University of Pittsburgh at Titusville

BACKGROUND: Up to 60% of patients with hepatitis C virus (HCV) genotype 1 infection do not have a sustained virologic response to therapy with peginterferon alfa plus ribavirin. METHODS: In this randomized, phase 3 trial, we evaluated the addition of telaprevir to peginterferon alfa-2a plus ribavirin in patients with HCV genotype 1 infection who had no response or a partial response to previous therapy or who had a relapse after an initial response. A total of 663 patients were assigned to one of three groups: the T12PR48 group, which received telaprevir for 12 weeks and peginterferon plus ribavirin for a total of 48 weeks; the lead-in T12PR48 group, which received 4 weeks of peginterferon plus ribavirin followed by 12 weeks of telaprevir and peginterferon plus ribavirin for a total of 48 weeks; and the control group (PR48), which received peginterferon plus ribavirin for 48 weeks. The primary end point was the rate of sustained virologic response, which was defined as undetectable HCV RNA 24 weeks after the last planned dose of a study drug. RESULTS: Rates of sustained virologic response were significantly higher in the two telaprevir groups than in the control group among patients who had a previous relapse (83% in the T12PR48 group, 88% in the lead-in T12PR48 group, and 24% in the PR48 group), a partial response (59%, 54%, and 15%, respectively), and no response (29%, 33%, and 5%, respectively) (P<0.001 for all comparisons). Grade 3 adverse events (mainly anemia, neutropenia, and leukopenia) were more frequent in the telaprevir groups than in the control group (37% vs. 22%). CONCLUSIONS: Telaprevir combined with peginterferon plus ribavirin significantly improved rates of sustained virologic response in patients with previously treated HCV infection, regardless of whether there was a lead-in phase. (Funded by Tibotec and Vertex Pharmaceuticals; REALIZE ClinicalTrials.gov number, NCT00703118.).

OBJECTIVE: This paper presents the final analysis of once-daily darunavir/ritonavir (DRV/r) vs. lopinavir/ritonavir (LPV/r) in treatment-naïve HIV-1-infected adults. METHODS: ARTEMIS (AntiRetroviral Therapy with TMC114 ExaMined In naïve Subjects; NCT00258557) was a randomized, open-label, phase-III, 192-week trial. Patients were stratified by baseline HIV-1 RNA and CD4 count, and randomized to once-daily DRV/r 800/100 mg or LPV/r 800/200 mg total daily dose (either once or twice daily) plus tenofovir/emtricitabine. RESULTS: Of 689 randomized patients receiving treatment (DRV/r: 343; LPV/r: 346), 85 and 114 patients in the DRV/r and LPV/r arms, respectively, had discontinued by week 192. Noninferiority was shown in the primary endpoint of virological response (HIV-1 RNA < 50 copies/mL) [DRV/r: 68.8%; LPV/r: 57.2%; P < 0.001; intent to treat (ITT)/time to loss of virological response; estimated difference in response 11.6% (95% confidence interval 4.4-18.8%)]. Statistical superiority in virological response of DRV/r over LPV/r was demonstrated for the primary endpoint (P = 0.002) and for the ITT non-virological-failure-censored analysis (87.4% vs. 80.8%, respectively; P = 0.040). No protease inhibitor (PI) primary mutations developed and only low levels of nucleoside reverse transcriptase inhibitor (NRTI) resistance developed in virological failures in both groups. Significantly fewer discontinuations because of adverse events were observed with DRV/r (4.7%) than with LPV/r (12.7%; P = 0.005). Grade 2-4 treatment-related diarrhoea was significantly less frequent with DRV/r than with LPV/r (5.0% vs. 11.3%, respectively; P = 0.003). DRV/r was associated with smaller median increases in total cholesterol and triglyceride levels than LPV/r. Changes in low- and high-density lipoprotein cholesterol were similar between groups. Similar increases in aspartate aminotransferase and alanine aminotransferase for DRV/r and LPV/r were observed. CONCLUSION: Over 192 weeks, once-daily DRV/r was noninferior and statistically superior in virological response to LPV/r, with a more favourable gastrointestinal profile, demonstrating its suitability for long-term use in treatment-naïve patients.

