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1. The effect of lifelong endurance exercise on cardiovascular structure and exercise function in women

   https://doi.org/10.1113/JP278503  

   Carrick‐Ranson, Graeme ; Sloane, Nikita M. ; Howden, Erin J. ; Bhella, Paul S. ; Sarma, Satyam ; Shibata, Shigeki ; Fujimoto, Naoki ; Hastings, Jeffrey L. ; Levine, Benjamin D. ( May 2020 , The Journal of Physiology)

   The beneficial effects of sustained or lifelong (>25 years) endurance exercise on cardiovascular structure and exercise function have been largely established in men.

   The current findings indicate that committed (≥4 weekly exercise sessions) lifelong exercise results in substantial benefits in exercise capacity (), cardiovascular function at submaximal and maximal exercise, left ventricular mass and compliance, and blood volume compared to similarly aged or even younger (middle‐age) untrained women.

   Endurance exercise training should be considered a key strategy to prevent cardiovascular disease with ageing in women as well as men.

   This study was a retrospective, cross‐sectional analysis of exercise performance and left ventricular (LV) morphology in 70 women to examine whether women who have performed regular, lifelong endurance exercise acquire the same beneficial adaptations in cardiovascular structure and function and exercise performance that have been reported previously in men. Three groups of women were examined: (1) 35 older (>60 years) untrained women (older untrained, OU), (2) 13 older women who had consistently performed four or more endurance exercise sessions weekly for at least 25 years (older trained, OT), and (3) 22 middle‐aged (range 35–59 years) untrained women (middle‐aged untrained, MU) as a reference control for the appropriate age‐related changes. Oxygen uptake () and cardiovascular function (cardiac output (); stroke volume (SV) acetylene rebreathing) were examined at rest, steady‐state submaximal exercise and maximal exercise (maximal oxygen uptake,). Blood volume (CO rebreathing) and LV mass (cardiac magnetic resonance imaging), plus invasive measures of static and dynamic chamber compliance were also examined.(p < 0.001) and maximal exerciseand SV were larger in older trained women compared to the two untrained groups (∼17% and ∼27% forand SV, respectively,versusMU; ∼40% and ∼38%versusOU, allp < 0.001). Blood volume (mL kg⁻¹) and LV mass index (g m⁻²) were larger in OTversusOU (∼11% and ∼16%, respectively, bothP ≤ 0.015) Static LV chamber compliance was greater in OT compared to both untrained groups (median (25–75%): MU: 0.065 (0.049–0.080); OU: 0.085 (0.061–0.138); OT: 0.047 (0.031–0.054),P ≤ 0.053). Collectively, these findings indicate that lifetime endurance exercise appears to be extremely effective at preserving or even enhancing cardiovascular structure and function with advanced age in women.

    

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2. Modelling the relationships between haemoglobin oxygen affinity and the oxygen cascade in humans

   https://doi.org/10.1113/JP277591  

   Shepherd, John R. A. ; Dominelli, Paolo B. ; Roy, Tuhin K. ; Secomb, Timothy W. ; Hoyer, James D. ; Oliveira, Jennifer L. ; Joyner, Michael J. ( July 2019 , The Journal of Physiology)

   Haemoglobin affinity is an integral concept in exercise physiology that impacts oxygen uptake, delivery and consumption.

   How chronic alterations in haemoglobin affinity impact physiology is unknown.

   Using human haemoglobin variants, we demonstrate that the affinity of haemoglobin for oxygen is highly correlated with haemoglobin concentration.

   Using the Fick equation, we model how altered haemoglobin affinity and the associated haemoglobin concentration influences oxygen consumption at rest and during exercise via alterations in cardiac output and mixed‐venous.

   The combination of low oxygen affinity haemoglobin and reduced haemoglobin concentration seenin vivomay be unable to support oxygen uptake during moderate or heavy exercise.

