Normal CO2 Levels Research Articles

Release your inhibitions: The role of post-inhibitory rebound and synaptic inhibition in the generation of expiratory activity.

Release your inhibitions: The role of post-inhibitory rebound and synaptic inhibition in the generation of expiratory activity.

Concept of neuroprotective NICU

Neurodevelopmental outcomes are of paramount importance for every clinician as the survival rates of term and preterm babies have continued to improve. We aim to provide a framework for developing a Neuroprotective Neonatal Intensive Care Unit (NICU) by describing five main domains below. We achieve this in our NICU by a multidisciplinary team consisting of neonatologists, respiratory therapist, occupational therapist, physiotherapist, social worker, pharmacist, and a dietician. This approach needs to be individualised for each unit based on the resources and services available.I. Neuro assessment: clinical neuro assessment remains the most important tool with strong predictive value for long-term outcomes. It is important to develop other tools of assessment like comfort and pain scoring. We use COMFORTneo scale as a standard of care.1 Neuroimaging is another important factor as part of the assessment. We have a local guideline to decide on the frequency and the timing of the neuroimaging such as cranial ultrasound and MRI.II. Neuroprotection: antenatal magnesium sulphate and antenatal steroids have become an established treatment in most units.2 Interventions like total body cooling have significantly improved the outcomes for babies with hypoxic ischemic injury. One challenge faced in these babies is the ability to provide active cooling during transport when these babies are born outside cooling centres. Optimal nutrition is another important element for the developing brain. We developed neonatal nutritional guidelines in collaboration with the clinical pharmacist and a dietician. Introduction of starter parenteral nutrition bags for out of hours use in line with evidence-based feeding guidelines are known to improve the outcomes. We practice the golden hour protocol for all babies born before 28 weeks gestation and have introduced intraventricular haemorrhage (IVH) prevention bundles3 for the same cohort of babies. Even though individual components of these bundles do not have strong evidence, there is some benefit when these interventions are offered as a bundle. Our care bundle involves midline positioning, using log roll, minimal handling, maintaining normothermia, avoiding IV boluses, and maintaining normal CO2 levels etc.III. Neuromonitoring: tools like amplitude-integrated electroencephalogram (aEEG), near-infrared spectroscopy (NIRS), and onsite MRI are gaining popularity. eEEG should be routinely used in hypoxic ischemic encephalopathy (HIE) babies when available. All team members should be trained in its application and interpretation. NIRS is a developing modality used by only a few units to monitor the cerebral oxygenation. We have recently started to pilot these machines.IV. Neurodevelopment: the environment of the NICU has been shown to affect the developing brain. Strategies should be developed to optimise babies sleeping by reducing lighting and noise levels. We use positioning tools like boundaries and midliners as part of their neurodevelopment.V. Neurointervention: we use therapeutic techniques like auditory, tactile, visual, and vestibular (ATVV) stimulation.4 It is an evidence-based technique used to increase alertness in medically stable preterm infants. We use Prechtl's Qualitative Assessment of General Movements observational tool.5 It is the most predictive tool (98% sensitivity) for detecting cerebral palsy. This helps provide targeted treatment at an earlier stage.

The Hypoxic Ventilatory Response is Blocked by AMPK Deletion in Catecholaminergic, but not Adrenergic Cells

