Physiology Flashcards
1
Q
What is internal respiration
A
Intracellular mechanisms which consume oxygen and produce carbon dioxide
2
Q
What is external respiration
A
Sequence of events leading to exchange of oxygen and carbon dioxide between external environment and cells of the body
3
Q
Steps of external respiration
A
Ventilation - Gas exchange between atmosphere and alveoli in the lungs
Exchange O2 and CO2 between air in alveoli and blood coming into lungs
Transport O2 and CO2 in blood between lungs and tissues
Exchange O2 and CO2 between blood and tissues
4
Q
What is ventilation
A
Mechanical process of moving air between atmosphere and alveolar sacs
5
Q
How is lesser pressure in lungs compared to atmosphere achieved
A
During inspiration, lungs move outwards, increasing volume. This leads to a decrease in pressure exerted by the gas.
6
Q
What forces hold thoracic wall and lungs close
A
Intrapleural fluid cohesiveness - Water molecules in intrapleural fluid are attracted to each other and resist being pulled apart. Hence, pleural membrane stick
Negative intrapleural pressure - Subatmospheric intrapleural pressure creates a transmural pressure gradient across lung wall and chest wall
7
Q
What happens to diaphragm during inspiration
A
It flattens out, increasing volume of thorax vertically
8
Q
Contraction of which muscles help in inspiration
A
External intercoastal muscles, contraction lifts rib cage
9
Q
Which is an active process, in or exspiration
A
Inspiration
10
Q
What is Pneumothorax
A
Air in pleural cavity, abolishes pressure gradient
11
Q
Pneumothorax symptoms
A
Chest pain, shortness of breath (dyspnoea)
Hyperresonant percussion note, decreased or absent breath sounds
12
Q
Normal pressure gradients in the lung
A
Intraalveolar/Intrapulmonary - 760 mm Hg
Intrapleural/Intrathoracic - 756 mm Hg
13
Q
What causes lungs to recoil during expiration
A
Elastic connective tissue in lungs and alveolar surface tension
14
Q
Which alveoli have a higher tendency to collapse
A
Smaller alveoli due to LaPlace law
15
Q
What is pulmonary surfactant
A
Pulmonary surfactant is a mixture of proteins and lipids secreted by type II alveolar cells
16
Q
Function of pulmonary surfactant
A
Pulmonary surfactant is interspersed between water molecules lining the alveoli and helps lower surface tension. This prevents collapse of alveoli
17
Q
What is respiratory distress syndrome of new born
A
New borns may not have enough pulmonary surfactant lining the alveoli. The baby has to make very strenuous inspiratory efforts in an attempt to overcome high surface tension and inflate the lungs
18
Q
Another factor for keeping the alveoli open
A
Alveolar interdependence
19
Q
What is alveolar interdependance
A
Mutual supporting structures, termed interdependence, combine with surfactants tension lowering property provide physical stability. If an alveolus starts to collapse, the surrounding alveoli are stretched and then recoil, exerting expanding forces in the collapsing alveolus to open it.
