Mechanics Of Breathing Flashcards
(89 cards)
1
Q
What is the definition of breathing?
A
The bodily function that leads to ventilation of the lungs, also known as external respiration
2
Q
What is the definition of ventilation?
A
The process of moving gases in (inspiration) and out (expiration) of the lungs
3
Q
What are obstructive diseases?
A
Diseases that obstructs airflow in the lungs
4
Q
What are restrictive diseases?
A
Diseases that cause the loss of elasticity in the lung tissue, chest wall or the thorax
5
Q
What are examples of obstructive conditions affecting ventilation?
A
- asthma
- chronic obstructive pulmonary disease
- lung cancer
6
Q
What are examples of restrictive conditions affecting ventilation?
A
- intrinsic e.g. pulmonary fibrosis
- extrinsic e.g. pneumothorax, disorders of the thoracic skeleton
7
Q
What pressure differences are required for inspiration
A
Inspiration when barometric pressure is greater than alveolar pressure
8
Q
What pressure differences are required for expiration?
A
Expiration when barometric pressure is less than alveolar pressure
9
Q
What is Boyle’s law for pressure changes occurring secondarily to thoracic volume changes
A
P is inversely proportional to the volume of an enclosed space
P ∝ 1/V
10
Q
Which inspiratory muscles are used in quiet breathing ?
A
- diaphragm flattens
- external intercostals contract to stabilise ribcage, moving it up and out to increase the lateral and antero-posterior diameter of the thorax
- internal intercostals relaxed
11
Q
Which inspiratory muscles are used in breathing with increased effort?
A
- diaphragm
- external intercostals move ribcage up and out
- accessory muscles (neck muscles and shoulder girdle muscles). Neck muscles pull the ribcage up, pectoralis major and latissimus dorsi pull the ribcage outwards
- Sternocleidomastoids elevate the sternum, scalenus major and minor muscles elevate the first two ribs and sternum
12
Q
Describe the diaphragm
A
- Thin, dome shaped layer of muscle and tendon that separates the abdominal cavity from the chest cavity
- Attaches at the costals in the lower ribcage, high in the front of the sternum and deeply in the back of the spine
- Also attaches at the central tendon, uses central tendon and attachments to leverage itself during inhalation
13
Q
What are the expiratory muscles used in quiet breathing?
A
elastic recoil of tissues, diaphragm relaxes, external intercostal muscles relax
14
Q
What are the expiratory muscles used in breathing with increasing effort?
A
- internal intercostals contract
- oblique, transversus and rectus abdominis muscles pull the ribcage downwards
- contraction of the abdominal muscles also increase intra-abdominal pressure and pulls the ribcage downwards and medially in forced expiration.
15
Q
How is the diaphragm innervated?
A
Phrenic nerves - nerves that come from the cervical = C3, C4, C5
16
Q
How are the intercostals innervated?
A
segmental thoracic nerves from the relevant levels of the thoracic spinal cord
17
Q
How is the level of injury of the spinal cord nerves relevant to which mechanism works?
A
Everything above the nerves which are injured still function but the muscles below would be paralysed
(if injury is C5 and above, the diaphragm will not function)
e.g. if thoracic nerves were injured, the muscles below would stop working
18
Q
During inspiration what happens to the alveolar and intrapleural pressure?
A
alveolar pressure goes up and intrapleural pressure goes down (difference increases)
19
Q
During expiration what happens to the alveolar and intrapleural pressure?
A
Alveolar pressure goes down and intrapleural pressure goes up (difference decreases)
20
Q
What is pneumothorax? How do you recognise it on a chest scan?
A
- air gets into the pleural space and the lung collapses
- increased blankness, no white striations showing blood vessels in lung area
- organs pushed to other side more
21
Q
What is a tension pneumothorax?
A
Increase in pressure pushes heart and stops the heart from filling with blood so there is not enough to pump around the body
22
Q
What is pleural effusion? How is it recognised on a chest scan?
A
- Fluid leaks into the pleural space which can be caused by heart failure
- costodiaphragmatic recess
23
Q
How could you clinically assess if there is a pneumothorax or pleural effusion?
A
Can use hands to find magnitude of chest expansion, one side of the chest moves more than the other when breathing
24
Q
How can the volume of air moving in and out of the lungs be measured?
A
Using a spirometer (traditional or modern)
Modern apparatus has a head which measures flow of air and is converted by a connected computer
25
What is the definition of tidal volume?
The volume of air moved in or out of the lungs during normal breathing
26
What are the typical values of tidal volume at rest and during exercise?
At rest: 6-7 ml/kg
During exercise : 15ml/kg
*However all lung volumes are dependant on age, sex and height
27
What is the definition of inspiratory reserve volume?
- After a normal expiration, the measurement of the volume taken after maximal inspiration.