During hypoxia, ventilatory adjustments are critical to the maintenance of adequate oxygen (O2) delivery, for example during sleep or ascent to altitude (1). We recently demonstrated that the AMP‐activated protein kinase (AMPK), a ubiquitously expressed metabolic sensor (2), protects against hypoventilation and apnea during hypoxia (3). Here, we further investigated the circuit mechanism by which AMPK deficiency impacts the hypoxic ventilatory response (HVR). Using unrestrained whole‐body plethysmography, we compared the effects on the HVR of mice with dual deletion of the AMPK‐α1/α2 catalytic subunits in all catecholaminergic (TH‐positive) cells with the HVR of mice with AMPK‐α1/α2 deletion targeted to adrenergic cells alone (Phenylethanolamine N‐methyltransferase (PNMT)‐positive). Relative to controls (AMPK‐α1/α2 floxed), mice with TH‐Cre driven AMPK deletion (TH AMPK‐α1/α2 dKO) exhibited hypoventilation, characterized by marked attenuation of minute ventilation (p<0.0001) during each minute of exposures to severe hypoxia (8% O2). By contrast, in mice with PNMT‐Cre driven AMPK deletion (PNMT AMPK‐α1/α2 dKO) the HVR was augmented rather than attenuated, although this only reached significance relative to controls (AMPK‐α1/α2 floxed and PNMT Cre) when taken as averages for the whole 10min period of exposure to severe hypoxia (p<0.001–0.0001). As one might expect given these outcomes, the HVR of PNMT AMPK‐α1/α2 dKO mice was significantly greater than that for TH AMPK‐α1/α2 dKO during each full minute of hypoxia (p<0.0001). Furthermore, the apnea‐duration index (ADI) was significantly augmented in TH AMPK‐α1/α2 dKO mice compared to controls (p<0.01–0.0001). By contrast, PNMT AMPK‐α1/α2 dKO mice exhibited a reduction in the average ADI compared to controls (p<0.05–0.01). This reduction in the ADI for PNMT AMPK‐α1/α2 dKO mice was primarily due to a lower number of apneas during the first 3 to 4 minutes of hypoxic exposure, the ADI being comparable to controls between 4 and 10 min. Accordingly, the ADI of PNMT AMPK‐α1/α2 dKO was attenuated at each time point throughout the 10min exposure to hypoxia when compared to TH AMPK‐α1/α2 dKO mice (p<0.0001). In conclusion, we have uncovered a split in the AMPK‐dependent regulation of the catecholaminergic respiratory network during hypoxia, where the HVR is promoted by AMPK‐dependent modulation of noradrenergic inputs, but opposed by AMPK‐dependent modulation of adrenergic inputs. AMPK may thus protect against hypoventilation and apnea through noradrenergic signaling, and might aid restoration of normal CO2 levels during hypoxic hyperventilation through adrenergic signaling (4).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Elevated pCO2 Affects Feeding Behavior and Acute Physiological Response of the Brown Crab Cancer pagurus.

Anthropogenic climate change exposes marine organisms to CO2 induced ocean acidification (OA). Marine animals may make physiological and behavioral adaptations to cope with OA. Elevated pCO2 may affect metabolism, feeding, and energy partition of marine crabs, and thereby affect their predator-prey dynamics with mussels. Therefore, we examined the effects of simulated future elevated pCO2 on feeding behavior and energy metabolism of the brown crab Cancer pagurus. Following 54 days of pre-acclimation to control CO2 levels (360 μatm) at 11°C, crabs were exposed to consecutively increased oceanic CO2 levels (2 weeks for 1200 and 2300 μatm, respectively) and subsequently returned to control CO2 level (390 μatm) for 2 weeks in order to study their potential to acclimate elevated pCO2 and recovery performance. Standard metabolic rate (SMR), specific dynamic action (SDA) and feeding behavior of the crabs were investigated during each experimental period. Compared to the initial control CO2 conditions, the SMRs of CO2 exposed crabs were not significantly increased, but increased significantly when the crabs were returned to normal CO2 levels. Conversely, SDA was significantly reduced under high CO2 and did not return to control levels during recovery. Under high CO2, crabs fed on smaller sized mussels than under control CO2; food consumption rates were reduced; foraging parameters such as searching time, time to break the prey, eating time, and handling time were all significantly longer than under control CO2, and prey profitability was significantly lower than that under control conditions. Again, a two-week recovery period was not sufficient for feeding behavior to return to control values. PCA results revealed a positive relationship between feeding/SDA and pH, but negative relationships between the length of foraging periods and pH. In conclusion, elevated pCO2 caused crab metabolic rate to increase at the expense of SDA. Elevated pCO2 affected feeding performance negatively and prolonged foraging periods. These results are discussed in the context of how elevated pCO2 may impair the competitiveness of brown crabs in benthic communities.

