| abstract |
A device in a lung ventilator for measuring the tidal volume for exhaled gas volume, comprising a rigid container divided in two separate compartments by a flexible, substantially freely movable, internal partition wall so that the sum of the volumes of the two compartments is always constant and independent of the position of the partition wall. One compartment is connected to a conduit leading to the respiratory ways of the patient during the exhalation phase of the ventilation cycle of the ventilator so as to receive the gas being exhaled by the patient and to the ambient atmosphere during the inhalation phase of the ventilation cycle. The other compartment in the container is connected to a device for injecting a predetermined constant gas flow into this other compartment. The injection of this constant gas flow is started at the end of the exhalation phase of the ventilator, when the communication between the first compartment in the container and the conduit leading to the respiratory ways of the patient is interrupted, and is automatically interrupted when said first compartment has attained its smallest possible volume, that is when it has been emptied of all exhaled gas. The device for injecting the constant gas flow in the second compartment of the container is preferably controlled from a pressure transducer sensing the gas pressure in said second compartment. The duration of the constant gas flow injected in the second compartment of the container is measured; this duration being directly proportional to the gas volume exhaled by the patient during the preceding exhalation phase. |