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Several aspects of the four-electrode resistivity technique were studied with special emphasis on the theoretical determination of penetration depth and sample volume in anisotropic media such as (cardiac) muscle. Moreover, the presence of a thin disturbing layer on top of the medium under study was analyzed. A four-electrode sensor was developed for the measurement of local myocardial resistivity in two orthogonal directions. The sensor was applied to the epicardium of anesthetized open chest dogs and, as an example, results are given on the frequency dependence (5-60 kHz) and the changes during the cardiac cycle of longitudinal and transverse myocardial resistivity.

The comparative study of conductance-derived stroke volulme (SV), derived as a result of single and dual-excitation of the conductance catheter with SV by electromagnetic (EM) flow probes surrounding the ascending aorta, is conducted in six anesthetized open-chest dogs. The dual-excitation technique is a modified form of the conductance method, and makes use of two extra electrodes on the conductance catheter, which are aimed at generating a more uniform intracavitary electric field. The slope of the linear relation between SV, determined by flow probes and by multielectrode catheter, is augmented by the use of the dual- excitation technique.

Aims The aim of this study was to validate the tricuspid annular plane systolic excursion/systolic pulmonary artery (PA) pressure (TAPSE/PASP) ratio with the invasive pressure–volume (PV) loop-derived end-systolic right ventricular (RV) elastance/PA elastance (Ees/Ea) ratio in patients with heart failure with reduced ejection fraction (HFREF) and secondary pulmonary hypertension (PH). Methods and results The relationship of TAPSE and TAPSE/PASP with RV-PV loop (single-beat)-derived contractility Ees, afterload Ea, and Ees/Ea was assessed in 110 patients with HFREF with and without secondary PH. The results were compared with other surrogate parameters such as the fractional area change/PASP ratio. The association of the surrogates with all-cause mortality was evaluated. In patients with PH (n  = 74, 67%), TAPSE significantly correlated with Ees (r  = 0.356), inverse with Ea (r  = −0.514) but was most closely associated with Ees/Ea (r  = 0.77). Placing TAPSE in a ratio with PASP slightly reduced the relationship to Ees/Ea (r  = 0.71) but was more closely related to the parameters of PA vascular load, diastolic RV function, and RV energetics. The area under the curve of TAPSE/PASP and TAPSE for discriminating overall survival in receiver operating characteristic analysis was not different (P  = 0.78. Prognostic relevant cut-offs were 17 mm for TAPSE and 0.38 mm/mmHg for TAPSE/PASP. Both parameters in multivariate cox regression remained independently prognostically relevant. Conclusion TAPSE is an easily and reliably obtainable and valid surrogate parameter for RV–PA coupling in PH due to HFREF. Putting TAPSE into a ratio with PASP did not further improve the coupling information or prognostic assessment. Trial Identifier DRKS—German Clinical Trials Register (DRKS00011133; https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00011133). [ABSTRACT FROM AUTHOR]

Aims Restrictive mitral annuloplasty (RMA) can provide a durable solution for functional mitral regurgitation (MR), but might result in obstruction to antegrade mitral flow. Aim of this study was to assess the magnitude of change in mitral valve area (MVA) during exercise after RMA, to relate the change in MVA to left ventricular (LV) geometry and function, and to assess its haemodynamic and clinical impact. Methods and results Bicycle exercise echocardiography was performed in 32 patients after RMA. Echocardiographic data at rest and during exercise were compared with preoperative echocardiographic data. Clinical endpoints were collected following the study visit. MVA increased during exercise in 25 patients (1.6 ± 0.4 cm2 to 2.0 ± 0.6 cm2, P  < 0.001), whereas MVA decreased in 7 patients (1.8 ± 0.5 cm2 to 1.5 ± 0.4 cm2, P  = 0.020). Patients with an increased MVA showed a significant reduction in LV volumes at rest compared to preoperatively, and an increase in stroke volume and cardiac output (CO) during exercise. In patients with decreased MVA, LV reverse remodelling was absent and myocardial flow reserve limited. Patients with decreased exercise MVA had a higher increase in mean pulmonary artery pressure (PAP) with respect to CO and worse survival 36 months after the study visit (69±19% vs. 92±5%, P  = 0.005). Conclusions Both increased and decreased MVA were observed during exercise echocardiography after RMA for functional MR. Change in MVA was related to the extent of LV geometrical and functional changes. A decreased MVA during exercise was associated with a higher increase in mean PAP with respect to CO, and worse survival. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the definitions and applications of 'spaced learning' and to propose future directions for advancing its study and practice in health professions education. Method: The authors searched five online databases for articles published on spaced learning in health professions education prior to February 2018. Two researchers independently screened articles for eligibility with set inclusion criteria. They extracted and analysed key data using both quantitative and qualitative methods. Results: Of the 2972 records retrieved, 120 articles were included in the review. More than 90% of these articles were published in the last 10 years. The definition of spaced learning varied widely and was often not theoretically grounded. Spaced learning was applied in distinct contexts, including online learning, simulation training and classroom settings. There was a large variety of spacing formats, ranging from dispersion of information or practice on a single day, to intervals lasting several months. Generally, spaced learning was implemented in practice or testing phases and rarely during teaching. Conclusions: Spaced learning is infrequently and poorly defined in the health professions education literature. We propose a comprehensive definition of spaced learning and emphasise that detailed descriptions of spacing formats are needed in future research to facilitate the operationalisation of spaced learning research and practice in health professions education. Digging into the educationally strategic phenomenon of spaced learning, the authors discover variety that leads them to propose a comprehensive definition and emphasise that detailed format descriptions are needed to facilitate further development. [ABSTRACT FROM AUTHOR]

