CO2 storage and release in the deep Southern Ocean on millennial to centennial timescales.

The cause of changes in atmospheric carbon dioxide (CO2) during the recent ice ages is yet to be fully explained. Most mechanisms for glacial-interglacial CO2 change have centred on carbon exchange with the deep ocean, owing to its large size and relatively rapid exchange with the atmosphere1. The Southern Ocean is thought to have a key role in this exchange, as much of the deep ocean is ventilated to the atmosphere in this region2. However, it is difficult to reconstruct changes in deep Southern Ocean carbon storage, so few direct tests of this hypothesis have been carried out. Here we present deep-sea coral boron isotope data that track the pH-and thus the CO2 chemistry-of the deep Southern Ocean over the past forty thousand years. At sites closest to the Antarctic continental margin, and most influenced by the deep southern waters that form the ocean's lower overturning cell, we find a close relationship between ocean pH and atmospheric CO2: during intervals of low CO2, ocean pH is low, reflecting enhanced ocean carbon storage; and during intervals of rising CO2, ocean pH rises, reflecting loss of carbon from the ocean to the atmosphere. Correspondingly, at shallower sites we find rapid (millennial- to centennial-scale) decreases in pH during abrupt increases in CO2, reflecting the rapid transfer of carbon from the deep ocean to the upper ocean and atmosphere. Our findings confirm the importance of the deep Southern Ocean in ice-age CO2 change, and show that deep-ocean CO2 release can occur as a dynamic feedback to rapid climate change on centennial timescales.

A novel approach to antibiofilm susceptibility testing using a thermo-reversible matrix.

OBJECTIVE: Biofilm microorganisms are known to have a much higher tolerance to antimicrobials compared to their planktonic equivalents. Therefore, traditional antimicrobial susceptibility testing may not extrapolate to clinical treatment of infections of biofilm origin, and as a result, there is a need to not only develop antimicrobials with antibiofilm activity, but also suitable in vitro testing methods for their evaluation. In this study, we report on a novel method of antibiofilm testing using a thermo-reversible matrix (poloxamer 407), coupled with live/dead staining of bacteria cultured from the matrix. METHOD: Pseudomonas aeruginosa (NCIMB 8626) was cultured in medium containing poloxamer 407 at 37°C for 24 hours to generate biofilms. The preparation was cooled to liquefy the poloxamer and allow recovery of the biofilm cells, which were then stained with SYTO9 to determine viability following exposure to four antimicrobials: polyhexanide, octenadine dihydrochloride, povidone-iodine and silver carbonate. Over an 8-minute time period, fluorescence levels were spectrophotometrically measured and compared with bacterial controls, cultured in the absence of poloxamer and without antimicrobial. RESULTS: Untreated cells showed no reduction in viability over this period. Importantly, planktonic cells were more susceptible to test agents compared with those of a 'biofilm' phenotype cultured in poloxamer. Antibiofilm activity was evident for all of the test agents, with highest relative activity seen with octenadine dihydrochloride. CONCLUSION: In summary, a novel and relatively rapid approach to screen compounds for antibiofilm activity has been described. The method uses standard laboratory equipment and can be readily adapted to test a wide range of microorganisms and other antibiofilm compounds. DECLARATION OF INTEREST: This research was, in part, supported by Advanced Medical Solutions in the form of a Knowledge Transfer Project. Mr J. Nosworthy was employed by Advanced Medical Solutions. There are no other conflicts of interests to declare.

Effects of inspiratory muscle training on exercise responses in Paralympic athletes with cervical spinal cord injury.

We asked whether specific inspiratory muscle training (IMT) improves respiratory structure and function and peak exercise responses in highly trained athletes with cervical spinal cord injury (SCI). Ten Paralympic wheelchair rugby players with motor-complete SCI (C5-C7) were paired by functional classification then randomly assigned to an IMT or placebo group. Diaphragm thickness (B-mode ultrasonography), respiratory function [spirometry and maximum static inspiratory (PI ,max ) and expiratory (PE ,max ) pressures], chronic activity-related dyspnea (Baseline and Transition Dyspnea Indices), and physiological responses to incremental arm-crank exercise were assessed before and after 6 weeks of pressure threshold IMT or sham bronchodilator treatment. Compared to placebo, the IMT group showed significant increases in diaphragm thickness (P = 0.001) and PI ,max (P = 0.016). There was a significant increase in tidal volume at peak exercise in IMT vs placebo (P = 0.048) and a strong trend toward an increase in peak work rate (P = 0.081, partial eta-squared = 0.33) and peak oxygen uptake (P = 0.077, partial eta-squared = 0.34). No other indices changed post-intervention. In conclusion, IMT resulted in significant diaphragmatic hypertrophy and increased inspiratory muscle strength in highly trained athletes with cervical SCI. The strong trend, with large observed effect, toward an increase in peak aerobic performance suggests IMT may provide a useful adjunct to training in this population.

