I think it's definitely talking about some type of damper for the ventilation system. What I'm not entirely sure about is whether it's describing opposed blade dampers (more commonly expressed as registro de lâminas opostas)
http://www.difustherm.com.br/acessorios.htm

or parallel blade dampers (I've not been able to track down the Portuguese term for that type).

Because parallel blade dampers physically resemble venetian blinds more closely than opposed blade dampers would, I am inclined to believe that is the type of dampers being described.

Also, I believe parallel blade dampers are used in applications where the main function is to either shut off or allow full air flow. (Opposed blade dampers are used in applications where it is important to allow partial airflow much of the time, such as heating/cooling air handlers where you want to have more control than just on and off).