Objective
I sought to demonstrate a new device that measures the pulling on an infant during a vaginal delivery.
Study Design
The Peisner Platform (US Patent 6,684,165; Canadian patent 2,436,154) utilizes Newton’s Third Law to measure the force/vector of delivering a baby. Ten patients at term with a singleton fetus in the vertex presentation were recruited for this pilot study. The platform measured the forces/vectors on the fetal head during the delivery. The primary outcomes were the graphs of the force/vector on the fetus and duration of that force.
Results
The pulling force exerted on the fetus ranged from 31.7–135.4 N over 8-51 seconds. Force vectors were often negative early, and positive later.
Conclusion
This new device, which measures the pulling force and vector of delivering a baby, has been successfully demonstrated.
The Peisner Platform (US Patent 6,684,165; Canadian patent 2,436,154) is a new device that measures how much force and the vector of that force an obstetrician or midwife exerts on an infant during a vaginal delivery. Although there has been a previous attempt to measure this force no practical device currently exists for this purpose. This paper is the introduction of this device to the medical and scientific community. The primary goal of this pilot study was to demonstrate the concept that this device can measure the force and vector that is exerted on a fetus by an obstetrical provider during a vaginal delivery. Since there are so many factors that can influence a delivery (eg, parity, infant size, length of the labor, operative vaginal delivery, medical complications), this study was not designed to address them but merely prove that the device works as described.
Device Description
The Peisner Platform is an application of Newton’s Third Law: for every action or force, there is an equal and opposite reaction or force. It does not touch the mother or the baby and is merely a platform with sensors that is placed on the floor at the foot of the bed. The obstetrician/midwife stands or sits on the platform as the infant is delivered. By Newton’s Third Law, as long as that obstetrician/midwife touches nothing but the fetus, any force that is exerted on the fetus is also present in the opposite direction at the surface of the platform. The vector of that force is also present in the opposite direction at the surface of the platform.
The easiest way to explain the device is by example. To determine how hard you pull on a hook on the ceiling, place an ordinary bathroom scale on the floor. Suppose you weigh 150 lb. If you pull on the hook and the scale reads 120 lb, the pulling force is 30 lb.
With regard to Newton’s Third Law, the downward force of 30 lb on the hook produces an equal and opposite reaction upward force of 30 lb at the bathroom scale. Since the previous downward force on the scale was 150 lb (your weight), the upward reaction force of 30 lb decreases the net downward force to 120 lb, which becomes the reading on the scale.
The Peisner Platform is basically a modified bathroom scale that measures force in 3 dimensions: both lateral directions in addition to the downward force. It was completely designed by the author and was built by Futek (Irvine, CA), a company that manufactures force transducers for complex purposes including experiments on the International Space Station and NASA’s space shuttle. In fact, the 3-dimensional transducers in this system were originally designed for the advanced Resistive Exercise Device for the International Space Station. The platform is a rigid piece of aluminum whose 4 corner legs are the 3-dimensional sensors (Futek model MTA400).
The complete system produces 12 electrical signals that correspond to the x, y, and z forces from the 4 leg sensors. The signals are amplified by a strain gauge amplifier (Futek model CSG110) and fed into a digitizer (model USB-1616FS; Measurement Computing Corp, Norton, MA) that is transmitted to a laptop computer through a USB cable. The platform is presented in Figures 1 and 2 . TracerDaq software (Measurement Computing Corp) receives the 12 signals and uploads them into a spreadsheet at 10 samples per second. Prior to its use, the platform passed the standard hospital electrical safety inspection.
The calculation of the force is an application of the Pythagorean theorem. In 2 dimensions, the hypotenuse of a right triangle is equal to the square root of the sum of each of the sides squared. If the sides of a triangle are labeled “a” and “b,” and the hypotenuse is labeled “c,” the mathematical formula is: <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='c=a2+b2′>c=a2+b2−−−−−−√c=a2+b2
c = a 2 + b 2
. This also works in 3 dimensions, which is the basis of the calculation of the force at the platform ( Figure 3 ). In this case the force (f) is calculated from the x, y, and z forces from the leg transducers: <SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='f=x2+y2+z2′>f=x2+y2+z2−−−−−−−−−−√f=x2+y2+z2
f = x 2 + y 2 + z 2
.
