More Like this

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.

    

   more » « less
2. Intra‐pulmonary arteriovenous anastomoses and pulmonary gas exchange: evaluation by microspheres, contrast echocardiography and inert gas elimination

   https://doi.org/10.1113/JP277695  

   Stickland, Michael K. ; Tedjasaputra, Vincent ; Seaman, Cameron ; Fuhr, Desi P. ; Collins, Sophie É. ; Wagner, Harrieth ; van Diepen, Sean ; Byers, Bradley W. ; Wagner, Peter D. ; Hopkins, Susan R. ( September 2019 , The Journal of Physiology)

   Imaging techniques such as contrast echocardiography suggest that anatomical intra‐pulmonary arteriovenous anastomoses (IPAVAs) are present at rest and are recruited to a greater extent in conditions such as exercise. IPAVAs have the potential to act as a shunt, although gas exchange methods have not demonstrated significant shunt in the normal lung.

   To evaluate this discrepancy, we compared anatomical shunt with 25‐µm microspheres to contrast echocardiography, and gas exchange shunt measured by the multiple inert gas elimination technique (MIGET).

   Intra‐pulmonary shunt measured by 25‐µm microspheres was not significantly different from gas exchange shunt determined by MIGET, suggesting that MIGET does not underestimate the gas exchange consequences of anatomical shunt.

   A positive agitated saline contrast echocardiography score was associated with anatomical shunt measured by microspheres. Agitated saline contrast echocardiography had high sensitivity but low specificity to detect a ≥1% anatomical shunt, frequently detecting small shunts inconsequential for gas exchange.

   The echocardiographic visualization of transpulmonary agitated saline microbubbles suggests that anatomical intra‐pulmonary arteriovenous anastomoses are recruited during exercise, in hypoxia, and when cardiac output is increased pharmacologically. However, the multiple inert gas elimination technique (MIGET) shows insignificant right‐to‐left gas exchange shunt in normal humans and canines. To evaluate this discrepancy, we measured anatomical shunt with 25‐µm microspheres and compared the results to contrast echocardiography and MIGET‐determined gas exchange shunt in nine anaesthetized, ventilated canines. Data were acquired under the following conditions: (1) at baseline, (2) 2 µg kg⁻¹ min⁻¹i.v.dopamine, (3) 10 µg kg⁻¹ min⁻¹i.v.dobutamine, and (4) following creation of an intra‐atrial shunt (in four animals). Right to left anatomical shunt was quantified by the number of 25‐µm microspheres recovered in systemic arterial blood. Ventilation–perfusion mismatch and gas exchange shunt were quantified by MIGET and cardiac output by direct Fick. Left ventricular contrast scores were assessed by agitated saline bubble counts, and separately by appearance of 25‐µm microspheres. Across all conditions, anatomical shunt measured by 25‐µm microspheres was not different from gas exchange shunt measured by MIGET (microspheres: 2.3 ± 7.4%; MIGET: 2.6 ± 6.1%,P = 0.64). Saline contrast bubble score was associated with microsphere shunt (ρ = 0.60,P < 0.001). Agitated saline contrast score had high sensitivity (100%) to detect a ≥1% shunt, but low specificity (22–48%). Gas exchange shunt by MIGET does not underestimate anatomical shunt measured using 25‐µm microspheres. Contrast echocardiography is extremely sensitive, but not specific, often detecting small anatomical shunts which are inconsequential for gas exchange.

    

   more » « less
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.

    

   more » « less
4. Developmental changes in oxygen consumption and hypoxia tolerance in the heat and hypoxia‐adapted tabasco line of the Nile tilapia Oreochromis niloticus , with a survey of the metabolic literature for the genus Oreochromis

   https://doi.org/10.1111/jfb.13945  

   Burggren, Warren W. ; Mendez‐Sanchez, Jose F. ; Martínez Bautista, Gil ; Peña, Emyr ; Martínez García, Rafael ; Alvarez González, Carlos A. ( April 2019 , Journal of Fish Biology)

   The genusOreochromisis among the most popular of the tilapiine cichlid tribe for aquaculture. However, their temperature and hypoxia tolerance, if tested at all, is usually tested at temperatures of 20–25°C, rather than at the considerably higher temperatures of 30–35°C typical of tropical aquaculture.

