Respiratory Mechanics 2

Question 1

identify the inspiratory muscles and accessory muscles of respiration

Answer 1

major inspiratory muscles (contract every inspiration; relaxation causes passive expiration - diaphragm and external intercostal muscles

accessory muscles of inspiration (contracts only during forceful inspiration) - sternocleidomastoid, scalenus, pectoral

muscles of active expiration (contacts only during active expiration) - abdominal muscles and internal intercostal muscles

Question 2

explain the lung volumes and capacities and the use of spirometry in measuring these

Answer 2

spirometer measures ventilation - identifies obstructive and restrictive abnormal patterns
spirometry does not measure residual volume and hence total lung volume

tidal volume (normal breathing) - 0.5L

inspiratory reserve volume (additional volume of air inhaled after tidal volume) - 3.0L

expiratory reserve volume (additional volume of air exhaled by maximal contraction beyond normal volume of air after resting tidal volume) - 1.0L

residual volume (minimum volume of air remaining in lungs after maximal expiration. Will increase when elastic recoil of lungs is lost; emphysema) - 1.2L

inspiratory capacity (maximum volume of air inspired at end of normal quiet expiration; TV+IRV) - 3.5L

functional residual capacity (volume of air in lungs at end of normal passive expiration; ERV + RV) - 2.2L

vital capacity (maximum volume of air that can be moved out during single breath following maximal inspiration; IRV+TV+ERV) - 4.5L

total lung capacity (total volume of air lungs can hold; VC+RV) - 5.7L

Question 3

illustrate the changes in dynamic lung volumes in obstructive and restrictive lung disease

Answer 3

volume time curve allows you to determine;
forced vital capacity - maximum volume that can be forcibly expelled from the lungs following maximum inspiration)
forced expiratory volume in one second - volume of air that can be expired during first second of expiration in FVC determination

dynamic lung volumes useful in diagnosing obstructive and restrictive lung disease
obstructive - FEV1/FVC ration <70% (low)
restrictive - FVC and FEV1 is lower than normal

Question 4

identify the factors which influence airway resistance

Answer 4

airway resistance;
F (flow) = deltaP (pressure)/R (resistance)

resistance to flow in the airway normally is very low and therefore air moves with small pressure gradient
primary determinant of airway resistance is the radius of the conducting airway
parasympathetic stimulation - bronchoconstriction
sympathetic stimulation - bronchodilation

disease states (e.g. COPD, asthma) can cause significant resistance to air flow 
expiration is more difficult than inspiration;
during inspiration the airways are pulled open by the expanding thorax - intrapleural pressure falls
during expiration the chest recoils - intrapleural pressure rises

Question 5

introduce the concept of using the peak flow meter to estimate the peak flow rate in patient with obstructive lung disease

Answer 5

the peak flow meter gives an estimate peak flow rate and assess airway function
the test is useful in patients with obstructive lung disease (COPD, asthma)
it is measured by the patient giving a short, sharp below into the peak flow meter
the best of 3 attempts is rally taken
peak flow rate in normal adults varies with age and height

Question 6

define the compliance of lungs and explain how it can be affected by disease

Answer 6

pulmonary compliance;
during inspiration the lungs are stretched -
compliance is a measure of effort the has to go into stretching or distending the lungs,
volume change per unit of pressure change across the lungs,
the less compliant the lungs are, the more work is required to produce a given degree of inflation

decreased pulmonary compliance;
pulmonary compliance is decreased by factors such as pulmonary fibrosis, puloamry oedema, lung collapse, pneumonia, absence of surfactant ,
decreased pulmonary compliance means greater change in pressure is needed to produce a given change in volume (i.e. lungs are stiffer). This causes shortness of breath especially on exertion
decrease pulmonary compliance may cause restrictive pattern of lung volumes in spirometry (FVC is lower)

increased pulmonary compliance;
complacent may become abnormally increased if the elastic recoil if the lungs is lost
increased compliance occurs in emphysema. Patent shave to work harder to get the air out of the lungs - hyperinflation of lungs
dynamic airway obstruction will also be aggravated in patients with obstructed airway and emphysema caused by COPD
compliance also increases with increasing age

Question 7

define what is meant by the term ‘work of breathing’ and outline some factors which increases the work of breathing

Answer 7

working breathing normally requires 3% of total energy expenditure for quiet breathing
lungs normally operate at about half full
work of breathing is increased in following situations;
pulmonary compliance decreased
airway resistance increased
elastic recoil decreased
when there is a need for increased ventilation