Description:
BACKGROUND, BRIEF SUMMARY AND OBJECTIVES OF THE INVENTION
The present invention relates to a therapeutic device and, more particularly, to a control system for tilting or inclining a bed or platform in order to regulate as much as possible within limits certain medical conditions of a patient supported thereon.
Medical science has recognized the value of oscillatory therapy wherein a patient is slowly tilted back and forth in accordance with selected responses and conditions such as arterial diseases of the lower extremities, shock, respiratory disturbances involving paralysis of respiration, phlebitis, stroke, and others are generally improved. A most appropriate exemplary application for oscillatory therapy is the control of blood systolic and diastolic pressures by elevating or lowering the patient's feet and head as conditions require.
Tiltable platforms or beds have been utilized therapeutically to affect or influence patient physical characteristics for many years. Assemblies of this nature are illustrated, for example, in U. S. Pat. Nos. 3,200,416; 3,247,528; 3,293,667; 3,392,723; 3,584,321; and 3,609,779. Various control mechanisms for establishing the tilt or incline of these devices are well known and include pneumatically operated oscillators, mechanically geared elevators, electrical drives and numerous variations of these components. All of these control systems depend, however, on manual actuation by an operator or patient to mobilize the apparatus and to achieve the desired degree of tilt or incline.
The present invention includes a tiltable bed control system which is automatically actuated in response to controlling parameters, i.e., the patient's systolic and diastolic blood pressure, wherein the desired degree of tilt or incline is automatically established by continuously sensing and measuring these controlling parameters and determining whether or not they fall within predetermined and preselected limits.
Specifically, the control system comprising the present invention is designed to adjust automatically the incline of a tiltable bed or platform and the supported patient in response to blood pressure values which are monitored continuously by an appropriate sensing device. Desired values of systolic and diastolic blood pressure are measured, and if the patient's blood pressure exceeds preset upper pressure limits, the head or upper end of the tiltable bed is raised sufficiently to bring the blood pressure within the preset limits. If the patient's blood pressure falls below lower preset limits, the head or upper end of the tiltable bed is lowered sufficiently to bring the blood pressure back within the preset limits. In addition, special procedures are incorporated to minimize excessive motion of the bed or platform and to provide a series of preplanned motions in response to certain physiological variables.
From the foregoing, it will be apparent that a primary objective of the present invention is to provide a control system of the type described for a tiltable surface wherein controlled oscillatory motion of the surface is completely automated and requires a minimum of manual supervision.
Another object of the present invention is to provide an automatic control system for a tiltable surface which will cause the surface to tilt in a direction that will tend to maintain the blood pressure of a patient within a specified, acceptable range.
Yet another object of the present invention is to provide a control system for a tiltable surface of the type described which can be used for therapeutic purposes in any situation where meaningful physical parameters can be measured and controlled by oscillatory motion of the surface.
These and other objects of the present invention will become more apparent after a consideration of the following detailed specification taken in conjunction with the accompanying drawings where like characters of reference designate like parts throughout the several views.
FIGURE DESCRIPTION
FIG. 1 is a schematic block diagram of a very basic embodiment of the present invention wherein a tiltable surface is selectively oscillated by directing polygraph blood pressure readings to a control unit which will in turn oscillate the surface within predetermined limits in response to the readings obtained from the polygraph.
FIG. 2 is another schematic block diagram of a more sophisticated system for automatically controlling the oscillatory motion of a tiltable surface wherein blood pressure readings are directed through a control unit to the appropriate components of the motor directly controlling the oscillatory motion of the tiltable bed.
FIG. 3 is a block diagram of the preferred embodiment of a tiltable surface automated control system specifically illustrating the basic components and the various overriding and supplemental functions found necessary and useful in carrying out the present invention.
FIG. 4 is a table reflecting tiltable surface motion as a function of blood pressure errors.
FIG. 5 is a table reflecting a number of typical conditions which will generate warning signals.
DETAILED DESCRIPTION OF THE DISCLOSURE
Referring now to the drawings and particularly to FIG. 1, a patient 10 is positioned horizontally on a tiltable bed or surface 12 suitably elevated above a working surface 14 by an appropriate supporting component 16. A motor 18 is included in the supporting component to tilt the bed 12 as it is selectively actuated by cooperative elements which will be subsequently described.
A polygraph 20 may be used for monitoring blood pressure of human beings. By the use of an appropriate transducer, signals received by the polygraph can be suitably converted and transmitted to a control unit 22 in a form which will selectively activate or deactivate bed motor 18 carried by supporting structure 16. By conventional electrical circuitry, the motor 18 can be driven in one direction when signals of one nature are received and driven in the opposite direction when signals of another and decidedly different nature are received. Depending upon the nature of the received signals, the motor 18 can be activated to inclination of the bed 12 in one direction or another.
