Respiratory Pathophysiology Flashcards
what are the functions of the repsiratory system
- gas exchange
- regulate pH in body
- protect from infection
- communication via speech
what is the pH of the body (ECF)
7.4
what are the 2 types of respiration
internal (gylcolysis etc) and external (movement of gases between air and body’s cells)
2 types of circulation
pulmonary - between heart and lungs
systemic - goes to all areas of body
what is the net volume of gas exchanged in lungs
250ml/min O2 : 200ml/min CO2
what is the respiration rate at rest
12-18 breaths/min
What is the upper respiratory tract composed of?
nose, pharynx (throat), larynx (voice box)
What is the lower respiratory tract composed of?
trachea, bronchus and lungs
what is contained in the thoracic cavity
heart and lungs
What separates the thoracic cavity from the abdominal cavity?
diaphragm
how many lobes are there in each lung and how is lobe separated
right - 3 lobes, horizontal fissure between superior and middle. oblique fissure between middle and inferior
left - 2 lobes, oblique fissure
what is the pleural cavity
space between lungs and chest wall
What keeps the trachea from collapsing?
C-shaped cartilaginous rings, semi-rigid
“patency” open airway
how is the right primary bronchi different to the left
it is wider and more vertical form
what is the conducting zone
trachea, bronchi, bronchioles, no gas exchange takes place
‘dead space’
how can resistance to air flow be altered
by activity of bronchial smooth muscle
- contract - smaller - inc resistacne
- relax - inc diameter - dec resistance
what are alveoli
air sacs in the lungs
what do the elastic fibres around alveoli do
for passive tissue recoil (go back)
used in expiration to push air out
what are type 1 cells in alveoli
main cell for wall of alveoli, v thin, gas exchange occurs
capillary always adjacent to them
what are type 2 cells in alveoli
secrete surfactant, no gas exchange
what is the capacity of the lungs
6L
What is tidal volume?
volume of air inhaled in a single breath - 500ml
and then exhaled
what is the air left in the lungs after expiration called
functional residual capacity
made up of expiratory reserve volume + residual volume
What is inspiratory reserve volume?
Amount of air that can be forcefully inhaled after a normal tidal volume inhalation
What is expiratory reserve volume?
Amount of air that can be forcefully exhaled after a normal tidal volume exhalation
What is vital capacity?
max vol of air you can breathe out
what is residual volume
air remaining in lungs after maximum expiration
what is the purpose of residual volume in lungs
prevents alveoli from collapsing and easier to inflate in next inspiration
allow gas exchange between breaths
what is dead space
passageways that transport air but are not available for gaseous exchange
what is the volume of dead space in conducting airways
150ml
What is the pleural cavity?
around each lung
fluid filled
surrounded my membrane
between lungs and rib cage
what are the 2 types of pleural membrane
visceral (inner) and parietal
What is the visceral pleura?
covers the outer surface of the lungs and goes into the fissures
what is the parietal pleura
lines the thoracic cavity
what is in the pleural cavity and its purpose
intra pleural fluid
allow membrane to stick together and glide across each other
creates cohesive force, chest wanting to expand//alveoli elastic wanting to recoil
what is boyles law
how the pressure exerted by gas is inversely proportional to volume.
inc volume = dec pressure
what are the muscles for inspiration
diaphragm, external intercostals (scalenes + stermocleidomastoids)
diaphragm contracts and volume inc
what are the muscles for expiration
internal intercostals
abdominal muscles
What do the external intercostals do?
the raise the ribcage upwards and outwards to increase volume
what are the 3 types of pressure in the thoracic cavity
1) intra thoracic (alveolar) pressure - inside lungs (neg/pos)
2) intra pleural pressure - in pleural cavity (neg)
3) transpulmonary pressure - dif between alveolar and intrapleural pressure (pos)
what is pressure measured in
mmHg
kPa
What is the purpose of surfactant
detergent like fluid
reduces surface tension and prevents alveoli from collapsing
air/water interface
it reduces attraction between H2O molecules, inc lung compliance
What is compliance?
