealed by the IRS data suggest caution in the interpretation of diffuse 8 micron emission as arising from PAH carriers alone. The metallicity of NGC 1705 falls at the transition level of 35% solar found by Engelbracht and collaborators; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 micron emission. A radio continuum non-detection, NGC 1705 deviates significantly from the canonical far-IR vs. radio correlation. (Abridged)Comment: ApJ, in press; please retrieve full-resolution version from http://www.astro.wesleyan.edu/~cannon/pubs.htm

Complexity on Small Scales: The Metallicity Distribution of the Carina Dwarf Spheroidal Galaxy

The Carina dwarf spheroidal (dSph) galaxy is the only galaxy of this type that shows clearly episodic star formation separated by long pauses. Here we present metallicities for 437 radial velocity members of this Galactic satellite. We obtained medium-resolution spectroscopy with the multi-object spectrograph FLAMES at the ESO VLT. Our target red giants cover the entire projected surface area of Carina. Our spectra are centered at the near-infrared Ca triplet, which is a well-established metallicity indicator for old and intermediate-age red giants. The resulting data sample provides the largest collection of spectroscopically derived metallicities for a Local Group dSph to date. Four of our likely radial velocity members of Carina lie outside of this galaxy's nominal tidal radius, supporting earlier claims of the possible existence of such stars beyond the main body of Carina. We find a mean metallicity of [Fe/H]=-1.7 dex. The formal full width at half maximum of the metallicity distribution is 0.92 dex, while the full range of metallicities spans ~-3.0<[Fe/H]<0.0 dex. The metallicity distribution might be indicative of several subpopulations. There appears to be a mild radial gradient such that more metal-rich populations are more centrally concentrated, matching a similar trend for an increasing fraction of intermediate-age stars. This as well as the photometric colors of the more metal-rich red giants suggest that Carina exhibits an age-metallicity relation. Indeed the age-metallicity degeneracy seems to conspire to form a narrow red giant branch despite the considerable spread in metallicity and wide range of ages. The metallicity distribution is not well-matched by a simple closed-box model of chemical evolution, but requires models that take into account also infall and outflows. (Abridged)Comment: 29 pages, 13 figures, 6 tables, accepted for publication in the A

The Nature of Infrared Emission in the Local Group Dwarf Galaxy NGC 6822 As Revealed by Spitzer

We present Spitzer imaging of the metal-deficient (Z ~30% Z_sun) Local Group dwarf galaxy NGC 6822. On spatial scales of ~130 pc, we study the nature of IR, H alpha, HI, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at H alpha (as found in previous studies). The global ratio of dust to HI gas in the ISM, while uncertain at the factor of ~2 level, is ~25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to HI gas are about a factor of five higher than the global value in NGC 6822. There are strong variations (factors of ~10) in the relative ratios of H alpha and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different H alpha/IR ratios compared to those found in more metal-rich environments. The H alpha and IR emission is associated with high-column density (> ~1E21 cm^-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.Comment: ApJ, in press; please retrieve full-resolution version from http://www.astro.wesleyan.edu/~cannon/pubs.htm

Relation between cannabis use and subcortical volumes in people at clinical high risk of psychosis

Among people at genetic risk of schizophrenia, those who use cannabis show smaller thalamic and hippocampal volumes. We evaluated this relationship in people at clinical high risk (CHR) of psychosis. The Alcohol and Drug Use Scale was used to identify 132 CHR cannabis users, the majority of whom were non-dependent cannabis users, 387 CHR non-users, and 204 healthy control non-users, and all participants completed magnetic resonance imaging scans. Volumes of the thalamus, hippocampus and amygdala were extracted with FreeSurfer, and compared across groups. Comparing all CHR participants with healthy control participants revealed no significant differences in volumes of any ROI. However, when comparing CHR users to CHR non-users, a significant ROI × Cannabis group effect emerged: CHR users showed significantly smaller amygdala compared to CHR non-users. However, when limiting analysis to CHR subjects who reported using alcohol at a ‘use without impairment’ severity level, the amygdala effect was non-significant; rather, smaller hippocampal volumes were seen in CHR cannabis users compared to non-users. Controlling statistically for effects of alcohol and tobacco use rendered all results non-significant. These results highlight the importance of controlling for residual confounding effects of other substance use when examining the relationship between cannabis use and neural structure

No reserve in isokinetic cycling power at intolerance during ramp incremental exercise in endurance-trained men.

During whole-body exercise in health, maximal oxygen uptake (V̇O2max) is typically attained at or immediately prior to the limit of tolerance (LoT). At the V̇O2max and LoT of incremental exercise, a fundamental, but unresolved, question is whether maximal evocable power can increase above the task requirement, i.e. whether there is a "power reserve" at the LoT. Using an instantaneous switch from cadence-independent to isokinetic cycle ergometry, we determined maximal evocable power at the limit of ramp-incremental exercise. We hypothesized that in endurance-trained men at LoT, maximal (4s) isokinetic power would not differ from power required by the task. Baseline isokinetic power at 80rpm (PISO; measured at the pedals) and summed integrated EMG from 5 leg muscles (∑iEMG) were measured in 12 endurance-trained men (V̇O2max=4.2±1.0 l•min(-1)). Participants then completed a ramp-incremental exercise test (20-25W•min(-1)), with instantaneous measurement of PISO and ∑iEMG at the LoT. PISO decreased from 788±103W at baseline to 391±72W at LoT, which was not different from the required ramp-incremental flywheel power (352±58W; p>0.05). At LoT, the relative reduction in PISO was greater than the relative reduction in the isokinetic ∑iEMG (50±9 vs. 63±10% of baseline; p<0.05). During maximal ramp incremental exercise in endurance-trained men, maximum voluntary power is not different from the power required by the task, and is consequent to both central and peripheral limitations in evocable power. The absence of a power reserve suggests both the perceptual and physiological limits of maximum voluntary power production are not widely dissociated at LoT in this population