Considerations in Tractor Seating for Operators with Skin, Sensory, or

Motor ImpairmentsCarla Wilhite

University of New Mexico2013 National AgrAbility Workshop

Minneapolis, Minnesota

Objectives of Session

• Describe the basics of a dynamic system of seating and operation environment of the tractor operator.

• Identify seating issues and health related variables for people with disabilities and impairments using tractor seating.

• Discuss current intervention strategies, issues, and gaps in our knowledge.

The situation

• Farmers and ranchers with disabilities DO return to operating agricultural machinery.

• Once we get them there, we have to make an educated guess about appropriate cushions and supports.

The Holy Grail of Seating

• Human comfort• Stability• Safety• Prevent Injury• Provide multiple

degrees of freedom

Review previous work on the subject

• National AgrAbility Project-University of Wisconsin

• 2004-2008– Therese Willkomm– Mark Novak– Jim Hubbard– C. Kerry Jones

Problem is MORE than pressure

Problems can result in….

• Pressure ulcers• Skin tears• Lacerations• Punctures• Abrasions• Bruising• DEATH

Multiple Systems

Which system causes the effects on the other systems?

The Human

Features of the Basic Human Frame’s systems

– Skeletal system– Muscle and connective

tissue system– Joints (hinges, ball &

sockets, etc.)– Fat for padding and

energy storage– Skin (protective envelope)– Anatomical “norms”

The Human

• Features of human’s organ systems– Cardio-vascular– Pulmonary– Digestive System/Viscera– Genito-urinary– These systems bring in

and expel our fuel:• oxygen/carbon dioxide• Food/elimination• Liquids/urination

The Human System

• Features of neurological systems

• “Two-way radio”– Afferent– Efferent

• Central nervous system• Peripheral nervous

system• Cognitions• Behavioral/Emotional

The Tractor

Environmental Systems

Human Interface

How can we deal with all this complexity?

• Tried and true tools:– Seeking cause and effect– Experimental control– Statistics/probabilities– Qualitative

• Newer tools– Systems thinking– Feedbacks (= - +)– Randomness/patterns

Basic Features of Research Methods for Looking into Problems

• Quantitative– Example: Studying the pressure

map between the seat cushion and the human body

– Hypothesis– Must have a sample– Must control for ALL other variables

except pressure.– Often under laboratory conditions– May have an “intervention”

condition (i.e. type of seat cushion)– Looking for the “cause and effect”

relationships usually expressed in correlations, probabilities, etc. rendered by statistical methods

• Qualitative– Learning about person’s

perceptions of function while on the seat cushion

– Person’s perceptions of stability on the seat cushion

– Person’s beliefs about ease of transferring on/off the seat cushion

– Learning about a person’s health behaviors (i.e. nutrition, pressure relief, hydration)

– Looking for the themes in the data that produce a hypothesis.

Linear Models

A + B = C-or-A + B–D=C-or-(A x B)–D=CProblems are often constructed as linear issues, but they aren’t usually.

Dynamical Systems Features• The effect of a given input

depends on other conditions in the system.

• Must comprehend the functioning of the system as a whole.

• Complex systems include heterogeneous agents at various levels, contact structures between agents, adaptations, nonlinear dynamics and stochasticity.

• These features lead to the emergence of patterns at various scales (ex. Time)

• Nonlinear effects: effects distant in space and time, unanticipated effects, large effects of small changes in initial conditions, and outcomes that are strongly dependent on the history and order of past events.

• Stochastic: non-determinable, random.

• The state of stochastic system is determined by the systems predictable actions and by a random element.

• Feedbacks are not always reinforcing or positive (can be negative or even balancing)

How do linear models and dynamical models look graphically?

Pressure Occludes capillaries

Results in pressure

ulcer

Pressure Ulcer

Human- Micro

Tractor -Human

Linear Description of Pressure Ulcer

Dynamic Description of Pressure Ulcer Relative health

and behavior of the human system

Microclimate between body and seat: pressure, moisture, temperature, friction, shear

Macroclimate between environment and tractor: temperature, vibration, ground forces

Aggregate of factors

Developing our mental model

Key methodology in systems approaches

• Virtual method– Formal models and

simulations– Require a lot of data– Become large and

complicated rapidly– Must begin with a basic

model and gradually be expanded, thus empirical data is necessary

• Systems tools– Agent models

• Agents given traits and behavior rules, model run over and over again over time to obtain a distribution of possible outcomes for the specified system.

– System dynamics models• Even more sophisticated

Some Suggested Accessible Data to Collect

• Pressure mapping on tractor seats

• Presence of moisture and temperature in the microclimate

• Braden Scale risk factor profile of tractor operators with SCI

• Ease of transfers to/from seat• Perceptions of stability and

function on seat cushions

Pressure: Interesting artifacts! • Student Research (Kennington,

Boeser, & Wilhite, 2011)• N=2 (1 male, 1 female): good

health and no current decubiti• Intervention conditions: No

cushion, low profile, mid-profile ROHO

• Low profile better than no cushion, but midprofile better yet.

• Caveats: does midprofile allow safe and secure ride?

Discussion: Next Steps• What do we know about

seating issues today?• What knowledge are we

using to make decisions about seating interventions?

• What are the gaps in our knowledge about seating issues?

• How urgent is this issue compared to others?

• What aspects of seating issues can we hypothesize and study using linear/statistical methods right now?

• What resources do we need? (money, treasure, people, equipment)

• Who needs to be at the table?

• How will farmers with SCI benefit?