Comparison of Cough Assist in Mechanical Ventilator on the Differences of Rheological Property and Lung Mechanics

Abstract

Background: At last year's Open Forum, we reported on different lung mechanics, driving pressure, ventilation mode, presence / absence of PEEP, and migration distance of mucus stimulants (MS) with different viscoelasticity, using the cough assist function of VOCSN ventilator. In this study, we also compared and examined the migration distance of MS with different viscoelasticity due to changes in different lung mechanics, driving pressure, and rise time.

Methods: We measured the movement distance of the MS in PCV A/C mode under the following conditions. 1) Four types of lung mechanics: compliance (Cst) 50mL/cm H₂O and airway resistance (Raw) 5cm H₂O/L/s in normal lung, restrictive lung (Cst 30 and Raw 5), obstructive lung (Cst 50 and Raw 20) and mixed lung (Cst 30 and Raw 20). 2) 4 types of driving pressure were insufflation/exsufflation 30/-30, 30/-40, 30/-50 and 30/-60cm H₂O. 3) The two types of inspiratory rise times were 1 (fast) and 6 (slow). Under the above conditions, the movement distance was measured using two types of MS. A 1% lysis of MS is potage-like, corresponding to the secretion of chronic bronchitis, and a 4% lysis MS is jelly-like, close to the viscoelasticity of a mucus plug during an asthmatic attack. The analysis of the ventilatory dynamics was measured 5 times under each condition using flow analyzer PF300, and the average value was compared. This research is conducted after obtaining approval from Showa University Ethics Review Board.

Results: 1) Regarding sputum viscoelasticity, as we have previously reported, the greater the negative pressure of cuff assist, the greater the movement distance of MS (P <0.05). 2) In 1% MS, the movement distance increased with rise time 6 in obstructive and mixed lungs, but the rise time difference did not affect as negative pressure increased. 3) With 4% MS, the shorter the rise time, the longer the movement distance, but if negative pressure became stronger, the rise time will not affect. 4) Rise time did not affect the peak inspiratory flow. 5) The peak expiratory flow increased with increasing negative pressure (P <0.05).

Conclusions: From these results, it seemed that the effective setting method was to set the rise time slow and increase the negative pressure in the case of obstructive lung and low viscoelasticity sputum. For sputum with high viscoelasticity, it was more effective to set the rise time faster and the negative pressure stronger.