Will research sharing keep pace with the Internet?
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Animals↗
Biomedical subjects
Richard K Johnson
Publications and source records attributed to Richard K Johnson.
Multiscale drivers of water chemistry of boreal lakes and streams.
The variability in surface water chemistry within and between aquatic ecosystems is regulated by many factors operating at several spatial and temporal scales. The importance of geographic, regional-, and local-scale factors as drivers of the natural variability of three water chemistry variables representing buffering capacity and the importance of weathering (acid neutralizing capacity, ANC), nutrient concentration (total phosphorus, TP), and importance of allochthonous inputs (total organic carbon, TOC) were studied in boreal streams and lakes using a method of variance decomposition. Partial redundancy analysis (pRDA) of ANC, TP, and TOC and 38 environmental variables in 361 lakes and 390 streams showed the importance of the interaction between geographic position and regional-scale variables. Geographic position and regional-scale factors combined explained 15.3% (streams) and 10.6% (lakes) of the variation in ANC, TP, and TOC. The unique variance explained by geographic, regional, and local-scale variables alone was <10%. The largest amount of variance was explained by the pure effect of regional-scale variables (9.9% for streams and 7.8% for lakes), followed by local-scale variables (2.9% and 5.8%) and geographic position (1.8% and 3.7%). The combined effect of geographic position, regional-, and local-scale variables accounted for between 30.3% (lakes) and 39.9% (streams) of the variance in surface water chemistry. These findings lend support to the conjecture that lakes and streams are intimately linked to their catchments and have important implications regarding conservation and restoration (management) endeavors.
Carbon↗
Setting expectations for the ecological condition of streams: the concept of reference condition.
An important component of the biological assessment of stream condition is an evaluation of the direct or indirect effects of human activities or disturbances. The concept of a "reference condition" is increasingly used to describe the standard or benchmark against which current condition is compared. Many individual nations, and the European Union as a whole, have codified the concept of reference condition in legislation aimed at protecting and improving the ecological condition of streams. However, the phrase "reference condition" has many meanings in a variety of contexts. One of the primary purposes of this paper is to bring some consistency to the use of the term. We argue the need for a "reference condition" term that is reserved for referring to the "naturalness" of the biota (structure and function) and that naturalness implies the absence of significant human disturbance or alteration. To avoid the confusion that arises when alternative definitions of reference condition are used, we propose that the original concept of reference condition be preserved in this modified form of the term: "reference condition for biological integrity," or RC(BI). We further urge that these specific terms be used to refer to the concepts and methods used in individual bioassessments to characterize the expected condition to which current conditions are compared: "minimally disturbed condition" (MDC); "historical condition" (HC); "least disturbed condition" (LDC); and "best attainable condition" (BAC). We argue that each of these concepts can be narrowly defined, and each implies specific methods for estimating expectations. We also describe current methods by which these expectations are estimated including: the reference-site approach (condition at minimally or least-disturbed sites); best professional judgment; interpretation of historical condition; extrapolation of empirical models; and evaluation of ambient distributions. Because different assumptions about what constitutes reference condition will have important effects on the final classification of streams into condition classes, we urge that bioassessments be consistent in describing the definitions and methods used to set expectations.
Ecosystem↗
Neural pattern in the human pollical distal phalanx.
A morphological study of the neural pattern in the human ungual region of the pollical distal phalanx was carried out on eight male cadavers. The dissections showed a palmar neural arrangement consisting of four designated ungual nerves, two proximal and two distal, for each of the ulnar and radial palmar digital nerves at the lateral sides of the thumb. This neural configuration was associated with the compartmentalization of its ungual pulp, the difference between the type of sensory receptors within the ungual pulp, the overlapping of the tactile composition at the thumb tip, seen clinically after laceration of one of the palmar digital nerves, and the sensory supply to the nail bed in the dorsal portion of the thumb. The proximal ungual pulp compartment had a single proximal medial ungual nerve, which did not appear, as far as visually possible, to overlap at the midline of the proximal ungual pulp. In contrast, the distal ungual pulp compartment was supplied by a medial and a lateral ungual nerve, both of which did appear to overlap to their contralateral sides in the thumb tip. A single proximal dorsal sensory nerve branched dorsally from each of ulnar and radial palmar digital nerves at the level of the proximal ungual pulp to supply the nail bed on the dorsum of the thumb.
Cadaver↗
Representativity of a mid-lake surface water chemistry sample.
A mid-lake sample is the conventional sampling strategy used in lake chemistry monitoring programs. Hence, addressing the question of how representative a mid-lake sample is of in-lake conditions is important for interpreting changes in long-term monitoring programs. Our hypotheses were that; (i) the location of a sampling site within a lake will affect its representativity and (ii) a mid-lake sample could be considered representative of average surface water physico-chemistry. We focused on the surface water chemistry in 34 Swedish lakes. To obtain a wide diversity of lake types, the lakes were classified according to mean depth, water residence time, and three main ecoregions. Two sampling seasons were selected, representative of high and low biological activity and stratified and non-stratified conditions, respectively. Ten samples were collected in each lake. The mid-lake samples differed significantly from the nine remaining samples in less than 4% of the total number of two-sample t-tests performed. Samples collected close to lake inlets differed from the other samples more often than samples collected in the central parts of the lakes. We concluded that the location of a sampling site within a lake may affect the sample's representativity of lake water chemistry, and that a mid-lake surface water sample could be considered representative of surface water chemistry.
