The effect of the bite plane splint on the electromyographic silent period duration

An electromyographic study of the masseter and anterior part of the temporalis muscles was performed on ten patients presenting temporomandibular joint dysfunction symptoms. The EMG silent periods (SP) produced in the open-close-clench cycle and jaw-jerk reflex were compared for duration before and after treatment with an occlusal bite splint. Following use of the splint, there was a shortening of SP indicating the possible use of the duration of SP as a diagnostic measurement, and also as an indication of treatment effectiveness.     

Plasma catecholamine and haemodynamic responses to surgical endodontic anaesthetic protocols

The effects of varying clinically relevant patterns of anaesthetic-vasoconstrictor combinations used for peri-radicular surgery on plasma concentrations of catecholamines and haemodynamic responses was studied in the canine model. Five mongrel dogs were anaesthetized with sodium pentobarbital. A femoral canula was inserted to measure central blood pressure and an ECG was used to monitor heart rate and any associated arrhythmias. Femoral venous blood samples were drawn before initial injection and at 3 and 10 min after injections. Plasma catecholamine concentrations were determined using high pressure liquid chromatography (HPLC). Injection protocols used three time periods, 30, 60 and 90s, with solutions containing 1:100000 and 1:50000 adrenaline. No significant changes in heart rates or presence of arrythymias were noted over the experimental protocol. Catecholamine levels in pico moles mL^-1 were within the normal range at the 3-min sample level. At the 10-min sample time there was a more erratic range of concentrations, with most samples within the normal range. This may have been due to endogenous release of catecholamines in specific animals. The data identified trends in both the haemodynamic parameters and plasma catecholamine levels that can legitimately support the careful use of higher levels of a vasoconstrictor when patient profiles and surgical needs dictate.     

From the Cover: Species interactions and the structure of complex communication networks

