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Pressure-volume relations of the respiratory system in healthy children
A Thorsteinsson1, A Larsson, C Jonmarker
1Department of Anesthesia, University Hospital, Lund, Sweden.
Insights
Respiratory system pressure-volume (P-V) curves in children show significant changes with growth. Maximum respiratory system compliance (Crsmax) correlates with length, and specific compliance decreases with age.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Anesthesiology
Background:
- Understanding respiratory mechanics in children is crucial for clinical management.
- Static pressure-volume (P-V) curves provide insights into lung compliance and elasticity.
- Limited data exists on P-V relationships across a wide pediatric age range.
Purpose of the Study:
- To characterize static pressure-volume (P-V) relationships of the respiratory system in healthy children aged 1 month to 16 years.
- To investigate how respiratory system compliance and lung volumes change with growth.
- To determine the lung volume at which maximum compliance occurs in relation to total lung capacity (TLC).
Main Methods:
- Obtained static P-V curves during anesthesia and muscle paralysis in 48 healthy children.
- Used an airway interrupter technique to measure pressure and calculate volume changes during deflation.
- Measured functional residual capacity (FRC) using tracer gas washout and plotted P-V curves assuming FRC at zero pressure.
Main Results:
- Maximum respiratory system compliance (Crsmax) strongly correlated with child length (Crsmax = 7.7 x 10(-4) x length^2.38).
- The pressure at Crsmax was lower in infants (6 cm H2O) than older children (12 cm H2O).
- Total lung capacity (TLC) per kg body weight increased with age, and the FRC/TLC ratio was higher in infants.
Conclusions:
- Respiratory system P-V relationships change significantly with growth, particularly in the first year of life.
- The lung volume (%TLC) at which maximum compliance occurs remains relatively constant across all ages studied.
- Specific compliance (Crsmax/TLC) decreases with age, indicating changes in lung elasticity relative to lung size.
Abstract:
Static pressure-volume (P-V) curves of the respiratory system were obtained in 48 healthy children (1 mo to 16 yr of age) during anesthesia and muscle paralysis. The lungs were inflated to a pressure of 25 to 40 cm H2O, and during the subsequent deflation an interrupter placed in the airway tubing opened and closed every 0.16 s. Airway flow was integrated to obtain the volume decrement between consecutive flow interruptions. Airway pressure was measured during interruptions, and a curve relating pressure to lung volume was plotted, assuming the lung volume at zero pressure to equal functional residual capacity (FRC). FRC was measured using tracer gas washout. The maximum slope of the P-V curve (maximum compliance = Crsmax, ml/cm H2O) was closely related to length (in centimeters) of the child: Crsmax = 7.7 x 10(-4) x length2.38; r = 0.97. The pressure coinciding with Crsmax was 6 +/- 1 cm H2O (mean +/- SD) in infants (1 to 6 mo of age) and 12 +/- 1 cm H2O in older children (> 1.5 yr of age). Total lung capacity (TLC) per kg body weight increased with age and was 52 +/- 13 ml/kg in infants and 87 +/- 11 mg/kg in older children. The FRC/TLC ratio was greater in infants (38 +/- 4%) than in older children (30 +/- 5%). The lung volume coinciding with Crsmax was nearly the same at all ages, when expressed as a percentage of TLC: 62 +/- 3%. Specific compliance of the respiratory system, that is, Crsmax/TLC, decreased with growth and was 0.044 +/- 0.006 cm H2O-1 in infants and 0.035 +/- 0.004 cm H2O-1 in older children. It is concluded that although the P-V relations of the respiratory system changed markedly with growth, especially during the first year of life, the lung volume (%TLC) at which maximum compliance occurred varied little.