Design criteria for the reduction of shear forces in beds and seats.

Both with respect to the aspect of pressure sores and of comfort, the inclination of backrest and seat are, amongst other factors, important design criteria. In this study the combination of seat and backrest inclination which reduces shear forces on the seat in passive seating forms the centre of attention. A biomechanical model was developed to predict these combinations and a new measurement apparatus was used for verification of the model on 10 healthy subjects (age 24.4 S.D. 2.1 yr, height 1.77 S.D. 0.08 m, mass 66.3 S.D. 11 Kg). For chairs it was found that when little shear is accepted, a fixed inclination between seat and backrest can be chosen between 90 degrees and 95 degrees. For beds a parabolic relationship was found between seat and backrest inclination with a maximum seat inclination of 20 degrees at a backrest inclination of 50 degrees. When lying with the knees bent to a position with equal inclination of thighs and shanks, the model predicts a shear force on the seat that shoves the person into the bed for every combination of seat and backrest inclination.

[1]  D. Hobson.  Comparative effects of posture on pressure and shear at the body-seat interface. , 1992, Journal of rehabilitation research and development.

[2]  G A Hoek van Dijke,et al.  Influence of shear on skin oxygen tension. , 1994, Clinical physiology.

[3]  L. By,et al.  Skin stress and blood flow in sitting paraplegic patients. , 1984, Archives of physical medicine and rehabilitation.

[4]  C J Snijders,et al.  Stabilograph, an accurate instrument for sciences interested in postural equilibrium. , 1973, Agressologie: revue internationale de physio-biologie et de pharmacologie appliquees aux effets de l'agression.

[5]  L. Bennett,et al.  Shear vs pressure as causative factors in skin blood flow occlusion. , 1979, Archives of physical medicine and rehabilitation.

[6]  G A Hoek van Dijke,et al.  A new instrument for the measurement of forces on beds and seats. , 1993, Journal of biomedical engineering.

[7]  P Branton,et al.  An evaluation of train seats by observation of sitting behaviour. , 1967, Ergonomics.

[8]  M. Kosiak,et al.  Etiology and pathology of ischemic ulcers. , 1959, Archives of physical medicine and rehabilitation.

[9]  David J. Oborne,et al.  Ergonomics at work , 1982 .

[10]  Dinsdale Sm,et al.  Decubitus ulcers: role of pressure and friction in causation. , 1974, Archives of physical medicine and rehabilitation.

[11]  L M Vistnes,et al.  Differential Response of Skin and Muscle in the Experimental Production of Pressure Sores , 1980, Plastic and reconstructive surgery.

[12]  M. Manley,et al.  Repetitive mechanical stress and denervation in plantar ulcer pathogenesis in rats. , 1980, Archives of physical medicine and rehabilitation.

[13]  A Grieco,et al.  Sitting posture: an old problem and a new one. , 1986, Ergonomics.

[14]  J W HARMAN,et al.  The significance of local vascular phenomena in the production of ischemic necrosis in skeletal muscle. , 1948, The American journal of pathology.

[15]  L. Bennett,et al.  Skin blood flow in seated geriatric patients. , 1981, Archives of physical medicine and rehabilitation.

[16]  M. Kosiak,et al.  Etiology of decubitus ulcers. , 1961, Archives of physical medicine and rehabilitation.

[17]  S M REICHEL,et al.  Shearing force as a factor in decubitus ulcers in paraplegics. , 1958, Journal of the American Medical Association.