Marked Excursion Research Articles

The Anatomic Position of the Sciatic Nerve During Percutaneous Retrograde Posterior Column Fixation is Determined by Hip Position.

There are multiple established patient positions for placement of a percutaneous retrograde posterior column screw for fixation of acetabulum fractures. The sciatic nerve is at risk of injury during this procedure, as it lies adjacent to the start point at the ischial tuberosity. The purpose of this study is to define how the position of the sciatic nerve, relative to the ischial tuberosity, changes with respect to the patient's hip position. In a cohort of 11 healthy volunteers, ultrasound was used to measure the absolute distance between the ischial tuberosity and the sciatic nerve. Measurements were made with the hip and knee flexed to 90 degrees to simulate supine and lateral positioning, and with the hip extended to simulate prone positioning. In both positions, the hip was kept in neutral abduction and neutral rotation. The distance from the lateral border of the ischial tuberosity to the medial border of the sciatic nerve was greater in all subjects in the hip flexed position versus the extended position. The mean distance was 17 mm (range, 14-27 mm) in the hip extended position, and 39 mm (range, 26-56 mm) in the hip flexed position (P < .001). The sciatic nerve demonstrates marked excursion away from the ischial tuberosity when the hip is flexed compared with when it is extended. The safest patient position for percutaneous placement of a retrograde posterior column screw is lateral or supine with the hip flexed to 90 degrees.

Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event

The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago, but within the 160 Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils. This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology.

Temporal changes in the cumulative piecewise gradient of a variant of the Gutenberg–Richter relationship, and the imminence of extreme events

It is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution. For a long-term dataset, the overall slope of this logarithmically transformed distribution is usually indicated by a best-fit straight line and expressed as a b-value. This slope is stable and normally lies between 0.8 and 1.2, the actual value depending on the region examined, and the threshold selected for data completeness. The linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run, and with appropriate reservations, may even be extrapolated to magnitudes that are beyond recent experience. We suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution, with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution. An emergence, through time, of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low-end piecewise gradients of this distribution. A marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent, larger event. On two separate occasions, in 1982 and 1997, such temporal variations were seen in the magnitude distributions of sequences of events near Tobago, West Indies, and used to anticipate subsequent damaging mainshocks. The recognition of temporal departures from overall linearity of the magnitude–frequency relation, in a suitable dataset, may thus provide an evidential element that can contribute to earthquake forecasting. This phenomenological approach was used in the analysis of the NEIC global dataset of earthquakes of magnitude 6.1 and bigger, for the period 1973–2003, to explore its wider applicability. Trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake, perhaps exceeding magnitude 8.5; such an event did occur shortly afterwards in the form of the great Sumatran earthquake of 2004/12/26. Following that event, global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins, indicating that another similar event was likely. The second Sumatran earthquake on 2005/03/28 satisfied that projection. Since that time, a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake (or earthquakes) in the magnitude range 8.6–9.0 or even greater. This contribution describes the piecewise gradient approach and examines its application to global earthquake data.

A prospective controlled study of neonatal morbidities in infants born at 36 weeks or more gestation to Women with diet-controlled gestational diabetes (GDM-class Al).