   The physiological implications, with regard to exercise, of altered haemoglobin affinity for oxygen are not fully understood. Data from the Mayo Clinic Laboratories database of rare human haemoglobin variants reveal a strong inverse correlation (r = −0.82) between blood haemoglobin concentration andP₅₀, an index of oxygen affinity [Hb = −0.3135(P₅₀) + 23.636]. In the present study, observedP₅₀values for high, normal and low oxygen‐affinity haemoglobin variants (13, 26 and 39 mmHg) and corresponding haemoglobin concentrations (19.5, 15.5 and 11.4 g dL⁻¹respectively) are used to model oxygen consumption as a fraction of delivery at rest ( = 0.25 L min⁻¹, cardiac output = 5.70 L min⁻¹) and during exercise ( = 2.75 L min⁻¹, cardiac output = 18.9 l min⁻¹). With high‐affinity haemoglobin, the model shows that normal levels of oxygen consumption can be achieved at rest and during exercise at the assumed cardiac output levels, with reduced oxygen extraction both at rest (16.8% high affinityvs. 21.7% normal) and during exercise (55.8% high affinityvs. 72.2% normal). With low‐affinity haemoglobin, which predicts low haemoglobin concentration, oxygen consumption at rest can be sustained with the assumed cardiac output, with increased oxygen extraction (31.1% low affinityvs. 21.7% normal). However, exercise at 2.75 l min⁻¹cannot be achieved with the assumed cardiac output, even with 100% oxygen extraction. In conclusion, the model indicates chronic alterations inP₅₀associate directly with Hb concentration, highlighting that human Hb variants can serve as ‘experiments of nature’ to address fundamental hypotheses on oxygen transport and exercise.

    

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3. Neurovascular and cortical responses to hyperoxia: enhanced cognition and electroencephalographic activity despite reduced perfusion

   https://doi.org/10.1113/JP279453  

   Damato, Elizabeth G. ; Flak, Tod A. ; Mayes, Ryan S. ; Strohl, Kingman P. ; Ziganti, Aemilee M. ; Abdollahifar, Alireza ; Flask, Chris A. ; LaManna, Joseph C. ; Decker, Michael J. ( July 2020 , The Journal of Physiology)

   Extreme aviation is accompanied by ever‐present risks of hypobaric hypoxia and decompression sickness. Neuroprotection against those hazards is conferred through fractional inspired oxygen () concentrations of 60–100% (hyperoxia).

   Hyperoxia reduces global cerebral perfusion (gCBF), increases reactive oxygen species within the brain and leads to cell death within the hippocampus. However, an understanding of hyperoxia's effect on cortical activity and concomitant levels of cognitive performance is lacking. This limits our understanding of whether hyperoxia could lower the brain's threshold of tolerance to physiological stressors inherent to extreme aviation, such as high gravitational forces.

   This study aimed to quantify the impact of hyperoxia upon global cerebral perfusion (gCBF), cognitive performance and cortical electroencephalography (EEG).

   Hyperoxia evoked a rapid reduction in gCBF, yet cognitive performance and vigilance were enhanced. EEG measurements revealed enhanced alpha power, suggesting less desynchrony, within the cortical temporal regions.

   Collectively, this work suggests hyperoxia‐induced brain hypoperfusion is accompanied by enhanced cognitive processing and cortical arousal.

   Extreme aviators continually inspire hyperoxic gas to mitigate risk of hypoxia and decompression injury. This neuroprotection carries a physiological cost: reduced cerebral perfusion (CBF). As reduced CBF may increase vulnerability to ever‐present physiological challenges during extreme aviation, we defined the magnitude and duration of hyperoxia‐induced changes in CBF, cortical electrical activity and cognition in 30 healthy males and females. Magnetic resonance imaging with pulsed arterial spin labelling provided serial measurements of global CBF (gCBF), first during exposure to 21% inspired oxygen () followed by a 30‐min exposure to 100% . High‐density EEG facilitated characterization of cortical activity during assessment of cognitive performance, also measured during exposure to 21% and 100% . Acid‐base physiology was measured with arterial blood gases. We found that exposure to 100% reduced gCBF to 63% of baseline values across all participants. Cognitive performance testing at 21% was accompanied by increased theta and beta power with decreased alpha power across multiple cortical areas. During cognitive testing at 100% , alpha activity was less desynchronized within the temporal regions than at 21% . The collective hyperoxia‐induced changes in gCBF, cognitive performance and EEG were similar across observed partial pressures of arterial oxygen (), which ranged between 276–548 mmHg, and partial pressures of arterial carbon dioxide (), which ranged between 34–50 mmHg. Sex did not influence gCBF response to 100% . Our findings suggest hyperoxia‐induced reductions in gCBF evoke enhanced levels of cortical arousal and cognitive processing, similar to those occurring during a perceived threat.

