Gadoxetic acid-enhanced magnetic resonance imaging significantly influences the clinical course in patients with colorectal liver metastases.

BACKGROUND: Gadoxetic acid (Primovist™)-enhanced magnetic resonance imaging (P-MRI) scans have higher accuracy and increased detection of small colorectal liver metastases (CRLM) compared to CT scans or conventional MRI scans. But, P-MRI scans are still inconsistently acquired in the diagnostic work up of patients with CRLM. The aim of this study was to determine the influence of P-MRI scans on treatment plan proposition and subsequently the clinical course of the patient. METHODS: Eighty-three consecutive patients with potentially resectable CRLM based on a conventional CT scan underwent P-MRI scanning prior to treatment. Treatment plans proposed by the multidisciplinary team were compared before and after P-MRI scanning and related to the final treatment and diagnosis, the accuracy for the CT scan and P-MRI scan was calculated. RESULTS: P-MRI scans led to a change of treatment in 15 patients (18%) and alteration of extensiveness of local therapy in another 17 patients (20%). All changes were justified leading to an accuracy of 93% for treatment proposition based on P-MRI scan, compared to an accuracy of 75% for the CT scan. CONCLUSIONS: P-MRI scans provide additional information that can aid in proposing the most suitable treatment for patients with CRLM and might prevent short-term reintervention.

Four-month metacarpal bone mineral density loss predicts radiological joint damage progression after 1†year in patients with early rheumatoid arthritis: exploratory analyses from the IMPROVED study.

AIM: To assess whether in early (rheumatoid) arthritis (RA) patients, metacarpal bone mineral density (BMD) loss after 4 months predicts radiological progression after 1 year of antirheumatic treatment. METHODS: Metacarpal BMD was measured 4 monthly during the first year by digital X-ray radiogrammetry (DXR-BMD) in patients participating in the IMPROVED study, a clinical trial in 610 patients with recent onset RA (2010 criteria) or undifferentiated arthritis, treated according to a remission (disease activity score<1.6) steered strategy. With Sharp/van der Heijde progression ≥0.5 points after 1 year (yes/no) as dependent variable, univariate and multivariate logistic regression analyses were performed. RESULTS: Of 428 patients with DXR-BMD results and progression scores available, 28 (7%) had radiological progression after 1 year. Independent predictors for radiological progression were presence of baseline erosions (OR (95% CI) 6.5 (1.7 to 25)) and early DXR-BMD loss (OR (95% CI) 1.5 (1.1 to 2.0)). In 366 (86%) patients without baseline erosions, early DXR-BMD loss was the only independent predictor of progression (OR (95% CI) 2.0 (1.4 to 2.9)). CONCLUSIONS: In early RA patients, metacarpal BMD loss after 4 months of treatment is an independent predictor of radiological progression after 1 year. In patients without baseline erosions, early metacarpal BMD loss is the main predictor of radiological progression.

A two-step treatment strategy trial in patients with early arthritis aimed at achieving remission: the IMPROVED study.

OBJECTIVES: To assess which treatment strategy is most effective in inducing remission in early (rheumatoid) arthritis. METHODS: 610 patients with early rheumatoid arthritis (RA 2010 criteria) or undifferentiated arthritis (UA) started treatment with methotrexate (MTX) and a tapered high dose of prednisone. Patients in early remission (Disease Activity Score <1.6 after 4 months) tapered prednisone to zero and those with persistent remission after 8 months, tapered and stopped MTX. Patients not in early remission were randomised to receive either MTX plus hydroxychloroquine plus sulfasalazine plus low-dose prednisone (arm 1) or to MTX plus adalimumab (ADA) (arm 2). If remission was present after 8 months both arms tapered to MTX monotherapy; if not, arm 1 changed to MTX plus ADA and arm 2 increased the dose of ADA. Remission rates and functional and radiological outcomes were compared between arms and between patients with RA and those with UA. RESULTS: 375/610 (61%) patients achieved early remission. After 1 year 68% of those were in remission and 32% in drug-free remission. Of the randomised patients, 25% in arm 1 and 41% in arm 2 achieved remission at year 1 (p<0.01). Outcomes were comparable between patients with RA and those with UA. CONCLUSIONS: Initial MTX and prednisone resulted in early remission in 61% of patients with early (rheumatoid) arthritis. Of those, 68% were in remission and 32% were in drug-free remission after 1 year. In patients not in early remission, earlier introduction of ADA resulted in more remission at year 1 than first treating with disease-modifying antirheumatic drug combination therapy plus prednisone.