Infants of gestational diabetes mellitus (GDM)-A1 women are unlikely to experience the marked excursion in maternal glucose levels that may characterize insulin-requiring GDM (class-A2) or insulin-dependent diabetes (IDDM). However, infants born to GDM-A1 women are traditionally managed like infants born to GDM-A2 or IDDM women. To examine monitoring protocols for infants of GDM-A1 women, and to examine the efficacy of early and frequent feedings to prevent and to treat hypoglycemia. A total of 92 of 101 infants born to GDM-A1 women (diabetic group) and 68 of 83 infants born to nondiabetic women (control group) at > or=36 weeks of gestation were prospectively monitored for the development of hypoglycemia and other morbidities. Blood glucose screening was performed in the diabetic group every 30-60 minutes three times, starting soon after birth and then at 3-hour intervals for 24 hours. Liberal feedings were started shortly after birth and provided every 3 hours for at least 24 hours. All women with GDM-A1 had an HbA1c measured before delivery. Both the diabetic and control groups had similar demographics, including LGA incidence. Blood glucose readings before feedings were low (<40 mg/dl) in 24 of 92 infants (26.1%) from the diabetic group and in 20 of 68 control infants (29%). After the start of oral feedings, all but four diabetic and three control infants had subsequent glucose readings > or =40 mg/dl. No infant had symptoms of hypoglycemia and none from the diabetic group had birth trauma, hypoxic-ischemic encephalopathy, polycythemia, hypocalcemia, or hypomagnesemia. Hypoglycemic episodes in the infants from the diabetic group could be managed with oral feedings alone. Birth weight, gestational age, sex, Apgar scores, and maternal HbA1c levels could not predict low glucose readings on initial screening in infants from the diabetic group. The incidence of hypoglycemia in infants born to GDM-A1 women at > or =36 weeks of gestation is similar to control infants born to nondiabetic women. Low blood glucose levels during the first few hours of life can be prevented or treated with early and frequent oral feeding.

Stable-isotope and elemental trends in Pleistocene sabkha dolomites; descending meteoric water vs. sulfate reduction

ABSTRACT A 55 m thick Pleistocene dolomite section was sampled in 33 borings in the Arabian Gulf, offshore of Al Jubayl, Saudi Arabia. The regional setting, suite of sedimentary structures, abundance of evaporites (crystals, nodules, and chickenwire horizons), and geochemistry of the dolomite are all consistent with accumulation as part of a series of vertically stacked sabkha depositional complexes. Analyses of the ordering, stoichiometry, and overall stable-isotope composition indicate that after dolomitization the sediment underwent diagenesis in contact with meteoric waters. Stable-isotope analyses of 385 samples have demonstrated that within this sequence there are four correlatable horizons that display marked excursions to low 13C values; some shifts exceed 6% between vertically adjacent samples. The 18O values show a similar, but less pronounced, shift to low values at the same stratigraphic horizons. The samples with low 13C and 18O values have a greater admixture of fine-grained siliciclastics, are light gray (i.e., reducing conditions), and have higher concentrations of Fe, Mn, and Zn than other parts of the deposit. These diagenetic attributes, especially the marked change in 13C values, may be due to either diagenesis due to the descent of meteoric water beneath a soil horizon or diagenesis associated with bacterially mediated sulfate-reduction processes; sulfate reduction is the favored hypothesis. It is envisioned that after the initial dolomitization diagenesis associated with bacterially mediated sulfate reduction of laterally extensive microbial mats within the top parts of sabkha sequences produced the correlatable horizons of low 13C and 18O values.

Excursion and strain of the median nerve.

Five fresh-frozen transthoracic cadaver specimens (ten upper extremities) were dissected in order to measure excursion and strain of the median nerve at the wrist and the elbow in association with different positions of the shoulder, elbow, wrist, and fingers. The relationships between motions of the joints and excursion and strain at the wrist and the elbow as well as between excursion and strain were also determined. When the wrist was moved from 60 degrees of extension to 65 degrees of flexion, the median nerve at the wrist underwent a mean total excursion of 19.6 millimeters (9.2 +/- 1.38 millimeters [mean and standard deviation] in extension and 10.4 +/- 1.50 millimeters in flexion). The change in strain was not measurable secondary to nerve-wrinkling. Motion of the fingers from hyperextension to full flexion caused a mean total excursion of 9.7 millimeters (6.3 +/- 1.31 millimeters in hyperextension and 3.4 +/- 1.04 millimeters in flexion) and a change in strain of 19.0 per cent. This change in strain became more pronounced when the wrist and the fingers moved in synergy. Such strain, if constant, has been shown to decrease microvascular perfusion and nerve conduction in rabbits. With motion of the shoulder, the mean total excursion of the median nerve at the elbow was 9.1 millimeters (4.4 +/- 1.64 millimeters in abduction and 4.7 +/- 1.81 millimeters in adduction) and the change in strain was 13.3 per cent. With motion of the elbow, the mean total excursion was 12.3 millimeters (12.3 +/- 4.20 millimeters in flexion and zero millimeters in the resting position) and the change in strain was not measurable because of the wrinkle effect in flexion. With motion of the wrist, the mean total excursion was 5.6 millimeters (4.3 +/- 1.95 millimeters in extension and 1.25 +/- 0.81 millimeters in flexion) and the change in strain was 14.8 per cent. With motion of the fingers, the mean total, excursion was 3.4 millimeters (2.6 +/- 1.13 millimeters in hyperextension and 0.80 +/- 0.92 millimeter in flexion) and the change in strain was 10.3 per cent. Motion of the wrist and the fingers induced profound excursion of the median nerve at the wrist, whereas motion of the shoulder and the elbow induced marked excursion of the median nerve at the elbow. These excursions were much more pronounced when a number of joints were moved in a composite manner. Any factor that might limit normal excursion, such as scarring, could induce strains that could adversely affect the function of the median nerve. The finding that the position and movement of the limb had a profound effect on excursion and strain of the median nerve at the wrist and the elbow may aid in the understanding of the pathophysiology of median-nerve neuropathy.

