Andrew Clarke

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I am a passionate writer with strong taste for literary works and continuously write on diverse subjects. Here you will find collections of articles pinned down on random reflections.

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Papers by Andrew Clarke

Heyde's syndrome revisited anaemia and aortic stenosis

Internal medicine journal, Jan 9, 2017

The association of anaemia with aortic stenosis (AS) has been recognised for over 50 years but al... more The association of anaemia with aortic stenosis (AS) has been recognised for over 50 years but although there have been a number of sporadic reports there are little data on the prevalence of this syndrome. We sought to compare the prevalence of anaemia in adults with AS with that of controls who had undergone coronary artery bypass grafting (CABG). We conducted a retrospective cohort study comparing pre-procedural levels of haemoglobin in 1537 adults who underwent aortic valve replacement (AVR) for AS with 8025 contemporaneous patients who had CABG. We hypothesised that the prevalence of anaemia in patients with AS would be significantly higher than in the control group. 30.1% in the AVR group were anaemic compared to 16.2% in the CABG group. The mean haemoglobin concentration measured across the whole population was significantly lower (132 g.L(-1) ) in AVR patients than in those who underwent CABG (138 g.L(-1) ). In a multivariable model haemoglobin levels varied significantly by...

Transcatheter Mitral Valve Replacement for Patients With Symptomatic Mitral Regurgitation: A Global Feasibility Trial

Journal of the American College of Cardiology, Jan 20, 2016

Symptomatic mitral regurgitation (MR) is associated with high morbidity and mortality that can be... more Symptomatic mitral regurgitation (MR) is associated with high morbidity and mortality that can be ameliorated by surgical valve repair or replacement. Despite this, many patients with MR do not undergo surgery. Transcatheter mitral valve replacement (TMVR) may be an option for selected patients with severe MR. This study aimed to examine the effectiveness and safety of TMVR in a cohort of patients with native valve MR who were at high risk for cardiac surgery. Patients underwent transcatheter, transapical delivery of a self-expanding mitral valve prosthesis and were examined in a prospective registry for short-term and 30-day outcomes. Thirty patients (age 75.6 ± 9.2 years; 25 men) with grade 3 or 4 MR underwent TMVR. The MR etiology was secondary (n = 23), primary (n = 3), or mixed pathology (n = 4). The Society of Thoracic Surgeons Predicted Risk of Mortality was 7.3 ± 5.7%. Successful device implantation was achieved in 28 patients (93.3%). There were no acute deaths, strokes, or...

A Re-appraisal of the Habitability of Planets Around M Dwarf Stars

Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are e... more Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.

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Hydrogen peroxide and nitric oxide as signalling molecules in plants

Journal of Experimental Botany, May 15, 2002

It is now clear that hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) function as signalling mo... more It is now clear that hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H 2 O 2 generation, from a variety of sources. H 2 O 2 is removed from cells via a number of antioxidant mechanisms, both enzymatic and nonenzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H 2 O 2 and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H 2 O 2 and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.

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Stress and the geographic distribution of marine and terrestrial animals

... Physiological inference (eg Zachariassen et al., 1987; Garland and Adolph, 1991; Navas, 1996)... more

The Southern Ocean Benthic Fauna and Climate Change: A Historical Perspective: Discussion

Philosophical Transactions of the Royal Society B Biological Sciences, Nov 1, 1992

Environmental change is the norm and it is likely that, particularly on the geological timescale,... more Environmental change is the norm and it is likely that, particularly on the geological timescale, the temperature regime experienced by marine organisms has never been stable. These temperature changes vary in timescale from daily, through seasonal variations, to long-term environmental change over tens of millions of years. Whereas physiological work can give information on how individual organisms may react phenotypically to short-term change, the way benthic communities react to long-term change can only be studied from the fossil record. The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time. Nevertheless, certain features do suggest the operation of vicariant processes, and climatic cycles affecting distributional ranges and ice-sheet extension may both have enhanced speciation processes. The overall cooling of southern high-latitude seas since the mid-Eocene has been neither smooth nor steady. Intermittent periods of global warming and the influence of Milankovitch cyclicity is likely to have led to regular pulses of migration in and out of Antarctica. The resultant diversity pump may explain in part the high species richness of some marine taxa in the Southern Ocean. It is difficult to suggest how the existing fauna will react to present global warming. Although it is certain the fauna will change, as all faunas have done throughout evolutionary time, we cannot predict with confidence how it will do so.

