2.3 Mechanics of Breathing Flashcards
how are respiratory pressures described
- relative to atmospheric pressure pressure exerted by air surrounging the body)
atm = 760 mm Hg
negative resp pressure: less than Patm
Positive resp pressure: greater than Patm
Zero resp pressure: equal to Patm
what is intrapulmonary pressue
– Pressure in alveoli (also called intra-alveolar pressure)
– Fluctuates with breathing and always eventually equalizes with Patm
what is intrapleural pressure
Pip
- Pressure in pleural cavity (fluctuates with breathing)
** Always a negative pressure (
- > Usually ~4 mm Hg less than Ppul
- fluid level must be kept at a minimum -> excess is pumped out by lymphatic system
- if fluid accumulates, positive Pip pressure develops and lung collapses
what promotes lung collapse
*tlaking about intrapleural pressue
- two inward forces promtoe lung collape
1. Lungs’ natural tendency to recoil because of elasticity *lungs want to assuem smallest size)
2. Surface tension of alveolar fluid pulls on alveoli to try and reduce alveolar size
what forces promtoe lung collapse
- Lungs natural tendency to recoil bc of elastcity
- Surface tension`of alveolar fluid pulls on alveoli to try reduce alveolar size
* elasticity in chest wall pulls thorax outward (tends to enlarge lungs)
- Negative Pip is affected by these opposing forces but is maintained by strong adhesive force between parietal and visceral pleurae
*thoracic cavity prevents it from collapse countering tendence to recoil and surface tension
What is transpulmonary presure
* ALWAYS -ve, usually -4 mmHg
- raspulmonrary pressure = Ppul - Pip
- pressure that keep lung spaced open and keeps lungs from collapse
- greater transpulmonary pressure, the larger the lungs weill be -> more neg = larger lungs
• Negative Pip must be maintained to keep lungs inflated
Lungs will collapse if Pip = _____
• Pip =Ppul or Pip =Patm
what are the 4 pressues to know
- atmospheric pressue Patm = 0 mmHg aka 760 mmHg
Intraplural pressure Pip -4mmHg (756 mmHg)
- transpulmonary pressure 4mm Hg (diff between atm and -4mmHg)
intrapulmonary pressure Ppul mmHg
effects of changes in volume and changes in pressure on ventilation
– Volume changes lead to pressure changes
– Pressure changes lead to flow of gases to equalize pressure
boyles law
Gases always fill the container they are in
– Pressure (P) varies inversely with volume (V)
P1V1 = P2V2
describe quiet inspriation
Active process involving inspiratory muscles (diaphragm and external intercostals)
- action of diaphragm: contracts and moved inferiorly, flattens -> INC thoracic voume
intercoastal muscles: external contract, rib cage is lifted up and out -> INC thoracic volume
- lungs are stretched as they are pulled out with thoracic cage causing intrapulmonary pressure to drop by 1mmHg (becomes more negative
*Ppul < Patm
- air flows into lungs, down its pressure gradient until Ppul = Patm
- Pip lowers to 6mm Hg less than Patm
describe forced deep inspirations
- can occur during vigorous excercise or in ppl wtih COPD
- activates accessory muscles: Scalenes, sternocleidomastoid, and pectoralis minor (plus external intecostals and diaphagm)
*Erector spinae muscles of back also help to straighten thoracic curvature
- act to further inc thoracic cage size, create larger pressure gradient so more air is drawn in
describe quiet expiration,
typically passive
- inspiratory msucles relax, thoracic cavity volume decreases and lungs recoil
- Volume decrease causes intrapulmonary pressure (Ppul) to increase by +1 mm Hg
- Ppul > Patm so air flows out of lungs down its pressure gradient until Ppul = Patm
describe forced expiration
active process that uses oblique & transverse abdominal muscles, as well as internal intercostal muscles
intrapulmonary and intrapleural pressure during ventilation
- intrapulmonary:
- inspiration: pressure inside lung decreases as lung volume increases
- during expiration: pressure increases
- intrapleiral pressure
- inspiration: pleural caity pressure becomes more negative as chest wall expands
- returns to intial vlaue as chest wall recoils
volume of breathe during ventilation
0.5L of air moves into and out of lungs in each breath
what are the factors that affect pulmonary ventilation
- three physical factors the ease of air passage and amount of energy required for ventilation
- ariway resitance
- alveolar surface tension
- lung compliance
what is airway resistance
- caused by frication: major nonelastic source of resistance to gas flow’ occurs in airways
Relationship between flow (F), pressure (deltaP) and resistance (R) F=P/R
*deltaP = pressure gradient btwn atm and alveoli
why is airway resistance usually insignificant
- Diameters of airways in first part of conducting zone are huge
- progressive branching of airways as they get smaller leads to an increase in total croos sectional area
- any resitance usually occurs in medium sized bronchi
- resistance disappears at termianl bronchioles where diffusion is what drives gas movement
describe alveolar suface tension
- attraction of liquid molecules to one another at a gas-liquid interface
- > tendsto draw liquid molecules closer together and reduce contact with dissimilar gas molecules
- > Resists forces that increase surface area of liquid
*Water has a very high surface tension and tends to cause alveoli to shrink to smallest size/ collapse
what is surfactant
what produces it
detergent-like lipid and protein complex that helps reduce alveolar surface tension of alveolar fluid
- prevents alveolar collapse
- produced by type II alveolar cells
what is infant respiratory distress syndrome (IRDS)
how do you treat it?
Insufficient quantity of surfactant in premature infants
- results in collapse of alveoli after each breath
- treatment: spraying natural or synthetic surfactant into newborns air passages
- > Positive pressue devices also help alveoli open betwen breaths
- > severe cases may require mechanical ventilation
*Survivors of mechanical ventilation may develop bronchopulmonary dysplasia, chronic childhood lung disease
describe lung compliance
Measure of change in lung volume w/ given change in transpulmonary pressure
*how much stretch lung has
- norally high bc of distensibility of lung issue and surfactant (dec alveolar surface tension)
*high lung compliance means easier for lugns to expand
mathematical representation of lung compliance
ΔCL =ΔVL/ Δ(Ppul - Pip)
ΔCL equals compliance
ΔVL equals change in lung volume,
Δ(Ppul - Pip) equals change in transpulmonary pressure
