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Original / research
 
An Exercise in Import Substitution of the Electrode Used in Extra Corporeal Shock Wave Lithotripter (ESWL)
R Karunanithi*, V Pugalendhi*, TMR Panicker**, M Paul Korath***, Placid Rodriguez#, K Jagadeesan+
 

Abstract
Extracorporeal Shock-Wave Lithotripsy is a leading technique used in urology for the non-invasive treatment of kidney and ureteric stones. In this technique, uroliths are broken by pressure waves into fragments small enough to be naturally passed. The electrode material used in the lithotripter, which is a consumable, has to be imported from the original equipment supplier at an exorbitant cost. We undertook an exercise in import substitution of the electrode material with a view to finding a cheaper, indigenous but appropriate material for the purpose. The indigenous electrode we chose for generating shocks in the lithotripter was evaluated at KJ Hospital Research and Postgraduate Centre, Chennai and compared for its performance in generating shock waves, the intensity of the wave, durability and the pain caused to the patient. Both the indigenous and imported electrode materials were subjected to analysis at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. The studies show that the indigenous electrode can act as a good import substitute.
 

Introduction
Urolithiasis (kidney stones) is a disease afflicting a significant part of the human race since the early days of civilization and is one of the common diseases of the urinary system. Several therapeutical techniques are available for destruction and removal of calculi. Extra corporeal shock wave lithotripsy (ESWL) is one of them, which has revolutionized the treatment of urinary stones. The rapid acceptance and wide spread use of this technique has made it a highly successful procedure and preferred method of treatment for over 80% of patients with kidney stones.3

Principle
The underlying physical principles of shockwave treatment for calculi in the human urinary and biliary tracts are generation of shock waves outside the body, focusing the waves onto an area distant from the generation area, coupling of the shock wave into the body and localization and positioning of the respective treatment target into the treatment focus.

Aims and Objectives
Our aim is to test the efficacy of an indigenous electrode “Silver Steel” as a substitute for the imported electrode for generating shock waves in the Technomed International Sonolith-3000 lithotripter functioning at our unit at KJ Hospital Research and Postgraduate Centre, Chennai - 84 for treating patients with kidney stones. The “Silver Steel” electrode wire is widely available in the local market at a low cost of about Rs.100/- per meter compared to the high cost of about $800 USD with the assembly for the imported electrode.

Material and Methods
Lithotripsy uses shock waves to pulverize urinary calculi (kidney stones) in-vivo non-invasively. In contrast, other methods of stone removal require open surgery (surgical nephrotomy), extraction of the stone through a puncture in the side of the patient (percutaneous extraction) or the insertion of an ureteroscope via the urethra with subsequent stone fragmentation and removal by mechanical means. All invasive procedures carry a higher risk of infection and complications than non-invasive procedures such as lithotripsy.

The shock waves externally generated are transmitted through the patient’s skin and pass harmlessly through the patient’s soft tissue. The shock waves pass through the kidney, get focused at and strike the stone.1 At the stone boundary, energy is lost, and this causes small cracks to form at the edge of the stone. The same effect occurs when the shock wave exits the stone. With successive shocks, the cracks open up, and in turn forms sub-cracks or branch cracks.2 Eventually, the stone is reduced to small particles; The process generally takes about 1 hour during which up to 2,000 shocks are administered. The patient will experience some discomfort during the treatment depending on the patient’s pain tolerance. Analgesics may be administered to make the patient more comfortable. The pulverized stone particles are flushed out of the kidney via ureter naturally during urination over the next few days.

Fig. 1a : Schematic representation of the sensor connected with the cathode ray oscilloscope (CRO) Fig. 1b : Schematic representation of the sensor connected with the cathode ray oscilloscope (CRO)
   
Fig. 2a : Schematic representation of the amplitude of the pulse in the cathode ray oscilloscope (CRO) Fig. 2b : Photograph of the amplitude of the pulse in the cathode ray oscilloscope (CRO)

