19. Respiratory System Practicals Flashcards
Outline the principal muscles associated with inspiration and expiration
The inspiratory muscles include:
o The diaphragm
o The accessory muscles
The accessory muscles include:
o External intercostals (infero-medial direction)
o Scalene
o Sternocleidomastoid (SCM)
The expiratory muscles include:
o Internal intercostals (infero-lateral direction)
o The internal and external oblique
o Rectus abdominis
Outline the additional non-respiratory actions of the principal respiratory muscles
Accessory muscles control air movement during other behaviours such as speech, laughter, coughing, sneezing, and vomiting
The diaphragm is an essential muscle in childbirth and is also used when vomiting
The rectus abdominis is used during laughing and coughing
The sternocleidomastoid is involved in movement of the head
Outline how contraction of inspiratory muscles causes the chest wall to expand and the lungs to enlarge
The diaphragm contracts and is pulled downwards, increasing the super-inferior dimensions of the thorax
The external intercostals contract, pulling the ribs up and out, increasing the antero-posterior dimensions of the thorax
The increased volume decreases the pressure, causing a pressure gradient; air rushes into the lungs, filling them
Outline how contraction of expiratory muscles causes the chest wall to contract and the lungs to reduce in size
The internal intercostal muscles, along with the oblique muscles and rectus abdominis causes the ribs to be pulled in and down decreasing the antero-posterior dimensions of the thorax
The diaphragm relaxes and is pushed upwards, decreasing the supero-inferior dimensions of the thorax
A pressure gradient is generated and so air is pushed out
Outline how these muscles will be differentially activated during different breathing states
The diaphragm alone is used in quiet breathing
The external intercostals are used on increased demand
The scalene, sternocleidomastoid and accessory expiratory muscles only are used in exercise or during high demand
Describe how to measure the respiratory volumes and capacities of the lung
Lung volumes are measured by spirometry
Height and weight of the subject are recorded first, followed by a minute of breathing at rest
The subject then breathes from the spirometer wearing a nose clip for 30 seconds; after a few normal breaths, a maximum inspiration and a slow maximum respiration are measured
This should ideally be repeated in different postures
The spirometer cannot be used to measure the residual volume (RV), and therefore cannot measure either
the functional residual capacity (FRC) or the total lung capacity (TLC)
These values must be obtained by the inert gas dilution technique:
o A tracer gas (helium) is used, which mixes with the air in the lungs but does not diffuse out; the volume is then determined by the amount that this gas is diluted as it mixes with the air in the lungs
Define Tidal Volume
Tidal Volume (VT)
The volume of air inspired in a single spontaneous breath
= ~500ml
Define Inspiratory Reserve Volume
Inspiratory Reserve Volume (IRV)
The additional volume that could be maximally inspired after a tidal volume inspiration
= ~3100ml
Define Expiratory Reserve Volume
Expiratory Reserve Volume (ERV)
The additional volume that could be maximally expired after a tidal volume expiration
= ~1200ml
Define Vital Capacity
Vital Capacity (VC)
The volume of air that is possible to maximally exhale following a maximal inspiration
= IRV + VT + ERV
= ~4800ml
Define Inspiratory Capacity
Inspiratory Capacity (IC)
The volume of air that it is possible to inspire at the end of a normal quiet expiration
= VT + ERV
= 3600ml
Define Residual Volume
Residual Volume (RV)
The volume of air remaining within the lungs and airways at the end of a normal quiet expiration
= ~1200ml
Define Functional Residual Capacity
Functional Residual Capacity (FRV)
The volume of air contained within the lungs and airways at the end of a tidal volume expiration; this is the equilibrium volume at which elastic recoil exactly balances the chest wall forces
= RV + ERV
= ~2400ml
Define Total Lung Capacity
Total Lung Capacity (TLC)
The volume of air contained within the lungs and airways at the end of a maximal inspiration
= RV + ERV + VT +IRV
= ~6000ml
Which individualised factors may influence the value of lung volume/capacities?
These volumes can be influenced by body weight, height, age and gender
There are charts that help predict these values
However, there will be inter-subject variability
Which lung volumes/capacities can be measured buy the use of a simple spirometer
The spirometer cannot be used to measure the residual volume (RV), and therefore cannot measure either the functional residual capacity (FRC) or the total lung capacity (TLC)
How are lung volumes/capacities that cannot be measured by a simple spirometer measured?
The inert gas dilution technique is used
How might the lung volumes/capacities change during exercise?