Altered carbon turnover processes and microbiomes in soils under long-term extremely high CO2 exposure.

There is only limited understanding of the impact of high p(CO2) on soil biomes. We have studied a floodplain wetland where long-term emanations of temperate volcanic CO2 (mofettes) are associated with accumulation of carbon from the Earth's mantle. With an integrated approach using isotope geochemistry, soil activity measurements and multi-omics analyses, we demonstrate that high (nearly pure) CO2 concentrations have strongly affected pathways of carbon production and decomposition and therefore carbon turnover. In particular, a promotion of dark CO2 fixation significantly increased the input of geogenic carbon in the mofette when compared to a reference wetland soil exposed to normal levels of CO2. Radiocarbon analysis revealed that high quantities of mofette soil carbon originated from the assimilation of geogenic CO2 (up to 67%) via plant primary production and subsurface CO2 fixation. However, the preservation and accumulation of almost undegraded organic material appeared to be facilitated by the permanent exclusion of meso- to macroscopic eukaryotes and associated physical and/or ecological traits rather than an impaired biochemical potential for soil organic matter decomposition. Our study shows how CO2-induced changes in diversity and functions of the soil community can foster an unusual biogeochemical profile.

La prise en charge des méningites bactériennes graves de l’enfant en 2016

Bacterial meningitis is a severe infection of the central nervous system with significant impact on survival and functional outcome. Complications are related to the release of bacterial components in the subarachnoid space closed to the brain. Three types of complications are distinguished: septic shock that alters the oxygen delivery, intracranial hypertension (ICH) that may alter the cerebralperfusion pressure and severe metabolic disorders like hyponatremia. The management is based on an early diagnosis allowing initiating antibiotics within the first hour. An associated corticosteroids treatment with dexamethasone improves the prognosis of pneumococcal and Haemophilus meningitis. The identification of septic shock signs should be rapid to initiate fluid bolus and sometimes vasopressors in order to maintain a good organ perfusion. The detection of altered level of consciousness is a crucial indication of ICH. Control of intracranial pressure (ICP) as well as a good hemodynamic is based on a continuous monitoring of ICP and arterial pressure in order to assure an adapted cerebral perfusion pressure. Cerebrospinalfluid (CSF) drainage is one of the most eflicient means to control ICP as resorption of CSF is often altered in bacterial meningitis. Seizures should be avoided, the sedation-pain control optimized and ventilation adapted to assure normal oxygenation and normal CO₂ levels. Hyponatremia is most often related to a salt wasting syndrome linked to aquaporin's deregulation. Its rapid correction is required to avoid worsening of the cerebral oedema.

Proton Pump Inhibition Increases Rapid Eye Movement Sleep in the Rat

Increased bodily CO2 concentration alters cellular pH as well as sleep. The proton pump, which plays an important role in the homeostatic regulation of cellular pH, therefore, may modulate sleep. We investigated the effects of the proton pump inhibitor “lansoprazole” on sleep-wakefulness. Male Wistar rats were surgically prepared for chronic polysomnographic recordings. Two different doses of lansoprazole (low: 1 mg/kg; high: 10 mg/kg) were injected intraperitoneally in the same animal (n = 7) and sleep-wakefulness was recorded for 6 hrs. The changes in sleep-wakefulness were compared statistically. Percent REM sleep amount in the vehicle and lansoprazole low dose groups was 9.26 ± 1.03 and 9.09 ± 0.54, respectively, which increased significantly in the lansoprazole high dose group by 31.75% (from vehicle) and 34.21% (from low dose). Also, REM sleep episode numbers significantly increased in lansoprazole high dose group. Further, the sodium-hydrogen exchanger blocker “amiloride” (10 mg/kg; i.p.) (n = 5) did not alter sleep-wake architecture. Our results suggest that the proton pump plays an important role in REM sleep modulation and supports our view that REM sleep might act as a sentinel to help maintain normal CO2 level for unperturbed sleep.

