Measurements of airway mechanics in spontaneously breathing young children

The relation of pressures in- and expanding the airway lumen. EPP=equal pressure point; P_ex=dynamic compression by pleural and peribronchial pressure; P_in=pressure inside airways.

Deflation volume-pressure curves of the lung at different ages (obtained from studies on excised lungs).²¹ With increasing age up to young adulthood, the curves become straighter and, at a given lung volume, elastic recoil pressure is greater. The curve from elderly individulas resembles that from a 7-year-old respiratory system.

General set up of oscillation system.

A sinusoidal pressure wave causes a flow wave that is analysed using Fourier analysis. From the relationship of pressure and flow changes, resistance (R) and reactance (X) can be calculated. The absolute values of pressure and flow make up the value of the resistance, and the time it takes pressure changes to change the flow makes up reactance. The combination of both parameters makes up impedance.

Interrupter resistance. During tidal breathing, a short interruption of airflow (V′) causes changes in respiratory system pressure that can be measured at the mouth (P_mo). P_int is computed by back extrapolation of a line through two points, centred at 30 and 70Msec (which are blocked averages of pressure during 10Msec) to the point at 15Msec from the start of occlusion (t=0).⁵⁴