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Rezer, Marciano, Santos, Souza: Flow Analyzer for Blood Pump

J Global Clinical Engineering Vol.3 Issue 1: 2020  44

Received April 2, 2019, accepted June 16, 2020, date of publication August 19, 2020

Flow Analyzer for Blood Pump 
By R.L. Rezer1, M.A. Marciano2, A.A. Santos,1 and W.K. Souza1  
1 Moinhos de Vento Hospital/Clinical Engineering, Porto Alegre, Brasil.
2 Moinhos de Vento Hospital/Clinical and Hospital Engineering, Porto Alegre, Brasil.

ABSTRACT

Medical equipment that supports life, relieves diseases, and overcomes disabilities can also cause damage and death due to 
operational failures, user failures, and misuse.  Hemodialysis machines include roller pumps that control the flow of blood, and 
these pumps have to be calibrated accurately to ensure they are working properly. 
This article describes the development of a low-cost, open source prototype that automates the flow analysis (measurement and 
recording) of the blood pumps in hemodialysis machines. Being able to accurately inspect the machine’s operation improves 
the quality and safety of its use. Through this technology (this process automation), it is believed equipment downtime and 
total tests cost will be reduced. 
This device has a system that collects data in real time, generated by the blood pump dialysis. Mathematical calculations are 
used to present flow information, including the standard deviation of the measurement, which is reported at the end of the test 
in an objective and simple way. Through a software and human machine interface (HMI), the test can be monitored and generate 
a report that contains the name and model of the equipment, the quantitative results of the flows, and the standard deviations 
of the measurements. The device can be used by clinical engineering teams in preventive maintenance and after corrective 
maintenance, as a control practice, making the calibration process easier and more cost-effective. 

Keywords – Hemodialysis, Quality Control, Biomedical Analyzer, Arduino. 

Copyright © 2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY): Creative Commons - Attribu-
tion 4.0 International - CC BY 4.0. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) 
are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is 
permitted which does not comply with these terms.

INTRODUCTION
Renal insufficiency occurs when the kidneys are unable 

to function properly.1 Hemodialysis is performed from 
a venous access allowing high blood flow. The blood is 
transported through an extracorporeal circulation system 
to a capillary filter, where it is purified and then returned 
to the body. It is usually performed three times a week, 
for an interval of three to four hours.2 Hemodialysis is 
susceptible to adverse events (AE) since it involves several 
risk factors, such as complications of invasive procedures, 
the use of complex equipment, critical patients, high 
patient turnover, and the administration of potentially 
dangerous drugs.3

The increasing use of hemodialysis worldwide is 
worrying specialists, researchers, managers, and health 
professionals. Data from the World Health Organization 
indicate that, annually, tens of millions of people worldwide 
suffer disabling injuries or death due to AEs following 
hemodialysis.4

Medical equipment that supports life, relieves dis-
eases, and overcomes disabilities can also cause damage 
and death due to operational failures, user failures, and 
misuse.5 Hemodialysis machines include roller pumps 
that control the flow of blood. The pumps should contain 
various alarms and other devices to ensure patient safety. 

Specific calibration is an important step for the correct 
operation of the equipment because the volume infused 
is the main parameter of the pump. It is essential that the 
methodology used in calibration be adequate for the tests 
to be validated as failure to do so can cause complications, 
including phlebitis, venous spasm, and pulmonary edema.6 
The tests involve two parts – a qualitative evaluation 
(consisting of visual inspection of the structural condi-
tions of equipment, parts, modules, and accessories) and 
quantitative tests (consisting of measuring or simulation 
of the parameters and/or the biomedical magnitude of 
the equipment).7 Some trials are still done manually 
making the process time-consuming and decreasing the 
availability of dialysis equipment in a busy center. The 
calibration of the rollers involves adjusting the distance 
between the roller and the rigid bed (occlusion).8 At pres-
ent, to perform calibration of the blood pump assembly, a 
precision scale, a graduated glass, and a digital timer are 
used, all of them traceable. Among the restrictions of this 
method are the uncertainties generated by the technical 
measurement process itself and the delay to carry out 
the measurements.9

The main objective of this work is to develop a flow 
measurement device for blood pumps of hemodialysis 
machines. Whereas flows generated by hemodialysis 
machines are greater than 1200 mL/h (maximum flow 
measured by the analyzers present in the market). The 
specific objectives to be achieved are (a) improving the 
process of inspecting the operation of the device, (b) re-
ducing equipment downtime, (c) reducing costs related 
to the process of inspecting and testing quantitatively 
the equipment, and (d) improving the quality and safety 
of equipment use. For this development of the process 
automation, open source devices will be used, reducing 
the cost of the process. 