20
Q
Major inspiratory muscles
A
Diaphragm and external intercoastal muscles
21
Q
Muscles during forceful inspiration
A
Sternocleiodomastoid, scalenus, pectoral
22
Q
Muscles of active expiration
A
Abdominal and internal intercoastal muscles
23
Q
What is tidal volume (TV)
A
Volume of air entering or leaving the lungs during a single breath (0.5L)
24
Q
What is inspiratory reserve volume (IRV)
A
Extra volume of air that can be inspired over the typical resting tidal volume (3 L)
25
What is expiratory reserve volume (ERV)
Extra volume of air that can be expired beyond the normal volume of air after resting tidal volume (1 L)
26
What is residual volume (RV)
Minimum volume of air in the lungs after maximal expiration (1.2 L)
27
What are the 4 lung volumes
Tidal volume, inspiratory reserve volume, expiratory reserve volume and residual volume
28
What is inspiratory capacity (IC)
Maximum volume of air that can be inspired at the end of a normal quiet expiration (3.5 L)
IC = IRV + TV
29
What is functional residual capacity (FRC)
Volume of air in lungs at end of normal passive expiration (2.2 L)
FRC = ERV + RV
30
What is vital capacity (VC)
Maximum volume of air that can be moved out during a single breath following a maximal inspiration (4.5 L)
VC = TV + IRV + ERV
31
What is total lung capacity (TLC)
Total volume of air lungs can hold (5.7 L)
| TLC = VC + RV
32
When does residual volume increase
When elastic recoil of lungs is lost, e.g. emphysema
33
What do volume time curves help determine
FVC - Forced vital capacity which is the maximum volume that can be forcibly expelled from lungs following a maximum inspiration
FEV1 - Forced expiratory volume in 1 s which is volume of air that can be expired in the first second of expiration
34
Normal FEV1/FVC ratio
FEV1/FVC > 70% is normal
35
What are dynamic lung volumes
Lung volumes that depend on rate of air flow
36
FEV1/FVC ratio in obstructive vs restrictive lung disease
Obstructive lung disease, FEV1/FVC < 70%
| Restrictive lung disease, FEV1/FVC > 70%, FVC is reduced
37
What is reduced in restrictive lung disease, FEV1 or FVC
FVC and FEV1 hence ratio of FEV1/FVC is unchanged
| However they are both reduced
38
What part of ANS causes bronchodilation
Sympathetic stimulation
39
Which is harder, expiration or inspiration when diseased
Expiration
40
What happens to intrapleural pressure during in and expiration
Intrapleural pressure follows intralveolar pressure
| Intrapleural pressure falls during inspiration and rises during expiration
41
What is dynamic airway compression
Rising pleural pressure during expiration compresses the alveoli and airway. This causes the wheezing sound heard in patients with obstructive disease
42
When is peak flow useful
To assess obstructive lung disease: Asthma and COPD
43
What pattern does decreased pulmonary compliance cause in spirometry
Restrictive pattern of lung volume
44
What can cause increased pulmonary compliance
Is elastic recoil is lost: emphysema. Patients have to work harder to get air out of lungs
45
Relation between compliance and age
Compliance increases with age
46
When does work of breathing increase?
Pulmonary compliance is decreased, airway resistance increased, elastic recoil decreased or need to increase ventilation
47
Formula for pulmonary ventilation
Pulmonary ventilation = Tidal volume * Respiratory rate (
| 0.5 L * 12 breaths/min = 6 L
48
What is alveolar ventilation
(Tidal volume - dead space) * Respiratory rate
| (0.5 - 0.15) * 12 = 4.2 L
49
Why is it better to increase depth of breathing than RR
Due to presence of anatomical dead space
50
What does transfer of gases between body and atmosphere depend on
Ventilation - Rate at which air passes the lungs
| Perfusion - Rate at which blood passes the lungs
51
Which part of lung has maximum blood flow and ventilation
Bottom lung has maximum blood flow whereas top lung has maximum ventilation
52
What is alveolar dead space
Ventilated alveoli not adequately perfused with blood
53
What is physiological dead space
Anatomical dead space - Alveolar dead space
54
Ventilation perfusion match in the lungs
Increase in CO2 due to increased perfusion decreases airway resistance leading to increase airflow
Increase in 02 due to increased ventilation causes pulmonary vasodilation which increases blood flow
55
Effect of O2 on arterioles
O2 vasodilates pulmonary arterioles whereas it vasoconstricts systemic arterioles
56
What affects rate of gas exchange across alveolar membrane
Partial pressure gradient of O2 and CO2
Diffusion coefficient for O2 and CO2
Surface area of alveolar membrane
Thickness of alveolar membrane
57
What is the respiratory exchange ratio (RER)
Ratio between amount of CO2 produced in metabolism and O2 used. RER = 0.8
58
Equation for partial pressure of oxygen in alveolar air
Alveolar gas equation -
| PAO2 = PiO2 - (PaCO2/0.8)
59
Which gas is more soluble in membranes
CO2 is more soluble than O2. Solubility of gas in membranes is diffusion coefficient. The diffusion coefficient of CO2 is 20 times that of O2.
