Rapid response of nonstructural carbohydrate allocation and photosynthesis to short photoperiod, low temperature, or elevated CO2 in Pinus strobus.

During autumn, decreasing photoperiod and temperature temporarily perturb the balance between carbon uptake and carbon demand in overwintering plants, requiring coordinated adjustments in photosynthesis and carbon allocation to re-establish homeostasis. Here we examined adjustments of photosynthesis and allocation of nonstructural carbohydrates (NSCs) following a sudden shift to short photoperiod, low temperature, and/or elevated CO2 in Pinus strobus seedlings. Seedlings were initially acclimated to 14 h photoperiod (22/15°C day/night) and ambient CO2 (400 ppm) or elevated CO2 (800 ppm). Seedlings were then shifted to 8 h photoperiod for one of three treatments: no temperature change at ambient CO2 (22/15°C, 400 ppm), low temperature at ambient CO2 (12/5°C, 400 ppm), or no temperature change at elevated CO2 (22/15°C, 800 ppm). Short photoperiod caused all seedlings to exhibit partial nighttime depletion of starch. Short photoperiod alone did not affect photosynthesis. Short photoperiod combined with low temperature caused hexose accumulation and repression of photosynthesis within 24 h, followed by a transient increase in nonphotochemical quenching (NPQ). Under long photoperiod, plants grown under elevated CO2 exhibited significantly higher NSCs and photosynthesis compared to ambient CO2 plants, but carbon uptake exceeded sink capacity, leading to elevated NPQ; carbon sink capacity was restored and NPQ relaxed within 24 h after shift to short photoperiod. Our findings indicate that P. strobus rapidly adjusts NSC allocation, not photosynthesis, to accommodate short photoperiod. However, the combination of short photoperiod and low temperature, or long photoperiod and elevated CO2 disrupts the balance between photosynthesis and carbon sink capacity, resulting in increased NPQ to alleviate excess energy.

Improving the predictions of leaf photosynthesis during and after short-term heat stress with current rice models.

In response to increasing global warming, extreme heat stress significantly alters photosynthetic production. While numerous studies have investigated the temperature effects on photosynthesis, factors like vapour pressure deficit (VPD), leaf nitrogen, and feedback of sink limitation during and after extreme heat stress remain underexplored. This study assessed photosynthesis calculations in seven rice growth models using observed maximum photosynthetic rate (Pmax ) during and after short-term extreme heat stress in multi-year environment-controlled experiments. Biochemical models (FvCB-type) outperformed light response curve-based models (LRC-type) when incorporating observed leaf nitrogen, photosynthetically active radiation, temperatures, and intercellular CO2 concentration (Ci ) as inputs. Prediction uncertainty during heat stress treatment primarily resulted from variation in temperatures and Ci . Improving FVPD (the slope for the linear effect of VPD on Ci /Ca ) to be temperature-dependent, rather than constant as in original models, significantly improved Ci prediction accuracy under heat stress. Leaf nitrogen response functions led to model variation in leaf photosynthesis predictions after heat stress, which was mitigated by calibrated nitrogen response functions based on active photosynthetic nitrogen. Additionally, accounting for observed differences in carbohydrate accumulation between panicles and stems during grain filling improved the feedback of sink limitation, reducing Ci overestimation under heat stress treatments.

The effect of elevated CO2 on photosynthesis is modulated by nitrogen supply and reduced water availability in Picea abies.

It is assumed that the stimulatory effects of elevated CO2 concentration ([CO2]) on photosynthesis and growth may be substantially reduced by co-occurring environmental factors and the length of CO2 treatment. Here, we present the study exploring the interactive effects of three manipulated factors ([CO2], nitrogen supply and water availability) on physiological (gas-exchange and chlorophyll fluorescence), morphological and stoichiometric traits of Norway spruce (Picea abies) saplings after 2 and 3 years of the treatment under natural field conditions. Such multifactorial studies, going beyond two-way interactions, have received only limited attention until now. Our findings imply a significant reduction of [CO2]-enhanced rate of CO2 assimilation under reduced water availability which deepens with the severity of water depletion. Similarly, insufficient nitrogen availability leads to a down-regulation of photosynthesis under elevated [CO2] being particularly associated with reduced carboxylation efficiency of the Rubisco enzyme. Such adjustments in the photosynthesis machinery result in the stimulation of water-use efficiency under elevated [CO2] only when it is combined with a high nitrogen supply and reduced water availability. These findings indicate limited effects of elevated [CO2] on carbon uptake in temperate coniferous forests when combined with naturally low nitrogen availability and intensifying droughts during the summer periods. Such interactions have to be incorporated into the mechanistic models predicting changes in terrestrial carbon sequestration and forest growth in the future.

