Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.
Admitted for 180 days â Canadians admitted in âVisitor for Pleasureâ or B-2 status without a B-2 visa in hand are deemed to be admitted for 180 days under current US Customs and Border Protection (CBP) interpretation of the rules.
How Long You Can Stay in the U.S. on a B-2 Visa Compared to on the VWP. If you enter the United States on a visa waiver, your maximum stay will be 90 days.With a B-2 tourist visa, by contrast, you will normally be allowed to stay for up to six months.Whatâs more, with a B-2 visa, you can apply to extend your stay even longer. You would like to visit the United States for no longer than three months (90 days) as a visitor for either pleasure (or business). 2  You do not intend to stay in the U.S. permanently.