Diaphragm (optics) photographic lens is called an iris diaphragm. In the early years of photography, a lens could be fitted with one of a set of interchangeable diaphragms , often as brass strips known as Waterhouse stops or Waterhouse diaphragms. The iris diaphragm in most modern still and video cameras is adjusted by movable blades, simulating the iris of the eye. The diaphragm has two to twenty blades (with most lenses today featuring between five and ten blades), depending on price and quality of the device in which it is used. Straight blades result in polygon shape of the diaphragm opening, while
Diaphragm pacing an electric current through electrodes that are attached internally. The diaphragm contracts, expanding the chest cavity, causing air to be sucked into the lungs (inspiration). When not stimulated, the diaphragm relaxes and air moves out of the lungs (expiration). According to the United States Medicare system, phrenic nerve stimulators are indicated for "selected patients with partial or complete respiratory insufficiency" and "can be effective only if the patient has an intact phrenic nerve and diaphragm". Common patient diagnoses for phrenic nerve pacing include patients with spinal cord injury, central sleep apnea (i.e., Ondine's curse), and diaphragm paralysis. There are currently