Dynamic Mechanics of Breathing Flashcards
What are dynamic mechanics of breathing?
mechanical properties affecting flow of air into and out of lung as volume changes with time
What are the forces of the dynamic mechanics?
resistance
flow
turbulence
What is the equation for flow?
Flow = deltaP/R
What is the equation for resistance?
R=8nl/pi r4
Why is the resistance of small tubes actually lower?
the cumulative resistance is actually lower despite the smallest tubes having greater resistance
What is the airflow resistance factor in the trachea?
100%
What is the airflow resistance factor in the 17th branch?
0.9%
What are the factors determining resistance in the airway?
lung volume and branching
bronchiolar smooth muscle tone
density and viscosity of gases
What is the density and viscosity of gases affected by?
altitude
What decreases the radius of bronchiolar smooth muscle?
parasympathetic activity
ACh
Irritants
Decreased alveolar PCO2
What increases the radius of the bronchiolar smooth muscle?
sympathetic activity
pulmonary stretch
NAdr
Adr B2-adrenoceptors
What is the issue with asthma and resistance?
contraction of parabronchial smooth muscle raises upper airway resistance
What happens to the molecular diffuse rate and what does this cause in asthamatics?
molecular diffusion rate in upper airway slows and results in poor gas exchange in the respiratory acinus
What causes the alveolar pCO2 to rise in asthmatics?
gas fails to penetrate the distal regions of the respiratory zone
What causes the asthmatic wheeze?
increased turbulence in the airway
What is the asthmatic wheeze complicated by?
dichotomous branching causing turbulence
What is used to measure airway resistance?
whole body plethysmography
How is the plethysmography system calibrated?
have the subject breathing against a closed shutter
How is airway resistance calculated from the plethysmography?
R = deltaPa/V
What values are V and Pa during expiration?
both are positive
What is used to calculate the negative deltaPa during inhalation?
the positive deltaPbox
What is used to measure V?
pneuomotachometer
What value is V when inhaling?
negative
WHat happens to resistance during inhalation?
resistance falls as gas flow and lung volume increase
What does the increased resistance do during exhalation?
helps to keep airway pressure high to maximise gas movement out of alveoli
What does smooth muscle contraction cause?
dynamic compression leading to upper airway resistance
What can dynamic compression be compared to?
squeezing a toothpaste tube with the lid still on and then releasing the lid
What does upper aireway resistance do?
helps gas clearance from the alveoli
What do you see in moderate COPD?
inhalation and exhalation are both a bit fuzzy
larger resistance change between inhalation and exhalation
-15 to 15cmH2O
What is normally seen in an inhalation exhalation cycle?
pressure change from -5 to 5cmH2O
What is seen in severe COPD?
normalish inhalation phase to +5cmH2O
exhalation phase is fuzzy and tends to fail due to increased resistance
What can be seen over time with moderate COPD?
high resistive pressure during inhalation and exhalation
What can be seen over time with severe COPD?
nearly normal resistive pressure during inhalation and very deep resistive pressure during exhalation
What happens in COPD?
alveoli destruction
reduced surface area
reduced elasticity
What work is involved in breathing?
the energy required to overcome the elastic and non-elastic resistances
What are the equations involved in work?
Work = force * distance Work = pressure * volume
What work is required during inspiration?
energy input required to overcome elastic component
energy input required to overcome surface tension
What work is involved in exhalation?
energy input to overcome airway and tissue resistance
What work can be expected from normal breathing?
540ish
What work can be expected from panting?
672 - surface tension and airway resistance, dynamic compression
What work can be expected from deep breathing?
660 - overcoming the elastic component
