Briefly describe the factors that affect lung compliance.

[Click here to toggle visibility of the answers]

College Answer

Main points/concepts expected in answer.

  • Surfactant • increases lung compliance • decreases surface tension at alveolar air -water- interface •prevents small alveoli from collapsing •accounts for most of hysteresis in intact lung
  • Lung elastic recoil • lung compliance changes in disease states
  • Lung volume • lung compliance greatest around FRC • lung compliance reduced at low and high lung volumes • gravitational effects on regional lung compliance
  • Pulmonary blood volume • pulmonary venous congestion reduces lung compliance
  • Lung size • specific compliance = lung compliance / FRC
  • Dynamic lung compliance • influenced by airways resistance • lung compliance measured during normal breathing • less than static lung compliance • frequency dependence

Discussion

This brief but comprehensive examiner comment should serve as some sort of benchmark for what the rest of them should look like. Even though the pass rate for this question was 14%, the examiners did not waste time lamenting the intellectual poverty of their trainees. They just gave you the answer they expected, and left you to lambast yourself for getting it wrong. 

There is little one can do to improve on the college answer. Using the Part One compliance section as a guide, the following tabulated alternative was produced:

Factors which Affect Respiratory Compliance
Lung complianceChest wall compliance

Increased  lung compliance

  • Lung surfactant
  • Lung volume: compliance is at its highest at FRC
  • Posture (supine, upright)
  • Loss of lung conective tissue associated with age
  • Emphysema

Increased chest wall complance

  • Ehler-Dahlos syndrome and other connective tissue diseases associated with increased connective tissue elasticity
  • Rib resection
  • Cachexia
  • Flail segment rib fractures
  • Open chest (eg clamshell)

Decreased static lung compliance

  • Loss of surfactant (eg. ARDS)
  • Decreased lung elasticity
    • Pulmonary fibrosis
    • Pulmonary oedema
  • Decreased functional lung volume
    • Pneumonectomy or lobectomy
    • Pneumonia
    • Atelectasis
    • Small stature
  • Alveolar derecruitment
  • Alveolar overdistension

Decreased dynamic lung compliance

  • Increased airway resistance (eg. asthma)
  • Increased air flow (increased resp rate)

Decreased chest wall compliance

  • Structural abnormalities
    • Kyphosis / scoliosis
    • Pectus excavatum
    • Circumferential burns
    • Surgical rib fixation
  • Functional abnormalities
    • Muscle spasm, eg. seizure or tetanus
  • Extrathoracic influences on chest/diaphragmatic excursion
    • Obesity
    • Abdominal compartment syndrome
    • Prone position

References

References

Harris, R. Scott. "Pressure-volume curves of the respiratory system." Respiratory care 50.1 (2005): 78-99.

Mead, Jere, and James L. Whittenberger. "Physical properties of human lungs measured during spontaneous respiration." Journal of Applied Physiology 5.12 (1953): 779-796.

Lutfi, Mohamed Faisal. "The physiological basis and clinical significance of lung volume measurements." Multidisciplinary respiratory medicine 12.1 (2017): 3.

Rahn, Hermann, et al. "The pressure-volume diagram of the thorax and lung." American Journal of Physiology-Legacy Content 146.2 (1946): 161-178.

Bunta, Emil. "The Relation of Intrapleural Pressure and Pulmonary Collapse in Artificial Pneumothorax." American Review of Tuberculosis 33.2 (1936): 203-214.

Hurtado, Alberto, et al. "Studies of total pulmonary capacity and its Sub-divisions. Vi. Observations on cases of obstructive pulmonary emphysema." The Journal of clinical investigation13.6 (1934): 1027-1051.

Morgan, Thomas E. "Pulmonary surfactant." New England Journal of Medicine 284.21 (1971): 1185-1193.

von Neergaard, Kurt. "Neue Auffassungen uber einen Grundbegriff der Atemmehanik: die Retraktionskraft der Lunge, abhagig von der Oberflachenspannung in den Alveolen." Z. Gesamte Exp. Med. 66 (1929): 373-394.

Radford Jr, E. P. "Static mechanical properties of mammalian lungs." Handbook of physiology 1 (1964): 429-449.

Lachmann, B., B. Robertson, and J. Vogel. "In vivo lung lavage as an experimental model of the respiratory distress syndrome." Acta anaesthesiologica Scandinavica 24.3 (1980): 231-236.

Escolar Castellón, J. de D. "Lung histeresis: a morphological view." Histology and histopathology (2004).

Guyatt, A. R., et al. "Reproducibility of dynamic compliance and flow-volume curves in normal man." Journal of applied physiology 39.3 (1975): 341-348.

Katsoulis, K. Konstantinos, Konstantinos Kostikas, and Theodore Kontakiotis. "Techniques for assessing small airways function: Possible applications in asthma and COPD." Respiratory medicine 119 (2016): e2-e9.

Kannangara, Oliver, Jennifer L. Dickson, and J. Geoffrey Chase. "Specific compliance: is it truly independent of lung volume?." IFAC-PapersOnLine 51.27 (2018): 299-304.