60
What does a big gradient between arterial (PaO2) and alveolar oxygen indicate (PAO2)
Problem with gas exchange or left-right shunt in heart
61
Ficks's law of diffusion
Amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to to it's thickness
62
What do walls of alveoli contain
Flattened type 1 alveolar cells. Space inside contains alveolar macrophage whereas type 2 alveolar cells secrete pulmonary surfactant
63
Major influence on the rate of gas transfer
Partial pressure gradient of O2 and CO2
64
What is Henry's law
Amount of gas dissolved in a liquid is proportional to the partial pressure of the gas in equilibrium with the liquid
65
How is most oxygen transported in the body
Bound to heamoglobin and dissolved oxygen in blood
66
Oxygen binding to haemoglobin
Each haemoglobin has 4 haem groups. One haem group can bind to one O2 molecule.
67
What determines oxygen delivery to tissues
Oxygen content of arterial blood and cardiac output
68
What is oxygen delivery index
```
DO2I = CaO2 * Cl
DO2I = Oxygen content of arterial blood * Cardiac index
```
69
What determines oxygen content of blood
```
CaO2 = 1.34 * Hb * SaO2
CaO2 = 1.34 * Haemoglobin concentration * %Hb saturation with O2
```
70
Convert kPa to mmHg
Multiply by 7.5
71
Binding of one O2 to Hb increase affinity for more?
True, sigmoid shape curve
72
Significance of steep lower part of sigmoid curve in % Hb saturation vs blood PO2
Peripheral tissues get a lot of oxygen for a small drop in capillary PO2 as easier for O2 to dissociate
73
What is the Bohr effect
Bohr effect states that Hb O2 binding affinitiy is inversely related to acidity and concentration of CO2. Since more CO2 is released from metabolically active tissue, there is a fall in pH leading to release O2 from Hb
74
By what effect do metabolically active tissues get more O2
Bohr effect, oxygen dissociation curve shifts right
75
How is foetal haemoglobin (Hb) different from adult heamoglobin
Foetal hemoglobin has 2 alpha and 2 gamma subunits. This interacts less with 2,3 - bisphosphoglycerate in red blood cells. Hence, HBf has higher affinity for O2 than Hb and O2-Hb dissociation curve shifts to the left
76
Significance of foetal haemoglobin
Foetal haemoglobin allows O2 transfer from mother to foetus even if PO2 is low
77
Where is myoglobin present
In skeletal and cardiac muscle
78
Myoglobin-PO2 dissociation curve
Hyperbolic curve, releases O2 at very low PO2
79
Presence of myoglobin in blood indicates?
Muscle damage and can damage kidneys eventually
80
Function of Myoglobin
Provides short term storage of O2 for anaerobic conditions
81
How is CO2 transported in blood
Dissolved (10), bicarbonate (60) and carbamino (30)
82
How is bicarbonate formed in blood
CO2 + H2O = H2CO3 = H+ + HCO3-
| This is mediated by Carbonic Anhydrase in RBC
83
What is choride shift
HCO3- forms from CO2 in RBCs. Thus, rise in intracellular bicarbonate leads to bicarbonate export and chloride intake using anion exchanger protein. This ensures the reaction proceeds from CO2 to HCO3- and not the other way round
84
Haemoglobin has a higher affinity for?
CO2 to form carbamino-haemoglobin
85
What is the Haldane effect
Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
86
What effects work in synchrony to facilitate O2 liberation and CO2 and CO2 generated H+ at tissues
Bohr effect and Haldane effect
87
Haldane effect shifts CO2 dissociation curve to?
The right
88
Haldane effect at lungs
Blood picks up O2 at the lungs, decreasing affinity for CO2 and CO2 generated H+
89
How do red blood cells exchange CO2 for O2 in alveoli
Closer to the lungs, CO2 concentration falls. This leads to dissociation of H+ from Hb shifting the concentration towards CO2 formation. The decrease in bicarbonate (HCO3_) levels reverses chloride shift with HCO3- moving into RBC. This leads to more formation of CO2 via carbonic anhydrase which is exchanged for O2 due to concentration gradient.
