Quantitative assessment of the presence of a single leg separation in Björk-Shiley convexoconcave prosthetic heart valves.

RATIONALE AND OBJECTIVES: The authors developed an analytic software package for the objective and reproducible assessment of a single leg separation (SLS) in the outlet strut of Björk-Shiley convexoconcave (BSCC) prosthetic heart valves. METHODS: The radiographic cinefilm recordings of 18 phantom valves (12 intact and 6 SLS) and of 43 patient valves were acquired. After digitization of regions of interest in a cineframe, several processing steps were carried out to obtain a one-dimensional corrected and averaged density profile along the central axis of each strut leg. To characterize the degree of possible separation, two quantitative measures were introduced: the normalized pit depth (NPD) and the depth-sigma ratio (DSR). The group of 43 patient studies was divided into a learning set (25 patients) and a test set (18 patients). RESULTS: All phantom valves with an SLS were detected (sensitivity, 100%) at a specificity of 100%. The threshold values for the NPD and the DSR to decide whether a fracture was present or not were 3.6 and 2.5, respectively. On the basis of the visual interpretations of the 25 patient studies (learning set) by an expert panel, it was concluded that none of the patients had an SLS. To achieve a 100% specificity by quantitative analysis, the threshold values for the NPD and the DSR were set at 5.8 and 2.5, respectively, for the patient data. Based on these threshold values, the analysis of patient data from the test set resulted in one false-negative detection and three false-positive detections. CONCLUSIONS: An analytic software package for the detection of an SLS was developed. Phantom data showed excellent sensitivity (100%) and specificity (100%). Further research and software development is needed to increase the sensitivity and specificity for patient data.

Determinants of end-systolic pressure during different load alterations in the in situ left ventricle.

Because of the strong dependency of the end-systolic pressure-volume relation on the type of transient loading intervention in the in situ left ventricle (LV), experiments in the basal inotropic state in 16 open-chest anesthetized dogs were reanalyzed to find additional variables to model and predict end-systolic pressure (ESP) of both afterloading and preloading interventions by a single equation. Random-coefficients regression analysis was performed on 22 experiments in the basal inotropic state simultaneously, yielding an overall R2 of 0.97. The major part of total variance of ESP was due to linear terms of end-systolic volume (ESV) (74%) and stroke volume (SV) (19%). The SV effect was consistently negative and quantitatively quite important. An average load-independent end-systolic elastance of 6.7 mmHg/ml and an average SV effect of -5.7 mmHg/ml ejected were estimated, separating the "force-length" property from shortening effects in the in situ LV. History-related effects appeared to be only minor.

Prolonged dilation with an autoperfusion balloon catheter for refractory acute occlusion related to percutaneous transluminal coronary angioplasty.

OBJECTIVES: Efficacy and safety of redilation by an autoperfusion balloon catheter over several hours were investigated in this retrospective and observational study. BACKGROUND: Acute occlusion, refractory to redilation, is a serious complication of coronary angioplasty. METHODS: Of 1,123 patients who underwent angioplasty, 83 had a refractory acute occlusion. Thiry-five patients were treated with extended dilation. Seven had stable, 19 unstable and 6 postinfarction angina and 3 had an acute infarction at the time of angioplasty. The duration of dilation was (mean +/- SD) 17 (+/- 6) h. RESULTS: Angiographically successful redilation, with a mean residual percent diameter stenosis of 13.5% (+/- 11.6%), was achieved in 22 (67.7%) of 34 patients. Five patients underwent bypass surgery. Three patients, who were poor surgical candidates, died. There was one new Q wave infarction and one death that occurred during extended dilation; one death and four operations were related to reocclusion immediately (< or = 30 min) after catheter withdrawal; and one death and one operation were related to in-hospital reocclusion. Overall success, defined as angiographic success and freedom from major events, was obtained in 20 (57%) of 35 patients (95% confidence interval 41% to 73%). Of the variables studied, only multilesion dilation was significantly (p = 0.018) associated with an unfavorable outcome. During a mean follow-up period of 13.8 (+/- 6.1) months, two patients underwent repeat angioplasty, one sustained an infarction and three underwent elective bypass surgery. CONCLUSIONS: In approximately half of the patients (20 [57%] of 35), an initial angioplasty failure due to refractory occlusion could be reverted to a successful procedure by prolonged dilation with an autoperfusion balloon catheter.

