The epidemiology of diabetes mellitus and diabetic retinopathy

The paper presents the results of examining the hydrodynamics of artificial heart valves (AHVs) manufactured in Russia and foreign countries. All the AHVs under study have been used in clinical practice for over 10 years and they are different in design. The hydrodynamics of AHVs was examined under static and pulsating flow through the valve. Photochromic imaging (PCI) was used for flow imaging. PCI is based on preparation of simulating blood (model physiological solution) in the medium, colour labels under laser radiation. The recording of colour label movement in the flow behind the valve using a speed camera makes it possible to follow flow hydrodynamics behind AHVs. The advantage of PCI over other methods is that the instant structure of flow behind the valve can be recorded just in the same section at any moment of an operating cycle. Based on the experimental data obtained by PCI, a procedure for comparative analysis of the hydrodynamic characteristics of AHVs was developed.     

Preparation, storage, transportation and use of heart valves for allotransplantation

Thanks to the co-operation with Czech and Slovak Transplant Centres and with some of the Departments of Pathology and Forensic Medicine 274 hearts were collected for allograft heart valves (AHV) processing during 1992-1995. The Cardiac surgeon dissected the aortic valve with the root and the pulmonary artery trunk with the valve. Tissues were antibiotically (ATB) sterilised in cultivation medium E 199 (24 hours at 37 degrees C). ATB concentrations (mg/ml): Cepharin 0.2, Azlocilin 0.2, Tobramycin 0.08 and Amphotericin B 0.1 for harvesting at post-mortem (P) or Miconazol 0.05 for sterile retrieval during multiorgan harvesting (MOH). After sterilisation AHV were stored at 4 degrees C. 49 AHV were infected even after ATB treatment-15 of 35 collected at P (43%) and 35 of 218 procured during MOH (16%)-(p < 0.01-ch2 test). After serological screening of the donor and microbiological testing the AHV were released for clinical use. Most AHV were programmed cooled to the temperature of liquid nitrogen (-196 degrees C), in which they were stored at the Allograft Heart Valves Cryobank. Cryoprotection was achieved by 10% dimethylsulphidoxide. CONCLUSION: A technology of harvesting, processing, storage and transportation of AHV, was introduced. It enabled the routine use in many cardiac surgical units. The AHV Cryobank was established. 131 AHV were used clinically between 1992 and 1995 (transportation as far as 1300 km). 108 AHV (82.4%) were used for repair of complex congenital heart defects, while 23 (17.6%) were used for aortic valve and/or root replacement.     

Expression of microfibrillar proteins by bovine bladder urothelium

OBJECTIVE: To compare hydrodynamic characteristics of a new bileaflet heart valve, the CarboMedics kinetic cardiac valve prosthesis, with those of a St. Jude Medical (SJM) heart valve. METHODS: Hydrodynamic characteristics were determined in the mitral and aortic positions of a Vivitro Systems pulse duplicator for size 23 Kinetic aortic values, size 23 SJM aortic valves, size 29 Kinetic mitral valves and size 29 SJM mitral valves. Test conditions were 72 beats per min with cardiac outputs of 2, 5 and 7 l/min. Values of forward flow pressure drop (delta P), regurgitant and energy loss were determined for each valve. The test results for the two valve designs were compared by valve size. RESULTS: The test results show that both the size 23 and size 29 Kinetic valves have 8-14% lower delta P values and 5-10% greater effective orifice area (EOA) values. The size 29 Kinetic mitral valve has a 1-2 ml lower regurgitant volume, while the size 23 Kinetic aortic valve has a 0.5 ml greater regurgitant volume than the corresponding SJM values. These factors combine to provide a 5-10% lower energy loss for size 23 Kinetic aortic valves and a 15-25% lower energy loss for size 29 Kinetic mitral valves over the cardiac cycle than for corresponding sizes of SJM valves. CONCLUSIONS: The Kinetic valve's fluid dynamics are superior to equivalent sizes of SJM valves. This is especially impressive considering that the tissue annulus diameters for Kinetic valves are approximately 0.5 mm less than equivalent size SJM valves. The primary reasons for the superior hydrodynamic performance of Kinetic valves are (1) the larger orifices which result in lower forward flow delta P values and (2) the opening angles, which have been customized for each valve size to minimize energy loss.     