Impact of cancer-associated mutations in CC chemokine receptor 2 on receptor function and antagonism.

CC chemokine receptor 2 (CCR2), a G protein-coupled receptor, plays a role in many cancer-related processes such as metastasis formation and immunosuppression. Since âˆ¼ 20 % of human cancers contain mutations in G protein-coupled receptors, ten cancer-associated CCR2 mutants obtained from the Genome Data Commons were investigated for their effect on receptor functionality and antagonist binding. Mutations were selected based on either their vicinity to CCR2's orthosteric or allosteric binding sites or their presence in conserved amino acid motifs. One of the mutant receptors, namely S101P2.63 with a mutation near the orthosteric binding site, did not express on the cell surface. All other studied mutants showed a decrease in or a lack of G protein activation in response to the main endogenous CCR2 ligand CCL2, but no change in potency was observed. Furthermore, INCB3344 and LUF7482 were chosen as representative orthosteric and allosteric antagonists, respectively. No change in potency was observed in a functional assay, but mutations located at F1163.28 impacted orthosteric antagonist binding significantly, while allosteric antagonist binding was abolished for L134Q3.46 and D137N3.49 mutants. As CC chemokine receptor 2 is an attractive drug target in cancer, the negative effect of these mutations on receptor functionality and drugability should be considered in the drug discovery process.

Towards personalized treatment: predictors of short-term HAQ response in recent-onset active rheumatoid arthritis are different from predictors of rapid radiological progression.

OBJECTIVE: Personalized treatment depends on the treatment goals. Current prediction models to guide initial treatment choices focus on radiological damage progression. However, for some patients this outcome is less relevant, whereas short-term functional ability is relevant to all. Do these various treatment goals share the same predictors? METHODS: Data for 497 patients from the Dutch Behandel Strategieen (BeSt) study of treatment strategies for early rheumatoid arthritis (RA), randomized to initial monotherapy or combination therapy, were used. Predictors of short-term functional disability [Health Assessment Questionnaire (HAQ) score ≥ 1 after 3 months of treatment] were identified with logistic regression analyses. Predicted risks of a HAQ score ≥ 1 were determined for each treatment group and for each subpopulation. RESULTS: At baseline, 76% of patients had a HAQ score ≥ 1 (mean 1.7 ± 0.5). After 3 months of treatment this score was achieved by 40% (mean HAQ score 1.5 ± 0.5). Baseline HAQ score, pain, the Ritchie Articular Index (RAI), and treatment group were significant independent predictors for a HAQ score ≥ 1; the presence of rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) antibodies, and baseline radiological damage were not. With cut-offs of 35% and 60%, the risk of a HAQ score ≥ 1 was high for 47% and low for 20% of the patients treated with initial monotherapy. Risks were markedly reduced in the combination therapy groups, also in unfavourable risk profiles. CONCLUSION: In recent-onset active RA, baseline HAQ score, pain, and initial treatment are predictors for a HAQ score ≥ 1 after 3 months. Known predictors of radiological damage were not predictive of short-term functional disability. The choice of the best initial treatment thus depends on the relevance of various outcome measures for an individual patient.

Inflation and deflation timing of the AutoCAT 2 WAVE intra-aortic balloon pump using the autoPilot mode in a clinical setting.

The primary goal of this observational clinical study was to register the occurrence of incorrect inflation and deflation timing of an intra-aortic balloon pump in autoPilot mode. The secondary goal was to identify possible causes of incorrect timing. During IABP assistance of 60 patients, every four hours a strip was printed with the IABP frequency set to 1:2. Strips were examined for timing discrepancies beyond 40 ms from the dicrotic notch (inflation) and the end of the diastolic phase (deflation). In this way, 320 printed strips were examined. A total of 52 strips (16%) showed incorrect timing. On 24 of these strips, the incorrect timing was called incidental, as it showed on only one or a few beats. The other 28 cases of erroneous timing were called consistent, as more than 50% of the beats on the strip showed incorrect timing. We observed arrhythmia in 69% of all cases of incorrect timing. When timing was correct, arrhythmia was found on 13 (5%) of 268 strips. A poor quality electrocardiograph (ECG) signal showed on 37% of all strips with incorrect timing and 11% of all strips with proper timing. We conclude that inflation and deflation timing of the IABP is not always correct when using the autoPilot mode. The quality of the ECG input signal and the occurrence of arrhythmia appear to be related to erroneous timing. Switching from autoPilot mode to operator mode may not always prevent incorrect timing.

