Transonic Systems Research Articles

DEVELOPMENT OF A PUMP OUTPUT ESTIMATION ALGORITHM USING MOTOR CURRENT FOR A PULSATILE IMPLANTABLE VAD

The authors developed an algorithm for estimation of the blood pump output using a waveform feature parameter in motor current signal in a pulsatile implantable ventricular assist device with pancake shaped blood sac and pusher-plate on a cylindrical cam. The waveform feature in the motor current during systole period that has high correlation to blood sac filling volume is the duration when the motor current is higher than a specific level in one systole period that can he related to effective stroke volume or the filling volume. The analysis is based on both in vitro and in vivo data. The estimated flow rate showed high correlation to the measured value. Estimated relative filling volume ranged from 26% to 94% depending on the preload and the pump rate. The actual flow rate was measured by an ultrasound flow meter (Tl06, Transonic Systems Inc., USA). The correlation between the estimated and the measured flow rate was investigated by a least square regression analysis. The correlation coefficient at the pump rate of 50 to 100 bpm was 0.9455 ± 0.0085. The error between the estimated and the measured flow rate was ranged from −0.5 to +0.2 L/min over all conditions. Errors in different afterload conditions were −0.5 ∼−0.1 L/min at 80mmHg, −0.3 ∼ +0.2 L/min at 100mrnHg. and −0.2 ∼ +0.1 L/min at 120mmHg, respectively. In the motor current signal analysis, the systolic peak showed high correlation to the afterload and was considered to improve the accuracy of flow estimation.

Myocardial Protection During Cabg Procedures: "The Optimal Flow For Bloodcardioplegia During Aortic Occlusion Is Regulated By The Heart Itself"

Myocardial protection remains an important, much discussed subject in cardiac surgical practice. Literature describes different methods. A minimal haemodilutional method of arresting and protecting the heart using warm oxygenated patient blood directly from the oxygenator is described by Calafiore et.al. bloodcardioplegiaflow (BCF) during aortic occlusion is regulated by a rollerpump. Following a defined protocol, a syringepump is set to deliver the highly concentrated potassiumsolution in the bloodcardioplegia line. Myocardial protection remains an important, much discussed subject in cardiac surgical practice. Literature describes different methods. A minimal haemodilutional method of arresting and protecting the heart using “warm” oxygenated patient blood directly from the oxygenator is described by Calafiore et.al. bloodcardioplegiaflow (BCF) during aortic occlusion is regulated by a rollerpump. Following a defined protocol (table 3), a syringepump is set to deliver the highly concentrated potassiumsolution in the bloodcardioplegia line. Figure 1 Table 3: Blood cardioplegia intervals This method of protecting the heart during aortic crossclamping appears to be more effective then cold crystalloid cardioplegia. However, using a defined BCF can be at a disadvantage because this method does not take into consideration the myocardial mass and functional status of the heart. To overcome these limitations we modified the Calafiore-method in the “Isala”-method to provide pressure/afterload regulated cardioplegia flow delivery. BCF is generated by the centrifugalpump which is integrated in our extra corporeal circuit and situated before the oxygenator. Oxygenated blood derived from the recirculationport of the oxygenator is supplemented with concentrated potassiumsolution (2 mmol/ml) and delivered directly to the myocardium through an aortic-root cannula (figure 1 and table 1). Myocardial Protection During Cabg Procedures: The Optimal Flow For Bloodcardioplegia During Aortic Occlusion Is Regulated By Heart Itself 2 of 5 Figure 2 Table 1: Components extra corporeal circuit Figure 3 Figure 1: Extra corporeal circuit BCF is measured with an ultrasonic flowmeter (HT311, Transonic Systems). value of the BCF depends on the pressure at the outletport, which equals arterial linepressure, the length of the cardioplegia line, the pressuredrop over the aortic-root cannula or saphenous vein cannula (figure 2) and, most important, the functional status of the heart and the resistance of the myocardial vasculature. Figure 4 Figure 2: Pressuredrop coronary cannula To achieve a potassium concentration of either 20 mmol/l (initial dose) or 10mmol/l (maintenance dose) the settings of the potassium syringepump are based on the measured flowrate and the patients systemic potassium concentration. This 'Isala'-technique results in a selfregulated BCF with the advantages of a centrifugalpump such as an automatic pressure limitation in the bloodcardioplegia system and the heart itself. BCF gives additional information about the presence and degree of aortic insufficiency and also about the quality of the anastomoses. This pilot-study compares the 'Isala' technique with the Calafiore technique and with the use of cold St.Thomas Hospital II cardioplegia. 60 consecutive patients (20 in each group) scheduled for first time coronary bypass surgery were enrolled in this study. All patients were operated on by the same cardiac surgeon. There were no significant differences between the groups regarding to ECC time, aortic crossclamping time and number of anastomoses (table 2). We observed that the BCF was higher with the 'Isala' technique (figure 3). Myocardial Protection During Cabg Procedures: The Optimal Flow For Bloodcardioplegia During Aortic Occlusion Is Regulated By Heart Itself 3 of 5 Figure 5 Figure 3: Blood cardioplegia flow duration of bloodcardioplegia delivery was shorter with the Isala technique (figure 4). amount of potassium administered equals the Calafiore technique (table 2). Figure 6 Table 2: Patient data Figure 7 Figure 4: Bloodcardioplegia perfusion time We observed that the CK and CK-mb was lower with the 'Isala'-technique compared with the Calafioreor crystaloid technique (figure 5). Figure 8 Figure 5: CK and CK-mb In conclusion we find the 'Isala'-technique a safe and easy method of delivering an optimal BCF during aortic occlusion and that it can be used safely for any cardiac surgical procedure requiring myocardial arrest. selfregulating characteristics of the 'Isala'-technique showed that the flow for bloodcardioplegia depends on the (metabolic) demands of the heart itself and that it varies between 100 and 550 ml/min. We observed a better myocardial protection during CABG procedures. optimal and/or maximal duration of the ischaemic intervals and the duration of the bloodcardioplegia delivery has to be investigated. Further research is necessary to determine the clinical improvement using this technique.

