Crural diaphragm pacemaker and method for treating esophageal reflux disease

An electronic pacemaker is used to counter-act crural diaphragm relaxation thereby preventing and/or treating gastroesophageal reflux. The pacemaker can be implantable, or be connected to the skeletal muscles of the crural diaphragm through the skin. A sensor is used to identify spontaneous intermittent relaxations of the diaphragm. During these spontaneous intermittent relaxations, one or more electrodes are used to stimulate the skeletal muscles of the crural diaphragm to cause contraction of the lower esophageal sphincter.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is related to therapeutic gastroenterology and, more 
particularly, to an electrical stimulating device and method used to pace 
the crural diaphragm. 
2. Description of the Prior Art 
Gastroesophageal reflux is commonly treated using pharmaceuticals or by 
surgical procedures. In the pharmaceutical approach, the disease is 
treated most efficiently using H2 receptor antagonists and proton pump 
inhibitors. This class of drug is widely used in the U.S. and throughout 
the world, and sales of these products are believed to total more than 
$20,000,000,000 annually. The major disadvantage of pharmaceutical therapy 
is that it is a suppressive therapy and does not treat the cause of the 
disease. Thus, the pharmaceuticals must be consumed every day for the 
entire life of the patient. Surgical treatment is typically performed only 
when the symptoms and situation are fairly advanced, and poses the 
problems inherent in any major operation. 
U.S. Pat. No. 5,423,872 to Cigeina describes pacing of the stomach to alter 
its natural rhythm. The principle espoused in Cigeina is that by altering 
the rhythm, one can either delay or speed up gastric emptying. Cigeina 
indicates that many different disorders including reflux disorders can be 
treated using the rhythm altering methodology. Cigeina suggests that 
reflux disorders can be treated by using the electrical stimulator during 
a digestive rest phase to promote sphincter release. However, the Cigeina 
device is not likely to be effective for treating such disorders because 
it contemplates stimulating smooth muscles, and electrical stimulation of 
the smooth muscles of the lower esophageal sphincter will result in 
relaxation of the sphincter rather than contraction. 
U.S. Pat. No. 5,292,344 to Douglas discloses a percutaneously placed 
electrical gastrointestinal pacemaker which provide for both sensing and 
electrical pacing of the stomach. Like Cigeina, Douglas contemplates 
pacing the smooth muscle of the lower esophageal sphincter or stomach. 
Furthermore, Douglas is primarily directed to the treatment of stomach 
arrhythmias, not reflux disorders. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a crural diaphragm pacemaker. 
It is another object of this invention to provide a method of treating 
gastroesophageal reflux disease by selectively applying electrical 
stimulation to the skeletal muscles of the crural diaphragm. 
According to the invention, electrical pacing is used to override crural 
diaphragm inhibition during intermittent or transient lower esophageal 
sphincter relaxations (TLESR), and thereby treat gastroesophageal reflux. 
An implantable or external electrical pacemaker is connected to 
electrode(s) positioned on the crural diaphragm. When crural diaphgram 
inhibition is sensed during TLESR, the crural diaphragm is electrically 
stimulated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 shows an example of an electrical pacemaker designed for pacing the 
crural diaphragm according to the present invention. FIGS. 2a-b illustrate 
the pacing concept of this invention in the prevention of gastroesophageal 
reflux. It should be understood by those of skill in the art that the 
components used in the pacemaker as well as the mode of operation 
discussed below in connection with FIG. 1 could be varied considerably 
within the scope of the claimed invention. In addition, while the major 
role of the pacemaker is to treat esophagus reflux disease as explained in 
conjunction with FIGS. 2a-b, the pacemaker may also be useful in the 
treatment of achalasia and other esophageal motor disorders that are 
related to dysfunction of the crural diaphragm 
With reference to FIG. 1, myoelectric signals are received from by 
electrode pairs 1 and 2 placed on the patient's costal and crural 
diaphragm muscle tissue, respectively. These electrodes may be composed of 
or be plated with platinum, iridium, or other suitable materials. The 
costal diaphragm electrodes 1 and crural diaphragm electrodes 2 will be 
implanted surgically through a small incision in the patient's abdomen, 
either through a laparascopy or an open approach. Once the electrodes are 
positioned, the wires connected to the electrodes 1 and 2 will be tunneled 
under the skin. In the case of an external pacemaker unit which may be 
ideal for temporary use, the wires will be connected to a pacemaker that 
is preferably worn by the patient using a belt placed around the abdomen 
or chest. In the case of a permanent implantable device, the pacemaker 
will ideally be implanted under the skin of the abdominal wall. The 
pacemaker has the following functions: 
A) It will sense and/or record electromyography signals from the crural and 
costal diaphragm simultaneously. 