- measured from end inspiration to max vol of inspiration
28
What is the typical value of inspiratory reserve volume for a 70kg male?
3,000 ml
29
What is the definition of expiratory reserve volume?
- After normal inspiration, the maximal expired breath
- measured from end expiration to maximal volume of expiration
30
What is the typical value of expiratory reserve volume for a 70kg male?
1,500ml
31
What is the definition of residual volume?
The air remaining in the lungs after maximal expiration
32
Why is there residual air left after maximal expiration?
The thorax is rigid in nature and the pleural attachments of the lungs to the chest prevent complete emptying of the lungs
33
What is a typical measure of the residual volume in a 70kg male?
1,000 ml
34
How can residual volume be measured?
(Cannot be measured by spirometry)
- Air contains a fixed concentration of N2 that is neither absorbed or produced by the body, if all N2 is washed out and volume is measured, the volume of air that was in the lungs can be estimated
- To wash N2 from lungs, subject breathes O2 (N2 free) and breathes out through a turbine volume-flow meter for a few minutes
- 2 minutes required in healthy adult but longer with people with asthma or emphysema
- expired gas collected and N2 concentration measured and volume determined
35
What is the equation used to calculate residual volume using N2 measurements?
Volume of gas in the lung (V) x concentration of N2 in the lung = volume of gas exhaled x concentration of N2 in gas exhaled
36
How do you calculate total lung capacity?
TV + IRV + ERV + RV
37
How do you calculate vital capacity?
TV + IRV + ERV
38
How do you calculate functional residual capacity?
ERV + RV
39
What is vital capacity?
After maximal inspiration make a maximal expiration
40
What is the typical value of vital capacity for a 70kg male?
5,000 ml
41
What is a restrictive lung disease that affects lung volumes and/or capacities?
Pulmonary fibrosis
- Reduced RV, FRC, VC and TLC
42
What are obstructive lung diseases that affect lung volumes and/or capacities?
asthma, COPD, emphysema
- Increased RV
- TLC may be reduced (COPD) or increased (emphysema)
- FRC is increased in emphysema
43
What is the functional residual volume (FRC) dependant on?
The compliance of the lungs and chest wall
44
What is the definition of compliance? Equation?
Change in lung volume per unit change in intrathoracic pressure.
C = ΔV/ΔP
45
How can compliance be measured clinically?
- Spirometry for volume
- Oesophageal balloon for pressure (passes from throat to the chest, passes diaphragm and enters the stomach)
46
What is recoil pressure?
Measures the tendency for the lungs or chest wall to collapse
47
How do you find the recoil pressure of the lung?
P(alveoli) - P(pleura)
- Intrapleural pressure is always negative compared to atmospheric pressure so a positive value for the lungs is calculated normally
- positive value means the lungs move in
48
How do you find the recoil pressure of the chest wall?
P(pleura) - P(barometric)
- Assumption that atmospheric pressure is at 0
- positive value means chest wall moves, negative means it moves out
49
At maximal expiration, what does compliance of the lung show?
Glottis is open so alveolar pressure is always the same as atmospheric pressure, pressure in pleural space increases towards 0 (but never reaches 0) as volume is being squeezed out.
Lungs move in, high compliance
50
At end expiration (tidal breathing), what does compliance of the lung show?
Higher recoil pressure, so lower compliance but still high overall, compared to at maximal expiration
51
What does compliance of the lung show at peak inspiration?
Highest recoil pressure, low compliance
52
At maximal expiration, what does compliance of the chest wall show?
Closed glottis, relaxed muscles and negative recoil pressure.
Chest wall trying to re-expand.
53
At expiration with open glottis and muscles still relaxed, what is the compliance of the chest wall?
recoil pressure less negative compared to maximal expiration with closed glottis
54
Maximal inspiration with closed glottis and relaxed muscles, what is the compliance of the chest wall?
Recoil pressure becomes positive and increases from maximal expiration
55
When are the lung and chest wall recoil pressures equal but opposite?
FRC is the relaxation point when this happens, the compliance of the lung and chest cancel each other out.
56
What are diseases associated with reduced compliance?
- pulmonary fibrosis
- kyphoscoliosis (a lateral deviation of the curvature of the spine)
- Circumferential burn (tissue scar goes all around the body, as the scar matures shrinks and squeezes on chest, causing patient to inadequately ventilate). Treatment is escharotomy = cut through burn scar
57
What are diseases associated with increased compliance?
- emphysema
- Obstructive pulmonary disease (narrowing of small airways and destruction of the respiratory airway) = tissue destruction so lung becomes increasingly elastic and there is less resistance to stretching so increased compliance
58
What is much of adult lung disease attributable to?
Tobacco
59
Why is compliance not equal throughout the lung?