Relationship between effective ionic dialysance and in vivo urea clearance during hemodialysis

Effective ionic dialysance (EID) can be measured from dialyzer inlet and outlet conductivity changes following two steps of dialysate conductivity. Relationships between EID and in vivo urea clearances were studied four times per hemodialysis treatment in eight patients, each undergoing six hemodialysis treatments (192 data sets). Dialyzer blood flow was varied from 190 to 500 mL/min. Dialysate flow was constant (751 to 771 mL/min), and a standard dialyzer (700 HG; Cobe, Lakewood, CO) was used. Double samples were drawn for arterial, venous, and dialysate urea measurements. Two laboratory values were missing. Twelve unreliable laboratory values indicated by divergent results were excluded. Urea clearances were calculated by formulae converting whole-blood to blood-water urea clearances. EID was measured using Diascan (Gambro-Dasco, Medolla, Italy). Mass balance was checked by comparison of dialysate and blood-water urea clearances. Divergent results between dialysate and blood-water urea clearance values led to the exclusion of an additional three laboratory values. A small error (4.2%) in urea mass balance was found (dialysate greater than blood-water urea clearances). A total of 175 data sets were compared. EID showed excellent correlation with blood-water urea clearances (r = 0.92) over the line of identity, with a mean difference of −3.5 mL/min (−1%), and similarly with dialysate urea clearances (r = 0.92; mean difference, −13.4 mL/min; −5%). For both blood- and dialysate-side comparisons, differences increased with greater clearances. Because EID is an effective clearance and urea clearance is a measure of dialyzer clearance, the curves were corrected for cardiopulmonary recirculation; access recirculation was zero (Transonic monitor; Transonic Systems Inc, Ithaca, NY). For cardiopulmonary recirculation correction, cardiac output and access flows were assumed to be 6.4 L and 1.46 L/min. Corrected data show EID correlates with blood-side urea clearance (r = 0.92), with a mean difference of +7.3 mL/min (3.3%), and is constant over the range of clearances. EID correlated with dialysate urea clearance (r = 0.92) with virtually no difference. The difference on the blood side is consistent with the urea mass balance error found. These data indicate that EID using Diascan can provide an accurate indication of effective urea clearances obtained during hemodialysis and is of value in monitoring dialysis adequacy. © 2001 by the National Kidney Foundation, Inc.

