Mechanics of Breathing Flashcards
what proportion of the deaths are attributable to respiratory disease
36%
what is the definition of breathing
the bodily function that leads to ventilation of the lungs also known as external respiration
define ventilation
the process of moving gases in and out of the lungs
define mechanics of breathing
decries the structural and physiological bases of ventilation
what are the two types of disease affecting ventilation and what are some examples
obstructive conditions:
asthma, COPD, lung cancer
restrictive conditions: intrinsic: pulmonary fibroids
extrinsic - pneumothorax, disorders of the thorax skeleton
what is the difference in barometric pressure during inspiration and expiration between the atmosphere and the alveoli
inspiration: Pb (atmospheric pressure) > Pa (alveolar pressure)
expiration: Pa > Pb
what is 1 atm of pressure equal to in terms of kPa, bar, mmhm and cmH20
1 atm = 101.3 kPa
= 1.013 bar
= 760 mmHg
= 1033 cmH2O
what is a change in pressure dependant on
cycle of pressure changes in the chest
according to boyles law what happens after thoracic volume changes
alveolar pressure changes
P = 1/V
what are the difference sin muscle groups between quiet breathing and increasing effort
quiet = diaphragm and external intercostal muscle (inspiration)
increasing effort: accessory muscles involved such as neck muscles (pull rib cage up) and shoulder girdle muscles
what happens in quiet breathing during expiration and increasing effort
quiet breathing = elastic recoil of tissue
increasing effort = internal intercostal muscles and abdominal muscle walls
what innervates intercostals
segmenta thoracic nerves
where does the diaphragm originate from
the neck and becomes a muscle therefore innervated by the cervical nerve
what happens to the intrapleural space during thoracic cage expansion
causes an increasing negative pressure meaning air comes into lungs
how does a traditional spirometer work
Measurement of the basic lung volumes and capacity
Counterbalanced using a weight
Cylinder down pen up
Breathes in pen moves up and vice versa
what is tidal volume and its typical values
the volume of air moved in or out of the lungs during normal breathing
at rest: 6-7 ml/kg
exercise: 15 ml/kg
what is the inspiratory reserve volume and what is its typical value
after normal expiration take as deep a breath as possible
70kg male - 3,000ml
what is the expiatory reserve volume
and its typical value
after normal inspiration, breath out as deeply as possible
70 kg male - 1,500 ml
which values on a spirometer do restrictive lung diseases affect
reduced RV, FRC, VC, TLC
what do obstructive lung diseases such as asthma, COPD and emphysema affect
increased RV
TLC may be reduced in COPD but reduced in emphysema
FRC increased in emphysema
what is FRC
functional residual capacity - dependant on the compliance of the lungs and chest wall
what is compliance
defined as the change in lung volume per unit change in intrathoracic pressure
C = change in V/ change in pressure
if something is very compliant it means it doesn’t take much effort to stretch it
what is the normal tendency of the lung
to collapse
what is the calculation for recoil pressure of the lung
Palv - Ppl
what is the recoil pressure of the lung at maximal expiration
0 - - 3 = +3 cmH2O
what is the recoil pressure of the lung at peak inspiration
+ 30cmH2O
what is the recoil pressure of then lung during tidal breathing
+5 cmH2O
how do you calculate the recoil pressure of the chest wall
Ppl - Pbs (body surface)
what are the three steps for measuring and calculating the recoil pressure of the chest wall
maximal expiration, close glottis, relax muscles
Ppl - Pbs = -30 - 0 = -30cmH2O
what happens when we maximally expire in terms of the chest wall and intrapleural pressure
generates very negative intrapleural pressure and therefore chest wall wants to spring out for inspiration to occur
describe the graph of a composite chest wall and lung compliance
at FRC the recoil pressure is 0
FRC is the relaxation point of the respiratory system when chest wall and lung recoil pressures are equal but opposite
what surgery is formed during circumferential burn
escharotomy
how does scoliosis affect compliance
reduces compliance as ribs don’t expand as well as they normally should
what happens to compliance during emphysema
increases compliance as elastic tissue is destroyed meaning less want to recoil
describe how gravity affects compliance throughput the length of the lungs
Spaces at the bottom are more closed off than those at the top
Alveoli even at the bottom are not completely shut
According to position in the lung alveoli have a difference in compliance – steeper curve at the bottom of the graph then flattens off at the top
bigger change in the basal alveoli compared to the upper alveoli – upper don’t open that much – better ventilation at the bottom of the lungs
ie when you breath the top alveoli don’t stretch that much as they are already quite open
what is closing capacity
The closing capacity is the volume in the lungs at which its smallest airways, the respiratory bronchioles, collapse
what happens if the closing capacity exceeds FRC
alveoli independent lung regions will be poorly ventilated
what happens to alveoli when FRC is smaller than closing capacity
you get closure of some of the alveoli
does closing capacity ever change
no
what is the equation for the law of laplace
Pressure = (2 x Thickness x Tension)/Radius
how can tension within a sphere be decreased at constant pressure
increasing the thickness of the sphere wall
how does surface tension work
potential energy is minimised through reducing surface area to volume ratio by formation of a sphere
what specifically is the role of surfactant
Acts as a detergent to reduce alveolar surface tension Increases pulmonary compliance Prevents atelectasis Aids alveolar recruitment Minimises alveolar fluid
which syndrome causing less surfactant
infant respiratory distress
what cells produce surfactant
type 2 alveolar cells
what is the composition of surfactant
90% phospholipid 10% protein
what happens to surfactant as alveolar volume increases
becomes more dispersed which equalises pressure between alveoli of different sizes
ie there is less tension from spread out surfactant in larger sized alveoli
what is it called when the relationship between he intrathoracic pressure and the lung volume during tidal breathing
hysteresis
what causes hysteresis
at small lung volumes:
reduced compliance
airway calibre
what is the equation for flow in the lungs
Flow = (k.change in P.r^4)/L
define laminar and terminal flow
Laminar flowis where the air is flowing through the tube in parallel layers, with no disruption between the layers, and the central layers flowing with greater velocity. Turbulentflowis when the air is not flowing in parallel layers, but direction, velocity and pressure within theflowof air become chaotic.
which flows are where in the lungs
upper alveoli more turbulent flow
laminar flow in lower branches
what does a vitalograph spirometer do
measures the forced vital capacity FVC
the forced expiratory volume in 1 second (FEV1)
what does a peak flow meter measure
PEFR
what causes reduction in FVC and FEV1
COPD (obstructive defect)
Restrictive defect such as pulmonary fibrosis
what does the FEV1/FVC ratio distinguish between
obstructive and restrictive conditions
ratio < 0.7 = obstructive
ration > 0.7 = restrictive
what is the difference between asthma and chronic obstructive lung disease
asthma airways are reversible via B adrenorecpetor agonist salbutamol
COPD is irreversible
what is the work of breathing
the energy used in inspiration to overcome elastic forces is stored as potential engird which is dissipated in expiration
work is expended in the form of heat during inspiration and expiration to overcome resistance forces
what is the equation for work
volume x pressure
what happens to minimal work of breathing in restrictive and obstructive conditions
restrictive: work is minimised with rapid volume small volume breaths
obstructive work is minimised with large volume slow breaths
