Lung Volumes & Capacities Flashcards
Consequence of decreased expansion of lung parenchyma
Decreased lung capacity
What do intrinsic lung diseases alter
Lung parenchyma
What do extrinsic lung diseases affect
- Pleura
- Chest wall
- Neuromuscular apparatus
What does tidal volume vary with
Exercise
Posture
Decreases with restrictive diseases
Inspiratory reserve vol
when is it needed
What decreases IRV
Effect of restrictive lung disease on IRV
- Max vol of air inspired above tidal vol inspiration
- = 3 L
- Reservoir for when increased ventilation is required
- Increased air intake during exercise
- Increased tidal volume DECREASES IRV
- IRV decreases with restrictive lung disease
Expiratory Reserve Vol
Effect of RLD on ERV
- Max vol of air expired after a tidal volume expiration
- 1.1 L
- ERV decreases with RLD
Functional Residual Capacity
Formula
- Vol of air in lungs at the end of normal expiration
- = 2.3L (40% total lung capacity)
- FRC = RV + ERV
Consequences of increased ERV
Emphysema
Air trapping
Loss of elastic recoil
Consequnce of decreased ERV
Increased elastic recoil
Inspiratory capacity
Formula
- Largest vol that can be inspired from resting end expiration
- = 3.5 L
- IC = TV + IRV
He dilution method
Amount before equilibration = C1 x V1 = amount after
C2 x (V1 + V2)
V2 = V1 (C1 - C2)/C2 = FRC
https://en.wikipedia.org/wiki/Helium_dilution_techniquee
Importance of FRC
- Keeps small airways open
- Helps maintain blood PaO2 constant
- Dilution of noxious gases (lowest in newborn - prone to noxious toxins)
B.A.E.
3 results of an increase in FRC
- Emphysema (decreased elastic recoil)
- Asthma
- Bronchiolar obstruction (air trapping)
3 results of a decrease in FRC
- Pulmonary fibrosis
- kyphoscolosis
- increased movement of diaphragm (obesity, painful thoracic abdominal wound)
Vital capacity
formula
Vol change that occurs between maximal inspiration and maximal expiration (4.8 L)
VC = IRV + TV + ERV
What is total lung capacity
- = 5.8 L
- TLC = VC + RV
Minute respiratory volume
Formula
Value @ rest
Value during exercise
- Volume of air moved into or out of the lung in 1 min
- TV x resp rate
- REST - 500 ml (12 breaths/min) = 6L/min
- EXERCISE - 3-4 L (30 breaths/min) = 90-120L/min
Forced vital capacity
What is it equal to
Vol of air forcefully expired in 6 s after max inspiration
= VC
Forced exp vol 1 second (FEV1)
What is used to characterise lung disease
Total volume of air that can be exhaled forcefully in 1s from TLC (L)
Majority can be exhaled < 3s in normal people
=> 75-80% of VC in 1st second
FEV1/FVC is used to characterise lung disease
Apart from being bound to Hb, how is O2 carried in blood
Dissolved
Obey’s Henry’s Law
Amount dissolved is proportional to the partial P ONLY
1 mmHg PO2 => 0.003 ml O2 dissolves in 100 ml blood
Amt of O2 needed to be delivered to tissues vs how much is actually delivered (by dissolution)
15 ml delivered, but resting O2 consumption = 250 ml/min
O2 capacity
Max amt of O2 that can be bound to Hb
How much O2 does 1g of Hb bind to
1.39 ml of O2
What is normal blood Hb
Hence calculate O2 capacity
15g/100ml
=> 15 x 1.39 = 20.8 ml/100ml = O2 CAPACITY
Formula for O2 saturation with Hb
O2 combined with Hb/O2 capacity x 100
Saturation of arterial blood @ PO2 of 100 mmHg
97.5%
Saturation of mixed venous blood @ PO2 of 40 mmHg
75%
not all O2 used
What is the cut off of co-operative binding
50 mmHg
3 advantages of co-operative binding
- Flat upper portion - alveolar PO2 can drop significantly with little effect on the carriage of O2
- As RBC takes up O2 along the capillary, a large partial pressure difference for O2 between alveolar gas and capillary blood exists even when most O2 has been transferred
- Steep lower portion => that tissues can withdraw large amts of O2 from blood for small drop in tissue capillary
Hb value in:
- Polycythaemia
- Normal blood
- Anaemia
- 20
- 15
- 10
Effect of pH on O2 demand conc
Higher pH => increased affinity (more basic)
Lower pH => decreased affinity (more acidic)
Effect of PCO2 on O2 saturation (Bohr effect)
High PCO2 decreases O2 saturation
Low PCO2 increases O2 saturation
Effect of temperature on O2 saturation
COLDER temps INCREASE affinity
WARMER temps DECREASE affinity
Effect of exercise on O2 unloading
- Increase in temperature
- Increase in PCO2
- Decrease in pH
All pormote O2 unloading due to decreased affinity for O2
What is 2,3-DPG
With what condition is there increased 2,3-DPG
Glycolytic intermediate that accumulates in uniquely high levels in RBCs
Increased 2,3-DPG is linked with hypoxia
Recently, A Cat Arrived Home Purring Constantly
7 conditions that exhibit increased 2,3-DPG
- Acclimatisation to high altitudes
- Chronic lung disease - emphysema
- Anemia
- Hyperthyroidism
- Right to left shunt
- Congenital heart disease
- Pulmonary vascular disease
Tissue hypoxia
Abnormally low PO2 in tissues
Hypoxic hypoxia
Low arterial PO2 - pulmonary diease
Anaemic hypoxia
Decreased ability to carry O2 - anaemia/CO poisoning
Circulatory/stagnant hypoxia
Decreased blood flow - shock, local obstruction
Histotoxic hypoxia
Toxic substance stops tissue using available O2 (cyanide)
inhibits Ox Phos => inability to generate ATP - energy needed by cancer cells because they’re growing so fast - therefore cyanide is a drug used for cancer treatment
How is CO2 carried in blood (3)
CO2 and Henry’s Law
- Dissolved in plasma - 7%
- Bicarbonate - 70%
- Carbamino compounds - 23%
CO2 (like O2) obeys Henry’s law - however CO2 is 20x more soluble than O2
Conc is directly proportional to PCO2
Where is the conversion of H2O and CO2 to H2CO3 SLOW
Where is it RAPID
SLOW in plasma
RAPID in RBC due to carbonic anydrase
also cerebrospinal fluid
(dissociation of H2CO3 is fast without enzyme)
What is high in RBC (2)
Which compound can diffuse out
What compund replaces the ion diffusing out
[HCO3-] and [H+]
HCO3- diffuses out
H+ cannot diffuse out
Cl- diffuses in and replaces HCO3-, maintaining electroneutrality
Which is less acidic - Hb or HbO2
therefore which one is a better acceptor of H+
Hb is less acidic than HbO2
therefore Hb is a better acceptor of H+
What does O2 unloading in peripheral blood help
CO2 loading
What is the Haldane effect
Pulmonary capillaries oxygenation helps unload CO2
What are carbamino compounds
CO2 combines with terminal amino groups in blood proteins
Reduced Hb can bind more CO2 than HbO2
