US20070089236A1

US20070089236A1 - Isolation device for shock reduction in a neonatal transport apparatus

Info

Publication number: US20070089236A1
Application number: US11/540,743
Authority: US
Inventors: Michael Bailey-VanKuren; Amit Shukla
Original assignee: Individual
Current assignee: Miami University
Priority date: 2005-09-29
Filing date: 2006-09-29
Publication date: 2007-04-26

Abstract

A device in combination with a neonatal transport cart that reduces the amount of energy transmitted to the surface upon which an infant rests during transport. A pair of plates, one of which is mounted to the incubator and the other of which is mounted to the stretcher, has a gap between the substantially parallel plates. The gap contains springs, preferably gas springs, with a spring rate in a range and a damping effect. The springs reduce the energy transmission to the infant by the stretcher or other platform.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates generally to mechanisms for transporting newborn infants by ground or air transportation.
2. Description of the Related Art
Neonatal transport is the transport of newborn infants to a medical facility to provide critical care. Transportation is typically accomplished via ground, such as by ambulance, and air, such as by airplane or helicopter. The transportation of neonatal patients by conventional means, such as in neonatal transport systems attached to medical stretchers in ambulances, exposes the patients to physical shock and vibration communicated through the relatively rigid structures, and this shock is often detrimental to the medical condition of the patient. Current neonatal transport systems do not include an effective subsystem for shock suppression.
Neonatal patients often exhibit extreme sensitivity to external stimuli including physical manipulation. The result of external stimuli is often manifested by a change in heart rate or breathing rate ultimately affecting the oxygenation rate (% oxygen) in the bloodstream.
Poor rear suspension with a narrow wheel base and high center of gravity, as well as poor road conditions, can lead to uncomfortable bouncing of a medical stretcher. This may be detrimental to some patients, especially those with orthopedic injuries. Relating to air transport, gravitational forces can lead to variations in cardiac output, and the shifting of a patient due to motion or vibration could be disastrous for one who has a cervical spine injury. Vibration and noise can be disconcerting to the patient, lead to increased anxiety, and be manifested physiologically by increased blood pressure, heart rate, diaphoresis, and combativeness.
Transportation can increase the stress of the infant. Some conditions may worsen during transport due to the vibrations and bumps of the ride, and chest tubes may move and get dislodged with the movement or vibrations of the ambulance. Noise and vibration have a greater effect on neonates, and medical equipment can also be adversely affected.
Despite the adverse effects of transportation on neonatal patients, there has been little advancement in this field. The existing neonatal transport cart is an adult stretcher with approximately 450 pounds of instrumentation and equipment mounted on the support platform, as illustrated in FIG. 1. The neonatal equipment includes an incubator (also referred to as an isolette), temperature monitoring instruments, and vital sign indicators. In all, the value of this system is often close to $500,000. Transport teams utilize these carts for moving critical patients. Accelerations experienced in a typical transport system can be as high as 2.5 g.
The prior art does not contain a suitable solution for the problem of the transmission of shock and vibration to neonatal patients. The need exists for a system to reduce the transmission of kinetic energy to neonatal patients.

