14
Int. J. Biomedical Engineering and Technology, Vol. x, No. x, 200x 439 Copyright © 2008 Inderscience Enterprises Ltd. Design and development of a low-cost spirometer with an embedded web server Vivek Agarwal Department of Electrical Engineering, Indian Institute of Technology, Bombay, India E-mail: [email protected] N.C.S. Ramachandran Texas Instruments, Bangalore, India E-mail: [email protected] Abstract: Spirometers are used to measure lung capacity and response of lungs and chest during physical therapy. They reveal whether the patient’s dyspnoea is due to cardiac or pulmonary dysfunction and are used to detect asthma. Unfortunately their application is limited due to high instrument cost and lack of specialist doctors. This paper details the development of a low-cost, portable spirometer built around an MEMS pressure sensor for detecting airflow and pressure. The instrument has an embedded web server and ethernet connection which enables a distantly located doctor to examine the patient online during an emergency or otherwise. Keywords: spirometer; web server; pressure sensor; MEMS; home spirometry; dynamic lung function; ethernet; biomedical instrumentation. Reference to this paper should be made as follows: Agarwal, V. and Ramachandran, N.C.S. (2008) ‘Design and development of a low-cost spirometer with an embedded web server’, Int. J. Biomedical Engineering and Technology, Vol. x, No. x, pp.xxxxxx. Biographical notes: Vivek Agarwal received Bachelor’s Degree in Physics from Delhi University, India in 1985, Master’s Degree in Electrical Engineering from the Indian Institute of Science, Bangalore, India in 1990 and PhD Degree in Electrical Engineering from the University of Victoria, Canada in 1994. After briefly working with Statpower Technologies, Canada, he joined the Department of Electrical Engineering, Indian Institute of Technology, Bombay, India, where he is currently a Professor. His main fields of interest are power electronics and electronic systems. He is a senior member of IEEE, fellow of IETE and a life member of ISTE. N.C.S. Ramachandran obtained a Bachelor’s Degree in Electronics Engineering from Kakatiya Institute of Technology and Sciences, Warangal, India and a Master’s Degree in Electrical Engineering with specialisation in Electronic Systems from Indian Institute of Technology, Bombay, India. He is currently working as a front end RTL design engineer in the field of micro-electronics in Texas Instruments, Bangalore, India. His areas of interest are in high speed and low power digital design. Author: Please check if authors affiliation is ok and indicate who the corresponding author is.

Ijbet 1407 Agarwal and Ramachandran

Embed Size (px)

DESCRIPTION

design of spirometer

Citation preview

Page 1: Ijbet 1407 Agarwal and Ramachandran

Int. J. Biomedical Engineering and Technology, Vol. x, No. x, 200x 439

Copyright © 2008 Inderscience Enterprises Ltd.

Design and development of a low-cost spirometer with an embedded web server

Vivek Agarwal Department of Electrical Engineering, Indian Institute of Technology, Bombay, India E-mail: [email protected]

N.C.S. Ramachandran Texas Instruments, Bangalore, India E-mail: [email protected]

Abstract: Spirometers are used to measure lung capacity and response of lungs and chest during physical therapy. They reveal whether the patient’s dyspnoea is due to cardiac or pulmonary dysfunction and are used to detect asthma. Unfortunately their application is limited due to high instrument cost and lack of specialist doctors. This paper details the development of a low-cost, portable spirometer built around an MEMS pressure sensor for detecting airflow and pressure. The instrument has an embedded web server and ethernet connection which enables a distantly located doctor to examine the patient online during an emergency or otherwise.

Keywords: spirometer; web server; pressure sensor; MEMS; home spirometry; dynamic lung function; ethernet; biomedical instrumentation.

Reference to this paper should be made as follows: Agarwal, V. and Ramachandran, N.C.S. (2008) ‘Design and development of a low-cost spirometer with an embedded web server’, Int. J. Biomedical Engineering and Technology, Vol. x, No. x, pp.xxx–xxx.

Biographical notes: Vivek Agarwal received Bachelor’s Degree in Physics from Delhi University, India in 1985, Master’s Degree in Electrical Engineering from the Indian Institute of Science, Bangalore, India in 1990 and PhD Degree in Electrical Engineering from the University of Victoria, Canada in 1994. After briefly working with Statpower Technologies, Canada, he joined the Department of Electrical Engineering, Indian Institute of Technology, Bombay, India, where he is currently a Professor. His main fields of interest are power electronics and electronic systems. He is a senior member of IEEE, fellow of IETE and a life member of ISTE.

