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BACKGROUND: Historically, single port valveless pneumatic blood pumps have had a high incidence of thrombus formation due to areas of blood stagnation and hemolysis due to areas of high shear stress. METHODS: To ensure minimal hemolysis and favorable blood washing characteristics, particle image velocimetry (PIV) and computational fluid dynamics (CFD) were used to evaluate the design of a new single port, valveless counterpulsation device (Symphony). The Symphony design was tested in 6-h acute (n=8), 5-day (n=8) and 30-day (n=2) chronic experiments in a calf model (Jersey, 76 kg). Venous blood samples were collected during acute (hourly) and chronic (weekly) time courses to analyze for temporal changes in biochemical markers and quantify plasma free hemoglobin. At the end of the study, animals were euthanized and the Symphony and end-organs (brain, liver, kidney, lungs, heart, and spleen) were examined for thrombus formations. RESULTS: Both the PIV and the CFD showed the development of a strong moving vortex during filling phase and that blood exited the Symphony uniformly from all areas during ejection phase. The laminar shear stresses estimated by CFD remained well below the hemolysis threshold of 400 Pa inside the Symphony throughout filling and ejection phases. No areas of persistent blood stagnation or flow separation were observed. The maximum plasma free hemoglobin (<10mg/dl), average platelet count (pre-implant = 473 ± 56 K/µl and post-implant = 331 ± 62 K/µl), and average hematocrit (pre-implant = 31 ± 2% and post-implant = 29 ± 2%) were normal at all measured time-points for each test animal in acute and chronic experiments. There were no changes in measures of hepatic function (ALP, ALT) or renal function (creatinine) from pre-Symphony implantation values. The necropsy examination showed no signs of thrombus formation in the Symphony or end organs. CONCLUSIONS: These data suggest that the designed Symphony has good washing characteristics without persistent areas of blood stagnation sites during the entire pump cycle, and has a low risk of hemolysis and thrombus formations.

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A computer program is described for beat-to-beat analysis of cardiovascular parameters from high-fidelity pressure and flow waveforms. The Hemodynamic Estimation and Analysis Research Tool (HEART) is a post-processing analysis software package developed in Matlab that enables scientists and clinicians to document, load, view, calibrate, and analyze experimental data that have been digitally saved in ascii or binary format. Analysis routines include traditional hemodynamic parameter estimates as well as more sophisticated analyses such as lumped arterial model parameter estimation and vascular impedance frequency spectra. Cardiovascular parameter values of all analyzed beats can be viewed and statistically analyzed. An attractive feature of the HEART program is the ability to analyze data with visual quality assurance throughout the process, thus establishing a framework toward which Good Laboratory Practice (GLP) compliance can be obtained. Additionally, the development of HEART on the Matlab platform provides users with the flexibility to adapt or create study specific analysis files according to their specific needs.

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Alternative therapies for treating heart failure patients are being explored to provide effective options for patients with progressive heart failure. Cardiac assist devices that promote myocardial recovery may be a potential solution. Ventricular assist devices (VAD) have demonstrated long-term efficacy and intraaortic balloon pumps (IABP) have shown short-term successes. In this paper, testing of a hybrid counterpulsation device (CPD) that couples the attributes of device longevity (VAD) with less invasive surgery (IABP) is presented. Hemodynamic and ventricular pressure-volume responses to a 40 ml CPD and 40 ml IABP were evaluated in vitro in an adult mock circulation and in vivo in a large animal heart failure model. The CPD is a flexing diaphragm ventricle with a controlled stroke volume up to 85 cc through a single, valveless cannula. In this study, the CPD was cannulated to the brachiocephalic artery to provide 40 ml of counterpulsation support. The CPD effectively provided diastolic augmentation increasing coronary flow and afterload reduction. These results were comparable to IABP. These preliminary studies suggest that CPD may be an effective therapy for treating patients with early stage heart failure.

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Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) that may better facilitate myocardial recovery than VAD by controlling the afterload seen by the ejecting heart is being developed. The AVD concept is to enable any user-defined input impedance (IM) with resistance (R) and compliance (C) components. In this study, a pulse duplicator was used to test the efficacy of the AVD concept for two control strategies in an adult mock circulation: (1) R-C in series and (2) 2-element Windkessel (R-C in parallel) using instantaneous impedance position control (IIPC) to maintain a desired value or profile of R and C. In vitro experiments were performed and the resulting cardiovascular pressures, volumes, flows, and the afterload (R and C) seen by the LV during ejection for simulated cardiac failure were recorded and analyzed. Our results indicate that setting the AVD to lower IM reduced LV volume and pressure, restored LV stroke volume, and increased coronary flow. The IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile, but are susceptible to measurement noise.

