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Mechanical aspects of chest wall distortion
Journal of Applied Physiology (Bethesda, Md. : 1985)
|August 1, 1985
Summary
Respiratory system distortion significantly reduces tidal volume (VT) during spontaneous breathing, decreasing it to about half of the passive inflation value in rats and infants. This indicates that the relaxation curve reflects compensated, not absent, distortion.
Area of Science:
- Respiratory Physiology
- Comparative Physiology
Background:
- During passive breathing, rib cage (RC) expansion correlates with applied pressure (Pab).
- Similarities in Pab-tidal volume (VT) relationships during passive and spontaneous breathing depend on equal Pab action on RC or compensatory muscle action.
Purpose of the Study:
- To investigate the relationship between abdominal pressure (Pab) and tidal volume (VT) during passive and spontaneous breathing.
- To determine the extent of rib cage (RC) distortion during spontaneous breathing in rats and infants.
Main Methods:
- Passive VT-Pab relationships were established in anesthetized rats and sleeping infants by occluding airways during expiration.
- Active breathing VT was measured and compared to passive VT at equivalent Pab or abdomen motion (AB) levels.
Main Results:
- In rats and infants, spontaneous breathing VT was significantly lower (55% and 49%, respectively) than passive VT for a given Pab.
- Phrenic stimulation in rats showed VT close to spontaneous breathing, suggesting diaphragm dominance.
- Occasional breaths with large RC expansion matched or exceeded passive VT at iso-Pab.
Conclusions:
- Rib cage distortion during spontaneous breathing reduces VT to approximately half of the passive volume.
- Respiratory system behavior on the relaxation curve signifies compensated distortion, not its absence.