Reverse audience effects on helping in cooperatively breeding marmoset monkeys.

Cooperatively breeding common marmosets show substantial variation in the amount of help they provide. Pay-to-stay and social prestige models of helping attribute this variation to audience effects, i.e. that individuals help more if group members can witness their interactions with immatures, whereas models of kin selection, group augmentation or those stressing the need to gain parenting experience do not predict any audience effects. We quantified the readiness of adult marmosets to share food in the presence or absence of other group members. Contrary to both predictions, we found a reverse audience effect on food-sharing behaviour: marmosets would systematically share more food with immatures when no audience was present. Thus, helping in common marmosets, at least in related family groups, does not support the pay-to-stay or the social prestige model, and helpers do not take advantage of the opportunity to engage in reputation management. Rather, the results appear to reflect a genuine concern for the immatures' well-being, which seems particularly strong when solely responsible for the immatures.

Towards integrating joint action research: Developmental and evolutionary perspectives on co-representation.

Joint action has increasingly become a key topic to understand the emergence of the human mind. The phenomenon is closely linked to several theoretical concepts, such as shared intentionality, which are difficult to operationalize empirically. We therefore employ a paradigm-driven, bottom-up approach, and as such discuss co-representing the partner's and one's own actions as key mechanism for joint action. After embedding co-representation in the broader landscape of related theoretical concepts, we review neurobiological, ontogenetic, and phylogenetic studies, with a focus on whether co-representation and its flexible deployment should be construed as a low- or high-level cognitive process. The empirical findings convergently suggest that co-representation does not require strong inhibitory skills or mentalistic understanding and occurs automatically. Moreover, more cooperative species are better at flexibly suppressing co-representation when required for cooperation success, and frequently rely on cooperation markers, such as mutual gaze. We thus contribute to closing the current gap between theoretical concepts related to joint action research and their empirical investigation, and end by highlighting additional approaches for doing so.

A convergent interaction engine: vocal communication among marmoset monkeys.

To understand the primate origins of the human interaction engine, it is worthwhile to focus not only on great apes but also on callitrichid monkeys (marmosets and tamarins). Like humans, but unlike great apes, callitrichids are cooperative breeders, and thus habitually engage in coordinated joint actions, for instance when an infant is handed over from one group member to another. We first explore the hypothesis that these habitual cooperative interactions, the marmoset interactional ethology, are supported by the same key elements as found in the human interaction engine: mutual gaze (during joint action), turn-taking, volubility, as well as group-wide prosociality and trust. Marmosets show clear evidence of these features. We next examine the prediction that, if such an interaction engine can indeed give rise to more flexible communication, callitrichids may also possess elaborate communicative skills. A review of marmoset vocal communication confirms unusual abilities in these small primates: high volubility and large vocal repertoires, vocal learning and babbling in immatures, and voluntary usage and control. We end by discussing how the adoption of cooperative breeding during human evolution may have catalysed language evolution by adding these convergent consequences to the great ape-like cognitive system of our hominin ancestors. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Trade-offs between vocal accommodation and individual recognisability in common marmoset vocalizations.

Recent studies find increasing evidence for vocal accommodation in nonhuman primates, indicating that this form of vocal learning is more prevalent than previously thought. Convergent vocal accommodation (i.e. becoming more similar to partners) indicates social closeness. At the same time, however, becoming too similar may compromise individual recognisability. This is especially problematic if individual recognisability is an important part of the call function, like in long-distance contact calls. In contrast, in calls with a different function, the trade-off between signalling social closeness and individual recognisability might be less severe. We therefore hypothesized that the extent and consequences of accommodation depend on the function of a given call, and expected (1) more accommodation in calls for which individual identity is less crucial and (2) that individual identity is less compromised in calls that serve mainly to transmit identity compared to calls where individual recognisability is less important. We quantified vocal accommodation in three call types over the process of pair formation in common marmoset monkeys (Callithrix jacchus, n = 20). These three call types have different functions and vary with the degree to which they refer to individual identity of the caller. In accordance with our predictions, we found that animals converged most in close contact calls (trill calls), but less in calls where individual identity is more essential (phee- and food calls). In two out of three call types, the amount of accommodation was predicted by the initial vocal distance. Moreover, accommodation led to a drop in statistical individual recognisability in trill calls, but not in phee calls and food calls. Overall, our study shows that patterns of vocal accommodation vary between call types with different functions, suggestive of trade-offs between signalling social closeness and individual recognisability in marmoset vocalizations.

