| BackgroundPatients with a loss of micturition desire have a lot of difficulty in daily life,which gives their families and society gigantic burden. They have to rely on scheduled urination, which has, of course, a lot of disadvantages. Micturition alent devices (MADs) that can continuously monitor urinary bladder volume or pressure and alert the patient to urinate at right time may hopefully become an alternative for the treatment of loss of micturition desire. Several design protocols have been reported in the literature from 1970s, but they have some serious defects and can not be used clinically.ObjectivesFirst To introduce design and manufacture of a new micturition alent device on the principle of a compass.Second To validate the feasibility of the micturition alert device on the principle of a compass.Third To study the effect of the geomagnetic field on a micturition alert device on the principle of a compass.Fourth To study the primary parameters of the micturition alert device on the principle of a compass for the product design and clinical application of the device.Fifth To investigate the biocompatibility of silicon membrane embedded permanent magnets which are internal part of the micturition alert device on the principle of a compass.Sixth To measure the lower abdominal wall thickness which is one of important parameters of the device in adults for the product design and clinical application of the device.MethodsFirst The rationality and feasibility of the new micturition alent device on the principle of a compass was demonstrated by introducing the principle, elementary structure of the device.Second The feasibility of the micturition alert device on the principle of a compass was validated using home-made model of the device in vitro simulated test and vivo animal test.Third The effect of the geomagnetic field on a micturition alert device on the principle of a compass was studied in vitro simulated test and the possible protection measures were discussed.Fourth The primary parameters of the micturition alert device on the principle of a compass and their interaction rules were studied in vitro simulated test.Fifth The biocompatibility of silicon membrane embedded permanent magnets which are internal part of the device was evaluated both in vitro and in vivo including cytotoxicity test, sensitization test, primary skin irritant test and acute general toxicity test. Both the reaction of animals and pathology of the local tissue were observed after permanent magnets were implanted.Sixth The thickness of the lower abdominal wall was measured using ultrasound in 100 adults. The thickness of the lower abdominal wall at superior border of the pubic symphysis and 1,2,3,4 and 5cm above the pubic symphysis were measured using MRI in 37 adults.ResultsFirst This new micturition alent device on the principle of a compass patented by the national intellectual property rights bureau consists of an external alarm system and an internal permanent magnet. The permanent magnet is embedded with a silicon membrane. The alarm system is in fact an alarm controlled by a special switch which functions similarly to a compass and is therefore named a compass-switch. The alarm system can show the direction of the magnetic field where the central support axis is located. The alarm system is fixed on the lower abdominal wall outside and the permanent magnet is fixed on the bladder anterior wall. Any change in bladder volume would cause the change of the magnet position, which in turn causes the change of the magnetic field where the alarm is located and drives the hand of the alarm system to rotate. When the bladder volume reaches the preset value, the alarm buzzes automatically, alerting the patient to urinate. The design is characterized with simple structure and low power consumption when compared with other designs. A simple model of the alarm system included the dial, the compass switch, the buzzer, the power switch and the power supply and the latter four elements connected in series by wires to form the circuit. The compass switch consisted of the central support axis, the magnetic hand and the para-support axis. The hand was perpendicularly fixed on the central support axis and turned around the longitudinal axis of the central support axis. The central support axis and the para-support axis were made of non-magnetic metal of good conductivity. The N45 Brand NdFeB permanent magnetic rod with 3 mm in diameter took place of the magnetic hand because the magnetism of a common magnetic hand was not strong enough to work sensitively. A usual hand was then added that was made of non-magnetic metal of good conductivity. The hand and the magnetic rod were parallel and both fixed on the central support axis. Thus the hand, the magnetic rod and the central support can simultaneously turn around the longitudinal axis of the central support axis. The central support axis passes transversely through the gravity of the magnetic rod.Second In vitro simulated test, the correlation between the value of the model and the position of the magnet was significant(r>0.622,P<0.05), and more over, the correlation was one to one when the thickness of abdominal wall was from 2 to 4cm.The model began buzzing at the position of the magnet of 6.1, 6.3, 6.7 and 7.4cm