Respiration Mechanics Flashcards
What are the inspiratory and accessory muscles of respiration
Major inspiratory muscles - Diaphragm and external intercostal muscles
Accessory muscles of inspiration - sternocleidmastoid, scalenus, pectoral (during forceful inspiration)
Muscles of active expiration - abdominal muscles and internal intercostal muscles
Explain the lung volumes
Tidal volume (TV) - volume of air entering or leaving lunges during a single breath 0.5L
Inspiratory reserve volume (IRV) - extra Volume of air that can be maximally inspired over and above the typical resting tidal volume 3.0L
Expiration reserve volume (ERV) - Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after resting tidal volume 1.0L
Residual volume (RV) - Minimum volume of air remaining in the lungs even after maximal expiration 1.2L
Explain the lung capacities
Inspiratory Capacity (IC) - Maximum volume of air that can be inspired at the end of a normal quiet expiration (IC= IRV + TV) 3.5L
Functional residual capacity (FRC) - Volume of air in lungs at end of normal passive expiration (FRC = ERV + RV) 2.2L
Vital capacity (VC) - Maximum volume of air that can be moved out during a single breath for the max more inspiration (VC = IRV + TV + ERV) 4.5L
Total Lung capacity (TLC) - total volume of air the lungs can hold (TLC = VC + RV) 5.7L
Explain Spirometry
Pulmonary function test which measures lung function and assesses breathing patterns
TV, IRV, ERV, IC and VC can be measured by simple spirometry
Volume time curve allows you to determine:
- forced vital capacity (FVC) - Maximum volume that can be forcibly expelled from the lungs following a maximum inspiration
- forced expiratory volume in one second (FEV1) - Volume of air that can be expired during the first second of expiration in an FVC determination
FEV1/FVC ratio - The proportion of the forced vital capacity that can be expired in the first second = (FEV1/FVC) x 100% - normally more than 75%
What happens to the lung volumes in obstructive and restrictive lung disease
Airway obstruction: low or normal FVC, low FEV1, low FEV1/FVC%
Lung restriction: low FVC, low FEV1, normal FEV1/FVC%
Combination of obstruction and restriction: low FVC, low FEV1, low FEV1/FVC%
What factors influence airway resistance
Resistance to flow in the airway normally is very low and therefore air moves with a small pressure gradient
Radius of conducting airway is the primary determinant of airway resistance
Disease states can cause significant resistance to airflow
What is dynamic airway obstruction and effects on normal people
The rising intrapleural pressure during active expiration compresses the alveoli and airway. Pressure applied to alveolus helps push air out of lungs
No problems in normal people as increased airway resistance causes an increase in airway pressure upstream. Helps to open airways by increasing driving pressure between alveolus and airways
significance of dynamic airway compliance during expiration in patients with airway obstruction
Where there’s an obstruction (COPD or asthma) diving pressure between alveolus and airway is lost over obstructed segment. Causes a fall in airway pressure along the airway downstream resulting in airway compression by the rising pleural pressure during active expiration
significance of dynamic airway compliance during expiration in patients with airway obstruction
Where there’s an obstruction (COPD or asthma) diving pressure between alveolus and airway is lost over obstructed segment. Causes a fall in airway pressure along the airway downstream resulting in airway compression by the rising pleural pressure during active expiration
Explain how a peak flow meter is used
Gives an estimate of peak flow rate which assesses airway function
Useful in patients with obstructive lung disease
Define the compliance of lungs
Compliance is the measure of effort that has to go into stretching or distending the lungs
Change in lung volume per unit change in transmural pressure gradient across the lung wall
Less compliant the lungs are, more work is required to produce a given degree of inflation
Decreased pulmonary compliance
Decreased by factors such as Pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia and absence of surfactant
Means greater change in pressure is needed to produce a given change in volume - lungs are stiffer. Causes shortness of breath
May cause a restrictive pattern of lung volumes in spirometry
Increased pulmonary compliance
Compliance may become abnormally increased if the elastic recoil of lungs is lost
Occurs in emphysema - patients have to work harder to get air out of lungs - hyperinflation of lungs
Also increases with age
What is “work of breathing” and factors which increase this
Work of breathing is a reflection of energy needed to overcome impeding elements of the respiratory system
Quiet breathing requires about 3% of total energy expenditure
Is increased when:
- pulmonary compliance is decreased
- airways resistance is increased
- elastic recoil is decreased
- there’s a need for increased ventilation