Conversion of conductance catheter data to absolute ventricular volumes requires assessment of parallel conductance ([G.sup.P]). We determined the accuracy of [G.sup.P] obtained by the hypertonic saline method [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] compared with angiographically derived [G.sup.P] [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and quantified the variabilities of [G.sup.P] for the dual-field conductance catheter method in nine anesthetized sheep studied at baseline, treated with dobutamine, and subjected to volume loading and [Beta]-blockade. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] showed an excellent linear correlation [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] = 1.002 [multiplied by] [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] + 0.001 [[Omega].sup.-1], [R.sup.2] = 0.92), and Bland-Altman analysis yielded a nonsignificant bias and narrow limits of agreement (bias [+ or -] 2SD = 0.002 [+ or -] 0.112 [[Omega].sup.-1]). Within-animal variability of [G.sup.P] was very similar with both methods and was due to changes in blood conductivity rather than geometrical changes. Variability between animals was significant (26.3% of mean for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and 25.7% for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and thus warrants individual assessment. Variations during the cardiac cycle were not significantly different from zero. With biplane angiography used as gold standard, the hypertonic saline method accurately determines [G.sup.P] for the dual-field conductance catheter over a wide range of hemodynamic conditions. angiography; left ventricular volume; sheep; ventricular function

Enhanced systolic function of the right ventricle during respiratory distress syndrome in newborn lambs. Am J Physiol Heart Circ Physiol 280: H392-H400, 2001.--Respiratory distress syndrome (RDS) causes pulmonary hypertension. It is often suggested that this increased afterload for the right ventricle (RV) might lead to cardiac dysfunction. To examine this, we studied biventricular function in an experimental model. RDS was induced by lung lavages in seven newborn lambs. Five additional lambs served as controls. Cardiac function was quantified by indexes derived from end-systolic pressure-volume relations obtained by pressure-conductance catheters. After lung lavages, a twofold increase of mean pulmonary arterial pressure (from 15 to 34 mmHg) was obtained and lasted for the full 4-h study period. Stroke volume was maintained (5.2 [+ or -] 0.6 ml at baseline and 6.1 [+ or -] 1.4 ml at 4 h of RDS), while, RV end-diastolic volume showed only a slight increase (from 6.5 [+ or -] 2.3 ml at baseline to 7.7 [+ or -] 1.3 ml at 4 h RDS). RV systolic function improved significantly, as indicated by a leftward shift and increased slope of the end-systolic pressure-volume relation. Left ventricular systolic function showed no changes. In control animals, pulmonary arterial pressure did not increase and right and left ventricular systolic function remained unaffected. In the face of increased RV afterload, the newborn heart is able to maintain cardiac output, primarily by improving systolic RV function through homeometric autoregulation. biventricular function; end-systolic pressure-volume relation; homeometric autoregulation; pulmonary hypertension

De Vroomen, Maartje, Robbert H. Lopes Cardozo, Paul Steendijk, Frank Van Bel, and Jan Baan. Improved contractile performance of right ventricle in response to increased RV afterload in newborn lamb. Am. J. Physiol. Heart Circ. Physiol. 278: H100-H105, 2000.--Pulmonary hypertension results in an increased afterload for the right ventricle (RV). To determine the effects of this increased afterload on RV contractile performance, we examined RV performance before and during 4 h of partial balloon occlusion of the pulmonary artery and again after releasing the occlusion in nine newborn lambs. RV contractile performance was quantified by indexes derived from systolic RV pressure-volume relations obtained by a combined pressure-conductance catheter during inflow reduction. An almost twofold increase of end-systolic RV pressure (from 22 to 38 mmHg) was maintained during 4 h. Cardiac output (CO) (0.74 [+ or -] 0.08 1/min) and stroke volume (4.3 [+ or -] 0.4 ml) were maintained, whereas end-diastolic volume (7.9 [+ or -] 1.3 ml) did not change significantly during this period. RV systolic function improved substantially; the end-systolic pressure-volume relation shifted leftward indicated by a significantly decreased volume intercept (up to 70%), together with a slightly increased slope. In this newborn lamb model, maintenance of CO during increased RV afterload is not obtained by an increased end-diastolic volume (Frank-Starling mechanism). Instead, the RV maintains its output by improving contractile performance through homeometric autoregulation. conductance catheter; end-systolic pressure-volume relation; homeometric autoregulation; pulmonary hypertension; right ventricular function.