P69 A study of the prevalence of hypoxaemia, hypercapnia, hyperoxaemia and acidosis in hospital blood gas specimens (with clinical outcomes)

IntroductionSome clinicians take an aggressive approach to supplemental oxygen therapy to avoid the dangers of hypoxaemia but many patients, especially those with COPD, are at risk from uncontrolled oxygen therapy....

Pulmonary Embolism Due to Popliteal Venous Aneurysm

A 33-year-old man was admitted to our hospital for shortness of breath on exertion. His symptoms started suddenly a week before admission when he was driving a car and worsened daily. He was amateur football player and had no history of hypertension, dyslipidemia, diabetes mellitus, smoking, or leg injury. On admission, an arterial pulse oxygen saturation monitor showed that his arterial blood oxygen saturation was 94% with room air. His blood pressure was 114/82 mm Hg and his pulse rate was 92/min with regular rhythm. His height was 162 cm and body weight was 62 kg. No other outstanding physical abnormalities were observed. Laboratory data showed slightly an elevated C-reactive protein level of 0.87 mg/dL with a normal white blood cell count of 6100 cells/mL. Arterial blood sampling revealed a normal CO2 level of 41 mm Hg and pH of 7.42 with low oxygen tension (52 mm Hg). An ECG showed a small S wave in lead I and a small Q wave and inverted T wave in …

Electron transport is the functional limitation of photosynthesis in field‐grown Pima cotton plants at high temperature

ABSTRACTRestrictions to photosynthesis can limit plant growth at high temperature in a variety of ways. In addition to increasing photorespiration, moderately high temperatures (35–42 °C) can cause direct injury to the photosynthetic apparatus. Both carbon metabolism and thylakoid reactions have been suggested as the primary site of injury at these temperatures. In the present study this issue was addressed by first characterizing leaf temperature dynamics in Pima cotton (Gossypium barbadense) grown under irrigation in the US desert south‐west. It was found that cotton leaves repeatedly reached temperatures above 40 °C and could fluctuate as much as 8 or 10 °C in a matter of seconds. Laboratory studies revealed a maximum photosynthetic rate at 30–33 °C that declined by 22% at 45 °C. The majority of the inhibition persisted upon return to 30 °C. The mechanism of this limitation was assessed by measuring the response of photosynthesis to CO2 in the laboratory. The first time a cotton leaf (grown at 30 °C) was exposed to 45 °C, photosynthetic electron transport was stimulated (at high CO2) because of an increased flux through the photorespiratory pathway. However, upon cooling back to 30 °C, photosynthetic electron transport was inhibited and fell substantially below the level measured before the heat treatment. In the field, the response of assimilation (A) to various internal levels of CO2 (Ci) revealed that photosynthesis was limited by ribulose‐1,5‐bisphosphate (RuBP) regeneration at normal levels of CO2 (presumably because of limitations in thylakoid reactions needed to support RuBP regeneration). There was no evidence of a ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) limitation at air levels of CO2 and at no point on any of 30 A–Ci curves measured on leaves at temperatures from 28 to 39 °C was RuBP regeneration capacity measured to be in substantial excess of the capacity of Rubisco to use RuBP. It is therefore concluded that photosynthesis in field‐grown Pima cotton leaves is functionally limited by photosynthetic electron transport and RuBP regeneration capacity, not Rubisco activity.

Hypocapnia decreases the amount of rapid eye movement sleep in cats.