Isotopic evidence for increased carbon and nitrogen exchanges between peatland plants and their symbiotic microbes with rising atmospheric CO2 concentrations since 15,000 cal. year BP.

Whether nitrogen (N) availability will limit plant growth and removal of atmospheric CO2 by the terrestrial biosphere this century is controversial. Studies have suggested that N could progressively limit plant growth, as trees and soils accumulate N in slowly cycling biomass pools in response to increases in carbon sequestration. However, a question remains over whether longer-term (decadal to century) feedbacks between climate, CO2 and plant N uptake could emerge to reduce ecosystem-level N limitations. The symbioses between plants and microbes can help plants to acquire N from the soil or from the atmosphere via biological N2 fixation-the pathway through which N can be rapidly brought into ecosystems and thereby partially or completely alleviate N limitation on plant productivity. Here we present measurements of plant N isotope composition (δ15 N) in a peat core that dates to 15,000 cal. year BP to ascertain ecosystem-level N cycling responses to rising atmospheric CO2 concentrations. We find that pre-industrial increases in global atmospheric CO2 concentrations corresponded with a decrease in the δ15 N of both Sphagnum moss and Ericaceae when constrained for climatic factors. A modern experiment demonstrates that the δ15 N of Sphagnum decreases with increasing N2 -fixation rates. These findings suggest that plant-microbe symbioses that facilitate N acquisition are, over the long term, enhanced under rising atmospheric CO2 concentrations, highlighting an ecosystem-level feedback mechanism whereby N constraints on terrestrial carbon storage can be overcome.

Effects of alfaxalone, propofol and isoflurane on cerebral blood flow and cerebrovascular reactivity to carbon dioxide in dogs: A pilot study.

Propofol total intravenous anesthesia is a common choice to anesthetize patients with increased intracranial pressure, reducing cerebral blood flow while maintaining cerebrovascular reactivity to CO2. Propofol and alfaxalone are commonly used for total intravenous anesthesia in dogs, but the effects of alfaxalone on cerebral blood flow and cerebrovascular reactivity to CO2 are unknown. Our hypothesis was that alfaxalone would not be significantly different to propofol, while isoflurane would increase cerebral blood flow and decrease cerebrovascular reactivity to CO2. Six healthy hound dogs were evaluated in this randomized crossover trial. Dogs were anesthetized with 7.5 mg/kg propofol, 3 mg/kg alfaxalone or 8 % sevoflurane, mechanically ventilated and maintained with propofol (400 µg/kg/min), alfaxalone (150 µg/kg/min) or 1.7 % end-tidal isoflurane, respectively, with one week washout between treatments. Cerebral blood flow and cerebrovascular reactivity to CO2 during hypercapnic and hypocapnic challenges were measured using arterial spin labelling and blood oxygen level-dependent magnetic resonance imaging sequences, respectively. Median (interquartile range, IQR) normocapnic cerebral blood flow was significantly lower (P = 0.016) with alfaxalone compared to isoflurane, in the whole brain 15.39 mL/min/100 g (14.90-19.90 mL/min/100 g) vs. 34.10 mL/min/100 g (33.35-43.17 mL/min/100 g), the grey matter 14.57 mL/min/100 g (13.66-18.72 mL/min/100 g) vs. 32.37 mL/min/100 g (31.03-42.99 mL/min/100 g), the caudal brain 15.47 mL/min/100 g (13.37-21.45 mL/min/100 g) vs. 36.85 mL/min/100 g (32.50-47.18 mL/min/100 g) and the temporal lobe grey matter 18.80 mL/min/100 g (15.89-20.84 mL/min/100 g) vs. 43.32 (36.07-43.58 mL/min/100 g). Median (IQR) hypocapnic cerebrovascular reactivity to CO2 was significantly higher (P = 0.016) for alfaxalone compared to isoflurane 8.85 %S/mm Hg (6.92-10.44 %S/mm Hg) vs. 3.90 %S/mm Hg (3.80-4.33 %S/mm Hg). Alfaxalone maintained lower cerebral blood flow and higher hypocapnic cerebrovascular reactivity to CO2 than isoflurane.

