Product Design Specifications

Version 9: Oct. 19, 2001
Andrew Hoyord, Bern Jordan, Dana Mueller,
Paul Thottakara, and Paul Victorey

Function

Doctors are now finding it necessary to test patients experiencing pain or numbness for neurological damage and warm/heat sensitivity by applying hot sensations to their skin. A device that heats up to a "warm" and "hot" target temperatures could be used by the physician as a prescreening method before a quantitative sensory test is recommended. This device should be convenient to use and safe to apply to patients.

Client Requirements

The product should:

Be safe and not burn patients; i.e. the temperature must never rise above 50°C
Heat up to target temperatures of 38°C and 45°C relatively quickly (within 1°C)
Maintain the target temperature through several successive tests on the same patient
Have a probe surface with an area of 4.0 cm²
Indicate when the probe surface has reached the target temperature
Indicate when the probe has been applied to a patient's skin for five seconds
Be convenient to use and easy to clean with alcohol and/or soap and water
Attach to a Welch Allyn ophthalmoscope/otoscope handle or some other common clinical-setting power source

Design Requirements

Physical and Operational Characteristics
Performance:	The probe surface should heat from room temperature to 38°C and 45°C (within 1°C) within 30 seconds [check with Client again on this because tests have showed 1 minute warm-up time to reach 38°C]. The heating element should use minimal power from the battery. The device should be able to be used to test a maximum 10 patients on a single charge, each including up to 3-4 minutes of testing at 38°C and 3-4 minutes of testing at 45°C.
Safety:	The probe temperature must not exceed 50°C in any event (including user abuse and circuit element failure). The risk of electrical shock to user and patient must be minimized. A five-second timer should be used to alert physician to remove device from patient's skin. To minimize pathogen transmission, the probe should be able to withstand frequent washing with soapy water and alcohol. The probe must be free of sharp edges, rough surfaces, or spaces that would allow for pinching.
Accuracy and Reliability:	The device should heat up to within 1°C of the specified target temperature. Once target temperature is reached, the temperature should remain constant until power is turned off. The five-second timer to limit patient contact should be accurate to within 0.1 s. With repeated use, the device should consistently attain target temperatures. Probe temperature (or temperature display) should not be dependent on battery strength.
Life in Service:	Device should be able to withstand frequent cleaning with soap water and alcohol. The device will be used on at most 20 patients per day, up to 10 minutes for each (max 200 minutes on per day). Two to ten years of use expected before replacement.
Shelf Life:	Indefinite if kept at room temperature free from high humidity and excessive dust.
Operating Environment:	The device will be used under normal indoor hospital/clinical conditions (20-25°C, 1 atm pressure, less than 60% relative humidity, and very little dust) by trained physicians. The probe will primarily be used on a patient's hands and feet. The skin may possibly be moist.
Ergonomics:	Size of probe should allow for full contact to the skin of the various areas of the body tested. Placement of operator controls should not cause undue strain in the hand, wrist, or fingers. Operation with only one hand is desired. The device will be kept relatively simple with as few buttons as possible. The buttons included will be clearly labeled as to what their specific function is. Any movable controls should only have slight frictional resistance. Controls should be adequately spaced apart and sized large enough to be recognized by touch.
Size and Shape:	The probe surface should be circular and 4.0 cm² in area. The entire device should roughly be the size of the normal head attachments to the battery pack (ophthalmoscope or otoscope heads). The size of any numerical display should be larger than 5 mm tall.
Weight:	The attachment should weigh no more than 225 g. The mass of the probe tip should be minimized to conserve battery power, yet large enough to maintain temperature when applied to the skin.
Materials:	All exterior materials must withstand alcohol and soap washing. The heated probe must be made of a non-corrosive material with high thermal conductivity. The body of the instrument should be made of a non-conducting material to prevent heat loss of the probe tip. Standard electrical components will be used for the circuitry.
Production Characteristics
Quantity:	One prototype device for client's use, possibly more if successful design.
Target Product Cost:	The attachment should cost no more than existing attachments for eye and ear testing which run $100-150. The prototype may cost up to $300.
Miscellaneous
Standards and Specifications:	FDA standards applying to electrical, and electrical medical devices if the device becomes mass-produced. If it is just an experimental device, it is necessary to obtain an NIH human subjects protocol. These standards are yet to be found out.
Customer:	Customer requirements listed above.
Patient Related Concerns:	Patients will be concerned with the safety of the device.
Competition:	This device will be used to prescreen patients before recommending quantitative sensory testing; a battery of sensory tests that checks for temperature sensitivity and other stimuli. There exist large AC powered heated probes used for the same type of neurological exam the device will be used for. There exists no competition from Welch Allyn (they are not interested in producing a thermal probe for neurological examinations).