OBJECTIVE: In a sample of methadone-maintained breastfeeding women and a matched group of formula-feeding women, this study evaluated concentrations of methadone in breast milk among breastfeeding women and concentrations of methadone in maternal and infant plasma in both groups. METHODS: Eight methadone-maintained (dose: 50-105 mg/day), lactating women provided blood and breast milk specimens on days 1, 2, 3, 4, 14, and 30 after delivery, at the times of trough and peak maternal methadone levels. Paired specimens of foremilk and hindmilk were obtained at each sampling time. Eight matched formula-feeding subjects provided blood samples on the same days. Infant blood samples for both groups were obtained on day 14. Urine toxicological screening between 36 weeks of gestation and 30 days after the birth confirmed that subjects were not using illicit substances in the perinatal period. RESULTS: Concentrations of methadone in breast milk were low (range: 21.0-462.0 ng/mL) and not related to maternal dose. There was a significant increase in methadone concentrations in breast milk over time for all 4 sampling times. Concentrations of methadone in maternal plasma were not different between groups and were unrelated to maternal dose. Concentrations of methadone in infant plasma were low (range: 2.2-8.1 ng/mL) in all samples. Infants in both groups underwent neurobehavioral assessments on days 3, 14, and 30; there were no significant effects of breastfeeding on neurobehavioral outcomes. Fewer infants in the breastfed group required pharmacotherapy for neonatal abstinence syndrome, but this was not a statistically significant finding. CONCLUSION: Results contribute to the recommendation of breastfeeding for methadone-maintained women.

OBJECTIVE: The Paliperidone Palmitate Research in Demonstrating Effectiveness (PRIDE) study compared the effects of once-monthly paliperidone palmitate with daily oral antipsychotics on treatment failure in adults with schizophrenia. METHOD: The PRIDE study is a 15-month, randomized, multicenter study (May 5, 2010, to December 9, 2013) of adult subjects with a DSM-IV diagnosis of schizophrenia and a history of incarceration. Subjects were randomly assigned to once-monthly paliperidone palmitate injections or daily oral antipsychotics (randomly assigned from 7 acceptable, prespecified oral antipsychotics) for 15 months. The primary end point was time to first treatment failure, defined as arrest/incarceration; psychiatric hospitalization; suicide; treatment discontinuation or supplementation due to inadequate efficacy, safety, or tolerability; or increased psychiatric services to prevent hospitalization. Time to first treatment failure was determined by a blinded event-monitoring board and analyzed with the Kaplan-Meier method. RESULTS: In this study, 450 patients were randomly assigned, and 444 were included in the intent-to-treat population. Paliperidone palmitate was associated with significant delay in time to first treatment failure versus oral antipsychotics (hazard ratio, 1.43; 95% CI, 1.09-1.88; log rank P = .011). Observed treatment failure rates over 15 months were 39.8% and 53.7%, respectively. Arrest/incarceration and psychiatric hospitalization were the most common reasons for treatment failure in the paliperidone palmitate and oral antipsychotic groups (21.2% vs 29.4% and 8.0% vs 11.9%, respectively). The 5 most common treatment-emergent adverse events for the paliperidone palmitate treatment group were injection site pain (18.6% of subjects), insomnia (16.8%), weight increased (11.9%), akathisia (11.1%), and anxiety (10.6%). CONCLUSIONS: In a trial designed to reflect real-world management of schizophrenia, once-monthly paliperidone palmitate demonstrated superiority compared to oral antipsychotics in delaying time to treatment failure. TRIAL REGISTRATION: Clinicaltrials.gov Identifier: NCT01157351.

Childhood overweight and obesity are major health problems with immediate and long-term consequences of staggering magnitude. Despite this, there are few preventive and therapeutic strategies of proven effectiveness available to public health and clinical practitioners. Accruing such evidence is currently and appropriately a health policy priority, but there is an urgent need to intervene even before comprehensive solutions are fully established. The aim of this Clinical Report on Overweight Children and Adolescents is to present information on current understanding of pathogenesis and treatment of overweight and obesity. We report on the epidemiology, molecular biology and medical conditions associated with overweight; on dietary, exercise, behavioral, pharmacological and surgical treatments; and on the primary prevention of overweight in children and adolescents.