Effects of cerebrospinal fluid loss and epidural blood patch on cerebral blood flow in swine

Background and Objectives: The purpose of this study was to test the hypothesis that loss of cerebrospinal fluid (CSF) causes cerebral vasodilatation, which is reversible with peridural injection of autologous blood. Methods: Ten pigs were anesthetized with an infusion of propofol and remifentanil and mechanically ventilated to normocapnia with air and oxygen (60%). Cisternal puncture was performed and increments of 1 mL of cerebrospinal fluid were aspirated. After each milliliter was removed, hemodynamic and respiratory variables and cerebral blood flow (CBF) were measured, the latter with a transdural laser Doppler flowmeter (BLF 21; Transonic Systems Inc, Ithaca, NY) through a cranial burr hole. After 9 mL of CSF had been removed, 10 mL autologous blood was injected into the lumbar epidural space, and the CBF and other variables were measured immediately and 5 minutes thereafter. Ten milliliters of autologous blood was then injected subdurally and the measurements repeated. Data were analyzed for significant differences from the baseline and previous values by repeated analysis of variance. Results: CBF increased from 44.7 ± 7.97 tissue perfusion units (TPU) (mean ± SEM) at baseline to 75.3 ± 13.53 TPU after removal of the first 7 mL of CSF ( P < .0001). Following injection of 10 mL of blood into the epidural space, CBF immediately decreased to 47.6 ± 9.18 TPU. After subdural injection of blood, the CBF decreased further to 20 ± 3.77 TPU. Conclusions: The increase in CBF probably represents cerebral vasodilatation. The immediate return of CBF to baseline values after epidural injections of blood, and to lower values after subdural injections of blood, was probably due to vasoconstriction. The data suggest that postdural puncture headache, and its successful treatment with epidural blood patch, can probably be ascribed to cerebrovascular dynamics. Reg Anesth Pain Med 2001;26:401-406.

Establishment of a Simple Method for Measurement of Chronic Blood Flow in Uterine Artery of Pregnant Cows

Blood flow to the gravid uterine horn of seven multiparous Holstein cows (mean±SD, BW = 625.5±82.4kg; age = 4.7±1.7 yr; parity = 2.9±1.1 yr) was measured from d 225 of gestation to parturition using transit-time ultrasonic blood flow probes placed around the middle uterine artery. Surgery was conducted on d 215 of gestation. The cows were sedated with xylazine and local anesthesia (procaine or bupivacain hydrochloride) during surgery. The surgical operations were conducted at the flank of standing cows. A transit time ultrasonic flow probe (“S” series, diameter 12 or 14mm, Transonic Systems Inc., Ithaca, NY) was fitted surgically around the uterine artery of each cow. Surgery was completed within 2h of anesthesia, and the animals recovered rapidly following surgery. Uterine blood flow (UBF, L/min) was recorded at 10-s intervals for 1395min; these values were averaged to determine UBF. Cows exhibited normal gestation lengths (279.1±7.4 d), gave birth to normal healthy calves (birth weight = 40.6±6.6kg), and had no retained placentas. The UBF increased significantly (P<0.01) from d 225 (6.67±2.47) to d 249 (8.23±2.89) of gestation, but the latter UBF was similar to that of d 266 (8.38±2.70). The increased UBF after d 225 indicates increased demand of nutrients of fetus with the progress of gestation. The range of mean UBF varied widely among individual cows from 4.1 L/min to 12.2 L/min. Our method is useful for chronic measurement of UBF in cows for nutritional or physiological studies and does not require sophisticated facilities or special surgical technique.

Flow quantification of the non-occlusive excimer laser-assisted EC-IC bypass.