Usefulness of magnetic resonance imaging for managing patients with prosthetic carbon valve in the mitral position

The safety, findings and clinical usefulness of magnetic resonance (MR) imaging were assessed in patients with a prosthetic carbon valve in the mitral position. In vitro deflection, heating and image distortion due to the magnetic field of a 1.5 tesla MR machine were examined in three carbon valves (CarboMedics, St. Jude Medical and Bj?rk-Shiley valves). In vivo MR imaging of the left ventricular horizontal long-axis, vertical long-axis and short-axis views was performed by electrocardiographically synchronized spin echo and field (gradient) echo techniques in eight patients with prosthetic mitral carbon valves, consisting of six CarboMedics valves, one St. Jude Medical valve and one Bj?rk-Shiley valve. No deflection and significant heating was seen in all three valves in vitro. Although little image distortion was shown in the CarboMedics and St. Jude Medical valves, a small distortion toward the frequency encoded direction was seen in the Bj?rk-Shiley valve but caused no difficulty in assessing the surrounding images. Four of the eight patients had normal sinus rhythm and the other four had atrial fibrillation. The prosthetic valves were depicted as signal voids in the images taken by both spin echo and field echo techniques in vivo. Clear structural information with little image distortion of the adjacent tissues of the prosthetic valves were obtained in all patients, although the image of the Bj?rk-Shiley valve which contained stainless steel in the frame had a slightly stronger distortion than those of the CarboMedics and St. Jude Medical valves which contained titanium. The stainless wire suture material used to close the sternal incision was depicted as a signal void, and the areas of the signal loss were larger in the images taken by the field echo technique than those by the spin echo technique. The images taken by the spin echo technique in patients with atrial fibrillation had reduced quality due to the irregularity of repetition time. Cine MR imaging by the field echo technique showed physiological mitral regurgitant jets as signal loss within the flowing blood, which appeared as high signal intensity, bidirectionally in the bileaflet mechanical valve and unidirectionally in the monoleaflet mechanical valve. An abnormal cavity was seen behind the basal left ventricular myocardium in one patient with a CarboMedics valve. The wall of the abnormal cavity was disrupted abruptly and the rest of the wall consisted of pericardium and adjacent tissue in the image taken by the spin echo technique. The image taken by the field echo technique showed an abnormal jet flow from the basal part of the left ventricular cavity into the abnormal cavity, which was compatible with left ventricular pseudoaneurysm. Two-dimensional echocardiography and Doppler color flow mapping disclosed the abnormal cavity and the abnormal flow inside, but failed to show the connection between the left ventricle and the cavity due to reverberation of the ultrasound signal by the prosthetic valve. These findings suggest that MR imaging is a safe and promising method to assess the complications and valvular function in patients with a prosthetic carbon valve in the mitral position.     

M-mode and two-dimensional echocardiography of heart valve prosthesis dysfunction

The diagnostic efficacy of M-Mode and 2-d echocardiography for the detection of malfunctioning prosthetic valves was studied in twenty-nine patients with prosthetic valves and clinical deterioration. Echocaradiographic abnormalities were found in 8 of 12 patients with confirmed valve dysfunction; 30.8% of the cases had false negative echo tracings. In 17 patients with normal echocardiographic pictures of the valves another cause of clinical deterioration was found (congestive heart failure, pericardial effusion, aneurysm of aortic root). In this study M-Mode and 2-d echocardiography had an excellent diagnostic accuracy rate in distinguishing congestive heart failure from valve dysfunction. Comparing the data of M-Mode and 2-d registration, both methods are found to be complementary. A major advantage of the 2-d echocardiography is its enhanced spatial orientation, whereas M-Mode echocardiography enables better evaluation of valve movements and corresponding time intervals and recognition of quick movements and fibrillations.     

