Intravascular bubble composition in guinea pigs: a possible explanation for differences in decompression risk among different gases.

Differences in risk of decompression sickness (DCS) that have been observed among inert gases may reflect differences in gas solubility or diffusivity or both. A higher risk gas might generate a larger volume of evolved gas during decompression, thereby increasing the probability of DCS. If this hypothesis is correct, the composition of bubbles that develop during decompression should reflect such gas differences. Unanesthetized guinea pigs were compressed to depths ranging from 250 to 350 fsw with air, He-O2 (21% O2) or one of a number of N2-He-O2 or N2-Ar-O2 mixtures (21% O2). Animals were held at depth from 15 to 60 min, then decompressed slowly (60 fsw/min) or rapidly (less than 15 s) to 5 fsw. If severe DCS developed, as judged by changes in physiologic variables, death usually occurred quickly. Gas/blood samples were then immediately withdrawn from the right atrium or the inferior vena cava, and the gas phase analyzed for He, N2, Ar, O2, and CO2 via gas chromatography. Bubbles from all dives contained 5-9% CO2, 1-4% O2, with the balance inert gas. Bubbles after N2-He-O2 dives contained substantially more N2 than He (up to 1.9 times more) compared to the dive mixture; bubbles after N2-Ar-O2 dives contained more Ar than N2 (up to 1.8 times more). For N2-He-O2 dives, the actual inert gas makeup of bubbles was dependent on the time-at-depth and the decompression profile. Results may reflect differences among He, N2, and Ar in tissue solubility/diffusivity and gas exchange rates, and support the rank order of increasing DCS risk (He less than N2 less than Ar) and rate of gas exchange (N2 less than He) observed previously during rat dives.     