N.C.S. Ramachandran obtained a Bachelor’s Degree in Electronics Engineering from Kakatiya Institute of Technology and Sciences, Warangal, India and a Master’s Degree in Electrical Engineering with specialisation in Electronic Systems from Indian Institute of Technology, Bombay, India. He is currently working as a front end RTL design engineer in the field of micro-electronics in Texas Instruments, Bangalore, India. His areas of interest are in high speed and low power digital design.

Author: Please check if authors affiliation is ok and indicate who the corresponding author is.

Page 2: Ijbet 1407 Agarwal and Ramachandran

440 V. Agarwal and N.C.S. Ramachandran

1 Introduction

A spirometer is used to conduct a set of medical tests that are designed to identify and quantify defects and abnormalities of various lung conditions in human respiratory system (Fishman, 1998; Hyatt et al., 1997). These tests also help in monitoring the response of lungs to medical treatment. With the help of a spirometer, Chronic Obstructive Pulmonary Disease (COPD) can be detected well in advance (American Thoracic Society, 1995a). Monitoring cough and wheezing may not provide an accurate assessment of the severity of asthma in a patient. With the help of the breathing tests conducted using a spirometer, the response and improvement in an asthma patient’s condition during the treatment can be monitored accurately. This improves the quality of treatment by reducing the judgement errors. American Thoracic Society (ATS) has recommended these breathing tests for all those who have a family history of chronic respiratory illness, cough or dyspnea and even for habitual smokers (American Thoracic Society, 1995b). In fact, this test is mandatory to confirm the physical fitness for entry into government services and the armed forces in many countries.

Spirometer measures the flow and volume of gas (air) moving in and out of the lungs during a breathing manoeuvre (Downing, 1995). The measured flow and volume values are plotted as graphs called the spirograms that are used for diagnosis of the patient. A brief overview of the terms used in these tests, types of spirograms and the relation between them, is included in a subsequent section.

Several methods (Figure 1) are used to realise spirometers (Fishman, 1998; Weber, 1999). The spirometers are based on the measurement of either the flow rate or the volume of gas inhaled and exhaled during respiration. The pressure measurement system depicted in Figure 1(c) is, in fact, also a flow rate measurement-based method where the flow rate is indirectly determined by measuring the pressure (e.g., orifice or Venturi tube meters). Few methods reported in the literature to realise spirometers are briefly discussed in the subsequent sections.

Figure 1 Various methods of obtaining spirograms: (a) by volume measurement; (b) by flow rate measurement and (c) by pressure measurement

(a) (b) (c)

Some of the spirometers are constructed based on magnetostriction principle. Good quality ferromagnetic material is available for this type of spirometers (Nakesch and Pfutzner, 1995). These spirometers have advantage in the situation where the sensor is required to be changed frequently. However, such spirometers have to be calibrated more frequently (each time the sensor is changed, calibration is required). Further, the relation between the flow rate and the output voltage is also very complex in these spirometers.

Page 3: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 441

Some other spirometers use direct measurement by collecting the gas in a container. In these spirometers, the volume collected must be temperature compensated and the container for collection of the gas should be leak proof and at the same time should not offer any resistance while breathing. Also, care should be taken regarding the condensed water vapour on the walls of the container. Some spirometers are also developed using flow time monitor method (Lim et al., 1998). These spirometers have an improved mouthpiece, which makes them suitable even for paediatric use. A major disadvantage of these spirometers is that they can be used only in conjunction with a computer or a laptop. Another drawback of these spirometers is that they use preset pressure transducer switches, so there is no continuous monitoring of the input signal.

Another (digital) spirometer, based on the principle of hot wire sensor, has been proposed by Lin et al. (1998), This spirometer exhibits good performance but replacing of sensor is expensive. However, this digital spirometer can be connected to a nearby computer, which can be very advantageous. Many a times these tests need to be performed right at the time of the asthma attack. It is very unlikely that a doctor will be present with the patient at that moment. A possible solution is to embed a web server and make the device (spirometer) network available for online treatment.

