In an announcement yesterday health experts had warned that office workers sit at their computer screens for long periods without a break have an increased risk of being affected by deep vein thrombosis.

This warning was issued after reports that a computer programmer from Bristol almost died after a 12-hour stint in front of his screen in what is believed to be one of the first cases in the UK of a growing phenomenon dubbed e-thrombosis emerged.

Beverley Hunt, medical director of the charity Lifeblood, said that very few office workers were aware that they could be affected in the same way as air travel passengers. Dr Hunt explained that immobility is a key factor in causing thrombosis. The term e-thrombosis was coined after a 32-year-old man in New Zealand inexplicably suffered a pulmonary embolism. He often spent 12 hours a day at his computer and did not stand up for hours.

Yesterday a Bristol computer programmer Chris Simmons, 41, told how he collapsed in agony after spending 12 hours at his screen and was unable to move. A few days later he had begun to cough up blood. When he underwent an MRI scan a pulmonary embolism, a blood clot that travelled from his leg and lodged in his lung was spotted. Mr Simmons, who works from home, is a vegetarian and not overweight but he has changed his routine. "Now I get up from the computer more often, even if it it's just to play with the cats for 10 minutes, or make a cup of tea," he said.