Neoproterozoic of the Mackenzie Mountains, northwestern Canada

Neoproterozoic strata of the Mackenzie Mountains are more than 10 km thick, and comprise two supergroups of differing style. The Mackenzie Mountains Supergroup (4–6 km thick), an epicratonic succession of mainly shallow-water siliciclastic and carbonate strata, contains detrital zircons dated at 1080 Ma and is cut by dykes and plugs dated at 780-778 Ma. The overlying Windermere Supergroup (5–7 km thick) comprises basal rift deposits and glacial diamictites that are overlain by three, kilometre-scale, siliciclastic to carbonate “Grand Cycles” deposited on a passive margin. “Grand Cycles” in the eastern Mackenzie Mountains were deposited in a shallow-water setting, whereas contemporaneous cycles in the western Mackenzies were deposited on a continental slope; mapping of successive shelf-margin positions reveals southwestward progradation. The Windermere Supergroup is unconformably overlain by the Ingta Formation, which contains the Proterozoic-Cambrian boundary. Subtrilobite Cambrian strata are approximately 1.5 km thick, and are overlain by trilobite-bearing Lower Cambrian carbonates of the Sekwi Formation. Fossils are abundant and biostratigraphically useful in these Neoproterozoic strata. Acritarchs, carbonaceous megafossils, and microbial structures occur throughout the entire succession, but are especially well preserved in the Little Dal Group of the Mackenzie Mountains Supergroup. Edicara-type fossils first appear below the second Windermere glacial unit (Ice Brook diamictite), and range upwards through 2.5 km of strata to near the top of the Windermere; three distinctive assemblages corresponding to the Twitya, Sheepbed, and Blueflower formations can be recognized. The Neoproterozoic-Cambrian boundary occurs within the Ingta Formation, and is marked by an abrupt change from simple, subhorizontal burrows ( Planolites-Torrowangea Assemblage) to complex feeding burrows of the Phycodes Assemblage. Small shelly fossils of Nemakit-Daldyn aspect occur in the upper part of the Ingta Formation, slightly above the basal Cambrian boundary. The presence of two glacial diamictites in the Windermere and numerous sequence boundaries and flooding surfaces throughout the succession provides opportunities for regional and global event correlation. The palaeomagnetic record shows three hair-pin curves that should be recognizable in continents attached to Laurentia. Carbonate interbeds throughout the succession typically yield relatively unaltered carbon isotope ratios; C and Sr chemostratigraphy shows marked excursions that appear to be globally correlatable.

