overview of respiration and respiratory mechanics (R2) Flashcards
accessory musces of inspiration
(contract only during forceful inspiration)
- sternocleidomastoid
- scalenus
muscles of active inspiration
(contract only during active inspiration)
- internal intercostal muscles
- abdominal muscles
major muscles of inspiration
(contract every inspiration; relaxation causes expiration)
- external intercostal muscles
- diaphragm
- (ribs and sternum are also involved)
tidal volume (TV)
- volume of air entering or leaving the lungs during a single breath
- average value = 500ml
inspiratory reserve volume (IRV)
- extra volume of air that can be maximally inspired over and above the typical resting tidal volume
- average value = 3000ml
inspiratory capacity (IC)
- maximum volume of air that can be inspired at the end of a normal quiet expiration (IC=IRV+TV)
- average value = 3500ml
expiratory reserve volume (ERV)
- extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
- average value = 1000ml
residual volume (RV)
- minimum volume of air remaining in the lungs even after a maximal expiration
- average value = 1200ml
functional residual capacity (FRC)
- volume of air in lungs at end of normal passive expiration (FRC = ERV + RV)
- average value =2200ml
vital capacity (VC)
-maximum volume of air that can be moved out during a single breath following a maximal inspiration
(VC = IRV + TV + ERV)
-average value = 4500ml
total lung capacity (TLC)
-maximum volume of air that the lungs can hold
(TLC = VC =RV)
-average value = 5700ml
forced expiratory volume in one second (FEV1): Dynamic Volume
- volume of air that can be expired during the first second of expiration in an FVC (forced vital capacity)
- average volume = FEV1%= FEV1/FVC ratio, normally >75%
factors that affect normal predicted values of lung volumes and capacities
age, gender, height etc
spirometry definition/ function
-common office test used to assess how well your lungs work by measuring how much air you inhale, how much you exhale and how quickly you exhale. Spirometry is used to diagnose asthma, chronic obstructive pulmonary disease (COPD) and other conditions that affect breathing
spirometry for dynamic lung volumes (volume time curve)
allows you to determine;
- FVC
- FEV1
- FEV1% (FEV1/FVC ratio)
effect of lung diseases on spirometry results
- airway obstruction causes low/normal FVC, low FEV1, and low FEV1/FEC%
- lung restriction causes low FVC, low FEV1 and normal FEV1/FVC%
- combination of obstruction and restriction causes low FVC, low FEV1 and low FEV1/FVC%
airway resistance
- F=change inP/R (where F=flow, P=pressure, R=resistance)
- resistance to flow in the airway normally is very low and therefore air moves with a small pressure gradient
primary determinant of airway resistance
radius of conducting airway
what effect does parasympathetic stimulation have of the bronchi
bronchoconstriction
what effect does sympathetic stimulation have on the bronchi
bronchodilatation
what can cause significant resistance to airflow
disease states(e.g COPD/chronic obstructive pulmonary disease or asthma)
which stage of breathing is most difficult to carry out
expiration
what happens to intrapleural pressure during inspiration
falls
what happens to intrapleural pressure during expiration
rises
dynamic airway compression in normal people
- causes no problems
- the rising pleural pressure during active expiration compresses the alveoli and airway
- pressure applied to the alveoli helps to push air out of lungs
- the pressure applied to the airway is not desirable-tends to compress it
- the increased airway resistance causes an increase in airway pressure upstream, this helps to open the airways by increasing the driving pressure between the alveolus and the airway (ie. the pressure downstream)
dynamic airway compression during active expiration in patients with airway obstruction
- if there is an obstruction (eg. asthma or COPD), the driving pressure between the alveolus and airway is lost over the obstructed segment, this causes a fall in airway pressure along the airway downstream resulting in airway compression by the rising pleural pressure during active expiration
- diseased airway are also more likely to collapse
- the problem becomes worse if the patient also has decreased elastic recoil of the lungs (eg. a patient with emphysema and obstructed airway caused by COPD)
peak flow meter
-gives an estimate of peak flow rate, which assesses airway function
- test is useful in patients with obstructive lung disease (eg.
asthma and COPD)
-measured by patient giving short sharp blow into the peak flow meter (average of 3 attempts is usually taken)
peak flow rate in normal adults
varies with age and height
pulmonary compliance
(during inspiration the lungs are stretched)
- compliance is the measure of effort that has to go into stretching or distending the lungs
- it is the volume change per unit of pressure change
factors that decrease pulmonary compliance
pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence of surfactant
what is the effect of decreased pulmonary compliance
- the less compliant the lungs are, the more work is required to produce a given degree of inflation/ greater change in pressure is needed to produce a given change in volume (ie. lungs are stiffer)
- this causes shortness of breath especially on exertion
effect of decreased pulmonary compliance on spirometry
may cause restrictive pattern of lung volumes (FVC is less)
what can cause increased pulmonary compliance
- may become abnormally increased if the elastic recoil of the lungs is lost
- increased pulmonary compliance occurs in emphysema, patients have to work harder to get the air out of the lungs (hyperinflation of the lungs)
- compliance also increases with age
what is effected in patients with obstructed airway and emphysema caused by COPD
- dynamic airway compression is aggravated
- pulmonary compliance is increased(?)
normal work of breathing
- normally requires 3% of total energy expenditure for quiet breathing
- lungs normally operate at about “half full”
what situations increase the work of breathing
- decrease in pulmonary compliance
- increase in airway resistance
- decrease in elastic recoil
- a need for increased ventilation
