Involving the field of medical devices, especially the method of judging expiration or inhalation during lung function measurement.
Background technology:
: The functions of various organs of the human body can only work normally when there is sufficient oxygen supply. The human body's oxygen supply depends entirely on the breathing of the lungs. During the breathing process, the lungs absorb oxygen and expel the metabolite carbon dioxide. Pulmonary function measurement can be used to determine the respiratory function of the test subject, which has practical clinical significance in identifying the type of airway obstruction and evaluating pulmonary function before thoracic and abdominal surgery. With the advancement of technology, pulmonary function testers have gradually developed from traditional float-type and rotary-type to portable electronic testers. In this type of electronic lung function tester, the flow sensor is one of its key components. As shown in Figure 1, the differential pressure flow sensor designed using the Venturi principle includes two pressure ports on the flow sensor. The low-pressure port 1001 is set at the throat 1003, and the high-pressure port 1002 is set at the throat. Air inlet part 1004. When detecting exhalation parameters, the airflow first passes through the high-pressure pressure port, and then enters the low-pressure pressure port at the throat. Due to the small aperture at the throat, the airflow is compressed and accelerated, the pressure loss is relatively large, and the flow rate decreases. However, the high-pressure pressure port It is in front of the throat, so it will not affect the flow test accuracy. If the flow sensor is used to detect inhalation parameters, the airflow will first pass through the low-pressure pressure port at the throat. The airflow pressure will be lost and the flow rate will decrease. Then it will enter the high-pressure pressure port. The detected flow rate will be significantly smaller. Therefore, based on The differential pressure flow sensor based on the Venturi tube principle cannot detect the bidirectional flow of expiration and inhalation at the same time using two pressure holes. In order to detect the bidirectional flow of exhalation and inhalation at the same time, the differential pressure flow sensor is designed using the venturi principle as shown in Figure 2 and uses four pressure ports. It is necessary to add a high-pressure sensor to the inhalation air inlet 1005. Pressure port 1002, adding a low-pressure pressure port 1001 to the throat will inevitably increase the length of the throat 1003, and the length of the entire flow sensor will increase accordingly. There are many pressure ports and the structure is complex, which is not conducive to the miniaturization of the detection instrument. . As shown in Figure 3, the gas flow sensor is designed using the orifice plate principle. Since the thickness of the orifice plate 1006 is less than 0.02D (pipe diameter), the air flow pressure loss is small and does not affect the bidirectional flow detection accuracy of exhalation and inhalation. However, since the inhalation flow of the human body is much smaller than the expiration flow, two sets of pressure ports are used to detect the expiration and inhalation flow simultaneously. The sensitivity of the inhalation detection is not enough, so four pressure ports 1007 are used, with two pressure differences. The sensor 1008 includes a high-range differential pressure sensor and a low-range differential pressure sensor. The high-range differential pressure sensor is used to detect expiratory flow, and the low-range differential pressure sensor is used to detect inspiratory flow to improve the sensitivity of inspiratory flow detection. However, due to the use of two sets of differential pressure sensors with different ranges, two sets of calibration systems need to be used when calibrating the flow sensor. This will not only increase the complexity of the instrument and reduce reliability, but also increase the production process, manufacturing cost and The complexity of after-sales maintenance. Pulmonary function tests include ventilation function, ventilation function, respiratory regulation function, pulmonary circulation function, etc. The measurement of multiple physiological parameters of pulmonary function requires continuous detection of respiratory air flow. At present, the existing pulmonary function meter determines the expiratory state or inspiratory state by comparing it with the zero point value of the pressure difference sensor. The zero point value needs to be calibrated regularly and requires professionals to cooperate with the software to operate, which is relatively cumbersome. During calibration, use a standard 3L calibration cylinder to push and pull at a constant speed multiple times to simulate human exhalation and inhalation. Since the expiration volume of the calibration cylinder is equal to the inhalation volume, both are 3L, so the sensor corresponding to half of the total volume can be calculated. The output value is the zero point value of the sensor. The value greater than the zero point is exhalation, and the value less than the zero point is inhalation. Environmental temperature and humidity, changes in atmospheric pressure, and frequency of use will cause the zero point of the sensor to drift. Therefore, the zero point value of the sensor needs to be calibrated regularly, otherwise large errors will occur.
Since the maximum expiratory flow rate in pulmonary function testing is much greater than the maximum inspiratory flow rate, in order to improve the sensitivity of inspiratory flow detection, it is necessary to increase the pressure of the second high-pressure pressure port. According to Bernoulli's principle of fluid dynamics, the relationship between flow rate and pressure difference satisfies formula (I), where d is the diameter of the low-pressure pressure port at the throat, and D is the diameter of the second high-pressure pressure port at the suction inlet. , ρ is the density of the fluid. When D becomes larger, the pressure difference Δp corresponding to a certain flow rate will also become larger accordingly.