Do marmosets understand others' conversations? A thermography approach.

What information animals derive from eavesdropping on interactions between conspecifics, and whether they assign value to it, is difficult to assess because overt behavioral reactions are often lacking. An inside perspective of how observers perceive and process such interactions is thus paramount. Here, we investigate what happens in the mind of marmoset monkeys when they hear playbacks of positive or negative third-party vocal interactions, by combining thermography to assess physiological reactions and behavioral preference measures. The physiological reactions show that playbacks were perceived and processed holistically as interactions rather than as the sum of the separate elements. Subsequently, the animals preferred those individuals who had been simulated to engage in positive, cooperative vocal interactions during the playbacks. By using thermography to disentangle the mechanics of marmoset sociality, we thus find that marmosets eavesdrop on and socially evaluate vocal exchanges and use this information to distinguish between cooperative and noncooperative conspecifics.

The use of infrared thermography to investigate emotions in common marmosets.

Measuring body surface temperature changes with infrared thermography has recently been put forward as a non-invasive alternative measure of physiological correlates of emotional reactions. In particular, the nasal region seems to be highly sensitive to emotional reactions. Several studies suggest that nasal temperature is negatively correlated with the level of arousal in humans and other primates, but some studies provide inconsistent results. Our goal was to establish the use of infrared thermography to quantify emotional reactions in common marmosets (Callithrix jacchus), with a focus on the nasal region. To do so we exposed 17 common marmosets to a set of positive, negative and control stimuli (positive: preferred food, playback of food calls; negative: playback of aggressive vocalizations, teasing; control: no stimulus). We compared nasal temperature before and after the stimuli and expected that highly aroused emotional states would lead to a drop in nasal temperature. To validate the thermography measure, we coded piloerection of the tail as an independent measure of arousal and expected a negative correlation between the two measures. Finally, we coded physical activity to exclude its potential confounding impact on nasal temperature. Our results show that all predictions were met: the animals showed a strong decrease in nasal temperature after the presentation of negative arousing stimuli (teasing, playback of aggressive vocalizations). Furthermore, these changes in nasal temperature were correlated with piloerection of the tail and could not be explained by changes in physical activity. In the positive and the control conditions, we found systematic sex differences: in males, the preferred food, the playbacks of food calls, as well as the control stimulus led to an increase in nasal temperature, whereas in females the temperature remained stable (preferred food, control) or decreased (playback of food calls). Based on naturalistic observations that document higher food motivation and competition among female marmosets, as well as stronger reactions to separation from group members in male marmosets, these sex differences corroborate a negative correlation between arousal and nasal temperature. Overall, our results support that measuring nasal temperature by infrared thermography is a promising method to quantify emotional arousal in common marmosets in a fully non-invasive and highly objective way.

A multicenter study of noncompliance with continuous ambulatory peritoneal dialysis exchanges in US and Canadian patients.

