A theoretical analysis of respiratory mechanics in mechanical ventilation / 中华危重病急救医学

ABSTRACT

As a non-physiological way of ventilation, mechanical ventilation has a great effect on the respiratory mechanics. The biggest problem of artificial airway is that it brings extra airway resistance to the respiratory tract. For different parts of the lung, positive pressure ventilation could cause different mechanic states. We can find the formation and influencing factors of transpulmonary pressure, transchest wall pressure, trans-lung-chest pressure, trans-diaphragmatic pressure, trans-pulmonary-diaphragmatic pressure, intrapleural pressure, plateau pressure and driving pressure, by analyzing the mechanic state in a unit area of the chest or diaphragm position in the way of basic mechanics. It is obviously different in the pulmonary pressure gradient caused by inspiratory driving between in spontaneous breathing and in mechanical ventilation. The pressure is transmitted from the periphery to the center in spontaneous breathing in physiological state, playing a traction role for lung tissue. The pressure is transmitted from the center to the periphery in positive pressure ventilation without spontaneous breathing, playing a pushing role for lung tissue. It can be divided into two stages in positive pressure ventilation with spontaneous breathing. The first stage is from inspiratory trigger effort to trigger sensitivity. It is similar to spontaneous inspiration in physiological state. The pressure gradient in this stage is from the peripheral to center. But the period is very short. The second stage is the positive pressure ventilation progress after the trigger sensitivity. The pressure gradient is caused by the pulling of the patient's spontaneous inhalation and the pushing of the positive pressure ventilation of the ventilator. There is a certain complementarity in the distribution and transmission of pressure, especially for non-physiological positive pressure ventilation. Therefore, through these basic mechanical analysis, clinical medical staff can better understand the impact of mechanical ventilation on respiratory mechanics.