A Pilot Study on the Effect of Peer Support on Quality of Life of Adolescents with Autism Spectrum Disorder and Gender Dysphoria.

Gender dysphoria (GD) and Autism Spectrum Disorder (ASD) co-occur relatively often, but there is no evidence-based treatment for this specific group. Therefore, we examined the effects of a group intervention for adolescents with ASD and GD in a pilot study with a pre-post-test design. The adolescents completed questionnaires on quality of life, self-esteem, gender dysphoric feelings, and social responsiveness. Results show that participating in this peer support group seems to increase aspects of quality of life, i.e., increased parent-reported psychological well-being and decreased psychological complaints. Even though more research is needed, these results indicate that peer support is an invaluable part of treatment for adolescents with ASD and GD.

A matrix risk model for the prediction of rapid radiographic progression in patients with rheumatoid arthritis receiving different dynamic treatment strategies: post hoc analyses from the BeSt study.

OBJECTIVES: To develop a matrix model for the prediction of rapid radiographic progression (RRP) in subpopulations of patients with recent-onset rheumatoid arthritis (RA) receiving different dynamic treatment strategies. METHODS: Data from 465 patients with recent-onset RA randomised to receive initial monotherapy or combination therapy were used. Predictors for RRP (increase in Sharp-van der Heijde score > or =5 after 1 year) were identified by multivariate logistic regression analysis. For subpopulations, the estimated risk of RRP per treatment group and the number needed to treat (NNT) were visualised in a matrix. RESULTS: The presence of autoantibodies, baseline C-reactive protein (CRP) level, erosion score and treatment group were significant independent predictors of RRP in the matrix. Combination therapy was associated with a markedly reduced risk of RRP. The positive and negative predictive values of the matrix were 62% and 91%, respectively. The NNT with initial combination therapy to prevent one patient from RRP with monotherapy was in the range 2-3, 3-7 and 7-25 for patients with a high, intermediate and low predicted risk, respectively. CONCLUSION: The matrix model visualises the risk of RRP for subpopulations of patients with recent-onset RA if treated dynamically with initial monotherapy or combination therapy. Rheumatologists might use the matrix for weighing their initial treatment choice.

Use of methotrexate in undifferentiated arthritis.

The prognosis of patients with undifferentiated arthritis (UA) may vary from self-limited to severe destructive rheumatoid arthritis (RA). Based on the chance that these patients will develop RA and based on the safety profile of a course of methotrexate for 30-90 days, many clinicians consider using methotrexate in this patient category using the "n of 1" trial principle. During the last few years, more data on interventions in UA have become available that provide guidance in the prescription of drugs to UA patients.

Optimal dosage and route of administration of methotrexate in rheumatoid arthritis: a systematic review of the literature.

OBJECTIVES: To review systematically the available literature on the optimal dosage and route of administration of methotrexate in patients with rheumatoid arthritis (RA), as an evidence base for generating clinical practice recommendations. METHODS: A systematic literature search was carried out in MEDLINE, EMBASE, Cochrane Library and American College of Rheumatology/European League Against Rheumatism meeting abstracts, searching for randomised controlled trials evaluating various dosages or routes of administration of methotrexate in RA. Articles that fulfilled predefined inclusion criteria were systematically reviewed and the quality was appraised. Effect sizes and odds ratios for clinical, radiological and toxicity outcomes were calculated and directly or indirectly compared between study groups using methotrexate in different dosages or by different routes. RESULTS: A total of 38 publications out of 1748 identified references was included in the review. Start doses of 25 mg/week or fast escalation with 5 mg/month to 25-30 mg/week were associated with higher clinical effect sizes and more (gastrointestinal) adverse events in comparison with doses of 5-15 mg/week or slow escalation. Starting with 15 mg/week subcutaneous versus oral methotrexate was associated with higher clinical efficacy but more withdrawal due to toxicity in early RA. In longstanding RA, after failure on 15-20 mg/week orally, a switch to 15 mg/week intramuscularly with subsequent dose escalation did not result in increased efficacy. CONCLUSIONS: Starting on methotrexate 15 mg/week orally, escalating with 5 mg/month to 25-30 mg/week, or the highest tolerable dose, with a subsequent switch to subcutaneous administration in the case of an insufficient response, seems to be the optimal evidence-based dosing and routing recommendation for methotrexate in RA.

Multinational evidence-based recommendations for the use of methotrexate in rheumatic disorders with a focus on rheumatoid arthritis: integrating systematic literature research and expert opinion of a broad international panel of rheumatologists in the 3E Initiative.