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Aside from the traditional diagnostic tools used to assess cardiac performance, such as blood pressure and cardiac output, cardiac source parameters can also be used as an indication of overall cardiac health. The cardiac source parameters under investigation are myocardial visco-elastic properties. The objective of this study is to model the left ventricle using electrical circuits, then use these models to estimate the cardiac source parameters. Two electrical models of the left ventricle have been developed, using a resistor (R) to model viscous losses, a capacitor (C) to represent inverse elastance, and a time-varying pressure source, which models the left ventricular pressure during an isovolumic beat. One model uses a single resistor and the other uses the two elements (R and C) in parallel. The differential equations describing these models have been derived, and a minimization procedure was used to adjust values of R and C in the differential equations until a good agreement between experimental and calculated left ventricular pressure was reached. Preliminary results indicate that the model including a parallel combination of R and C provides a better fit between experimental and calculated pressures. It is hoped that these parameters may one day provide clinicians with yet another diagnostic tool to help discover the source of cardiac disorders.

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The role of physiological elastance (Ep) in maximizing external work (EW) transfer is not well understood and has not been investigated during microgravity and increased acceleration conditions. By better understanding this relationship, cardiovascular control mechanisms for meeting metabolic demands during normal gravity and altered acceleration stresses may be elucidated. Therefore, the objectives of this study were to determine the effect of Ep in maximizing EW of the left ventricle and to investigate this relationship during altered acceleration states. Ventricular and arterial parameters were estimated using established lumped parameter models from isolated beats of experimental data. These data were obtained during parabolic flight (0 and approximately 2 Gz) and centrifuge runs (approximately 1 to approximately 4 Gz) where acceleration was used to drive the cardiovascular system into a wide range of physiologic operating and coupling conditions. Parameter estimates at each Gz level were used in a series of computer simulations in which Ep was varied over a wide range to find the point of maximum EW for that coupling condition. Cardiac output and mean arterial pressure were maintained throughout the simulation process by adjusting heart rate. Results of the simulation showed that as arterial elastance decreased from its initially estimated (physiologic) value, external work increased slightly and as elastance increased, external work decreased. In particular, we found that the arterial elastance was set at a point near that which would produce maximal external work. In addition, it was found that altered Gz states may affect the Ep-EW relationship.

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Effects of prescribed doses of ketamine five minutes after application and influences of transesophageal echocardiography (TEE) on left ventricular, systemic arterial, and baroreflex responses were investigated to test the hypothesis that ketamine and/or TEE probe insertion alter cardiovascular function. Seven rhesus monkeys were tested under each of four randomly selected experimental conditions: (1) intravenous bolus dose of ketamine (0.5 ml), (2) continuous infusion of ketamine (500 mg/kg/min), (3) continuous infusion of ketamine (500 mg/kg/min) with TEE, and (4) control (no ketamine or TEE). Monkeys were chronically instrumented with a high fidelity, dual-sensor micromanometer to measure left ventricular and aortic pressure and a transit-time ultrasound probe to measure aortic flow. These measures were used to calculate left ventricular function. A 4-element Windkessel lumped-parameter model was used to estimate total peripheral resistance and systemic arterial compliance. Baroreflex response was calculated as the change in R-R interval divided by the change in mean aortic pressure measured during administration of graded concentrations of nitroprusside. The results indicated that five minutes after ketamine application heart rate and left ventricular diastolic compliance decreased while TEE increased aortic systolic and diastolic pressure. We conclude that ketamine may be administered as either a bolus or continuous infusion without affecting cardiovascular function 5 minutes after application while the insertion of a TEE probe will increase aortic pressure. The results for both ketamine and TEE illustrate the classic "Hawthorne Effect," where the observed values are partly a function of the measurement process. Measures of aortic pressure, heart rate, and left ventricular diastolic pressure should be viewed as relative, as opposed to absolute, when organisms are sedated with ketamine or instrumented with a TEE probe.