Physical and Operational Characteristics

Performance:

The probe surface should heat from room temperature to 38°C and 45°C (within 1°C) within 30 seconds [check with Client again on this because tests have showed 1 minute warm-up time to reach 38°C].

The heating element should use minimal power from the battery.

The device should be able to be used to test a maximum 10 patients on a single charge, each including up to 3-4 minutes of testing at 38°C and 3-4 minutes of testing at 45°C.

Safety:

The probe temperature must not exceed 50°C in any event (including user abuse and circuit element failure).

The risk of electrical shock to user and patient must be minimized.

A five-second timer should be used to alert physician to remove device from patient's skin.

To minimize pathogen transmission, the probe should be able to withstand frequent washing with soapy water and alcohol.

The probe must be free of sharp edges, rough surfaces, or spaces that would allow for pinching.

Accuracy and Reliability:

The device should heat up to within 1°C of the specified target temperature. Once target temperature is reached, the temperature should remain constant until power is turned off.

The five-second timer to limit patient contact should be accurate to within 0.1 s.

With repeated use, the device should consistently attain target temperatures. Probe temperature (or temperature display) should not be dependent on battery strength.

Life in Service:

Device should be able to withstand frequent cleaning with soap water and alcohol.

The device will be used on at most 20 patients per day, up to 10 minutes for each (max 200 minutes on per day).

Two to ten years of use expected before replacement.

Shelf Life:

Indefinite if kept at room temperature free from high humidity and excessive dust.

Operating Environment:

The device will be used under normal indoor hospital/clinical conditions (20-25°C, 1 atm pressure, less than 60% relative humidity, and very little dust) by trained physicians.

The probe will primarily be used on a patient's hands and feet. The skin may possibly be moist.

Ergonomics:

Size of probe should allow for full contact to the skin of the various areas of the body tested.

Placement of operator controls should not cause undue strain in the hand, wrist, or fingers.

Operation with only one hand is desired. The device will be kept relatively simple with as few buttons as possible. The buttons included will be clearly labeled as to what their specific function is. Any movable controls should only have slight frictional resistance. Controls should be adequately spaced apart and sized large enough to be recognized by touch.

Size and Shape:

The probe surface should be circular and 4.0 cm² in area.

The entire device should roughly be the size of the normal head attachments to the battery pack (ophthalmoscope or otoscope heads).

The size of any numerical display should be larger than 5 mm tall.

Weight:

The attachment should weigh no more than 225 g.

The mass of the probe tip should be minimized to conserve battery power, yet large enough to maintain temperature when applied to the skin.

Materials:

All exterior materials must withstand alcohol and soap washing.

The heated probe must be made of a non-corrosive material with high thermal conductivity.

The body of the instrument should be made of a non-conducting material to prevent heat loss of the probe tip.

Standard electrical components will be used for the circuitry.

Production Characteristics

Quantity:

One prototype device for client's use, possibly more if successful design.

Target Product Cost:

The attachment should cost no more than existing attachments for eye and ear testing which run $100-150. The prototype may cost up to $300.

Miscellaneous

Standards and Specifications:

FDA standards applying to electrical, and electrical medical devices if the device becomes mass-produced. If it is just an experimental device, it is necessary to obtain an NIH human subjects protocol.

These standards are yet to be found out.

Customer:

Customer requirements listed above.

Patient Related Concerns:

Patients will be concerned with the safety of the device.

Competition:

This device will be used to prescreen patients before recommending quantitative sensory testing; a battery of sensory tests that checks for temperature sensitivity and other stimuli. There exist large AC powered heated probes used for the same type of neurological exam the device will be used for. There exists no competition from Welch Allyn (they are not interested in producing a thermal probe for neurological examinations).

Contact: BME design webmaster - bmedesgn@cae.wisc.edu
Owner: Willis Tompkins, Ph.D. - tompkins@engr.wisc.edu
Markup by: Bern Jordan
Content updated: 25 October 2001
Page updated: 22 September 2003, B.J.