Posture-related overdrainage: comparison of the performance of 10 hydrocephalus shunts in vitro

OBJECTIVE: Approximately 10 to 30% of shunt revisions may be attributed to posture-related overdrainage. The susceptibility of various hydrocephalus shunts to overdrainage of cerebrospinal fluid requires independent laboratory evaluation. METHODS: Shunts were tested in vitro by using precise computer-controlled equipment that was able to evaluate pressure-flow performance curves under various conditions. Hydrodynamic resistance and opening, closing, and operational pressures were evaluated for at least 28 days with normal (atmospheric) and decreased (-23 mm Hg, based on the International Standard Organization/Draft International Standard 7197 standard, which simulates conditions in upright body positions) outlet pressures. RESULTS: Ten different models of valves have been tested to date (Medtronic PS Medical Delta valve, flow-control valve, and lumboperitoneal shunt, Heyer-Schulte in-line, low-profile, and Pudenz flushing valves, Codman-Medos programmable and nonprogrammable valves, Sophy programmable valve, and Cordis Orbis-Sigma valve). The majority of these valves produced significantly negative (less than -10 mm Hg) average intracranial pressures in vertical body positions. In conjunction with nonphysiologically low hydrodynamic resistance (with the exception of the Orbis-Sigma valve, Medtronic PS Medical lumboperitoneal shunt, and Heyer-Schulte in-line valve), this may result in overdrainage related to body posture. The clinically reported rate of complications related to overdrainage is probably reduced by the long distal catheter, which increases the resistance of these valves by 100 to 200%. A few shunts (the Delta valve, low-profile valve, and Pudenz flushing valve with anti-siphon devices) offer reasonable resistance to negative outlet pressure, preventing complications related to overdrainage, but all valves with siphon-preventing devices may be blocked by increased subcutaneous pressure. CONCLUSION: Shunts without mechanisms preventing very low intracranial pressure in vertical body positions should be identified and avoided for patients likely to develop complications related to cerebrospinal fluid overdrainage.     

Transcranial Doppler ultrasound signals associated with prosthetic heart valves: an in vitro study

The application of transcranial Doppler (TCD) ultrasonography to asymptomatic prosthetic heart valve patients can result in detection of localized bursts of high intensity signals, similar to those caused by the passage of emboli. The origin of these signals is not known. In order to investigate this phenomenon in a simplified, more controllable environment, a TCD machine was used to record flow downstream from mechanical prosthetic heart valves in a mock circulatory loop. The model, which uses a saline solution seeded with silk particles (< 15 micrometers) as the circulatory fluid, recreates the principal hydrodynamic characteristics of the left heart and systemic circulation. Reproducibility of the system was established through repeated testing of a Monostrut valve. Three different mechanical valve types, (Monostrut, Medtronic Hall, St. Jude Medical) were tested over a range of simulated cardiac outputs, and the effect of valve size was investigated with four Omniscience tilting disc valves (21, 23, 25 and 29 mm). Average energy of the reflected Doppler signal was used to quantify the amount of high intensity Doppler signal, QTCD. TCD signals recorded in vitro were visually and aurally similar to those found in prosthetic heart valve patients. All valve types generated exponentially more QTCD with increasing simulated cardiac output. Differences amongst valve types were only significant at higher flow outputs, with the Monostrut valve producing the greatest QTCD. Larger valves consistently generated greater QTCD than smaller valves. In conclusion, TCD signals found in prosthetic heart valve patients can be reproduced, at least qualitatively, using a mock circulatory loop which does not incorporate the formed elements of blood.(ABSTRACT TRUNCATED AT 250 WORDS)     

Re: Proportionate mortality among union members employed at three Texas refineries

