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© 2013, Copyright the Authors Artificial Organs © 2013, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Novel Pulsatile Diagonal Pump for Pediatric Extracorporeal Life Support System *†Shigang Wang, †Allen R. Kunselman, and *†Akif Ündar *Department of Pediatrics, Surgery and Bioengineering, Penn State Hershey Pediatric Cardiovascular Research Center; and †Public Health and Sciences, Penn State Milton S. Hershey Medical Center, Penn State Hershey College of Medicine, Penn State Hershey Children’s Hospital, Hershey, PA, USA

Abstract: A novel pulsatile rotary flow pump has been used in clinical extracorporeal life support (ECLS) in Europe.The objective of this study is to evaluate the Medos Deltastream DP3 diagonal pump (Medos Medizintechnik AG, Stolberg, Germany) in a simulated pediatric ECLS system. The ECLS circuit consisted of a Medos Hilite 800LT hollow fiber membrane oxygenator (Medos Medizintechnik AG), a Medos Deltastream DP3 diagonal pump, a 10Fr Terumo TenderFlow Pediatric Arterial Cannula (Terumo Corporation, Tokyo, Japan), and an arterial/ venous tubing. All trials were conducted at flow rates ranging from 200–800 mL/min (in 200 mL/min increments) under a blood temperature of 35°C using human blood (hematocrit 40%). The postcannula pressure was maintained 60 mm Hg by a Hoffman clamp. Real-time pressure and flow data were recorded using a Labview-based acqui-

sition system (National Instruments, Austin, TX, USA). The results showed that the Medos Deltastream DP3 can generate effective pulsatile flow without backflow, provide higher flow rates and pressures than nonpulsatile flow, and then create surplus hemodynamic energy and more total hemodynamic energy than nonpulsatile flow. Pulsatility increased with increased speed differential values and flow rates, while the oxygenator pressure drop increased at an acceptable level. The Medos Deltastream DP3 diagonal pump can provide adequate quality of pulsatility without backflow, and generate more hemodynamic energy under pulsatile mode in a simulated pediatric ECLS system. Key Words: Pulsatile flow—Novel diagonal pump —Medos DP3—Cardiopulmonary bypass—Extracorporeal life support—Pediatric.

Extracorporeal life support (ECLS) has become standard treatment for low cardiac output after pediatric and congenital cardiac surgical repair and fulminant myocarditis or end-stage cardiomyopathy. ECLS serves as a bridge to recovery, long-term left ventricular assist, or transplantation (1–5). During ECLS, the patient’s native heart is still working. We hope that the blood pump can provide pulsatile flow to partially take over the pumping ability of the failed heart. Centrifugal blood pumps are usually used in

ECLS, thanks to their non-occlusiveness and relative safety. Many centrifugal pumps are currently available in clinical practice, but few of them can generate pulsatile flow without backflow, which happens to be due to their non-occlusive characteristics (6,7). Roller pumps can easily create pulsatile flow, but in a closed ECLS system, using roller pumps decreases application safety. Roller pump are occlusive and can rupture the circuit when tubing downstream of the roller pump is blocked or twisted. Usage of roller pumps may also lead to hemolysis or cavitation when tubing upstream of the roller pump is obstructed. Therefore, a bladder reservoir at the venous line and pressure-servo controllers at both sites of the pump should be used for increased safety. A special pulsatile non-occlusive roller pump could be used in ECLS systems (8,9). However, in such applications, raceway tubing must be regularly replaced for long duration use due to tubing wear. Axial flow pumps are seldom used in ECLS systems, and are only mainly employed

doi:10.1111/aor.12015 Received August 2012; revised September 2012. Address correspondence and reprint requests to Dr. Akif Ündar, Department of Pediatrics—H085, Penn State Hershey College of Medicine, 500 University Drive, P.O. Box 850; Hershey, PA 17033-0850, USA. E-mail: [email protected] Presented in part at the 8th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion held June 13–16, 2012 in Istanbul, Turkey.