90
FVC is reserved in Asthma or COPD
Asthma
91
What is peak expiratory flow rate (PEFR)
Person's maximum speed of expiration as measured by peak flow meter
92
PEFR in obstructive vs restrictive
Less in obstructive, unchanged in restrictive
93
FEV1 in obstructive vs restrictive
Less in obstructive and restrictive
94
FVC in obstructive vs restrictive
Normal in asthma, reduced in COPD and restrictive
95
FEV1/FVC in obstructive vs restrictive
< 75% in obstructive, >75% in restrictive
96
FEV1 response to B2-agonist in obstructive vs restrictive
>15% in Asthma, <15% in COPD, no response in restrictive
97
What is bronchial challenge testing
Patient is adminstered methacholine/histamine/mannitol. These are markers of airway hyper-responsiveness and cause bronchoconstriction. A fall of 20% in FEV1 is calculated and compared to healthy individuals
98
What is bronchial challenge testing used for
To assess allergic or occupational asthma
99
How can exercise induced asthma be tested for
Exercise testing. Decrease in FEV1 or PEF post exercise is indicative.
100
Use of full cardiopulmonary exercise test (CPET)
Differentiate cardiac vs respiratory dyspnoea
| It monitors heart rate vs oxygen uptake vs ventilatory rate
101
TCL in emphysema
Increase
102
TLC in restrictive lung disease
Decreases
103
What is transfer factor for carbon monoxide (TLCO)
Also called diffusing capacity of lungs for carbon monoxide (DLCO). It measures ability of the lungs to transfer gas from inhaled air to RBC in pulmonary capillaries.
104
DLCO manoeuvre advantage
Easier for elderly patients to perform the ten second breath holding in DLCO that forced exhalation in spirometry
105
How can airway resistance be measured
Plethysmography or impulse oscillometry
106
More sensitive method than spirometry in differentiating small and large airway obstruction
Impulse oscillometry; sound waves are superimposed on normal tidal breathing and disturbances to flow and pressure by external waves are used to calculate resistance to airflow
107
Exhaled breath nitric oxide (FeNO)
Non-invasive marker of eosinophilic airway inflammation in asthma. Not useful in smokers with COPD as nitric oxide is suppressed by smoking
108
What do high levels of nitric oxide in asthmatics show
(> 35ppb) Uncontrolled asthmatic inflammation. Used as as adjunct to bronchial challenge
109
Major respiratory rhythm generator
Medulla oblongata by network of neurons called Pre-Botzinger complex. They display pacemaker activity near the upper end of medulla respiratory control centre
110
Neural activity leading to inspiration
Rhythm is generated by Pre-Botzinger complex. This excites dorsal respiratory group neurones (inspiratory) which fire in bursts. This firing causes contraction of inspiratory muscles - inspiration. Cessation of firing causes passive expiration
111
How does active expiration occur
Increase firing of dorsal neruones excites ventral neurones. These activate internal intercoastal muscles, abdominals etc to cause forceful expiration.
112
Parts of pons respiratory centre
Pneumotaxic center and apneustic center
113
How is inspiration terminated
Firing of dorsal neurones causes stimulation of the pneumotaxic center. This terminates inspiration.
114
What is apneusis
Breathing with prolonged inspiratory gasps and brief expiration due to absence of pneumotaxic center in pons.
115
Function of apneustic center in pons
Apneustic neurones stimulates inspiratory area of medulla prolonging inspiration.
116
Respiratory rhythm control in the brain
Rhythm is generated in medulla: Pre-Botzinger complex (generates rhythm), dorsal neurones (contraction and inspiration) and ventral neurones (forceful expiration). Rhythm is controlled in the pons: pneumotaxic center (terminates inspiration) and apneustic center (prolongs inspiration)
117
Respiratory centers are influenced by?
