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Introduction: Prolonged and frequent standing is associated with an increased prevalence of venous disease in the lower extremities, but there is a lack of scientifically based recommendations regarding acceptable or not acceptable work-related standing exposures. The pathophysiology of venous disease suggests that lower extremity edema may serve as a surrogate parameter for venous stress and the associated development of venous disease. Therefore, we present the development of a model based on the physiological parameter “oedema development” due to occupational standing exposure.

Methods: The risk model is based on laboratory measurements and literature studies that provide insight into the relationship between long-term occupational standing exposure and venous disease. The model development is based on laboratory measurements of lower leg volume and electrical impedance of lower leg tissue. Data were collected from 134 subjects in four laboratory studies applying different experimental conditions. The conditions ranged from uninterrupted walking to a few steps per minute, short and long cycles of standing and walking, and sitting. Subjects were required to stand, walk, sit, or alternate between standing and walking in a randomized, balanced order for 25 to 120 minutes with cycle durations ranging from 10 seconds to 10 minutes. Edema development, i.e. the accumulation of tissue fluid in the interstitium, was measured in the studies by water plethysmography and spectral impedance measurement in the frequency range of 0.8 to 1.2 kHz. The choice of mathematical functions for modelling the influences of the different independent variables for the multidimensional regression model was based on methodological, i.e. physical-medical-physiological considerations, and the fitting of the regression functions was based on the Gauss-Newton approximation method for solving non-linear minimisation problems.

Results: Edema development was modeled using four-dimensional nonlinear regression including the variables exposure duration, proportion of time spent standing and walking, proportion of time spent sitting, and cycle time. The conversion of edema into occupational risk of venous disease was based on published epidemiological literature on venous disease in association with long-term occupational standing exposure.

Discussion/Conclusion: Modeling the risk of venous disease in the lower extremities due to occupational standing enables to evaluate and design standing work on the basis of the physiological stress caused by work-related standing. However, edema formation as an indicator of venous stress - and thus as a surrogate for venous disorders - is not an exclusively valid or all-encompassing criterion for assessing the effects of occupational standing. Equally important, for example, are the effects of occupational standing on the spine in the lower back and on the joints of the lower extremities. For a more comprehensive consideration of occupational standing, the model presented here needs to be expanded in the future to include additional physiological outcome measures as well as a validation (currently in progress by our working group).