A universal challenge faced by animal species is the need to communicate effectively against a backdrop of heterospecific signals. It is often assumed that this need results in signal divergence to minimize interference among community members, yet previous support for this idea is mixed, and few studies have tested the opposing hypothesis that interactions among competing species promote widespread convergence in signaling regimes. Using a null model approach to analyze acoustic signaling in 307 species of Amazonian birds, we show that closely related lineages signal together in time and space and that acoustic signals given in temporal or spatial proximity are more similar in design than expected by chance. These results challenge the view that multispecies choruses are structured by temporal, spatial, or acoustic partitioning and instead suggest that social communication between competing species can fundamentally organize signaling assemblages, leading to the opposite pattern of clustering in signals and signaling behavior.One of the core principles of animal communication is that signals should be detectable and convey an accurate message against a noisy background (1–3). This background can involve direct overlap of sounds, as in the case of masking by simultaneous signals (4, 5), or simply the co-occurrence of different species using confusingly similar signals at the same location (6–8). As most animals communicate within assemblages of related species, the problem of signal interference is widespread and may have far-reaching implications for the evolution of signals and signaling behavior. This concept—variously termed the “noisy neighbors” hypothesis (9) or “cocktail party problem” (10)—has attracted much attention over recent years. However, the extent to which it provides a general explanation for patterns of signaling in animal communities remains contentious (6, 8).The traditional view is that the signaling strategies of animals are shaped by limiting similarity among competitors, much as competition for ecological resources is thought to promote partitioning of niche space (11–13). Partitioning of signal space may occur if species compete for position near overcrowded transmission optima, and, concurrently, if overlap in signal design impairs the detection or discrimination of signals mediating mate choice and resource competition (14). Under these conditions, mechanisms of selection against misdirected aggression (e.g., character displacement) or the production of unfit hybrids (e.g., reinforcement) are predicted to drive phenotypic divergence (9), whereas similar mechanisms may lead to related species signaling at different times or in different locations (13). These pathways theoretically lead to structural, temporal, and spatial partitioning of signals and signalers in animal assemblages, but tests of these patterns have produced mixed results (6, 11, 15).A contrasting possibility is that selection for signal divergence is weak and that co-occurring species instead show the opposite pattern of signal clustering (16). One potential driver of this pattern is that shared habitats can exert convergent selection on signals (17). Another is that signals often have dual function in mate attraction and resource defense (18), potentially mediating competition among closely related species for ecological resources (19). Thus, multispecies choruses may operate to some degree as extended communication networks, not only within species (20) but between species. The effect of such a network would be to increase the likelihood of interspecific communication involving closely related species with similar signals. A pattern of signal clustering caused by communication among similar congeners may be further exaggerated when competitive interactions among species promote signal similarity (16). This process may occur when individuals with convergent agonistic signals have higher fitness because they are better at defending resources against both conspecific and heterospecific competitors, driving convergent evolution (21, 22). Taken together, these alternative views suggest that the most pervasive effect of species interactions on animal communication systems may not be partitioning, as generally proposed, but synchrony and stereotypy among competing species.Progress in resolving these opposing viewpoints has been limited because most studies of signaling assemblages have compiled lists of species co-occurring at particular localities and then compared multiple assemblages across regional scales (6, 15). This approach may be misleading because of spatial biases in phylogenetic relationships and habitat. On the one hand, sympatric species tend to be significantly older than allopatric species, at least within radiations (23, 24), and thus the signals of co-occurring lineages may be more divergent than expected by chance simply because they have had more time to diverge, exaggerating the evidence for partitioning. Conversely, species co-occurring at local scales may be less divergent because they are segregated by habitat across a study site and therefore are unlikely to signal together. Although some studies (7, 11) partially overcome these issues by sampling assemblages from single points in space, none has considered the effects of habitat and the potential role of competitive interactions among related species (16). Moreover, previous studies have generally assessed partitioning in relatively small assemblages (<30 species), reducing both the likelihood of competition over transmission optima and the power of statistical tests.Here, we sample >90 signaling assemblages (Fig. S1) containing a combined total of >300 species (Dataset S1) to assess the role of species interactions in structuring and organizing the dawn chorus of Amazonian rainforest birds. Each assemblage comprised species producing acoustic signals, identified from standardized 120-min sound recordings taken at points distributed across a single study locality. We also restricted analyses to 10-min time blocks and assumed that assemblages of species signaling in these blocks were forced to discriminate among each other (i.e., they were each other’s background noise) and also that they had an increased likelihood of signaling simultaneously (i.e., directly masking each other’s signals). We use the term cosignaling to describe pairs of species signaling during the same 10- or 120-min time block and thus not necessarily signaling simultaneously. We coded all assemblages for habitat and time of day, calculated the acoustic similarity of cosignaling species using spectrographic analyses of voice recordings, and estimated the evolutionary relatedness of cosignaling species using a hierarchical taxonomic framework.Our null hypothesis states that species interactions have no effect on chorus structure and thus that species with similar signals are randomly distributed in space and time (Fig. 1A). The distance between signals in observed choruses should not differ significantly from that expected by chance, accounting for habitat and evolutionary relationships. We envisage two scenarios that may falsify the null. The partitioning hypothesis predicts that signal design is evenly spaced across communities, with a larger distance between co-occurring signals than predicted by chance (Fig. 1B). The network hypothesis predicts that competing species interact using phylogenetically conserved signals and thus that signals are clustered in distribution, with a smaller distance between co-occurring signals than predicted by chance (Fig. 1C). The partitioning and network hypotheses involve different forms of species interaction with opposing effects on chorus structure. Although we do not measure species interactions directly, we follow standard approaches in assuming that such interactions predict patterns in the trait structure of assemblages (25).Open in a separate windowFig. 1.Predictions of three hypotheses proposed to structure multispecies choruses, illustrated using hypothetical seven-species choruses with signal design plotted in multivariate signaling space. The null hypothesis that species interactions have no effect predicts that signal structure is random (A), generating an intermediate mean nearest-neighbor distance d. The partitioning hypothesis predicts an evenly spaced signal structure (B) reflected in larger values for d. The network hypothesis predicts that related species will signal together, causing signals to be clustered around optima (C), and generating small values for d. We test these predictions by assessing whether d, viewed across a sample of communities, is higher or lower than expected by chance. We calculated d in two ways: d₁ (Upper) is the mean nearest neighbor distance [nnd] across all community members; and d₂ (Lower) is the mean nnd across the three pairs of species with most similar signals.Our aims were to (i) quantify acoustic properties of signals transmitted in the dawn chorus; (ii) estimate the degree of signal similarity among cosignaling species; and (iii) compare the observed distribution of signal properties with that expected by chance. We also consider spatial explanations for chorus structure, including the reduced cosignaling of species with similar signals through spatial partitioning. This form of segregation may occur because ecological competition is elevated in tropical bird communities (26), causing parapatric (27) or “checkerboard” distributions (28) among closely related species, thus potentially leading to apparent signal partitioning by competitive exclusion. The network hypothesis predicts the opposite pattern as closely related species should synchronize their signaling activity using shared territorial signals. We test these predictions by comparing 120-min (spatially segregated) and 10-min (nonsegregated) choruses and using taxonomic relatedness to estimate the degree of cosignaling between close relatives.The Amazonian dawn chorus provides one of the world’s most diverse multispecies signaling assemblages and an ideal system for exploring the effects of competition on signaling strategies for three reasons. First, visibility is hampered by dense vegetation, and thus long-distance signaling is forced into one modality (acoustic communication). Second, background noise levels are extremely high as a result of other organisms, including insects, amphibians, and primates, suggesting that selection for partitioning of acoustic signals should be maximized (12). Finally, many tropical species are permanently resident and apparently interspecifically territorial, using acoustic signals to mediate competitive interactions with heterospecifics (18, 26, 29). In combination, these factors imply that large numbers of species compete both for ecological resources and a narrow window of optimal signaling space (7, 30), providing a context in which to test the relative importance of acoustic partitioning and interspecific communication networks.     