change in volume relative to change in pressure
ability of lungs to expand under pressure (stretchability)
what does low and high compliance mean
low - small inc in lung volume for large dec in ip pressure (difficulty breathing in)
high - large inc in lung volume for small dec in ip pressure (difficulty breathing out)
what is ventilation
movement of air in and out of the lungs
What is pulmonary ventilation?
total air movement in/out lungs L/min
what is alveolar ventilation
fresh air getting to alveoli and therefore gas exchange L/min
What is Dalton’s Law?
The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently
What is atmospheric pressure?
760 mmHg
how do you calculate partial pressure
percentage of air we breathe x atmospheric pressure
e.g. 21% (O2 in air) x 760 = 160mmHg
how does the air we breathe in become diluted
saturated w water vapour
dead space
mix w residual volume
what is the alveolar partial pressure of oxygen and CO2
O2 - 100mmHg (13.3kPa)
CO2 - 40mmHg (5.3kPa)
46mmHg (6.2kPa)
what is bronchial circulation
bronchial arteries provide oxygenated blood to lung tissue
nutritive
what is pulmonary circulation
circulation between heart and lungs
gas exchange
high flow, low pressure system
how does o2 and co2 diffuse in body
due to differences in partial pressure
PaO2 - 100mmHg , tissue Pp is 40mmHg
PaCO2 - 40mmHg, tissue pp is 46mmHg
what affects the rate of gas exchange in lungs
- proportional to pp gradient
- gas solubility
- surface area
- thickness of membrane
- distance
what is emphysema
alveoli become damaged, reduces surface area and loss of elasticity, low PO2 in pulmonary vein
what is fibrosis
thickened alveolar membrane (resist expansion), slows gas exchange + loss of compliance = >alveolar ventilation
what is pulmonary oedema
fluid in the interstitial space between alveoli and capillary - inc distance = rate of gas exchange is slower
what is asthma
chronic inflammation of the airways, inc airway resistance, dec airway ventilation
PO3 low in alveoli and vein
what are obstructive lung diseases
obstruction of air flow, on expiration usually
e.g. asthma, COPD
what are restrictive lung dieseases
restrict lung expansion, on inspiration
e.g. fibrosis, oedema, pneumothorax, infant respiratory distress syndrome
what can be used to measure lung function
spirometer
static - volume exhaled
dynamic - time taken to exhale a certain vol measured
what is FEV1 and FVC and the ratio
FEV1 - forced expiratory volume in 1 second
FVC - forced vital capacity, how much air can be expired in total
FEV1/FVC - 80% ratio stays same
What is perfusion?
blood flow reaching alveoli
what is shunt in the lungs
alveoli less ventilated which means theres and increase in CO2 and decrease in O2 in blood because its not being replenished, will dilute oxygen content, affect pp gradient for diffusion .
Ventilation < Perfusion
what is the control to shunt
constrict blood vessels in response to hypoxia
minimise blood sent to poorly ventilated areas
dilate bronchioles to inc ventilation
what is alveolar dead space
Alveoli that are ventilated but not perfused due to collapse of them
Ventilation > Perfusion
what is the control to alveolar dead space
pulmonary vasodilation to increase O2 in blood
bronchial constrictions for fall in CO2
more ventilation and perfusion at base of lungs than apex
base of lungs more blood flow than ventilation as arterial pressure > alveolar pressure - compresses the alveoli
How does O2 travel in the blood?
bound to haemoglobin protein in rbc, 197ml per L
in solution in plasma 3ml per L
5 L of blood in total
How does CO2 travel in the blood?