Recent evidence suggested that noncompliance (NC) with continuous ambulatory peritoneal dialysis (CAPD) exchanges may be more common in US than in Canadian dialysis centers. This issue was investigated using a questionnaire-based method in 656 CAPD patients at 14 centers in the United States and Canada. NC was defined as missing more than one exchange per week or more than two exchanges per month. Patients were ensured of the confidentiality of their individual results. Mean patient age was 56 +/- 16 years, 52% were women, and 39% had diabetes. The overall admitted rate of NC was 13%, with a rate of 18% in the United States and 7% in Canada (P < 0.001). NC was more common in younger patients (P < 0.0001), those without diabetes (P < 0.001), and employed patients (P < 0.05). It was also more common in black and Hispanic than in Asian and white patients (P < 0.001). NC was more common in patients prescribed more than four exchanges daily (P < 0.0001) but was not affected by dwell volume. On multiple regression analysis, the independent predictors of NC, in order of importance, were being prescribed more than four exchanges per day, black race, being employed, younger age, and not having diabetes. Being treated in a US unit did not quite achieve significance as a multivariate independent predictor. These findings suggest that NC is not uncommon in CAPD patients and is more frequent in US than in Canadian patients. However, country of residence is less powerful as a predictor of NC than a variety of other demographic and prescription factors.

The Kidney Outcomes Prediction and Evaluation (KOPE) study: a prospective cohort investigation of patients undergoing hemodialysis. Study design and baseline characteristics.

PURPOSE: The purpose of the Kidney Outcomes Prediction and Evaluation (KOPE) study, was to more fully characterize the end-stage renal disease (ESRD) population with respect to social, psychological, and clinical characteristics, and to prospectively study the biomedical, social, and psychological factors that influence a range of ESRD outcomes in a large observational study of black and white patients on hemodialysis. This paper focuses on the KOPE study design as well as characteristics of patients at baseline. METHODS: KOPE was a prospective cohort investigation of patients treated at four dialysis centers in Forsyth County, North Carolina. Participants were interviewed at the dialysis centers, semi-annually over a 3 1/2 year period. Prevalent cases who were being treated with hemodialysis at the initiation of the study were enrolled into KOPE. Incident cases were subsequently enrolled as they presented to the participating units for hemodialysis. A total of 304 prevalent and 162 incident cases were enrolled into the study. The baseline health and sociodemographic characteristics of KOPE participants reported in this paper were obtained from medical records and Southeast Kidney Council data. Laboratory values taken within a 30-day interval around the baseline interview are also reported. RESULTS: KOPE participants differ from national statistics on race, age, and gender. Differences between KOPE participants and patients living in the region, but who did not participate in the study, can be explained by our recruitment criteria. CONCLUSIONS: KOPE will enable the characterization of the ESRD population, identification of factors related to poor outcomes, and identification of opportunities for interventions to prevent death and morbidity.

Effects of hemodialysis on prostate-specific antigen.

We undertook a prospective study to evaluate the effects of hemodialysis on serum prostate-specific antigen (PSA) in 26 male patients with end-stage renal disease as a clinical model for assessing the role of the kidney in PSA clearance. Patients ranging in age from fifty-one to eighty-three years (mean 64.8 years) underwent phlebotomy immediately before and after outpatient hemodialysis on a Monday/Wednesday/Friday or Tuesday/Thursday/Saturday schedule, with serum PSA values determined by the Abbott IMX Microparticle Enzyme Immunoassay. The mean +/- standard deviation for all post-dialysis PSA levels, 2.43 +/- 3.74, was significantly greater than that for pre-dialysis levels, 2.11 +/- 3.19 (p = 0.04). However, no statistically significant differences were found on comparing the combined pre- and post-dialysis PSA values over the course of the study (p = 0.2733) or when sequential pre-dialysis (p = 0.28) and post-dialysis (p = 0.92) levels were analyzed separately. We conclude that PSA is not eliminated by hemodialysis, and our results infer that it is not cleared by renal mechanisms.

Endocrine crises. Hypokalemia.

Hypokalemia is a common and potentially life-threatening electrolyte disturbance. This article reviews normal potassium homeostasis and transcellular potassium movement. In addition, extrarenal and renal causes of hypokalemia are discussed. The authors conclude this article with a simple approach to evaluation and management of hypokalemia in the intensive care unit setting.

Significance, epidemiology, and prevention of peritoneal dialysis catheter infections.