For six years, we used the Excimer laser-assisted nonocclusive anastomosis technique for high-flow revascularization of the brain in patients with either nonclippable and noncoilable giant aneurysms of the internal carotid or basilar artery or progressive stroke associated with occlusive disease of the internal carotid artery. The aim of this study is to assess the blood flow capacity of this type of Extra-Intracranial bypass and its haemodynamic behaviour over time. Twenty-six patients with a giant aneurysms and 8 patients with occlusive disease of the internal carotid artery were treated with the nonocclusive Excimer laser assisted EC-IC bypass. intra-operatively, direct measurements of flow in the EC-IC bypass were performed in all patients (Transonic Systems, Inc., Ithaca. NY). Postoperatively, follow up measurements of flow were performed with MR angiography in 14 patients with a giant aneurysm after occluding the internal carotid artery, and 7 patients with occlusive carotid disease. The mean flow in the laser assisted bypasses in the group of patients with a giant aneurysm was 158 ml/min after ligation or balloon occlusion of the ICA. The mean flow of the laser assisted bypass in the group of patients with ICA occlusive disease was 130 ml/min. A comparison with data on flow capacity of conventional EC IC bypasses is made. A demonstrated increase of flow in the bypass during follow up is discussed from a haemodynamic point of view. The results of this study demonstrate that the flow capacity of the nonoccluding excimer laser assisted bypass is much higher than the capacity of the conventional, more peripherally located conventional EC IC bypass, and should therefore be denoted as High-Flow EC IC bypass. Consequently, this type of bypass can be a powerful and safe tool in new revascularization strategies.

Noninvasive transcutaneous determination of access blood flow rate

Current indicator dilution techniques for determining the vascular access blood flow rate (Qa) require reversal of the dialysis blood lines and are time consuming. We have recently described an indicator dilution technique for determining Qa using a novel optical transcutaneous hematocrit (Hct) sensor that does not require reversal of the dialysis lines, and have validated the accuracy of this method (TQa) in vitro. This study compared results using the TQa method with those obtained using a similar indicator dilution technique but which required reversal of the dialysis lines (HD01 Monitor, Transonic Systems, Ithaca, NY, USA) during routine hemodialysis in 59 patients (25 native fistulas and 34 synthetic grafts). The sensor for the TQa method was placed on the skin directly over the access to measure changes in Hct approximately 25 mm downstream of the venous needle. A single 30 mL bolus of saline was infused into the dialyzer venous line over approximately six seconds without reversal of the dialysis blood lines, and the vascular access flow rate was calculated using indicator dilution methods from the time-dependent decrease in the Hct downstream of the venous needle. Two additional small-scale studies were performed to assess the effect skin pigmentation and to evaluate further the reproducibility of the TQa method. Qa values determined by the TQa method were highly correlated with those determined by the HD01 method (N = 72, R2 = 0.948, P < 0.001) over the range of 153 to 2,042 mL/min. There was no significant difference between vascular access flow rates determined by the TQa method and those determined by the HD01 Results from one small-scale study showed that the relationship between Qa values determined by the TQa and the HD01 methods was similar when tested only among black patients (N = 12), suggesting that skin pigmentation is not an important determinant of the accuracy of the TQa The second small-scale study showed that the intratreatment coefficient of variation for the TQa method was 7.8 +/- 5.6% (N = 14). : These results show that transcutaneous measurement of Qa is an accurate, simple, and fast technique for determining Qa without requiring the reversal of the dialysis blood lines.

Cranial rhythmic impulse related to the Traube-Hering-Mayer oscillation: comparing laser-Doppler flowmetry and palpation.

The primary respiratory mechanism (PRM) as manifested by the cranial rhythmic impulse (CRI), a fundamental concept to cranial osteopathy, and the Traube-Hering-Mayer (THM) oscillation bear a striking resemblance to one another. Because of this, the authors developed a protocol to simultaneously measure both phenomena. Statistical comparisons demonstrated that the CRI is palpably concomitant with the low-frequency fluctuations of the THM oscillation as measured with the Transonic Systems BLF 21 Perfusion Monitor laser-Doppler flowmeter. This opens new potential explanations for the basic theoretical concepts of the physiologic mechanism of the PRM/CRI and cranial therapy. Comparison of the PRM/CRI with current understanding of the physiology of the THM oscillation is therefore warranted. Additionally, the recognition that these phenomena can be simultaneously monitored and recorded creates a new opportunity for further research into what is distinctive about the science and practice of osteopathic medicine.