Experimental Setup
In this study, we used Technomed International Sonolith-3000 lithotripter with a truncated ellipsoidal reflector (Outer diameter-245 mm, Inner diameter - 221 mm and depth - 165 mm). The lithotripter was operated at the typical clinical setting of 14 kV to 12 kV and 1-Hz pulse repetition rate. A sensor was connected as shown in the diagram at the focal point (F2) (Fig. 1), where the shock waves are focused after getting reflected from the semi ellipsoid brass symmetrical hemispherical reflector, the pressure waveform (Fig. 2) at the beam focus (F2) of the lithotripter has a typical peaks with positive and negative deflections.2
The pulse in the CRO was monitored and the amplitude of the wave (both the upper and lower deflections) was noted. Thirty such readings are recorded and tabulated (Table 1). The procedure was repeated for 14 KV and 12 KV for both the electrode pairs. For generating the shock waves an indigenous electrode “silver steel” with the same dimension as the imported electrode 85 mm long and 1.5 mm dia was used.

At 14 KV the average amplitude for the indigenous electrode is 78.8 mV and it is 74 mV for imported electrode, at 12KV it is 75.3 mV, and 74.4 mV respectively for indigenous and imported electrode (Fig. 3).

Calculations
Theoretically the pressure at the focus is 480 bars/V6
The average readings for the indigenous electrode.
At 14 KV is 78.5 mV therefore the pressure is 480 x 78.5/1000 = 37.68 bars
At 12 KV is 75.3 mV therefore the pressure is 480 x 75.3/1000 = 36.14 bars
The average readings for the imported electrode
At 14 KV is 74.4 mV therefore the pressure is 480 x 74.4/1000 = 35.52 bars
At 12 KV is 74.0 mV therefore the pressure is 480 x 74/1000 = 35.71 bars

Fig. 3 : a : Carbides in the indigenous electrode, which are uniformly distributed.
             b : In the imported electrode the carbides are 2-4 mm; some larger chunky
                  carbides (7-9 mm) are occasionally seen

From the calculations it is noticed that for the indigenous electrode the pressure at the focal point is slightly higher than that for the imported electrode for the same distance in separation of the electrodes. This would imply that the discomfort or pain felt by the patient is very slightly higher with the indigenous electrode; this could be alleviated by suitable local analgesics. Another difference is in the durability of the electrode measured by the electrode usage with the number of shocks; and it was found to be 1300 shocks/mm in the indigenous “silver steel” and 2000 shocks/mm in the imported electrode. This means that for a typical 2000 shocks required for a treatment, about 1.53 millimetres of the indigenous electrode would be consumed as against only 1 millimeter of the imported electrode.

Table 1 : Reading from the CRO

Sl No.