Heavy caffeine intake in pregnancy and sudden infant death syndrome. New Zealand Cot Death Study Group.

AIMS: To examine the association between maternal caffeine consumption during pregnancy and the risk of sudden infant death syndrome (SIDS). METHODS: A nationwide case-control study surveying parents of 393 SIDS victims and parents of 1592 control infants. Caffeine consumption in each of the first and third trimesters was estimated by questionnaire. Heavy caffeine intake was defined as 400 mg/day or more (equivalent to four or more cups of coffee per day). RESULTS: Infants whose mothers had heavy caffeine consumption throughout their pregnancy had a significantly increased risk for SIDS (odds ratio 1.65; 95% confidence interval 1.15 to 2.35) after adjusting for likely confounding factors. CONCLUSION: Caffeine intake has been associated with fetal harm and now SIDS. Reducing heavy caffeine intake during pregnancy could be another way to lessen the risk of SIDS. This needs confirmation by others.

The relationship of selenium status to respiratory outcome in the very low birth weight infant.

OBJECTIVE: To examine the relationship between plasma and erythrocyte selenium and glutathione peroxidase (GPx) levels in premature infants and outcome measures. DESIGN: Prospective observational longitudinal study. SETTING: Two regional neonatal intensive care units in the South Island of New Zealand, an area with low soil selenium. PATIENTS: Seventy-nine infants with birth weights less than 1500 g or gestation less than 32 weeks admitted within 48 hours of birth from November 1992 through November 1993. MAIN OUTCOME MEASURES: Oxygen requirement at 28 days (chronic lung disease), or 36 weeks postmenstrual age and for all or most of the time from birth (bronchopulmonary dysplasia), total days in oxygen, retinopathy of prematurity, periventricular hemorrhage, or ventricular dilatation. RESULTS: Initial infant plasma selenium and GPx levels were about two thirds of maternal levels and fell a further 30% in 28 days. In contrast to adults, there was a poor correlation in infant plasma between selenium and GPx at birth and 28 days. Plasma selenium at 28 days was significantly lower in infants with chronic lung disease and bronchopulmonary dysplasia. After controlling for gestational age and age when fully fed orally, 28-day plasma selenium was significantly associated with the log of total days of oxygen requirement, each drop of 0.1 mumol/L in 28-day selenium being associated with a 58% increase in days of oxygen dependency. No significant associations of other parameters of selenium status and respiratory outcome were found, and there were no significant associations of any parameters of selenium status with other outcome measures. CONCLUSIONS: This study demonstrates for the first time in human infants that low plasma selenium levels are significantly associated with an increased respiratory morbidity. Whether selenium deficiency is etiologically important in determining the respiratory outcome or the result of sickness in the infant should be investigated in a randomized, controlled trial.

Effects of parenteral L-carnitine supplementation on fat metabolism and nutrition in premature neonates.

The effects of parenteral L-carnitine supplementation on fat metabolism, nutrient intake, and plasma and erythrocyte carnitine concentrations were studied in 43 very low birth weight infants. Infants were randomly assigned to control or carnitine-supplemented (50 mumol/kg per day) groups within two weight categories: group 1, 750 to 1000 gm, and group 2, 1001 to 1500 gm. Plasma total, free, and acyl carnitine levels, erythrocyte carnitine levels, serum beta-hydroxybutyrate and triglyceride levels, and total fat intake were monitored weekly until 50% of total caloric intake was met enterally. Neonates receiving carnitine had higher plasma carnitine levels than control groups (total carnitine: group 1, 75.2 +/- 22.9 vs 9.6 +/- 2.7 mmol/ml; group 2, 61.6 +/- 31.2 vs 13.0 +/- 9.2 nmol/ml). Levels of beta-OH-butyrate decreased from baseline in control neonates (group 1, 0.12 +/- 0.06 to 0.03 +/- 0.02 mmol/L; group 2, 0.11 +/- 0.03 to 0.05 +/- 0.02 mmol/L); they remained unchanged in supplemented groups. Thus ketogenesis appeared less impaired in infants receiving supplements. Supplemented group 2 tolerated more fat than control group 2; triglyceride levels remained acceptable in all groups. Carnitine group 2 had greater weight gain than control group 2 during the first 2 weeks of life. We conclude that very low birth weight infants requiring prolonged parenteral nutrition have carnitine deficiency with impaired ketogenesis. Parenteral administration of carnitine appears to alleviate this metabolic disturbance.