Physiological Evaluation of the Results of Myocardial Revascularization in Patients with Ischemic Heart Disease

Intraoperative assessment of the myocardial blood flow was performed in different heart areas in 94 patients with ischemic heart disease prior to and after myocardial revascularization. An ALF-21 laser–Doppler flowmeter (Transonic Systems Inc.) was used to measure the myocardial blood flow near the anterior and posterior surfaces of the left ventricle (LVasand LVps, respectively) and the anterior surface of the right ventricle (RVas). According to the results of revascularization, the patients were divided into four groups: group I with increased myocardial blood flow in all areas tested, group II and group III with blood flow redistributed along LV and RV, and group IV with moderately decreased myocardial blood flow in all test areas. All groups showed a postoperative decrease in blood flow differences between different myocardium areas and the leveling of blood flow in the whole myocardium. The efficiency of revascularization depended on a number of factors, including the initial level of myocardial blood flow, completeness of revascularization of ischemic areas, the number and quality of bypass grafts, and the patients' age. The most pronounced positive results were observed in patients under the age of 60 years.

Variation of intra-access flow early and late into hemodialysis.

Intra-access flow (Qac), measured by ultrasound dilution, is a reliable method for screening for access dysfunction. Because of a reduced circulating volume and a relative decrease in blood pressure at the end of hemodialysis (HD), we hypothesized that Qac could be significantly reduced when measured late into HD. Fifty patients were prospectively evaluated for variation in Qac early and late into HD. There were 33 native fistulae and 17 synthetic grafts. Six separate measures of Qac were performed for each patient by ultrasound dilution (Transonic HD01 hemodialysis monitor; Transonic Systems, Inc., Ithaca, NY): three within the first 30 minutes and three within the last 30 minutes of HD. Session time was 3.5 or 4 hours, and mean net ultrafiltration was 3.3 +/- 0.9 L/HD. Early and late into HD, mean arterial pressure (MAP) decreased from 100.0 +/- 14.6 to 92.8 +/- 17.8 mm Hg, heart rate from 73 +/- 11 to 79 +/- 15 bpm, and hematocrit increased from 34 +/- 3 to 38 +/- 4%. For the whole group, mean Qac decreased from 1,101.7 +/- 566.7 to 972.5 +/- 515.6 ml/min (p = NS); when Qac was corrected for a MAP of 100 mm Hg, the reduction remained nonsignificant (from 1,101.7 to 1,048.0 ml/min). When considering native and synthetic fistulae separately, the drop in Qac was still nonsignificant (from 1,098.9 +/- 613.4 to 983.2 +/- 593.2 for native fistulae versus 1,107.2 +/- 480.5 to 999.8 +/- 379.8 ml/min for grafts, p = NS). Overall, the percent reduction in Qac early versus late into HD was 11.7%, whereas it reached only 4.9% when access flows corrected for MAP were considered. We conclude that variation in Qac during HD is relatively small, especially when values are corrected for MAP. Therefore, according to our results, Qac measures by using the ultrasound dilution method made at any time during HD should be reliable for most patients.

BLOOD FLOW IN RAT CAROTID ARTERY AFTER MECHANICAL INJURY

Introduction. Reactive neointimal proliferation following mechanical injury in rat carotid artery is a commonly used animal model for postangioplasty restenosis. The majority of studies dealing with prevention of restenosis use the anatomical index of neointimal area as the only indicator for success of intervention. The goal of our study is to characterize blood flow in injured carotid arteries. Such information will provide an essential data to be used in studies of the effects of vasoactive anesthetic drugs given to patients with carotid artery stenosis. Methods. The left common carotid artery of 24 Sprague-Dawley rats weighting 350-450 g was injured by three passages of inflated 2F Fogarty catheter under general anesthesia. Blood flow was assessed in the common carotid artery before injury and 30 min after injury. The rats were recovered and a second operation was performed at different time points to study flow in the injured artery. Measurements were performed at 4, 7, 14 and 21 days after injury. For flow measurements an Ultrasonic Blood Flowmeter (Transonic Systems Inc., USA) with microcirculation probe 1RB was used. We also measured flow in other 8 rats at 14 days after injury and compared the flow in the injured artery to the right, uninjured, common carotid artery. Degree of anatomical narrowing was determined by ratio of neointima area to media area (I/M), measured by morfometric computerized planimetry. Results. (Table 1)Table 1Reduction in flow was found immediately after injury and was followed by slow rise in flow to up to 80% of baseline. In the 8 rats studied at 14 days flow in the left common carotid artery was 62% of the flow value in the right uninjured common carotid artery. Neointimal proliferation was not found at the 4th day and only in two rats at 7th day. Significant proliferation was observed at the 14th and 21st day, I/M ratio was 1,28 +/- 0.6 and 1,17 +/- 0.1 accordingly. Discussion. Blood flow in rat carotid artery continued to rise progressively up to 21st day after mechanical injury despite progressive neointimal proliferation and lumen narrowing. Characterization of blood flow in the narrowed rat carotid arteries may serve as a potent research tool for the study of vasoactive anesthetics.