Artificial Organs 2013, 37(1):37–47

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for ventricular assist systems. Diagonal flow pumps, a subset of rotary pumps, can also be used in cardiopulmonary bypass (CPB) procedures and ECLS systems. The new Medos Deltastream DP3 pump (Medos Medizintechnik AG, Stolberg, Germany) is such a diagonal flow pump. Deltastream DP3 uses a hightech ceramic bearing, a magnetic coupling, and a separated pump head (10). More importantly, it can provide pulsatile flow without backflow. The Deltastream DP3 has been approved for extended clinical ECLS use in children and adults in Europe (11,12). The objective of this study was to evaluate the particular pulsatile rotary blood pump in a simulated pediatric ECLS system and to examine the effectiveness of its pulsatile flow. MATERIALS AND METHODS Experimental circuits The ECLS circuit consisted of a Medos Hilite 800LT hollow fiber membrane oxygenator (Medos Medizintechnik AG) (Table 1), a Deltastream DP3 centrifugal pump (Table 2), 1/4 in. inner diameter (ID) ¥ 1/16 in. wall ¥ 180 cm of arterial tubing, 1/4 in. ID ¥ 1/16 in. wall ¥ 195 cm of venous tubing, 1/4 in. ¥ 20 cm of tubing connected oxygenator to blood pump, a 10Fr Terumo TenderFlow Pediatric arterial cannula (Terumo Corporation, Tokyo, Japan), and an ECMO-TEMP SMS-3000 heatercooler unit (Seabrook, Inc., Cincinnati, OH, USA) (see Fig. 1). A pediatric Capiox CX*CR10NX cardiotomy reservoir (Terumo Corporation) served as a pseudo patient. The height between the inlet port of pump head and blood level in cardiotomy reservoir was 30 cm. A Hoffman clamp was placed at a postcannula site to maintain a given postcannula pressure during all trials. The ECLS circuit was first primed with lactated Ringer’s solution, and then packed human red blood cells were added into the circuit to maintain the blood hematocrit at 40%. The pseudo patient was kept at 300 mL. The total priming volume of the circuit was 500 mL.

TABLE 1. The specifications of Medos Hilite 800LT hollow fiber oxygenator Items Blood flow rate Static priming volume Hollow fiber type ID/OD Gas exchanger surface

Artif Organs, Vol. 37, No. 1, 2013

Medos Hilite 800LT 0–800 mL/min 55 mL Plasma tight hollow fiber (polymethylpentene) 200/380 mm 0.32 m2

TABLE 2. The specifications of Medos Deltastream DP3 pump head Items Flow rate Rotational speed Pressure difference Priming volume Pulsatile mode Speed differential value Systole/diastole ratio Frequency

Medos Deltastream DP3 pump head 0–8 L/min 500–10 000 rpm 0–600 mm Hg 16 mL 100–2500 rpm in steps of 100 30–70% 40–90 bpm

Experimental designs Trials were conducted at flow rates ranging from 200 to 800 mL/min (in 200 mL/min increments) under blood temperature of 35°C. The postcannula pressure was maintained at 60 mm Hg during all trials. Two Transonic ultrasound flow probes (Transonic Systems, Inc., Ithaca, NY, USA) were placed at a preoxygenator site and a precannula site. Five Maxxim disposable pressure transducers (Maxxim Medical, Inc., Ithaca, NY, USA) were placed at preoxygenator, postoxygenator, precannula, postcannula, and prepump sites. The Medos Deltastream DP3 pump setting for pulsatile flow was set at a frequency of 90 bpm, systole/diastole ratio 70/30 in one cycle, and 500 rpm (P500), 1500 rpm (P1500), or 2500 rpm (P2500) of the speed differential values, respectively. In this particular study, pulsatile flow settings were selected based on our previous experiences. Currently, we are conducting more pilot studies to evaluate different pumps settings on the impact of pulsatile morphology (shape and size) and hemodynamic energy levels in pediatric and adult ECLS circuits.

Data acquisition The pressure transducers and outputs of flowmeter were connected to a signal conditioning unit (SC2345, National Instruments, Austin, TX, USA), linked with a data acquisition device (NI USB-6521, National Instruments), and finally connected to a computer via a universal serial bus port. A customized user interface based on Labview 7.1 software for Windows (National Instruments) was designed to record real-time data at 1000 samples per second. A 20 s segment of pressure and flow waveforms was recorded at all sites. The entire process was repeated six times for each unique combination, yielding a total of 96 trials. The hemodynamic energy created by pulsatile flow was qualified by related mathematical formulas. With

PULSATILE ECLS

39

FIG. 1. The experimental ECLS circuit.

