The Sensex at the Bombay Stock Exchange, which tumbled by 191 points in opening trade today, stood 227 points in the negative territory at 16,144. The 30-share index had lost 1,198 points over the past seven sessions.In a similar fashion, the wide-based National Stock Exchange Nifty index was trading 65 points down at 4,841.Meanwhile, in the Asia region, Japan's Nikkei Index fell by 0.21 per cent, while Hong Kong's Hang Seng Index was down by 1.86 per cent in early trade today.