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The objective was to determine whether a previously developed technique for biological aortic valves could predict flow through a mechanical valve. An electrical analog model of the aortic valve that includes compliance, resistance, and inertance parameters, and corresponding second order differential equations was used to predict flow given a pressure gradient, as previously reported. Simulated pressures and flow were recorded by using a pulse duplicator system. The heart rate was varied from 60 to 180 bpm, and the stroke volume was varied from 22 to 67 cc. Resistance, inertance, and compliance parameters of the governing differential equation were estimated by using a least-squares fit to the measured flow at 120 bpm and 50 cc stroke volume. By using these parameter estimates, flow was calculated for other heart rates and stroke volumes. To achieve a better flow prediction, a nonlinear filter (third order polynomial range calibration equation) was applied to the output of the linear model (flow). The mean error, full-scale error, and spectral error in magnitude and phase between measured and predicted flow were compared. Error in mean flow ranged from 3% at medium flow rates to 90% at low flow rates. The maximum and minimum full scale errors were 12% and 5%, respectively. Error in the harmonics of measured and calculated flow ranged from 0% to 55%. Larger errors were usually present at the higher harmonics. The agreement between measured and calculated flow was better at normal and high flows but rather poor at low flows. The nonlinear filter (range calibration equation) was unable to account for the discrepancies between the measured and calculated flow over all flow ranges. It seems that this linear model and nonlinear filter have limited application, and an alternate nonlinear approach may produce better results.

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BACKGROUND AND PURPOSE: Cardiac and arterial responses to prescribed doses of propofol and etomidate in rhesus monkeys were compared. METHODS: Intravenously administered induction doses of propofol (2 mg/kg of body weight) or etomidate (1 mg/kg) followed by continuous intravenous infusions of propofol (200 microg/kg/min) or etomidate (100 microg/kg/min) were administered. Left ventricular and right atrial access catheters were implanted for long-term use, along with a transit-time flow probe on the ascending aorta, and pericardial electrocardiogram leads. A dual sensor 3-F micromanometer was used to measure left ventricular pressure and aortic pressure, and an active redirectional transit-time probe measured aortic flow. Noordergraaf's four-element model was used to estimate total peripheral resistance and systemic arterial compliance. RESULTS: Significant (P < 0.01) decreases in mean arterial pressure, heart rate, and myocardial contractility were accompanied by an increase in systemic arterial compliance associated with propofol and etomidate. Only minimal changes in left ventricular diastolic pressure, cardiac output, stroke volume, and total peripheral resistance were found for both drugs. The changes associated with propofol are comparable to results in human beings, whereas the changes associated with etomidate did not agree with results of published human studies. CONCLUSION: The significant cardiovascular alterations associated with both agents were attributed to reductions in heart rate, although the possibility exists that negative inotropic effects may have had a role.

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The study of hemodynamics associated with coronary atherosclerotic stenosis has been limited due to the lack of a safe, accurate, and reliable technique to create an artificial stenosis in an animal model. Existing techniques have often resulted in myocardial infarction (MI) or severe injury to the vessel and have been difficult to accurately quantify and reproduce. We developed a new technique to create an artificial stenosis in the native left anterior descending (LAD) coronary artery using a hemoclip in an experimental off-pump coronary artery bypass graft (CABG) animal model that overcomes these limitations. The native LAD was dissected at its proximal end and a hemoclip was applied to create varying degrees of artificial stenosis in 30 mongrel dogs during experimental off-pump CABG procedures. The precise application of the hemoclip was predetermined using a mathematical formula to calculate the reduced circumference required to create a specific stenosis. Using these calculations, artificial stenoses of 25%, 50%, 75%, and 90% were created in the LAD. Postoperative angiography demonstrated only 5-10% error between the true (angiography) and estimated (hemoclip technique) stenosis values. In all cases, the vessel remained intact without any apparent external trauma, and no indications of MI were present during electrocardiograph (ECG) monitoring. The creation of an artificial coronary stenosis using the hemoclip technique was safe, reliable, easy, and accurate.

