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Search Results: 1 - 10 of 148594 matches for " Peter T. Macklem "
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Complex systems and the technology of variability analysis
Andrew JE Seely, Peter T Macklem
Critical Care , 2004, DOI: 10.1186/cc2948
Abstract: Biological systems are complex systems; specifically, they are systems that are spatially and temporally complex, built from a dynamic web of interconnected feedback loops marked by interdependence, pleiotropy and redundancy. Complex systems have properties that cannot wholly be understood by understanding the parts of the system [1]. The properties of the system are distinct from the properties of the parts, and they depend on the integrity of the whole; the systemic properties vanish when the system breaks apart, whereas the properties of the parts are maintained. Illness, which presents with varying severity, stability and duration, represents a systemic functional alteration in the human organism. Although illness may occasionally be due to a specific singular deficit (e.g. cystic fibrosis), this discussion relates to illnesses characterized by systemic changes that are secondary to multiple deficits, which differ from patient to patient, with varied temporal courses, diverse contributing events and heterogeneous genetic contributions. However, all factors contribute to a physiological alteration that is recognizable as a systemic illness. Multiple organ dysfunction syndrome represents the ultimate multisystem illness, really representing a common end-stage pathway of inflammation, infection, dysfunctional host response and organ failure in critically ill patients, and frequently leading to death [2]. Although multiple organ dysfunction syndrome provides a useful starting point for discussion regarding complex systems and variability analysis [3], the application of variability analysis to other disease states is readily apparent and exciting.Life is composed of and characterized by rhythms. Abnormal rhythms are associated with illness and can even be involved in its pathogenesis; they have been termed 'dynamical diseases' [4]. Measuring the absolute value of a clinical parameter such as heart rate yields highly significant, clinically useful information. Howeve
The Abdominal Circulatory Pump
Andrea Aliverti, Dario Bovio, Irene Fullin, Raffaele L. Dellacà, Antonella Lo Mauro, Antonio Pedotti, Peter T. Macklem
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005550
Abstract: Blood in the splanchnic vasculature can be transferred to the extremities. We quantified such blood shifts in normal subjects by measuring trunk volume by optoelectronic plethysmography, simultaneously with changes in body volume by whole body plethysmography during contractions of the diaphragm and abdominal muscles. Trunk volume changes with blood shifts, but body volume does not so that the blood volume shifted between trunk and extremities (Vbs) is the difference between changes in trunk and body volume. This is so because both trunk and body volume change identically with breathing and gas expansion or compression. During tidal breathing Vbs was 50–75 ml with an ejection fraction of 4–6% and an output of 750–1500 ml/min. Step increases in abdominal pressure resulted in rapid emptying presumably from the liver with a time constant of 0.61±0.1SE sec. followed by slower flow from non-hepatic viscera. The filling time constant was 0.57±0.09SE sec. Splanchnic emptying shifted up to 650 ml blood. With emptying, the increased hepatic vein flow increases the blood pressure at its entry into the inferior vena cava (IVC) and abolishes the pressure gradient producing flow between the femoral vein and the IVC inducing blood pooling in the legs. The findings are important for exercise because the larger the Vbs the greater the perfusion of locomotor muscles. During asystolic cardiac arrest we calculate that appropriate timing of abdominal compression could produce an output of 6 L/min. so that the abdominal circulatory pump might act as an auxiliary heart.
