CBT2 Ventilation and gas exchange Flashcards
(119 cards)
1
Q
Define Tidal volume (TV or V small T)
A
The volume of air inspired and expired during regular breathing (i.e. gentle normal breathing not deep breathing)
2
Q
Define Inspiratory reserve volume (IRV)
A
The volume of air that can be inspired after a tidal inspiration
3
Q
Define Expiratory reserve volume (ERV)
A
The volume of air that can be expired after a tidal expiration
4
Q
Define Residual volume (RV)
A
The volume of air that cannot be emptied from the lungs, no matter how hard you expire. This is fixed because of the lung-chest wall interface
5
Q
How do you calculate the total lung capacity? (TLC)
A
RV + IRV + TV + ERV
6
Q
How do you calculate the functional residual capacity (FRC)
A
RV + IRV. The volume of air in the lungs following a tidal expiration at rest. This capacity represents the “default” volume of the lungs, when the lung recoil (inwards) and chest recoil (outwards) are in equilibrium
7
Q
How do you calculate inspiratory capacity (IC)
A
TV + IRV. The maximum volume of air the lungs can draw in from the equilibrium FRC point
8
Q
How do you calculate vital capacity (VC)
A
TLC – RV; or, TV + IRV + ERV. The volume of air between the maximum and minimum achievable volumes (range)
9
Q
What factors affect all the different breathing and lung volumes?
A
Height is the most influential, but others include:
- age
- genetics
- aerobic
- fitness
- disease
- developmental exposure to altitude
10
Q
What does dead space describe? (V small D)
A
Generic term that describes parts of the airways that do not participate in gas exchange (e.g. conducting and respiratory airways)
11
Q
What are the three types of dead space?
A
1) Anatomical dead space
2) Alveolar dead space
3) Physiological dead space
12
Q
Describe Anatomical dead space
A
This includes the entirety of the conducting airways and the upper respiratory tract (oral/nasal cavity, pharynx and larynx). This value cannot be measured using standard spirometry. It requires a dilution test with a known volume of inert gas (e.g. helium)
13
Q
Describe Alveolar dead space
A
This includes respiratory tissues unable to participate in gas exchange, usually due to an absent or inadequate blood flow. In healthy individuals, this volume is effectively zero
14
Q
Describe Physiological dead space
A
This is the sum of anatomical and alveolar dead space volumes
15
Q
How many generations are there in the conducting zone?
A
16 generations
16
Q
Typically how many ml are there in the anatomical dead space?
A
150ml in adults at FRC
17
Q
What are non-perfused parenchyma?
A
Alveoli without a blood supply
18
Q
How many generations is the respiratory zone?
A
7 generations
19
Q
How many ml is the respiratory zone in adults? (referred to as alveolar ventilation)
A
350ml
20
Q
What is the amount of air moving in and out of the lungs per minute referred to?
A
pulmonary ventilation (V small E)
21
Q
How is pulmonary ventilation calculated?
A
TV x breathing frequency
22
Q
What is the primary function of breathing?
A
Ventilation of the alveolar tissue
23
Q
What is alveolar ventilation?
A
The amount of air per minute reaching the gas exchange surface
24
Q
How do you calculate alveolar ventilation during tidal breathing?
A
It is equal to the difference between tidal volume and dead space multiplied by breathing frequency (V small alv = ((VT - VD) x Rf).
25
Typically, for every generation further down the airway there is a divergence in the path associated with a _____ decrease in the pressure and velocity of airflow.
50%
26
At rest, how are the mechanical forces of the lungs balanced?
At equilibrium
27
How can the balance of mechanical forces be distorted, in order to stimulate ventilation?
Increasing pressure outside of the lung, or decreasing pressure inside the lung
28
What is positive-pressure breathing?
Increasing pressure outside of the lung (e.g. a patient on a ventilator)
29
Explain negative-pressure breathing, i.e. inhalation under normal conditions
The respiratory muscles decreases intrathoracic pressure (diaphragm contracts downward towards the abdomen and the external intercostal muscles pull the ribcage outwards and upwards) by creating a partial vacuum; the lung as an elastic expandable tissue stretches to fill the space which sucks air in from the outside the body to normalise the pressure.
30
At rest, with no activation of the respiratory muscles, the volume of the lungs is equal to the ________
functional residual capacity (FRC)
31
Explain exhalation
The fixed intrapleural volume must comply and hence the lung must expand. In this case, the force of the diaphragmatic contraction/chest wall expansion exceeds the recoil force of the lung tissue. At the end of inspiration, the chest wall force subsides and lung recoil passively empties the lungs.