Indigenous electrodes
Imported electrodes
Pulse height
at 14 KV
Pulse height
at 12 KV
Pulse height
at 14 KV
Pulse height
at 12 KV
Upper
half
Lower
half
Total
Upper
half
Lower
half
Total
Upper
half
Lower
half
Total
Upper
half
Lower
half
Total
1.
3.6
4.2
7.8
4.2
4.0
8.2
4.2
3.2
7.4
3.6
3.9
7.5
2.
3.8
4.5
8.3
3.8
4.0
7.8
3.6
3.4
7.0
3.4
2.6
6.0
3.
3.0
3.8
7.7
3.2
3.7
6.9
4.2
3.2
7.2
3.1
4.2
7.3
4.
3.9
3.8
7.7
3.2
3.7
6.9
4.2
4.0
8.2
4.0
4.1
8.1
5.
3.7
4.0
7.7
3.9
4.1
8.0
4.2
3.8
8.0
4.0
4.1
8.1
6.
3.5
4.0
7.5
3.9
2.8
6.7
4.0
4.0
8.0
2.7
3.7
6.4
7.
3.7
4.0
7.7
4.0
3.3
7.3
4.0
4.0
8.0
3.6
3.7
7.3
8.
4.0
3.3
7.3
4.1
3.8
7.9
4.2
3.7
7.9
4.2
3.3
7.5
9.
4.0
4.0
8.0
4.0
4.0
8.0
4.2
2.5
6.7
4.1
3.3
7.4
10.
3.8
4.0
7.8
4.0
4.0
8.0
4.0
3.5
7.5
4.0
3.5
7.5
11.
4.0
4.0
8.0
3.8
3.0
6.8
4.0
3.8
7.8
4.1
4.1
8.2
12.
4.0
3.7
7.7
4.1
3.9
8.0
3.8
3.9
7.7
4.1
3.1
7.2
13.
4.0
4.0
8.0
4.0
3.2
7.2
4.0
4.0
8.0
4.1
4.3
8.4
14.
4.0
4.0
8.0
4.0
3.3
7.3
4.2
4.0
8.2
4.1
4.2
8.3
15.
3.8
3.2
7.0
4.0
3.8
7.8
2.5
3.9
6.4
4.0
4.0
8.0
16.
3.6
3.7
7.3
4.0
3.5
7.5
4.0
3.0
7.0
3.2
3.8
7.0
17.
4.0
4.2
8.2
3.8
3.3
7.1
3.8
3.9
7.7
2.8
3.4
6.2
18.
3.8
4.0
7.8
3.8
3.8
7.6
2.7
4.0
6.7
3.6
3.7
7.3
19.
3.9
4.1
8.0
4.2
3.3
7.5
3.5
4.0
7.5
4.1
3.2
7.3
20.
3.9
4.0
7.9
4.0
2.8
6.8
4.0
2.9
6.9
4.0
3.8
7.7
21.
37.
4.5
8.2
4.2
3.8
8.0
3.9
2.5
6.4
3.9
3.8
7.8
22.
3.9
4.2
8.1
4.0
4.0
8.0
3.9
4.0
7.9
4.0
3.9
7.9
23.
4.2
4.2
8.4
3.8
3.6
7.4
4.0
3.8
7.8
4.0
4.0
8.0
24.
4.2
3.8
8.0
3.0
4.0
7.0
4.0
4.0
8.0
4.0
3.5
7.5
25.
4.2
4.1
8.3
3.8
4.0
7.8
3.2
3.6
6.8
4.0
3.0
7.0
26.
4.2
3.9
8.1
4.1
3.3
7.4
3.0
3.0
6.0
4.0
3.0
7.0
27.
4.0
4.2
8.2
4.1
3.2
7.3
3.8
3.2
7.0
3.4
3.1
6.5
28.
4.0
4.0
8.0
4.0
4.0
8.0
4.0
3.0
7.0
4.0
4.0
8.0
29.
4.2
4.2
8.4
4.2
4.0
8.2
4.0
3.8
7.8
3.7
3.0
6.7
30.
4.0
3.3
7.3
4.2
4.0
8.2
4.1
3.5
7.6
4.1
4.0
8.1
Average pulse x 10 mV }
7.85
7.53
7.40
7.44

 

Chemical Analysis and Metallography of the Two Electrodes
Silver Steel is a 1% Carbon 1% Cr tool steel supplied centreless ground to close tolerances available in 1, 2 or 3 meter lengths, (hardened: Water Quenched from 790/820 C) and Tempered 100/320 C). It is readily available in the Indian market and the cost is only Rs.100/- per meter.

The imported electrode is of length 8.5 cm and 1.5 mm diameter that costs around $ 800 USD for the whole assembly (Indian Rs.36,000/- per electrode. The success with the indigenous “silver steel” electrode as a substitute for the costly imported electrode, at KJ Hospital Research and Postgraduate Centre, Chennai, with only two minor disadvantages, those of a slightly higher pressure and consequent very minor (manageable) discomfort to the patient and a slightly higher electrode usage rate prompted us to carry out a comparative metallurgical study4,5 of the two electrodes at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. Some salient aspects of above studies are reported below.

 

Table 2 : Chemical analysis of the 1.5 mm diameter imported electrode material
Sr. No. Elements Conc (%) Method of analysis
1. Iron 71.5 AAS*
2. Tungsten 4.5 Gravimetry
3. Calcium 0.055 AAS
4. Molybdenum 4.2 ICP-OES#
5. Chromium 3.5 ICP-OES
6. Vanadium 2.0 ICP-OES
7. Nickel 0.30 ICP-OES
8. Manganese 0.17 ICP-OES
9. Silicon 0.28 ICP-OES
10. Cobalt 0.42 ICP-OES
11. Copper 0.08 ICP-OES
Table 3 : Analysis of the 1.5 diameter indigenous electrode material
Sr No. Elements Conc (%) Method of analysis
1. Iron Matrix-94% AAS*
2. Carbon 1.0 Combustion
3. Calcium 0.006 ICP-OES
4. Chromium 1.0 ICP-OES
5. Nickel 0.11 ICP-OES
6. Maganese 0.25 ICP-OES
7. Cobalt 0.18 ICP-OES
9. Bismuth 0.016 ICP-OES
10. Molybdenum <0.012 ICP-OES
11. Tungsten <0.012 ICP-OES
12. Vanadium <0.012 ICP-OES
13. Aluminium <0.012 ICP-OES
14. Magnesium <0.012 ICP-OES
15. Lead <0.010 ICP-OES
*AAS - Atomic absorption specto\roscopy; #ICP-OES - Inductively coupled plasma optical emission spectroscopy