&lt;b&gt;&lt;i&gt;Background/Aims:&lt;/i&gt;&lt;/b&gt; Some sodium glucose co-transporter 2 (SGLT2) inhibitors are approved for the treatment of patients with type 2 diabetes mellitus (T2DM) with an estimated glomerular filtration rate (eGFR) of ≥45 ml/min/1.73 m&lt;sup&gt;2&lt;/sup&gt;. The efficacy and safety of canagliflozin, an approved SGLT2 inhibitor, was evaluated in patients with stage 3 chronic kidney disease (CKD; eGFR ≥30 to &lt;60 ml/min/1.73 m&lt;sup&gt;2&lt;/sup&gt;). &lt;b&gt;&lt;i&gt;Methods:&lt;/i&gt;&lt;/b&gt; This analysis used integrated data from four randomized, placebo-controlled, phase 3 studies that enrolled patients with T2DM and stage 3 CKD. Results are presented for the overall population as well as subgroups with stage 3a CKD (eGFR ≥45 and &lt;60 ml/min/1.73 m&lt;sup&gt;2&lt;/sup&gt;) and stage 3b CKD (eGFR ≥30 and &lt;45 ml/min/1.73 m&lt;sup&gt;2&lt;/sup&gt;). &lt;b&gt;&lt;i&gt;Results:&lt;/i&gt;&lt;/b&gt; Among all subjects studied with stage 3 CKD, placebo-subtracted reductions in HbA&lt;sub&gt;1c&lt;/sub&gt; (-0.38 and -0.47%; p &lt; 0.001), body weight (-1.6 and -1.9%; p &lt; 0.001), and systolic blood pressure (-2.8 and -4.4 mm Hg; p &lt; 0.01) were seen with canagliflozin 100 and 300 mg, respectively. Decreases in HbA&lt;sub&gt;1c&lt;/sub&gt;, body weight, and systolic blood pressure were examined in the stage 3a and 3b CKD subgroups, with greater decreases in HbA&lt;sub&gt;1c&lt;/sub&gt;, -0.47% (-0.61, -0.32) and body weight in subjects in stage 3a CKD, -1.8% (-2.3, -1.2) with canagliflozin 100 mg. Initial declines in eGFR were seen early following treatment initiation with canagliflozin, but trended towards baseline over time. The most common adverse events with canagliflozin included genital mycotic infections and adverse events related to reduced intravascular volume likely secondary to osmotic diuresis. &lt;b&gt;&lt;i&gt;Conclusion:&lt;/i&gt;&lt;/b&gt; In subjects&lt;b&gt; &lt;/b&gt;with T2DM and stage 3 CKD, canagliflozin reduced HbA&lt;sub&gt;1c&lt;/sub&gt;, body weight, and blood pressure, and was generally well tolerated.

Growing perceptions that students exploit information technology to evade academic assignments prompted surveys of student attitudes about unethical uses of information technology (e.g., cutting and pasting excerpts from Web sites without attribution) at two institutions. Students at a private church-affiliated college rated cheating behaviors as more offensive than their counterparts at a regional campus of a major research university. However, ordinal rankings of academically dishonest behaviors at both institutions were surprisingly similar (rho = .90). Further, students who rated such behaviors as being more serious, typically valued idealism, the ethical principle of doing no harm to others, and disapproved of high sensation-seeking activities involving alcohol, drugs, and sex.

The goal of this study was to estimate the effectiveness in actual clinical practice of recombinant human platelet-derived growth factor (rhPDGF) for the treatment of diabetic neuropathic foot ulcer (DNFU). Previously published pivotal trials have shown that by the 20th week of care 35 percent more ulcers healed in the group randomized to receive rhPDGF than those who did not receive rhPDGF (i.e., a relative risk [RR] of about 1.35). This represents an estimate of the efficacy of rhPDGF under the tightly controlled conditions of randomized clinical trials. Treatment effectiveness under standard clinical practice was estimated in a retrospective cohort study, controlling for treatment selection bias using propensity scores. We noted 24,898 individuals with a DNFU, of whom 9.6 percent received rhPDGF. We successfully created a propensity score model that evenly balanced many wound characteristics between those who received rhPDGF and those who did not. We created five groups, which varied from those least likely to receive rhPDGF to those most likely to receive rhPDGF. The RR, controlling for the propensity, to receive rhPDGF for a healed wound after treatment with rhPDGF as compared with standard care was 1.32 (1.22, 1.38). With respect to amputation, the RR for undergoing amputation after receiving rhPDGF was 0.65 (0.54, 0.78) as compared with those who did not receive rhPDGF. Within the limitations of our study, rhPDGF is more effective than standard therapy in both helping a wound to heal and preventing amputation, and its effect is similar to the efficacy estimates from previously published randomized controlled trials.

