Patent Application
20100324432
1. Field of the Invention
The present invention relates to methods and devices for monitoring at least one physiological parameter that relates to the activity of the digestive system of a patient.
2. Description of the Prior Art
A modern major health concern is the increasing proportion of the human population who are so overweight that they suffer from obesity. Obesity is a leading cause of premature deaths and is associated with other health problems such as high blood pressure, heart disease, strokes, breathing disorders, cancer and musculoskeletal problems.
The treatment of obesity is complex as there are many factors which contribute to a person becoming obese, the major ones are considered to be lack of exercise and overeating. In order to reduce the amount that a patient eats it is known to use gastric stimulation. The theory behind this is that stimulation of the gastroenteric system (the stomach's own nervous system) or the vagal nerve between the stomach and the brain by electrical impulses will lead more quickly to the patient having a feeling of satiety and consequently the patient will stop eating earlier than he or she previously would, thereby reducing the amount of overeating of the patient. Implantable devices and methods for gastric stimulation are known from US patent application US2005/0149142. In order to avoid excessive battery draining and to increase the longevity of the implanted device it is known to stimulate the gastroenteric system only when the patient has commenced eating. US2005/0149142 teaches a number of ways in which eating by a patient can be detected by a monitoring a physiological parameter that reflects activity of the patients stomach. Such parameters including gastric electrical activity, trans-abdominal impedance, blood glucose levels, insulin levels, stomach acid levels, motion of the stomach, distension of the stomach or other mechanical indicators of stomach activity.
It is known that the energy consumption of the digestive system (which normally is defined as including the stomach, spleen, pancreas, liver, small bowel and colon) increases due to the increase of gastric activity which follows the ingestion of food. This increase in energy consumption is reflected, amongst others, by an increase in blood to, and perfusion of, the organs in the digestive system. As shown schematically in
Typically the portal venous blood flow is 1200 ml/min in the fasting state but it may increase to 2000 ml/min following a meal. The SMA blood flow can double from 500 to 1000 ml/min within 15 minutes of food ingestion, the increase being dependent on caloric load, food volume and type. Similarly the CA blood flow can increase from 800 ml/min to 1100 ml/min following feeding.
The present invention is directed to medical devices and methods for detecting feeding of a patient in order to control the activity of a digestive system stimulating device. This is achieved by monitoring at least one physiological parameter that relates to the activity of the digestive system of the patient and causing a stimulating regime to commence when the at least one physiological parameter indicates that feeding has commenced. Although, as stated above, normally the digestive system is defined to include the stomach, spleen, pancreas, liver, small bowel and colon, for the invention described in the present patent application, changes in the blood flow or perfusion of the small bowel and colon occur too long after the ingestion of food to be useful in detecting that eating has begun. Consequently, in the following the expression “digestive system” will be taken to mean the stomach, spleen, pancreas and liver unless stated otherwise, as changes in the blood flow and perfusion of these organs occur quickly after the onset of eating. Preferably measurements of parameters relating to blood flow to the digestive system are taken on blood vessels that feed these organs, namely the left gastric artery, the hepatic artery, the portal vein, the celiac artery and the lienal artery.
In one embodiment of the present invention a monitored parameter is the blood flow to an organ in the digestive system of the patient. In another embodiment of the present invention a monitored parameter is the perfusion of an organ in the digestive system of the patient. In a further embodiment of the present invention at least two parameters are monitored, one of which is the blood flow to an organ in the digestive system of the patient and another of which is the perfusion of an organ in the digestive system of the patient. In yet another embodiment of the present invention at least two parameters are monitored, all of which are the blood flow to one or more organs in the digestive system of the patient. In still further an embodiment of the present invention at least two parameters are monitored, all of which are the perfusion of one or more organs in the digestive system of the patient.