    

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4. Positive interactions between an exotic invader and moss biocrusts vary across life stage and correspond with the effect of water pulses on soil nitrogen

   https://doi.org/10.1111/1365-2435.13831  

   Slate, Mandy L. ; McLeod, Morgan Luce ; Callaway, Ragan M. ( June 2021 , Functional Ecology)

   The size and frequency of resource pulses can affect plant interactions and increase the abundance of invasive species relative to native species. We examined resource pulses generated during the desiccation and rehydration of communities of native biological soil crust (biocrust)‐forming mosses, in the context of positive associations between biocrusts and the invasive forb,Centaurea stoebe.

   We surveyedCentaureaand biocrust cover and evaluated how interactions amongCentaurea, biocrusts and water pulses influenced plant biomass and soil nitrogen in a field experiment.Centaureaseedling and biocrust interactions were also compared in a greenhouse experiment to evaluate differences related to life stage.

   In field surveys,Centaureaand biocrusts were positively associated. Across water pulse treatments, biocrust biomass decreased whenCentaureawas removed, indicating thatCentaureafacilitated biocrusts. Biocrusts did not affect adultCentaureain the field, butCentaureaseedling biomass was greater when grown with biocrusts in the greenhouse. Water pulses did not affect plant biomass, but interactions betweenCentaureaand biocrusts corresponded with variation in the effect of water pulses on soil nitrogen which were not evident whenCentaureaor biocrusts were grown alone. Twenty‐four hours after large water pulses were added, soilwas nine times higher in plots where biocrusts andCentaureaco‐occurred compared with small water pulse plots. In these same plots, soiltended to be lower at the end of the experiment.

   These results highlight positive interactions between an invasive exotic forb and native moss biocrust. Water pulses influenced soil nitrogen availability when both plants co‐occurred, but did not affect plant biomass, suggesting that resource pulses and species interactions can interact to affect ecosystem processes.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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5. Overcoming the challenge of small effective sample sizes in home‐range estimation

   https://doi.org/10.1111/2041-210X.13270  

   Fleming, Christen H. ; Noonan, Michael J. ; Medici, Emilia Patricia ; Calabrese, Justin M. ; Matthiopoulos, ed., Jason ( August 2019 , Methods in Ecology and Evolution)

   Technological advances have steadily increased the detail of animal tracking datasets, yet fundamental data limitations exist for many species that cause substantial biases in home‐range estimation. Specifically, the effective sample size of a range estimate is proportional to the number of observed range crossings, not the number of sampled locations. Currently, the most accurate home‐range estimators condition on an autocorrelation model, for which the standard estimation frame‐works are based on likelihood functions, even though these methods are known to underestimate variance—and therefore ranging area—when effective sample sizes are small.

   Residual maximum likelihood (REML) is a widely used method for reducing bias in maximum‐likelihood (ML) variance estimation at small sample sizes. Unfortunately, we find that REML is too unstable for practical application to continuous‐time movement models. When the effective sample sizeNis decreased toN ≤ (10), which is common in tracking applications, REML undergoes a sudden divergence in variance estimation. To avoid this issue, while retaining REML’s first‐order bias correction, we derive a family of estimators that leverage REML to make a perturbative correction to ML. We also derive AIC values for REML and our estimators, including cases where model structures differ, which is not generally understood to be possible.

   Using both simulated data and GPS data from lowland tapir (Tapirus terrestris), we show how our perturbative estimators are more accurate than traditional ML and REML methods. Specifically, when(5) home‐range crossings are observed, REML is unreliable by orders of magnitude, ML home ranges are ~30% underestimated, and our perturbative estimators yield home ranges that are only ~10% underestimated. A parametric bootstrap can then reduce the ML and perturbative home‐range underestimation to ~10% and ~3%, respectively.

   Home‐range estimation is one of the primary reasons for collecting animal tracking data, and small effective sample sizes are a more common problem than is currently realized. The methods introduced here allow for more accurate movement‐model and home‐range estimation at small effective sample sizes, and thus fill an important role for animal movement analysis. Given REML’s widespread use, our methods may also be useful in other contexts where effective sample sizes are small.

    

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