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Measurement of low-frequency respiratory impedance in infants
1Institute for Child Health Research and Princess Margaret Hospital, Perth, Australia.
Insights
This study demonstrates that low-frequency respiratory impedance (Zrs) measurements are feasible in sedated infants during brief Hering-Breuer reflex-induced apnea. This method successfully partitions airway and tissue impedance, offering new insights into infant respiratory mechanics.
Area of Science:
- Pediatric Respiratory Physiology
- Bioengineering and Biomedical Measurement
- Pulmonary Mechanics Research
Background:
- Assessing respiratory system mechanical properties in infants is crucial for diagnosing and managing lung diseases.
- Traditional methods for measuring respiratory impedance (Zrs) require apnea, which is challenging to achieve and maintain in infants.
- Existing techniques often struggle to differentiate between airway and tissue contributions to overall respiratory impedance.
Purpose of the Study:
- To investigate the feasibility of obtaining reliable low-frequency respiratory impedance (Zrs) data in sedated infants during short, reflex-induced apneic periods.
- To evaluate the ability of this method to separately estimate the mechanical properties of the airways and the tissues in the infant respiratory system.
- To establish a non-invasive technique for partitioning airway and tissue impedance in a pediatric population.
Main Methods:
- Utilized the Hering-Breuer reflex with end-inspiratory airway occlusion to induce brief apnea in five sedated infants (9-16 months).
- Employed a computer-controlled system to deliver mechanical breaths and apply airway occlusion via a face mask.
- Connected a loudspeaker-in-box system to deliver pseudorandom oscillations (0.5-20.75 Hz) for 6 seconds, measuring Zrs.
- Analyzed averaged Zrs spectra using a model incorporating airway resistance (Raw), inertance (Iaw), and tissue damping (G) and elastance (H).
Main Results:
- Consistent Zrs data fitting the model were obtained up to 15 Hz with a low average fitting error (0.89 ± 0.11 cm H2O·s/L).
- Key respiratory parameters were quantified: Raw = 10.0 ± 2.1 cm H2O·s/L, Iaw = 0.061 ± 0.014 cm H2O·s²/L, G = 28.6 ± 4.9 cm H2O/L, H = 141 ± 55 cm H2O/L.
- Tissue hysteresivity (G/H) was determined to be 0.218 ± 0.061, indicating measurable tissue mechanical properties.
Conclusions:
- Short apneic periods, evoked by the Hering-Breuer reflex, are sufficient for collecting reliable low-frequency Zrs data in sedated infants.
- This technique effectively partitions respiratory impedance into airway and tissue components, offering valuable insights into infant pulmonary mechanics.
- The findings support the use of this non-invasive method for detailed respiratory system assessment in infants, aiding in clinical diagnosis and research.
Abstract:
Low-frequency respiratory impedance (Zrs) data permit the separate estimation of the mechanical properties of the airways and the tissues, but they are difficult to collect in humans because of the need for apneic conditions. We exploited the apneic phase produced by invoking the Hering-Breuer reflex with end-inspiratory airway occlusion in five sedated infants aged 9 to 16 mo. A computer-controlled pump and solenoid valves were used to inflate the supine infants through a face mask to a transrespiratory pressure of 20 cm H2O and to affect the airway occlusion. A loudspeaker-in-box system was connected to the mask through a side-arm, and small-amplitude pseudorandom oscillations containing 23 frequency components between 0.5 and 20.75 Hz were applied for 6 s. Four consecutive measurements were made in each infant, and the averaged Zrs spectra were evaluated on the basis of a model containing the frequency-independent resistance (Raw) and inertance (law) of the airways, and the viscous damping (G) and elastance (H) parameters of the constant-phase compartment of the chest wall and parenchymal tissues. The measured Zrs values were consistent with the model up to 15 Hz, and the average fitting error was 0.89 +/- 0.11 (SD) cm H2O.s/L. The following parameter values were obtained: Raw = 10.0 +/- 2.1 cm H2O.s/L, law = 0.061 +/- 0.014 cm H2O.s2/L, G = 28.6 +/- 4.9 cm H2O/L, H = 141 +/- 55 cm H2O/L. The tissue hysteresivity (G/H) values were 0.218 +/- 0.061. Our results indicate that, in short apneic periods evoked by the Hering-Breuer reflex, reliable low-frequency Zrs data can be collected to partition the tissue and airway impedances in sedated infants.