Carbon dioxide and light curves and leaf gas exchange responses to shade levels in bell pepper (Capsicum annuum L.).

Vegetable crops grown under shade nets typically show increased yield and quality. However, little is known about the photosynthetic responses at various CO2 and light levels under nets. This study aimed to determine carbon dioxide (A/Cc) and light (A/I) curves and leaf gas exchange response of bell pepper plants grown under nets at various shade levels. Experiments were conducted in the spring-summer of 2016 and 2018 in Tifton, Georgia (GA), USA, with five shade treatments [0 % (open field), 30 %, 47 %, 63 %, and 80 %]. The A/Cc curves revealed that plants grown at 30 % shade and in the open field had similar carboxylation, electron transport, and triose phosphate utilization rates. The A/I curves showed that gross and net photosynthesis were highest at 30 % shade. The 30 % shade had similar stomatal conductance, intercellular CO2, electron transport rate, and water use efficiency compared to the open field. The A/Cc and A/I curves and the leaf gas exchange parameters explained the intrinsic causes for the higher net photosynthesis at 30 % shade than in open-field bell pepper. The information from A/Cc-curves, A/I-curves, and leaf gas exchange is applicable in modeling photosynthesis and predicting primary productivity for C3 plants in elevated-CO2 and altered-light environments.

Blood Flow and Respiratory Gas Exchange in the Human Placenta at Term: A Data Update.

Reliable measurements using modern techniques and consensus in experimental design have enabled the assessment of novel data sets for normal maternal and foetal respiratory physiology at term. These data sets include (a) principal factors affecting placental gas transfer, e.g., maternal blood flow through the intervillous space (IVS) (500 mL/min) and foeto-placental blood flow (480 mL/min), and (b) O2, CO2 and pH levels in the materno-placental and foeto-placental circulation. According to these data, the foetus is adapted to hypoxaemic hypoxia. Despite flat oxygen partial pressure (pO2) gradients between the blood of the IVS and the umbilical arteries of the foetus, adequate O2 delivery to the foetus is maintained by the higher O2 affinity of the foetal blood, high foetal haemoglobin (HbF) concentrations, the Bohr effect, the double-Bohr effect, and high foeto-placental (=umbilical) blood flow. Again, despite flat gradients, adequate CO2 removal from the foetus is maintained by a high diffusion capacity, high foeto-placental blood flow, the Haldane effect, and the double-Haldane effect. Placental respiratory gas exchange is perfusion-limited, rather than diffusion-limited, i.e., O2 uptake depends on O2 delivery.

Use of Fluoxetine to Augment the Inter-Ictal Hypercapnic Ventilatory Response in Patients with Epilepsy: A Pilot Study.

Background: Severe peri-ictal respiratory dysfunction is a potential biomarker for high SUDEP risk and correlates with an attenuated hypercapnic ventilatory response (HCVR). Prior studies suggest a potential role for selective serotonergic reuptake inhibitors in modifying the HCVR, but this approach has not been studied in the epilepsy population. Objectives: To assess the feasibility of using fluoxetine to augment HCVR in epilepsy patients. Methods and Material: An inter-ictal HCVR was measured using a CO2 rebreathing technique in patients with epilepsy aged 18-75 years. Eligible participants were randomized to fluoxetine or placebo, and the HCVR was repeated at the end of week 4. Primary outcomes were recruitment and retention rate. Results: Of the 30 subjects enrolled, 22 were randomized (mean: 3.8 subjects/3 months), with a retention rate of 100% in fluoxetine and 95% in placebo. Conclusions: Our results demonstrate feasibility for a larger definitive future study to assess the efficacy of fluoxetine in augmenting HCVR.

Dead space washout by intentional leakage flow during conventional ventilation of premature infants-an experimental study.