Sleep is disturbed at high altitudes. Low PO2 levels at high altitude cause hyperventilation, which results in secondary hypocapnia (low PaCO2 levels). Thus, although sleep disruption at high altitudes is generally assumed to be caused by hypoxia, it may instead be the result of hypocapnia. To determine whether hypocapnia disrupts sleep. Four cats were studied for a total of 345 hours of sleep recordings. Two methods were used to test this idea. First we studied their sleep when the cats breathed oxygen concentrations (15% and 10%) equivalent to those at approximately 12,000 feet and 21,000 feet. Then we studied their sleep again in response to the same hypoxic stimuli but with CO2 added to the inspirate to maintain normal CO2 levels. Second, we used mechanical hyperventilation to vary the levels of CO2 while maintaining normal O2 levels. Hypoxia (10% O2) decreased the amount of rapid eye movement sleep to about 20% of normal, and adding back CO2 restored rapid eye movement sleep to approximately 70% of normal. Periodic breathing and apneas were not observed during hypoxia in sleep. When mechanical hyperventilation lowered the CO2 to 85%, 75%, and 65% of normal, rapid eye movement sleep decreased progressively from a control level of 17% of total recording time to 12%, 7%, and 4%, respectively. We conclude that hypocapnia rather than hypoxia may account for most of the sleep disturbance at high altitudes.

Foliar antioxidant status of plants from naturally high‐CO2 sites

We compared the foliar antioxidant status of native Agrostis stolonifera L. communities growing at two distinct CO2‐enriched sites of geothermal origin (E) and at a control field location with normal CO2. Compared to the control, plants from both E‐sites showed an increased size of the GSH pool, essentially due to enhanced GSSG levels, and a consequent decrease in the ratio between reduced and oxidised glutathione forms. Such differences were maintained and even enhanced in the vegetatively‐propagated progenies of control and E‐plants, grown under both greenhouse conditions and normal CO2 levels. The above results confirmed previous observations on native and crop plants exposed to elevated CO2. It is therefore suggested that changes in the glutathione redox balance might be of adaptive significance under conditions of permanent exposure to high CO2.

Different CO2 levels during incubation interact with hatching time and ascites susceptibility in two broiler lines selected for different growth rate

Embryos from ascites sensitive (AS) and resistant lines (AR) were subjected during the third week of incubation to a high CO2 (0.4%) (HC) or normal CO2 level of 0.2% (NC) in the incubators. The effect on embryonic and hatching parameters and growth, ascites sensitivity and related physiological parameters was followed. At NC conditions AR embryos hatch earlier than AS ones but this difference completely disappeared under HC condition, since hatching time of the AS line was reduced. Moreover, AS embryos showed slightly lower T4 and T3 levels than AR embryos. Embryos of both lines incubated at HC had higher plasma T3 concentrations than those incubated at NC. Chickens that had been incubated at HC level showed less ascites mortality than those incubated at NC. RV/TV ratios were higher in NC birds compared with HC ones. It is concluded that different ventilation levels during incubation interact with total incubation time and thereby influence ascites susceptibility.

Phosphorus‐deficiency effects on response of symbiotic N2 fixation and carbohydrate status in soybean to atmospheric CO2 enrichment

The impact of phosphorus (P) deficiency on response of symbiotic N2 fixation and carbohydrate accumulation in soybean (Glycine max [L.] Merr.) to atmospheric CO2 enrichment was examined. Plants inoculated with Bradyrhizobium japonicum MN 110 were grown in growth chambers with controlled atmospheres of 400 and 800 μL CO2 L‐1 and supplied either 1.0 mM‐P (P‐sufficient) or 0.05 mM‐P (P‐deficient) nitrogen (N)‐free nutrient solution. When plants were supplied with sufficient P, CO2 enrichment significantly increased whole plant dry mass (83%), nodule mass (67%), total nitrogenase activity (58%), and N (35%) and P (47%) accumulation at 35 days after transplanting (DAT). Under sufficient P supply, CO2 enrichment significantly increased starch concentrations in nodules compared to the normal atmospheric CO2 treatment. Under normal CO2 levels (400 μL L‐1) nonstructural carbohydrate concentration (starch plus soluble sugar) was significantly higher in leaves of P‐deficient plants than in leaves of P‐sufficient plants in which nonstructural carbohydrate concentration exhibited a strong diurnal pattern. Under deficient P supply whole plant dry mass, symbiotic N2‐fixation parameters, and N and P accumulation were not enhanced by atmospheric CO2 enrichment. Phosphorus deficiency decreased nonstructural carbohydrate accumulation in nodules at the end of a 10‐day period in which functional activity was developing by 86% relative to P‐sufficient controls. While P deficiency elicited significant increases in the nonstructural carbohydrate concentration in leaves, it caused significant decreases in the nonstructural carbohydrate concentration in nodules over the diurnal cycle from 30 to 31 DAT. Collectively, these results indicate that the lack of a symbiotic N2‐fixation response to atmospheric CO2 enrichment by P‐deficient plants may be related to the decreased carbohydrate status of nodules.

