Respiration Flashcards
Purpose of respiratory system
maintain arterial blood-gas homeostasis
Respiratory system 4-step process
systemic gas exchange - CO2 into blood
gas transport
alveolar gas exchange - CO2 into alveoli
pulmonary ventilation - into atmosphere
Epiglottis
separate upper/lower respiratory tracts
Airways
trachea
bronchi
bronchioles
terminal bronchioles
respiratory bronchioles
alveolar ducts
alveolar sacs
Pulmonary gas exchange
across pulmonary capillary
diffusion high to low partial pressure
Type I alveolar cell
~95% of internal surface of alveolus
critical for gas exchange
Type II alevolar cells
release surfactant - a molecule that lowers surface tension
without = collapse
Fick’s law of diffusion
volume of gas proportional to surface area/thickness x diffusion coefficient x pressure gradient
proportional
Volume of gas dependent on
surface area
thickness
diffusion coefficient
pressure gradient (alveolar to arterial)
Why is the blood-gas barrier ideal for gas exchange?
very thin
vast surface
Mechanics of breathing
inspiration = volume thoracic activity increases as respiratory muscles contract
bucket hadle motion of ribs = increase lateral diameter of thorax
pump handle motion of ribs = increase anteroposterior diameter of thorax
Muscles of inspiration
diaphragm
external intercoastal muscles
scalenes
sternocleidomastoid
= increase pulmonary ventilation
Muscles of expiration
rectus abdominis
internal intercostal muscles
external oblique
Measure of diaphragmatic fatigue
bilateral phrenic nerve stimulation
Ohm’s law
current = voltage/resistance
flow directly proportional to pressure difference
inversely proportional to resistance
Poiseuille’s law
resistance dependent upon length and radius of tube
Exercise-induced asthma
flow limited during exercise
breath at high lung volume
end expiratory volume = higher at rest
resistance to flow becomes higer
Pulmonary ventilation equation
.v = vt x fb
v = volume
.v = volume per unit of time
t = tidal
fb = breathing frequency
Dead space
volume of air not particpiating in gas exchange (vd)
150mL in healthy individuals
Va = (vt - vd) x fb
Forced vital capacity
max volume air that can be forcefully expired after max inspiration
COPD
increased airway resistance
reduced forced vital capacity
sig reduced forced expiratory volume in one sec
Dynamic hyperinflation in COPD
increased end-expiratory lung volume
increased work of breathing
increased breathing discomfort
Respiratory muscle fatigue
not occur during prolonged heavy exercise
Ventilatory response to constant load steady-state exercise phases:
phase 1 - immediate increase in Ve
phase 2 - exponential increase in Ve
phase 3 - plateau - steady state
Hyperpnoea
PaCO2 regulation due to proprtional changes in alveolar ventilation and metabolic rate
insert equation
Ventilatory threshold
ventilation increases lineraly with exercise intensity until a point (Tvent)
~50-75% VO2 peak
after Tvent - ve increase exponentially resting in hyperventilation (decrease PaCO2)
Exercise-induced arterial hypoxaemia
50% highly-trained males duirng heavy exercise
majority females
reduction in PaO2 of >/10 mmHg from rest
occur because ventilatory demand exceeds capacity
EIAH caused due to:
diffusion limitation
V/Q mismatch
relative hypoventilation
Changes in breathing patterns during exercise
onset exercise - changes Ve achieved by increasing Vt
heavy exercise - Vt plateaus and further increase in Ve achieved by fb
insert diagram
Work equation
work = force x volume
total work = sum of elastic, flow-resistive and inertial forces
Oesophageal pressure
estimate of pleural pressure
used to calculate mechanical work of breathing during exercise
Respiratory central pattern generators loacted
within brainstem
pons
medulla
3 main groups of neurons
ventral respiratory group (inspiratory/expiratory)
dorsal respiratory group (inspiratory)
pontine respiratory group (modulatory)
Motor outputs
effectors
resistance muscles
pump muscles (diaphragm)
Feedback inputs
sensors
peripheral chemoreceptors
central chemorecptors
Feedforwards inputs
muscle afferents
CO2 flow
Peripheral chemoreceptors
detects changes in PO2 of blood perfusing systemic and cerebral circulation
located at aortic arch and cartoid body
relays sensory info to medulla via vagus nerves
decrease PaCO2 = increase Ve
temp, adrenaline and CO2 stimulate peripheral chemoreceptors
Central chemoreceptors
loacted in ventral surface of medulla (RTN)
sensitive to change in PaCO2/H+ of cerebral spinal fluid
other areas sensitive - cerebellum
Chemoreceptor feedback
Chemoreceptors detect error signals (disturbances to blood-gas homeostasis)
Central and peripheral chemoreceptors respond to increasing PaCO2ordecreasing PaO2or pH
Premotor neurons in the dorsal respiratory group areactivated
Inspiratory muscle contract, increasingሶVE
Changes inሶVEelicit changes in PaO2, PaCO2and pH, thusrestoring blood-gas balance
Ventilatory response to O2
curvilinear
below ~65 mmHg
Ventilatory responses to CO2
linear
changes in paCO2 elict much greater changes in Ve
Ventilatory control during moderate exercise
no change in mean paCO2 = primary stimulus is feedforward in origin
central neurogenic
peripheral neurogenic
peripheral chemoreceptors - fine tune breathing
Ventilatory control during heavy exercise
PaCO2 falls = inhibit breathing
Tvent metabolites accumulate = stimulate breathing
feedforward - central neurogenic, peripheral neurogenic
feedback - central chemorecptors, peripheral chemoreceptors
increased body temp
augmented muscle afferent input
Effects of endurance training on respiration
Ve 20-30% lower vs untrained
decrease metabolite accumulation
decrease afferent feedback
decrease ventilatory drive
How do lungs adapt to training?
