mechanics of breathing pressures and work Flashcards
what is the shape of the diaphragm
large dome-shaped muscle
what is the function of the diaphragm
active muscle in breathing
what are the 3 major apertures of the diaphragm
- IVC at T8
- esophagus at T10
- aorta at T12
- I ate 10 eggs at noon
what are the posterior attachments of the diaphragm
attaches posteriorly to L1 and L2 via left and right cura or tendinous extensions
what is the arcuate ligament
left and right cura come together to form arch
what are the anterior attachments of the diaphragm
bottom of the sternum
what are the lateral attachments of the diaphragm
- ribs 6-12 and costal cartilages
- forms costal part of diaphragm
what is the innervation of the diaphragm
- cervial segments (C3,4,5)
- creates phrenic nerve
C345 keeps the diaphragm alive
- creates phrenic nerve
what does the phrenic nerve do
contains motor and sensory nerve fibers to support the diaphragm
what do the lower thoracic nerves do
lower thoracic nerves innervate the periphery
what happens to the diaphragm during expiration
relaxed and reaches 5th thoracic segment
what happens to the diaphragm during inspiration
contracts downwards
what happens to the lungs during inspiration
- lung has elastic recoil that is inwardly directed
- inspiration causes a negative pressure within the alveoli which allows air to rush into the lungs
what do the intercostals as a whole do during inspiration
they stiffen the chest wall and prevent intercostal spaces from being sucked inwards
what does the external intercostals do during inspiration
assists the expansion during inspiration by increasing the antero-posterior and lateral diameter of the thorax
what do the internal intercostals do during expiration
decreasing thoracic volume
what do scalene muscles from the cervical vertebrae to the first rib and the sternocleidomastoid do
help elevate the rib cage
what does the anterior abdominal wall do during inspiration
muscles relax to allow for full descent of the diaphragm during inspiration and contract during forced inspiration
how does bronchial circulation return to the heart
azygos or pulmonary vein
what is respiration
respiration describes the exchange for CO2 for O2 deep in the lungs and tissues
what is ventilation
ventilation describes the process by which we move air into and out of the lungs for gas exchange
what do accessory muscles do
accessory muscles of respiration are recruited to generate extra force, required to move the large volumes of air during deep breathing
what are the accessory muscles of expiration
Rectus and transversus abdominis and the internal and external obliques- expiration
what is intrapleural pressure
intrapleural pressure is the pressure within the pleural space
what is the pleural space
Pleural space is the visceral pleura lining long in the parietal pleura lining the chest wall
what is the intrapleural pressure under normal conditions
negative
what is the alveolar pressure
pressure within the alveoli
what is the alveolar pressure during inspiration
negative
what is the alveolar pressure during expiration
positive
what is the alveolar pressure when there is no air movement
equal/0
what is the alveolar pressure when there is no air movement
equal/0
what is transpulmonary pressure
It is the difference between the pressure inside and outside of a system
how do you calculate transpulmonary pressure
It is calculated by subtracting the intrapleural pressure from that Alveolar pressure
why must transpulmonary pressure be positive
for the alveoli and the lung to expand
what is Boyle law
- As volume of the close system increases the pressure decreases
- As volume of the close system decreases, the pressure increases
what happens to the alveolar pressure when the diaphragm contracts
the alveolar volume expands and the Alveolar pressure decrease.