Catheter infections are a major cause of morbidity, catheter loss, and transfer to hemodialysis. These infections are mainly due to S. aureus. To date, treatment is less than optimal. Therefore, the primary goal should be prevention of catheter infections. Prevention is based on improving catheter design and implantation technique while using careful exit-site care. Prophylaxis with antimicrobials such as intranasal mupirocin or the use of silver-impregnated catheters appears promising as a way to reduce the risk of developing S. aureus infections. To optimize patient outcome, one must focus on these preventive measures.

Recommendations for clinical practice and research needs directed at reducing morbidity and mortality in peritoneal dialysis.

These presentations highlighted some of the current research needs in peritoneal dialysis. They are not meant to eclipse other important issues, such as adequacy and nutrition. These needs have become apparent as the therapy has evolved and progressed. They in fact are a testament to the increasing acceptance, use, and development of the therapy and suggest that there is potential for even further advancement for the therapy of peritoneal dialysis in the future.

Effect of peritoneal dialysis prescription and peritoneal membrane transport characteristics on nutritional status.

These data suggest that dialysis dose is one of the major determinants of protein and energy intake in PD patients and that higher doses of dialysis tend to improve outcome. The data also suggest that with a long time on PD the peritoneal membrane probably has some underlying histological changes that preclude it from optimally responding to injury and may predispose it to irreversible damage. A possible early finding in this case is an increase in peritoneal transport in patients whose transport was initially stable. Peritoneal membrane transport properties are an important determinant of not only dialysis dose, but also nutritional status via both direct and indirect means. It is therefore important to identify the individual patient's peritoneal membrane transport characteristics. These transport characteristics may change over time. High transporters on CAPD represent a unique challenge. They have ultrafiltration problems and a tendency toward protein malnutrition presumably due to increased dialysate protein losses while on CAPD. One must consider that malnutrition in a rapid transporter may be due to the fact that the patient is on the wrong PD therapy. A change to NIPD may rectify some of the biochemical parameters, but these patients may not always improve. Reasons for this occasional lack of improvement are multifactorial, but emphasize our need to look at each patient as an individual and not focus only on laboratory parameters.

Incremental initiation of dialysis: one center's experience over a two-year period.

OBJECTIVE: This pilot study describes our center's experience with peritoneal dialysis (PD) over the past 2 years using a "healthy start" dialysis protocol with an incremental approach to prescription management. DESIGN: Nonrandomized, prospective pilot study. SETTING: Single PD unit of a university teaching hospital. PATIENTS: Thirteen PD patients who initiated dialysis at our center from April 1997 to June 1999. METHODS: Patients initiating PD with residual renal Kt/V of 1.0 - 2.0/week were invited to participate. They were given an initial dialysis prescription so that total (residual renal + dialysis) weekly Kt/V exceeded 2.0. The dialysis prescription was "incrementally" increased as residual renal function (RRF) declined. Data collected for all patients included monthly serum chemistries, residual renal weekly Kt/V and creatinine clearance (CCr) at 1- to 2-month intervals, and peritoneal weekly Kt/V and CCr at 3-month intervals and 1 month after each prescription change. RESULTS: To date, we have followed 13 patients on our incremental PD protocol for a total of 159.3 patient-months. Mean serum albumin concentration and mean normalized protein equivalent of nitrogen appearance (nPNA) were stable throughout the study. Mean total Kt/V and CCr remained above the recommended targets of 2.0/wk and 60 L/wk, respectively. Residual renal function declined rather slowly in our PD patients. One patient died from complications of aortic valve surgery and a second died from pneumonia. A third patient died from peritonitis. One patient required a new Tenckhoff catheter after catheter migration. Three patients were temporarily switched to hemodialysis after a hernia repair, a pleural leak, and elective native/transplant nephrectomies, respectively. Two patients were permanently switched to hemodialysis: one after an episode of peritonitis, the second after accidentally damaging his PD catheter. CONCLUSIONS: Providing incremental dialysis to maintain adequate total small solute clearance has been technically feasible in our patient population. However, a larger than expected number of complications was seen in our study. Fortunately, complications were easier to manage due to the presence of RRF. Because this study was not designed to compare outcome with that observed after traditional initiation of dialysis, further large-scale studies are needed.