METHODS

Method Flow

Figure 1 shows the flow of the steps followed for 
the development of this work. With the data specified, 
calculated, modeled, and simulated, the prototype was 
designed, developed, and tested.

Initially a group of studies was organized to evaluate 
possible solutions for a low-cost prototype for the blood 
pump flow analyzer. Several follow-ups were conducted 
at the hemodialysis center, along with the nursing group 
to measure the real complications of the conventional 
hemodialysis therapy. As shown by the flowchart if Figure 
1, the other steps are described below.

In order to perform this stage, three calculations were 
used: one to generate the flow, another to generate the 
volume, and a third to determine the standard deviation, 
within the limits of the processor and the requirements 
to analyze the blood pump flow, according to the follow-
ing equations:

FIGURE 1. Flow of the working method.

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Rezer, Marciano, Santos, Souza: Flow Analyzer for Blood Pump

47 J Global Clinical Engineering Vol.3 Issue 1: 2020J Global Clinical Engineering Vol.3 Issue 1: 2020  46

Rezer, Marciano, Santos, Souza: Flow Analyzer for Blood Pump

 Conversions

Through the equations, Tables 1, 2, and 3 were de-
veloped with parameters for program development and 
report generator. The largest number of variables of the 
circular constant or Ludolph number (called “π”, being 
π = 3.14159265) was used to obtain the most accurate 
number possible.

Programming

At this stage the Arduino platform was programmed 
(Figure 2), with a C language principle. Based on Tables 
1 and 2, the volume and flow were described in the pro-
gram. After this stage, the ultrasound sensor signal was 
programmed, making it a height meter to detect the volume 
of water and the valve, as a mechanism for releasing the 
water from the container in order to keep the blood pump 
always on, without overflowing the graduated container. 
The maximum level of volume was limited to 800 mL, and 
the minimum was 50 mL for the beginning of the readings.

Finally, the serial port was programmed where the 
name of the technician, the type of equipment, and the 
date and time of the service execution were introduced. 
On the display it shows only the flow values and the 

(1)

(2)

(3)

TABLE 1. Conversion – Relation between Height (cm) and 
Volume (mL) in the Recipient 

(1) v=hπr2

Direct Reading 
Container (mL)

Direct Reading
Height (cm)

Calculated
Volume (mL) 

0 0 0

50 0.63665 50.00237407

100 1.2733 100.0047481

150 1.90995 150.0071222

200 2.5466 200.0094963

250 3.18325 250.0118704

300 3.8199 300.0142444
Considering r = 5.0000

TABLE 2. Conversion – Relation between Volume (mL) and 
the Time (minute)

(2) Q=  volume/time

Volume (mL) Time (minutes) Flow (mL/min)

50 1 50

300 6 50

600 12 50
This table represents the analysis of a flow of 50 mL/minute.

TABLE 3. Conversion – Relation between Flow Readings and 
the Standard Deviation of the Readings Performed in the 
Range of 50 mL/Minute

Reading 
numbers

Flow 
(mL/min)

Standard deviation 
(mL/min)

1 51

1
2 50

3 49

4 51

5 49

FIGURE 2. Electronic diagram of the circuit with the Arduino 
Platform.

standard deviation. Figure 3 shows the flow and standard 
deviation in the display, data transmitted by the serial 
port and the final report.

MATERIALS

Peripherals

Peripherals installation – The system used a selector switch. 
The power to the board and the peripherals was through 
a computer source. For the control of the electromechani-
cal device (valve), which is responsible for the release of 
water from the container, a normally open 5V relay was 
used. The ultrasound sensor (HC-SR04) was applied to 
read the height of the water in the container, connected 
directly to the Arduino´s inlet. The display uses I2C com-
munication to transmit data from the Arduino to the HMI 
(Human Machine Interface). We used a serial output for 
communication of the Arduino with the computer. We can 
see the circuit of the project in Figure 2.