Once the pressure has become negative air flows into the alveoli
what happens to alveolar pressure when expiration occurs
Expiration occurs when the diaphragm relaxes in the alveoli volume decreases, so the pressure increase
what is minute ventilation (VE)
calculates the total volume of gas entering the lungs per minute
how do you calculate VE
VE= Vt(tidal volume) x RR (resp rate)
what is dead space
Dead space ventilation is a volume of gas that does not participate in respiration
where does dead space ventilation occur
- It occurs in the conducting (bronchial tree) and respiratory (alveoli) zones
what is anatomical dead space
anatomical dead space consists of the areas of the lungs that are structurally, incapable of gas exchange e.g. trachea, bronchi, and the terminal bronchioles
what is alveolar dead space
Alveolar dead space consists of the alveoli that cannot participate in gas exchange, due to insufficient perfusion
what is alveolar ventilation
alveolar ventilation (Va) is the rate of air that reaches the alveoli and participates in ventilation
how do you calculate alveolar ventilation (Va)
- Va-(Vt-Vd) x RR
- Vd is physiologic dead space
what is Vd/Vt
Vd/Vt is the ratio of dead space to tidal volume
how do you calculate Vd/Vt
Vd/Vt = (PaCO2 - PeCO2) / PaCO2
what is PaCO2
is the partial pressure of carbon dioxide in the arterial blood
what is PeCO2
PeCO2 is the partial pressure of carbon dioxide in the expired (exhaled) air.
what is cellular respiration
Metabolism of nutrients in cells (Kreb’s cycle) consuming O2 and releasing CO2
what is Tidal Volume (VT)
volume of each breath
what is the mechanics of inspiration
- Intercostal muscles elevate and evert the ribs
- Diaphragm moves downward
- Scalene muscles (inserted into the first 2 ribs) raise the upper ribs and push the sternum forward
- Sloping lower ribs rise and move out
what is bucket handle action
Sloping lower ribs rise and move out = the bucket handle action and the transverse diameter of the chest wall ↑
what is pump action
Scalene muscles (inserted into the first 2 ribs) raising the upper ribs and push the sternum forward (pump action) and ↑the A-P diameter of the thoracic cavity
what happens at the end of inspiration
recoil of lungs and chest wall
what kind of ventilation usually occurs for adults at rest
diaphragmatic
what is the overall action of muscles during inspiration
- Diaphragm contracts
- Intercostal muscles contract
- Bucket-handle
- Scalene muscles contract
- Sternum rises
- This causes AP expansion of the thoracic cavity
is expiration an active or passive process
passive
why does expiration occur
Occurs due to elastic recoil of the lungs and the chest wall
what is the pressure like during expiration
During expiration, both intrapleural pressure and alveolar pressures rise
what is required during forced expiration
Forced expiration(eg coughing/sneezing) requires contraction of the abdominal walls which push the diaphragm upward
what type of pressure determines wether air will enter or leave the lungs
intra-alveolar
why does intrapleural pressure not equilibrate with the atmosphere
pleural space is closed and fluid filled.
how does the chest wall affect pressure
Chest wall exerts a distending pressure on the pleural space which is transmitted to the alveoli to increase their volume, lower the pressure, and generate airflow inwards
what does distending mean
swell or cause to swell by pressure from inside.
what is the transpulmonary pressure equal and opposite to
elastic recoil pressure of the lungs
So it sucks the lungs out and sucks the lungs back in, ensuring the lungs don’t collapse
what is functional residual capacity (FRC)
FRC = the volume of air left in the lungs at the end of a normal breath
what are the respiratory muscles like at FRC
relaxed and the lungs and chest wall recoil in opposite directions
what is the recoil like at FRC
the outward recoil of the chest wall exactly balances the inward recoil of the lungs
what is the volume of air determined by at FRC
the elastic properties of the lungs and the chest wall
what affects FRC
- Pulmonary fibrosis: lungs are stiff and small, ↑ elastic recoil, then FRC is ↓
- Emphysema: loss of alveolar tissue and ↓ elastic recoil, then FRC is ↑
what is impedance
Impedance = Frictional Airway Resistance and Elastic Resistance to stretching of the lungs and chest wall
what are the elastic forces on the lungs
To breathe in, the inspiratory muscles contract to overcome the impedance offered by the lungs and chest wall
what is lung compliance
the ability of the lungs to stretch and recoil during ventilation (CL = change in lung volume/unit change in distending pressure)
what is the distending pressure
is the pressure difference across the lung = alveolar-intrapleural pressure
what is the mechanics of compliance
- On exhalation, there is elastic recoil of lungs
This is balanced by the tendency of chest wall to recoil in opposite direction - At end of quiet expiration, the pressures balance
what is static pressure
- The curve flattens as the lung volume approaches TLC. The inspiratory curve is slightly different from the expiratory curve = hysteresis
- Hysteresis is a common property of elastic bodies
- Static lung compliance is the slope of the steepest part of this curve (just above FRC)
how is the dynamic pressure-volume loop obtained
from continuous measurements of intrapleural pressure and volume during a normal breathing cycle.