OBJECTIVES:We established an in vitro model to investigate the effects of valve sizing on the hemodynamic characteristics and leaflet motion of the Toronto SPV valve (St Jude Medical, Inc, St Paul, Minn). METHODS: Nine valves were first implanted in fresh porcine aortic roots and then retested in glutaraldehyde-treated porcine aortic roots. Three valves were 1- to 2-mm oversized, 3 were 1- to 2-mm undersized, and there were 3 size-for-size implantations. The elasticities of the aortic roots and the composite roots were measured in the pressure range between 0 and 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and regurgitation were measured and the effective orifice area and performance index were calculated for each root. Leaflet motion was recorded on videotape. RESULTS: The external diameter of the fresh root increased by 35% as the hydrostatic pressure rose from 0 to 120 mm Hg, as compared with 11% for the glutaraldehyde-treated root. Valve implantation in the fresh root reduced the distensibility to 22% but did not change distensibility in the glutaraldehyde-treated root. The effective orifice area was dependent on the valve size, with the transvalvular gradient decreasing as the valve size increased. For the same size of valve the hydrodynamic parameters were slightly better if the valve was undersized by 1 mm. A significant difference in favor of the undersized valves was found in open-leaflet bending deformation. CONCLUSION: Leaflet motion of the stentless porcine aortic valve in vitro is improved if the valve is slightly undersized, and this may be beneficial to the long-term durability of the prosthesis.     

Tissue-type plasminogen activator (t-PA) lysis of aortic and mitral valve thrombosis

Valve thrombosis is one of the most serious complications after prosthetic valve replacement. We report the use of tissue-type plasminogen activator (t-PA) in the treatment of a patient with thrombosed aortic and mitral valves. Thrombolysis resulted in immediate hemodynamic improvement and resolution of congestive heart failure, thereby avoiding surgical intervention. Based on our experience, thrombolysis with t-PA is an effective alternative in the treatment of thrombosed prosthetic valves.     

MIEBACH激光焊机压板回路分流集流阀寿命短的原因分析#br#

介绍了分流集流阀的结构特点和工作原理,对某APL常化酸洗机组的MIEBACH激光焊机压板升降液压回路分流集流阀使用寿命较短的原因进行了详细分析。分析结果表明：该分流集流阀原设计选型额定流量无法满足现场实际流量,阀芯动作时冲击较大,频繁动作冲击造成阀芯断裂损坏。在调节液压回路中的其他液压阀无法解决这一问题后,根据实际流量和工况对分流集流阀进行改造升级,在保证焊机压板升降动作正常的同时,也彻底解决了分流集流阀寿命短的问题。     

Application of color Doppler flow mapping to calculate orifice area of St Jude mitral valve

BACKGROUND: The effective orifice area (EOA) of a prosthetic valve is superior to transvalvular gradients as a measure of valve function, but measurement of mitral prosthesis EOA has not been reliable. METHODS AND RESULTS: In vitro flow across St Jude valves was calculated by hemispheric proximal isovelocity surface area (PISA) and segment-of-spheroid (SOS) methods. For steady and pulsatile conditions, PISA and SOS flows correlated with true flow, but SOS and not PISA underestimated flow. These principles were then used intraoperatively to calculate cardiac output and EOA of newly implanted St Jude mitral valves in 36 patients. Cardiac output by PISA agreed closely with thermodilution (r=0.91, Delta=-0.05+/-0.55 L/min), but SOS underestimated it (r=0.82, Delta=-1.33+/-0.73 L/min). Doppler EOAs correlated with Gorlin equation estimates (r=0.75 for PISA and r=0.68 for SOS, P<0.001) but were smaller than corresponding in vitro EOA estimates. CONCLUSIONS: Proximal flow convergence methods can calculate forward flow and estimate EOA of St Jude mitral valves, which may improve noninvasive assessment of prosthetic mitral valve obstruction.     

