Multiple tube flowmeter

Abstract

A gas flow measuring appartaus especially useful in a spirometer produces increased gas flow sensitivity and accurate gas flow rate measurements, especially at low gas flow rates. The apparatus includes a breath transmission passage, first and second ports spaced apart axially along the passageway, and a gas flow meter connected across the ports for measuring gas flow rate in the passageway. A plurality of elongated small diameter hollow tubes are mounted within the passageway proximate the locations at which the gas flow measuring ports communicate with the passageway. The small diameter tubes act as a restriction within the passageway for causing gas flow entering the passageway to flow past and through the tubes and toward the outer walls of the passageway, thereby producing a pressure drop across the ports that results in measurable gas flow rate measurements at the flowmeter. The small diameter hollow tubes may be mounted in an elongated restriction tube in the passageway proximate the gas flow measuring ports, or the hollow tubes also may be mounted to the inner wall of the passageway, both in arrangements which increase the gas flow rate measuring sensitivity of the flowmeter, while producing substantially negligible resistance to gas flow that produces a laminar and substantially uniform gas flow pattern along the outer walls of the passageway.