OBJECTIVE: Invasive mechanical ventilation poses a strong risk factor for the development of chronic lung disease in preterm infants. A reduction of the dead space as part of the total breathing volume would reduce the ventilation effort and thereby lower the risk of ventilator-induced lung injuries. In this experimental study, we compared the efficacy of mechanical dead space washout via uncontrolled and controlled leakage flow in their ability to eliminate CO2 during conventional ventilation in preterm infants. METHODS: Three frequently used neonatal ventilators, operating under standard conventional ventilating parameters, were individually connected to a test lung. To maintain a constant physiological end-expiratory pCO2 level during ventilation, the test lung was continuously flooded with CO2 . A side port in the area of the connector between the endotracheal tube and the flow sensor allowed breathing gas to escape passively or in a second experimental setup, regulated by a pump. Measurements of end-expiratory pCO2 were taken in both experiments and compared to end-expiratory pCO2 levels of ventilation without active dead space leakage. RESULTS: Following dead space washout, a significant reduction of end-expiratory pCO2 was attained. Under conditions of uncontrolled leakage, the mean decrease was 14.1% while controlled leakage saw a mean reduction of 16.1%. CONCLUSION: Washout of dead space by way of leakage flow is an effective method to reduce end-expiratory pCO2 . Both controlled and uncontrolled leakage provide comparable results, but precise regulation of leakage allows for a more stable ventilation by preventing uncontrolled loss of tidal volume during inspiration.

The Effect of CO2 Pressure and Flow Variation on Carbon Particles Spread During Pneumoperitoneum: An Experimental Study.

Background: A correlation between atypical recurrences and minimally-invasive surgery has been suggested in case of urothelial cancer; however, few data are available on the role of pneumoperitoneum in terms of gas flow and intra-abdominal pressure. The objective of the study is to analyze the impact of CO2 pneumoperitoneum variation on an inert material as surrogate of neoplastic cells. Material and Methods: We designed an experimental model mimicking pneumoperitoneum in three settings: sealed flow (no leakage), pulsatile flow (alternating efflux and influx), and continuous flow (AirSeal® insufflator). Each experiment was characterized by a predetermined gas flow and pressure, trocar distance, and position from the particles. Hounsfield density (HD) variation in the areas of interest was measured as index of graphite powder dispersion. A Linear Regression Model was used to measure the correlation between modifiable variables and HD. Results: HD was lower in the pulsatile compared to both the sealed and continuous flows (p < 0.03). On multivariate analysis for sealed setting, flow and total gas liters delivered (i.e., gas leakage) were inversely and independently related to HD (all p < 0.03). In pulsatile setting, trocar position, trocar distance, and gas flow independently predicted HD (all p < 0.03). In continuous setting, gas pressure was directly and independently related to HD (p = 0.004) due to decreased pneumoperitoneum stability and increased CO2 liters delivered. In case of inflow trocar positioned laterally to the particles, low flow (1 L/min), or low pressure (8 mmHg), HD values recorded in the three settings were all overlapping (all p > 0.05). Conclusions: Flow and pressure setting, inflow trocar distance and contiguity from the tumor, and pneumoperitoneum stability may be all crucial components in minimally invasive surgery. In vivo, these variables should be considered as potential risk factors for tumor cells spread within the abdominal cavity. Clinical Trial Registration number: NCT01740011.

Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur?

Current carbon cycle models attribute rising atmospheric CO2 as the major driver of the increased terrestrial carbon sink, but with substantial uncertainties. The photosynthetic response of trees to elevated atmospheric CO2 is a necessary step, but not the only one, for sustaining the terrestrial carbon uptake, but can vary diurnally, seasonally and with duration of CO2 exposure. Hence, we sought to quantify the photosynthetic response of the canopy-dominant species, Quercus robur, in a mature deciduous forest to elevated CO2 (eCO2) (+150 µmol mol-1 CO2) over the first 3 years of a long-term free air CO2 enrichment facility at the Birmingham Institute of Forest Research in central England (BIFoR FACE). Over 3000 measurements of leaf gas exchange and related biochemical parameters were conducted in the upper canopy to assess the diurnal and seasonal responses of photosynthesis during the 2nd and 3rd year of eCO2 exposure. Measurements of photosynthetic capacity via biochemical parameters, derived from CO2 response curves, (Vcmax and Jmax) together with leaf nitrogen concentrations from the pre-treatment year to the 3rd year of eCO2 exposure, were examined. We hypothesized an initial enhancement in light-saturated net photosynthetic rates (Asat) with CO2 enrichment of ≈37% based on theory but also expected photosynthetic capacity would fall over the duration of the study. Over the 3-year period, Asat of upper-canopy leaves was 33 ± 8% higher (mean and standard error) in trees grown in eCO2 compared with ambient CO2 (aCO2), and photosynthetic enhancement decreased with decreasing light. There were no significant effects of CO2 treatment on Vcmax or Jmax, nor leaf nitrogen. Our results suggest that mature Q. robur may exhibit a sustained, positive response to eCO2 without photosynthetic downregulation, suggesting that, with adequate nutrients, there will be sustained enhancement in C assimilated by these mature trees. Further research will be required to understand the location and role of the additionally assimilated carbon.