B) It will analyze the electromyography signals and will determine whether 
there is an inhibition of the crural diaphragm signal in the absence of an 
inhibition of the costal diaphragm. That is, the pacemaker will sense 
selective inhibition in the crural diaphragm which takes place during 
periods of spontaneous TLESR. 
C) After sensing inhibition, the pacemaker will provide electrical 
stimulation to the crural diaphragm to electrically pace the muscles of 
the crural diaphragm and thereby override the inhibition. 
It has been determined that spontaneous TLESR is the key mechanism of 
gastroesophageal reflux. The concept of selective crural diaphragm 
inhibition during TLESR has been observed in humans and animals. Studies 
in animals have demonstrated that electrical stimulation of the crural 
diaphragm increases the lower esophageal pressure. 
With reference to FIG. 2a, it can be seen that during spontaneous TLESR and 
acid reflux, the patient's respiratory activity and the activity of the 
patient's costal diaphragm (as indicated by the repetitive Electromyogram 
(EMG) signal) remain unchanged. However, activity of the crural diaphragm 
is inhibited, the lower esophageal sphincter pressure drops and the pH in 
the esophagus decreases and becomes more acidic. 
With reference to FIG. 2b, it can be seen that, according to this 
invention, by electrically pacing the crural diaphragm during the TLESR 
period with an intermittent pacing signal, the lower esophageal sphincter 
pressure is increased, and this increase in pressure results in preventing 
the occurrence of reflux as indicated by the steady pH signal. Thus, this 
invention contemplates sensing inhibition of the crural diaphragm during 
TLESR, and pacing the crural diaphragm to increase lower esophageal 
sphincter pressure and thereby prevent or reduce reflux. The preferred 
embodiment of the invention is to monitor both the costal and crural 
diaphragms of the patient and to begin pacing when the crural diaphragm is 
inhibited while the costal diaphragm is not inhibited. Pacing would 
preferably be at the same frequency as the costal diaphragm contraction 
and would end when the crural diaphragm resumes normal functions. The 
optimum pacing frequency for each patient can vary and might be "learned" 
by monitoring the particular patient's crural diaphragm contractions and 
deducing the optimum frequency from these sensed signals. In addition, 
pacing might simply be performed each time crural diaphragm inhibition is 
detected. 
With reference back to FIG. 1, crural diaphragm myoelectric signals pass 
through an analog signal selector 3 before further processing. The analog 
signal selector 3 allows the crural diaphragm electrodes 2 to be used for 
monitoring crural diaphragm myoelectric signals as well as for electrical 
stimulation of the crural diaphragm muscle tissue during TSLER. 
Alternatively, different electrodes could be used for sensing and 
stimulation. Costal and crural diaphragm signal conditioning and 
amplification circuits 4 and 5, respectively, provide appropriate 
band-pass filtering and amplification of costal and crural myoelectric 
signals with significant attenuation of caridac, electrical stimulation 
and other electrical artifacts. Costal and crural diaphragm signal 
threshold detectors 6 and 7, respectively, accept processed signals from 
costal and crural diaphragm signal conditioning and amplification circuits 
4 and 5, and detect the presence of a costal or crural diaphragm 
contraction when the incoming signal amplitude exceeds a voltage threshold 
set by the pacemaker microcomputer 8. 
The pacemaker microcomputer 8 preferably is a single chip microcomputer 
system such as a Motorola.RTM. MC68HC711 or Microchip PIC device with 
on-board core processor, random access memory (RAM), read only memory 
(ROM), electrically erasable programmable read only memory (EEPROM) for 
non-volatile storage of pacing parameters and status and serial/parallel 
input/output devices (I/O). 
Crural diaphragm stimulation electronics 9 provide signal stimulation to 
the patient's crural diaphragm muscle tissue during TLESK by passing an 
electrical signal to the crural diaphragm electrodes 2 through the 
device's analog signal selector 3. The stimulation signal produced by the 
crural stimulation electronics 9 preferably takes the form of a constant 
current square wave with frequency between 40 and 400 hertz with a duty 
cycle of 10-50%. The pacemaker's stimulation level is preferably 
adjustable between 100 microamperes and 10 milliamperes. The duration of a 
crural diaphragm stimulation cycle is preferably adjustable between 1.5 
and 2.5 seconds. As shown in FIG. 1, the pacemaker microcrontroller 8 
should be connected to the crural diaphragm electronics 9 and be capable 
of setting stimulation frequency, duty cycle, duration and stimulation 
level through software control. 