Color preference in red–green dichromats

Around 2% of males have red–green dichromacy, which is a genetic disorder of color vision where one type of cone photoreceptor is missing. Here we investigate the color preferences of dichromats. We aim (i) to establish whether the systematic and reliable color preferences of normal trichromatic observers (e.g., preference maximum at blue, minimum at yellow-green) are affected by dichromacy and (ii) to test theories of color preference with a dichromatic sample. Dichromat and normal trichromat observers named and rated how much they liked saturated, light, dark, and focal colors twice. Trichromats had the expected pattern of preference. Dichromats had a reliable pattern of preference that was different to trichromats, with a preference maximum rather than minimum at yellow and a much weaker preference for blue than trichromats. Color preference was more affected in observers who lacked the cone type sensitive to long wavelengths (protanopes) than in those who lacked the cone type sensitive to medium wavelengths (deuteranopes). Trichromats’ preferences were summarized effectively in terms of cone-contrast between color and background, and yellow-blue cone-contrast could account for dichromats’ pattern of preference, with some evidence for residual red–green activity in deuteranopes’ preference. Dichromats’ color naming also could account for their color preferences, with colors named more accurately and quickly being more preferred. This relationship between color naming and preference also was present for trichromat males but not females. Overall, the findings provide novel evidence on how dichromats experience color, advance the understanding of why humans like some colors more than others, and have implications for general theories of aesthetics.Individuals vary in their perceptual experience of the world, and sometimes this variation is caused by genetic differences (1–4). Dichromacy is a form of color-vision deficiency affecting about 2% of human males in which only two of the three types of retinal cone photoreceptors are functional because of genetic factors (1, 2). Protanopes, deuteranopes, and tritanopes lack cone photoreceptors sensitive to long (L), medium (M), and short (S) wavelengths, respectively. Accordingly, dichromats’ color discrimination is poorer, and their spectral sensitivity is slightly shifted to longer wavelengths (deuteranopes) or is moderately shifted to shorter wavelengths (protanopes) compared with that of normal trichromats (common observers; see table 3.6 in ref. 5).In normal trichromats, cone responses are the input signals for two chromatic cone opponent mechanisms, red–green and yellow–blue, based on L−M and S−(L+M) cone responses, respectively, and one achromatic mechanism, mainly based on L+M responses (1). Traditionally it has been considered that protanopes and deuteranopes lack functionality in the red–green mechanism, because this opponent mechanism is based on the comparison of L and M cone responses, and one of those cone types is affected. (Thus such observers are called “red–green dichromats.”) However, research also has shown that a large proportion of red–green dichromats have residual activity in this mechanism with increasing stimulus size (over 3°; see refs. 6, 7), resulting in surprisingly good color naming (8–11). The origin of such red–green residual activity remains unknown and is open to several explanations (7, 10, 12, 13). Other research has shown that protanopes and deuteranopes also exhibit minor alterations in the performance of the achromatic and yellow–blue mechanisms (see figures 4 and 5 in ref. 14). These functional alterations in red–green dichromacy also affect color naming: Moreira et al. (15) have developed a model that explains 94% of the color-naming variance in protanopes and 96% of that in deuteranopes. The color naming of dichromats suggests that, at least in some circumstances, dichromat color perception is supported by red–green residual activity (R–G_res), in addition to yellow–blue and achromatic mechanisms (modeled as s′ and L*_T in ref. 15). These mechanisms also might be relevant for other aspects of dichromats’ color perception, such as color preference.Although there has been much research on dichromats, their affective response to color has not been systematically investigated previously. Some visual simulations of how different stimuli appear to dichromats (16) have been demonstrated to work reasonably well (17). For example, these simulations suggest that some hues that appear reddish to common observers would appear desaturated and brownish for dichromats—a hue that normal trichromats typically dislike (18). Do dichromats also dislike a brownish appearance? Alternatively, if dichromats perceive a brownish appearance more commonly than trichromats, does this increased perception alter their preference for that appearance relative to other hues? Could dichromats’ and trichromats’ color preferences, like naming, be surprisingly similar if a residual red–green mechanism feeds into dichromats’ color preference?Investigating color preference in dichromats may provide insight into how they perceive color and also may shed light on the origins of color preference and inform ways to test further theories and models of color preference. Decades of color research have indicated a systematic pattern of preference in trichromats: Blue hues are commonly preferred, and yellow–green hues are commonly disliked (18–20). This pattern has been so systematic across studies that some have claimed it is universal, although others have pointed out that cross-cultural differences in color preference can be found also (21). Patterns of color preference have been explained in terms of the emotional response to color (22) and in terms of the valence of objects associated with colors (18).Another theory is that color preferences can be summarized in terms of the cone contrast between a color and its background (19). Supporting this theory, around 70% of the variance in preference across a set of hues could be explained by L−M and S−(L+M) cone contrasts for British and Chinese trichromats (19). However, other studies have failed to account for this much of the variance with cone contrasts alone (18, 21). Palmer and Schloss (18) extended the model, adding achromatic contrast and saturation as predictors, but accounted for only 37% of the variance. If the cone-contrast model works, we should find altered patterns of color preference in dichromats that reflect their altered color vision. If so, we should be able to model dichromat color preference, as Moreira et al. (15) did for color naming, using a model tailored for dichromats’ altered cone-opponent mechanisms.The current study investigates color preference in male dichromat (protanopes and deuteranopes) and trichromat observers (males and females). Color preference was measured for a set of 24 colors from the Berkeley Color Project (BCP) (18), comprising saturated, light, and dark versions of eight hues used in prior studies of trichromat color preference (18, 20, 21) and also the focal colors of the basic color categories (Fig. S1). The type of dichromacy was confirmed through the use of a set of color-vision tests including the Nagel anomaloscope. Observers rated their preference for the colors twice and also named the colors. Color preferences were compared across groups. To test the cone-contrast model, trichromat color preferences were modeled with trichromat cone contrasts as in Hurlbert and Ling (19). Dichromat color preferences then were modeled with cone contrasts that take into account dichromats’ altered cone responses. In addition, we explore the relationship between color naming and color preference in dichromats and trichromats, investigating whether color categorization, accuracy, speed, and consistency of naming predict how much a color is preferred.Open in a separate windowFig. S1.Thirty-five stimuli from the saturated (S), light (L), dark (D), and focal (F) sets presented against the background used in the experiment. Colors are only an approximation of those in the experiment because of reproduction inaccuracies.     