32
Resistance in the lung is proportional to.. ?
| Poiseuille's Law
- The viscosity of a fluid (including air) x the length of the tube
- and is inversely proportional to the fourth power of the radius
Resistance = 8nl/pie(r^2)
n=viscosity
l=length
33
Explain why resistance doesn't increase the deeper you get into the lungs
The constant generational divergence in the airways means that the cumulative cross-sectional area increases dramatically in the small airways (as you are dividing by the area in Poiseuille's equation, as the area increases, the resistance decreases)
34
Explain the resistance from generation 0>23
Resistance is greatest in the fourth generation of the respiratory network, after which it decreases exponentially.
35
What is the nomenclature to describe partial pressure of water vapour in expired air?
italic P small E H small 2 O
36
What is the nomenclature to describe the carbon dioxide content in mixed venous blood?
Cv̄CO small 2
37
What is the nomenclature to describe the oxygen saturation of Hb in arterial blood?
SaO small 2
38
What do these prefixes describe?
- P (italic)
- F
- S
- C
- Hb
```
P (italic)= Partial pressure (kPa or mmHg)
F= Fraction (% or decimal)
S= Hb Saturation (%)
C= Content (ml)
Hb= Volume bound to hb (ml)
```
39
What do these subscript letters mean?
- I
- E
- A
- a
- v̄
- P
- D
- I = inspired
- E = expired
- A = alveolar
- a = arterial
- v̄ = mixed venous
- P = peripheral
- D = dissolved
40
Who else can italics P be used?
if you were discussing arterial oxygen you could simply refer to PO2
41
What is the purpose of breathe?
Fundamentally, the purpose of breathing is to maintain oxygen delivery to cells that are undertaking aerobic respiration (the process of releasing stored energy from food).
42
What is the basic equation for respiration?
C6H12O6 +6O2 -> 6CO2 + 6H2O + energy
43
What is fick's law of diffusion?
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2) , the exchange surface area (A) and the diffusibility of the gas (D), and inversely proportional to the thickness (T) of the exchange surface.
44
What is the equation for fick's law
V gas = (A/T) x D x [P1 -P2]
45
What is Henry's law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the solubility (α) of the gas and the partial pressure (P) of the gas in equilibrium with that liquid.
46
What is the equation for Henry's Law?
C small D = αgas x Pgas
47
What is the composition of atmospheric gas?
- 78.2% nitrogen
- 20.9% oxygen
- 0.9% argon
- 0.04% carbon dioxide
- 0.01% a number of inert gases (neon, xenon, helium, hydrogen)
48
What is the barometric pressure at sea level? (P small B)
101.3 kPa (760 mmHg)
49
How do you calculate the partial pressure of gas within a mixture?
Multiply the barometric pressure by the fraction of the gas
| e.g. 101.3kPa x 0.209 = 21.3kPa which is the PO2 at sea level
50
How does therapeutic oxygen work?
This involves administration of a high oxygen (up to 100%) gas mixture via either a nasal cannula or a full-face mask. Depending on concentration and flow rate, this may increase the fraction of inspired oxygen (FIO2) above 60%; this will thereby increase the amount of oxygen that will dissolve in the blood.
51
Why would inspiring noxious gas be dangerous?
Inspiring noxious or polluted air can be problematic; perhaps because the amount of oxygen in that mixture is critically low, or because the mixture contains chemicals that interrupt the normal physiology (e.g. carbon monoxide)
52
As altitude increases, what happens to the ambient barometric pressure?
It reduces
53
When you increase altitude, are gas fractions changed to cause a reduction of oxygen percentage?
No, gas fractions stay the same but as P small B decreases, multiplying this with the fraction of the gas will equal lower PO2
54
What are the steps of respiratory conditioning
The air is warmed to a physiological temperature
The air is humidified to a PH20 of 6.3 kPa (100% saturation)
The air is slowed
The air is mixed with air already in the lungs
55
Why does respiratory conditioning occur?
Optimise gas exchange and to protect the lung tissue
56
Where does respiratory conditioning mainly occur?
mostly occurs in structures with a high blood flow caudally to the trachea (75%), or in the trachea only (25%)
57
When air is fully saturated with water vapour what is the PH2O? What can this value be used to calculate?
6.3kPa
| PO2 while breathing dry air at sea level
58
What happens to the P of H20, CO2 and O2 as atmospheric air enters the conducting airways and moves towards the respiratory airways?
PO2 decreases in conducting airways and respiratory airways
PCO2 increases in respiratory airways
PH2O increases conducting airways and respiratory airways
59
Why does the oxygen content decrease and the CO2 content increase as you reach the alveoli?