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OBJECTIVE: Flow probes have been introduced as a non-invasive means of anastomotic quality assessment in off-pump coronary artery bypass graft (CABG). Flow waveform morphology cannot reliably be assessed visually unless severe anastomotic stenosis is present ( > 90%). We applied spectral analysis techniques to determine whether the frequency content of graft flow can improve the surgeon's ability to detect anastomotic errors. METHODS: Forty-six mammary to left anterior descending artery (LAD) anastomoses were created in mongrel dogs during off-pump CABG surgery. Graft flow was measured using transit-time flow probes with the LAD closed, and the mammary graft patent and with varying degrees of stenosis. The degree of anastomotic stenosis was created by an artificial stitch and verified by random postoperative angiography. Spectral analysis of the graft flow waveforms was performed. Differences in the magnitude and phase components of the graft flow for the first five harmonics were determined for the varying anastomosis test conditions. Differences were determined using analysis of variance and least square means techniques. RESULTS: The magnitude of the fundamental (zeroth) harmonic was statistically different in the internal mammary artery (IMA) with 0-25% stenosis compared to IMA with 50-75% stenosis (P < 0.01 ). Further, the magnitude of the first, second, and fourth harmonics were statistically different in IMA with 0-25% compared to IMA with 75% (P < 0.01). The phase of the first harmonic was statistically different in IMA with 25% stenosis than IMA with 50% stenosis (P < 0.01 ). No differences in interaction between the LAD and IMA for all ranges of stenosis were detected (P > 0.50). CONCLUSION: Spectral analysis of graft flow waveforms may be beneficial in detecting lesser degrees of anastomotic stenosis (i.e. < 90%) compared to traditional visual assessment of mean graft flow and/or graft flow waveform morphology.

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Numerous parameter estimation techniques exist for characterizing the arterial system using electrical circuit analogs. These techniques are often limited by requiring steady-state beat conditions and can be computationally expensive. Therefore, a new method was developed to estimate arterial parameters during steady and transient beat conditions. A four-element electrical analog circuit was used to model the arterial system. The input impedance equations for this model were derived and reduced to their real and imaginary components. Next, the physiological input impedance was calculated by computing fast Fourier transforms of physiological aortic pressure (AoP) and aortic flow. The approach was to reduce the error between the calculated model impedance and the physiological arterial impedance using a Jacobian matrix technique which iteratively adjusted arterial parameter values. This technique also included algorithms for estimating physiological arterial parameters for nonsteady physiological AoP beats. The method was insensitive to initial parameter estimates and to small errors in the physiological impedance coefficients. When the estimation technique was applied to in vivo data containing steady and transient beats it reliably estimated Windkessel arterial parameters under a wide range of physiological conditions. Further, this method appears to be more computationally efficient compared to time-domain approaches.

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An in vitro pulsatile pump flow system that is capable of producing physiologic pressures and flows in a mock circulatory system tuned to reproduce the first nine harmonics of the input impedance of a rhesus monkey was developed and tested. The system was created as a research tool for evaluating cardiovascular function and for the design, testing, and evaluation of electrical-mechanical cardiovascular models and chronically implanted sensors. The system possesses a computerized user interface for controlling a linear displacement pulsatile pump in a controlled flow loop format to emulate in vivo cardiovascular characteristics. Evaluation of the pump system consisted of comparing its aortic pressure and flow profiles with in vivo rhesus hemodynamic waveforms in the time and frequency domains. Comparison of aortic pressure and flow data between the pump system and in vivo data showed good agreement in the time and frequency domains, however, the pump system produced a larger pulse pressure. The pump system can be used for comparing cardiovascular parameters with predicted cardiovascular model values and for evaluating such items as vascular grafts, heart valves, biomaterials, and sensors. This article describes the development and evaluation of this feedback controlled cardiovascular dynamics simulation modeling system.

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OBJECTIVE: The intra-operative assessment of the quality of anastomosis in minimally invasive coronary artery bypass surgery (CABG) is critical. Recent investigations demonstrated that flow probes used intra-operatively to assess anastomotic errors may give the surgeon a false sense of confidence as only severely stenotic anastomoses (>90%) could be reliably detected. We developed a neural network system using graft flow data and assessed its potential to improve anastomotic error detection. METHODS: Mammary to LAD grafts (n = 46) were constructed in mongrel dogs off-pump. Continuous beat-to-beat graft flow was recorded using transit-time flow probes. Various degrees of anastomotic stenoses (0-100%) were created by an additional suture. The degree of anastomotic stenosis was confirmed by postoperative angiography. A learning vector quantization neural network was created using heart rate, mean aortic pressure, mean systolic, maximum systolic, minimum systolic, mean diastolic, maximum diastolic, minimum diastolic, and mean graft flows. In addition, a spectral analysis of the flow waveforms was performed and the magnitude and phase of the first five harmonics were used to further develop the neural network. RESULTS: The neural network pattern recognition system was 94% accurate in detecting any stenosis >50%. To validate the model, a testing set was used with 20% of the data values, and the accuracy remained at 100% above chance alone. CONCLUSION: Pattern recognition of transit-time flow probe tracings using neural network systems can detect anastomotic errors significantly better than the surgeon's visual assessment, thereby improving the clinical outcome of minimally invasive CABG.