Validation of haemodialysis recirculation and access blood flow measured by thermodilution.

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. 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. 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. BTM thermodilution yields results which are consistent with the HDM ultrasound dilution technique with regard to both recirculation and access flow measurement.

Use of an extracorporeal arteriovenous tubing loop to measure cardiac output in intensive care unit patients by ultrasound velocity dilution.

Thermodilution cardiac output (CO) measurement requires heart catheterization and is known as a risk factor. The existing cannula in the radial artery in intensive care unit (ICU) patients can be used to measure CO by ultrasound dilution (COus). An arteriovenous shunt between the radial artery and cubital vein was created using a 25 cm tubing loop. An ultrasound flow dilution sensor was clamped on the tubing and connected to a modified HD01 monitor (Transonic Systems, Inc., Ithaca, NY). Calibration injections of 1 ml 0.9% NaCl were injected into the tubing. An intravenous bolus injection consisted of 10-20 ml 0.9% NaCl. Simultaneously, CO was measured by thermal dilution (COth; MI 166A, Hewlett Packard, Andover, MA). Each value for COth or COus was based on the average of three to five injections. Blood flow through the shunt was 10 to 26 ml/min. The comparison was made on 14 patients. In 33 measurements, the regression equation was COth = -0.08 + 1.02 COus (r = 0.97). In 22 cases, the difference between COth and COus was less than 5%, in 9 cases it was in the range of 5-10%, and in 2 cases it was in the range of 10-20%. The presence of arterial and venous lines in an ICU setting obviates the need for cardiac catheterization for the determination of CO.

A new approach to evaluate vascular access in hemodialysis patients.

We evaluated the importance of vascular access in hemodialysis patients using noninvasive methods with the Transonic Systems monitor in 108 patients. Most of these patients (84%) had native vein fistulas. We found that a blood flow rate of below 500 ml/min suggested the occurrence of vascular stenosis and justified confirmation by angiography. Increased recirculation could be evaluated readily and was detected in only 10% of patients. Finally, employing the evaluation of the Kt/V index, we found a good correlation between low flux through the fistula and a low Kt/V value.

Effective blood flow and recirculation rates in internal jugular vein twin catheters: Measurement by ultrasound velocity dilution

The ultrasound dilution technology (Transonic Systems, Ithaca, NY) is a reliable method to assess blood flow (Qb) and recirculation rates (R) in vascular access during hemodialysis. However, the information available on these parameters for central venous dialysis catheters remains scarce at this point. Real Qb and R were evaluated in 33 well- functioning TwinCath (Medcomp, Harleysville, PA) inserted as mid- or long-term hemodialysis vascular access (mean duration since insertion, 270 +/- 253 days); all were implanted into the right internal jugular vein with their multiperforated distal tips located in the superior vena cava or right atrium. Several types of dialysis machines were used (Monitral and AK100, Hospal-Gambro, Lyon, France; 2008E and 4008E, Fresenius, Bad Homburg, Germany). Real Qb was measured with the ultrasound dilution method and compared with the set Qb (indicated by the dialysis machine); R, also evaluated by ultrasound dilution, was evaluated at various Qb with nonreversed lines; therefore, a total of 121 measures were performed. Arterial and venous pressures (PA and PV) were recorded simultaneously. The 33 measures at a set Qb of 200 mL/min showed a mean effective Qb of 210 +/- 18 mL/min and a mean R of 5.3 +/- 5.3%. At a Qb of 300 mL/min, 33 repeated measures resulted in mean effective Qb of 303 +/- 21 mL/min and R of 8.5 +/- 7.0%; 28 measures performed at a set Qb of 350 mL/min showed that the effective Qb was 336 +/- 24 mL/min and that R was 7.8% +/- 6.7%. Finally, an effective Qb of 372 +/- 26 mL/min and an R of 10.9 +/- 8.6% were found for the 27 measures performed at an indicated Qb of 400 mL/min. The difference between indicated and effective Qb was particularly significant for set Qb equal to or above 350 mL/min (P < 0.001). Variable correlations were observed between obtained parameters: Qb eff and R (r = 0.34), PV and R (r = 0.36), Qb eff and PV (r = 0.78), Qb eff and PA (r = 0.71), and PV and PA (r = 0.53). In conclusion, TwinCath delivers an effective Qb of nearly 375 mL/min when Qb is set at 400 mL/min on most dialysis machines. Mean R in TwinCath varies between 5% and 11% for Qb within the range of 200 to 400 mL/min. In well-functioning TwinCath, the ratio between PV and Qb remains usually below 0.5. (Am J Kidney Dis 1998 Jan;31(1):87-92)