Lipid peroxidation as a measure of oxygen free radical damage in the very low birthweight infant.

(ABSTRACTOxygen free radical mediated tissue injury is implicated as a major factor in the pathogenesis of the long term complications seen in the premature infant, and direct evidence of their role in the development of these long term problems is lacking. A prospective observational study of 78% of very low birthweight infants admitted to a level III neonatal intensive care unit in 1992 was undertaken to determine the relationship between lipid peroxidation products, antioxidant activity, and outcome. Lipid peroxidation (malondialdehyde-thiobarbituric acid, MDA-TBA) and antioxidant activity (vitamin E and glutathione peroxidase activity) were measured in 22 very low birthweight infants in the cord blood and the infant's blood at 24 hours, 48 hours, and 1 week of age and correlated with outcome measures. The normal range for these measures was established in the cord blood samples of 48 consecutive healthy full term infants. The concentration of MDA-TBA at 1 week correlated with the number of days of oxygen treatment and number of days of positive pressure ventilatory support. Controlling for gestational age and antenatal complications simultaneously the MDA-TBA concentration remained significantly associated with the number of days of oxygen treatment and the number of days of positive pressure ventilatory support. Glutathione peroxidase was low in the premature and full term infants consistent with the low concentrations of selenium known to be present in southern New Zealand. There was evidence of a quadratic relationship between vitamin E at 1 week and the total number of days of supplementary oxygen requirement, with both high and low values associated with increased oxygen requirement. This association, however, did not remain after controlling for gestational age and antenatal complications. These results support the role of oxygen free radicals in mediating tissue damage associated with the development of chronic lung disease in the premature infant.

Apnea and rapid eye movement sleep excess in the piglet during recovery from hyperthermia.

This investigation tested the hypothesis that artificially induced mild hyperthermia and recovery from hyperthermia in the developing newborn piglet (2-10 d of age) alter sleep state patterns and respiratory control. Continuous measurements of sleep state, respiratory pattern, carbon dioxide production and oxygen consumption were made before, during, and after a 3-h period of sustained hyperthermia. During hyperthermia, rectal temperatures were raised a mild 1-1.5 degree C above normal, well below the levels likely to cause severe physiologic distress in this species. This resulted in a disruption of the sleep state pattern characterized by a decrease in duration of rapid eye movement (REM) episodes, whereas immediately afterwards, during recovery, the amount of REM sleep increased. In some cases the amount of REM sleep in recovery more than doubled the basal level. Apneas were rarely observed during hyperthermia, but in recovery there was an increase in the total amount of time spent in apnea in both REM and non-rapid eye movement sleep states with a predominance in the REM state. Arousal responses to chemostimulation were not affected at this time. We conclude that the sleeping newborn piglet does indeed show marked changes in sleep state pattern (particularly REM sleep) and in the amount of apnea recorded during and immediately after only a mild increase in core temperature.

Effects of dopexamine on hemodynamics and oxygen consumption after beta blockade in lambs.