in solution in plasma 77%
7% dissolved in plasma
23% haemoglobin
what is the O2 demand of resting tissue
250ml/min
what is the reservoir of O2
1000ml/min
as 200ml x 5 (cardiac output) = 1000
only 25% O2 used by tissue in resting state
explain haemoglobins components
4 haeme groups, contain Fe2+
4 chains, 2 alpha, 2 beta HbA
what affinity does CO have for haemoglobin
250x greater affinity and difficult to dissociate
what is CO2 bound to in plasma
70% react to enzyme - carbonic anhydrase = carbonic acid, dissociate to bicarbonate ions and H+ ions
go into plasma, exchange Cl- ions, H+ ions bind to deoxyhaemoglobin
23% to deoxyhaemoglobin form carbamino comounds
7% dissolved in plasma
whats myoglobin
O2 carrier molecule only in cardiac and skeletal muscle
higher affinity for O2, stores O2 more
what are the dif types of hypoxia
Hypoxaemic Hypoxia Anaemic Hypoxia Stagnant Hypoxia Histotoxic Hypoxia Metabolic Hypoxia
what is hypoxia
Inadequate supply of oxygen to tissues
what is Metabolic Hypoxia
oxygen delivery to the tissues does not meet increased oxygen demand by cells.
what is Histotoxic Hypoxia
poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide
what is Stagnant Hypoxia
Heart disease results in inefficient pumping of blood to lungs/around the body
what is Anaemic Hypoxia
Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency).
what is Hypoxaemic Hypoxia
most common. Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology.
in steady state, net vol of gas exchanged in lungs per unit time is equal to net vol gas exchanged in tissue
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the thoracic cavity increases volume on inspiration so the pressure decreases and is less than atmospheric pressure so air moves in
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on inspiration the diaphragm contracts (flattens out) so the volume increases
on expiration diaphragm relaxes so pressure increases above atmospheric pressure so air moves out
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70% efficient breathing, 500ml of air exhaled is dead space air too - 150ml
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greater tidal volume = greater alveolar ventilation (can be hyperventilation)
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in obstructive lung disease the rate air is exhaled is much more slow as much more pressure is required to push the air out the alveoli, low compliance
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PP of O2 in plasma determines degree of O2 binding to haemoglobin
saturation complete after 0.25s contact w alveoli
total contact time - 0.75s
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affinity of haemoglobin for oxygen changes under different conditions, affinity decreases when exercising to give off more O2 to tissue
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PaO2 not same as arterial O2 concentration
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what is ventilatory control
requires stimulation of the (skeletal) muscles of inspiration
via phrenic (diaphragm) and intercostal nerves (external)
is normally subconscious
entirely dependent on signalling from the brain (sever spinal cord above origin of phrenic nerve (C3-5) breathing ceases)
where is ventilatory control located
within ill defined centres located in the pons and medulla (Respiratory Centres)
what do respiratory centres have their rhythm modulated by
emotion
voluntary over-ride
mechano-sensory input from thorax
chemical composition of blood - detected by chemoreceptors
whats do the Dorsal Respiratory Group of neurons innervate
Inspiratory muscles Via phrenic and intercostal nerves
whats do the ventral Respiratory Group of neurons innervate
Tongue, pharnyx, larynx, expiratory muscles
what are the 2 types of chemoreceptors
Central and Peripheral Chemoreceptors
what are chemoreceptors
sensors that detect changes in CO2, O2, and pH that affect rhythm of breathing
describe central chemoreceptors
medulla
respond directly to [H+] on CSF arounf brain (directly reflects PCO2)
- primary ventilatory drive
- reflex stimulation of ventilation by rise in [H+]
describe Peripheral Chemoreceptors
carotid and aortic bodies
respond primarily to PO2 (not O2 content) and plasma [H+]
- secondary ventilatory drive
what happens to individuals with chronic lung disease, what do they rely on to stimulate ventilation and why
usually rely on PaCO2 level to stimulate ventilation
in CLD PaCO2 becomes elevated chronically
become desensitised to PCO2 and rely on changes in PaO2 to stimulate ventilation
What will happen to respiration rate in an anaemic patient with normal lung function, who has a blood oxygen content half the normal value?