Impact of wearing a surgical and cloth mask during cycle exercise.

We sought to determine the impact of wearing cloth or surgical masks on the cardiopulmonary responses to moderate-intensity exercise. Twelve subjects (n = 5 females) completed three, 8-min cycling trials while breathing through a non-rebreathing valve (laboratory control), cloth, or surgical mask. Heart rate (HR), oxyhemoglobin saturation (SpO2), breathing frequency, mouth pressure, partial pressure of end-tidal carbon dioxide (PetCO2) and oxygen (PetO2), dyspnea were measured throughout exercise. A subset of n = 6 subjects completed an additional exercise bout without a mask (ecological control). There were no differences in breathing frequency, HR or SpO2 across conditions (all p > 0.05). Compared with the laboratory control (4.7 ± 0.9 cmH2O [mean ± SD]), mouth pressure swings were smaller with the surgical mask (0.9 ± 0.7; p < 0.0001), but similar with the cloth mask (3.6 ± 4.8 cmH2O; p = 0.66). Wearing a cloth mask decreased PetO2 (-3.5 ± 3.7 mm Hg) and increased PetCO2 (+2.0 ± 1.3 mm Hg) relative to the ecological control (both p < 0.05). There were no differences in end-tidal gases between mask conditions and laboratory control (both p > 0.05). Dyspnea was similar between the control conditions and the surgical mask (p > 0.05) but was greater with the cloth mask compared with laboratory (+0.9 ± 1.2) and ecological (+1.5 ± 1.3) control conditions (both p < 0.05). Wearing a mask during short-term moderate-intensity exercise may increase dyspnea but has minimal impact on the cardiopulmonary response. Novelty: Wearing surgical or cloth masks during exercise has no impact on breathing frequency, tidal volume, oxygenation, and heart rate However, there are some changes in inspired and expired gas fractions that are physiologically irrelevant. In young healthy individuals, wearing surgical or cloth masks during submaximal exercise has few physiological consequences.

Computational tools for inversion and uncertainty estimation in respirometry.

In many physiological systems, real-time endogeneous and exogenous signals in living organisms provide critical information and interpretations of physiological functions; however, these signals or variables of interest are not directly accessible and must be estimated from noisy, measured signals. In this paper, we study an inverse problem of recovering gas exchange signals of animals placed in a flow-through respirometry chamber from measured gas concentrations. For large-scale experiments (e.g., long scans with high sampling rate) that have many uncertainties (e.g., noise in the observations or an unknown impulse response function), this is a computationally challenging inverse problem. We first describe various computational tools that can be used for respirometry reconstruction and uncertainty quantification when the impulse response function is known. Then, we address the more challenging problem where the impulse response function is not known or only partially known. We describe nonlinear optimization methods for reconstruction, where both the unknown model parameters and the unknown signal are reconstructed simultaneously. Numerical experiments show the benefits and potential impacts of these methods in respirometry.

Regulation of apoptosis by Pacific oyster Crassostrea gigas reveals acclimation strategy to CO2 driven acidification.

