Respiration 1 Flashcards
What are the main functions of the respiratory system? (4)
Provide oxygen and remove carbon dioxide
Phonation
Protection from microbes and other foreign matter
Regulate blood pH
Why is the transport of gases in the blood referred to as bulk flow?
Blood carrying the gases is pumped around the body (gases do not move through blood)
What is the main difference between bronchi and bronchioles?
Cartilage is present in bronchi only
Why does bronchiole smooth muscle contract?
Prevent irritants and particles entering the alveoli
How many alveoli does one human lung have?
400 million
What is the surface area of your lungs?
85m squared
How thin can the walls of the alveoli be?
As little as 0.2um
What is diffusion of a gas across a membrane proportional to?
(Surface area/thickness) x gas permeability
What is tidal volume?
Volume of air breathed in per breath during normal steady/quiet breathing
500ml
What is inspiratory reserve volume?
Maximum amount that lung volume can be increased by above tidal volume
3000ml
What is expiratory reserve volume?
Maximum amount of air that can be exhaled after tidal volume has been expired
1200ml
What is residual volume?
Volume of air remaining in lungs after maximum exhalation
1200ml
What are capacities?
Sum of two or more volumes
What is inspiratory capacity the sum of and what is its average value?
Tidal volume + inspiratory reserve volume
3500ml
What is (forced) vital capacity the sum of and what is its average value?
Tidal volume + inspiratory reserve volume + expiratory reserve volume
4700ml
What is functional residual capacity the sum of and what is its average value?
Residual volume + expiratory reserve volume
2400ml
What is total lung capacity the sum of and what is its average value?
Residual volume + expiratory reserve volume + inspiratory reserve volume + tidal volume
5900ml
Why can a spirometer not be used to directly measure residual volume?
Lungs cannot be completely emptied so no ‘baseline’ can be recorded
What is ventilation?
Exchange of air between atmosphere and alveoli
What is V̇E and how do you calculate it?
Minute ventilation
Total ventilation per minute = breathing rate x tidal volume
What is V̇A?
Alveolar ventilation
Volume of fresh air reaching alveoli per minute
How do you calculate V̇A?
Minute ventilation - dead space ventilation (~4200ml/min)
What is the anatomical dead space and its average value?
Volume of purely conducting airways ~150ml
What are the standard units of pressure?
kPa
What is the equivalent of 1kPa in mmHg?
7.5mmHg
What is Darcy’s law regarding ventilation?
Flow = (Palv - Patm)/R
In between breaths, what is Palv relative to Patm and how can we tell?
0
No air flow so no gradient present
What is Boyle’s law regarding pressure?
Pressure of gas at a constant temperature is inversely proportional to the volume of its container
How is the negative pressure between the pleura generated when at functional residual capacity?
Respiratory muscles are relaxed
Inward recoil of lungs is balanced by outward recoil of chest wall
What is intrapleural pressure?
Pressure between pleural membranes
Usually negative
What does transpulmonary pressure do and how is it calculated?
Palv - Pip
Transmits changes in pressure from chest expansion to alveoli
Describe the steps involved in inspiration.
- Nerves stimulate diaphragm and other inspiratory muscles to contract to expand chest wall
- Pip falls to -0.7kPa
- Ptp increases so alveoli expands
- Palv falls by Boyle’s law
- Air moves into lungs down pressure gradient
Describe the steps involved in expiration.
- Nerves decrease firing to diaphragm and intercostals (relaxation)
- Expanded chest wall recoils inward
- Pip and Ptp return to pre-inspiratory level
- Expanded lungs reduce in size
- Air is compressed, increasing Palv and forcing air out of lungs
Which muscles (other than diaphragm) are most helpful in forced expiration?
Abdominals
Where is airway resistance most significant?
Conducting airways
Especially middle order bronchi
Why don’t bronchioles increase resistance more than bronchi even though they have smaller diameters?
Much more numerous and arranged in parallel
What type of air flow occurs in quiet breathing?
Laminar
Why is your breathing noisy during heavy exercise?
Turbulent air flow
How does congestion affect air flow?
Increases resistance so decreases air flow
What type of disease is increased airway resistance a feature of?
Obstructive lung disease
Give three examples of obstructive lung diseases.
Asthma
Chronic bronchitis
Emphysema
What is asthma?
Obstructive lung disease
Smooth muscle is hypersensitive to constrictors
Smooth muscle thickening and inflammation
What is chronic bronchitis?
Obstructive lung disease
Inflammation
Hypertrophied glands in airways produce excess mucus
What is Poiseuille’s law (basic)?
Resistance is inversely proportional to radius to the power of 4
How is flow and radius connected (simple)?
Flow is proportional to radius to the power of 4
What are examples of dilators of airway smooth muscle?
Carbon dioxide
Adrenaline - β2-adrenoceptors
What are examples of constrictors of airway smooth muscle?
Vagus nerve - ACh and M3 receptors
Inflammatory mediators
How does Ptp affect bronchioles during inspiration?
Expands bronchioles via lateral traction exerted by connective tissue
How is lung compliance calculated?
Change in lung volume/change in Ptp
What is lung compliance?
Measure of how easily lungs are expanded by a given change in pressure
Determines the amount of work that must be done by respiratory muscles
How is Ptp measured?
Subject inhales in steps from residual volume to total lung capacity
At each step, measure volume inspired and Pip
No airflow so Palv = Patm so Ptp = -Pip
On a lung volume/Ptp graph, how can you calculate the lung compliance?
Find the slope/gradient of the curve
What determines lung compliance?
Resistance of tissues to stretch influenced by extracellular matrix composition
Resistance due to surface tension in alveoli
How does lung fibrosis affect compliance?
High resistance of tissues to stretch
Decreased compliance
How does emphysema affect compliance?
Low resistance of tissues to stretch
Increased compliance
What does abnormally low compliance suggest?
Fibrosis - restrictive lung diseases
What does abnormally high compliance suggest?
Emphysema - obstructive lung diseases
What is emphysema?
Tissue destruction causes alveolar spaces to fuse which decreases surface area
Bronchioles collapse more easily on expiration which traps air
What is surface tension?
Force at an air-fluid interface caused by water molecules attracting each other and forming intermolecular bonds
What is the equation linking pressure, radius and surface tension (Laplace)?
P = 2T/r
If there was no surfactant, what would happen to relatively smaller alveoli?
Much greater internal pressure due to Laplace’s law
Air moves down pressure gradient into larger alveoli and smaller alveoli collapse - impairs gas exchange
Why do we need surfactant in alveoli?
Reduces surface tension to protect lungs/alveoli from collapsing
How does surfactant work to protect from collapse?
Greater concentration of surfactant in smaller alveoli so surface tension is lower
Hence internal pressure of smaller alveoli becomes almost equal to larger alveoli
No flow/collapse
What are two simple pulmonary tests used to measure lung function?
Vitalographs
Peak flow meters
What is a vitalograph?
Plots changes in lung volume over time during a single forced expiration
How can a vitalograph be used to give evidence for different lung diseases?
Obstructive diseases - unable to force out 75% volume in one second but lung volume is normal (decreased FER<50%)
Restrictive diseases - force out more than 75% volume in one second but unable to expand lung to full (increased FER>90%)
How do you calculate forced expiratory ratio?
Forced expiratory volume in one second / forced vital capacity
What does a peak flow meter measure?
Peak expiratory flow rate
How can you work out the peak expiratory flow rate from a vitalograph?
Find the gradient at the start of the breath (steepest gradient)