Evaluation of prosthetic valve function and associated complications

Significant advances in imaging modalities have occurred to evaluate prosthetic valve function and associated complications. These developments involve predominantly the introduction of Doppler technology for the non-invasive determination of gradients and valve areas and TEE for an improved assessment of valve structure, function, and associated complications. The current role of cinefluoroscopy is mostly to complement TEE in the evaluation of motion of mechanical prosthetic valves in the aortic position. Cardiac catheterization is now rarely needed to assess valve function. Diagnosis of prosthetic valve obstruction can be performed in the majority of cases with transthoracic Doppler echocardiography. Differentiation of valve obstruction from normal valve function in small valves with high flow conditions, however, may be difficult. Because of this and the variability in normal valves among different prostheses, knowledge of the type and size of the implanted valve is essential. Patients and ultrasound laboratories are encouraged to seek and provide this information on a routine basis. Although transthoracic echocardiography is the main diagnostic modality for the serial evaluation of prosthetic valve function, it is important to recognize its limitations in assessing prosthetic mitral regurgitation and evaluating structural abnormalities of prosthetic valves. These are the situations in which TEE has the most impact. A summary of general indications of TEE in prosthetic valves is provided in Table 6. Finally, a baseline transthoracic Doppler study is essential in the overall follow-up and serial evaluation of valve function. For future comparisons, the best indices of valve functions are those obtained for patients as their own control, from a baseline Doppler echocardiographic study performed early after the operation.     

A videofluoroscopic comparison of straw and cup drinking: the potential influence on dental erosion

Tracheostoma valves are often required in the rehabilitation process of speech after total laryngectomy. Patients are thus able to speak without using their hands to close the tracheostoma. The improved Groningen tracheostoma valve consists of a "cough" valve with an integrated ("speech") valve, which closes for phonation. The cough valve opens as the result of pressure produced by the lungs during a cough. The speech valve closes by the airflow produced by the lungs, thus directing air from the lungs into the esophagus at a deliberately chosen moment. An experimental setup with a computer-based acquisition program was developed to measure the pressure at which the cough valve opened and the flow at which the speech valve closed. In addition, the airflow resistance coefficient of the tracheostoma valve was defined and measured with an open speech valve. Both dry air from a cylinder and humid expired air were used. Results showed a pressure range of 1-7 kPa to open the cough valve and a flow range of 1.2-2.7 l/s to close the speech valve. These values were readily attained during speech, while the flow range occurred above values reached in quiet breathing. The device appeared to function well in physiological ranges and was optimally adjustable to an individual setting. No significant differences were measured between air from a cylinder and humid expired air. Findings showed that methods used to obtain results could be employed as a reference method for comparing aerodynamic characteristics of tracheostoma valves.     

Effects of structural configuration of prosthetic aortic valves upon coronary blood flow

This study was performed in order to determine the effects of the structural configuration of prosthetic aortic valves upon coronary blood flow. A pulse-duplicating system was utilized to which a rigid model of the root of the aorta and the left artery were attached. A stented normal human valve, stented porcine valve, pivoting disc valve, tilting disc value and a caged ball valve were tested at stimulated resting conditions. The results showed that the pulse configuration and proportions of coronary flow that were systolic and diastolic changed with various valves. There was no significant reduction of the mean simulated coronary flow with the porcine valve or disc valves. Coronary flow was augmented with the caged ball valve. These differences were interpreted as being due to several fluid dynamic phenomena. These were piston effects, inertia of reversed blood flow, torque and the effects resulting from the unique pressure distribution on each valve.     

The use of enzyme activated milk for in vitro simulation of prosthetic valve thrombosis