BRIEF SUMMARY OF THE INVENTION

The invention is an apparatus for reducing the transmission of kinetic energy from a support platform to an incubator upon which an infant is resting. The apparatus comprises a first plate mounted to the support table and a second plate spaced from the first plate to form a gap. In a preferred embodiment, the first plate is substantially parallel to the second plate and the second plate is mounted to the incubator. At least one spring is mounted in the gap between the first and second plates, the spring further comprises a plurality of gas springs mounted in the gap, and each of said springs is mounted to the plates.
In a more preferred embodiment, some gas springs are mounted to the plates in a reverse configuration to prevent damage to other of said springs. This reverse configuration prevents the gas springs from being damaged under tensile force.
The invention is a shock suppression system designed to fit between the isolette and the stretcher platform. This location facilitates the use of an existing quick disconnect mechanism and minimizes the ergonomic implications on the transport team personnel.
An air spring based system is disclosed in which air springs are mounted between a pair of stiff plates. One plate is for mounting to the isolette, and the other plate is for mounting to the support platform, such as a stretcher. The system dynamics show that effective attenuation of the vibrations can be achieved by the air springs. The effect of increasing pressure in the air springs is presented. Furthermore, the pressure in the air springs and the configuration of the air springs affect the transport cart system response at low frequencies. Therefore, the dynamic model of the transport cart is a valuable tool in the process for redesign of the neonatal transport cart.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side view in perspective illustrating a conventional neonatal transport cart and isolette.
FIG. 2 is a side view illustrating the preferred embodiment of the present invention in an operable position on a transport cart.
FIG. 3 is a table containing air spring stiffness equation parameters.
FIG. 4 is a table containing nominal system parameters.
FIG. 5 is a schematic illustration of a neonatal transport cart in combination with the vibration absorber of the present invention.
In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or term similar thereto are often used. They are not limited to direct connection, but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional Application No. 60/721,630 filed Sep. 29, 2005 is incorporated herein by reference.
The preferred embodiment of the present invention is shown in FIG. 2. The invention includes a pair of plates 10 and 12 arranged in a substantially parallel relationship. The plates 10 and 12 are preferably sheet metal, such as stainless steel, but could be aluminum, wood, composite or any other suitable material in sheet form. The upper plate 10 mounts, in an operable position, to the underside of the isolette 8 (see FIG. 1). The lower plate 12 mounts, in an operable position, to the upper surface of the neonatal transport cart 40, shown in FIG. 2. The plates 10 and 12 can mount to the respective structures using screws, adhesives, specialized brackets that clamp or any other conventional fastener. Furthermore, the transport cart 40 is but one of many types of support platforms upon which the invention can be mounted. Other conventional supports can be used in combination with the invention. The conventional structures operate in a conventional manner, except for the effect of the invention, as will be described below.
The plates 10 and 12 are separated by a gap, and at least one air spring is interposed in that gap, with firm attachment to each of the plates 10 and 12. It is preferred that multiple air springs mount to the plates 10 and 12 in the gap, and it is most preferred that nine air springs are mounted in the gap, with two at each corner of the rectangular plates 10 and 12, and one in the center. However, the number of air springs must be at least one, and there is no theoretical upper limit to the number of air springs. Of course, because of the cost of air springs, there will be a practical upper limit to the number.
The air springs 20, 22, 24, 26 and 28 mount at their upper ends to the upper plate 10 using a screw-threaded shaft extending upwardly through an opening in the plate 10 and a nut fastened on the opposite side of the plate 10. The air springs 20-28 mount at their lower ends to the lower plate 12 using similar fasteners. The air springs 20, 22, 26 and 28 are mounted at the four corners of the rectangular plates 10 and 12, and the spring 24 mounts centrally of the plates 10 and 12 by fastening to the plates 10 and 12 in a manner similar to the springs positioned at the peripheral edges of the plates.
Each of the corner air springs 20, 22, 26 and 28 is a conventional spring, such as, for example, a Firestone Industrial model 2M2A Air Mount. The central air spring 24 can be, for example, a model 16 Air Mount. Of course, substitute air springs can be used, as will be understood by the person having ordinary skill. Still further, other springs, whether mechanical, magnetic, elastomeric or any other type, can be used in place of the air springs 20-28, as will be understood. For example, it is contemplated that mechanical springs in combination with dampers, such as dashpots or friction brakes, can be substituted for the preferred air springs, with resulting practical effects that will be understood by the person having ordinary skill in the art.
The air springs 20-28 are designed to sustain a compressive load applied by the plates 10 and 12, which tends to bring the plates closer to one another. Although not shown in FIG. 2, it is preferred that an additional air spring be mounted at each corner of the plates 10 and 12 in order to protect the springs 20, 22, 26 and 28 under tensile loads applied by the plates 10 and 12. These tensile load-protecting springs prevent the springs 20-28 from being pulled apart or otherwise damaged by movement of the plates 10 and 12 away from one another.