lungs/airways not adapt
respiratory muscles stronger/more fatigue resistant
maladaptive adaptations = airways hyperresponsivensss in skiers/swimmers
Pulmonary system limit max exercise performance?
Exercise-induced arterialhypoxaemia(EIAH)
Exercise-induced laryngeal obstruction (EILO)
Expiratory flow limitation
Respiratory muscle fatigue
Intrathoracic pressure effects on cardiac output
Dalton law
total pressure of gas mixture is equal to some of pressure that each gas would exert independently
Pair = Pn2 + Po2 + PCo2
Partial pressure of gas
Pgas = Fgas x Pbar
760mmHg sea level
Partial pressure of inspired O2 and CO2
159
0.3 mmHg
Gas exchange impairment
arterial PO2 (~100mmHg) slighlty less than alveolar PO2 (~105 mmHg)
Cellular respiration
O2 consumed and CO2 produced
venous PO2 decreased to 40 mmHg
venous PCO2 increased to 46 mmHg
Pulmonary circulation process
Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs
Gas exchange between the alveoli and pulmonary capillaries occurs
Oxygenated blood is returned to the left atrium via the pulmonary vein
Oxygenated blood is pumped around the systemic circulation to systemic cells
Pulmonary circulation
low pressure
low resistance
thin walled, little smooth muscle
accepts entire cardiac output
not redistribute blood flow
Pulmonary vascular resistance
decreases during exercise
due to recruitment of pulmonary capillaries
What does gas exchange require?
matching of ventilation to blood flow
ideal V/Q is 1
Upright lung
blood flow increases disproportionatly more than ventilation from the top to bottom of lung
due to effects of gravity
Upon exercise V/Q improves due to
increased tidal volume
increased pulmonary artery pressure
worsens during heavy exercise
How is oxygen carried in the blood?
dissolved (2%)
combined with haemoglobin (98%)
Henry’s law
amount dissolved O2 proportional to partial pressure
Haemoglobin
blood chemically bound to haemoglobin
transport 4 molecules of O2
amount O2 transported as oxyhaemoglobin dependent upon Hb mass
Bohr shift
oxygen dissociation curve
right shift
due to rise in H+ ions, CO2 and body temp from exercise
facilitates unloading of O2 in active tissue
Myoglobin
O2 binding protein in muscles
high affinity O2 = unloads at very low PO2
shuttles O2 from muscle cell membrane to mitochondria for aeroic respiration
provides intramuscular O2 storage
How is CO2 carried in the blood?
dissolved (10%)
bound to haemoglobin (20%)
bicarbonate (70%)
20x more soluble than O2
Carbon dioxide transport
HCO3- leaves cell and Cl- moves into cell to maintain neutrality (chloride shift)
H+ binds to Hb to form HHb which binds to CO2 to create carboamino Hb
most CO2 forms reversable reaction when bound with water
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
Ventilation and acid base balance
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
increase in CO2 during exercise = increase in H+ = decrease arterial pH = stimulate breathing via feedback loop
How is CO2 transported in arterial blood?
bicarbonate
Cartoid bodies
chemoreceptors sensitive to changes in arterial ph, PCO2 and PO2
Tidal volume
amount of gas moved per breath
FEV1/FVC pulmonary function test
ratio of forced expiratory volume in first second to forced vital capacity of lungs
0.60 = suggestive of airway obstruction
normal = 0.75-85
Changes in ventilatory patterns during exercise
important to ensure optimal mechanics of breathing are realised
to reduced risk of respiratory fatigue
increased tidal volume = dead space ventilation remains small
Graded exercise test
ventilation during transition from rest to moderate exercise achieved by:
increase breathing frequency
increase tidal volume
Effect on ventilation
small increase arterial PCO2 = greater effect
compared to small decrease in PO2
Ventilation-perfusion relationship
gas exchange requires a matching of ventilation to blood flow
ideal = 1
above 1 = more air than blood
below 1 = less air than blood
Upright lung
blood flow increases disproportionately more than ventilation from top to bottom of the lungs
due to effects of gravity
Lungs
enclosed within membranes (pleura)
intrapleural pressure < atmospheric pressure = prevent alveoli collapse
