The Prod algometer

Extensively validated, used globally with dogs, cats, rabbits, chickens, pigs, sheep, horses, cows and donkeys and cited in many research publications.

“I’ve used several high-quality industrial devices to determine nociceptive mechanical thresholds on animals: only the ProdPlus provides the versatility and reliability that the measurement requires.” Professor Ignacio Álvarez Gómez de Segura, University of Madrid

THE PROD RANGE OF ALGOMETERS are designed to make mechanical threshold testing on animals as easy and accurate as possible. Uniquely, the measurement head sits on a cushion of air. This is because, unlike humans, animals don’t keep still for testing and movement can affect the data from traditional dial and force sensors. In the Prod range of algometers, the air cushion absorbs any movement without distorting the threshold force reading.

THERE ARE NO BUTTONS TO PRESS: just touch the probe against the subject and the red and green lights will guide you to increase the pressure at a controlled rate. At threshold, simply withdraw the Prod; the peak reading of force is stored and displayed automatically in Newtons.

USE OF THE PROD is now accepted as Recognised Veterinary Practice for clinical pain management. Click here for a bibliography of 20 published papers and posters using Prod algometers. (For Topcat’s full bibliography of 90 papers click here.) For a quotation, or to discuss your application, please ring Mike on +44 (0)7739 913696 or email me mike@topcatmetrology.co.uk.

PROD: “Pressure Rate Onset Device”: As soon as tissue pressure is detected, the red and green guide lights activate, teaching you to increase the pressure at a constant, preset rate: press too hard and the red light glows; press too little and the green light glows. With a little practise, people find that they can achieve repeatable application of the force at a known rate- an important point for publication.

FORCE RANGE AND TIP DIAMETER: The Prod can be used to apply forces up to 25N. This is lower than the range of some other algometers because we consider to be the maximum that a clinician can apply smoothly and repeatably to most conscious animals. For small species even this is too much: 25N would just slide a kitten sideways across the table and for this reason, we always recommend smaller tips rather than more force, with the aim of achieving a baseline that allows headroom to either increase the threshold for an analgesic effect, or to reduce it for hyperalgesia.

1 CM TIPS ARE TOO BIG: Some publications report using 1cm² tips which results in forces of up to 250N to achieve a response on a horse and, as seen in the graph below, a large spread in the data. Taken from a review poster that Topcat presented (ACVA Capetown, 2012) of published papers using instruments of many different force ranges, it reinforces Topcat’s view that forces above 100N are very difficult to apply to an animal in a controlled manner.

Recent research by Topcat (some of it on ourselves) indicates that tip diameters above 8mm should usually be avoided (as they require large, impractical forces) and that the ideal diameter (for dogs, cats etc) is 2-4mm.   We therefore supply the basic Prod with a 2mm or a 4mm tip.

1MM TIPS ARE AVAILABLE for cattle, sheep and other prey species whose natural behaviour pattern is not to show a pain response (as it singles them out as the weak one of the herd). The tips are smooth, flat and interchangeable, with an edge radius of 10% of the diameter.  ProdPro is supplied with tips from 1-8mm and an extension piece for probing soft tissue.

PEAK-HOLD FACILITY: The Prod will retain and display the highest reading of force since the reset button was last pressed. This is preferable to just retaining the last reading when the Prod was withdrawn or, with a limb mounted actuator, when the animal lifted its leg at threshold; at leg lift, the tendon behind the canon bone relaxes and up to 20% of the force reading can be lost as slack in the mounting strap. The effect, we have found, is most noticeable with horses.

THERE ARE 3 INSTRUMENTS:  the entry level Prod, ProdPlus with interchangeable actuators and ProdPro for use with our range of  limb-mounted mechanical actuators.  On the right, ProdPlus is being used at the University of Gent with an angled actuator to assess post-operative pain in kittens. Click here for some more information.

THE PROD IS SMALL, DARK-COLOURED AND HAS NO TRAILING LEADS. This makes it “non-scary” for animal subjects, especially those already recovering from surgery or trauma (very important with a behavioural response). The instrument fits the palm of the hand allowing even prey species to be approached. A horse won’t mistake the Prod for a worming syringe!

FOR LIMBS RATHER THAN WOUND SITES, our pneumatic limb actuators provide a completely natural environment: The animal will quickly acclimate to wearing the set (with a dummy on the contra-lateral limb) with just a flexible tube connecting to the ProdPro (held by the tester or placed on a bench). Unknown to the animal, the stimulus is applied by depressing a syringe to pressurise the line and the behavioural response is not influenced by the need to approach the subject.

DON’T STOP TALKING as you press the syringe: some animals will recognise the sudden silence after a while. Our tip is to have a radio on in the background.

WITH AN EXTENSION POLE, ProdPlus can be used with wildlife and untamed animals. The pressure line transmits the air pressure back from the actuator to the Prod algometer, allowing the force to be applied sensitively without endangering the measurement unit. The system can even be used with cattle in a crush with the longer extension piece shown here.

THE ENTRY LEVEL PROD:

• 2 or 4mm tip
• digital display of force, in Newtons, with peak hold facility
• red and green rate lights for a rate of 2N/sec
• battery low light
• protective plastic case
• manual

TECHNICAL SPECIFICATION:

• Force range: 0.5-25N
• Accuracy: ±0.5N (ProdPlus, ProdPro)
• Accuracy: ±1N (Prod)
• Weight: 260g
• Battery life: 10 hours on 1 PP3 (not supplied)

KEY FEATURES OF THE PROD ALGOMETER RANGE:

• Designed specifically for animal testing
• “Soft” measurement head with air cushion
• Self-contained and easy to hold (no trailing leads)
• “Non-scary” to animals
• Realistic force range for testers to apply
• Can be used with limb mounted actuators as well
• Range of tips to allow study design for optimal headroom (both for analgesic effect and for detection of hyperalgesia)

 “I find the Prod useful in getting a measurement of force at which an animal responds to guide pain management therapy and assess its effect.” Dr Griet Haitjema, The Animal Hospital, Murdock, Western Australia

Every Prod Algometer is calibrated in a measurement fixture against a reference force transducer. But we then also test the Prod, hand held, at strange angles and with a deliberately shaking hand, against the reference to ensure that the device will still measure properly under real life conditions when working with animals.