OBJECTIVES: To develop evidence-based recommendations for the use of methotrexate in daily clinical practice in rheumatic disorders. METHODS: 751 rheumatologists from 17 countries participated in the 3E (Evidence, Expertise, Exchange) Initiative of 2007-8 consisting of three separate rounds of discussions and Delphi votes. Ten clinical questions concerning the use of methotrexate in rheumatic disorders were formulated. A systematic literature search in Medline, Embase, Cochrane Library and 2005-7 American College of Rheumatology/European League Against Rheumatism meeting abstracts was conducted. Selected articles were systematically reviewed and the evidence was appraised according to the Oxford levels of evidence. Each country elaborated a set of national recommendations. Finally, multinational recommendations were formulated and agreement among the participants and the potential impact on their clinical practice was assessed. RESULTS: A total of 16 979 references was identified, of which 304 articles were included in the systematic reviews. Ten multinational key recommendations on the use of methotrexate were formulated. Nine recommendations were specific for rheumatoid arthritis (RA), including the work-up before initiating methotrexate, optimal dosage and route, use of folic acid, monitoring, management of hepatotoxicity, long-term safety, mono versus combination therapy and management in the perioperative period and before/during pregnancy. One recommendation concerned methotrexate as a steroid-sparing agent in other rheumatic diseases. CONCLUSIONS: Ten recommendations for the use of methotrexate in daily clinical practice focussed on RA were developed, which are evidence based and supported by a large panel of rheumatologists, enhancing their validity and practical use.

Risk and management of liver toxicity during methotrexate treatment in rheumatoid and psoriatic arthritis: a systematic review of the literature.

OBJECTIVES: To systematically review the literature on liver toxicity in rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients treated with methotrexate (MTX), as an evidence base for generating clinical practice recommendations for the management of MTX and the indication for a liver biopsy (LB) in case of elevated liver enzymes (LE). METHODS: A systematic literature search was carried out in MEDLINE, EMBASE, Cochrane Library and ACR/EULAR meeting abstracts. Data on the incidence of elevated LE, subsequent adjustments in MTX therapy and the prevalence of fibrosis/cirrhosis in pre-MTX and post-MTX LB were pooled. RESULTS: Forty-seven out of 426 identified references were included in the systematic review. For RA, the incidence rate of elevated LE in the first three years of MTX use was 13/100 patient-years with a cumulative incidence of 31%. MTX was permanently discontinued in 7%, paused or reduced in 26% and continued without any adjustment in 67% of patients with an abnormal test. After 4 years of MTX use, LB showed in 15.3% of the (unrelated) cases mild fibrosis, in 1.3% severe fibrosis and in 0.5% cirrhosis, while pre-MTX biopsies showed 9%, 0.3% and 0.3% abnormalities, respectively. For PsA, evidence is limited. Additional studies suggest that cumulative MTX dose and serial LE elevations among other risk factors are related to liver pathology. CONCLUSIONS: This review suggests that LE elevations during MTX therapy are a frequent but transient problem, that serial abnormal LE tests might be associated with liver pathology, but that cirrhosis is relatively rare. It is, however, not clear from the literature how therapy should be adjusted in case of elevated LE and to what extent MTX independently attributes to liver toxicity.

Prognostic value of heart rate variability during long-term follow-up in patients with mild to moderate heart failure. The Dutch Ibopamine Multicenter Trial Study Group.

OBJECTIVES: We sought to assess the prognostic value of heart rate variability measures, including Poincaré plots, in patients with mild to moderate chronic heart failure. BACKGROUND: Mortality is high in patients with heart failure, and many of them die suddenly. However, identification of high risk patients, particularly those with an increased risk for sudden death, has remained difficult. METHODS: We studied 95 patients with heart failure (mean [+/- SD] age 60 +/- 8 years, left ventricular ejection fraction 0.29 +/- 0.09, New York Heart Association functional class II [81%] and III [19%]) during up to 4 years of follow-up. Heart rate variability measures and Poincaré plots were obtained from 24-h Holter recordings. RESULTS: During follow-up, 17 (18%) of the 95 patients died. In 15 patients, death was cardiac related (11 patients experienced sudden death). None of the conventional time and frequency domain measures of heart rate variability were related to survival. In contrast, abnormal Poincaré plots identified a significantly higher risk for all-cause cardiac death (Cox proportional hazards ratio 5.7, 95% confidence interval [CI] 1.6 to 20.6, univariate analysis) and for sudden cardiac death (hazards ratio 6.8, 95% CI 1.5 to 31.4) compared with those with normal Poincaré plots. Patients with abnormal Poincaré plots were shown to have a lower left ventricular ejection fraction (0.26 +/- 0.10 vs. 0.31 +/- 0.08, p < 0.05) and higher plasma norepinephrine concentrations (506 +/- 207 pg/ml vs. 411 +/- 175 pg/ml, p < 0.05). In multivariate analysis, abnormal Poincaré plots still had independent prognostic value, both for all-cause cardiac mortality and for sudden cardiac death (hazards ratio 5.3, 95% CI 1.2 to 17.1, hazards ratio 4.5, 95% CI 1.0 to 27.5, respectively. CONCLUSIONS: Heart rate variability analysis, as assessed by Poincaré plots, has independent prognostic value in patients with mild to moderate chronic heart failure and identifies an increased risk for all-cause and sudden cardiac death in these patients.