Microcontroller

The Arduino Mega was used in this prototype, a free 
hardware and code platform that has its own compiler, 
designed to reach people who have little programming 
knowledge. The microcontroller used is the ATmel AT-
mega 2560, an 8-bit microcontroller of advanced RISC 
architecture. It has 256 KB Flash (plus 8 KB that are used 
for the bootloader), 8 KB RAM and 4 KB EEPROM. There 
are 16 MIPS, operating on 16 MHz. Arduino based on 
Atmel ATmega, among which we can highlight 3 serial 
communication channels, 16 analog inputs and 15 PWM 
outputs. It has also SPI,12C communication and 6 pins for 

external interruptions. The Mega2560 board has 54 pins 
of digital inputs and outputs that can be used as input or 
output. The pins operate at 5V voltage and can supply or 
drain up to 40 mA. Each pin has internal pull-up resistor 
which can be software-enabled. It has 16 analog inputs 
(pins A0 to A15), where the conversion can be made with 
a resolution of 10 bits, that is, the value will be converted 
between 0 and 1023.

Ultrasound

The HC – SR04 ultrasound module provides 2 to 400 cm 
without contact and measuring function, with precision 
of 3 mm.

HMI 

In order for the simulator to have mobility and an easy 
interface between the operator and the device, it was 
decided to use the HMI system of the Arduino platform 
with I2C communication.

Power Supply 

Standard 12V, 2.3A, real power of 500 Watts, efficiency 
> 70%, TBF of 100,000 hours, 25ºC, internal protection 
against OVP / OCP / SCP short circuit, AC input with 
manual switching 110 / 220 V, low acoustic noise, cables 
with protective cover, thermal cooling control system, 120 
mm silent fan, technical standards IEC60950 (electrical 
safety), IEC61000 (electromagnetic safety) and On / Off 
switch.

Relay

NA/NF of 5V.

Valve

Valve with 12V solenoid.

Mechanical Assembly

For the assembly of the device, 5 threaded rods of ½ with 
nut and washer were used, 1 50x50cm acrylic sheet, as 
shown in its assembly in figure 6.

Container

A cylindrical container was used as a reservoir, graduated 
with a total volume of 1000 mL.

FIGURE 3. Data shown on the serial output.



Rezer, Marciano, Santos, Souza: Flow Analyzer for Blood Pump

49 J Global Clinical Engineering Vol.3 Issue 1: 2020J Global Clinical Engineering Vol.3 Issue 1: 2020  48

Rezer, Marciano, Santos, Souza: Flow Analyzer for Blood Pump

Flange

A flange of ½ inch was attached to the bottom of the 
container for the water outlet.

Connector

A connector with the same diameter of the extender used 
in the conventional hemodialysis kit was installed for 
liquid inflow into the container.

RESULTS

To obtain the final results of the electronic part, the 
circuit was assembled. After the connection of the ultra-
sound sensor to the valve in the Arduino platform, four 
tests were performed and the analyzer responded satis-
factorily. The final report is shown in Figure 3.

To obtain the final results of the mechanical part, the 
set was assembled as shown in Figure 4. After assembly 
of all electronic and mechanical parts, four tests were 
performed. With the design mounted, the set responded 
satisfactorily as shown in Figure 5.

After the complete assembly of the prototype in the 
initial verification form, bench tests were performed 
comparing the readings from this prototype with those 
from conventional manual methods. After all adjustments, 
a test with the blood pump of the hemodialysis machine 

was performed. At the end of the test, a detailed analysis 
report was generated.

CONCLUSIONS

Tools and support devices in the analysis and simulation 
of biomedical information are of great value in mitigating 
the risks related to the use of biomedical devices.

This article describes the development of an automated 
blood flow analyzer prototype to improve quality standards 
in the tests performed by clinical engineering services 
on hemodialysis machines. This prototype was found to 
reduce equipment downtime, reduce costs related to the 
testing process, and increase the safety of therapy with 
hospital devices that use blood pumps.

CONFLICT OF INTEREST

The authors declare that they have no conflict of interest.

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FIGURE 4. Mechanical design of the flow simulator for blood 
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FIGURE 5. The final project.

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