Comparison between force-velocity and end-systolic pressure-volume characterization of intrinsic LV function.

We reanalyzed experiments in in situ hearts of 16 open-chest anesthetized dogs, in which two different loading interventions were performed, i.e., an occlusion of the descending aorta (InP) and a rapid volume infusion (InV). Previous studies had demonstrated that the end-systolic elastance (Ees) of the InP was substantially larger than the Ees of the InV suggesting either a load dependency of Ees as such, or an increase in contractility during InP. The data were reanalyzed in the light of the muscular pump concept by plotting peak normalized velocity of circumferential shortening versus a global representative force approximating the left ventricle by a sphere. In all but one experiment the points of the two interventions are located on a single relationship over a very broad range of forces (from 397 to 2,461 g between the control states of experiments and from 602 to 3,278 g difference between control and highest load within experiments). The virtual independence of the force-velocity relation (FVR) and the dependence of the end-systolic pressure-volume relation (ESPVR) on the type of loading intervention can be ascribed to the fact that the former is assessed early during ejection and is therefore less influenced by shortening deactivation and internal resistance than the ESPVR. We conclude that the FVR offers a more consistent characterization of intrinsic LV function than the ESPVR.

Identifiability of left ventricular end-systolic pressure-volume relationships.

A widely accepted model of the left ventricle (LV) consisting of a time-varying elastance and a nonlinear internal resistance was investigated to make inferences about the identifiability of its parameters by means of simulated experiments. We aimed to retrieve maximum elastance (Emax) and dead volume (Vd) by the usual slope method or end-systolic pressure-volume relations (ESPVR) and by model-based parameter identification. The ESPVR deviated increasingly from the assigned values with increasing internal resistance depending on the type of loading intervention. Model-based parameter identification proved to be hampered by considerable error propagation if applied to single contractions with noise on the data. Better results were obtained by reducing the number of parameters to be estimated or by combining contractions with different loading conditions. The LV model was also matched with experimental data in three open-chest anesthetized dogs when both methods of estimation were used. The trend of ESPVR was in accordance with the model predictions, with larger Emax and larger Vd observed with arterial rather than with venous loading. Inclusion of an internal resistance in the classical elastance model can explain the dependence of the ESPVR on the type of loading intervention. However, application of model-based parameter identification indicates that the model fails to represent the entire systolic pressure-volume time course of the in situ LV.

Gas transport in a model derived from Hansen-Ampaya anatomical data of the human lung.

The anatomical data of the human lung published by Hansen and Ampaya are used in a model of gas transport in the lung. The Bohr dead space is calculated from solutions of a transport equation where diffusivity is given by an empirical formula obtained by Sherer et al. A satisfactory agreement is found with experimental data obtained from simultaneous washouts of H2 and SF6 for respiratory frequencies ranging between 15 and 60 min-1 and tidal volumes between 200 and 1,800 ml. The results support the idea that molecular diffusion is the main but not the only physical phenomenom which intervenes in gas mixing during breathing.

Transport of H2 and SF6 in the lung.

The dead spaces for hydrogen and sulfur hexafluoride are predicted from the solution of a partial differential equation, applied to Weibel's morphometric data of the lung, and including longitudinal convection and diffusion coupled with instantaneous radial diffusion. Traces of H2 and SF6 were washed in and out of the lungs of two normal subjects. Dead spaces for both gases were calculated from the wash-out curves by a least squares analysis. Prediction and experiment agree in the case of H2. The model overestimates the dead space for SF6 particularly for large tidal volumes and for high breathing frequencies. Several factors which can contribute to this disagreement are considered. From simulation experiments it is evident, that the dead space for SF6 is highly sensitive to factors which influence molecular dispersion in the region of respiratory bronchioles. Cardiogenic mixing and some sort of flow-dependent mixing in this zone cannot be ruled out. However, the experimental data can also be explained by choosing another set of morphometric data for the alveolated airways.