the help of the Shepard’s energy equivalent pressure (EEP) formula and simultaneous blood flow (f) and pressure (p) recorded by Labview software, EEP, surplus hemodynamic energy (SHE), and total hemodynamic energy (THE) were calculated in a time interval (t1 and t2) as follows (13): 2

EEP (mm Hg) = ∫ fpdt 1

∫

2

1

fdt

SHE (ergs cm 3 ) = 1332 ∗ (EEP − mean pressure) THE ( ergs cm 3 ) = 1332 ∗ EEP The constant 1332 converts pressure from units of mm Hg to dynes per square centimeter (1 mm Hg = 1332 dyn/cm2). Statistical analysis An analysis of variance model was fit to the continuous outcomes representing changes in location (e.g., change in mean arterial pressure from preoxygenator to postoxygenator) to compare the pulsatile modes (NP, P500, P1500, and P2500) at a given flow rate (200, 400, 600, and 800 mL/min). A linear mixedeffects model was fit to the continuous outcomes

(e.g., SHE and THE) to compare the pulsatile modes at a given location (preoxygenator, precannula, and/or postcannula) and flow rate (14). The linear mixed-effects model is an extension of linear regression that accounts for the within-subject variability inherent in repeated measures designs. In this study, the repeated factor is the location. For each outcome, P values were adjusted for multiplecomparisons testing using the Tukey-Kramer procedure. All hypotheses tests were two-sided and all analyses were performed using version 9.2 of the SAS System for Windows (SAS Institute, Inc., Cary, NC, USA). RESULTS Flow rates All pump flow rates increased under pulsatile mode compared with nonpulsatile mode (Table 3). With increased speed differential values, pump flow rate also increased (i.e., from 7.1 to 66.1% at 200 mL/ min group, 5.2 to 38.8% at 800 mL/min group) (Table 3). Figure 2 presents flow waveforms at different flow rates with pulsatile and nonpulsatile mode. No backflow was found during all trials under pulsatile mode. Artif Organs, Vol. 37, No. 1, 2013

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TABLE 3. Real flow rates, mean pressures, and oxygenator pressure drops (percentage increase compared with nonpulsatile mode in parentheses) under pulsatile (P) and nonpulsatile (NP) modes Mean pressure (mm Hg) Group

Mode

rpm

Flow rate (mL/min)

Preoxygenator

Postcannula

Pressure drop (mm Hg)

200 mL/min

NP P500 P1500 P2500 NP P500 P1500 P2500 NP P500 P1500 P2500 NP P500 P1500 P2500

3550 3750 4600 5400 4100 4300 5050 5850 4700 4900 5550 6350 5300 5500 6050 6850

215.7 ⫾ 0.2 230.9 ⫾ 0.6(7.1%)* 294.6 ⫾ 0.8(36.6%)* 358.3 ⫾ 1.6(66.1%)* 418.0 ⫾ 0.1 446.0 ⫾ 0.6(6.7%)* 542.3 ⫾ 1.5(29.8%)* 652.0 ⫾ 1.7(56.0%)* 615.4 ⫾ 0.2 652.8 ⫾ 0.8(6.1%)* 765.8 ⫾ 1.5(24.5%)* 910.6 ⫾ 2.0(48.0%)* 801.6 ⫾ 0.3 843.7 ⫾ 1.0(5.2%)* 952.6 ⫾ 1.8(18.8%)* 1113.0 ⫾ 1.8(38.8%)*

98.5 ⫾ 0.0 109.1 ⫾ 0.2(10.8%)* 152.6 ⫾ 0.3(54.9%)* 205.4 ⫾ 0.5(108.6%)* 117.8 ⫾ 0.0 129.4 ⫾ 0.2(9.8%)* 171.0 ⫾ 0.5(45.1%)* 225.0 ⫾ 0.7(90.9%)* 142.9 ⫾ 0.0 155.0 ⫾ 0.2(8.5%)* 194.3 ⫾ 0.4(36.0%)* 249.4 ⫾ 0.6(74.5%)* 170.9 ⫾ 0.0 183.7 ⫾ 0.3(7.5%)* 220.7 ⫾ 0.5(29.2%)* 277.0 ⫾ 0.6(62.1%)*

