Physiological considerations in seating.

Physiological changes occur with change of posture. Seating imposes significant effect on the cardiovascular, respiratory, abdominal, renal and neurological systems. The presence of severe skeletal deformities can significantly alter the physiological responses of the individual to changes in posture. In the case of severe kyphoscoliosis profound haemodynamic changes may occur. Lung perfusion has been shown to be posture dependent and the imposition of a specific seated position may have profound effects. This may compound existing lung problems for example bronchiectasis, which is not uncommon in these individuals, leading to hypoventilation. Abdominal compression which can occur with the patient in a flexed position can exacerbate a hiatus hernia, which can be both uncomfortable for the patient and may lead to feeding difficulties. The flexion at the hips of the lower limbs may also lead to problems of renal drainage especially where there is a catheter or other drainage appliance. Seating significantly affects many neurological reflexes. For example the presence of an extensor pattern can be helped by the adoption of a flexed position. The presence of pain can also influence the neurological response to a specific position. Those providing seating systems must consider the physiological effects that occur and compromise between these and the other requirements.