The Influence of Feeding on Oxygen Consumption and Nitrogen Excretion in the Antarctic Nemertean Parborlasia Corrugatus

Physiological Zoology, 1997

The large nemertean Parborlasia corrugatus is common in nearshore benthic marine habitats around ... more The large nemertean Parborlasia corrugatus is common in nearshore benthic marine habitats around Antarctica, where it is an important predator and scavenger. Oxygen consumption and nitrogen excretion rates in worms freshly sampled from the field were low but similar to those reported for other polar marine ectotherms. Nitrogen was excreted primarily as ammonia (87%), with smaller amounts of urea (4%) and amines (9%). The O:N atomic ratio was low (10.4), indicating that free or protein-derived amino acids were important metabolic substrates. When worms were fed at ration levels ranging from 20% to 110% of body mass, both oxygen demand and ammonia excretion increased after feeding in a classic specific dynamic action response. Peak postprandial oxygen consumption was low (range, 1.5-2.6 times the prefeeding rate), and the duration of the specific dynamic action was unusually long (&gt; 30 d). Both the energy used and the nitrogen excreted in the specific dynamic action scaled with meal size, although the fractions of ingested carbon and nitrogen used or lost were both very low, probably because of the large ration levels. We conclude that Parborlasia corrugatus has only a limited ability to increase its metabolic rate following a meal and, as a result, takes many days to process that meal fully.

The Marine Ecosystem of the West Antarctic Peninsula

Transapical Transcatheter Mitral Valve-in-Valve Implantation Using an Edwards Sapien 3 Valve

Heart, Lung and Circulation, 2016

We describe a successful transcatheter, transapical mitral valve implant within a failed mitral b... more We describe a successful transcatheter, transapical mitral valve implant within a failed mitral bioprosthesis (valve-in-valve) in a symptomatic 86-year-old patient with prohibitive surgical risks, using the new Sapien 3 balloon-expandable valve. Post-deployment echocardiographic profile of the valve-in-valve was satisfactory and the patient was discharged from hospital uneventfully. This is the first reported case of the Sapien 3 valve used in the mitral valve-in-valve setting.

Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca

Deep Sea Research Part Ii Topical Studies in Oceanography, Apr 1, 2006

For many decades molluscan data have been critical to the establishment of the concept of a globa... more For many decades molluscan data have been critical to the establishment of the concept of a global-scale increase in species richness from the poles to the equator. Low polar diversity is key to this latitudinal cline in diversity. Here we investigate richness patterns in the two largest classes of molluscs at both local and regional scales throughout the Southern Ocean. We show that biodiversity is very patchy in the Southern Ocean (at the 1000-km scale) and test the validity of historical biogeographic sub-regions and provinces. We used multivariate analysis of biodiversity patterns at species, genus and family levels to define richness hotspots within the Southern Ocean and transition areas. This process identified the following distinct sub-regions in the Southern Ocean: Antarctic Peninsula, Weddell Sea, East Antarctic---Dronning Maud Land, East Antarctic---Enderby Land, East Antarctic---Wilkes Land, Ross Sea, and the independent Scotia arc and sub Antarctic islands. Patterns of endemism were very different between the bivalves and gastropods. On the basis of distributional ranges and radiation centres of evolutionarily successful families and genera we define three biogeographic provinces in the Southern Ocean: (1) the continental high Antarctic province excluding the Antarctic Peninsula, (2) the Scotia Sea province including the Antarctic Peninsula, and (3) the sub Antarctic province comprising the islands in the vicinity of the Antarctic Circumpolar Current.

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Introduction - Antarctic ecology in a changing world

... In: Rogers, Alex D.; Johnston, Nadine M.; Murphy, Eugene J.; Clarke, Andrew, (eds.) Antarctic... more

The energy content of dragonflies (Odonata) in relation to predation by falcons

Bird Study, 1996

Function of penicillin-binding protein 2 in viability and morphology of Pseudomonas aeruginosa

Journal of Antimicrobial Chemotherapy, Mar 1, 2007

Objectives: To investigate the function of penicillin-binding protein 2 (PBP 2) in Pseudomonas ae... more

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Population dynamics of marine benthic invertebrates in Antarctic and subantarctic environments are there unique adaptions?