Higher brain centres - cerebral cortex, hypothalamus
Stretch receptors - Hering-Breuer reflex guards against hyperinflation of lungs
Juxtapulmonary (J) receptors - Stimulated by pulmonary capillary congestion and pulmonary oedema; also pulmonary emboli causes rapid, shallow breathing
Joint receptors - Joint movement
Baroreceptors - Decrease blood pressure, increase respiratory rate
118
Pulmonary stretch receptors are also known as
Hering-Breuer reflex
119
What contributes to increased ventilation during exercise
Joint receptors that increase breathing due to movement at joints
120
Factors increasing ventilation during exercise
Reflexes originating from body movement
Adrenaline release, impulse from cerebral cortex, increase in body temperature, accumulation of CO2 and H+ by active muscles
121
Where is the cough reflex centre
Medulla
122
Steps in cough reflex
Short intake of breath, closure of larynx, contraction of abdominal muscles (increase intra-alveolar pressure) and opening of larynx and expulsion of air
123
Chemical control of respiration is by
Blood gas tension especially CO2
124
Peripheral chemoreceptors that sense tension of O2, CO2 and H+ in the body are situated at
```
Carotid body (Hering's nerve part of glossopharyngeal)
Aortic body (Vagus nerve)
```
125
Central chemoreceptors that response to H+ of CSF are
Surface of medulla of brainstem
126
Only CO2, not H+ or HCO3-, can diffuse across blood-brain barrier. What can this cause?
CO2 and diffuse across the barrier and react with H20 leading to the formation of HCO3- and H+. This increases acidity of blood. This activates central chemoreceptors leading to an increase in depth and rate of inspiration.
127
What causes hypoxia at high altitudes
Decrease partial pressure of inspired oxygen (PiO2)
128
Acute response to hypoxia
Hyperventilation and increased cardiac output
129
Symptoms of acute mountain sickness
Nausea, headache, fatigue, tachycardia, dizziness, sleep disturbance, exhaustion, SOB, unconsciousness
130
Chronic adaptation to high altitudes hypoxia
Increased RBC production, 2,3-BPG produced within RBC (O2 offloaded more easily into tissues), number of capillaries, number of mitochondria, kidneys conserve acid to decrease arterial pH
131
Hypoxic drive is via what receptors
Peripheral chemoreceptors
132
H+ drive of respiration
Via peripheral chemoreceptors. Increase in non-carbonic acid H+ (eg: lactic acid during exercise, diabetic ketoacidosis) leads to hyperventilation in an attempt to remove CO2 from the body. This is imporant in acid-base balance in body
133
When does arterial oxygen level become important
If PO2 < 8 kPa
134
Type 1 vs type 2 respiratory failure
Type 1 - Hypoxia
| Type 2 - Hypoxia + Hypercarbia
135
What percentage do we try and keep the percent saturation at
90% sO2 which corresponds to oxygen partial pressure pO2 of 60mmHg
136
What is percent saturation of oxygen
The amount of haemoglobin bound by oxygen
137
What can very high oxygen levels cause
High CO2 levels leading to acidosis
138
Do all COPD patients retain oxygen
No, only 1 in
139
What chemoreceptors does the body generally use
CO2 chemoreceptors. Normal respiration is driven by amount of CO2 in arteries. Increase in CO2 leads to an increase in respiration
140
What is the hypoxic drive
A form of respiration in which the body uses oxygen chemoreceptors instead of CO2 chemoreceptors to regulate respiratory cycle
141
Where do you get low inspired oxygen
High altitudes with low barometric pressure
142
What is Ondine's curse
Central hypoventillary synrome (CHS) is a respiratory disorder that results in respiratory arrest during sleep
143
Shunting and dead space
Perfusion without ventilation is shunting
| Ventilation without perfusion is dead space
144
Is oxygen the therapy for breathlessness
No but it can help maximise potential, target the cause of breathlessness while eliminating hypoxaemia
145
Oxygen target for type 2 respiratory failure
88 - 92 %
146
Oxygen target for type 1 respiratory failure
94 - 98 %
147
Risk factors for type 2 hypercapnic respiratory failure
Moderate or severe COPD, kyphoscoliosis, severe obesity, neuromuscular disease, cystic fibrosis, brochiectasis.
148
What flow can nasal cannulae be used till
1 to 4 l/min
149
Variable performance mask flow limit
5 - 15 l/min
150
Venturi mask flow limit
Upto 250 l/min
