TECHNICAL DISCUSSION OF HOW THESE MONITORS WORK 

by Roger Rittenhouse V-MAX EHRM

Equine Performance Technology

The EKG electrical pulse is picked up (sensed) by the conductive electrodes- the pulse is sent to the transmitter by the leads, thus the leads and the electrodes MUST be low resistance and not induce any noise or static.The transmitter looks for these pulses. The transmitter will emit a RF burst (51khz) when the R wave of the QRS EKG exceeds a fixed level. This is to prevent small spikes and noise from triggering the transmitter. Once the transmitter fires, it shuts off until the post T wave of the EKG is passed. MOST of the time the T wave is of a lower voltage value to not trigger the transmitter - however SOME horse’s EKG  will double fire the transmitter. This is noted on the REC watch by the heart icon blinking TWO times for each pulse   FIX- reverse leads wires.

NOTE it is NOT REALLY necessary to hook the leads to the transmitter based on any ‘snap’ color. We did write directions to cover that since the transmitters we used were color coded. Our new models are solid blocks with no snaps or rubber flex  ends to go bad.  It does not matter how you connect the leads. If you can not get good readings one way, just reverse the leads.

So now we have the transmitter sending out a burst of RF for every beat of the heart AND maybe a few false bursts. We use the RECEIVER watch to detect and count these bursts and then to add them up  and compare to time then   display a beat per minute value.

DISPLAY

The receiver watch consists of  a time clock a computer and memory. Works as such:  a sample window opens - counts the transmitter pulses, closes, places the HR value in memory and displays the HR. IF during this read-window the electrode moves around - (carbon silicon rubber) a false spike is sent to the transmitter, if the spike is large enough the transmitter will fire and put out a signal - the receiver will try to count this as ‘real’ beat. This is called artifact. The computer in the receiver does not filter out this false signal. WHY - because ALL the monitors on the market today - including the new one from P.... -ALL-  are made using HUMAN HRM components. The design ASSUMES the CHESTBELT transmitter will be snugly strapped to the HUMAN chest. THUS no motion induced false signals. The mfgr of the human setup  provides information   advise to  this effect. The solution is to tighten the belt. Some of the assorted models from other mfgrs have a very slow update window, as in 5 to 8 seconds. None of the EHRM will filter this false signal out. The only one the did was a very costly EQUINE HRM   from EQB called EQUISTAT.(1985 to 1990) That monitor tried to filter out artifact but also did a  20SEC overall average thus you got a  flatter looking HR. It missed the highs and lows. It was the ONLY HRM designed for use with EQUINE.  ALL ‘horse ‘ HRM since then use the HUMAN components with adapted leads and transmitter  and then place it in boxes with a HORSE on the front.

Two ways to correct the error. Tighten the electrodes on the back and girth of the horse - means SUNG girth. Place electrodes in a less motion location -under saddle.

Number 2 is to GLUE on the electrodes. We did that over 12 years ago. The riders will not use this method nor would I. So we elected to use MOVEABLE  electrodes as did the other provider at the time.( There were only 2 - me and Bob Walz).

Next option, is to use a receiving device with a  SHORTER sample window, say 2 seconds. The components I have selected and  adapted use a 2 second sample count window.  So the probability of ‘seeing’ a false pulse in 2 seconds is much less then in 5 to 8  second sample window?

The logic is - count the 'pulse RF bursts' for the sample window time, compute the HR, store HR in memory, display   the pulse AFTER the memory buffer stack is full - ( 6 spots) takes 12 seconds to obtain an accurate valid pulse value. The displayed HR is a rolling 12 sec average. With a new value (count of pulses) every 2 seconds. Works on FIFO.  IF pulse signals are erratic the counts cannot be made - the receiver  will drop that sample and displays LAST known good pulse. When  ALL values in the memory are ‘defective’ then it gives you 0 ZERO. So the smaller the sample window the chances of a valid good  reading are improved. We still have motion and dry electrode artifact but YOU don't know that.   Well, now you do. I have one model from Acumen that does it different then any HRM out there - it reads for 5 or 6 Beats and  measures the TIME between beats, called R-TO-R, then displays the HR. This model is very susceptible to small changes in effort. It does appear to do OK with artifact but I get some wild readings when the electrodes are not correct.

The component mfgr with the shorter 2 second sample window is Cardiosport. 

So there you have the practical and a little techie explanation of the 'how and why'  of these neat little tools.

Hope this helped to explain a few of the issues and common misconceptions.  

BOTTOM LINE HERE. Riders who consistency make claims these do not work, are not accurate, just plain don’t know what they are talking about. Many fail to READ THE DIRECTIONS, think they know more then the developer, and do NOT understand the technical issues with reading an EKG HR nor the equipment used.