Architectures of anemometers using the electric equivalence principle

Being an important parameter in the measurement of pulmonary function, the resistance of the respiratory tract is given by the relation between the pressure variation and the airflow variation measured near the patient´s mouth. The airflow determination may be accomplished by measuring the velocity of the respiratory stream with the aid of a hot-wire sensor. Due to its small dimensions, this type of sensor does not produce significant increase of mechanical resistance to the patient´s respiratory airflow. Furthermore, the sensor will be submitted to less contamination by the substances composing the respiratory fluid. In this paper, we present an evaluation of circuits employing constant temperature hot-wire sensors, in response to both fluid velocity steps and respiratory airflow in patients at rest.