BACKGROUND AND AIM OF THE STUDY: Thrombosis remains a serious risk for patients with artificial heart valves and may be attributed in part to adverse blood flow patterns. Although the final assessment of a valve must follow years of clinical experience, in vitro flow analyses give valuable information prior to implantation. Laser Doppler velocimetry and computational fluid dynamics enable quantitative flow analyses to be made in vitro. Whilst these techniques highlight features such as areas of stasis, turbulence and high shear which may predispose to thrombus formation, the complex and time varying nature of the flow through valves makes it difficult to predict accurately potential sites of thrombus deposition and accumulation. METHODS: A technique is described which uses enzyme activated milk as a coagulable blood analogue to indicate flow related clotting. Milk flowing past a test valve or object was activated to clot downstream of the test piece after a certain time period. Milk clot was deposited clot at sites determined by the local flow disturbances. Milk clotting patterns produced on and around standard objects were compared with the transient flow patterns predicted around identical configurations to test the validity of computational flow analyses for predicting flow disturbances leading to clotting. Milk clots on valves were compared with examples of thrombus found on explanted valves of the same design. RESULTS: The sites of deposition were consistent with the predicted flow patterns around the two configurations of flow obstruction studied. Milk clotting patterns on valves corresponded with the early stages of thrombus on explanted valves of the same design. CONCLUSIONS: Whilst a coagulable milk mixture may be used to evaluate the risk of flow induced clot adherence, care must be taken when extrapolating to the clinical situation as other factors such as material properties, blood chemistry and concomitant disease must also be considered.     

Application of proximal isovelocity surface area method to determine prosthetic mitral valve area

BACKGROUND: In this study, we investigated the accuracy of orifice area determination of the prosthetic valve (Biocor) by using proximal isovelocity surface area method (PISA). Thirty-two patients (26 women, 6 men; mean age 44 +/- 8.1 years) were studied. Eleven patients were in normal sinus rhythm and the rest were in atrial fibrillation. Associated valvular lesions were mild aortic regurgitation in 12 patients and moderate tricuspid regurgitation in 19 patients. Sizes of prosthetic valves were 27 to 31, and implantation duration was 4 to 8 years. METHODS AND RESULTS: We analyzed the flow convergence zone proximal to the valve orifice with the concept of a hemispheric model. Mitral valve area (MVA) calculation was formulated by MVA = 2pi r2 x Va/Vm x (Vm/Vm-Va), where Vm is the maximal mitral velocity and Vm/Vm - Va is a correction factor to account for flattening of isotachs near the prosthetic orifice. MVA calculations by PISA were compared with pressure half-time (PHT), continuity equation (CONT), and color flow area (CFA) methods. Mitral valve areas were 2.17 +/- 0.17 cm2, 2.22 +/- 0.21 cm2, 2.19 +/- 0.22 cm2, and 2.16 +/- 0.17 cm2 in PISA, CFA, PHT, and CONT methods, respectively. Values in the comparison of MVA measurements by different methods were PISA vs PHT, r =.86; PISA vs CFA, r =.77; and PISA vs CONT, r =.89. CONCLUSIONS: The PISA method gives reliable estimates of large orifices such as prosthetic valves. Although the best correlation was seen with the CONT method, results of this study also confirmed that the PISA method can be applied with reasonable accuracy.     

Normal echocardiographic characteristics of the Sorin Bicarbon bileaflet prosthetic heart valve in the mitral and aortic positions

Doppler echocardiographic characteristics of normally functioning Sorin Bicarbon prostheses were prospectively assessed in 226 consecutive patients (135 male and 91 female patients, mean age 61 +/- 10 years) with 233 valves in the mitral (n = 67) and aortic (n = 166) positions whose function was considered normal by clinical and echocardiographic evaluation. Patterns of "normal" transprosthetic leakage were assessed with transthoracic echocardiography in all valves and with transesophageal echocardiography in six selected mitral valve prostheses. For the mitral valve prostheses, we found that peak and mean gradient, as well as pressure half-time, were not significantly different in either the 25 or the 31 mm valves (median values from 15 to 10 mm Hg, from 4 to 4 mm Hg, and from 70 to 83 ms; p = Not significant for all). On transthoracic study, 12 patients (17%) with a Sorin Bicarbon valve in the mitral position showed minimal transprosthetic leakage. On transesophageal study, all patients showed a transprosthetic leakage whose spatial distribution had a complex pattern: in planes orthogonal to the leaflet axis, two to four jets arising from the hinge points and converging toward the center of the valve plane could be visualized; in planes parallel to the leaflet axis, there were three jets, the two lateral ones diverging and the central one perpendicular to the valve plane. For the aortic valve prostheses, there was a significant decrease in transprosthetic gradients and an increase in effective orifice areas as prosthesis size increased. Peak and mean gradients decreased from a median value of 25 and 13 mm Hg in the 19 mm valves to 9 and 5 mm Hg in the 29 mm valves, respectively. Effective prosthetic valve area calculated with the continuity equation increased from a median value of 0.97 cm2 for the 19 mm size valves to 3.45 cm2 for the 29 mm size. With analysis of variance, effective prosthetic aortic valve area differentiated various valve sizes (F = 40.9, p < 0.0001) better than peak (F = 10.3, p < 0.0001) or mean (F = 8.04, p < 0.0001) gradients alone did. Furthermore, effective prosthetic aortic valve area correlated better than peak and mean gradients with prosthetic size (r = 0.76, r = -0.45, and r = -0.39, respectively). On transthoracic study, 109 patients (66%) showed minimal transprosthetic leakage. These normal values, obtained in a large number of patients with normofunctioning mitral and aortic Sorin Bicarbon valves, may help to identify Sorin Bicarbon prosthesis dysfunction.     