Estimation of diffusive resistance of bundle sheath cells to CO2 from modeling of C4 photosynthesis

Bundle sheath resistance to diffusion of CO2 (rc) is a critical component of C4 photosynthesis which allows accumulation of inorganic carbon in bundle sheath cells of C4 plants. Several analyses were made to evaluate the magnitude of rc in C4 plants. Experimental data on the O2 inhibition of photosynthesis (Dai et al. (1993) Plant Physiol 103: 83-90; (1995) Plant Physiol 107: 815-825) and rates of photorespiration (de Veau and Burris (1989) Plant Physiol 90: 500-511) in Z. mays at different stages of development were analyzed using mathematical models of C4 photosynthesis. In young and senescing leaves modeled values of rc and the CO2 partial pressure in bundle sheath cells (Cbs) were lower and fractional leakage of CO2 from bundle sheath cells (fL) was higher than in mature leaves. Diffusive resistance of bundle sheath cells of C4 plants was also evaluated by analyzing the response of photosynthetic rates to varying CO2 in Amaranthus edulis in which the C4 cycle was dysfunctional by chemical mutagenesis (Dever et al. (1995) J Exp Bot 46: 1363-1376) and in Sorghum bicolor, Panicum maximum and Panicum miliaceum in which the C4 cycle was chemically inhibited (Brown and Byrd (1993) Plant Physiol 103: 1183-1188). These analyses indicate that in mature leaves of C4 plants the values of rc are substantially lower (ca. 50-200 m(2) s mol(-1)) than previous suggested (ca. 500-1500 m(2) s mol(-1)) for C4 photosynthesis and that there is considerable leakage of CO2 from bundle sheath cells. Nevertheless, rc and Cbs values are sufficiently high in mature leaves to minimize photorespiration in C4 plants under normal levels of CO2.

Sensory physiological investigation of carbon dioxide receptors in lepidoptera

This report indicates that CO 2-receptors are present in labial palp pits of various species of Lepidoptera, suggesting this to be a common occurrence and not to be restricted to certain taxonomic groups. Stimulation of the carbon dioxide receptors revealed uniform response to increasing CO 2-concentrations and showed that receptors were responsive to the normal CO 2-level in surrounding air (0.03%). Similar molecules such as CS 2 did not elicit nearly as strong responses as carbon dioxide. The absolute levels of the dose-dependent responses in Lepidoptera showed great similarity to one another. Slight responses to stimulation by humidity or temperature were revealed to be actually dependent on trace CO 2. Therefore these receptors may be designated as olfactory unimodal cells. So called “natural complex odour”-receptors in Pieris were rigorously retested and are shown here to be simple CO 2-receptors. The biological function of these CO 2-receptors remains a matter of speculation. For the vast majority of Lepidoptera, small differences in CO 2-content of the immediate environment (the “microclimate”) would be measurable. However, for the fraction of Lepidoptera occasionally exposed to high CO 2-concentrations, the receptors could fulfill a more clear function.