Epic3antarctic Science 5 Pp 253 266, 1993

... THOMAS BREY&#x27; and ANDREW CLARKEZ IAlfied Wegener Institute for Polar and Marine Resea... more

Using archaeogenomic and computational approaches to unravel the history of local adaptation in crops

Our understanding of the evolution of domestication has changed radically in the past 10 years, f... more Our understanding of the evolution of domestication has changed radically in the past 10 years, from a relatively simplistic rapid origin scenario to a protracted complex process in which plants adapted to the human environment. The adaptation of plants continued as the human environment changed with the expansion of agriculture from its centres of origin. Using archaeogenomics and computational models, we can observe genome evolution directly and understand how plants adapted to the human environment and the regional conditions to which agriculture expanded. We have applied various archaeogenomics approaches as exemplars to study local adaptation of barley to drought resistance at Qasr Ibrim, Egypt. We show the utility of DNA capture, ancient RNA, methylation patterns and DNA from charred remains of archaeobotanical samples from low latitudes where preservation conditions restrict ancient DNA research to within a Holocene timescale. The genomic level of analyses that is now possible, and the complexity of the evolutionary process of local adaptation means that plant studies are set to move to the genome level, and account for the interaction of genes under selection in systems-level approaches. This way we can understand how plants adapted during the expansion of agriculture across many latitudes with rapidity.

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Growth rates of Antarctic krill, Euphausia superba: comparison of the instantaneous growth rate method with nitrogen and phosphorus stoichiometry

Limnology and Oceanography, 2004

Zooplankton growth rates are hard to measure directly, and proxy measurements are desirable to en... more Zooplankton growth rates are hard to measure directly, and proxy measurements are desirable to encompass the variety of species and scales of interest. The growth rate hypothesis of stoichiometric theory states that a negative relationship exists between nitrogen : phosphorus (N : P) stoichiometry and growth rate, driven by cellular ribosomal ribonucleic acid (rRNA) content. Despite the wealth of literature on the growth rate hypothesis, there exist no practical demonstrations of its use in the marine literature. We thus investigated whether this hypothesis could be the basis of a technique to estimate growth rates of Euphausia superba by comparing, for the same individual krill, elemental stoichiometry and growth rates derived from the instantaneous growth rate (IGR) method. These growth rates were the first IGR measurements from South Georgia; from within a restricted area over the course of just 1 month, these rates were highly variable, from negative to near maximum rates recorded for the species. Although there were significant differences in N : P ratio and phosphorus content between individuals and schools, there was no relationship between N : P ratio and growth rate when data were grouped by school. Thus, our data do not support the predictions of the growth rate hypothesis at an intraspecific scale. However, when all data were pooled, the mean values of growth rate and N : P ratio did fit the interspecific relationship established previously for freshwater zooplankton. We suggest that krill maintain the biochemical machinery for high growth potential and maintain high growth in summer to take advantage of short-term fluctuations in food.

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Probing the depths (Guest editorial)

Animals i temperatura a les regions polars

... animals i temperatura, els científics fan una diferencia important entre animals de sang cale... more

Veno-arterial ECMO in the Setting of Post-infarct Ventricular Septal Defect: A Bridge to Surgical Repair

Heart, Lung and Circulation, 2016

Extracorporeal membrane oxygenation (ECMO) is a complex rescue therapy utilised to provide circul... more Extracorporeal membrane oxygenation (ECMO) is a complex rescue therapy utilised to provide circulatory and/or respiratory support to critically ill patients who have failed maximal conventional therapy. The use of ECMO in adult cardiac surgery is not routine, occurring in a minority of critically ill patients, typically postoperatively. Presented here are three cases of post-infarct ventricular septal defect with cardiogenic shock managed preoperatively with ECMO support as a bridge to definitive surgical closure. We present a review of ECMO in the adult cardiac surgical population and highlight the potential role of preoperative ECMO for cardiogenic shock in the setting of post-infarct ventricular septal defect (PI VSD) as a bridge to definitive closure.

Low-temperature protein metabolism: seasonal changes in protein synthesis and RNA dynamics in the Antarctic limpet Nacella concinna Strebel 1908

Journal of Experimental Biology, Oct 1, 2002

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