Stream Temperature Dynamics in Upland Agricultural Watersheds

A numerical model to compute the free-surface flow hydrodynamics and stream temperature dynamics by solving the depth-averaged, 1D unsteady flow and heat transport equations is presented. The hydrodynamics model considers the effects of arbitrary stream geometry, variable slopes, variable flow regimes, and unsteady boundary conditions. The thermal transport model accounts for the effects of solar radiation, air temperature, relative humidity, cloud cover, wind speed, heat conduction between water and streambed, subsurface flow, and shading by riparian vegetation. The model is verified with measurements in a stream in an upland agricultural watershed located in Indiana. Diurnal variations in the streamflow and stream temperatures are highly transient. The proposed model predicted well the streamflow and stream temperatures that were measured every 15 min over 25 days. The results of this study demonstrate that the solar (shortwave) radiation and subsurface inflow are the most significant contributors to the stream heat budget.     

Efficiency of two pancreatic extracts in patients with cystic fibrosis

Mechanical cell damage was studied in vitro with three types of prostheses: Starr-Edwards, Kay-Shiley and Bj?rk-Shiley valves. Mechanical cell damage was found to be closely related to the flow characteristics in the prosthesis. Considering valves of similar orifice diameter, Bj?rk-Shiley valves produced the lowest rate of haemolysis. This is due to the improved haemodynamic characteristics of the valve which resulted from the laminar type of flow. With Starr-Edwards valves, smaller sizes produced unacceptably high rates of haemolysis. Increasing the mean forward flow across the valve resulted in a disproportionate rise in the energy loss and the rate of haemolysis when compared with Bj?rk-Shiley valves of similar annulus diameters.     

Programmed endothelial cell death induced by an avian hemangioma retrovirus is density dependent

Hemangiomas are localized tumors of vascular cells which appear frequently in humans and animals, and their mode of induction is unknown. Recently, a new field strain of avian retrovirus, avian hemangioma virus (AHV), was isolated from spontaneous hemangiomas in layer hens. Sequence analysis of the AHV genome revealed the presence of three prototypic retroviral genes, gag, pol, and env, but no oncogenes. AHV was capable of inducing hemangiomas in hens in vivo, but it induced a strong cytopathic effect in cultured endothelial cells. The AHV envelope glycoprotein, gp85, was found to be responsible for the cell-killing effect. Four independent lines of experimental evidence indicated that AHV induces a cytopathic effect through a typical programmed cell death, apoptosis: (i) morphological changes in cells visualized by light microscopy, (ii) nuclear condensation and fragmentation indicated by 4',6-diamidino-2- phenylindole staining, (iii) intranucleosomal degradation of DNA demonstrated by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling staining, and (iv) flow cytometry analysis of the DNA content of the infected cells. Quiescent endothelial G0/G1 cells were much more sensitive to AHV-induced apoptosis than actively dividing cells, suggesting that the AHV ability to induce apoptosis is dependent on the proliferative state of the infected cells.