The air springs 20-28 have both a spring rate and a measurable degree of damping. Thus, the air springs 20-28 provide not only a spreading of the application of the force applied through the cart to the isolette over a greater period of time, but they also dampen to reduce the transmission of energy through the invention. Thus, not all of the energy that is applied to the cart, such as by the floor of the ambulance in which the cart is riding, is transferred to the isolette. In fact, it is preferred that a substantial amount of energy is not transferred to the isolette, and this is accomplished by the invention.
The vibration isolation is achieved, in the preferred embodiment described above, using air springs between the stretcher and the isolette. Air springs are preferred for vibration isolation due to their low system natural frequencies (less than 5.0 Hz) which can be reduced by use of a reservoir. Further, the system natural frequencies do not change significantly with a change in load.
The spring rate of an air spring is not constant and is a function of the change in effective area, volume, and pressure. This stiffness of the air springs is related to two factors: the variation in volume, and the variation of effective area. This overall stiffness is given as: $F_{s} = \frac{{nP}_{1} V_{1}^{n} A}{V_{1}^{n + 1}} \cdot \frac{ⅆ V_{1}}{ⅆ h} - (P_{1} - P_{a}) \frac{ⅆ A}{ⅆ h}$
where F_sis the stiffness of the air spring system and the equation parameters are defined in FIG. 3. It is preferred that the stiffness of the air spring system range from no less than about 500 lb/in, and no more than about 4,500 lb/in. The preferred range is about 800 lb/in.
The 4.5 in. diameter spring 24 is positioned at the center of the plates 10 and 12 and the four 1.34 in. diameter springs 20, 22, 26 and 28 are placed at the corners of the plates 10 and 12. The theoretical system model, with reference to the schematic illustration of FIG. 5 and the equation parameters as defined in FIG. 4, is: $[\begin{matrix} M_{1} & 0 \\ 0 & M_{2} \end{matrix}] [\begin{matrix} {\ddot{x}}_{1} \\ {\ddot{x}}_{2} \end{matrix}] + [\begin{matrix} C_{1} + C_{2} & - C_{2} \\ - C_{2} & C_{2} \end{matrix}] [\begin{matrix} {\dot{x}}_{1} \\ {\dot{x}}_{2} \end{matrix}] + [\begin{matrix} K_{1} + K_{2} & - K_{2} \\ - K_{2} & K_{2} \end{matrix}] [\begin{matrix} x_{1} \\ x_{2} \end{matrix}] = [\begin{matrix} F \\ 0 \end{matrix}]$
where K₂is the stiffness of the air spring system. The stiffness of the air spring system is a function of the pressure in the springs as well as the configuration used. FIG. 5 shows the principle behind the invention: that the appropriate combination of spring rate and damping results in a device that greatly reduces the transmission of energy to the incubator upon which the infant is resting. Other apparatuses with spring and damping characteristics within the range described herein can be substituted for the preferred embodiment. For example, the central air spring can be 11.34 cm in diameter and the outer air springs can be 3.4 cm diameter.
The system natural frequency due to the inclusion of air springs was determined to be close to 3 Hz. Effective attenuation of the vibrations was achieved by the air springs, and “effective attenuation” is defined herein to include a range extending from about 10 Hz to about 18 Hz. Preferably, the system attenuates vibrations in the range of about 10.25 to about 17.09 Hz. At frequencies greater than about 10 Hz, the attenuation obtained for the various configurations was similar. However, at lower frequencies the response amplitude was considerably affected by the configuration.
The spring system is designed for damping in a range extending from just greater than zero to about 4.0%. Thus, the invention serves to dampen the oscillatory motion of the incubator resulting from the shock of the vibratory motion of the transport and to reduce the amount of energy transmitted to the isolette in the manner of a shock absorber. Some damping occurs due to stretching of the bladder in the air springs 20-28, although any shock absorber mechanism preferably has some measurable damping.
Because the stiffness of an air spring is a function of the pressure, an increase in air pressure results in higher stiffness. Thus, one contemplated alternative is to vary the pressure in the springs during use, such as by the conduits 30 and 32 having gas passages therein in fluid communication with the reservoirs of the springs 20-28. The gas passages in the conduits 30 and 32 are connected to a pneumatic ram or other pressure increasing and decreasing device (not shown). By compressing or expanding the gas through the conduits 30 and 32, the device thereby increases or decreases the pressure in the springs 20-28.
The invention was tested in three configurations at an increased pressure level to ascertain a suitable configuration. The test results revealed the effect of increasing pressure for the three possible configurations. It is expected that as the pressure in the air springs is increased, the amplification of the input at the damped natural frequency of the system model increases. Furthermore, an increase in air spring pressure increases the stiffness associated with the spring, which increases the natural frequency. The effective stiffness for each configuration differs due to the contributions of the individual springs and the corresponding pressure.
A configuration that consisted of smaller springs oriented at the corners of the rectangular plates displayed the greatest effect from an increase in pressure with a decrease in transmission at low frequencies. The inventor concluded that the absence of the large spring in the center explained some of this difference in response.
An air spring based system can effectively attenuate the vibrations experienced by the transport cart. Additionally, the air spring pressure and the air spring configuration can affect the system behavior at low frequencies. Still further, increased insight into the effect of the air spring pressure on the system response can assist the designer in air spring selection.
It is noted herein that alternative embodiments of the invention exist. It would not be possible to describe all such alternative embodiments herein. However, it will be understood that circular plates with numerous springs at the periphery could be substituted for the preferred embodiment shown in FIG. 2. Additionally, oval or triangular plates could be used with springs at positions that will be known by the person having ordinary skill from the description herein. The plates can be virtually any shape as can the arrangement of the springs between the plates.
This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.