As the fresh air enters the lungs it mixes with the functional residual capacity (ERV + RV). This reduces the oxygen content and increases the carbon dioxide in the air reaching the alveoli
60
How can you calculate the concentration of a dissolved gas in the blood in postalveolar venules? What units?
Henry’s law
| ml/dl or mldl^-1
61
How many ml in dl?
100
62
How many ml of O2 is there in a dl of blood?
0.32ml
63
What is the typical cardiac output?
5L/min
64
What is the rate of dissolved O2/min?
5000/100 = 50
50 x 0.32 = 16
16ml/min
65
What is the typical O2 consumption at rest?
250ml/min
66
Briefly, describe the structure of Haemoglobin
Tetrameric molecule consisting of four Hb monomers, each monomer consists of haem and globin
67
Describe Haem
a ferrous iron ion (Fe2+) at the centre of a tetrapyrrole porphyrin ring. This ligand is able to reversibly bind one molecule of oxygen. Once bound, haem, and the connected globin chain, undergo a conformational change in shape, which also affects other monomers within the molecule. This makes the remaining monomers more receptive to binding oxygen. (Allosteric)
68
Describe globin
A protein chain
69
What % of the blood is made up of erythrocytes? Plasma?
45% the remaining 55% is plasma
70
Is Haemoglobin toxic?
capable of damaging renal tubular epithelia causing renal failure – fortunately it is packaged inside erythrocytes (in the absence of a haemolytic blood disorder)
71
How do you measure the % of blood that is erythrocytes?
By measuring the haematocrit or packed cell volume: A known volume of blood is centrifuged and the heavy RBCs form a pellet at the bottom. The ratio of the depth of this pellet to the total volume of the tube is the packed cell volume PCV or haematocrit. This value is typically 40-50%
72
How many ml of blood/kilo mass?
70ml
73
Typically, what volume of blood is circulating?
5L
74
What is typical haemoglobin concentration?
150g/L
75
What is the binding capacity of Hb?
1.34ml O2/g
76
How can you calculate the amount of O2 bound to Hb and consequently the total volume of O2 in the blood?
Binding capacity of Hb (1.34ml O2/g) x volume of sample (15 ml) = 20ml O2/dl
5L of circulating blood, 50 x 20 = 1000ml of O2 in the blood at rest
1000ml O2 delivered/min
77
What is the proportion of O2 bound to Hb and dissolved in the blood?
2% in solution
| 98% bound to Hb
78
What does the allosteric behaviour of Hb mean for O2?
As molecules become more saturated they develop a greater affinity for binding additional oxygen molecules
79
What happens when Hb is fully deoxygenated? Explain the process to a fully oxygenated Hb
It shifts into a tense state: making it very difficult for the first oxygen to bind. Once the first O2 is bound, it triggers a conformational change into a more relaxed state. Making a greater affinity for the next O2 to bind, this process continues until the Hb is full (fully relaxed state)
80
What is the phenomenon of allosteric behaviour of Hb with O2 known as?
Cooperativity
81
What promotes O2 unloading? Explain the process
The binding site is for 2,3-diphosphoglycerate (2,3-DPG, or 2,3-BPG) in the centre of Hb becomes clear: a cofactor in red cell energy production found in RBCs. This molecule binds to the two beta subunits and pushes them into the tense state, promoting oxygen unloading.
82
How much greater is the affinity for the final binding site than for the first?
300x greater
83
What is the relationship between PO2 and oxygen in solution?
simple and linear
84
Across the physiological range of the lungs haemoglobin remains almost _____ saturated
fully
| shallow relationship
85
At the level of respiring tissues, there is a ____ relationship between PO2 and Hb saturation
Steep
86
Describe the change in PO2 and HbO2 for lungs and tissues
```
Lungs:
LARGE change in PO2
SMALL change in HbO2
Tissues:
SMALL change in PO2
LARGE change in HbO2
```
87
What does ODC stand for?
Oxygen dissociation curve
88
What factors can affect the ODC?
Low oxygen environments:
- acidosis
- hypercapnia (increased PCO2)
- increased temperature
- increased [2,3-DPG]
High oxygen environments:
- alkalosis
- hypocapnia
- decreased temperature
- decreased [2,3-DPG]
89
What direction does low O2 environments shift the ODC?
Right (decreased infinity)
90
What direction does high O2 environments shift the ODC?
Left (Increased affinity)
91
What is shifting of the ODC known as?
Bohr effect
92
What is polycythaemia?
a condition where the concentration of RBCs in the blood is much higher than normal, usually when the Hct/PCV is >55%.