During exercise the ventilation rate is increased, so the tidal volume will be increased; the tidal volume is the main value that changes
ERV, IRV, FRC and the IC all change
The values of RV, TLC and VLC cannot be changed at all
State which lung volumes/capacities (including RV, FRC, VC, TLC) are changed from normal for:
(1) A severe chronic restrictive lung disorder
(2) A severe chronic obstructive pulmonary disorder,
And give reasons for these changes
Severe chronic obstructive disease:
- VC would either be decreased or would remain constant; TLC could decrease based upon the VC changes
- FRC would increase, as would RV
- In an obstructive disease, the patient has hyper-inflated lungs from which it is difficult to expel air
Severe chronic restrictive disease:
- RV would be unchanged, whilst a decrease in VC (and TLC by extension) would occur
- FRC would be significantly reduced
- In restrictive conditions, the patients cannot fill their lungs as they cannot expand them enough; this
consequently lowers vital capacity greatly
Briefly describe two methods that can be used (indirectly) to evaluate airways resistance
Forced expiratory volume (FEV1) is measured using a vitalograph
Peak expiratory flow rate (PEFR) is measured using a peak flow meter
Define FVC and FEV1
Forced vital capacity (FVC): the maximum volume of air expired as forcefully and rapidly as possible following a maximum inspiration
Forced expiratory volume (FEV1): the volume of gas expired in the first one second of this manoeuvre
Explain why FEV1 may be reduced in both obstructive and restrictive lung disease
FEV1 may be reduced in both obstructive and restrictive lung disease:
o In restrictive disorders, there is a low compliance, so the vital capacity is much compromised
o Although vital capacity can be normal in obstructive disorders, airway narrowing results in a high resistance, which slows expiration
Explain the significance of the ratio FEV1/FVC and state an approximate normal value in a young healthy subject
The ratio FEV1/FVC is an estimate of airway resistance
The ratio should normally be around 1, as a healthy subject would be able to breathe out the air in his/her
Predict and explain the change (if any) in the ratio FEV1/FVC in obstructive lung disease
Vital capacity may be normal, but FEV1 is reduced due to airway resistance and so the ratio decreases
Predict and explain the change (if any) in the ratio FEV1/FVC in restrictive lung disease
Vital capacity is reduced dramatically, but airway resistance is normal, so both values decrease and the ratio stays the same
Explain why the Wright Peak Flow meter may be particularly useful for patients with asthma or COPD
It is small, inexpensive, and easy to use, which means that peak flow can be monitored at home
Patients can be educated to recognise when the values change to a degree that they should seek medical advice
State which values for FVC, FEV1, FEV1/FVC, and PEFR generally increase with increase in subject size as measured by the subject’s height
FVC, FEV1, FEV1/FVC ratio, and PEFR generally increase with increased subject size, as measured by height
State which values for FVC, FEV1, FEV1/FVC and PEFR generally decrease with age after peaking at about 20 years
FVC, FEV1, FEV1/FVC ratio, and PEFR generally decrease with age after peaking at 20
State which values for FVC, FEV1 and PEFR are lower in females than in males of the same age and height
FVC, FEV1, FEV1/FVC ratio, and PEFR are generally lower in females than in males of the same age and height
Which changes in structure and function may increase airway resistance
These changes in structure and function may increase airway resistance:
- Bronchoconstriction:
o Smooth muscle contracts in the wall of the airways
o This is frequently the case in asthmatics
- Physical blockage:
o An example is increased mucus secretion
o This leads to more viscous mucus, which is more difficult to remove and thus forms mucus plugs in airways
- Loss of radial traction (outward pull)
- Change to the airway wall structure:
o The lumen can narrow, which occurs frequently in asthmatics
- Airway inflammation:
o This leads to swelling of tissue and a reduction in luminal diameter
Indicate what happens to arterial PO2, PCO2 and O2 saturation during breath holding
Arterial PO2 decreases
Arterial PCO2 increases
Consequently, oxygen saturation of the blood falls:
o There is less oxygen for the haemoglobin to carry
o Carbon dioxide now binds to the haemoglobin to be carried back to the lungs to be removed
Indicate what effect the following manoeuvres have on arterial PO2, PCO2 and O2 saturation
Over-breathing of room air:
- Arterial PO2 increases
- Arterial PCO2 decreases
- O2 saturation remains constant
Normal:
- Arterial PO2 increases greatly
- pCO2 remains constant
- O2 saturation rises slightly
Over-breathing of oxygen:
- Arterial PO2 increases even more greatly
- pCO2 goes down
- O2 saturation rises slightly