Assessment of dialysis dose by measured clearance versus extrapolated data.

OBJECTIVE: To determine whether estimates of daily dialysis clearance of creatinine and urea, based on data from the 4-hour peritoneal equilibration test, correlate well with daily dialysis clearance measured by 24-hour dialysate collection in chronic ambulatory peritoneal dialysis patients. DESIGN: Prospective study in which each subject collected all dialysate from a 24-hour period and then immediately thereafter underwent a standard peritoneal equilibration test (PET). Daily clearances of creatinine and urea were calculated from 24-hour dialysate collections by standard methods and then were compared with several estimates of 24-hour clearance based on PET data. SETTING: Single peritoneal dialysis unit of a university teaching hospital. PATIENTS: Thirty-six stable patients on continuous ambulatory peritoneal dialysis (CAPD). MAIN OUTCOME: The estimated values for daily dialysis clearance both overestimated and underestimated the measured 24-hour clearance. The correlation coefficient between the extrapolations and the actual 24-hour clearances ranged from 0.63-0.68. The range of discordance for daily creatinine clearance was from -2530 mL/day to +2199 mL/day. For daily urea clearance, the range of discordance was from -2103 mL/day to +1940 mL/day. The peritoneal membrane transport characteristics of the individual patient did not predict whether the extrapolation overestimated or underestimated the measured daily clearance. CONCLUSION: Extrapolation of PET data is not a reliable method to estimate the dose of dialysis delivered to the patient. A 24-hour collection of dialysis is necessary for this determination.

24-hour dialysate collection for determination of peritoneal membrane transport characteristics: longitudinal follow-up data for the dialysis adequacy and transport test (DATT).

OBJECTIVE: To determine the ability of the dialysis adequacy and transport test (DATT) to monitor changes in peritoneal transport characteristics over time. SETTING: University-based peritoneal dialysis program. PATIENTS: One hundred patients on continuous ambulatory peritoneal dialysis who underwent 226 simultaneous DATTs and peritoneal equilibration tests (PET). METHODS: Retrospective analysis of DATT and PET data. RESULTS: The mean 24-hour dialysate-to-plasma creatinine (cr) concentration ratio (D/P cr) from the DATT was 0.70 +/- 0.10, and the mean four-hour D/P cr from the PET was 0.68 +/- 0.10. The correlation coefficient between the four-hour and 24-hour D/P cr was 0.81, and the standard error of estimate was 0.065. The mean (+/- SD) difference between the four-hour and 24-hour D/P cr was 0.023 +/- 0.061. Fifty-eight patients had two or more sequential DATTs and PETs. For these 94 sets of sequential DATTs and PETs, the mean (+/- SD) difference between the change in the four-hour D/P cr and the change in the 24-hour D/P cr was 0.020 +/- 0.024, and the standard error of estimate was 0.064. In 17 patients a change in dwell volume from 2.0 L to 2.5 L occurred between the first and second measures of peritoneal membrane transport characteristics. The mean (+/- SD) difference between the change in the four-hour D/P cr and the change in the 24-hour D/P cr was 0.036 +/- 0.055, and the standard error of estimate was 0.087. CONCLUSION: The DATT can be used to monitor for changes in peritoneal transport over time. It should not be used in patients receiving cycler therapy or in patients whose dwell times and dextrose concentrations vary markedly from day to day.

Comparison of peritonitis rates during long-term use of standard spike versus Ultraset in continuous ambulatory peritoneal dialysis (CAPD).