Sensors suitable for measuring such physiological parameters include, but are not limited to, photoplethysmographs, resistance sensors, impedance sensors, strain gauges, expandable cuffs, ultrasound detectors, (electro)magnetic flow detectors, vortex counters, elbow flow meters, thermistor flow meters and calorimetric flow meters.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
a) and 2b) shows schematically a first embodiment of a device for measuring perfusion to the stomach of a patient using a photoplethysmograph in accordance with the present invention.
a) and 4b) show schematically an embodiment of a device for measuring the diameter of a blood vessel in accordance with the present invention.
Changes in the blood flow of the digestive system of a patient can be used to determine if the patient has started to eat. These changes can be measured by taking measurements of a parameter related to blood flow directly at one or more organs or by measuring the blood flow through one or more arteries or veins connected to an organ or system of organs.
In a first embodiment of a sensing device 1 in accordance with the present invention, shown schematically in
In a second embodiment of a sensing device in accordance with the present invention, the intramuscular resistance or impedance of the stomach of a patient is measured by means of an impedance sensing device comprising two or more electrodes spaced close to each other across a portion of the stomach wall. Impedance measuring signals of predetermined currents/voltages are transmitted from one electrode and the tissue that the signal passes though before being received at the other electrode(s) modulates the signal so that the current/voltages received at the receiving electrode(s) will have different amplitudes and phase-angles. By choosing a frequency which is sensitive to changes in the perfusion of the tissue, changes in the phase-angle and amplitude can be used to identify a change in perfusion.
In a third embodiment of a device in accordance with the present invention, the resistance or impedance across a blood vessel related to the digestive system of a patient can be monitored in order to determine the flow inside it. Blood vessels in which the flow increases shortly after feeding has commenced (e.g. the left gastric artery, the hepatic artery, the portal vein, the celiac artery and the lienal artery) are preferred, as monitoring of these blood vessels allows stimulation to begin shortly after feeding has begun. The resistance of blood is lower than the resistance of other body tissues. Due to this, increases in the flow of blood to the digestive system, and the accompanying increase in the diameter of the blood vessels through which the blood flows, lead to a change in the impedance or resistance measured. If impedance is measured instead of resistance then it should preferably be measured at a low frequency since impedance measurements at a low frequency are dominated by the resistive component of the measurement. A sensing device could comprise sensing electrodes positioned diametrically-opposed each other on a blood vessel and changes in resistance or impedance between the electrodes analyzed. When the diameter of the blood vessel increases, which occurs when the blood flow through it increases, then the resistance across it changes due to changes in the average resistivity of the media between the electrodes. Furthermore, as the flow velocity increases, the orientation of the blood cells in the blood vessel changes. At low velocities the blood cells are randomly orientated but as the flow velocity increases the cells become orientated with the greatest surface area facing the stream. At measurement frequencies over 4 kHz the impedance measured inside the vessel is affected by this change in orientation and decreases as the flow velocity increase. If measurements are taken on a blood vessel at two different frequencies with different electrodes it is possible to obtain metrics related to both the blood velocity and the surface area of the blood flow. These can be combined to obtain the blood volume per unit time.
a) and 4b) show schematically an embodiment of a sensing device 43 for measuring the diameter of a blood vessel in accordance with the present invention. This device comprises a flexible cuff 45 which is placed around a blood vessel 47. Cuff 45 is flexible enough to follow movement of the wall 48 of the blood vessel 47 without restricting flow through the blood vessel, while at the same time staying in contact with the blood vessel. Cuff 45 is provided with a stretch sensor, for example a strain gauge, 50 which in positioned in the centre of the cuff. This stretch sensor 50 produces an output signal S which varies as the ends 51, 53 move closer and further apart due to changes in the diameter of the blood vessel. As increases in the diameter of a blood vessel can be assumed to reflect increases in the flow inside the vessel, data relating to the diameter of the blood vessel can be analyzed to determine if eating has commenced.
