Gases mixing and measuring for a medical device

A method for determining a characteristic of gases flowing through a respiratory gases measurement apparatus located coaxially within a gases mixing chamber of a respiratory gases delivery apparatus, along a gases flow path from a first end of the respiratory gases measurement apparatus to a second end of the respiratory gases measurement apparatus, the respiratory gases measurement apparatus comprising a first ultrasonic sensor positioned at the first end and a second ultrasonic sensor positioned at the second end, a downstream direction defined along the gases flow path from the first end to the second end and an upstream direction defined along the gases flow path from the second end to the first end, the method comprising:

• transmitting a downstream direction acoustic pulse train from the first ultrasonic sensor and detecting the downstream direction acoustic pulse train at the second ultrasonic sensor;
• determining a downstream time of flight based at least in part on the downstream direction acoustic pulse train;
• transmitting an upstream direction acoustic pulse train from the second ultrasonic sensor and detecting the upstream direction acoustic pulse train at the first ultrasonic sensor;
• determining an upstream time of flight based at least in part on the upstream direction acoustic pulse train, wherein one or both of the downstream direction acoustic pulse or the upstream direction acoustic pulse comprise a plurality of acoustic pulses, a time interval between transmission of two consecutive acoustic pulses of the plurality of acoustic pulses being shorter than the downstream or upstream time of flight;
• measuring temperature of gases flowing in the gases flow path;
• determining a flow rate of the gases based at least in part on the downstream time of flight, the upstream time of flight, and the temperature;
• and
• determining a gases concentration based at least in part on the downstream time of flight, the upstream time of flight, and the temperature.

A gas delivery apparatus, comprising:

• a controller;
• a gas mixing chamber configured to receive gases from a gases source, the gases mixing chamber comprising a gases flow path from a first end of the gases mixing chamber to a second end of the gases mixing chamber and at least one mixing element situated within the gases flow path;
• a gas measuring chamber configured to receive gases from the gases mixing chamber, the gas measuring chamber located coaxially within the gas mixing chamber, the gas measuring chamber comprising a gases flow path from a first end of the gas measuring chamber to a second end of the gas measuring chamber, wherein a downstream direction is defined along the gases flow path from the first end of the gas measuring chamber to the second end of the gas measuring chamber and an upstream direction is defined along the gases flow path from the second end of the gas measuring chamber to the first end of the gas measuring chamber;
• a first ultrasonic sensor positioned at the first end of the gases measuring chamber, the first ultrasonic sensor configured to transmit a downstream acoustic pulse train in a first measurement phase, to detect an upstream acoustic pulse train in a second measurement phase, and to send a first signal to the controller;
• a second ultrasonic sensor positioned at the second end of the gases measuring chamber, the second ultrasonic sensor configured to transmit the upstream acoustic pulse train in the second measurement phase, to detect the downstream acoustic pulse train in the first measurement phase, and to send a second signal to the controller;
• at least one temperature sensor configured to measure temperature of the gases flowing in the gases flow path;
• wherein the controller is configured to determine a flow rate of the gases by:
• identifying peaks in the upstream acoustic pulse train and the downstream acoustic pulse train created by the first ultrasonic sensor and the second ultrasonic sensor, wherein one or both of the downstream direction acoustic pulse or the upstream direction acoustic pulse comprise a plurality of acoustic pulses, a time interval between transmission of two consecutive acoustic pulses of the plurality of acoustic pulses being shorter than a time of flight in the downstream direction or a time of flight in the upstream direction;
• calculating an average time of flight in the upstream direction and an average time of flight in the downstream direction based on a number of the peaks received and the times of each of the received peaks;
• and
• determining the flow rate of the gases based at least in part on the average time of flight in the upstream direction and the average time of flight in the downstream direction, and the temperature measured by the at least one temperature sensor.