Online treatment occupies a prominent place in today’s world as internet provides access to the data from anywhere in the world through standard browser technology (Economou et al., 1996). Consulting a specialist, who is located far away from a patient, can be achieved through the internet (Levy and Lawrence, 1992; Szymanski, 2000). Web server also helps in maintaining and accessing the records of a patient. As the web servers have become a popular tool for sharing data, this feature may be embedded into the spirometer (Lovell et al., 2001; Finkelstein et al., 1998). This enables the spirometer to share the data with a doctor who may be located at a distant place (Levy and Lawrence, 1992; Szymanski, 2000).

By using a web-server-based spirometer, a physician can, for example perform online dynamic lung function test and obtain the results. Thus, Patient’s test results (graphs etc.) and symptoms are available online to the doctor. Functionally, an embedded web server can be as powerful as a full web server. The embedded web server knows all about the system in which it is embedded. It can provide access to the data and perform tasks as requested. It can activate routines to interpret the requests and modify applications via a standard Hyper Text Mark-up Language (HTML) browser. The embedded web server should also have appropriate signal processing capability (Leung et al., 1998) to deal with the acquired medical data from tests such as a pulmonary function test.

This paper presents the design and development of a simple, low-cost digital spirometer. A new feature of embedding a web server in a spirometer is described and implemented in the developed prototype. Spirometers with computer connectivity are available, but to the best of author’s knowledge, spirometer with embedded web-server technology has not been reported so far. All the details of this work are presented in the subsequent sections.

2 An overview of breathing tests

Breathing tests, also called pulmonary function tests, are designed to identify and quantify defects and abnormalities in the function of respiratory system (Yeginer et al., 2004). These tests can be broadly classified into two types, depending on the lung

Page 4: Ijbet 1407 Agarwal and Ramachandran

442 V. Agarwal and N.C.S. Ramachandran

characteristics that they measure. These are Gas Exchange Functions and Dynamic Lung Functions. The dynamic lung functions test the Forced Vital Capacity (FVC), Flow-Volume Curves, Maximum Voluntary Ventilation (MVV) and airway resistance. The dynamic lung function test is the most common test and highly informative and useful in most of the cases.

A typical spirogram is shown in Figure 2 (Fishman, 1998). The Y-axis in the graph represents the volume of the gas present in the lungs and the X-axis shows the time. The spirogram shows how the volume changes during a breathing action. The deep crest and trough in the graph are formed during a forced (full) respiration cycle, while the normal tidal waveform corresponds to relaxed breathing.

Figure 2 A typical spirogram showing the lung volume compartments in a volume-time graph

In the context of the health of lungs, two parameters are important. These are the volume and capacity of lungs. Volume denotes the amount of gas (air) in the lungs. Capacity is the combination of two or more volumes. The total volume of lungs is divided into four different types of capacities. The four types of volumes are shown in Figure 2, the Tidal Volume (TV), Expiratory Reserve Volume (ERV), Inspiratory Reserve Volume (IRV) and Residual Volume (RV) (Fishman, 1998). The four types of capacities are (Figure 2) Inspiratory Capacity (IC), Vital Capacity (VC), Functional Residual Capacity (FRC) and Total Lung Capacity (TLC).

The flow-volume spirogram is widely used to identify the lung problems. Forced vital capacity generally means forced expiratory vital capacity. This test involves two steps: a full inspiration to total lung capacity followed by a rapid forceful maximal expiration. The rate of airflow and the volume of air expelled within designated time intervals provide an indirect measure of the flow resistance properties of the lungs being tested. The time taken for total volume expulsion generally does not exceed 3 s. The volume expelled during first 1 second (FEV1) and the total air expelled (FEV) are calculated. From that information, the ratio of FEV1/ FEV is obtained. This ratio is very important for diagnosis. The relationship between the flow and volume provides useful information about pulmonary function. Sample flow-volume spirograms given in Figure 3 (American Thoracic Society, 1995a) show how the graphs appear for a healthy person and an unhealthy person.

The flow-volume curve depicts the relation between the lung volume and the maximum rate of airflow as lung volume changes during a forced expiration.

Page 5: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 443

Figure 3 The flow-volume spirograms corresponding to different levels of disabilities: (a) normal or a healthy person; (b) fixed airway obstruction; (c) extrathoracic obstruction and (d) airflow obstruction

(a) (b)

(c) (d)

3 Overview of the proposed system

An overview of the proposed system is presented with the help of a block diagram shown in Figure 4. The system consists of the following two major parts:

• The data acquisition unit

• The control and interface.