Ocean acidification (OA) has posed formidable threats to marine calcifiers. In response to elevated CO2 levels, marine calcifiers have developed multiple strategies to survive, such as taking advantage of apoptosis, but its regulation mechanism remains largely unknown. Here, we used the Pacific oyster Crassostrea gigas as model to understand the apoptotic responses and regulation mechanism at short- (7 d) to long-term (56 d) CO2 exposure (pH = 7.50). The apoptosis of hemocytes was significantly induced after short-term treatment (7-21 d) but was suppressed under long-term CO2 exposure (42-56 d). Similarly, caspase-3 and caspase-9 were also increased post short-term exposure and fell back to normal levels after long-term exposure. These data together indicated diverse regulation mechanisms of apoptosis through different exposure periods. Through analysis of the B-cell lymphoma 2 (Bcl-2) family mitochondrial apoptosis regulators, we showed that only CgBcl-XL's expression kept at high levels after 42- and 56-day CO2 exposure. CgBcl-XL shared sequence, and structural similarity with its mammalian counterpart, and knockdown of CgBcl-XL in hemocytes via RNA interference promoted apoptosis. The protein level of CgBcl-XL was significantly increased after long-term CO2 exposure (28-56 d), and its distribution in hemocytes became more concentrated and dense. Therefore, CgBcl-XL serves as an essential anti-apoptotic protein for tipping the balance of cell apoptosis, which may play a key role in survival under long-term CO2 exposure. These results reveal a potential adaptation strategy of oysters towards OA and the variable environment changes through the modulation of apoptosis.

The Impact of 6-Month Land versus Water Walking on Cerebrovascular Function in the Aging Brain.

INTRODUCTION: To examine the hypothesis that exercise training induces adaptation in cerebrovascular function, we recruited 63 older adults (62 ± 7 yr, 46 females) to undertake 24 wk of either land walking or water walking, or participate in a nonexercise control group. This is the first multi-interventional study to perform a comprehensive assessment of cerebrovascular function in response to longer term (6-month) training interventions, including water-based exercise, in older healthy individuals. METHODS: Intracranial blood flow velocities (middle cerebral artery (MCAv) and posterior cerebral artery) were assessed at rest and in response to neurovascular coupling, hypercapnic reactivity, and cerebral autoregulation. RESULTS: We observed no change in resting MCAv in response to either training intervention (pre vs post, mean (95% confidence interval), land walking: 65 (59-70) to 63 (57-68) cm·s-1, P = 0.33; water walking: 63 (58-69) to 61 (55-67) cm·s-1, P = 0.92) compared with controls and no change in neurovascular coupling (land walking: P = 0.18, water walking: P = 0.17). There was a significant but modest improvement in autoregulatory normalized gain after the intervention in the water-walking compared with the land-walking group (P = 0.03). Hypercapnic MCAv reactivity was not different based on exercise group (land: P = 087, water: P = 0.83); however, when data were pooled from the exercise groups, increases in fitness were correlated with decreases in hypercapnic reactivity (r2 = 0.25, P = 0.003). CONCLUSIONS: Although exercise was not associated with systematic changes across multiple domains of cerebrovascular function, our data indicate that exercise may induce modest changes in autoregulation and CO2 reactivity. These findings should encourage further studies of the longer-term implications of exercise training on cerebrovascular health.

Resting metabolic rate in adults with facioscapulohumeral muscular dystrophy.

This study aimed to determine whether resting metabolic rate (RMR) is altered in adults with facioscapulohumeral muscular dystrophy (FSHD). Eleven people with FSHD (51 ± 12yrs, 2 females) and 11 controls (48 ± 14 yrs, 2 females) completed 1 visit, including 30-minutes of indirect calorimetry and dual-energy X-ray absorptiometry (DXA) scanning. RMR was calculated from resting oxygen consumption/carbon dioxide production; regional/whole-body fat mass and lean mass were collected from the DXA scan. Absolute RMR was 15% lower in FSHD (p = 0.04); when normalized to regional/local lean mass, no differences in RMR were observed (p > 0.05). Absolute RMR was correlated with total lean mass for all participants combined (p < 0.01, r = 0.70, males only: p < 0.01, r = 0.81) and when analyzed separately (FSHD males: p = 0.001, r = 0.92 and control males: p = 0.004, r = 0.85). Whole-body lean mass was 16% lower in FSHD and leg, arm and appendicular lean mass were lower in FSHD (p < 0.05 for all), though trunk lean mass was not (p = 0.15). Whole-body fat mass was 45% higher in FSHD, with greater leg fat mass (p = 0.01), but not trunk or arm fat mass (p > 0.05 for both). When RMR was expressed relative to lean body mass, no differences in RMR were found, indicating that the lower levels of lean mass observed in FSHD patients likely contribute to the lower absolute RMR values. Novelty: RMR is lower among people with FSHD, as compared with controls. The reduced RMR among people with FSHD is due to disease-related loss in muscle mass and likely related to lower physical activity and/or exercise levels.