Circulatory effects of expiratory flow-limited exercise, dynamic hyperinflation and expiratory muscle pressure
P. T. Macklem
European Respiratory Review , 2006,
Abstract: This article reviews recent research in normal subjects exercising with and without expiratory flow limitation at 1 L·s–1 imposed by a Starling resistor in the expiratory line, and in patients with chronic obstructive pulmonary disease (COPD), using optoelectronic plethysmography to measure respiratory kinematics, combined with mouth, pleural and abdominal pressure measurements, to assess work of breathing and respiratory muscle performance. In normal subjects, flow-limited exercise resulted in the following: 1) Impaired exercise performance due to intolerable dyspnoea; 2) hypercapnia; 3) excessive respiratory muscle recruitment; 4) blood shifts from trunk to extremities; 5) a 10% reduction in cardiac output and a 5% reduction in arterial oxygen saturation, decreasing energy supplies to working respiratory and locomotor muscles. In both normal subjects and in COPD patients, dynamic hyperinflation did not always occur. Those patients that hyperinflated had worse lung function and less work of breathing, but better exercise performance than the others, in whom expiratory muscle recruitment prevented dynamic hyperinflation at the cost of increased work of breathing and excessive oxygen cost of breathing. This established an early competition between respiratory and locomotor muscles for available energy supplies. Dynamic hyperinflation is a better exercise strategy in chronic obstructive pulmonary disease than expiratory muscle recruitment, but the benefit it confers is small.
Chebyshev Sets, Klee Sets, and Chebyshev Centers with respect to Bregman Distances: Recent Results and Open Problems
Heinz H. Bauschke,Mason S. Macklem,Xianfu Wang
Mathematics , 2010,
Abstract: In Euclidean spaces, the geometric notions of nearest-points map, farthest-points map, Chebyshev set, Klee set, and Chebyshev center are well known and well understood. Since early works going back to the 1930s, tremendous theoretical progress has been made, mostly by extending classical results from Euclidean space to Banach space settings. In all these results, the distance between points is induced by some underlying norm. Recently, these notions have been revisited from a different viewpoint in which the discrepancy between points is measured by Bregman distances induced by Legendre functions. The associated framework covers the well known Kullback-Leibler divergence and the Itakura-Saito distance. In this survey, we review known results and we present new results on Klee sets and Chebyshev centers with respect to Bregman distances. Examples are provided and connections to recent work on Chebyshev functions are made. We also identify several intriguing open problems.
A simple model for cloud radiative forcing
T. Corti ,T. Peter
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: We present a simple model for the longwave and shortwave cloud radiative forcing based on the evaluation of extensive radiative transfer calculations, covering a global range of conditions. The simplicity of the model equations fosters the understanding on how clouds affect the Earth's energy balance. In comparison with results from a comprehensive radiative transfer model, the accuracy of our parameterization is typically better than 20%. We demonstrate the usefulness of our model using the example of tropical cirrus clouds. We conclude that possible applications for the model include the convenient estimate of cloud radiative forcing for a wide range of conditions, the evaluation of the sensitivity to changes in environmental conditions, and as a tool in education. An online version of the model is available at http://www.iac.ethz.ch/url/crf.
A simple model for cloud radiative forcing
T. Corti,T. Peter
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: We present a simple model for the longwave and shortwave cloud radiative forcing based on the evaluation of extensive radiative transfer calculations. The simplicity of the model equations fosters the understanding on how clouds affect the Earth's energy balance. In comparison with results from a comprehensive radiative transfer model, the accuracy of our parameterization is typically better than 20%. We demonstrate the usefulness of our model using the example of tropical cirrus clouds. We conclude that possible applications for the model include the fast estimate of cloud radiative forcing, the evaluation of the sensitivity to changes in environmental conditions, and as a tool in education.
Distribution of Siliceous-Walled Algae in Taylor Valley, Antarctica Lakes  [PDF]
Jonathan P. Warnock, Peter T. Doran
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.44064

The McMurdoDryValleysofAntarcticaare a unique environment characterized by extreme lows in temperature and precipitation, which supports a low diversity microbial and multicellular fauna and flora. Terrestrial biomass is largely limited to soil microbes and mosses, while perennially ice-covered lakes host aerobic and anaerobic microbial communities, algae, and a low diversity eukaryotic fauna. This study provides a scanning electron microscope survey of the distribution of siliceous-walled algae in the water columns and surface sediments of fourTaylorValleylakes. No patterns of distribution of algae, chrysophyte cysts and diatoms, are detected, suggesting that cores taken from perennially ice-covered lakes contain basin-wide records, rather than records specific to the lake depth or other lake-specific criteria. Since Taylor Valley lakes became perennially ice-covered, shifts in diatom assemblages in cores are more likely to record changes to sediment and microfossil transport, e.g. the dominance of eolian vs. stream input, rather than other ecological conditions. Basin-wide records are episodically overprinted by lake-specific events, as demonstrated by a marked increase of the stream diatom genus Hantzschia during a period of increased stream flow into East Lake Bonney.