The data acquisition unit has a transducer to acquire the voltage signal corresponding to the flow rate of the gas. This sensor is mounted in the mouthpiece, which is a standard 22 mm tube. The signal from the sensor (typically 2–10 mV) is amplified, filtered and digitised. The control and interface block has all the basic interface units like memory, etc. for the processor.

Figure 4 The block diagram of the proposed spirometer

Page 6: Ijbet 1407 Agarwal and Ramachandran

444 V. Agarwal and N.C.S. Ramachandran

A Liquid Crystal Display (LCD) and a keyboard are used for interaction between the user and the instrument. The block also has an Ethernet and serial communication interface for communication between this instrument and the user through another device.

The signal processing unit consists of an amplifier, a low-pass filter and an Analogue to Digital Converter (ADC). The microcontroller unit is based on Dallas 80C400 controller along with other peripherals. The serial port has the RS232 transceiver and connector. The Ethernet unit has the Ethernet physical device and RJ45 cable connector, Ethernet magnetics and related components. A detailed description of the working of these blocks and their components is given next.

3.1 The data acquisition unit

Spirometric data corresponds to the flow and volume of air during the breathing process. An indirect method of obtaining this data is by measuring the pressure across the mouthpiece of the spirometric device. The flow rate of fluid and the pressure are related as per Bernoulli’s equation:

2

2v Pgy C

ρ+ + = (1)

where v is the fluid velocity along the streamline, g is the acceleration due to earth’s gravity, y is the elevation in the direction of gravity, P is the pressure along the streamline, ρ is the fluid density and C is a constant. The acceleration due to gravity and density of air being constants during the time of measurement, the velocity of fluid turns out to be proportional to the square root of the pressure as below:

.v P∝ (2)

From this equation it can be inferred that the flow rate of the gas is equal to a constant times the square root of the pressure as given below:

.v k P= (3)

The pressure sensor measures the differential pressure across the mouthpiece and the corresponding flow rate is derived from the pressure value using equation (3). This flow rate, when integrated with respect to time, yields the volume of the gas flowing through the mouthpiece. The flow rate vs. volume relationship is shown in Figure 5. Motorola’s MPX2010 pressure sensor has been used in the mouthpiece of the spirometer to obtain the flow rate data.

This is an MEMS-based bulk micromachined, silicon piezo-resistor device (Motorola Inc., 2003) as shown in Figure 6. The piezo resistors of the sensor are arranged as a Wheatstone bridge circuit. The output voltage of this sensor is proportional to the differential pressure applied across the differential gauge element. The voltage signal due to imbalance in the bridge is amplified to be compatible with the input level of the ADC using an instrumentation amplifier. AD7812, a 12-bit, serial ADC is used for analogue to digital conversion. This ADC is configured to operate between 0.5–4.5 V analogue input range. Its output is in 2’s complement form. The converter has a ‘power down’ option which reduces the power consumption and increases the life of the battery. This is a particularly important consideration for portable instruments. The output of the ADC is

Page 7: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 445

serially obtained by the microcontroller with two of its port pins specifically dedicated for this purpose.

The amplified signal is filtered before being digitised by the ADC so as to eliminate the noise pickup due to Electro Magnetic Interference (EMI). An operational amplifier is configured as a Sullen-Key, two pole, unity gain, low-pass filter for this purpose (Franco, 2002).

Figure 5 The relation between (a) volume and (b) flow rate of the gas moving into and out of the lungs

Figure 6 A cross-sectional view of MEMS-based pressure sensor used in the spirometer

Source: Motorola Inc. (2003)

For flow time spirograms, 95% of signal energy lies within a bandwidth of 0–12 Hz. Therefore, the cut-off frequency of the filter is located at 12 Hz. A 2.5 V reference is used at the input of the instrumentation amplifier so as to add an offset voltage at its output. The output voltage swings from 0.5 V to 4.5 V with a 2.5 V DC offset which makes the signal free from 200 mV ground noise at the biased voltage. The analogue circuit, giving the connection details of the sensor, amplifier, filter and the ADC is shown in Figure 7. PCB layout is done carefully so that noise effects are minimised. The digital grounds are connected to the analogue grounds in such a way that minimum noise is induced into the analogue ground.

