SummaryObjective To determine the risk of venous thromboembolism (VTE) associated with prolonged work-and computer-related seated immobility.Design Case-control study in which cases were patients aged 18-65 years attending outpatient VTE clinics, and controls were patients aged 18-65 years admitted to CCU with a condition other than VTE. Interviewer-administered questionnaires obtained detailed information on VTE risk factors and clinical details. Main outcome measureThe relative risk of VTE associated with prolonged work-and computer-related seated immobility, defined as being seated at work and on the computer at home, at least 10 hours in a 24-hour period and at least 2 hours at a time without getting up, during the four weeks prior to the onset of symptoms that led to VTE diagnosis or CCU admission.Results There were 197 cases and 197 controls. Prolonged work-and computer-related seated immobility was present in 33/197 (16.8%) and 19/197 (9.6%) cases and controls, respectively. In multivariate analyses, prolonged work-and computer-related seated immobility was associated with an increased risk of VTE, odds ratio 2.8 (95% CI 1.2-6.1, P=0.013). The maximum and average number of hours seated in a 24-hour period were associated with an increased risk of VTE, with odds ratios of 1.1 (95% CI 1.0-1.2, P=0.008) and 1.1 (95% CI 1.0-1.2, P=0.014) per additional hour seated. ConclusionProlonged work-and computer-related seated immobility increases the risk of VTE. We suggest that there needs to be both a greater awareness of the role of prolonged work-related seated immobility in the pathogenesis of VTE, and the development of occupational strategies to decrease the risk. DECLARATIONS Competing interests None declared FundingThe study was

The objective of the research was to assess the effect on lower limb venous blood flow of sitting in two ergonomic chairs. In a cross-over design 12 healthy subjects had popliteal vein blood flow measured by Doppler ultrasound in different sitting positions, in the Aeron and airCentric chairs. Measurements were made lying prone, sitting with the leg flexed 90° and sitting with the leg flexed 120° in one chair, followed by the same measurements in the second chair, the order determined randomly. The primary outcome measure was popliteal vein peak systolic velocity. Simple paired t-tests and a mixed linear model were used to compare blood flow between chairs and different sitting positions. For the Aeron chair, the prone to 90° position resulted in a reduction in peak systolic velocity from 27.8 to 3.5cm/s, adjusted difference 21.0 (95% CI 17.3 to 24.8), and for the airCentric chair from 21.4 to 3.7cm/s, adjusted difference 21.2 (95% CI 17.4 to 24.9). There was no statistically significant difference in peak systolic velocity between the two chairs, in the two sitting positions. There was a marked reduction in popliteal vein blood flow with sitting, but no significant difference in effect between the two ergonomic chairs.