Assessment of Respiratory Function in Infants and Young Children Wearing Face Masks During the COVID-19 Pandemic.

Importance: Face masks have been associated with effective prevention of diffusion of viruses via droplets. However, the use of face masks among children, especially those aged younger than 3 years, is debated, and the US Centers for Disease Control and American Academy of Physicians recommend the use of face mask only among individuals aged 3 years or older. Objective: To examine whether the use of surgical facial masks among children is associated with episodes of oxygen desaturation or respiratory distress. Design, Setting, and Participants: This cohort study was conducted from May through June 2020 in a secondary-level hospital pediatric unit in Italy. Included participants were 47 healthy children divided by age (ie, group A, aged ≤24 months, and group B, aged >24 months to ≤144 months). Data were analyzed from May through June 2020. Interventions: All participants were monitored every 15 minutes for changes in respiratory parameters for the first 30 minutes while not wearing a surgical face mask and for the next 30 minutes while wearing a face mask. Children aged 24 months and older then participated in a walking test for 12 minutes. Main Outcomes and Measures: Changes in respiratory parameters during the use of surgical masks were evaluated. Results: Among 47 children, 22 children (46.8%) were aged 24 months or younger (ie, group A), with 11 boys (50.0%) and median (interquartile range [IQR]) age 12.5 (10.0-17.5) months, and 25 children (53.2%) were aged older than 24 months to 144 months or younger, with 13 boys (52.0%) and median (IQR) age 100.0 (72.0-120.0) months. During the first 60 minutes of evaluation in the 2 groups, there was no significant change in group A in median (IQR) partial pressure of end-tidal carbon dioxide (Petco2; 33.0 [32.0-34.0] mm Hg; P for Kruskal Wallis = .59), oxygen saturation (Sao2; 98.0% [97.0%-99.0%]; P for Kruskal Wallis = .61), pulse rate (PR; 130.0 [115.0-140.0] pulsations/min; P for Kruskal Wallis = .99), or respiratory rate (RR; 30.0 [28.0-33.0] breaths/min; P for Kruskal Wallis = .69) or for group B in median (IQR) Petco2 (36.0 [34.0-38.0] mm Hg; P for Kruskal Wallis = .97), Sao2 (98.0% [97.0%-98.0%]; P for Kruskal Wallis = .52), PR (96.0 [84.0-104.5] pulsations/min; P for Kruskal Wallis test = .48), or RR (22.0 [20.0-25.0] breaths/min; P for Kruskal Wallis = .55). After the group B walking test, compared with before the walking test, there was a significant increase in median (IQR) PR (96.0 [84.0-104.5] pulsations/min vs 105.0 [100.0-115.0] pulsations/min; P < .02) and RR (22.0 [20.0-25.0] breaths/min vs 26.0 [24.0-29.0] breaths/min; P < .05). Conclusions and Relevance: This cohort study among infants and young children in Italy found that the use of facial masks was not associated with significant changes in Sao2 or Petco2, including among children aged 24 months and younger.

The Scent of Life: Phoretic Nematodes Use Wasp Volatiles and Carbon Dioxide to Choose Functional Vehicles for Dispersal.

Hitchhikers (phoretic organisms) need vehicles to disperse out of unsuitable habitats. Therefore, finding vehicles with the right functional attributes is essential for phoretic organisms. To locate these vehicles, phoretic organisms employ cues within modalities, ranging from visual to chemical senses. However, how hitchhikers discriminate between individual vehicles has rarely been investigated. Using a phoretic nematode community associated with an obligate fig-fig wasp pollination mutualism, we had earlier established that hitchhiking nematodes make decisions based on vehicle species identity and number of conspecific hitchhikers already present on the vehicle. Here we investigate if hitchhikers can differentiate between physiological states of vehicles. We asked whether phoretic nematodes choose between live or dead vehicles present in a chemically crowded environment and we investigated the basis for any discrimination. We conducted two-choice and single-choice behavioral assays using single nematodes and found that plant- and animal-parasitic nematodes preferred live over dead vehicles and used volatiles as a sensory cue to make this decision. However, in single-choice assays, animal-parasitic nematodes were also attracted towards naturally dead or freeze-killed wasps. The volatile profile of the wasps was dominated by terpenes and spiroketals. We examined the volatile blend emitted by the different wasp physiological states and determined a set of volatiles that the phoretic nematodes might use to discriminate between these states which is likely coupled with respired CO2. We determined that CO2 levels emitted by single wasps are sufficient to attract nematodes, demonstrating the high sensitivity of nematodes to this metabolic product.