A statistical approach to persistent homology
Peter Bubenik,Peter T. Kim
Mathematics , 2006,
Abstract: Assume that a finite set of points is randomly sampled from a subspace of a metric space. Recent advances in computational topology have provided several approaches to recovering the geometric and topological properties of the underlying space. In this paper we take a statistical approach to this problem. We assume that the data is randomly sampled from an unknown probability distribution. We define two filtered complexes with which we can calculate the persistent homology of a probability distribution. Using statistical estimators for samples from certain families of distributions, we show that we can recover the persistent homology of the underlying distribution.
Comparison of efficient seasonal indexes
Peter T. Ittig
Advances in Decision Sciences , 2004, DOI: 10.1155/s1173912604000069
Abstract: Estimates of a seasonal index in the standard manner (from a moving average) introduce systematic error into the seasonal estimates if a trend is present. This paper shows that a logarithmic modification of the standard moving average procedure will cause it to be consistent with a trend and is an efficient alternative. This paper also compares several other efficient seasonal indexing procedures appropriate for routine business applications and shows some numerical results. The results indicate that it is possible to achieve an improvement in the precision of the seasonal index, in the seasonally adjusted data and in forecasts based upon this data, by considering logarithmic alternatives to standard seasonal indexing procedures. This improvement may be accomplished without a substantial increase in complexity or in the associated computational burden. The opportunities for improvement are shown to be greatest when the data contain substantial trend and seasonal aspects and when the trend has a percentage form. Some suggestions for forecasters are offered.
The key to advanced airways during cardiac arrest: well trained and early
Peter T Morley
Critical Care , 2012, DOI: 10.1186/cc10552
Abstract: One of the unanswered questions in cardiac arrest management is which approach to airway management is best: both the specific technique and the time to intervene. The International Liaison Committee on Resuscitation summarized this issue in its 2010 Consensus on Science document: 'There are no data to support the routine use of any specific approach to airway management during cardiac arrest. The best technique depends on the precise circumstances of the cardiac arrest, local guidelines, training facilities, and the competence of the rescuer' [2].Our understanding of this issue is taken one step further by an intriguing Japanese study that was published in the previous issue of Critical Care [1]. In this observational study from Osaka, 5,377 consecutive, witnessed, non-traumatic, out-of-hospital cardiac arrests (OHCAs) were treated with an advanced airway by emergency life-saving technicians (ELSTs) in the calendar years 2005 through 2008. The authors evaluated the time to advanced airway placement and the difference in outcomes between the use of endotracheal intubation (ETI) and the use of supraglottic airways (SGAs). The SGAs in use in Japan at the time of the study were the Combitube, the laryngeal mask airway (LMA), and the laryngeal tube.The primary outcome measure of this study was neurologically favorable 1-month survival, defined as a cerebral performance category score of 1 or 2. Favorable neurological outcomes were low (3.6%) but similar between ETI and SGAs. Although the ETI group had a number of adverse prognostic features (2 years older, four times as many receiving epinephrine, and 1.4 minutes more to insert the airway), there were actually some statistically significant short-term survival benefits seen in this group: a greater proportion of pre-hospital return of spontaneous circulation (ROSC) (16.6% versus 10.1%) and an increase in ROSC in the emergency department (47.8% versus 44.4%).During this study, CPR was performed according to the Japanese
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