Other sensors which can be used to determine flow rates include vortex counters and elbow flow meters. Vortex counters are based on the principle that an obstruction in a fluid flow can create vortices downstream of the obstruction. Every obstruction has a critical fluid flow rate at which vortex shedding occurs. Vortex shedding causes alternating low pressure zones downstream of the obstruction which exert a downstream pull force on the obstruction. Analysis by a control device of the frequency of the vortices and the force that the low pressure exerts on the obstacle can be used to determine the fluid flow rate. Elbow flow meters are based on the principle that a differential pressure exists when a flowing fluid changes direction due to a pipe turn or elbow—a high pressure node forms at the outside of the bend and a low pressure node forms at the inside of the bend. Pressure transducers can be attached at the inside and outside of a bend in a blood vessel and will detect different pressures due to the pressure differential at the bend. The data from the transducers can be processed by a control device to determine the fluid flow rate.
In a first method to operate a gastric stimulator in accordance with the present invention a patient is provided with a sensing device which can measure the perfusion, or changes in the perfusion, of an organ in the digestive system of the patient wherein increased organ activity may indicate that the patient has begun eating, or a sensing device which can measure the blood flow, or changes in the blood flow, in a blood vessel connected to the digestive system which blood vessel exhibits an increase in flow when the patient has begun eating. The sensing device produces an output signal which reflects variations in the perfusion of, or blood flow in, the organ or blood flow in the blood vessel. This output signal may be used to control a gastric simulator. This can be achieved by providing the sensing device with, or connecting the sensing device to, control means that can analyze the output signal and cause a control signal to be sent to the gastric stimulator to start its stimulating function when a first predetermined value of blood flow or perfusion indicating that feeding has started has been reached, and to stop its stimulating function when a second predetermined value is reached which indicates that feeding has finished or some other activity has been started or a predetermined period of time has elapsed, and which indicates that further stimulation is unnecessary. Alternatively the raw output signal can be transmitted from the sensing device to the gastric stimulator which itself analyses the output signal and determines from this analysis when gastric stimulation should be started and stopped or modified.
In a second method to operate a gastric stimulator in accordance with the present invention a patient is provided with two or more sensing devices, each of which can measure the perfusion of, or blood flow in, or changes in the perfusion of, or blood flow in, an organ in the digestive system of the patient wherein increased organ activity may indicate that the patient has begun eating and/or which can measure the blood flow or changes in the blood flow in a blood vessel connected to the digestive system which blood vessel exhibits an increase in flow when the patient has begun eating. The sensing devices each produce an output signal which reflects variations in the perfusion of the organ or blood flow in the blood vessel. One or more of these output signals may be used to control a gastric simulator. This can be achieved by providing the sensing devices with control means which can analyze the output signal and cause a control signal to be sent to the gastric stimulator to start its stimulating function when a first predetermined value of blood flow and/or perfusion indicating that feeding has started has been reached, and to stop its stimulating function when a second predetermined value is reached and which indicates feeding has finished or some other activity has been started or a predetermined period of time has elapsed, and that further stimulation is unnecessary. Alternatively the raw output signals can be transmitted from the sensing devices to the gastric stimulator which itself analyses the output signals and determines from this analysis when gastric stimulation should be started and stopped or modified.
When a system for the gastric stimulation of a patient is in use, it can be of interest to keep track of how often and how much a patient is eating. As described above, one way of detecting eating is by analyzing the blood flow to the stomach of the patent.
One way of keeping track of how many times a day the patient is eating would be to either count the number of eating occasions per day or, if storage of that information would be too memory-consuming, to create a histogram of the number of times the patient eats per day and to refresh the histogram at regular intervals, e.g. daily. As the amplitude and duration of increased blood flow to the stomach appears to be related to the number of calories ingested in a meal, it can be of interest to analyse the duration of increased blood flow to the stomach.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2007/000154 | 2/21/2007 | WO | 00 | 8/6/2009 |
