Mechanics of Breathing/Compliance Flashcards Preview

CVPR: Pulmonary > Mechanics of Breathing/Compliance > Flashcards

Flashcards in Mechanics of Breathing/Compliance Deck (11)
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Muscles involved in inspiration

  • diaphragm: contracts dome of muscle downward during inspiration
  • external intercostals: pull ribs forward and outward
  • accessory muscles: silent during normal breathing; elevate rib cage during icnreased respiratory load
    • sternomastoids
    • scalenes


Muscles involved in expiration

  • normal breathing = passive; no muscle contraction neccessary
  • active expiration is neccesary @ higher minute volumes
    • abdominal wall muscles: push diaphragm up w/contraction
    • internal intercostals: pull ribs downward and inward w/contraction


Diaphragmatic muscle fxn in disease states

  • force generated by diaphragm is a function of length
    • max forces @ 130% of resting length
    • tension generated decreases w/decreased length
  • COPD diseases: breathing occurs @ increased lung volumes --> diaphragm is more contracted/shorter = mechanical disadvantage


Intrapleural pressure definition (PIP)

  • pressure w/in the intrapleural space
  • source of PIP is the intrinsic elastic properties of the lung and the chest wall + lung/chest wall deviate from intrinsic positions if separate

    • ​lungs = more inflated 

    • chest wall = more deflated

  • ​opposing forces ==> negative PIP (vacuum-like) force that acts to essentially connect lungs to chest wall


Intrapleural pressure during inspiration/expiration

  • PIP is negative throughout breathing cycle
  • PIP = ~ -5 cm H2O @ end of expiration 
  • PIP = ~ -30 cm H2​O @ end of inspiration
    • increased pressure b/c lung tends to recoil towards intrinsic deflated position and exerts force on intrapleural space
  • P= pressure w/in lung ==> must reach negative values in order to inspire
    • PIP increase in negativity due to lung inflation allows this to happen


Transpulmonary pressure (PTP) definition

  • PTP = P- PIP


Elastic recoil pressure definition

  • during expiration ==> lung has inherent tendency to recoil back towards intrinsic equilibrium position
  • recoil ==> transient positive pressure = "elastic recoil pressure"


Compliance (C) definition

  • C = measure of elastic properties of the lung
  • C = [V2 - V1] / [P2 - P1] = "change in volume per unit change in pressure"
  • determined by plotting volume of air as function of PTP
  • inversely proportional to elasticity (i.e. high compliance = low elasticity)


Hysteresis definition

  • compliance differs w/inspiration and expiration
  • greater change in PTP pressure to produce a given volume change during inspiration
  • property of all elastic structures
  • due to combo of elastic properties and surface forces on pulmonary cells


Impacts of abnormal lung compliance

  • fibrosis ==> low compliance ==> difficult inspiration
  • emphysema ==> loss of elastic tissue ==> loss of elastic tissue/high compliance ==> difficult expiration


Abnormal chest wall impacts on breathing

  • chest wall must move properly in order to breath properly 
  • abnormalitys ==> reduction in volume change during breathing (tidal volume)
  • reduced tidal volume ==> reduced air flow in lungs