熊本大学学術リポジトリ

A Compact Nitric Oxide Supply for MedicalApplication

journal orpublication title

Digest of Technical Papers-IEEE InternationalPulsed Power Conference

volume 2007page range 752-755year 2007-06URL http://hdl.handle.net/2298/10319

doi: 10.1109/PPPS.2007.4345823

A COMPACT NITRIC OXIDE SUPPLY FOR MEDICAL APPLICATION∗

S. Sakai1, M. Matsuda1, D. Wang1, T. Kiyan1, T. Namihira1, H. Akiyama1, K. Okamoto2 and K. Toda1

1Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan

2Department of Intensive and Critical Care Medicine, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto city, Nagano 390-8621, Japan

∗ This Work supported by Industrial Technology Research Grant Program in ’05 from New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Abstract In 1987, Nitric oxide (NO) was identified as an effective treatment involving endothelium-derived relaxing factor (EDRF)1. NO has attracted lots of attention from the discovery. And now, NO is increasingly being used in medical treatments for some illness related lung. Currently a system of NO inhalation has a gas cylinder of N2 mixed with a high concentration of NO. However, this method is potentially risky due to the possibility of accidental leak of NO from the cylinder. In addition, gas cylinder is too heavy to carry around and too expensive to be used for all patients. Therefore, an on-site generation of NO would be highly desirable for patient, who is suffering lung disease, and medical doctors. Previous researches reported that NO is produced by pulsed arc discharge in the mixture of N2 and O2, and NO concentration increases with the increasing of pulse repetition rate and energy storage capacitance2-4. In this paper, the detail about a prototype of NO generator by pulsed arc discharge based on the optimal discharge condition has been reported. As the results, it is observed that NO concentration in the outlet gas is about almost 1000ppm and rise time is about 20 to 30 sec. These conditions are enough for NO inhalation therapy. Additionally, NO concentration is adjustable by changing pulse repetition rate.

Figure 1. NO inhalation treatment system

I.INTRODUCTION

It is well known that nitrogen oxide (NOx) is produced by nitrogen fixation of bacteria, combustion of fossil fuel, natural lightning stroke and so on. Bacteria produces nitric dioxide (NO2), and the other generate nitric oxide (NO). In the atmosphere, NO is oxidized to NO2 immediately by oxygen (O2) or ozone (O3).

Because NO2 is a green effect gas and toxic for human being, many researchers have studied about removable of NOx2-9. In contrast, there is not very much research about production of NOx10-12.

But NO is one of the most important molecules within the living human body. It is said that NO is related to the memory, attack on pathogen and vessel relaxation. Especially, vessel relaxation effect has got a lot of attention of the medical experts. This effect was found by Lous J. Ignarro et al. in 1987. They reported that NO works as endothelium-derived relaxing factor (EDRF) within the living body. From this discovery, some researchers started to study about application of NO for medical treatment. As a result, NO inhalation therapy has been used for some lung diseases such as acute respiratory distress syndrome (ARDS) or persistent pulmonary hypertention of the newborn (PPHN), in these days. It is said that NO gas, concentration of 1000 ppm and flow rate of 300 ml/min is needed for the treatment. Also concentration of NO2 must be below harmful level.

Currently a system of NO inhalation has a gas cylinder of nitrogen (N2) mixed with a high concentration of NO (Fig.1). NO from the gas cylinder is introduced to patients after attenuated by air and O2. However, this method is potentially risky due to the possibility of accidental leak of NO from the cylinder. In addition, gas cylinder is heavy to carry and expensive to be used for all patients. Therefore, an on-site production of NO would be highly desirable for patients and medical doctors.

Our previous researches10-11 showed that NO is produced by pulsed arc discharge in the mixture of N2 and O2 (air/simulant gas), and NO concentration increases with the increasing of pulse repetition rate and energy storage capacitance.

1-4244-0914-4/07/$25.00 ©2007 IEEE. 752

II.CONFIGURATION AND MECHANISM OF NITRIC OXIDE PRODUCTION

Fig. 2 is outside view of the supply. External sizes are

about 222 × 430 × 450 mm (height × width × length). This supply is chiefly composed of high-voltage dc power supply (HGR10-20P, Matsusada Precision Inc., Japan), discharge reactor, trigger circuit and mini pump (A.1F17N1.G12VDC, Hargraves Technology Corp., USA). Fig. 3 is inside view of the supply. Air inlet is at rear panel (right side of the Fig. 3) and outlet is at front panel (left side). Fig. 4 is connection diagram of the supply. The pump let ambient air (material gas of the NO) in and out through the discharge reactor at gas flow rate of 300ml/min. Discharge is applied when the ambient air introduced to the discharge reactor and produce NO.

Rod to plate electrode geometry was utilized as a discharge reactor. The outer diameter of and the length were 60 mm and 100 mm, respectively (Fig. 5). The rod and the plate electrodes were made of brass. The brass rod ending with a hemisphere had a diameter of 10 mm. The gap distance between the rod and the plate electrodes was fixed at 5 mm. The charging voltage to the capacitor was fixed at 13 kV, which is about 80 % value of self-breakdown voltage of the discharge reactor. Therefore, breakdown does not occur without trigger discharge, which is generated between GND electrode and spark plug. Trigger discharge is generated with trigger circuit and by means of fixing the rate of discharge, the rate of main discharge is adjustable. For the 1000 ppm of NO, pulse repetition rate is set to 220 Hz

Air consists chiefly of N2 and O2, and these molecules can be a material of NO. NO is produced or destructed as shown in following equations13.

