Validation of haemodialysis recirculation and access blood flow measured by thermodilution. (49/49462)

BACKGROUND: Recirculation (R) and access blood flow (Qac) measurements are considered useful indicators of adequate delivery of haemodialysis. It was the purpose of this study to compare measurements of R and Qac obtained by two different techniques which are based on the same principle of indicator dilution, but which differ because of the characteristics of the injection and detection of the different indicators used. METHODS: Recirculation measured by a thermal dilution technique using temperature sensors (BTM, Fresenius Medical Care) was compared with recirculation measured by a validated saline dilution technique using ultrasonic transducers placed on arterial and venous segments of the extracorporeal circulation (HDM, Transonic Systems, Inc.). Calculated access flows were compared by Bland Altman analysis. Data are given as mean +/- SD. RESULTS: A total of 104 measurements obtained in 52 treatments (17 patients, 18 accesses) were compared. Recirculation measured with correct placement of blood lines and corrected for the effect of cardiopulmonary recirculation using the 'double recirculation technique' was -0.02 +/- 0.14% by the BTM technique and not different from the 0% measured by the HDM technique. Recirculation measured with reversed placement of blood lines and corrected for the effect of cardiopulmonary recirculation was 19.66 +/- 10.77% measured by the BTM technique compared with 20.87 +/- 11.64% measured by the HDM technique. The difference between techniques was small (-1.21 +/- 2.44%) albeit significant. Access flow calculated from BTM recirculation was 1328 +/- 627 ml/min compared with 1390 +/- 657 ml/min calculated by the HDM technique. There was no bias between techniques. CONCLUSION: BTM thermodilution yields results which are consistent with the HDM ultrasound dilution technique with regard to both recirculation and access flow measurement.  (+info)

Caval contribution to flow in the branch pulmonary arteries of Fontan patients with a novel application of magnetic resonance presaturation pulse. (50/49462)

BACKGROUND: A complete understanding of fluid mechanics in Fontan physiology includes knowledge of the caval contributions to right (RPA) and left (LPA) pulmonary arterial blood flow, total systemic venous return, and relative blood flow to each lung. METHODS AND RESULTS: Ten Fontan patients underwent cine MRI. Three cine scans of the pulmonary arteries were performed: (1) no presaturation pulse, (2) a presaturation pulse labeling inferior vena cava (IVC) blood (signal void), and (3) a presaturation pulse labeling superior vena cava (SVC) blood. The relative signal decrease is proportional to the amount of blood originating from the labeled vena cava. This method was validated in a phantom. Whereas 60+/-6% of SVC blood flowed into the RPA, 67+/-12% of IVC blood flowed toward the LPA. Of the blood in the LPA and RPA, 48+/-14% and 31+/-17%, respectively, came from the IVC. IVC blood contributed 40+/-16% to total systemic venous return. The distributions of blood to each lung were nearly equal (RPA/LPA blood=0.94+/-11). CONCLUSIONS: In Fontan patients with total cavopulmonary connection, SVC blood is directed toward the RPA and IVC blood is directed toward the LPA. Although the right lung volume is larger than the left, an equal amount of blood flow went to both lungs. LPA blood is composed of equal amounts of IVC and SVC blood because IVC contribution to total systemic venous return is smaller than that of the SVC. This technique and these findings can help to evaluate design changes of the systemic venous pathway to improve Fontan hemodynamics.  (+info)

Plaque area increase and vascular remodeling contribute to lumen area change after percutaneous transluminal angioplasty of the femoropopliteal artery: an intravascular ultrasound study. (51/49462)

OBJECTIVE: The aim of the study was to assess the change in lumen area (LA), plaque area (PLA), and vessel area (VA) after percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery. METHODS: This was a prospective study. Twenty patients were studied with intravascular ultrasound (IVUS) immediately after PTA and at follow-up examination. Multiple corresponding IVUS cross-sections were analyzed at the segments that were dilated by PTA (ie, treated sites; n = 168), including the most stenotic site (n = 20) and the nondilated segments (ie, reference sites; n = 77). RESULTS: At follow-up examination, both the PLA increase (13%) and the VA decrease (9%) resulted in a significant LA decrease (43%) at the most stenotic sites (P =.001). At the treated sites, the LA decrease (15%) was smaller and was caused by the PLA increase (15%). At the reference sites, the PLA increase (15%) and the VA increase (6%) resulted in a slight LA decrease (3%). An analysis of the IVUS cross-sections that were grouped according to LA change (difference >/=10%) revealed a similar PLA increase in all the groups: the type of vascular remodeling (VA decrease, no change, or increase) determined the LA change. At the treated sites, the LA change and the VA change correlated closely (r = 0.77, P <.001). At the treated sites, significantly more PLA increase was seen in the IVUS cross-sections that showed hard lesion or media rupture (P <.05). No relationship was found between the presence of dissection and the quantitative changes. CONCLUSION: At the most stenotic sites, lumen narrowing was caused by plaque increase and vessel shrinkage. Both the treated sites and the reference sites showed a significant PLA increase: the type of vascular remodeling determined the LA change at follow-up examination. The extent of the PLA increase was significantly larger in the IVUS cross-sections that showed hard lesion or media rupture.  (+info)

A surrogate measure of whole body leucine transport across the cell membrane. (52/49462)

