respiratory physiology Flashcards
total mouth ventilation
frequency (breaths/min) x tidal volume (ml/breath)
dead space
space where air that never reaches alveoli hangs out. Around 150mL
respiration
exchange of O2 and CO2 between the tissues and the environment.
5 steps involved in respiration
ventilation, gas exchange between alveoli and capillary, gas transport, gas exchange between capillary and cell, cellular respiration
VO2max
maximum volume of oxygen we can deliver to tissues in our blood
functions of respiratory system
- provide oxygen
- eliminate CO2
- filter, warm and humidify air we breathe
- communication
- regulate pH of blood
- sense of smell
abbreviations F, f, I, E, V, A, a, c, v, B, D, P, PX, T
Fraction of gas in a mixture; Respiratory frequency; inhaled; exhaled; volume; alveolar; arterial; capillary; venous; barometric; dead space; pressure; pressure exerted by gas X; tidal volume
dot over quantity
Amount occurring in one minute
dalton’s law
partial pressure = fraction of individual gas x total gas pressure
Pgas = Fgas x Ptotal
- where Ptotal = Pbarometric = 760mmHg at sea level
- FO2 = 0.2093
- FCO2 = 0.0003
- FN2 = 0.7904
Boyle’s law and consequences
P1V1 = P2V2. In order to get air into lungs we need to generate a pressure gradient by changing lung volume
mechanism of inspiration
- Diaphragm and external intercostal muscles contract
- Increase in thoracic volume (increases vertical length and diameter of thoracic cavity)
- Lungs expand, increase volume
- decrease pressure (relative to atmosphere)
- Air moves into lungs
mechanism of expiration
- Inspiratory muscles relax
- Diaphragm moves upwards
- Decrease in thoracic volume and hence lung volume
- Increase alveolar pressure (relative to atmosphere)
- Air moves out of lungs. Usually passive, driven by elastic recoil of respiratory system back to resting volume. However can use accessory muscles to assist expiration
intrapleural space
- space between outside of lungs and inside of chest wall
- Lung tends to recoil inwards and chest wall tends to expand outwards so they pull away from each other
- Hence intrapleural pressure is sub-atmospheric
transpulmonary pressure
pressure difference between inside lungs and atmosphere. When you change this you change lung volume
lung compliance and effect of lung diseases on this
- measure of how easy it is to change lung volume (lung stiffness)
- With emphysema, less work is needed to change volume by the same amount (lungs are not very stiff)
- With fibrosis, more work is needed to change volume by same amount (lungs are v stiff) - low compliance
fibrosis
- Fluid lining alveoli exerts surface tension which causes them to contract / resist expansion - need to overcome this force to expand
- Surface tension reduced by surfactant
surfactant
- Reduces surface tension in alveoli i.e. makes them easier to expand
- Reduces attractive forces between fluid molecules lining alveoli
- Produced by alveolar type II cells
- mostly consists of phospholipids
- absent in premature infants, resulting in respiratory distress syndrome
factors affecting airway resistance
Resistance to flow determined by Poiseuille’s Law
- R = 8nl/πr4
- Where n = viscosity, l = length, r = radius
- R inversely proportional to r4
structures in airway affecting resistance
- Bronchoconstriction/dilation are important elements in airway resistance e.g. asthma
- Main area of resistance is in bronchi
- Most of the resistance to airflow arises in the upper airway and the first 6 generations of the lower airway
- Small airways contribute very little to airway resistance as they have very high total CSA
measuring lung volume
Spirometer
- breathe into and out of hollow bell inverted over water which measures volume exhaled/inspired
- Can measure how much or how fast
- Test response/effectiveness of therapy
tidal volume
- VT or TV
- About 500ml
- Volume of air moved in and out during normal quiet breathing
Inspiratory reserve volume (IRV)
- About 3L
- Extra volume that can be inspired with maximal inhalation - external intercostal muscles
expiratory reserve volume (ERV)
- About 1.5L
- Extra volume that can be exhaled with maximal effort - internal intercostal and abdominal muscles
residual volume (RV)
- About 1.2L
- Volume remaining in lungs after maximal exhalation
4 lung volumes
- tidal volume
- Inspiratory reserve volume (IRV)
- Expiratory reserve volume (ERV)
- Residual volume (RV)
4 lung capacities
- vital capacity
- total lung capacity
- inspiratory capacity
- functional residue capacity
vital capacity (VC)
- About 5L
- maximal breath in to maximal out – volume of air you can shift in/out of lungs
total lung capacity (TLC)
- About 6L
- Total volume in lungs when maximally full = VC + RV
Inspiratory capacity (IC)
tidal volume + IRV
functional reserve capacity (FRC)
- About 2.5L
- Volume at end of normal breath out
forced vital capacity
maximum breath in to maximum breath out (VC) - forced out as hard as possible
FEV1
Forced expiratory volume in one second
- Ratio of FEV1/FVC is normally around 0.80.
- < 0.70 indicates airways obstructed
alveolar ventilation VA
- Measures the flow of fresh gases into and out of the alveoli
- VA = frequency x (VT – VD)
factors affecting gas exchange (fick’s law)
how does diffusion constant affect gas exchange
- Diffusion constant depends on gas solubility and its molecular weight
- Per molecule, CO2 diffuses about 20x faster than O2 due to CO2 higher solubility
effect of emphysema on gas exchange
- Emphysema is a disease characterized by dilation of the alveolar spaces and - destruction of the alveolar walls.
- Since there is a decrease in the surface area of the lung (A) in emphysema, Fick’s law helps understand why patients with emphysema have decreased PO2 in blood
effect of fibrosis on gas exchange
- Pulmonary fibrosis involves thickening and scarring of the alveolar membranes – can arise from chronic inflammation, drugs, industrial chemicals
- Since there is an increase in the thickness of the alveoli (T) in pulmonary fibrosis, Fick’s law helps understand why such patients a decreased PO2 in blood
upper and lower case in lung abbreviations
- upper = gas phase
- lower = blood phase
Alveolar partial pressure of O2 (PAO2)
- about 100mmHg
- PAO2 depends on:
- PIO2 of inspired air
- Alveolar ventilation VA
- Oxygen consumption VO2
- atmospheric PO2 is usually constant so it 2) and 3) that are most important
Alveolar partial pressure of CO2 (PACO2)
- Kept constant at 40mmHg
- PACO2 depends on:
- PICO of inspired air
- Alveolar ventilation VA
- Carbon dioxide production VCO2
- Alveolar PCO2 is usually determined only by the balance between carbon dioxide production and alveolar ventilation, because atmospheric PICO2 is negligible
