Some 30 people in Japan have developed such symptoms after long flights as breathing difficulties, increased heart rate, chest pains, loss of consciousness, and interruption of blood circulation, a study conducted by a team of doctors showed Monday.

The victims of the so-called economy-class syndrome showed such symptoms after sitting in narrow seats for hours at a time.

The team, led by Hiroshi Morio, deputy head of the internal medicine department at the Narita Red Cross Hospital in Chiba Prefecture, will report their findings to a conference of the Japanese Association for Acute Medicine beginning Wednesday in Tokyo.

According to Morio, during a six-year period beginning in 1994, a total of 20 people were taken to hospitals after reporting breathing difficulties upon arrival at Narita airport.

Most of them were women aged 50 or older and they tended to be short and overweight, he said.

Doctors have confirmed that the patients suffered blood circulation problems in several parts of the lungs.

They were kept in hospital for two to three weeks to undergo treatment, including the administration of anticlotting drugs.

Pressure from the seats causes blood clotting to occur in the veins of the thighs and legs, Morio explained.

When patients stood up, the clots reached the lungs, causing breathing difficulties and other symptoms.

Morio said passengers are more likely to suffer the condition if they become dehydrated in the dry atmosphere of the planes.

Morio said 10 similar cases of hospitalization due to the syndrome were reported by other medical institutions in Japan.

About 200 cases of people suffering from the same syndrome have been reported abroad, and some of those have resulted in death.

Passengers in first or business class can also suffer from the symptoms, he said.