Overview of Respiration & Respiratory Mechanics (Lectures 1&2) Flashcards
What does internal respiration refer to?
The intracellular mechanisms that consume oxygen and produce carbon dioxide
What does external respiration refer to?
The sequence of events that allow the exchange of oxygen and carbon dioxide between the external environment and the cells in the body
What are the 4 steps of external respiration?
- Ventilation between atmosphere and alveoli
- Exchange of oxygen and carbon dioxide between air in alveoli & blood
- Transport fo CO2 and O2 between lungs & tissues
- Exchange of O2 & CO2 between blood and tissues
Which body systems are involved in external respiration?
Respiratory, Cardiovascular, Haematology, and Nervous System
What is ventilation?
Air flow from a region of higher to lower pressure
Which relation between alveoli and atmospheric pressure must exist to allow air to flow into the lungs?
The alveolar air pressure must be lower than atmospheric pressure
Inspiratory muscle contraction allows the thorax and lungs to _____
expand
What links the lungs to the chest wall?
Intrapleural fluid cohesiveness
Negative intrapelural pressure
What is meant by Intrapleural Fluid Cohesiveness?
That water molecules in the intrapleural fluid stick together so the pleural membranes stick together
What is meant by negative intrapleural pressure?
That the intrapleural pressure is lower than atmospheric pressure
How does negative intrapleural pressure contribute to Lung to chest wall linkage?
Creates a transmural pressure gradient across the lung wall so the lungs are forced to expand outwards while the chest is forced to squeeze inwards
Which pressures are involved in ventilation?
Atmospheric, intrapleural and intra-alveolar pressure
Contraction of the diaphragm is controlled by the ____ nerve?
Phrenic
Which mechanism causes movement of ribs that results in change in transverse diameter of the thorax
Bucket-Handle Mechanism
What is a pneumothorax?
Air in the Pleural space
What are main two types of pneumothorax?
Traumatic
Spontaneous
Why does a hole in the lung cause a pneumothorax?
Because air from the atmosphere flows down its concentration gradient and enters the pleural cavity; thus abolishing the transmural gradient
What gives the lungs their elastic behaviour?
Alveolar surface tension and elastic connective tissue
What is alveolar surface tension?
Attraction between water molecules at liquid air interface –> produces force to prevent stretching of the lungs in the alveoli
What would happen if the alveoli were lined only by water?
Surface tension would be too strong and the alveoli would collapse
What is LaPlace’s Law?
P = 2T/r P = inward directed collapsing pressure T = Surface tension r = radius of alveoli i.e. smaller alveoli have a higher tendency to collapse
What is the purpose of pulmonary surfactant?
Lower alveolar surface tension and prevent smaller alveoli from collapsing
What is Newborn Respiratory Distress Syndrome caused by?
Premature babies may have insufficient surfactant so they make every strenuous inspiratory efforts to overcome the high surface tension and inflate the lungs
What is alveolar interdependence
If an alveolus starts to collapse the surrounding alveoli are stretched & recoil exerting forces in collapsing alveolus to open it
What forces keep the alveoli open (3)?
Pulmonary surfactant
Transmural pressure gradient
Alveolar interdependence
What forces promote alveolar collapse?
Alveolar surface tension
Elasticity of stretched pulmonary connective tissue
What are the major muscles of inspiration?
Diaphragm
External intercostal muscles
Sternum
Ribs
What are the accessory muscles of Inspiration?
Sternocleidomastoid Scalenus Serratus anterior Pectoralis major Pectoralis minor Lattissimus dorsi
When are accessory muscles of inspiration used?
During forceful inspiration, either due to physiological or pathological reasons
When do the major muscles of inspiration contract?
Every inspiration; relaxation –> cause passive expiration
What is Tidal volume?
Volume of air entering/leaving the lungs during a single breath
What is the Inspiratory Reserve Volume (IRV)?
Extra volume that can be inspired above the typical resting tidal volume
What is the inspiratory capacity (IC)?
Maximum volume of air that can be inspired at the end of a normal quiet inspiration
What is the expiratory reserve volume (ERV)?
Extra volume of air that can be actively expired beyond normal volume of air after resting tidal volume
What is the residual volume (RV)?
Minimum volume of air remaining in the lungs after maximal expiration
What is the functional residual capacity (FRC)?
The volume of air at the end of a normal passive expiration (FRC = ERV + RV)
What is vital capacity?
The maximum volume of air the can be moved out during a single breath following a maximum inspiration (VC = IRV + TV + ERV)
What is the total Lung Capacity?
The maximum volume of air that the lungs can hold
TLC = VC + RV
What is Forced Vital Capacity?
Volume that can be forcibly expelled from the lungs following a maximum inspiration
What is the FEV1?
Forced Expiratory Volume in 1 second - the volume of air that can be expired during the 1st second of expiration in a FVC determination
What is the normal range of the FEV1/FVC ratio?
> 70%
How can FVC and FEV1 be determined?
Spirometry
What kind of FVC, FEV1, and FEV1/FVC ratio would andairway obstructive disease show?
FVC = low/normal FEV1 = low FEV1/FVC = low
What kind of FVC, FEV1, and FEV1/FVC ratio would an airway restrictive disease show?
FVC = low FEV1 = low FEV1/FVC = normal
What kind of FVC, FEV1, and FEV1/FVC ratio would a combination of airway restrictive and obstructive disease show?
FVC = low FEV1 = low FEV1/FVC = low
How can airflow be calculated?
F = change in pressure / resistance
Resistance in a normal airway is _____
very low
What is the primary determinant of airway resistance?
The radius of the conducting airway
What effect does parasympathetic stimulation have on the airways?
Bronchoconstriction
Wha effect does sympathetic stimulation have on the airways?
Bronchodilation
What is more difficult; inspiration or expiration?
Expiration
Why is expiration more difficult in patients with an airway obstruction?
Dynamic airway compression: if there is an obstruction the driving pressure between airway & alveolus is lost over the obstructed segment causing a fall in airway pressure along the airway downstream and resulting in airway compression by rising pleural pressure during active expiration
What worsens obstructive airways?
If the elastic recoil of the lungs is decreased
What is the purpose of a peak flow meter?
Gives an estimate of peak flow rate - assesses airway function in patients with an obstructive airway disease
What is pulmonary compliance?
Measure of the effort needed to stretch/distend the lungs
Which units are used to measure pulmonary compliance?
Volume change per unit of pressure
What can decrease pulmonary compliance?
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
Decreased pulmonary compliance may show a _______ lung disease pattern in spirometry?
Restrictive
When does pulmonary compliance increase abnormally?
if the lungs’ elastic recoil is lost
Dynamic airway obstruction is aggregated in patients with __________(3)
Obstructed airways
Emphysema
COPD
How much of total energy expenditure is normally needed for quiet breathing?
3%
In which cases is the work of breathing increased? (4)
Decreased pulmonary compliance
Increased Airway resistance
Decreased elastic recoil
If there is no need for increased ventilation
Which mechanism causes movement of ribs that results in change in anteroposterior diameter of the thorax?
Pump-Handle mechanism