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The objective was to develop a technique for calculating continuous, beat-to-beat aortic flow (AoF) using only left ventricular pressure (LVP) and aortic pressure (AoP). An electric analog model of the aortic valve was developed that includes resistance (R), inertance (L), and compliance (C) parameters, and resulting second order differential equations were derived. Aortic flow, AoP, and LVP recorded in eight subjects during a 5 day period and during lower body negative pressure (LBNP) were used to validate the model. Resistance, L, and C were estimated using a least-squares fit to the measured AoF on day 0 and during 0 mm Hg LBNP. For days 1-4, AoF was calculated using measured values of AoP and LVP and the R, L, and C values from day 0. Similarly, for LBNP, AoF was calculated using measured values of AoP and LVP, and the R, L, and C values from 0 mm Hg LBNP. The calculated and measured AoF were compared. Differences in cardiac output between the calculated and measured flows were less than 13.1+/-17% across days and under minor altered physiologic conditions (LBNP). Waveform morphology for the calculated AoF also agreed well with the measured AoF. Spectral analysis showed differences in magnitude and phase between measured and calculated aortic flow for the first five harmonics across days, less than 20+/-6% and 25+/-14 degrees, respectively. Preliminary evaluation indicates that our model works well for calculating flow through a biologic valve using LVP and AoP. We speculate that it may perform better for a mechanical valve, and if so it may be possible to develop an instrumented mechanical valve capable of continuous LVP, AOP, and AoF measurements.

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We assessed the acute cardiovascular changes of partial left ventriculectomy (PLV) in a patient with idiopathic dilated cardiomyopathy (IDCM) without mitral regurgitation. Acutely, PLV reduced left ventricular (LV) end-diastolic dimension and volume while increasing LV ejection fraction and cardiac output due to increased HR and SV. Substantial increases in LV filling pressure, possibly due to high LV end-systolic and diastolic elastances, were of concern clinically and the mechanism(s) of change remain unclear. However, one year follow-up showed remarkable improvements in NYHA and VO2 max while maintaining reduced LV volume, increased LVEF, and trivial MR.

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OBJECTIVE: Partial left ventriculectomy has been introduced as an alternative surgical therapy to heart transplantation. We performed a single-center, retrospective analysis of all patients with idiopathic dilated cardiomyopathy who underwent partial left ventriculectomy or heart transplantation or who were listed for transplantation to determine operative mortality rate, 12-month survival, freedom from death on the heart transplantation waiting list, and freedom from death or need for relisting for heart transplantation. METHODS: Patients who had partial left ventriculectomy (October 1996 to April 1998) were retrospectively compared with patients who were listed for heart transplantation (January 1995 to April 1998). Survival was assessed after the surgical procedure (partial left ventriculectomy vs heart transplantation) and from time of listing for heart transplantation to assess the additional impact of waiting list deaths. Freedom from death or relisting for heart transplantation was also compared. RESULTS: There was no difference in age or United Network for Organ Sharing status between the 2 groups. Twenty-nine patients with idiopathic dilated cardiomyopathy were listed for heart transplantation; 17 patients underwent transplantation, 6 patients died while on the waiting list, and 6 patients remain listed. One patient died after heart transplantation, and 1 patient required relisting. Sixteen patients had partial left ventriculectomy; 10 patients are in improved condition, 2 patients died (1 death early from sepsis and 1 death from progressive heart failure), and 4 patients required relisting for heart transplantation. Operative survival was 94% after partial left ventriculectomy and 94% after heart transplantation (P =.92). Postoperative 12-month Kaplan-Meier survival was 86% after partial left ventriculectomy and 93% after heart transplantation (P =.90). Twelve-month Kaplan-Meier survival after listing for heart transplantation was 75% due to death while on the waiting list (P =.76). Freedom from death or need for relisting for heart transplantation was 56% after partial left ventriculectomy and 86% after transplantation (P =.063). CONCLUSION: Operative and 12-month survival after partial left ventriculectomy and heart transplantation were comparable. However, despite their initial improvement, many patients who underwent partial left ventriculectomy required relisting for transplantation. Although partial left ventriculectomy is associated with acceptable operative and 12-month survival, it may prove to serve better as a bridge to transplantation in patients with idiopathic dilated cardiomyopathy rather than definitive therapy, given the number of patients who required relisting for transplantation.