59.9 ⫾ 0.0 69.2 ⫾ 0.2(15.6%)* 106.7 ⫾ 0.3(78.1%)* 153.1 ⫾ 0.5(155.7%)* 60.1 ⫾ 0.0 68.1 ⫾ 0.1(13.4%)* 97.4 ⫾ 0.3(62.2%)* 136.0 ⫾ 0.5(126.5%)* 60.2 ⫾ 0.0 66.9 ⫾ 0.1(11.1%)* 88.7 ⫾ 0.2(47.3%)* 119.4 ⫾ 0.4(98.2%)* 60.7 ⫾ 0.0 66.4 ⫾ 0.1(9.4%)* 83.4 ⫾ 0.2(37.5%)* 109.5 ⫾ 0.3(80.4%)*

6.8 ⫾ 0.0 7.1 ⫾ 0.0* 8.3 ⫾ 0.0* 9.2 ⫾ 0.1* 13.2 ⫾ 0.0 13.9 ⫾ 0.0* 16.2 ⫾ 0.1* 18.7 ⫾ 0.0* 19.6 ⫾ 0.0 20.6 ⫾ 0.0* 23.6 ⫾ 0.0* 27.2 ⫾ 0.0* 25.4 ⫾ 0.0 26.7 ⫾ 0.2* 29.6 ⫾ 0.1* 33.8 ⫾ 0.1*

400 mL/min

600 mL/min

800 mL/min

* P < 0.001, nonpulsatile (NP) versus pulsatile (P500, P1500, P2500).

Pressures The trends of mean pressures at the preoxygenator and postcannula sites exhibited a trend similar to the flow rates (Table 3). The pulsatile mode increased preoxygenator and postcannula mean pressures. Pump flow rates increased with increased speed differential values. With increased pulsatility and flow rates, negative pressure at prepump site also increased. Compared with nonpulsatile flow, the percentage increase diminished with faster flow rates. Figures 3–6 present all pressure waveforms at different flow rates with pulsatile and nonpulsatile flow. Oxygenator pressure drop The oxygenator pressure drops increased under pulsatile mode and with increased flow rates and speed differential values (Table 3). The maximal pressure drop was 33.8 mm Hg at an 800 mL/min flow rate with pulsatile mode and a 2500 rpm speed differential value. Hemodynamic energy The nonpulsatile flow cannot create the SHE as shown in Table 4. Pulsatile flow can generate SHE; the surplus hemodynamic energies increased with higher flow rates and speed differential values. The values of the surplus hemodynamic energies were highest at the preoxygenator site, and lowest at the postcannula site. Approximately 45–65% of SHE was delivered into the patient under pulsatile modes. The pulsatile flow generated more THE than the nonpulsatile flow. With increased flow rates and speed differential values, THE increased. Approximately 30–60% of THE were delivered into the patient. Artif Organs, Vol. 37, No. 1, 2013

DISCUSSION An ECLS system is a special procedure that uses artificial techniques to support circulatory and respiratory functions as a bridge to recovery, transplantation, or long-term ventricular assist. The blood pump is the power of the ECLS system, and it mimics the heart as it pumps the blood through artificial devices and then through the peripheral circulatory system of the body. It partially takes over the pumping function of the failed heart to maintain the patient’s “normal” physiological function. An ideal blood pump should have the characteristics of low priming volume, high output power, smoothly adjustable flow rate, load insensitivity, quietness, durability, ease of setup and operation, no blood trauma, no necessary anticoagulation, no mechanical failures, emergency operation by hand, and alternative pulsatile flow mode. Although there is not an ideal blood pump available now, many investigators are working to optimize and improve their technology in order to provide better blood pumps for clinical practice. There are three types of blood pumps used—roller pumps, rotary pumps, and pneumatic pumps. Among them, rotary pumps include axial pumps, centrifugal pumps, and diagonal pumps. Axial pumps and pneumatic pumps are seldom used in ECLS systems. Roller pumps are commonly used in CPB procedures because of simple operation and low cost, while they are not widely used in ECLS systems due to lower safety, periodic replacement of raceway tubing, and inconvenient mobility. Therefore, centrifugal pumps and diagonal pumps are the current blood pump used in ECLS systems. Their

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42 S. WANG ET AL.