Setting Roller Pump Occlusion With the Transonic HT109 Flowmeter

Setting the occlusion of a roller pump may be facilitated using the TRansonic HT109 Ultrasonic Flowmeter (Transonic Systems, Inc. Ithaca, NY) with non-invasive transducer. The process addresses the need to set occlusion quickly and accurately before initiation of extracorporeal membrane oxygenation (ECMO). This can be performed with the circuit tubing before blood prime and does not require opening the fluid filled ECMO apparatus to air. The principle is based on the fact that fluid flow through the tubing will change with roller occlusion. Using the Transonic flowmeter, a pre determined (partially occlusive) setting can be achieved by first determining the point of total occlusion, then decreasing occlusion a small percentage from this maximum (i.e., total) occlusion. Clinical application in 35 neonatal ECMO cases has shown the practice to be safe, reliable, and efficient.

Access flow measured during hemodialysis.

Hemodialysis accesses must supply adequate blood flow to perform hemodialysis and maintain access patency. Access flow (QA) is not measured routinely during hemodialysis. The purpose of this study was to evaluate whether access flow changes during hemodialysis and to determine which factors correlate with QA. The authors measured hemodialysis access flow by ultrasound dilution (QA-T) (Transonic HD01 hemodialysis monitor; Transonic Systems, Inc., Ithaca, NY) and duplex ultrasound, with time-domain correlation (QA-S) (Philips CVI Phillips Medical Systems, Santa Ana, CA) hourly, in 19 patients during hemodialysis. Mean arterial pressure (MAP) (Fresenius automated blood pressure cuff) and cardiac output (CO) (Transonic hemodialysis monitor; Transonic Systems, Inc.) also were measured sequentially. Using duplex ultrasound, access flow was unchanged. However, it fell 132 +/- 137 ml/m (p < 0.05) by ultrasound dilution in hr 4. Cardiac output fell 586 +/- 840 ml/ m (p < 0.05), and MAP fell 11.9 +/- 13.0 mmHg (p < 0.01). There were small positive correlations between CO and QA (correlation coefficient (r) = 0.32, QA-T; r = 0.27, QA-S; p < 0.05), and between CO and MAP (r = 0.35; p < 0.01). In conclusion, access flow, CO, and MAP decreased modestly during hemodialysis. Further studies are necessary to see if access flow is similar off dialysis, and whether in-line access flow measurements can decrease access thrombosis.

Validation study of a new transit time ultrasonic flow probe for continuous great vessel measurements.