Page 8: Ijbet 1407 Agarwal and Ramachandran

446 V. Agarwal and N.C.S. Ramachandran

Figure 7 The proposed circuit diagram showing the sensor, the amplifier, the low-pass filter and the ADC stages

3.2 The control and interface unit

A microcontroller, belonging to the Intel 8051 family, is used for the control and coordination of the overall spirometric actions as shown in Figure 8. Dallas 80C400 controller is selected for this purpose. This microcontroller reads the sampled data from the ADC at a rate of 50 Hz and evaluates its square root.

From the calibration table, the obtained square root value is corrected for offset errors. This corrected value corresponds to the flow rate and this is stored in a Nonvolatile Random Access Memory (NVRAM). 128 K Static RAM (SRAM) and 32 K NVRAM are used as memory of the microcontroller for storing the program code, the calibration values and the data (Figure 8). An LCD is used for display during stand alone operation. It has a RS232-based serial port for communication with the nearby computers. Ethernet physical device, connected for web server, is used as interface for communication on the internet.

Figure 8 The control and interface diagram of the proposed system

A keypad is provided for feeding data and user requirements into the microcontroller. This keypad has alphanumeric keys so that the user can enter the text or numbers into the spirometer as required during the operation of the device. Depending on the user requirement, the acquired data are processed for flow-time, volume-time and flow-volume curves. All the data manipulation is done using the recommended

Page 9: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 447

procedures of ATS standards. These values can be either stored in a computer or can be served to a remote client as a web server or communicated to a nearby computer, so that the data can be used for printouts or saved for future reference. The obtained spirometric data are displayed using a graphic LCD in a proper format. The display format is appropriately chosen so that a physician can interpret the values and the graphs accurately. Web server is implemented using Dallas 80C400 microcontroller. This microcontroller has inbuilt hardwired Transmission Control Protocol/Internet Protocol (TCP/IP) stack and the Media Access Control (MAC). The MAC is programmed for Media-Independent Interface (MII) mode of data transfer to the Ethernet Physical Device (Ethernet PHY). National instrument’s DP83846 is used as the PHY.

Apart from the TCP/IP stack feature, the Dallas microcontroller has also been used in the proposed application because it has eight general purpose I/O ports. Keyboard, LCD screen, etc. can all be directly connected to the microcontroller thereby avoiding interface ICs. As this microcontroller has many useful routines for ping, ipconfig, etc., which are programmed on chip, it makes programming easier.

The 80C400 is programmed for 100 TX, MII configuration. The address bits of DP83846 are configured accordingly. The output TX+, TX– and inputs RX+, RX– are connected to RJ45 cable connector via an isolation transformer. An RJ45 connector with built-in magnetics is used for this purpose. Dallas DS2502-E48 is used for MAC address configuration. Figure 9 shows the complete view of the developed hardware.

Figure 9 Detailed view of the developed spirometer with an embedded web server

The synthesis of hardware and software interface between microcontroller and the devices it controls, is done very carefully. Optimisation of synthesis is done so as to reduce the number of components, thus reducing the overall cost of the system. Offset adjustment of the operational amplifier, square root calculation for obtaining the flow rate and integration of flow rate for volume calculations are implemented in software. Port allocation of microcontroller is done in such a way that the number of peripheral devices is reduced to minimum possible. This also helps in efficient coding of device drivers. The spirometric measurements must be reproducible and must guarantee validity. For this purpose, these signals are modelled as exponential functions. These models are proposed so as to determine and estimate FVC and FEV1/FVC correctly for those patients who cannot fulfil the forced expiratory manoeuvre of 6s and a plateau phase at the end of forced expiration.

Page 10: Ijbet 1407 Agarwal and Ramachandran

448 V. Agarwal and N.C.S. Ramachandran

The web-server-based spirometer is helpful for interaction between doctor and patient in many ways (Economou et al., 1996; Lovell et al., 2001; Finkelstein et al., 1998):

• As this is portable, the doctor can easily carry it to the patient who has an asthma attack or a COPD. The doctor can observe the spirograms either on the LCD monitor on the device or by transferring the data from spirometer onto his personal computer.

• Due to the spirometer’s efficient user interface, the patient can test himself during an asthma attack and receive better treatment. As this is a low-cost instrument, more patients can afford to have their own spirometer.