Environmental Monitoring↗
Unusual entrapment neuropathy in a golf player.
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Adult↗
Rapid and accurate left ventricular surface generation from three-dimensional echocardiography by a catalog based method. Rapid LV surface generation by three-dimensional echo.
BACKGROUND: Quantitative analysis from three-dimensional (3D) echocardiography requires accurate reconstruction of left ventricular (LV) surfaces. This currently requires time-consuming manual image tracing. We describe and validate an alternative rapid method of generating LV surfaces. METHODS: A 3D-image set is acquired using transthoracic scanning. Images from five standard echo views are displayed and border points selected where anatomic landmarks are well defined. A LV surface is reconstructed as a convex weighted sum of LVs from a catalog of 80 LVs. The intersections of the surface with the five views are presented on these images. The routine may be rerun until the LV surface matches the images. One LV surface is generated in 3 min +/- 27 s. In 41 studies (19 normal, 15 previous infarction, seven cardiomyopathy) the volumes of the catalog-fit endocardial and epicardial surfaces were compared with volumes from surfaces reconstructed from full manual tracing. RESULTS: Over a wide range of LV volumes and ejection fraction (EF), the catalog-fit results correlated closely to those from manual tracing: end-diastolic volume (194 +/- 99 vs. 204 +/- 110 ml, y = 0.93x, R2 = 0.99, SEE = 19 ml, p < 0.001), end-systolic volume (122 +/- 95 vs. 131 +/- 106 ml, y = 0.92x, R2 = 0.99, SEE = 13 ml, p < 0.001), EF (42 +/- 16 vs. 42 +/- 15%, y = x, R2 = 0.99, SEE = 4%, p < 0.001) and mass (220 +/- 88 vs. 204 +/- 86 g, y = 1.1x, R2 = 0.99, SEE = 24 g, p < 0.001). The endocardial catalog surface was generated from an average of 20 points and three computational runs for both end-diastole and end-systole. CONCLUSIONS: The catalog method of LV reconstruction from 3D-echo provides accurate measurement of volume, EF and mass. The speed of the method is a major advantage.
Echocardiography, Three-Dimensional↗
Integrated surface model optimization for freehand three-dimensional echocardiography.
The major obstacle of three-dimensional (3-D) echocardiography is that the ultrasound image quality is too low to reliably detect features locally. Almost all available surface-finding algorithms depend on decent quality boundaries to get satisfactory surface models. We formulate the surface model optimization problem in a Bayesian framework, such that the inference made about a surface model is based on the integration of both the low-level image evidence and the high-level prior shape knowledge through a pixel class prediction mechanism. We model the probability of pixel classes instead of making explicit decisions about them. Therefore, we avoid the unreliable edge detection or image segmentation problem and the pixel correspondence problem. An optimal surface model best explains the observed images such that the posterior probability of the surface model for the observed images is maximized. The pixel feature vector as the image evidence includes several parameters such as the smoothed grayscale value and the minimal second directional derivative. Statistically, we describe the feature vector by the pixel appearance probability model obtained by a nonparametric optimal quantization technique. Qualitatively, we display the imaging plane intersections of the optimized surface models together with those of the ground-truth surfaces reconstructed from manual delineations. Quantitatively, we measure the projection distance error between the optimized and the ground-truth surfaces. In our experiment, we use 20 studies to obtain the probability models offline. The prior shape knowledge is represented by a catalog of 86 left ventricle surface models. In another set of 25 test studies, the average epicardial and endocardial surface projection distance errors are 3.2 +/- 0.85 mm and 2.6 +/- 0.78 mm, respectively.
Algorithms↗
Adult malrotation: a case report and review of the literature.
Midgut malrotation is an anomaly of fetal intestinal rotation that usually presents in the first month of life. It is rare for malrotation to present in adulthood. Symptomatic patients present either acutely with bowel obstruction and intestinal ischemia with a midgut or cecal volvulus, or chronically with vague abdominal pain. Chronic symptoms can often make the diagnosis difficult. Findings diagnostic of malrotation are described using several modalities such as barium studies, computed tomography (CT) scans, angiography, and often emergent laparotomy. Treatment remains the Ladd procedure originally described by Dr. Ladd in 1936. Complete resolution of acute obstruction or chronic abdominal pain is the result of a high index of suspicion for malrotation, appropriate diagnostic studies, and aggressive definitive surgical treatment. We present a case of malrotation in an adult who presented with chronic abdominal pain. Midgut malrotation is a congenital anomaly referring to either lack of or incomplete rotation of the fetal intestines around the axis of the superior mesenteric artery during fetal development. Most patients present with bilious vomiting in the first month of life because of duodenal obstruction or a volvulus. It is rare for this condition to present in adulthood. The true incidence in adults is difficult to estimate because most patients who remain are asymptomatic and their conditions are, therefore, never diagnosed. A literature review by von Flue et al cites 40 cases from 1923 to 1992. Patients who are symptomatic often present either acutely with bowel obstruction and intestinal ischemia with a midgut or cecal volvulus or chronically with vague abdominal pain. These symptoms are caused by peritoneal bands first described by Ladd in 1932. These bands run from the cecum to the right lateral abdominal wall. We present a case of malrotation in an adult who presented with chronic abdominal pain.
Abdominal Pain↗