Turbulent airflow meter for long-term monitoring in patient-ventilator circuits.

A new type of flowmeter is described which operates on the principle that pressure drop (deltaP) produced by turbulent volume flow (V) through a simple resistance chamber obeys a relation of V = K (deltaP)0.50. Data are given showing that the device follows a true power law with a single exponent for airflows ranging from 3.5 to 270 l/min. Standard instrumentation and a linearization circuit are used with the new flowmeter to provide linear steady-state and alternating airflow measurements up to peak rates of 150 l/min and frequency to 15 Hz. Data are presented comparing integrated airflow readings from the new turbulent flowmeter and a laminar-type flowmeter. The turbulent airflow meter appears to offer increased reliability for long-term patient monitoring use in patient-ventilator circuits.