To analyze the respiratory state of patients receiving mechanical ventilation by analyzing the shapes and influence factors of flow-time curve in the super early phase of expiration.

Two test lungs with different compliance (C) and two tubes with different resistance (R) were prepared. Four combinations were developed with one test lung coupled with one tube. The test lungs and tubes were then connected to a PB840 ventilator. The start points of expiratoration (the end point of inspiration) were set in three scenarios with different ventilation mode. First: different circuit pressure (Pc₀) and same alveolar pressure (Pa₀) and PEEP. Second case: different Pa₀ and same Pc₀ and PEEP. Third: different PEEP and same Pc₀ and Pa₀. The characteristics of the flow-time curves were observed. The effects of Pc₀, Pa₀, PEEP, C and R on the flow-time curves were also observed.

1．Two key points determined the morphological characteristics of flow-time curves in the super early phase. One was the point of peak flow (the maximum expiratory flow, V1). The other was the break point (the intersection point between the rapid decline and slow decline of flow volume, V4). 2. (1) The higher Pc₀ was, the greater V1 was, when the C, R, Pa₀, and PEEP were kept the same. (2) The higher Pa₀ was, the greater V1 and V4 were, when the C, R, Pc₀, and PEEP were kept the same. However, the degree of V4 rise is less than V1 rise. (3) The higher PEEP was, the smaller V1 and V4 were, when C, R, Pc₀, and Pa₀ were kept the same. (4) The greater R was, the smaller V1 and V4 were, when C,Pc₀, Pa₀, and PEEP were kept the same. (5) V1 and V4 did not change obviously when C changed, and Pc₀, Pa₀ and PEEP were kept the same.

The pressure of the circuit and the pressure of the alveolus at the end of inspiration affect the peak expiratory flow positively. But PEEP and the airway resistance do negatively. The pressure of the alveolus at the end of inspiration affects the break expiratory flow positively. But the PEEP value and airway resistance do negatively. The airway resistance affects the distance between the peak point and the break point positively. But the compliance does negatively.