Relations between carbohydrate, water status and adventitious root formation in leafy pea cuttings rooted under various levels of atmospheric CO2 and relative humidity

Three levels of atmospheric CO2 and 2 levels of relative humidity (RH) during the rooting period were tested for their effect on several factors presumed to influence adventitious root formation in leafy pea (Pisum sativum L. cv. Alaska) cuttings. Compared to normal CO2 levels (350 μl l−1), neither 1800 nor 675 μl l−1 CO2 affected the rooting percentage or the number of roots per cutting. However, 1800 μl l−1 CO2 increased root and shoot dry weight, root length, carbohydrate levels in the base of the cuttings and water potential (Ψw) of cuttings compared to normal levels of CO2. Compared to 87% RH. 55% RH decreased all of the above parameters, including the number of roots per cutting. A polyvinyl chloride antitranspirant (which partially blocks stomata and slows photosynthesis) applied simultaneously with 87% RH increased Ψw and root length but lowered all of the other above parameters, compared to 87% RH without antitranspirant. Increasing current photosynthate (products of photosynthetic activity after excision), carbohydrate, or Ψw either alone or together was associated with increased root system size but not necessarily with increased rooting percentage or root number. The data are consistent with a hypothesis that the number of roots per cutting increased with increasing current photosynthate and carbohydrate until some other factor became limiting. Also, the effect of Ψw on rooting percentage and root number was mediated through its effect on current photosynthate and carbohydrate.

Alterations in fatty acid oxidation in ischemic and reperfused myocardium

The focus of this review centered on describing the effects of excess fatty acids on myocardial recovery during reperfusion following ischemic stress. Effects on mechanical function were modest in our studies and are likely to remain difficult/impossible to measure due to the independent phenomenon of stunning which obfuscates and no doubt dominates the influences of other mechanical determinants. Mitochondria appear capable of again using long-chain fatty acids as a preferred substrate and in the presence of restored oxygen delivery can produce normal levels of CO2. These changes in oxidative metabolism are not mirrored by equal recoveries in mitochondrial energetics. Because of inefficiencies in electron transport and oxidative phosphorylation together with moderate uncoupling of electron transport from oxidative phosphorylation, ATP resynthesis is blunted. This explains in part the absolute decrease in contents of exchangeable nucleotides noted both in cytosol and mitochondria. Further impairments in recovery reside in the inability of the mitochondria to exchange adenine nucleotides into cytosol through the adenine nucleotide translocase antiport. These findings contribute to our understanding of mechanical stunning and may be of value in designing future strategies to optimize the handling of substrates during myocardial reperfusion.

Yawning: No effect of 3–5% CO 2, 100% O 2, and exercise

Using human college-age subjects, the present study tested the commonly cited but previously untested hypothesis that yawning is facilitated by higher than normal levels of CO2 or lower than normal levels of O2 in the blood by comparing the effect on yawning of breathing 100% O2 and gas mixtures with higher than normal levels of CO2 (3 or 5%) with compressed air, the control condition. If yawning is a response to heightened blood CO2, the CO2 mixtures should increase yawning rate and/or duration. If low blood O2 produced yawning, breathing 100% O2 should inhibit yawning. The CO2/O2 hypothesis was rejected because breathing neither pure O2 nor gases high in CO2 had a significant effect on yawning although both increased breathing rate. A second study found that exercise sufficient to double breathing rate had no effect on yawning. The two studies suggest that yawning does not serve a primary respiratory function and that yawning and breathing are triggered by different internal states and are controlled by separate mechanisms.

Carbon dioxide levels in the biosphere: Effects on plant productivity

Human society is now inadvertently conducting a great biological and environmental experiment, the outcome of which is not known. Atmospheric carbon dioxide (CO2) is increasing at the rate of 1.5 parts per million (ppm) per year. It has risen from 315 ppm to 340 ppm in the past 25 years — a 9% increase. Because CO2 is among the factors which can limit the growth of plants, the increase may be beneficial. An increase in plant growth due to “fertilization”; of extra CO2 has not been measured, but a 5 to 10% increase may already have occurred. Current data indicate that plants growing at higher than normal CO2 levels are more tolerant of water, temperature, light, and atmospheric pollutant stresses. There are effects on carbon metabolism, plant growth and development, microbial activity, and terrestrial and aquatic plant communities. The current rising level of atmospheric CO2 represents ,a dramatic change in a resource base and can affect the total biological productivity of the earth. A global change in a ...