Whole blood collection on filter paper is an effective means of obtaining samples for human immunodeficiency virus antibody assay

The suitability of collecting whole blood specimens on filter paper disks for HIV antibody assay was evaluated. ELISA and Western blot assay results were in complete agreement for serum and blood spot disk samples. Sensitivity of the two methods was tested using diluted whole blood and sera from HIV-seropositive individuals. Results demonstrate that ELISA and Western blot assays performed on punched-out disks of the blood-impregnated papers had the same sensitivities as those obtained with serum samples. This study suggests that whole blood collection on filter paper can be effectively substituted for serum sampling in HIV antibody screening programs.     

Kinesin-2 and photoreceptor cell death: requirement of motor subunits

Kinesin-2 function is essential for photoreceptor cell viability. The removal of one of the kinesin-2 motor proteins, KIF3A, by photoreceptor-specific conditional mutagenesis, has been shown to cause rapid photoreceptor cell degeneration. We have explored the possibility that the genes encoding the kinesin-2 motor proteins (KIF3A, KIF3B, and KIF3C)are linked to retinal disease, by examining retinas of knockout mice. We conclude that the reduced KIF3A and KIF3B in heterozygous animals, or the complete absence of KIF3C in homozygous animals does not affect photoreceptor cell survival. Photoreceptor cell death seems to be limited to conditions that, if systemic, are embryonic lethal, indicating that reduced function of the kinesin-2 motor genes is unlikely to underlie inherited retinal degeneration.     

Early steroid withdrawal in pediatric renal transplant: five years of follow-up

This prospective, comparative trial investigated the impact on mean change in height standard deviation score (SDS), acute rejection rate, and renal function of early steroid withdrawal in 96 recipients with 5 years of follow-up. Recipients under basiliximab induction and steroid withdrawal (SW: TAC/MMF; n = 55) were compared with a matched steroid control group (SC: TAC/MMF/STEROID, n = 41). SW received steroids until Day 6, SC decreased to 10 mg/m(2) within 2 months post-transplant. Five years after SW, the longitudinal growth (SDS) gain was 1.4 ± 0.4 vs. 1.1 ± 0.3 for SC group (p < 0.02). Height benefits in prepubertal and pubertal status in both groups were demonstrated in the delta growth trends (mixed model; p < 0.01). Biopsy-proven acute rejection in SW was 11% and 17.5%, SC (p: ns). Mean eGFR (ml/min/1.73 m(2)) at 5 years post-transplant was SW 80.6 ± 27.8 vs. 82.6 ± 25.1 for SC (p: ns). The death-censored graft survival rate at 1 and 5 years was 99 and 90% for SW; 98 and 96% for SC (p = ns). PTLD incidence in SW 3.3 vs. 2.5% in SC (p: ns). Five years post-transplant, early steroid withdrawal showed positive impacts on growth, stable renal function without increased acute rejection risk, and PTLD incidence.     

Local advantage in the visual processing of hierarchical stimuli following manipulations of stimulus size and element numerosity in monkeys (Cebus apella)

Previous studies suggest that monkeys process local elements of hierarchical visual patterns more quickly and more accurately than they process the global shape. These results could be indicative of differences between relatively high visual functions of humans and non-human primates. It is, however, important to rule out that relatively low-level factors can explain these differences. We addressed this issue with two experiments carried out on capuchin monkeys (Cebus apella) using matching-to-sample tasks featuring hierarchical stimuli. The first experiment assessed whether manipulations of stimulus size can affect the local advantage so far observed in this New World monkey species. An overall local versus global advantage still emerges in capuchins, irrespectively of the amplitude of the visual angle subtended by the hierarchical shapes. Moreover, a local-to-global interference, indicative of a strong local advantage, was observed for the first time. In the second experiment, we manipulated size and numerosity of the local elements of hierarchical patterns, mimicking procedures that in human perception relegate the local elements to texture and enhance a global advantage. Our results show that in capuchin monkeys, a local advantage emerges clearly even when these procedures are used. These results are of interest since extensive neurophysiological research is carried out on non-human primate vision, often taking for granted a similarity of visual skills in human and non-human primates. These behavioural results show that this assumption is not always warranted and that more research is needed to clarify the differences in the processes involved in basic visual skills among primates.