Changes in Vertebral Column Height (VCH) at Different Distance Intervals During a 3-Mile Walk

Background

The purpose of this study was to determine the changes in vertebral column height (VCH) of males and females, at every one-half mile, for a total walking distance of 3 miles.

Methods

Twenty males and twenty females between the ages of 21 and 40 years walked 3 miles on a treadmill maintaining a walking speed that the subject rated between 12 and 14 on Borg''s rate of perceived exertion scale. Blood pressure, heart rate, and VCH measurements were taken initially and at each half-mile interval throughout the three-mile walk. Vertebral column height (VCH) was measured from the spinous process of C7 to S2 using a standard tape measure.

Results

Significant differences existed in vertebral column height according to sex (F = 16.18; p < .05) and significant differences in vertebral column height at the different distances (F = 65.02: p < .0001). Significant changes occurred in the VCH between half-mile intervals only between 0.5 miles and 1.0 mile and between 1.0 mile and 1.5 miles during the walk. As found with a regression analysis, curvilinear relationship exists between the distance walked and VCH; with VCH decreasing throughout the distance of the walk.

Conclusions

Vertebral column height decreased in a curvilinear relationship throughout the distance of walking 3 miles in both males and females.     

What is a safe waiting time for coronary artery bypass surgery?

To determine the factors that influenced doctors' prioritization and decisions on safe waiting time for coronary artery bypass surgery, 50 'paper patients', based on a random sample of cases who actually had surgery, were assessed by 33 clinicians. We used linear regression models to reflect the impact of clinical and non-clinical 'cues' on safe waiting time and priority decisions. The benefits of surgery tended to be over-estimated. For example, the average perceived gain in life expectancy for patients with left main-stem disease was 6.74 years. However, models incorporating only the perceptions of benefit as independent variables (i.e. the anticipated symptom reduction, MI risk reduction and life expectancy extension), had only modest explanatory power (mean R2 was 0.55 for safe waiting time, and 0.56 for priority decisions). Models which incorporated perceptions of benefit and the cases' clinical and non-clinical characteristics had generally much higher explanatory power (mean R2, 0.83 and 0.86, respectively). Lifestyle and demographic variables had much less impact on the doctors' judgements than the major clinical cues of angina severity and left main-stem stenosis. Demographic and lifestyle cues had different impacts on safe waiting time and priority for about 25% of doctors.      

Blood transfusion exposure does not influence survival in patients with carcinoma of the breast

There is abundant evidence of immune modulation induced by exposure to blood transfusions. Some studies have demonstrated a detrimental effect of transfusion on the recurrence of malignant disease and survival. We retrospectively studied the impact of blood transfusion exposure on 229 patients with breast cancer who were seen from July 1973 to September 1980, had at least 5 years' follow-up and had been randomized by therapy at the time of diagnosis. The patients were divided into four groups according to transfusion history: Group 1 (111 patients), no transfusion; Group 2 (34 patients), first transfusion after mastectomy; Group 3 (41 patients), first transfusion at mastectomy; and Group 4 (43 patients), first transfusion before mastectomy. All transfused patients received red cells or whole blood or both. At the time of analysis, 124 (54%) of the patients had died. Only Group 2 was statistically associated with decreased survival; recurrence of disease was 85 percent in this group, compared with 53 percent to 61 percent in the other three groups (p = 0.006, log-rank test). In general, Group 2 patients received transfusions because of recurrent disease. We conclude that transfusions before or at mastectomy are not associated with increased recurrence or reduced survival in patients with breast cancer.     

Variation of Medicare Payments for Total Knee Arthroplasty

We analyzed the 2009 Medicare inpatient claims data and other databases to estimate Medicare payments for primary or revision total knee arthroplasty (TKA). The average Medicare hospital payment per procedure was $13,464 for primary TKA (n = 227,587) and $17,331 for revision TKA (n = 18,677). For both primary and revision TKAs Medicare payments varied substantially across patients, hospitals and healthcare markets. Less than one percent of primary TKA cases but seven percent of revision TKA cases triggered Medicare “outlier” payments, which were $10,000 or higher per case beyond regular diagnosis-related-group payments. Urban and major teaching hospitals were more likely to treat these unusually expensive cases. Hospitals in the Northeast and West regions tended to receive higher Medicare payments than hospitals in the Midwest.