Spirometer for pulmonary measurement

Claim 1

A spirometer comprising a vertically-oriented chamber having opposed front and back walls, an open top formed as a pair of exit passageways divided by an upper central bridge element between said front and back walls, and an open bottom formed as a pair of entrance passageways divided by a lower central bridge element between said front and rear walls; a hollow inlet member mounted to and projecting outwardly from said front wall at the lower end thereof; a hollow outlet member mounted to and projecting outwardly from said back wall at the lower end thereof, said outlet member including an outlet orifice of reduced diameter at the distal end thereof, the interior of said inlet and outlet members being joined to the interior of said chamber through said entrance passageways to allow the passage of air therethrough; a piston mounted in said chamber for vertical movement therein; a guide rod centrally mounted within said chamber, the opposed ends thereof being supported by said upper and lower central bridge elements, said piston having a vertical central throughbore whereby said piston is mounted on said guide rod; spring means mounted to said piston to urge said piston to a lower retracted position, said piston being movable upward along said guide rod in response to a flow of air through said inlet member into said chamber; an indicator mounted within said chamber for upward movement with said piston; a vertical slot located in a wall of said chamber; a shank extending from said indicator through said vertical slot and terminating in an enlarged head externally of said chamber; and a helical compression spring encircling said shank and entrapped between said indicator element and the inside face of said chamber bordering said slot.