The objective of this analysis was to develop a semi-mechanistic nonlinear disease progression model using an expanded set of covariates that captures the longitudinal change of Alzheimer's Disease Assessment Scale (ADAS-cog) scores from the Alzheimer's Disease Neuroimaging Initiative study that consisted of 191 Alzheimer disease patients who were followed for 2 years. The model describes the rate of progression and baseline disease severity as a function of influential covariates. The covariates that were tested fell into 4 categories: (1) imaging volumetric measures, (2) serum biomarkers, (3) demographic and genetic factors, and (4) baseline cognitive tests. Covariates found to affect baseline disease status were years since disease onset, hippocampal volume, and ventricular volume. Disease progression rate in the model was influenced by age, total cholesterol, APOE ε4 genotype, Trail Making Test (part B) score, and current levels of impairment as measured by ADAS-cog. Rate of progression was slower for mild and severe Alzheimer patients compared with moderate Alzheimer patients who exhibited faster rates of deterioration. In conclusion, this model describes disease progression in Alzheimer patients using novel covariates that are important for understanding the worsening of ADAS-cog scores over time and may be useful in the future for optimizing study designs through clinical trial simulations.

The contribution of E138 mutations to etravirine resistance was investigated. Amino acids at position E138 after failure with etravirine in DUET were A (n = 1), G (n = 5), K (n = 3), P (n = 1), Q (n = 5), and V (n = 2). At baseline, only E138A and Q were found at 3.0% and 2.5%, respectively. Virologic response (less than 50 copies/mL) was observed in six of 12 and eight of 10 patients with E138A and E138Q, respectively. Site-directed mutants harboring E138A/G/K/Q/R or S showed etravirine fold change values of 2.9, 2.4, 2.6, 3.0, 3.6, and 2.8, respectively. E138G, K, and Q were added to the existing etravirine-weighted genotypic score including 17 etravirine resistance-associated mutations.

OBJECTIVE: To evaluate disposition of fentanyl in goats after IV and transdermal administration. ANIMALS: 8 healthy 2-year-old goats weighing 31.8 to 53.6 kg (mean+/-SD, 40.4+/-7.5 kg). PROCEDURE: Each goat was given 2 treatments consisting of fentanyl administered IV (2.5 microg/kg of body weight) and via a transdermal patch (50 microg/h). There was a 2-month interval between treatments. Blood samples were collected at specified times and analyzed in duplicate to determine plasma fentanyl concentrations. Pharmacokinetic values were calculated, using a computerized modeling program. RESULTS: Administration of fentanyl was tolerated by all goats. Intravenous administration of fentanyl resulted in a transitory increase in rectal temperature that was not clinically important. Terminal elimination half-life after IV administration was 1.20+/-0.78 h, volume of distribution at steady state was 1.51+/-0.39 L/kg, and systemic clearance was 2.09+/-0.62 L/kg/h. Transdermal administration of fentanyl resulted in variable plasma concentrations, with peak plasma concentrations ranging from 1.12 to 16.69 ng/ml (mean+/-SD, 6.99+/-6.03 ng/ml) and time to peak concentration ranging from 8 to 18 hours (mean+/-SD, 13+/-4.5 hours). After removal of the transdermal patch, mean+/-SD terminal elimination half-life was 5.34+/-5.34 hours. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous administration of fentanyl (2.5 microg/kg) in goats results in a relatively short half-life that will limit its use for management of pain. Transdermal administration of fentanyl (50 microg/h) in goats results in variable plasma concentrations that may exceed those anticipated on the basis of a theoretical delivery rate, but stable plasma concentrations of fentanyl may not be achieved.

This chapter contains sections titled: The Safety Charter Selling Safety to Management The System Safety Effort Life Cycle Phases and the System Safety Process

We have observed in 11 infants, aged 2 years or less, a distinct clinicopathologic lesion responsible for tachyarrhythmias that were fatal in 96% (25/26) of previously reported cases. Nine of the 11 patients, who underwent electrophysiologic mapping and surgical excision of the lesion, have survived, with follow-up periods ranging from 1 month to 6 years. The morphologic findings in these 11 patients and in the 26 cases cited in the literature are reviewed. Pathogenic considerations have included viral-induced lesion, cardiomyopathy, neoplasm, and developmental disorder of Purkinje cells. We believe this lesion to be a myocardial hamartoma. Supportive evidence includes prevalence in infants, tumorlike growth pattern without mitotic figures, and association of other developmental abnormalities. Through electrophysiologic mapping, this myocardial hamartoma is potentially accessible to surgical excision and long-term cure.