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PULSATILE ECLS 45


79 786.2 ⫾ 39.8 98 512.7 ⫾ 204.5(23.5%)* 155 385.5 ⫾ 324.3(94.8%)* 225 190.0 ⫾ 501.1(182.2%)* 79 991.7 ⫾ 38.5 94 026.6 ⫾ 176.8(17.5%)* 139 620.8 ⫾ 381.6(74.5%)* 196 407.5 ⫾ 566.2(145.5%)* 80 232.8 ⫾ 26.0 91 157.8 ⫾ 137.2(13.6%)* 125 986.1 ⫾ 300.1(57.0%)* 170 914.7 ⫾ 418.9(113.0%)* 80 833.9 ⫾ 42.0 89 877.7 ⫾ 157.1(11.2%)* 118 128.6 ⫾ 267.7(46.1%)* 155 980.4 ⫾ 353.6(93.0%)* 128 560.3 ⫾ 21.2 148 519.6 ⫾ 244.9(15.5%)* 209 501.4 ⫾ 351.8(63.0%)* 283 678.8 ⫾ 541.8(120.7%)* 140 131.2 ⫾ 42.4 157 330.8 ⫾ 212.1(12.3%)* 213 142.1 ⫾ 466.5(52.1%)* 282 625.5 ⫾ 696.5(101.7%)* 157 708.3 ⫾ 24.3 173 772.6 ⫾ 216.4(10.2%)* 225 053.6 ⫾ 463.2(42.7%)* 291 568.6 ⫾ 561.4(84.9%)* 178 747.0 ⫾ 46.1 194 759.7 ⫾ 288.0(9.0%)* 243 921.3 ⫾ 474.5(36.5%)* 309 359.0 ⫾ 616.9(73.1%)* 800 mL/min

600 mL/min

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* P < 0.001, nonpulsatile (NP) versus pulsatile (P500, P1500, P2500). † P < 0.001, pulsatile P500 versus P1500 or P2500.

131 179.2 ⫾ 37.7 156 932.0 ⫾ 257.0(19.6%)* 228 906.5 ⫾ 422.5(74.5%)* 316 376.6 ⫾ 581.8(141.2%)* 156 960.6 ⫾ 23.6 178 769.8 ⫾ 253.4(13.9%)* 246 954.5 ⫾ 536.5(57.3%)* 330 093.6 ⫾ 648.9(110.3%)* 190 309.8 ⫾ 27.8 211 268.4 ⫾ 280.6(11.0%)* 277 131.4 ⫾ 571.9(45.6%)* 360 087.9 ⫾ 545.4(89.2%)* 227 645.6 ⫾ 56.2 248 875.5 ⫾ 368.2(9.3%)* 313 525.6 ⫾ 695.9(37.7%)* 397 322.3 ⫾ 653.9(74.5%)* 0.7 ⫾ 0.2 6847.7 ⫾ 51.4 14 296.6 ⫾ 151.6† 22 689.4 ⫾ 186.0† 0.4 ⫾ 0.0 4108.2 ⫾ 34.8 12 119.4 ⫾ 82.2† 18 575.0 ⫾ 220.6† 0.4 ⫾ 0.1 3066.5 ⫾ 37.2 11 613.7 ⫾ 119.4† 17 549.8 ⫾ 253.4† 0.4 ⫾ 0.0 2629.1 ⫾ 19.3 12 320.6 ⫾ 105.3† 17 699.5 ⫾ 102.4† NP P500 P1500 P2500 NP P500 P1500 P2500 NP P500 P1500 P2500 NP P500 P1500 P2500 200 mL/min

0.6 ⫾ 0.3 11 570.4 ⫾ 78.4 25 695.5 ⫾ 265.9† 42 734.4 ⫾ 213.2† 0.2 ⫾ 0.1 6437.5 ⫾ 50.1 19 145.9 ⫾ 141.3† 30 407.6 ⫾ 327.3† 0.4 ⫾ 0.1 4840.3 ⫾ 49.6 18 274.6 ⫾ 198.8† 27 944.3 ⫾ 415.7† 0.5 ⫾ 0.1 4191.2 ⫾ 30.0 19 496.8 ⫾ 135.2† 28 317.4 ⫾ 213.3†

0.3 ⫾ 0.1 6309.7 ⫾ 49.1 13 268.7 ⫾ 142.9† 21 210.6 ⫾ 174.9† 0.2 ⫾ 0.0 3299.5 ⫾ 28.5 9869.8 ⫾ 65.8† 15 198.9 ⫾ 179.1† 0.2 ⫾ 0.1 2033.9 ⫾ 23.2 7833.7 ⫾ 81.6† 11 873.4 ⫾ 167.1† 0.2 ⫾ 0.0 1468.5 ⫾ 9.8 7013.7 ⫾ 60.3† 10 167.5 ⫾ 59.2†

Precannula Precannula Mode Flow rate

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Preoxygenator

THE (ergs/cm3)

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S. WANG ET AL.