Rapid Germination of a Barley Mutant Is Correlated with a Rapid Turnover of Abscisic Acid Outside the Embryo.

In our study of the role of abscisic acid (ABA) in controlling the germination of barley grains, we tested a barley mutant line with a gigantum appearance (Hordeum distichum cv Quantum) for an ABA-insensitive phenotype by assaying germination in the presence of 10-4 M ABA. Dissected embryos of the mutant germinated at least 10 h earlier than did those of the wild type. The half-maximal concentrations of ABA inhibitory for germination were determined to be 5 x 10-4 M for the mutant and 10-6 M for the wild type. Expression of an ABA-induced Rab gene was studied to determine ABA responsiveness. The ABA concentration required for a half-maximal induction of Rab gene expression was 4 x 10-6 M in isolated embryos of both the mutant and wild type. This result suggests that ABA signal transduction pathways were not affected in the mutant. When isolated embryos were allowed to imbibe in water, ABA was released from the mutant and wild-type embryos at the same rate. However, the free ABA level in the incubation medium of the mutant showed a much faster decrease than that of the wild type, as demonstrated by two independent ABA assay methods (high-performance liquid chromatography and enzyme-linked immunosorbent assay). Our results suggest that turnover of ABA outside the embryo is a determining factor in the germination of barley seeds.

Identification of peptides for immunotherapy of cancer. It is worth the effort.

As the nature of the T cell immune response is defined by T cell receptor recognition of small protein fragments, referred to as peptides, the identification of peptides would lead us to understanding and directing the T-cell-mediated immune response. Immunogenic peptides might be used for vaccination and activation of the immune reaction against cancer- and virus-infected cells. Additionally, the knowledge of immunogenic peptides was expected to lead to blocking of allergic reactions and autoimmune diseases. Based on these assumptions, the search for immunogenic peptides was started in mice and man in the mid-1980s. After a decade of peptide identification and testing in vitro and in vivo, this may be a proper time to evaluate the results from the peptide-related work and determine the possible applications of this knowledge for the next decade. In this review we discuss the identification of peptides, their use in murine models, as well as clinical data from peptide vaccinations or therapies. Potential hazards and limitations of peptide use in immunotherapy and other possible applications for peptides or peptide motifs in immunotherapy are evaluated.

Effects of TGF-beta on the immune system: implications for cancer immunotherapy.

Transforming growth factor-beta (TGF-beta) is a potent regulator of numerous processes including hematopoiesis, cell proliferation, differentiation and activation. TGF-beta has pleiotropic and profound effects on the immune system and on hematologic malignancies, ie leukemia. It is the most potent immunosuppressor described to date. Evidence exists that the immunosuppressive potential of TGF-beta is an important promoter of malignant cell growth. This is partly caused by TGF-beta-induced interference with the generation of tumor-specific cytotoxic T lymphocytes, but also by TGF-beta-induced promotion of angiogenesis and tumor stroma formation. Until now, significant clinical responses have not been achieved with the current cancer immunotherapeutic approaches. One of the possible explanations for this failure is immunosuppression induced by tumor-derived TGF-beta. Here, several strategies to counteract the immunosuppressive effects of TGF-beta and the current limitations of these strategies will be discussed. Knowledge of the mechanisms by which TGF-beta interferes with the development of an anti-tumor response and of the strategies to counteract these immunosuppressive activities is crucial to improve the current cancer immunotherapeutic approaches.

A murine model for the effects of pelvic radiation and cisplatin chemotherapy on human papillomavirus vaccine efficacy.