Functional role of carbon dioxide on intermittent hypoxia induced respiratory response following mid-cervical contusion in the rat.

Intermittent hypoxia induces respiratory neuroplasticity to enhance respiratory motor outputs and is a potential rehabilitative strategy to improve respiratory function following cervical spinal injury. The present study was designed to evaluate the functional role of intermittent and sustained carbon dioxide (CO2) on intermittent hypoxia-induced ventilatory responses in rats with mid-cervical spinal contusion. The breathing pattern of unanesthetized rats at the subchronic and chronic injured stages was measured in response to one of the following treatments: (1) Intermittent hypercapnic-hypoxia (10 × 5 min 10%O2 + 4%CO2 with 5 min normoxia interval); (2) Intermittent hypoxia with sustained hypercapnia (10 × 5 min 10%O2 + 4%CO2 with 5 min 21%O2 + 4%CO2 interval); (3) Intermittent hypoxia (10 × 5 min 10%O2 with 5 min normoxia interval); (4) Intermittent hypercapnia (10 × 5 min 21%O2 + 4%CO2 with 5 min normoxia interval); (5) Sustained hypercapnia (100 min, 21% O2 + 4% CO2); (6) Sustained normoxia (100 min, 21% O2). The results demonstrated that intermittent hypoxia associated with intermittent hypercapnia or sustained hypercapnia induced a greater ventilatory response than sustained hypercapnia during stimulus exposure. The tidal volume was significantly enhanced to a similar magnitude following intermittent hypercapnic-hypoxia, intermittent hypoxia with sustained hypercapnia, and intermittent hypoxia in subchronically injured animals; however, only intermittent hypercapnic-hypoxia and intermittent hypoxia were able to evoke long-term facilitation of the tidal volume at the chronic injured stage. These results suggest that mild intermittent hypercapnia did not further enhance the therapeutic effectiveness of intermittent hypoxia-induced respiratory recovery in mid-cervical contused animals. However, sustained hypercapnia associated with intermittent hypoxia may blunt ventilatory responses following intermittent hypoxia at the chronic injured stage.

Long-Term m5C Methylome Dynamics Parallel Phenotypic Adaptation in the Cyanobacterium Trichodesmium.

A major challenge in modern biology is understanding how the effects of short-term biological responses influence long-term evolutionary adaptation, defined as a genetically determined increase in fitness to novel environments. This is particularly important in globally important microbes experiencing rapid global change, due to their influence on food webs, biogeochemical cycles, and climate. Epigenetic modifications like methylation have been demonstrated to influence short-term plastic responses, which ultimately impact long-term adaptive responses to environmental change. However, there remains a paucity of empirical research examining long-term methylation dynamics during environmental adaptation in nonmodel, ecologically important microbes. Here, we show the first empirical evidence in a marine prokaryote for long-term m5C methylome modifications correlated with phenotypic adaptation to CO2, using a 7-year evolution experiment (1,000+ generations) with the biogeochemically important marine cyanobacterium Trichodesmium. We identify m5C methylated sites that rapidly changed in response to high (750 µatm) CO2 exposure and were maintained for at least 4.5 years of CO2 selection. After 7 years of CO2 selection, however, m5C methylation levels that initially responded to high-CO2 returned to ancestral, ambient CO2 levels. Concurrently, high-CO2 adapted growth and N2 fixation rates remained significantly higher than those of ambient CO2 adapted cell lines irrespective of CO2 concentration, a trend consistent with genetic assimilation theory. These data demonstrate the maintenance of CO2-responsive m5C methylation for 4.5 years alongside phenotypic adaptation before returning to ancestral methylation levels. These observations in a globally distributed marine prokaryote provide critical evolutionary insights into biogeochemically important traits under global change.