Recommendations on Standards for the Design of Medical Diagnostic Equipment for Adults with Disabilities, Advisory Committee Final Report

II. Recommendations of Diagnostic Imaging Equipment Manufacturers on Transfer Surface Low Height

The aforementioned medical diagnostic imaging equipment manufacturers support a 19 inch minimum transfer surface low height for the following reasons:

1. A standard should set a minimum transfer surface low height requirement which is reasonable and achievable given the technical and engineering resource constraints upon the equipment manufacturer.

Diagnostic imaging equipment is comprised of both the image detectors/scanner, such as an x-ray scanner, or nuclear medicine cameras, or imaging equipment using a bore, such as CT, PET and MRI, as well as the table supporting the patient. It should be recognized that the table, which supports the patient who is undergoing the diagnostic imaging procedure, is an integral part of
that equipment, and its precise alignment with the imaging scanner/bore itself is essential to achieving diagnostic quality images.

It is important to recognize, given the integrated nature of the table to the system and its imaging performance, that a change of even a few inches in minimum transfer surface low height constitutes a significant engineering change to the device. Any such change must ensure there are no adverse effects to image quality, system performance, and patient safety. Complete scanner
re-testing and re-certification under our formal FDA quality system and design controls are needed to verify overall system performance and safety.

Moreover, the most significant of these design changes can result in cascading alterations to the scanner, potentially leading to unacceptable heating in the case of MR, impacts on image signal/quality, and changes in dose levels to ensure the same, effective, high quality images and increased examination times, that is, additional workflow steps. It should be noted that future design projects are in the works many years before they become commercially available.

2. There was no compelling evidence presented of significant access improvement for diagnostic imaging devices at 17 inches that would warrant the additional efforts, timing and resources.

During the meetings of the Advisory Committee, there was no compelling evidence presented in support of a minimum transfer low height of 17 inches as the new standard for access. The original Notice of Proposed Rulemaking (NPRM) proposal was for a minimum height in the range of 17 to 19 inches. This would have allowed a table that lowers to a 19 inch minimum height to meet the standard. There did not appear to be sufficient, solid evidence presented that 19 inches minimum height was not adequate, and that 17 inches was necessitated to provide access. It should also be recognized, that due to the precision work which is required in the design of diagnostic imaging equipment, and the necessity of compliance with regulatory requirements, with each inch of decrease in minimum height from 19 inches, the time and costs which are required for equipment re-design go up exponentially.

However, the Committee did agree that an additional requirement, that of adjustability up to 25 inches, was critical to ensure access, given the variety of mobility device seating heights. We believe the addition of the adjustability requirement delivers by far a larger increase in access than having a single minimum height of 17 inches. As a standard , we believe the increased access goal is well met by having a 19 inch minimum height and transfer height adjustability. Having an additional extension to the NPRM to require a fixed minimum of 17 inches would provide only a marginal increase in the population served (see Item 3 below for further details).

3. While it is ideal for transfer surfaces to be at the same height as the seat heights of mobility devices, there is evidence that non-level independent transfers are also feasible.

The original Notice of Proposed Rulemaking (NPRM) Preamble explains the motivation for a minimum transfer height of 17 inches with the following:

“Transfer surfaces that are adjustable to the same heights as the seat heights of mobility devices reduce the effort needed to transfer since patients do not have to lift their body weight to make up the difference between the two surfaces, in one direction or the other.” ¹

The NPRM then goes on to discuss wheelchair seat heights, with the 5th percentile lowest seat height being 17.3 inches, according to the IDeA study^2.

While it is ideal for transfer surfaces to be at the same height as the seat heights of mobility devices, there is evidence that independent transfers are also feasible with a seat height discrepancy of up to two inches. As is discussed in Section 3.3.1 of the full Committee report, the Committee considered the findings from the University of Pittsburgh Human Engineering Research Laboratories (HERL) study that looked at transfers, and how different conditions affect the abilities of wheeled mobility devices (WMD) users to transfer from their WMD to another surface^3. One of the goals of the study was to “determine acceptable ranges for non-level transfers (e.g. vertical height differences)”. A portion of the study’s results are shown in Table 1 below. It should be noted that the addition of a 3-inch gap next to the transfer surface (permitted by the Committee’s recommendation) may impact the percentages shown here, but information was not presented that directly correlated step height, gap, and ability to transfer. Further information would be needed to quantify this directly.

Table 1. A portion of the results presented in the HERL study to determine acceptable ranges for non-level transfers.

These findings suggest that those individuals with seat heights ≥18 inches high should be able to independently transfer to an adjustable-height transfer surface with a 19-inch minimum height, since the step in height will always be no more than one inch. For the small population of individuals with a seat height between 17.3 (5th percentile) and 18 inches, the maximum step height will be two inches. Based on this study, only about 14% of the individuals in this already very small population may need further assistance in transferring. In some instances, transfer or positioning supports may even be able to provide this assistance, thus maintaining independence of transfer. This study showed that adding a grab bar for patient support helped some wheelchair users to transfer at a height at which they could not transfer previously.

One of the Committee’s concerns regarding this particular study was that the study subjects did not necessarily reflect the general population of persons who use WMD. Of the people studied, 88 were men and 24 were women. A large number of subjects in the study were veterans who participated in organized sports-related events. The study did find, though, that the subjects’ daily activity levels apart from the time of those sports events did not differ from adult WMD users who live in the community. We do acknowledge the concern about the population studied and understand that the findings and percentages above may not provide strict guidance on how many people will be able to transfer given a non-level transfer situation. However, we believe that the insights from this study are very important to take into consideration when setting a minimum low height for transfer surfaces, since there are in fact many individuals who will be able to independently transfer with a 1 or 2-inch step height. While setting the minimum low height, we also believe it is important to specifically consider the individuals who will be impacted by this low height requirement. Many of the wheelchairs with low seat heights (especially in the 17-18inch range) are manual wheelchairs. Many manual wheelchair users may use more upper body strength in moving around for day-to-day activities than power wheelchair and scooter users do, and so a non-level transfer may not be as difficult for those individuals.

4. Diagnostic imaging devices require a trained technician present to aid all patients in accessing the table in the proper imaging position.

Diagnostic imaging devices operate with a high level of precision. It is important to recognize that proper patient positioning on the table for diagnostic imaging devices, whether they are x- ray, nuclear medicine, PET or MRI devices, is essential to achieving diagnostic quality images. In order to achieve diagnostic quality images, trained technologists are required to position all patients properly, regardless of the patient’s ability or disability to access the equipment.

¹ Notice of Proposed Rulemaking (NPRM). Preamble, page 18.

² IDeA Center Study at the University of Buffalo, New York: The Wheeled Mobility Anthropometry Project, Final
Report, page 49, Figure 3-5, reference to “All Device Types*”.

³ “The Impact of Transfer Setup on the Performance of Independent Transfers: Final Report”; Human Engineering
Research Laboratories, VA Pittsburgh Healthcare System, University of Pittsburgh.