Therapeutic human papillomavirus (HPV) vaccines for cervical cancer depend on a competent immune system to be effective. However, cancer patients are often found to be immunosuppressed, which could be attributable to prior radiation, chemotherapy, or the tumor burden itself. This study investigated whether pelvic radiation or cisplatin treatment affected the efficacy of an HPV vaccine and how long these effects lasted. Mice were given pelvic radiation, 2 Gy/day to a total dose of 45 Gy, or 5 mg/kg/week of cisplatin for 3 weeks. Mice were then immunized with an HPV-16 peptide vaccine between 0 and 16 weeks after their treatment. An ELISPOT analysis revealed that a reduced level of peptide-specific, IFNgamma-producing spleen cells was present in immunized mice treated previously with pelvic radiation or cisplatin compared with immunized mice that had not been treated. However, when mice were challenged with HPV-16-expressing tumor cells, immunized mice developed no tumors, regardless of prior treatment, whereas nonimmunized mice did develop tumors. Our results suggest that pretreatment with pelvic radiation or cisplatin alone does not prevent the induction of an effective immune response by a peptide vaccine. These data will have important implications for immunotherapeutic treatment of pretreated cancer patients, especially in the adjuvant setting when immunosuppression by tumor burden would be low.

Investigation of the parallel conductor model of impedance cardiography by means of exchange transfusion with stroma free haemoglobin solution in the dog.

To test one of the assumptions underlying the calculation of stroke volume--namely, that the transthoracic impedance consists of a parallel connection of a tissue impedance and a blood resistance--experiments were carried out on four dogs in which blood was gradually replaced by a stroma free haemoglobin solution, with the purpose of changing the blood resistance while leaving the tissue impedance unchanged. This was accomplished by exchange transfusion in such a way that the volume of the circulating fluid remained constant and the distribution of fluid volume between the fluid compartments was not altered. During the exchange transfusions the mean decrease in resistivity of the circulating fluid was 54%. The packed cell volume and resistivity of every volume of removed circulating fluid were measured. Just before each exchange the real and imaginary parts of the transthoracic impedance were measured. The packed cell volume decreased exponentially with the number of exchanges. This indicates that the circulating fluid volume remained constant during the exchange transfusion. From the packed cell volumes an estimate of the circulating fluid volume was made. Because of the parallel connection all calculations were based on the use of admittance, which is the reciprocal value of impedance. The real and imaginary parts of the transthoracic admittance were calculated from the measured values of the real and imaginary parts of the transthoracic impedance.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of the origin of the impedance cardiogram by means of exchange transfusion with stroma free haemoglobin solution in the dog.

PURPOSE OF INVESTIGATION - To determine the contribution of variations in orientation of erythrocytes (orientation effect) to the heart synchronous variations in thoracic impedance in impedance cardiography. DESIGN - The blood of four dogs was gradually replaced by stroma free haemoglobin solution, causing a decrease in resistivity and orientation effect. The decrease in orientation effect was used to determine the contribution of the orientation effect using an extended form of the "parallel conductor" model of the thorax (parallel connection of a tissue admittance Yt and a blood conductance Gb). SUBJECTS - Four adult splenectomised mongrel dogs. MEASUREMENTS and RESULTS - Packed cell volume and resistivity at body temperature of every volume of circulating fluid removed was measured. Real and imaginary parts of the transthoracic impedance and the modulus of the heart synchronous impedance variations were measured just before each exchange. The parallel conductor model was extended to account for the influence on Gb of packed cell volume and orientation of erythrocytes. Applying this extended model, the average variations in Gb at a packed cell volume of 40% were estimated to be 7.46%:3.03% due to volume variations, 4.43% due to orientation effect. After further extending the model to account for the influence of small changes in blood pressure and heart rate, the average volume variations were estimated to range from 2.8% to 3.3% and the average orientation effect from 4.1% to 4.7% at a packed cell volume of 40%. CONCLUSION - Resistivity of the blood is far from constant and the contributions of variations in blood conductivity and volume to the heart synchronous thoracic impedance are of comparable magnitude. The contribution of the volume variations is the sum of the volume variations in the contributing intrathoracic vessels. The effects of variations in orientation are added up in proportion to the relative volumes of the contributing vessels. The extensions of the parallel conductor model brought out all physiological factors determining the heart synchronous thoracic impedance variations: pulse pressures and flows, mean pressures and flows, compliances of all contributing blood vessels, packed cell volume and heart rate, as well as the relevant properties of blood: the relations between volume, flow and orientation effect and the change in orientation effect during decelerating flow.