It will stay the same
if lungs working normally, diffusion will take place normally = the amount of oxygen in solution in the plasma (PaO2) will be normal.
PaO2 is what the peripheral receptors monitor there will be no increase in RR
what effect do most gaseous anaesthetic agents have on RR, tidal volume and alveolar ventilation
increase RR,
decrease TV so decrease AV
how can barbiturates and opioids affect respiratory centres
can depress respiratory centres
dec sensitivity to pH and therefore response to PCO2 . Also dec peripheral chemoreceptor response to decreasing PO2.
what effect does nitrous oxide have on patients with chronic lung disease
could end up in respiratory failure as it blunts peripheral r chemoreceptor response to falling PaO2 and then no longer have ventilatory drive
where does plasma [H+] originate from
H+ originates from CO2
CO2 + H2O H2CO3 HCO3- + H+
Changes in plasma pH will alter ventilation via the peripheral chemoreceptor pathways
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what happens to ventilation if plasma pH falls ([H+] increases)
ventilation will increase (acidosis)
what happens to ventilation if plasma pH increases ([H+] falls)
ventilation will decrease
less [H+] = less CO2, need to slow down ventilation to retain co2
Normally pH is stable because all the CO2 produced is eliminated in expired air.
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what does hypoventilation cause
causing CO2 retention, leads to increased [H+] bringing about respiratory acidosis.
what does hyperventilation cause
blowing off more CO2, lead to decreased [H+] bringing about respiratory alkalosis
Hyperventilation: Ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/[H+]
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where is resistance to air flow greatest
in largest airways
in small airways the cross sectional area is greater
when does surfactant production begin in the foetus
25weeks gestation
complete at 36 weeks
what is anatomical dead space
150mL
volume of gas occupied by the conducting airways and this gas is not available for exchange
what gases is air composed of
nitrogen 79%
oxygen 21%
co2 0.03% (don’t breathe this in)
All gas molecules exert same pressure, so partial pressure increases with increasing [gas]mixture
ghh
during hyperventilation what happens to PO2 and PCO2
PO2 rises - 120mmHg
COS2 falls - 30mmHg
during hypoventilation what happens to PO2 and PCO2
PO2 falls - 30mmHg
CO2 rises - 100mmHg
at the apex of the lung is ventilation greater or less and why
ventilation declines
compliance is lower at apex
what is the partial pressure gradient at alveoli and tissues
ALVEOLI:
in blood PO2 40mmHg to 100mmg
PCO2 46mmHg diffuse to 40mmHg in alveoli
TISSUE:
in blood 100mmHg diffuse through to 40mmHg in tissue
…
what does the abbreviation A stand for
alveolar
what does the abbreviation a stand for
arterial blood
what is ventilation
air getting to alveoli
why is blood flow higher than ventilation at the base of the lungs
because arterial pressure exceeds alveolar pressure
why is blood flow less at the apex of the lungs
because arterial pressure is less than alveolar pressure. This compresses the arterioles.
blood flow declines faster than ventilation meaning
blood flow>ventilation at the base
ventilation>blood flow at the apex.
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what is shunt used to describe
describe the passage of blood through areas of the lung that are poorly ventilated
ventilation
what is pulmonary arterial pressure
25/8 mmHg
what determines how saturated haemoglobin is with O2
partial pressure of oxygen in blood
how quickly is haemoglobin saturated with O2 when at the alveoli
in 0.25s
total contact time 0.75s
whats 2.3-DPG
affinity of haemoglobin for oxygen is decreased
this chemical increases in situations w inadequate O2 supply (high altitude, heart/lung disease) and maintain O2 release in tissues
What is PaO2 and what is it determined by
O2 in solution in the plasma
determined by O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution
how much oxygen is bound to haemoglobin
98%