eOOeO ++→+2 (1) eDOOeO ++→+ )(1*

2 (2) )()( 2*3*

2 DNNOOAN u +→+∑+ (3) ONOODN +→+ 2

2* )( (4)

22 ONONOO +→+ (5) ONNNOaN u ++→+∑−

21'*

2 )( (6) ONNON +→+ 2 (7)

21* )( ONNODO +→+ (8)

223 ONONOO +→+ (9) Under the condition of high temperature plasmas, reaction starts with decomposition of the O2 to O atoms and the main source of NO is collision of )( 3*

2+∑uAN with

O atoms (eq.3). NO2 is produced in the gas flow outgoing the discharge in the reaction of NO and O3 (eq.7) or O2. Pulsed arc discharge has similar characteristics to lightning stroke and generates high temperature plasma. For these reasons, NO and NO2 are generated by lightning stroke or pulsed arc discharge in the atmosphere.

Figure 2. Outside view

Figure 3. Inside view

Figure 4. Connection diagram

Figure 5. Discharge reactor

Discharge reactor HV DC power

supply

Trigger circuit

HV side

GND side

Capacitor

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III.EXPERIMENTAL SETUP AND RESULTS

As stated above, NO supply includes the pulsed arc

discharge reactor, a charging capacitor (0.19 nF), a dc high-voltage generating device (HGR10-20P, Matsusada Precision Inc., Japan), a limiting resistor (5 MΩ), and a spark plug connected to a trigger pulse circuit. In the experiment, a rod to plate electrode geometry was utilized as a discharge reactor. The outer diameter of and the length of the discharge reactor were 60 mm and 100 mm, respectively (Fig. 5). The rod and the plate electrodes were made of brass. The brass rod ending with a hemisphere had a diameter of 10 mm. The gap distance between the rod and the plate electrodes was fixed at 5 mm. The charging voltage to the capacitor was fixed at 13 kV, which is about 80 % value of self-breakdown voltage of the discharge reactor in the all experiment. Pulse repetition rate is set to 220 Hz without characteristic experiment of pulse repetition rate. The applied voltage to the rod electrode was measured using a voltage divider (EP-50K, Pulse Electronic Engineering Co., Japan), which was connected between the rod (High voltage side) and the plate (Ground side) electrodes. The current through the discharge reactor was measured using a current transformer (Pearson current monitor Model 2877, Pearson Electronics, USA), which was located the return current to ground. In the experiment, an ambient air was taken by mini pump (A.1F17N1.G12VDC, Hargraves Technology Corp., USA) through the inlet and discharge reactor, and fed into a NO-NO2-NOx gas analyzer (Model42C-HL, Nippon Thermo Co., Japan) through the outlet at flow rate of 300 mL/min.

Fig. 6 shows the typical waveforms of the applied voltage to the discharge current into the discharge reactor during the pulsed arc discharge. It will be observed from Fig. 6 the current waveform shows damped oscillations.

From fig. 7, it will be observed that the concentration of NO as a function of the pulse repetition rate. The concentrations of NO increased linearly with increasing the pulse repetition rate due to increasing the input energy into the discharge. Concentration of NO achieved 1000 ppm, which is needed for NO inhalation treatment when pulse repetition is at 220 Hz. Additionally, this result shows concentration of NO is easily controlled by fixing of pulse repetition rate.

Fig. 8 shows the result of rise time experiment. It is observed that after 20 to 30 sec from the start of the discharge, NO concentration achieved almost about 1000 ppm. In the inhalation therapy, rise time of the concentration of NO is an important factor for the early treatment. From this result, it’s believed that rise time of the NO supply is enough for practical use.

Fig. 9 shows repeatability of the compact NO supply on NO concentration. Discharge switch was turned on at 10, 35 and 60, and turned off at 20, 45 and 70 minutes from the start. From the fig. 9, it is observed that every cycle

showed about 1000 ppm and after turning off the discharge switch, NO concentration decreased to almost 0 ppm instantly.

-10

-5

0

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0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

VoltageCurrent

Volta

ge, k

V Current, A

Time, µs Figure 6. Typical waveforms of applied voltage and discharge current into discharge reactor

0

200

400

600

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0 50 100 150 200

NO

con

cent

ratio

n, p

pm

Pulse repetition rate, pps Figure 7. Concentrations of NO as a function of pulse repetition rate

0

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0 20 40 60 80 100

NO

con

cent

ratio

n, p

pm

Time, s Figure 8. Concentrations of NO as a function of time

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0

200

400

600

800

1000

0 10 20 30 40 50 60 70 80

NO

con

cent

ratio

n, p

pm

Time, min Figure 9. Repeatability of the compact NO supply on NO concentration

IV.SUMMARY In this paper, the detail information about a prototype of NO generator by pulsed arc discharge based on the optimal discharge condition has been described. It is observed that NO concentration in the outlet gas is achieved about 1000 ppm and rise time is about 20 to 30 seconds (from the ambient air and at the conditions of charging voltage: 13 kV, energy strafe capacitance: 0.19 nF, pulse repetition rate: 220 pps, gas flow rate: 300ml/min). Additionally, NO concentration is adjustable by changing pulse repetition rate. Repeatability of the supply showed also good condition. Although NO2 is produced by the discharge, there are some commercial productions of NO-NO2 converter or reducing agents (ascorbic acid and so on23). Therefore, NO2 must be removed by these processes.

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[15] Chrzan, K. and Andino, J.M., “Electrical strength of air containing ozone and nitric oxides produced by intensive partial discharges”, IEEE Transactions on dielectrics and electrical insulation, Vol.8, pp.607-611, 2001

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