Abstract Ceroid-containing histiocytes are described for the first time in the spleen and marrow of a patient with ITP. Ceroid results from the oxidation and polymerization of unsaturated lipids and may appear in histiocytes in a variety of diseases. With the Wright or Giemsa methods, ceroid granules are stained sea-blue, and ceroid-containing macrophages appear as "sea-blue histiocytes." This sea-blue color is not pathognomonic for ceroid. Therefore, the finding of seablue histiocytes in the bone marrow should be followed by histochemical studies to confirm the presence of ceroid. The spleen from a case of the recently described "syndrome of the sea-blue histiocyte" showed numerous ceroid-containing macrophages. In view of the lack of specificity of the sea-blue histiocyte, it is suggested that the syndrome be renamed "idiopathic ceroid histiocytosis of spleen and marrow."

With healthcare representing a significant portion of the global economy, it is important to be able to understand the environmental impacts of this industry due to its size and nature of its operations.

Buprenorphine is approved as pharmacotherapy for opioid dependence in nonpregnant patients in multiple countries and is currently under investigation for pregnant women in the United States and Europe. This research evaluates the disposition of buprenorphine, opiates, cocaine, and metabolites in five term placentas from a US cohort. Placenta and matched meconium concentrations were compared, and relationships among maternal buprenorphine dose, placenta concentrations, and neonatal outcomes after controlled administration during gestation were investigated. Buprenorphine and/or metabolites were detected in all placenta specimens and were uniformly distributed across this tissue (coefficient of variation less than 27.5%, four locations), except for buprenorphine in three placentas. In two of these, buprenorphine was not detected in some locations and in the third placenta was totally absent. Median (range) concentrations were 1.6 ng/g buprenorphine (not detected to 3.2), 14.9 ng/g norbuprenorphine (6.2-24.2), 3 ng/g buprenorphine-glucuronide (1.3-5.0), and 14.7 ng/g norbuprenorphine-glucuronide (11.4-25.8). Placenta is a potential alternative matrix for detecting in utero buprenorphine exposure, but at lower concentrations (15- to 70-fold) than in meconium. Statistically significant correlations were observed for mean maternal daily dose from enrollment to delivery and placenta buprenorphine-glucuronide concentration and for norbuprenorphine-glucuronide concentrations and time to neonatal abstinence syndrome onset and duration, for norbuprenorphine/norbuprenorphine-glucuronide ratio and maximum neonatal abstinence syndrome score, and newborn length. Analysis of buprenorphine and metabolites in this alternative matrix, an abundant waste product available at the time of delivery, may be valuable for prediction of neonatal outcomes for clinicians treating newborns of buprenorphine-exposed women.

ABSTRACT The thermal oxidation of a biodiesel prepared from used vegetable oil was investigated using Fourier transform infrared (FTIR) spectroscopy. Spectral changes were observed in the hydroxyl, carbonyl, and cis/trans double bond regions for the control and Vitamin E–added samples. These spectral changes, increasing with increasing oxidation, were attributed to common oxidation products. IR results also suggested an oxidation-induced breakage of methyl ester linkages and agreed with those from selected physical property measurements. This preliminary study demonstrated the feasibility and potential of FTIR spectroscopy, a fast and reagent-free method, in assessing the oxidation state of biodiesel and providing understanding of its oxidative degradation.