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Anastomotic quality is a critical issue in minimally invasive coronary artery bypass surgery, particularly "off-pump". It is important to detect a "poor" anastomosis during the procedure so future re-operation can be avoided. Methods such as intraoperative angiography, thermal angiography, probing of the anastomosis, and graft flow measurement have been used intraoperatively to help identify anastomotic errors. With the evolution of stabilizers, graft patency rates for off-pump cases have improved, but many believe they are still not as high as those of the conventional procedure. For off-pump surgery to be accepted and practiced universally, patency rates must be equivalent to those of "on-pump" cases. Transit-time flow measurement has become an increasingly popular non-invasive method for assessing anastomotic quality. However, it is difficult to establish whether an anastomosis is patent based on mean graft flow alone. Spectral analysis of graft flow waveforms reveal characteristic patterns that identify intermediate ranges of stenosis between fully patent and totally occluded. Together, these two components of graft flow have been used in the construction of a neural network to help identify "faulty" anastomoses. Transit-time flow measurement is a non-invasive tool that can be beneficial in identifying fully patent or nearly occluded grafts, and may also help in distinguishing intermediate stenoses.

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We measured central venous pressure (CVP), plasma volume (PV), urine volume rate (UVR), and circulating hormones (renin activity (PRA), vasopressin (AVP), atrial natriuretic peptide (ANP), and cortisol) before and after acute volume infusion (Dextran-40) to test the hypotheses that head-down tilt bedrest (HDT) caused (1) a resetting of the CVP operating point and (2) attenuated urine excretion. Six rhesus monkeys underwent two experimental conditions (HDT and control, each of 48 hour duration) with each condition separated by nine days of ambulatory activities to produce a cross-over counterbalance design. One test condition was continuous exposure to 10 degrees HDT and the second test condition was a control, defined as approximately 12-14 hours per day of 80 degrees head-up tilt and 10-12 hours prone. Following 48 hours of exposure to either test condition, 20-minute continuous infusion of Dextran-40 was administered. CVP in HDT was lower than the control condition. Similar elevations in CVP occurred 30 min post-infusion in both test conditions, and returned to pre-infusion baseline levels between 22 and 46 h post-infusion in both treatments. The UVR response during infusion was attenuated by HDT despite similar elevation in CVP. Elevation in ANP and reduction in PRA at the end of infusion were greater in Control compared to HDT. No differences between control and HDT were detected for AVP and cortisol responses to infusion. Since CVP returned to its pre-infusion levels following volume loading in HDT and control conditions, it appeared that the lower CVP may reflect a new operating point about which vascular volume is regulated. Further, attenuated ANP and PRA responses during vascular volume loading may contribute to depressed UVR in low gravity exposure.

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OBJECTIVE: Flow probes are being used for intraoperative assessment of anastomotic quality during off-pump coronary artery bypass grafting (CABG). We conducted a survey with the cooperation of 19 international surgeons to assess the ability of surgeons to detect anastomotic errors by evaluating mean flow and flow waveform morphology. MATERIAL AND METHODS: Mongrel dogs underwent mammary to left anterior descending (LAD) grafting. Mean graft flow and flow wave morphology for varying degrees of anastomotic stenoses were recorded using transit-time flow probes. A questionnaire consisting of ten different recorded flow tracings and the corresponding mean flows were given to 20 surgeons from around the world. The surgeons were asked to determine the degree of stenosis and whether they would re-do the anastomosis based upon the mean flow and the flow tracings. RESULTS: All of the 19 surgeons that responded were able to clearly identify a highly stenotic graft (>90% stenosis). However, 24% would re-do a fully patent anastomosis, 58% accepted an anastomosis with moderate stenosis, and 72% accepted anastomoses with severe stenosis. CONCLUSIONS: Evaluation of flow tracing morphology and/or mean flows can be used to reliably detect nearly occluded anastomoses (>90% stenosis). However, surgeons should be cautious in assessing anastomoses with lesser degrees of stenosis, as they may be more difficult to reliably interpret.

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