2 Mechanics of Breathing Flashcards
Goals of Respiration
- distribute air & blood flow for gas exchange
- provide oxygen to tissues
- remove carbon dioxide from tissues
- maintain homeostasis for metabolic needs
Functions of Respiration
- mechanics of pulmonary circulation
- diffusion of O2 and CO2 between alveoli and blood
- transport of O2 & CO2 to and from tissues
- regulation of ventilation & respiration
External Respiration
- mechanics of breathing
- movement of gases
- gas transfer to lungs & tissues
- maintain body & cellular homeostasis
Internal Respiration
- intracellular oxygen metabolism
- cellular transformation
- Krebs cycle –> aerobic ATP generation
- mitochondria - O2 utilization
Ventilation goal
- to maintain an optimal composition of alveolar gas
- inspiration & expiration provide stable alveolar environment
Lung Physiology
~1.5% body weight
- alveolar tissue makes up 60% of lung
- 10% total blood volume resides in lungs
Alveoli Physiology
- very large surface area
- 40 times external body surface area
What changes alveolar pressure?
change in pleural pressure
Inspiration
- active phase
- pressure in alveolar ducts decreases
- it is negative pressure inhalation
Phrenic Nerve
- inspiratory
- innervated diaphragm
- C3-5
Intercostal Nerves
- T1-11
- innervate external intercostal muscles (EIM)
Diaphragm
- 75% of inspiratory effort
- contracts during inhalation –> abd contents forced down
- avg. movement down 1 cm during inspiration, can go 10 cm during forced inspiration
- paradoxical movement when denervated
Transdiaphragmatic Pressure
-effect of abdominal pressure on the chest wall mechanics is transmitted across the diaphragm
What physiological states can reduce FRC?
any state in which abdominal pressure is exerted on diaphragm
External Intercostals (EIM)
- 25% of inspiratory effort
- connect adjacent ribs
- contraction pulls ribs upward and outward
- paralysis/spinal - pt will feel as if they’re not breathing
Accessory Muscles
-assist with forced inspiration during periods of stress
Scalene Muscle
- accessory muscle
- attached cervical spine to apical rib
- elevates first 2 ribs during forced
Sternocleidomastoid Muscle
- accessory muscle
- attached base of skull to top of sternum and clavicle
- raises sternum during during inspiration
Expiration
- passive phase of breathing cycle
- chest muscles relax
- elastic recoil
- active during hyperventilation & exercise
Rectus Abdominus/abdominal obliques
-contraction raises diaphragm upward
Internal intercostal muscles
- assists by pulling ribs downward and inward
- exhalation
Transpulmonary Pressure
- pressure difference between alveolar pressure and pleural pressure
- alveoli more likely to collapse in children
Recoil Pressure
elastic forces which tend to collapse the lung during respiration
Pleural Space
visceral - thin serosal membrane that envelopes lungs
parietal - lines inner chest wall, diaphragm & lat mediastinum
Pleural Fluid
- lubrication between membranes
- maintains surface tension
- lymphatic draining maintains constant suction on pleura (-5 cmH20)
Pleural Pressure
- The pressure of the fluid in the space between the lung pleura (viscera) and the chest wall pleura (parietal)
- NEGATIVE! - if not, you’ve got a problem
TLC
total lung capacity
TLC = IRV + TV + ERV + RV
~ 5500 ml
VC
vital capacity
VC = IRV + TV + ERV
~ 4500 ml
IRV
inspiratory reserve volume
~2500 ml
ERV
expiratory reserve volume
~1500 ml
RV
residual volume
~ 1000 ml
IC
inspiratory capacity
IC = TV + IRV
~ 3000 ml
TV
tidal volume
avg 500 ml
FRC
functional residual capacity
FRC = ERV + RV
~ 2500 ml
Can spirometry measure RV?
No, FRC & TLC cannot be determined
Lung Compliance
- measure of lungs distensibility
- compliance = change in lung volume / change in lung pressure
I:E ratio
inspiration : expiration
normal 1:2
Elastic lung tissue…
- elastin & collagen fibers of lung parenchyma
- natural states is contracted coils
- elastic force generated when returning to coiled state
Surface air-fluid interface
2/3 of total elastic force in the lung
Surfactant
-synthesized fatty-acid product of type II pnuemocytes
DPPC
- dipalmitoyl phsphatidyl choline
- strongest surfactant molecule in surfactant mixture
- hydrophobic & hydrophilic opposing ends
Total Ventilation / Minute Ventilation
-total volume of air conducted into lungs per minute
Alveolar Ventilation
- volume of fresh air entering alveoli each minute
- steady state is achieved when supply matches demand
Anatomical Dead Space
~30% of TV
Wasted ventilation
- deviation from ideal ventilation relative to blood flow
- air available, blood not so much –> contributes to dead space
- ventilation/blood mismatch –> V/Q mismatch
Closing Volume & FRC
is the closing volume of the lung, at which small airways close, is greater than FRC, then small airways collapse –> atelectasis
Bernouli Effect
explains airway collapse
Laminar Flow
- parallel streams of flow
- velocity at center is 2x as fast
Poiseuille’s Law
describes resistance to flow through tube
- reducing radius by 16% –>double resistance to flow
- reduce radius by 50% –> increase resistance 16 fold
Ohm’s Law
P = F x R
Turbulent Flow
- tends to occur at higher flow rates
- pressure is no longer proportional to flow
- increase in density, velocity or resistance –> turbulence is more probable
Airway Resistance
- chief site is medium sized bronchi
- factors: lung volume, bronchial smooth muscle, density & velocity of inspired gas
Causes of bronchoconstriction
PSN, acetylcholine, low PCO2, direct stim, histamine, cold
How does gas density effect airway flow resistance
higher density = increased resistance to flow
What measures work of breathing
W = PxV
oxygen consumption - hyperventilation increases