Based on a mass-balance model, a surrogate measure of the whole body leucine transport into and out of cells under steady-state conditions was calculated as u/DeltaTTR, where u is the infusion rate of (stable label) leucine tracer and DeltaTTR is the difference between the tracer-to-tracee ratio of extracellular and intracellular leucine. The approach was evaluated in ten healthy subjects [8 males and 2 females; age, 31 +/- 9 (SD) yr; body mass index, 24.0 +/- 1.6 kg/m2] who received a primed (7.58 micromol/kg) constant intravenous infusion (7.58 micromol. kg-1. h-1) of L-[1-13C]leucine over 180 min (7 subjects) or 240 min (3 subjects). Five subjects were studied on two occasions >/=1 wk apart to assess reproducibility. Blood samples taken during the last 30 min of the leucine infusion were used to determine plasma leucine concentration (129 +/- 35 micromol/l), TTR of leucine (9.0 +/- 1.5%), and TTR of alpha-ketoisocaproic acid (6.7 +/- 0.8%). The latter TTR was taken as the measure of the free intracellular leucine TTR. The whole body inward and outward transport was 6.66 +/- 3.82 micromol. kg-1. min-1; the rate of leucine appearance due to proteolysis was 1.93 +/- 0.24 micromol. kg-1. min-1. A positive linear relationship between the inward transport and plasma leucine was observed (P < 0.01), indicating the presence of the mass effect of leucine on its own transport. The transport was highly variable between subjects (between-subject coefficient of variation 57%) but reproducible (within-subject coefficient of variation 17%). We conclude that reproducible estimates of whole body transport of leucine across the cell membrane can be obtained under steady-state conditions with existing experimental and analytical procedures.  (+info)

Do case studies mislead about the nature of reality? (53/49462)

This paper attempts a partial, critical look at the construction and use of case studies in ethics education. It argues that the authors and users of case studies are often insufficiently aware of the literary nature of these artefacts: this may lead to some confusion between fiction and reality. Issues of the nature of the genre, the fictional, story-constructing aspect of case studies, the nature of authorship, and the purposes and uses of case studies as "texts" are outlined and discussed. The paper concludes with some critical questions that can be applied to the construction and use of case studies in the light of the foregoing analysis.  (+info)

Do studies of the nature of cases mislead about the reality of cases? A response to Pattison et al. (54/49462)

This article questions whether many are misled by current case studies. Three broad types of style of case study are described. A stark style, based on medical case studies, a fictionalised style in reaction, and a personal statement made in discussion groups by an original protagonist. Only the second type fits Pattison's category. Language remains an important issue, but to be examined as the case is lived in discussion rather than as a potentially reductionist study of the case as text.  (+info)

Improved methods using the reverse transcriptase polymerase chain reaction to detect tumour cells. (55/49462)

Reverse transcriptase polymerase chain reaction (RT-PCR) is increasingly used to detect small numbers of circulating tumour cells, though the clinical benefit remains controversial. The largest single contributing factor to the controversy of its value is the different approaches to sample processing. The aim of this study was to compare the sensitivity and reproducibility of RT-PCR for the detection of tumour cells after four commonly used different methods of sample processing. Using RT-PCR, one tumour cell spiked in 2 ml of whole blood was detected after analysis of separated mononuclear cell RNA, whole blood total or poly-A+ RNA. No false positives were identified with any method. However, the reproducibility of tumour cell detection was reduced after isolation of the mononuclear cell fraction. Only analysis of poly-A+ RNA had a sensitivity of 100% in all the cell spiking experiments. In patient blood samples, analysis of poly-A+ RNA increased the number of blood samples positive for tyrosine hydroxylase (TH) mRNA compared with those positive after analysis of total RNA. This may reflect high levels of cDNA reducing the efficiency of the PCR. Isolation of poly-A+ RNA increases the sensitivity and reproducibility of tumour cell detection in peripheral blood.  (+info)

Infratentorial atrophy on magnetic resonance imaging and disability in multiple sclerosis. (56/49462)

Loss of tissue volume in the central nervous system may provide an index of fixed neurological dysfunction in multiple sclerosis. Recent magnetic resonance studies have shown a modest relationship between clinical disability rating scores and transverse sectional area of the cervical spinal cord. To explore further the relationship between atrophy and disability in multiple sclerosis, we estimated the volumes of infratentorial structures from MRIs in a cross-sectional study of 41 patients, 21 with relapsing-remitting multiple sclerosis and 20 with secondary progressive multiple sclerosis. We used the Cavalieri method of modern design stereology with point counting to estimate the volume of brainstem, cerebellum and upper cervical spinal cord from three-dimensional MRIs acquired with an MPRAGE (Magnetization-prepared Rapid Acquisition Gradient Echo) sequence. The volume of the upper (C1-C3) cervical spinal cord was significantly correlated with a composite spinal cord score derived from the appropriate Functional Scale scores of the Expanded Disability Status Scale (r = -0.50, P < 0.01). The cerebellar (r = 0.49, P < 0.01) and brainstem (r = 0.34, P < 0.05) volumes correlated with the Scripp's Neurological Disability Rating Scale scores. The upper cervical cord volumes (r = -0.39, P < 0.01), but not the brainstem or cerebellar volumes, were significantly associated with disease duration. MRI-estimated structural volumes may provide a simple index of axonal and/or myelin loss, the presumed pathological substrates of irreversible impairment and disability in multiple sclerosis.  (+info)