 

Table 4 : Summary of the analysis of the two electrodes

Sl No. Indigenous Electrodes Imported Electrode
1. The bulk chemical analysis indicates
the wire consists of alloying elements Cr, 		The bulk chemical analysis indicates the wire consists of alloying elements Cr, Mo, W, V.
2. Microstructure of the wire is ferrite with carbides distributed uniformly. Carbides of size 1-2 m were found generally well distributed. Microstructure of the wire is ferrite with carbides distribution uniformly. Carbides of size range 2-4 m were found generally well distributed while carbides of 7-9 m were observed less.
3. SEM/EDS analysis shows that the carbides are predominantly iron rich carbides. EPMA line scan analysis indicates the carbides.EPMA line scan analysis indicates the carbides have a higher amount of Cr as compared to matrix. EPMA analysis shows Fe dominant carbides generally and occasional reduction in Fe with peaking in W is observed which corresponds to bulk carbides.

Chemical Analysis
The results of the chemical analysis of the two electrode materials8 are presented in Tables 2 and 3. These estimates have an uncertainty of 5% for Atomic Absorption Spectroscopy (AAS), 4% for Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) had in 10% for Gravimetry.

Metallography and Microchemistry
The optical micrograph of the polished and etched surface is shown in figure below (Fig. 3); Fig. 3a is of the indigenous electrode and Fig. 3b is of the imported electrode. Both the microstructures consist of ferrite matrix with spheroidal carbides. A uniform hardness in the range of 430-450 VHN was obtained across several regions of the sample for the indigenous electrode. The imported electrode has a much higher hardness in the range 700-800 VHN. In the indigenous electrode the carbides are uniformly distributed. In the imported electrode the carbides are 2-4 mm; some larger chunky carbides (7-9 mm) are occasionally seen. The volume fraction of the carbides in the imported electrode is seen to be much higher than in the indigenous electrode.

The chemical composition obtained from the carbide and matrix by quantification of the spectra as well as by Electron Probe Micro Analysis (WDX) indicated that 2/3 of the Chromium in the steel goes to the carbides. The minute amounts of W, V and Mo present also are partitioned to the carbides. However the precipitates are predominantly Fe-rich (98%) and therefore essentially Fe (M)3C.

This latter result is very interesting and implies that the electrode is flux coated with calcium oxide and silica present in the flux along with part of the alloying addition, molybdenum also incorporated in the flux. Further, the chemistry and the microstructure of the imported electrode corresponds to AISI M2 Molybdenum high speed steel (equivalent to AFNOR 06-05-04-02/DIN 1.3343/UNS T11302) in the quenched and tempered condition. Compared to the silver steel, which is also tool steel, AISI M2 is high-speed tool steel highly alloyed with molybdenum, tungsten and vanadium. Consequently it has a much higher hardness and abrasion and wear-resistance than the silver steel. However as our studies have shown that the silver steel is adequate for the purpose though with two minor disadvantages.

Summary
The chemical and metallurgical characteristics of the two electrode materials and their performance in the lithotripter are summarized in Table 5.
The various analyses of the electrode such as its chemical, metallurgical characteristics and their performance in the shock wave lithotripter show that the indigenous electrode used at our unit can act as a good import substitute with much lower cost.

Discussion
The various analysis of the electrode such as its chemical, metallurgical and its performance in the shock wave lithotripsy shows that the indigenous electrode used at our unit can act as a good import substitute with much lower cost. From the calculations it was noticed that for the indigenous electrode the pressure at the focal point is slightly higher than the imported for the same distance in separation of the electrodes. Although the iron content of the electrode used at our unit is nearly 94% compared to the imported electrode, which has 71.5%, there is no notable difference in the performance of the indigenous electrode. The durability of the electrode also measured by measuring the size of the electrode after usage with the number of shocks, and it was found as 1300 shocks/mm in the indigenous and 2000 shocks/mm in imported electrode.