Continuous measurement of cardiac output is important during experimental and clinical cardiac surgery as an indicator of ventricular function. Previous flow probes underestimated flow secondary to position and flow (S-series probes; Transonic Systems, Inc., Ithaca, NY), required frequent calibrations (electromagnetic), and were cumbersome to use. The new A-series probe (ASP) by Transonic Systems, Inc., uses a new X method of ultrasonic illumination insensitive to perturbations in flow. The ASPs were found to be accurate during in vitro studies, but have not been validated in vivo. Six anesthetized pigs were instrumented for right atrium to left atrium bypass, and ASPs were placed on the ascending aorta and pulmonary artery. Baseline measurements included aortic (Ao) and pulmonic flow (P), and thermodilution (Td) cardiac output. Animals then were placed on right heart bypass, and flow was randomly varied from 1 to 6 L/min, and Ao flow was recorded. In addition, ASPs were rotated and their direction reversed. After data collection, the occlusive roller pump (RP) was calibrated using a timed collection method. Calibrated RP flows were plotted versus ASP flows, and regression was applied. There was no difference between mean Ao, P, and Td cardiac outputs at baseline. In addition, changes in position and direction of the probe did not affect measurement of flow. The ASPs showed a highly linear correlation with RP ([r = 0.98, p < 0.01] ASP[L/min] = 0.98 RP-0.032). During laminar flow states, ASPs are accurate and insensitive to position on the great vessels.

The mechanism of cardiac shunting in reptiles: a new synthesis.

The mechanism of cardiac shunting in reptiles is controversial. Recent evidence suggests that a right-to-left shunt in turtles results primarily from a washout mechanism. The mechanism that accounts for left-to-right (L-R) shunting is unresolved. This study used haemodynamic analysis and digital subtraction angiography to determine the mechanism of L-R cardiac shunting in the turtle Trachemys (Pseudemys) scripta. Animals were instrumented with ultrasonic blood flow probes (Transonic Systems, Inc.) for the measurement of total pulmonary blood flow and total systemic blood flow. In addition, catheters were inserted into the common pulmonary artery (PA), the systemic arteries, the left atrium and right atrium. These catheters were used for the measurement of blood pressure or for the infusion of radio-opaque material. Haemodynamic conditions were altered by electrical stimulation of the afferent (VAF) or efferent vagal nerves or by infusion of vasoactive drugs. Under control conditions, the peak systolic pressure in the systemic arteries was slightly higher than that in the PA (30.6 versus 28.3 mmHg; 4.08 versus 3.77 kPa), whereas diastolic pressure in the PA was significantly less than that in the systemic arteries (9.8 versus 24.4 mmHg; 1.31 versus 3.25 kPa). During VAF stimulation, the peak systolic pressures in the PA and aortae almost doubled. Diastolic pressure in the systemic arteries also doubled, but it increased by only 45% in the PA. Ejection of blood into the PA preceded that into the left aorta by 53 ms under control conditions. This difference increased (by as much as 200 ms) as the difference in the diastolic pressures between the two circulations increased during VAF stimulation. This resulted in the development of a large net L-R shunt. Under these conditions, digital subtraction angiography showed that the L-R shunt resulted from a combination of both washout and pressure mechanisms.

An alternative to radioactive microspheres for measuring regional myocardial blood flow, part 2: Laser-doppler perfusion monitor

To compare measurements of regional myocardial blood flow volume between microsphere measurement of regional flow (0.5- to 2- g tissue sampling) and a potential alternative measure, local flow (1 mm3) in the microcirculation measured by laser-Doppler perfusion monitor. Prospective, randomized, controlled. University research laboratory. Pigs. After anesthetization, in 5 pigs (25 to 30 kg), the left anterior descending coronary artery was isolated and its resting flow measured by a perivascular-Doppler flowmeter. Left ventricular pressure and first time derivative of left ventricular pressure were measured. The laser-Doppler probe needle (type N) (Model ALF-21, Transonic Systems, Inc, Ithaca, NY) was inserted 2 to 3 mm into the wall of the left ventricle, parallel to the coronary artery. All 5 pigs were subjected to 0 (control), 50% , 75%, and 100% constriction of the left anterior coronary artery. Measurements by radio-active microspheres correlated poorly with those by laser-Doppler and extremely poorly with those by perivascular Doppler flowmeter. For percent change from baseline in the constricted arterial zone, radioactive measurements correlated well with those by laser-Doppler but not those by Doppler flowmeter. Also, radioactive measurements of percent change in flow in the circumflex (nonconstricted) zone and laser-Doppler measurements in the constricted arterial zone did not correlate well. Laser-Doppler can be recommended for experimental research to monitor local flow. These measurements may relate to change in regional flow during normal perfusion and hypoperfusion. Before the laser-Doppler perfusion monitor can be used clinically, tissue trauma from the 0.55-mm needle needs to be evaluated.