SHE (ergs/cm3)

TABLE 4. Hemodynamic energy at different flow rate with pulsatile (NP) and nonpulsatile (P) modes (percentage increase with nonpulsatile mode in parentheses)

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advantages are higher safety, convenient mobility, and compact size, but few of them can provide pulsatile flow without backflow. We are particularly interested in the pulsatile flow within the ECLS system. Pulsatile flow settings, including pulse rate (40– 90 bpm), ratio of the systolic interval and diastolic interval (30–70%), and the speed differential value relative to the average value (100–2500 rpm), can be adjusted to vary the morphology (shape and size) of the pulsatility whenever necessary. Zero-flow mode can automatically increase rpm to push blood to prevent backflow. A pressure sensor, temperature sensor, blood level sensor, and flow probe with integrated bubble detection further strengthen its safety. The low priming volume (16 mL), wide range of flow rate (0–8 L/min), and rotation speed (500– 10 000 rpm) allow its use in pediatric and adult patients for up to 7 days (10–12). Our results showed that the Medos Deltastream DP3 is suitable for pediatric ECLS systems. It can generate adequate quality pulsatile pressure-flow waveforms without backflow in our simulated ECLS system. More hemodynamic energy was delivered to the patient under pulsatile mode than nonpulsatile mode, while the oxygenator pressure drop increased less than expected. After switching from nonpulsatile flow to pulsatile flow, flow rate also increased by 5.2– 66.1%. The largest percentage increase is at a low flow rate of 200 mL/min and a 2500 rpm speed differential value. The reason may be that the rotational speed increased from the initial setup in 70% of systolic duration and decreased in 30% of diastolic duration. Therefore, adjustment of the flow rate is necessary in mode conversion to prevent hyperperfusion or hypoperfusion. In addition, the Deltastream DP3 has other distinct advantages. The low priming volume is able to reduce hemodilution; a wide range of flow rates can cover neonates, infants, and children; fine adjustment of the flow rate allows for use on low body weight newborns; and the compactness of the pump head and console facilitate the transfer of patients. Maximum flow rate of the Hilite 800LT oxygenator is 800 mL/min. When it was used with a maximum flow rate and the mode of perfusion was switched to the pulsatile perfusion, flow rate increased over 1000 mL/min with different pulsatility settings.Therefore, further investigation is necessary to determine if the pulsatile flow causes any adverse effects when the maximum flow rate of the oxygenator is used in this particular experimental setting. In addition, because of the ECLS circuit resistance and the pseudo-patient pressure kept constant at a

PULSATILE ECLS certain level during all flow rates, the rpms of the DP3 system may seem to be higher. More experiments are needed to clarify if the level of rpm has any adverse effects on hemolysis at this particular neonatal setup. The only setting of the Medos Deltastream DP3 pump that is distinguishably lacking is a synchronous pulsatile perfusion mode. If Deltastream DP3 provides pulsatile flow with the same rhythm as the patient’s heart as well as adjustable start point delay of pulsatile flow, similar to an intra-aortic balloon pump, blood flow would be optimized and can further contribute to patient’s recovery. Another shortcoming is the change of flow rate when switching from nonpulsatile flow to pulsatile flow. The embedded algorithm should be reset to maintain the same flow rate between nonpulsatile mode and pulsatile mode in order to facilitate the operation. CONCLUSIONS The Medos Deltastream DP3 diagonal pump can provide adequate quality of pulsatility without backflow and generate more hemodynamic energies under pulsatile mode in a simulated pediatric ECLS system. Further improvements are needed for better optimizing pulsatile blood flow in the future. Acknowledgments: Special thanks go to Dr. Jürgen O. Böhm, Andreas Spilker from Medos Medizintechnik AG, Stolberg, Germany, and Dr. Ivo Simundic and Dr. Georg Matheis from Novalung GmbH, Heilbronn, Germany for lending the DP3 pump console and sending all disposables for this study.

47 REFERENCES

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