Conclusion
We can conclude that after a thorough examination of the electrode used at our unit as well as the imported electrode the indigenous electrode may serve as an import substitute, with comparable quality of performance at lesser cost and greater availability.

Acknowledgement
The authors would like to thank Mr. MP Vikraman, Senior Technologist, Department of Radiology, KJ Hospital Research and Postgraduate Centre, Chennai - 84, India, for his valuable contributions and timely help to execute the study. We are also grateful to Dr. Baldev Raj, director and the Scientists at Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam, for the chemical and the metallurgical investigations on the two electrode materials. One of us (PR) is grateful to Dr. VS Raghunathan Associate Director Materials Characterization Group IGCAR for useful discussions.

References

  1. Nalini M Guda, Susan Partington, Martin L Freeman. “Extracorporeal shock wave lithotripsy in the management of chronic calcific pancretitis: A meta-analysis” JOP. J Pancreas (Online) 2005; 6 (1) : 6-12.
  2. Ch. Chaussy, Munich. Extracorporeal shock wave lithotripsy-New aspects in the treatment of kidney stone disease 1982.
  3. Arunai Nambiraj. A study of the constituents and properties of urinary stones and its application to stone fragility in extracorporeal shock wave lithotripsy. A PhD Dissertation submitted to Anna University March 2000.
  4. Viswanathan KS, Srinivasan V, Thiruvengalasam, Sekhar JK. Indira Gandhi Center for Atomic Research Kallpakkam, private communication 2004.
  5. Parameswaran P, Terrrance ALE, Saroja S. Indira Gandhi Center for Atomic Research Kalpakkam, Private Communication 2004.
  6. Technomed International Sonolith-3000 lithotripter - Manual.

THE BURDEN OF CHRONIC KIDNEY DISEASE

Programmes to detect chronic kidney disease, linked to comprehensive primary and secondary prevention strategies, are needed urgently. Screening programme detected albuminuria in around 6-7% of the population of the city of Groningen. Detection of chronic kidney disease and predisposing conditions such as diabetes and hypertension led to effective interventions.

Patients with end stage renal disease comprise only a small percentage of people with chronic kidney disease.

Yet most clinical practice guidelines now recommend identifying those at risk-people with hypertension, diabetes, obesity, and other predisposing conditions or medicines as well as older people and relatives of patients with chronic kidney disease.

Screening of urine samples with dipsticks for albuminuria and proteinuria is useful as long as it is confirmed by quantitative spot urine analysis for albumin : creatinine ratio or protein: creatinine ratio. These tests are more accurate than those based on the analysis of 24 hour urine collections in view of the inaccuracies of the latter. Serum creatinine is a readily available and reliable indicator of chronic kidney disease but it may be altered by a variety of factors, and renal function may be compromised considerably before serum creatinine concentrations rise. Reporting of serum creatinine is nowadays often linked to that of a calculated glomerular filtration rate.

  1. Patients should be encounraged to give up smoking and to lose weight.
  2. Secondary prevention depends on tight control of blood pressure (to less than 130/80 mm Hg).
  3. Use of angiotensin converting enzyme inhibitors and angiotensin II receptor blockers concomitantly to reduce proteinuria (to less than 1 g/24 hours).
  4. Guidelines also recommend strict control of diabetes with an HbA1c level of around 7%.
  5. Statins may benefit patients with chronic kidney disease through preventing arteriosclerosis.
  6. Such a multifactorial approach to risk reduction may slow or even reverse declining renal function.

Rizwan A Hamer, A Meguide El Nahas, BMJ, 2006; 332 : 563-64.

 
 
*Research Scholar, **Dean of Faculty, ***Chief Physician, Director, KJ Hospital, +Founder and Director, KJ Hospital, Chairman, KJ Research Foundation; #DAE-BRNS Senior Scientist and Distinguished Visiting Professor, Raja Ramanna Fellow, Department of Metallurgical and Materials Engg. Indian Institute of Technology Madras, Chennai - 600 036 and Adviser, KJ Research Foundation, Chennai.
 
 
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