• As a web server is embedded into it, the patient and the doctor (who may be located far apart) can interact with each other in many ways. On the specialist’s request, the patient can take the test online. The specialist can simply logon to the website (i.e., spirometer’s web server), study the spirograms online and instruct the patient regarding the types of tests required. This eliminates the tedious and time-consuming process of first transferring the data to a computer from the spirometer and then sending it through fax or e-mail to the specialist.

4 Results and discussion

Various tests were performed on the developed spirometer to ascertain its performance. The behaviour of the pressure sensor was calibrated against high-pressure atmospheric air tank, with a regulator for various amounts of air flow. These calibrated values are stored in the NV RAM of the spirometer. Each time the test is conducted the obtained values are compared against these stored values and the flow rate is obtained. These flow-rate values are used for further processing.

Figure 10 shows the analogue voltage waveform at the output of the amplifier of the spirometer during a pulmonary test, obtained using a Tektronix make Digital Storage Oscilloscope (DSO), model No. 1002. This is the voltage corresponding to the pressure difference across the mouthpiece. The same data are also converted into digital form by the ADC and is stored into the memory of the device. The embedded microcontroller computes the important pulmonary functions from the stored data and displays them on the LCD. The spirometer can also interact with a nearby computer transmitting data using RS232 serial port. These data can be stored on a CD ROM or used for a printout.

Figure 10 A voltage waveform at the output of the amplifier obtained on a DSO

Page 11: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 449

Pulmonary tests were conducted on many individuals out of which two example flow-volume graphs are shown in Figures 11 and 12, respectively. The first case is that of a healthy individual while the second one is a patient having a fixed airway obstruction. Figures 11(a) and 12(a) show the voltage waveforms corresponding to the pressure difference across the mouthpiece, obtained using the DSO for the two persons. Figures 11(b) and 12(b) shown the flow-volume plots (drawn in MATLAB and displayed as a web page) to analyse the patients’ condition.

Figure 11 Results for the first individual: (a) voltage waveform and (b) web page showing the flow-volume spirogram

(a)

(b)

The spirometer’s web server handles requests from the remotely located specialist and sends the requested data using a standard browser. Figures 11(b) and 12(b) show typical screen shots of the spirograms obtained from the web server (as would be visible to the specialist). Both the spirograms and the pulmonary functions are displayed. The generated report also contains information related to when the test was performed, name and age of the patient and other relevant details. Selection tabs are visible at the top of the web page.

Page 12: Ijbet 1407 Agarwal and Ramachandran

450 V. Agarwal and N.C.S. Ramachandran

Figure 12 Results for the second individual: (a) voltage waveform; (b) web page showing the flow-volume spirogram and (c) an improved and more accurate spirogram corresponding to Figure 12(b)

(a)

(b)

(c)

Page 13: Ijbet 1407 Agarwal and Ramachandran

Design and development of a low-cost spirometer 451

5 Conclusions

Various sensors for flow measurements (Downing, 1995) have been studied and the MEMS-based pressure sensor has been used in the spirometer prototype, so as to reduce the size and cost of the instrument. The spirometric data are analysed and the parameters like FEV1 are computed as recommended by ATS. It is observed that the flow-volume spirograms are reasonably accurate and consistent with repeated trials. In fact, the spirograms can be further improved by using a more sophisticated algorithm. An example is shown in Figure 12(c), which corresponds to Figure 12(b).

This instrument is expected to be very useful as it is low cost, user friendly, portable and has a web server embedded in it. Not only can the remotely located patient consult a specialist, the specialist too can instruct the patient for specific test procedures and treatment. The total ‘bill of material’ cost of the developed spirometer is shown in Table 1. The cost will come down significantly if a large number of units are produced.

Table 1 Cost estimation of the proposed spirometer*

Device/Component Cost (USD) Microcontroller (DS80C400) 10.50 Instrumentation amplifier (INA 114) 04.20 Analogue to Digital Converter (ADS7812) 11.80 Operational amplifier (OPA 117) 00.80 Ethernet PHY (DP83846) 04.95 Graphic LCD 15.80 Keyboard, LAN RS232 connectors etc. 25.05 Sensor (MPX2010D) 06.90 Total ≈80.0

*Source of cost information is the corresponding website of the company. The actual cost can be obtained from the respective dealers.