FIG. 2 broadly illustrates a relatively simple control system particularly designed to regulate the incline of the tiltable bed 12 without the use of a polygraph. Here an appropriate electrical response unit monitors the blood pressure signals received by a conventional sensing device 24 from the patient, transmits these signals to a control unit which in turn regulates a motor control unit directly governing the operation of the tiltable bed motor 18. The monitoring device may be provided with a display or indicating component 26 for visual observance, and the motor control unit can be provided with a manual override so that an operator or the patient may at any time bypass the regulatory system and control the incline of the tiltable bed at will.
It will be understood that the various units included in the systems described above are comprised of conventional electric circuitry and components having physical composition and electrical characteristics which are well known and consistently within the capabilities of those skilled in the art of designing such systems.
FIG. 3 represents the preferred embodiment of the present invention and is directly associated with the control of a tiltable patient-bearing table in direct response to systolic and diastolic blood pressure measurements. While the embodiment is particularly pertinent to patient blood pressure control, obviously, numerous other physical parameters may be utilized to control the automated system as herein described when motion of the patient can be of therapeutic value.
In FIG. 3, the raw blood pressure data is obtained on a pulse-to-pulse basis from an appropriate sensing device 24 such as an indwelling catheter 25. From the catheter, the data are fed to systolic and diastolic peak blood pressure detectors 28 and to a counter 30. The purpose of the counter is to obtain blood pressure processing on a pulse-by-pulse of every nth pulse, wherein the n can be varied, for example, from 2 to 100.
As mentioned, values of systolic and diastolic blood pressure are detected by peak detectors and compared in a comparing unit 31 to preset values of systolic and diastolic ranges manually placed in the system through the use of the preset value unit 34. If the value of detected blood pressure is within the selected preset values, no error is stored in the systolic or diastolic error storage unit 36. However, if either the detected systolic or diastolic blood pressure or both is not within the selected preset values, an error bit is generated. Both positive errors and negative errors are stored and summed in the storage unit 38.
The circuitry and components used in this embodiment are designed so that if there are about 10 positive error bits of the last 12 samples of blood pressure, a positive error is generated either for systolic or diastolic blood pressure. Similarly, if there are about 10 negative error bits of the last 12 samples of blood pressure, a negative error is generated. The errors, if any, for systolic and diastolic blood pressure are fed to the logic unit 40 for further comparison and processing.
A mean blood pressure is derived in the present invention for the purpose of having data of recent history of blood pressure behavior to compare with more ancient history of blood pressure behavior. In certain cases of blood pressure errors relative to preset values, which will be discussed subsequently, the patient can be his own control and reference.
The mean blood pressure is first derived in a mean blood pressure unit 42 from the detected values of systolic and diastolic values in accordance with an equation such as
MBP = DBP + 0.6 (SBP-DBP) = 0.6 (SBP) + 0.4 (DBP)
where MBP is mean blood pressure, DBP is diastolic blood pressure, and SBP is systolic blood pressure.
A short-term mean blood pressure average is obtained by averaging, for example, the last 12 samples of mean blood pressure. A long-term mean blood pressure is also obtained by averaging, for example, the 96 samples of mean blood pressure processed just prior to the short-term 12 samples. The value of the short-term average is compared to the value of the long-term average in the comparing unit 44. If the two averages are within an error bound, no mean blood pressure error is generated. If the two mean blood pressure averages are not within an error bound, an error signal is generated. A positive error means the short-term mean blood pressure average is greater than the long-term mean blood pressure average.
The systolic blood pressure, diastolic blood pressure, and mean blood pressure errors, if any, are fed to the bed motion logic unit 40. Two parameters are checked before any logic operations are allowed to occur.
The first parameter check is to ensure that the systolic blood pressure is greater than an established value, for example, 110 mm Hg, and the second parameter check is to make sure that the difference between systolic and diastolic blood pressure is greater than an established value, for example, 20 mm Hg. The blood pressure data will be processed if the systolic blood pressure is greater than the established systolic value, in this case 110 mm Hg, and the difference between systolic and diastolic blood pressure is greater than 20 mm Hg. A catheter malfunction warning signal is generated at a warning unit 45 if the systolic blood pressure is greater than 110 mm Hg, but the difference between the systolic and diastolic blood pressure is less than or equal to 20 mm Hg. The catheter malfunction warning signal alerts attending personnel. No further blood pressure processing is done, and no change in the tiltable bed position can occur until the catheter is again functioning properly.
If the systolic blood pressure is less than 110 mm Hg and the difference between systolic and diastolic blood pressure is less than or equal to 20 mm Hg, a hypotension warning signal is generated and the system enters a hypotension procedure. Attending personnel are alerted, and the tiltable bed enters a special hypotension program described subsequently. If the systolic blood pressure is greater than 110 mm Hg and the difference between systolic and diastolic blood pressure is greater than 20 mm Hg, the tiltable bed is in its normal operating mode.
