A manifold is formed with a plurality of ports for connection to various components such as arterial-venous pressure generators, a syringe, and a source of fluid and pressure sensitive transducers. The manifold includes one or more rotary members which are selectively positioned for interconnecting selected ones of the components. Various sampling, flushing and pressure measuring operations may be performed by use of the manifold. The manifold further includes a venting port arrangement for venting the pressure sensitive transducers to the atmosphere when a pressure measurement is not being taken. This protects the transducer from overpressurization and consequential damage.