Claims

1. An apparatus for reducing the transmission of kinetic energy from a support table to an isolette in which an infant is resting, the apparatus comprising:

(a) a first plate mounted to the support table;

(b) a second plate spaced from the first plate to form a gap, the second plate being mounted to the isolette; and

(c) at least one spring mounted in the gap between the first and second plates.

2. The apparatus in accordance with claim 1, wherein the first plate is substantially parallel to the second plate.

3. The apparatus in accordance with claim 1, wherein said at least one spring further comprises a plurality of springs mounted in the gap, each of said springs being mounted to at least one of the plates.

4. The apparatus in accordance with claim 3, wherein said plurality of springs further comprises a plurality of gas springs mounted around a peripheral edge of the first plate and around a peripheral edge of the second plate.

5. The apparatus in accordance with claim 4, further comprising a central gas spring mounted to the first and second plates and positioned centrally of said plurality of gas springs.

6. The apparatus in accordance with claim 5, wherein at least some of said plurality of gas springs are mounted to the plates in a reverse configuration to prevent damage to other of said springs.

7. The apparatus in accordance with claim 1, wherein the stiffness of said at least one spring is in a range from about 500 lb/in and about 4,500 lb/in.

8. The apparatus in accordance with claim 7, wherein the stiffness of said at least one spring is about 800 lb/in.

9. The apparatus in accordance with claim 1, wherein an effective attenuation of the apparatus is in a range from about 10 Hz to about 18 Hz.

10. The apparatus in accordance with claim 9, wherein the effective attenuation of the apparatus is in a range from about 10.25 to about 17.09 Hz.

11. The apparatus in accordance with claim 1, wherein a damping rate is up to about 4.0%.