Effects of exogenous insulin on excursions and diurnal rhythm of plasma glucose in pregnant diabetic patients with and without residual β-cell function

The relative effects and consequences of split doses of exogenous insulin therapy (two thirds before breakfast and one third before the evening meal) on excursions and diurnal rhythm of circulating glucose during the 24-hour “metabolic clock” were examined. A longitudinal study in pregnant women with maturity-onset diabetes (N = 7) with substantial endogenous insulin secretion and juvenile onset diabetes (N = 6) with no measurable endogenous insulin secretion (judged by C-peptide measurement) was compared with identical studies performed in nondiabetic pregnant control subjects (N = 6). Plasma glucose levels determined at hourly intervals throughout the 24-hour meal-activity-sleep cycles revealed marked excursions of plasma glucose values with exaggerated hyperglycemia during the day hours and relative hypoglycemia at night in both types of diabetic pregnancies as compared to normal control pregnancies. The magnitude of glucose excursion was surprisingly large relative to the degree of increase in the mean 24-hour glucose levels and mean fasting blood glucose values. A striking disparity in the amount of exogenous insulin required to maintain glucose levels and diurnal rhythm toward the normal range in pregnant diabetic patients from second to the third trimester was observed. The degree of exogenous insulin increment imposed by pregnancy (from the second to third trimester) in juvenile-onset diabetes was relatively small (38%) and comparable to the increase in endogenous insulin (32%) found in nondiabetic pregnancies. In marked contrast, among patients with maturity-onset diabetes, in whom substantial endogenous insulin secretion was present, the corresponding increment in exogenous insulin was surprisingly large (98%) without a proportional reduction in 24-hour integrated glucose values. These findings indicate that the effects and consequences of exogenous insulin therapy between maturity-onset diabetes and juvenile-onset diabetes during pregnancy are clearly different. Our data further suggest that peripheral insulin resistance constitutes the major factor accounting for the persistence of hyperglycemia in maturity-onset diabetes. Although the mechanism by which the exaggeration of insulin resistance in maturity-onset diabetes with superimposed pregnancy remains unclear, there are at least three additive contributing events to consider: the inherent defect of insulin resistance in this type of diabetes, the pregnancy-induced insulin resistance, and the reduction in number or affinity of insulin receptors in target tissues occasioned by excessive exogenous insulin treatment.

210Po and 210Pb distributions in ocean water profiles from the Eastern South Pacific

Two ocean profiles from the Peru Basin from regions with different surface productivities were analyzed for total 210Pb and 201Po to evaluate the influence of particulates in the water column on their distribution. Comparison with a published 226Ra profile for the region was made. The profile closest to the coast, where upwelling and productivity are high, shows depletion of 210Pb relative to 226Ra at all depths, with particularly marked excursions from radioactive equilibrium at the surface and in the bottom water. 210Po appears to be deficient relative to 210Pb at depth as well. Mean residence times in the deep water, relative to particulate removal from the water column to the sediments, of about 100 years for 210Pb and about two years for 210Po are indicated. The profile northwest of the upwelling region shows the 226Ra 210Pb 210Po system close to equilibrium at all depths to 1500 m (except for the effect of atmospheric 210Pb input seen at the surface.

Cardiac Motion in Patients with Pericardial Effusion

Diagnostic ultrasound was used to record the movement of the anterior and posterior heart walls in 23 patients with proven pericardial effusion. Fifteen of these patients demonstrated heart-wall motion that could not be distinguished from the normal pattern. Two patients with acute cardiac tamponade exhibited markedly reduced cardiac motion. The ultrasoundcardiograms obtained from the remaining six patients indicated posterior displacement of the entire heart during systole. The extent of this cardiac displacement varied. Five of the six patients with excessive cardiac motion had malignant pericardial effusion, and four of the six had clinical evidence of cardiac tamponade. The two patients with the most marked excursions exhibited electrical alternation. The results of this study substantiate the theory that excessive cardiac motion may occur in some patients with pericardial effusion. Objective evidence is also provided in support of the positional etiology of electrical alternation associated with pericardial effusion. An attempt is made to identify some of the factors responsible for the observed abnormal cardiac motion, and some speculation is offered as to what role rotation might play in the cardiac displacement. This study also serves as an example of the type of cardiovascular investigation that can be performed with diagnostic ultrasound.