   We hypothesized that both larvae and adults of the heat and hypoxia‐adapted Tabasco‐line of the Nile tilapiaOreochromis niloticuswould be relatively hypoxia‐tolerant. Oxygen consumption rate (), Q₁₀and aquatic surface respiration (ASR) was measured using closed respirometry at 2 (c. 0.2 g), 30 (c. 2–5 g), 105c. (10–15 g) and 240 (c. 250 g) days of development, at 25°C, 30°C and 35°C.at 30°C was inversely related to body mass:c. 90 μM O₂g⁻¹/h in larvae down toc. 1 μM O₂g⁻¹/h in young adults. Q₁₀forwas typical for fish over the range 25–35°C of 1.5–2.0. ASR was exhibited by 50% of the fish at pO₂of 15–50 mmHg in a temperature‐dependent fashion. However, the largest adults showed notable ASR only when pO₂fell to below 10 mmHg. Remarkably, p_critforwas 12–17 mmHg at 25–30°C and still only 20–25 mmHg across development at 35°C. These values are among the lowest measured for teleost fishes. Noteworthy is that all fish maintain equilibrium, ventilated their gills and showed routine locomotor action for 10–20 min afterceased at near anoxia and when then returned to oxygenated waters, all fish survived, further indicating a remarkable hypoxic tolerance. Remarkably, data assembled forfrom >30 studies showed a > x2000 difference, which we attribute to calculation or conversion errors. Nonetheless, p_critwas very low for allOreochromissp. and lowest in the heat and hypoxia‐adapted Tabasco line.

    

   more » « less
5. The effect of O 2 and pressure on thiosulfate oxidation by Thiomicrospira thermophila

   https://doi.org/10.1111/gbi.12352  

   Houghton, Jennifer L. ; Foustoukos, Dionysis I. ; Fike, David A. ( June 2019 , Geobiology)

   Microbial sulfur cycling in marine sediments often occurs in environments characterized by transient chemical gradients that affect both the availability of nutrients and the activity of microbes. High turnover rates of intermediate valence sulfur compounds and the intermittent availability of oxygen in these systems greatly impact the activity of sulfur‐oxidizing micro‐organisms in particular. In this study, the thiosulfate‐oxidizing hydrothermal vent bacteriumThiomicrospira thermophilastrain EPR85 was grown in continuous culture at a range of dissolved oxygen concentrations (0.04–1.9 mM) and high pressure (5–10 MPa) in medium buffered at pH 8. Thiosulfate oxidation under these conditions produced tetrathionate, sulfate, and elemental sulfur, in contrast to previous closed‐system experiments at ambient pressure during which thiosulfate was quantitatively oxidized to sulfate. The maximum observed specific growth rate at 5 MPa pressure under unlimited O₂was 0.25 hr⁻¹. This is comparable to theμ_max(0.28 hr⁻¹) observed at low pH (<6) at ambient pressure whenT. thermophilaproduces the same mix of sulfur species. The half‐saturation constant for O₂() estimated from this study was 0.2 mM (at a cell density of 10⁵cells/ml) and was robust at all pressures tested (0.4–10 MPa), consistent with piezotolerant behavior of this strain. The cell‐specificwas determined to be 1.5 pmol O₂/cell. The concentrations of products formed were correlated with oxygen availability, with tetrathionate production in excess of sulfate production at all pressure conditions tested. This study provides evidence for transient sulfur storage during times when substrate concentration exceeds cell‐specificand subsequent consumption when oxygen dropped below that threshold. These results may be common among sulfur oxidizers in a variety of environments (e.g., deep marine sediments to photosynthetic microbial mats).

    

   more » « less