Abstract. Protection against Aeromonas salmonicida was determined by passive immunization and with various bacterin preparations. Rabbit antiserum was prepared against a rough, virulent strain of A. salmonicida (AS‐1R), the same strain boiled (AS‐1R, boiled), and an avirulent, smooth strain of this same isolate (AS‐1S). Cross‐absorption, cross‐passive protection and analysis by counter immunoelectrophoresis of various extraction methods were studied. It was shown that AS‐1R cells contained an additional antigen not present in AS‐1R (boiled) and AS‐1S cells. Antiserum to the AS‐1R antigen passively protected sockeye salmon, Oncorhynchus nerka (Walbaum), against a virulent challenge, and antisera to AS‐1R (boiled) and AS‐1S were not protective. The antigen was not destroyed by formalin or heat at 5°C for 60 min, but it appeared to be partially inactivated with proteolytic enzymes. The antigen was produced in casein yeast beef (CYB) broth up to 32 h but not thereafter, and low yields were obtained in tryptic soy or brain heart infusion (BHI) broth. It was extracted from cells with ethylenediamine tetraacetic acid (EDTA) and especially alkaline hydrolysis, but not with proteolytic enzymes or detergents. The detergents appeared to destroy the antigen. We concluded that the antigen was protein and is most likely the external A‐protein (AP) reported for rough, virulent strains of A, salmonicida . Various methods of preparing A. salmonicida bacterins were evaluated by determining the level of protective immunity induced in intraperitoneally (i.p.) vaccinated fish. Growth of cells in CYB or BHI broth resulted in production of only rough (autoagglutinated in saline) variants of A. salmonicida . Although only rough variants were associated with protective immunity, one strain was not protective, it was avirulent by bath challenge. Bacterins prepared in CYB were more efficacious than those grown in BHI, but inactivation with formalin, iodine, or glutaraldehyde worked equally well. However, boiling the bacterin or filtering the cells from the bacterin removed its efficacy. Methods of releasing the AP were evaluated by sonification, pH‐lysis, disaggregation and treatment with EDTA, and all treatments worked equally well. Also, precipitation on to aluminium or use of Freund's complete adjuvant did not significantly improve the protection. In parenterally vaccinated fish, protection was demonstrated by challenging the fish at various levels by bath, injection or cohabitation with infected fish. The best protection was demonstrated using the cohabitation challenge method. The potency and field efficacy of an A. salmonicida bacterin prepared in CYB broth and extracted with 5 mM EDTA was evaluated. Fish were vaccinated by i.p, injection and potency was determined in the laboratory by experimental challenge and in the field by natural challenge. Chinook salmon, O.ishawytschu (Walbaum), developed immunity within seven days at 10°C. The bacterin could be diluted up to 1:2000 without loss of potency. The field tests results were equivocal; however, (he prevalence of infection was lower in vaccinated fish.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Amnestic mild cognitive impairment MCI) represents the prodromal stage of Alzheimer's dementia and this disease progresses in a non‐linear fashion. • Disease progression depends on a variety of demographic, biochemical, genetic and cognitive factors. WHAT THIS STUDY ADDS • Baseline CSF biomarkers carry information about disease pathology and critical thresholds for these markers (Aβ and p‐tau 181P ) have been identified that allow segregation of the population into MCI progressers and non‐progressers. AIM The objective is to develop a semi‐mechanistic disease progression model for mild cognitive impairment (MCI) subjects. The model aims to describe the longitudinal progression of ADAS‐cog scores from the Alzheimer's disease neuroimaging initiative trial that had data from 198 MCI subjects with cerebrospinal fluid (CSF) information who were followed for 3 years. METHOD Various covariates were tested on disease progression parameters and these variables fell into six categories: imaging volumetrics, biochemical, genetic, demographic, cognitive tests and CSF biomarkers. RESULTS CSF biomarkers were associated with both baseline disease score and disease progression rate in subjects with MCI. Baseline disease score was also correlated with atrophy measured using hippocampal volume. Progression rate was also predicted by executive functioning as measured by the Trail B ‐test. CONCLUSION CSF biomarkers have the ability to discriminate MCI subjects into sub‐populations that exhibit markedly different rates of disease progression on the ADAS‐cog scale. These biomarkers can therefore be utilized for designing clinical trials enriched with subjects that carry the underlying disease pathology.

Phasic variations in the size, position, and geometry of the tricuspid valve annulus during the cardiac cycle were studied in five normal anethetized dogs 2-6 weeks after 8-11 lead beads had been sutured on the endocardial surface of the valve ring during cardiopulmonary bypass. Field-by-field measurements from biplane videoangiograms were used to assess changes in valve ring size and shape during control hemodynamic conditions and during increased heart rates. In addition, the percutaneous production of a complete atrioventricular block in two dogs enabled us to observe the effect of isolated atrial contractions on the valve annulus. During normal sinus rhythm, progressive narrowing of the annulus during atrial and ventricular contractions reduced its area by 20-39% of the maximal valve circumference during diastole; approximately two-thirds of the total ring narrowing was associated with atrial systole. These findings suggest that one of the functions of atrial contraction is the reduction in size of the atrioventricular valve orifices prior to the onset of ventricular systole.