Pulmonary impedance as an index of severity and mechanisms of neonatal lung disease.
The measurement of resistive and elastic components of the respiratory system in neonates has been used to define disease severity and the response to therapy. The lung resistance (RL) and dynamic lung compliance (CLdyn) partition the impediment to gas flow into two components, each of which may be altered independently. The concept of lung impedance (ZLdyn) is the combined effect of the elastic and resistive loads presented to the respiratory muscles, which determines the gas flow that will result from the pressures generated by the respiratory muscles. In a first order system where RL and CLdyn are single values (independent of volume or respiratory rate), ZLdyn is the vector sum of the reactive [1/2 pi fb x CLdyn)] and resistive (RL) components at the infant's breathing rate (fb), if the transpulmonary pressure (Ptp) generated by the respiratory muscles during spontaneous respiration can be modeled mathematically by a sinusoidal function. Furthermore, the phase angle (theta) between the impedance and the resistive component will represent the relative magnitude of the resistive and reactive components. The validity of this model can be establishing by comparing the calculated theta to the observed temporal difference (measured theta) between the Ptp and flow derived from the polygraph tracing. This hypothesis was tested in 10 spontaneously breathing neonates with lung disease of differing etiology and severity. No significant difference was found between the measured and calculated theta values (mean difference, 1.2 +/- 3.9 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)
Coates
A L
AL
McGill University, Montreal Children's Hospital Research Institute, Respiratory Medicine Division, Quebec, Canada.
Vallinis
P
P
Mullahoo
K
K
Seddon
P
P
Davis
G M
GM
D001997:Bronchopulmonary Dysplasia / Q000175:diagnosis*; D006801:Humans; D007231:Infant, Newborn; D008168:Lung / Q000503:physiopathology*; D008471:Meconium Aspiration Syndrome / Q000175:diagnosis*; D008954:Models, Biological; D008962:Models, Theoretical; D012127:Respiratory Distress Syndrome, Newborn / Q000175:diagnosis*; D015656:Respiratory Mechanics / Q000502:physiology*; D012132:Respiratory Muscles / Q000503:physiopathology; D014939:Work of Breathing / Q000502:physiology*