Gravity
60
What happens if the closing capacity exceeds FRC?
Alveoli in dependant lung regions will be poorly ventilated
61
What is the Law of Laplace?
P = 2t/r
where P = pressure
t = surface tension
r = radius of the bubble
62
How does the Law of Laplace affect the alveoli?
- Smaller the radius = larger the collapsing pressure
- smaller alveoli will collapse into larger alveoli if there is just water due to surface tension
- therefore surfactant reduces surface tension and prevents collapse
63
What are type 1 alveolar cells ?
Thin cells that line the alveoli for gas exchange
64
What are type 2 alveolar cells?
Produce and secrete the surfactant and lines the internal alveolar membrane
65
What is surfactant made up of?
90% phospholipid, 10% protein
66
What does surfactant do?
Acts as a detergent to reduce alveolar surface
- Increases pulmonary compliance
- prevents atelectasis (collapse of small airways)
- aids alveolar recruitment (re-expansion of previously collapsed alveoli)
- minimises alveolar fluid
67
What causes infant respiratory distress syndrome?
Deficiency in surfactant
68
What happens to the surfactant as alveolar volume increases?
- Surfactant becomes more dispersed, equalising pressure between alveoli of different sizes
- large alveolus = surfactant layer is thinner so less surface tension in larger alveoli
69
How can the relationship between intrathoracic pressure and lung volume during tidal breathing be represented?
inspiration = curve of sharp increase which is slowed and becomes sharper again
expiration = same as inspiration but reflected
The path of tidal breathing has a pattern called hysteresis
70
What are the causes of hysteresis at small lung volumes?
- reduced compliance of elastic structures
- airway calibre
changes in resistance cause hysteresis
71
What is the equation for laminar flow using airway calibre?
Flow = (k. ΔP. r4)/L
where k is a constant and r is radius
72
What is laminar flow and turbulent flow?
- Laminar = molecules travel straight and don't bump into each other (energy efficient)
- Turbulent = increased flow, calibre and branching and change in pressure increases by the power of 2
73
How are breath sounds heard in areas of high turbulent flow compared to less turbulent flow areas?
- In large airways breath is generated (highly turbulent)
- breath sounds heard over the lungs are attenuated by the distant airways ( less turbulent)
74
What are the characteristics of vesicular breath sounds?
- soft with low pitch, softer during expiration
- most commonly heard in lung bases and periphery
- inspiratory time longer than expiratory time
75
What are the characteristics of bronchial breath sounds?
- hollow or tubular sounds, higher pitched and louder than vesicular
- if heard in the peripheral of lungs, may be abnormal and suspicious of pneumonia, pleural effusion or atelectasis
- inspiration and expiration similar in duration, distinct pauses between inspiration and expiration
76
What is a vitalograph spirometer used to measure?
- forced vital capacity (FVC)
- forced expiratory volume in 1 second (FEV1)
77
What is a peak flow meter used to measure?
- peak expiratory flow rate (PEFR)
78
What does the graph for obstructive and restrictive pulmonary disease look like in terms of time and volume of exhaled air?
obstructive defect = gradual increase of volume of exhaled air with time, does not reach normal FVC and not as curved at start (smaller FEV1)
restrictive defect = significant decrease in FVC, increase in volume at start which slows quicker than normal expiration.
79
What is the FEV1/FVC ratio used to distinguish?
Used to distinguish between obstructive and restrictive conditions
- ratio < 0.7 = obstructive
- ratio > 0.7 = restrictive
80
What are the advantages of PEFR?
- patients can monitor their asthma or COPD at home
- less dependant on effort than FEV
81
What are the limitations of PEFR?
- Not as good as spirometry for measuring airflow limitation
- wide diurnal variations with highest readings in the evening and lowest in early hours of the morning
- only measures expiratory flow rate
82
what are the units used for PEFR?
unit used is L/min or L/s
83
Can FEV1 and PEFR be restored to normal in asthma (e.g. after salbutamol)?
Airway constriction is reversible
84
Can FEV1 and PEFR be restored to normal in COPD (e.g. after salbutamol)?
- airway constriction is irreversible (or nearly irreversible)
- <15% or <200mL/s improvement in FEV1 and PEFR after salbutamol
85
How is energy used, stored and dissipated in breathing?
- Energy is used in inspiration to overcome elastic forces, stored as potential energy and dissipates in expiration
- work is expended in the form of heat during inspiration and expiration to overcome resistance forces
86
What is the energy expenditure in health at rest?
2.5%
87
What is the energy expenditure at maximal hyperventilation?
30%
88
What is the energy expenditure in restrictive conditions?
work is minimised with rapid small volume breaths
89
What is the energy expenditure in obstructive conditions?
work is minimised with large volume slow breaths