how do you find the dynamic pressure-volume loop
- At the end of inspiration and expiration, airflow and alveolar pressures are zero
- The slope of the line joining these points is dynamic compliance
when is dynamic pressure different to static compliance
in lung disease- stiff lungs
when is the lung less compliant
in higher volumes
what is the area of the dynamic loop
is a measure of the work done against airway resistance
what does lung compliance depend of
how inflated or not it is
what is hysteresis
The compliance curves are different for inspiration and exhalation.
due to frictional resistance changes
when is compliance decreased
in a lung with interstitial fibrosis Compliance is decreased due to more stiff alveolar walls from scarring (called fibrosis)
when is compliance increased
in emphysema Compliance is increased due to loss of alveolar interdependence
when does laminar flow occur
During quiet breathing there is Laminar air flow in airways
what is laminar flow
- Gas particles move parallel to the walls of bronchi
- Centre layers move faster than outer ones creating a cone-shaped front
where does turbulent flow occur
Turbulent flow occurs at higher linear velocities in wide airways and near branch points
when does turbulent flow occur
Turbulent flow occurs in trachea during exercise = harsh breath sounds
what is airway resistance (RAW)
RAW is the pressure difference between the alveoli and mouth divided by the flow rate
what does RAW affect
RAW affects ventilation and has to be overcome (together with the elastic recoil) and inflate the lung
where does RAW originate
RAW originates from friction between air and mucosa
what does RAW depend on
radius of the conducting airways
tone of bronchial smooth muscle and epithelium
resting bronchomotor tone
how does the radius of conducting airways affect RAW
- Nose, pharynx and trachea = offer most resistance
- Mouth breathing eg during exercise decreases resistance
- Peripheral, smaller airways are affected by diseases → ↑ RAW
how does tone of bronchial smooth muscle and epithelium affect RAW
Parasympathetic nerve supply affects bronchomotor tone
β-adrenergic receptors → relaxation
Nitric Oxide causes bronchodilatation
how does Resting Bronchomotor tone affect RAW
- Bronchoconstriction: ↓ radius→ ↑ resistance → ↓ airflow
- Bronchodilatation: ↑ radius → ↓ resistance → ↑ airflow
how does acute asthma affect RAW
- Increased RAW
- Bronchoconstriction
- Mucosal oedema
- Mucus hypersecretion
- Mucus plugging
how does COPD affect RAW
- Bronchoconstriction
- Chronic mucosal hypertrophy
what are surface tension forces caused by
are caused by air-fluid interface in alveoli
when does surface tension change
with age and lung disease
how does surface tension occur
Cohesive forces between molecules at the surface of a bubble (alveolus) creates a tension which tends to shrink the bubble
what does surface tension do
Alveoli and small airways are inherently unstable → collapse during expiration → atelectasis
what is a pulmonary surfactant
mixture of phospholipids
what is pulmonary surfactant produced by
Type II pneumocytes
how does pulmonary surfactant aid ventilation
Hydrophilic and hydrophobic ends repel each other and interfere with liquid molecule attraction→ lowers surface tension
why is surfactant important
- Increases lung compliance because surface forces are reduced
- Promotes alveolar stability
- Prevents alveolar collapse
- Surface tension tends to suck fluid from capillaries into alveoli
- Important in defense against infection
how does surfactant prevent alveolar collapse
- small alveoli are prevented from getting smaller
- large alveoli are prevented from getting bigger