Continuous ambulatory peritoneal dialysis (CAPD) is an increasingly popular means of end-stage renal disease replacement therapy. Unfortunately, peritonitis continues to be a major source of both morbidity and mortality. The Ultraset incorporates a "flush-before-fill" concept which should theoretically decrease peritonitis rates when compared to the standard spike procedure, while allowing patients the convenience of disconnect. To investigate the impact of long-term use of the Ultraset on peritonitis rates, we conducted the following study. We prospectively compared 21 new CAPD patients using the standard spike to 20 new CAPD patients using the Ultraset. Peritonitis episodes, episodes of exit-site infection, and the association of peritonitis with exit-site infection were monitored. Peritonitis rates were 7.57 months/episode for the group using the standard spike vs. 27.79 months/episode in the group using the Ultraset. Exit-site infection rates were 22.21 months/infection with the standard spike vs. 37.05 months/infection with the Ultraset. Using Kaplan-Meier plots, there was a statistically significant difference in the estimated time to the first episode of peritonitis, but there was no statistically significant difference regarding the risk of exit-site infections.

Changes in peritoneal transport during the first month of peritoneal dialysis.

OBJECTIVE: To determine if peritoneal transport characteristics change during the initial month of peritoneal dialysis. DESIGN: Retrospective review of peritoneal equilibration test (PET) results in patients who received their first PET during the first two weeks of peritoneal dialysis (early PET group) versus patients who received their first PET between four and 28 weeks after the initiation of dialysis (late PET group). The initial PET values were compared to subsequent PET results obtained approximately seven months after the initial PET. SETTING: Peritoneal dialysis unit of a tertiary medical center. OUTCOME MEASURES: PET results and calculated mass transfer area coefficient (MTAC) values. PATIENTS: Thirty-four peritoneal dialysis patients in the early PET group and 17 peritoneal dialysis patients in the late PET group. RESULTS: In the early PET group, there was a statistically significant increase from the initial to follow-up values for both dialysate-to-plasma (D/P) creatinine and MTAC creatinine (p < 0.01) as well as a significant decrease for four-hour dialysate to initial dialysate ratios (D/Do) glucose (p = 0.08) and MTAC glucose (p < 0.05). In the late PET group, there was no significant change in any of these parameters with time. However, in the late PET group, there was a significant decrease in D/P urea values with time (p < 0.01), but not with MTAC urea. In addition, there were no differences over time in either group for serum albumin or hematocrit values. CONCLUSION: During the first two weeks of peritoneal dialysis, there tends to be a change in peritoneal transport characteristics in some patients. PET data obtained during this time period should be interpreted as preliminary.

Comparison of exit-site infections in disconnect versus nondisconnect systems for peritoneal dialysis.

OBJECTIVE: To determine if disconnect systems reduce the incidence of exit-site infections when compared to nondisconnect systems. DESIGN: We prospectively monitored exit-site infections and peritonitis rates in 96 disconnect patients (Y-set, automated peritoneal dialysis (APD)) and 60 nondisconnect patients (spike, ultraviolet connection device (UVXD)). SETTING: A freestanding chronic peritoneal dialysis unit staffed by physicians from both a medical school and a private setting. PATIENTS: All patients who began peritoneal dialysis at our unit were monitored, regardless of cause of end-stage renal disease (ESRD) or age. INTERVENTION: Patients were dialyzed using the system (Y-set, spike, etc.) most appropriate for their life-style and their ability to administer self-care. MAIN OUTCOME: We attempted to follow disconnect and nondisconnect patients for a similar median time on dialysis and compared differences in exit-site infections. RESULTS: Peritonitis rates (episodes/pt year) were reduced for disconnect (0.60) versus nondisconnect (0.99) systems (p = 0.0006). Despite the marked reduction in peritonitis rates, there was no difference in exit-site infection rates (0.35 vs 0.38), the time to the first exit-site infection, or the time to the first catheter removal for disconnect versus nondisconnect groups. When individual systems were compared, differences in exit-site infection rates (episodes/pt years) were noted (0.62,spike; 0.26,UVXD; 0.32,Y-set; 0.41,APD). CONCLUSION: We found no overall difference in exit-site infection rates for disconnect versus nondisconnect systems, despite a reduction in peritonitis rates for disconnect systems.