OBJECTIVES: Dopexamine is a synthetic catecholamine with predominantly beta 2 and dopaminergic adrenergic receptor activities. We investigated its effects on systemic and myocardial hemodynamics and oxygen consumption (VO2) in a newborn species and studied its predominant mechanism of action. DESIGN: Prospective dose-response study with each animal serving as it own control. SUBJECTS: Eight chronically instrumented, unanesthetized lambs, 9 to 11 days of age. INTERVENTIONS: After surgical instrumentation and recovery for 72 hrs, animals were infused with dopexamine at increasing doses (1, 10, and 100 micrograms/kg/min) for 5 mins each before and after beta 1 (metoprolol) and beta 1, beta 2 (propranolol) adrenergic receptor blockade. All studies were performed during normoxia. MEASUREMENTS AND MAIN RESULTS: Heart rate (HR) increased with increasing infusion rates of dopexamine and systemic arterial pressure and vascular resistance decreased. Cardiac index, left ventricular pressure development, and systemic VO2 were unchanged, as was the rate x pressure product. Left circumflex coronary artery blood flow and myocardial VO2 were unaltered. After beta 1-blockade, dopexamine produced an increase in HR and decreased systemic arterial pressure and vascular resistance. After beta 1-adrenergic receptor blockade, no change was noted in systemic or myocardial VO2, coronary blood flow, or rate x pressure product. After beta 1, beta 2-blockade with propranolol, increasing infusion rates of dopexamine resulted in decreases in systemic pressure and vascular resistance. CONCLUSIONS: Dopexamine produced significant cardiovascular effects mediated primarily by beta 2-adrenergic receptors, and also produced residual peripheral arterial vasodilation after combined beta 1- and beta 2-blockade. The latter finding suggests that dopaminergic receptor stimulation may partly mediate dopexamine's effects in newborn lambs.

Relieving pain through ordinariness in nursing: a phenomenologic account of a comforting nurse--patient encounter.

This article describes a nursing encounter between Sue, a nurse, and Becky, a patient. Sue and Becky related to one another through a sense of shared humanity that not only relieved some of Becky's pain, but also created some possibilities for changing patterns in her life that had been built up over a long period. The article suggests that nurses and patients relate to one another through their affinity as humans. Within the context of caring, nurses such as Sue are ordinary people perceived as being extraordinarily effective by the very ways in which their humanness shines through their knowledge and skills to make their whole being with patients something more than just professional helping. An implication for nursing knowledge arising from Sue's and Becky's interaction, and from the study generally, is the need to reconceptualize the nurse as person, so that nurses are described not only in terms of their professional roles and functions but also as people who share the everyday human qualities of their patients.

From helper to human: a reconceptualization of the nurse as person.

This paper explores the nature of the nurse as person, as represented by nursing literature and in the author's own research, by considering the tendency nurses have to perceive as different the characteristics of nurses and patients as human beings. Nursing scholars have tended to categorize nurses and patients into discrete 'compartments' that are convenient for descriptive purposes, but nevertheless have had a tendency to limit people's essential humanness. The metaparadigm concept of person in nursing can take on a different meaning if people are regarded in terms of their oneness, rather than by their separateness. A brief introduction will be given to some meanings generated in some nursing research, which described the effects of ordinariness as they were manifested by nurses and patients in everyday nursing unit life. The possibility is raised that a reconceptualization of the nurse could describe the nurse, not only as a professional helper, but also as a human, whose effectiveness is enhanced through a sense of shared humanity with patients.

Blood selenium and glutathione peroxidase levels and dietary selenium of free-living and institutionalized elderly subjects.

The purpose of this study was to evaluate the selenium status of healthy free-living and institutionalized elderly people. For the 36 free-living elderly dietary selenium intake averaged 94 +/- 44 micrograms Se/day and a positive correlation coefficient was found between dietary selenium and dietary calories (r = 0.46; P less than 0.05), dietary protein (r = 0.60; P less than 0.01), and dietary fat (r = 0.43; P less than 0.05). Diet histories from the institutionalized subjects revealed a strong correlation coefficient between selenium and carbohydrate (r = 0.51; P less than 0.005) and selenium and calories (r = 0.44; P less than 0.05). Mean erythrocyte and plasma selenium levels for the free-living subjects were 0.20 +/- 0.06 micrograms/ml and 0.10 +/- 0.03 micrograms/ml, respectively, while mean erythrocyte glutathione peroxidase (GSH-Px) activity was 27.5 +/- 5.0 units/g protein. For the free-living subjects positive correlation was found between dietary selenium and erythrocyte selenium levels (r = 0.38; P less than 0.05) but no correlation existed between dietary selenium and plasma selenium (r = 0.13; P greater than 0.05) and RBC GSH-Px (r = -0.15; P greater than 0.05). The dietary selenium levels and blood selenium and GSH-Px levels were above the levels found in populations proposed to be at risk for selenium deficiency. Thus, these elderly appear to have adequate selenium status.