The bed motion as a function of blood pressure errors is given in the representative table designated FIG. 4. In that table, the systolic and diastolic errors are relative to preset values for systolic and diastolic values, and the mean errors are derived as discussed earlier. For example, if there is a positive error in the systolic blood pressure and no error in the diastolic blood pressure, the head end of the tiltable bed is raised to lower the blood pressure. The angular volocity of the tiltable bed is of any convenient and reasonable value, but preferably around 10° per minute or less. This relatively low velocity is preferred to avoid undue motion sensation by the patient, and to allow time for physiological adjustment to a new bed incline angle. The bed angle is preferably restricted to lie between +25° and -12°. Beyond these limits, problems might well arise relating to patient comfort and stability on the bed.
The time duration of the tiltable bed motion is limited in two ways. First, if the blood pressure error disappears, the bed is stopped at the angle where the error disappeared. Secondly, the bed arc is preferably divided into about 8° increments with the horizontal position serving as a reference. The tiltable bed angle is detected by a potentiometer connected to the pivot point of the table. The analog voltage from the potentiometer is fed to an A/D converter, which has a change in digital code each 4°.
The 8° increments in the tiltable table arc are chosen for several reasons. It has been found that a change in the tilt angle of less than about 8° does not produce a significant change in blood pressure. A change in tilt angle of more than about eight degrees produces a significant change in blood pressure, but the physiological system is not able to adjust to a change in the tilt angle sufficiently rapidly to prevent an overshoot of the tiltable bed angle in either the positive or the negative direction.
To prevent excessive over or undershooting of the tiltable bed angle, a special routine is activated whenever the tiltable bed angle crosses an 8° boundary. When the bed angle crosses an 8° boundary, a change in digital bed angle code is detected, and the bed is automatically stopped for about 30 seconds. This allows time for the patient's blood pressure to adjust to the new bed angle and to obtain and process blood pressure data at the new bed angle. At the end of the waiting period, bed operation is returned to the normal mode of operation described previously.
In addition to the normal mode of operation and the 8° increment routine, two other special procedures are provided. These procedures are referred to as the "check" routine and the "hypotension" routine.
The purpose of the check routine is to periodically check the position of the tiltable bed and to attempt to return the bed near the horizontal position for the patient's comfort. For the positive angles, if the bed angle is greater than about 4°, and has remained within an 8° increment for a time in minutes selected by, for example, the attending physician, the bed angle is decreased by about 8°, with a positive 4° as the lower limit. When the bed angle has been decreased for about 8°, the table is stopped in the new position for approximately 2 minutes. This pause is sufficiently long to allow adjustment to the new angle and to obtain and process data at the new bed angle. At the end of the waiting period, the bed operation is returned to the normal mode.
For negative angles, the check routine will allow the tiltable bed angle to be less than zero degrees for 2 minutes which is preset in the system. At the end of the preset 2 minutes, the table is returned to the zero degree position, and is stopped for 2 minutes. At the end of the waiting period at zero degrees, the bed operation is returned to the normal mode.
The hypotension routine is initiated when the systolic blood pressure is less than or equal to an established value, for example, 110 mm Hg and the difference between the systolic and diastolic blood pressure is less than an established value, for example again, 20 mm Hg. When this routine is activated, the tiltable bed is returned to the horizontal position without any pauses at the 8° increment or interruptions from the check routine. The bed then remains in the horizontal position for 2 minutes. At the end of the 2-minute waiting period, the bed operation is returned to the normal mode. If the blood pressure is still classified as hypotension, the bed angle is decreased below zero degrees, and the check routine is activated as described earlier. The check routine then controls the tiltable bed angle. The hypotension and check routine combination is terminated when the measured blood pressure no longer is classified as hypotensive at the end of the check routine 2 minute waiting period at the zero degree position. The bed operation is returned to the normal mode.
In any mode of operation, a warning system is provided. This system provides checks and warning signals when the systolic or diastolic blood pressure or bed angle exceed certain bounds. A typical set of warning conditions is shown in the table designated FIG. 5. Also included in this table are the catheter malfunction and hypotension conditions. Warning signals might well be conveyed to attending personnel by, for example, flashing lights, or other appropriate means.
Several general applications and one specific embodiment of the present invention have been described. It is to be understood that these representative examples are not to be construed as a limitation in any way on the present unique concept. The present invention may well have application in any area where human physical parameters may be utilized to control, within limits, particular bodily conditions. For example, the invention may be used to control cerebral spinal fluid pressure by sensing the magnitude of that pressure and positioning the bed at an angle to decrease the pressure. Additionally, cardiac rate may also be regulated with certain limits by, for example, positioning the patient in another relationship if a rapid heartbeat is detected. Other applications will be obvious to those skilled in the area of technical medicine.
While there has been described an automated control system for regulating a patient's blood pressure or other physical characteristics, obviously alterations and variations in the representative examples may be made without departing from the spirit and scope of the present invention. Such changes and improvements are contemplated within the scope of the appended claims.