when the thickness of abdominal wall was 2, 3, 4 and 5cm respectively. In animal test, the value of the model was 74.6±0.9, 79.6±1.2, 84.5±0.9, 90.1±0.8, 95.5±1.1, 101.8±2.1, 110.5±2.9 and 121.9±3.5°at the filling volume of 25, 50, 75, 100, 125, 150, 175 and 200 ml. They were positively correlated with one to one (r =1, P<0.01). When the bladder filling was preset at 150 ml, the model began buzzing at a factual filling of 147.6±8.0 ml, with the deviation error being less than 15 ml (10%). The shifting distance of the magnet from the initial filling state to 200 ml was 32.8±1.1mm.Third The geomagnetic field had no effect on the findings tested by the micturition alert device if the central fulcrum of the device parallelled with the direction of the geomagnetic field. The maximal effect occurred if the central fulcrum was vertical to the direction of the geomagnetic field. A moderate effect occurred corresponding to the acute angle between the central fulcrum and the geomagnetic field. Moreover, the effect was correlated with the position of body, the placement of permanent magnet and the thickness of abdominal wall.Fourth The value of the alarm system was correlated with the position of ferrite permanent magnet only when the thickness of simulated abdominal wall was 2cm(r=0.632,P=0.021), otherwise not(r<0.5,P>0.05). The correlation between the value of the alarm system and the position of NdFeB permanent magnets was significant(r>0.622,P<0.05), and intensified with the increasing diameter of NdFeB permanent magnets, but weakened with the increasing thickness of simulated abdominal walls.Fifth No sensitization, no stimulation, no acute general toxicity was observed except slight cytotoxicity to silicon membrane embedded permanent magnets. Wound healing was normal after muscular implantation of permanent magnets in 8 rabbits, one of which died from emaciation and others lived with excellent tolerance. The grade was 1 of the inflammatory reaction and fibrous capsule of the local tissue around the grafts. Among 8 dogs of the experimental group, one died from operation complications 10 hours after operation, another dog had intestinal obstruction 3 weeks after operation because iron wires in the intestinal tract was attracted by the permanent magnet and the other 6 dogs and 4 dogs of the control group were killed 1 year after operation which showed excellent tolerance with no abnormality in spirit, appetite, urine or stool and without any infection. Adhensions occurred between the epiploon and the bladder wall around permanent magnets in these 10 dogs. The fibrous capsule around permanent magnets was thin, the local bladder wall below permanent magnets was thickened, but the bladder mucosa was normal. The grade was 2 of the inflammatory reaction and fibrous capsule of the local tissue around the grafts. The findings of urine before and after operation were normal.Sixth The thickness of the lower abdominal wall was 2.34±0.66cm. The lower abdominal wall thickness was positively correlated with the weight, BMI and the distance from the measuring point to umbilicus(P<0.05), and was negatively correlated with bladder volume, laterolateral and craniocaudal diameters of the bladder(P<0.05), Their was no correlation of the lower abdominal wall thickness with gender, age, height and anterior-posterioral diameters of the bladder(P>0.05). The thickness of the lower abdominal wall at superior border of the pubic symphysis and 1,2,3,4 and 5cm above the pubic symphysis was 5.26±1.65, 3.45±1.34, 3.10±1.03, 3.02±1.05, 2.92±0.97 and 2.95±0.98 cm. Their was no correlation of the lower abdominal wall thickness with bladder volume(P>0.05).ConclusionsFirst The new micturition alent device on the principle of a compass was demonstrated with reasonable design, simple structure and low power consumption.Second It was feasible for the micturition alert device on the principle of a compass.Third The effect of the geomagnetic field was correlated with body position on the findings tested by the device. Some measures may be taken to avoid or decrease the effect of the geomagnetic field on the device.Fourth The thickness of abdominal walls, the position and magnetism of permanent magnets are three important parameters of the device. They are correlated with and affect each other. Reasonable parameters may optimize the device. NdFeB permanent magnets of 3mm thickness and 10mm diameter may meet the need for the patients with an abdominal wall from 2cm to 6cm thickness; stronger permanent magnets for the patients with an abdominal wall more than 6cm thickness and weaker permanent magnets for the patients with an abdominal wall less than 2cm thickness.Fifth Silicon membrane embedded permanent magnets used in the device has excellent biocompatibility to meet the criteria for clinical application.Sixth The mean thickness of the lower abdominal wall measured using ultrasound was 2.34cm, and its 95% confidence interval was 22.1~24.7cm. The mean thickness of the lower abdominal wall measured using MRI at superior border of the pubic symphysis and 1, 2, 3, 4 and 5cm above the pubic symphysis was 5.26, 3.45, 3.10, 3.02, 2.92 and 2.95cm respectively, and its 95% confidence interval was 4.71~5.81, 3.01~3.90, 2.76~3.45, 2.67~3.37, 2.60~3.25 and 2.62~3.28cm.
|
PDF Full Text Request