As discussed above, the pacemaker has two preferred embodiments. The first 
embodiment is a portable, Walkman.RTM. sized, battery operated device worn 
external to the patient's body. Costal and crural diaphragm electrical 
connections would be achieved using transcutaneous electrodes. The second 
preferred embodiment would be an implantable design that would be used for 
long-term treatment on a permanent or semi-permanent basis. Both 
embodiments would preferably operate as "on-demand" units. That is, as 
discussed above, electrical pacing would be implemented only when crural 
diaphragm inhibition exists. No pacing would occur when the crural 
diaphragm is not inhibited. 
An externally worn pacemaker would preferably have a number of I/O devices 
allowing the physician to set pacing parameters and monitor pacing status. 
For example, FIG. 1 shows a keypad device 10 which keypad interface 
circuitry 11 which allows the physician to program pacemaker parameters 
such as stimulation frequency/duty cycle, stimulation level, stimulation 
duration, costal and crural detector thresholds and costal/crural 
diaphragm contraction delay time. These parameters would be stored in the 
pacemaker's microcontroller 8 non-volatile EEPROM memory. FIG. 1 also 
shows a liquid crystal display (LCD) used by the physician or patient to 
monitor pacing status or verify previously stored pacing parameters. One 
particular use of the LCD 12 and keypad 10 would be for the physician to 
initiate a timed study where it is important to know the exact number of 
crural diaphragm stimulation cycles the device has administered to the 
patient in a twenty four hour period. To begin the study, the physician 
would enter a command through keypad 10 upon which time the real time 
clock time keeping element 13 would begin a twenty four hour countdown. 
During that twenty four hour period, the pacemaker's microcontroller 8 
would accumulate and record crural diaphragm stimulation cycles. At the 
end of the study, the total number of crural diaphragm stimulation cycles 
administered to the patient within the previous twenty four hour period 
would be indicated on the LCD 12. 
Communications module 14 would allow the crural diaphragm pacemaker to 
communicate with a personal computer or other similar device. Similar to 
the keypad 10 and LCD 12 functions, a personal computer could be used to 
program pacing parameters and monitor pacing status. In the case of an 
externally worn pacemaker, communications interface 14 could be an RS-232C 
type serial interface for connection to the serial port of a personal 
computer. This connection to an external personal computer can be 
optically isolated in order to ensure against electrical hazard to the 
patient. 
An implantable crural diaphragm pacemaker would not include keypad 10, 
keypad interface circuitry 11 or LCD display 12. All communications with 
the implantable pacemaker would be trhough communications interface module 
14 which in this case would take the form of a transcutaneous wireless 
transceiver. This wireless interface would be used for programming and 
monitoring pacing parameters and status, and possibly for recharging the 
implantable pacemaker's batter power source. 
Both external and implantable pacemakers should have a power supply and 
battery monitor circuit 15 which would be used to alert the patient or 
physician of a low battery power situation. In the case of an external 
pacemaker, this warning could be communicated to the patient or physician 
through the LCD 12 or RS-232C type communications module 14. In the case 
of an implantable pacemaker, a low battery warning would be communicated 
to the physician through the transcutaneous wireless communications module 
14. In either case, low battery status should be stored in the system 
microcontroller's 8 non-volatile EEPROM memory. 
It is envisioned that certain alternate embodiments of the crural diaphragm 
pacemaker would involve modification of the technique used by the device 
to detect the presence of a costal or crural diaphragm contraction. One 
alternative implementation would used digital signal processing (DSP) 
techniques wherein costal and crural diaphragm signal threshold detectors 
6 and 7 would each be replaced by a system composed of an 
analog-to-digital conversion (ADC) followed by a DSP processor. The ADC 
would sample the analog signals produced by costal and crural diaphragm 
signal conditioning and amplification circuits 4 and 5, respectively, and 
convert these analog samples into digital data. This digital information 
would then be passed to a DSP processor which would be able to identify 
the presence of a costal or crural diaphragm contraction, by processing 
the data through fast fourier transform (FFT) or digital filtering 
algorithms. The DSP processor used for this application could be a Texas 
Instruments.RTM. TMS320C40 or other similar device. In another alternative 
embodiment, the crural diaphragm pacemaker would employ the use of back 
propagation electronic neural networks as a replacement for costal and 
crural diaphragm signal detectors 6 and 7. Back propagating neural 
networks have the ability to identify or "learn" the unique electrical 
signature of a costal or crural diaphragm contraction after being 
conditioned or "trained" by costal and crural diaphragm myoelectric 
signals over a period of time. 
While the invention has been described in terms of its preferred 
embodiments, those skilled in the art will recognize that the invention 
can be practiced with modification within the spirit and scope of the 
appended claims.