The developed spirometer has the ability to communicate with a personal computer in two ways, namely through a serial port RS232 connection and through internet or Local Area Network (LAN). This facilitates the storage of spirometric data for analysis and/or records (database), printouts and other usage. To provide increased patient data protection, the firmware of the proposed system can be suitably modified for encrypted transmission over internet. In the near future, such systems are expected to provide inexpensive medical care to thousands of patients.

Acknowledgements

The authors are grateful to C. Chandramouli and Chetan Patki of Applied Power Electronics Lab, Department of Electrical Engineering, IIT-Bombay, India, for their help.

Page 14: Ijbet 1407 Agarwal and Ramachandran

452 V. Agarwal and N.C.S. Ramachandran

References American Thoracic Society (1995a) ‘Standards for the diagnosis and treatment of patients with

chronic obstructive pulmonary disease’, American Journal of Respiratory Care Medicine, Vol. 152, pp.S77–S120.

American Thoracic Society (1995b) ‘Standardization of spirometry’, American Journal of Respiratory Care Medicine, 1994 update, Vol. 152, pp.1107–1136.

Downing Jr., W.G. (1995) ‘Electronic measurements of pulmonary mechanics’, WESCON ‘95. Conference Record, November, pp.644–649.

Economou, G.P.K., Goumas, P.D. and Spiropoulos, K. (1996) ‘A novel medical decision support system’, IEEE Control and Computing Journal, pp.177–183.

Finkelstein, J., Cabrera, M.R. and Hripcsak, G. (1998) ‘Web-based monitoring of asthma severity: a new approach to ambulatory management’, IEEE International Conference on Information Technology Applications in Biomedicine, Washington, pp.139–143.

Fishman, A.P. (1998) Pulmonary Diseases and Disorders, 2nd ed., Vol. 3, McGraw-Hill Book Co., New York.

Franco, S. (2002) Design with Operational Amplifiers and Integrated Circuitsm, 3rd ed., Tata McGraw-Hill, New Delhi, ISBN 007-232084-2.

Hyatt, R.E., Scanlon, P.D. and Nakamura, M. (1997) Interpretation of Pulmonary Function Tests, Lippincott-Raven, Philadelphia, New York, ISBN 0 316 26261 7.

Leung, T.S., White, P.R., Cook, J., Collis, W.B., Brown, E. and Salmon, A.P. (1998) ‘Analysis of the second heart sound for diagnosis of pediatric heart disease’, IEE Proc.-Sci. Meas. Technol., Vol. 145, November, pp.285–290.

Levy, A.H. and Lawrence, D.P. (1992) ‘Data acquisition and the computer-based patient record’, in Ball, M.J. and Collen, M.F. (Eds.): Aspects of the Computer-based Patient Record, Springer-Verlag, New York, pp.125–139.

Lim, J.P.K., Warwick, W.J. and Hamen, L.G. (1998) ‘Pulmonary function measurement using flow time monitor’, IEEE Engineering in Medicine and Biology, Vol. 20, No. 6, pp.3199–3202.

Lin, C.W., Wang, D.H., Wang, H.c. and Wu, H.D. (1998) ‘Prototype development of digital spirometer’, Proc. IEEE conference on Engineering in Medicine and Biology, Vol. 20, No. 4, pp.1786–1788.

Lovell, N.H., Magrabi, F., Celler, B.G., Huynh, K. and Garsden, H. (2001) ‘Web-based acquisition, storage and retrieval of bio medical systems’, IEEE Engineering in Medicine and Biology, Vol. 20, No. 4, pp.38–44.

Motorola Inc. (2003) Sensor Device Data Book, Motorola Inc., DL200/D Rev. Nakesch, H. and Pfutzner, H. (1995) ‘Alternative sensor principles for the detection of human

respiration using amorphous ferromagnetic materials’, Proc. First Regional IEEE Conference of the Biomedical Engineering Society of India, 15–18 February, pp.1/17–1/18.

Szymanski, J.W. (2000) ‘Embedded internet technology in process control devices’, Factory Communication Systems, Proceedings, September, pp.301–308.

Weber, J.G. (1999) The Measurement, Instrumentation and Sensors Handbook, CRC Press, Boca Raton.

Yeginer, M., Ciftci, K., Cini, U., Sen, I., Kilinc, G. and Kahya, Y.P. (2004) ‘Using lung sounds in classification of pulmonary diseases according to respiratory subphases’, Proceedings of the 26th Annual International Conference of the IEEE EMBS, San Francisco, CA, USA, 1–5 September, pp.482–485.