93
How does polycythaemia affect the ODC?
stretches the ODC upwards, meaning that for a given PO2 there is no change in HbO2 saturation but a marked increase in blood oxygen content.
94
How does anaemia affect the ODC?
The ODC is pushed downwards as there is a lower concentration of haemoglobin, markedly reducing the overall oxygen-carrying capacity of the blood.
95
What are on the X and Y axis of the ODC curve?
```
X = PO2 (kPa)
Y = HbO2 saturation (%)
```
96
What is the principal factor controlling the Hb-O2 relationship?
Partial pressure of dissolved oxygen
97
What should blood in venous circulation be called and why?
```
mixed venous ( v̄ )
It still contains 75% of the O2 that arterial blood contains (at rest)
```
98
Why does venous blood contain 75% of O2 that arterial blood has?
Metabolic demand for O2 is low at rest
99
Describe the movement of O2 from lung to Hb
By diffusion O2 passed from the alveolar space, into the pulmonary epithelial cells, into the interstitial space, into vascular endothelial cells, into the plasma, into red blood cells, and then it binds to molecules of Hb that are not fully saturated.
100
When deoxygenated blood reaches the respiratory exchanges surface, what happens?
It rapidly equilibrates with alveolar gas (0.25 s)
101
After equilibrium what % is SaO2?
100%
102
After equilibrium what happens PaO2?
It is equal to PAO2
103
How does some deoxygenated blood enter circulation? What does it cause?
From the bronchial venous drainage
This deoxygenated blood dilutes the PaO2 to 12.7 kPa (95 mmHg) and the SaO2 to 97%
In total, the oxygen content (CaO2) is still slightly more than 20 mL·dL-1, which is a delivery rate of about 1000 mL·min-1 (assuming a cardiac output (Q) of 5 L·min-1.
104
When arterial blood reaches systemic capillary beds, what happens and why?
The tissue PO2 is considerably lower than PaO2. This gradient promotes diffusion of oxygen from the plasma into the endothelial cells, into the interstitium, into the respiring cells, and into the mitochondria.
105
As soon as the PaO2 starts to decrease at tissues, what happens?
oxygen unloads from Hb (according to the ODC) and follows the dissolved oxygen down the concentration gradient and out of the circulation.
106
Once the blood enters the venous circulation what happens the PO2, SvO2 and CaO2?
the PO2 has been reduced to 5.3 kPa and SvO2 to 75%. CaO2 is reduced to 15 mL/dl, which is a 5 mL/dl reduction from the precapillary vessel.
107
What is oxygen consumption denoted by?
VO2
108
For a cardiac output of 5L/min, what is the oxygen flux?
250ml/min (idk why!?)
109
Which is more soluble, O2 or CO2?
CO2, so it diffuses into the plasma more quickly
110
What does CO2 form wen it combines with H2O? What does this lead to?
H2CO3
| H2CO3 dissociates into H+ and HCO3- (bicarbonate) which can cause a fall in the pH below 7.4
111
When PCO2 of the plasma increases what happens to the CO2?
CO2 diffuses into erythrocytes that contain carbonic anhydrase, which accelerates the conversion of CO2 and H2O to H2CO3 by 5000-fold
112
When H2CO3 dissociates, how does HCO3- leave?
HCO3- is pumped out by an AE1 exchanger which imports Cl- to maintain membrane electroneutrality
113
When Cl- is influxed, during carbon dioxide transport, what happens next and why?
An influx of H2O which helps keep the cell hydrated
114
During carbon dioxide transport, how is the pH of the cell maintained?
It is kept buffered by globin chains which contain residues (e.g. Histamine) that are active proton acceptors. Some CO2 can be bound to the amine group and N-terminal of globin chains by adding a carboxyl group (i.e. -NH2 to -NHCOOH).
115
Whilst maintaining the pH of erythrocytes during CO2 transport, what happens to the Hb?
This turns Hb into HbCO2 (carbaminohaemoglobin)
116
When deoxygenated blood reaches the lungs what happens to the CO2 bound?
CO2 in solution diffuses out into the alveoli which reverses all other binding mechanisms. HCO3- re-enters the erythrocytes, recombines with H+ to form H2CO3 which reconverts into CO2 and H2O
117
Why is COPD associated with increased airway resistance?
- mucus hypersecretion
| - airway inflammation
118
Patients can COPD patients be treated?
Using bronchodilators and supplemental oxygen to increase O2 absorption
119
Why is COPD a problem?
- surface area of the lungs is reduced due to emphysemic breakdown of lung tissue
- the lung volumes increase due to air trapping
