Lecture 2 - Mechanics of breathing Flashcards
definition of breathing
bodily function that leads to ventilation of the lungs
also known as external respiration
Ventilation definition
Process of moving gases in - inspiration and out (expiration) of the lungs
Mechanics of breathing involves…
describes the structural and physiological bases of ventilation
in what 2 ways do diseases affect ventilation
obstructive conditions: asthma, COPD, lung cancer
Restrictive:
Intrinsic : pulmobary fibrosis
extrinsic: pneumothorax, disorders of thoracic skeleton
How will gas flow?
through patent airways according to the pressure gradient between atmosphere (barometric pressure) and alveoli
Pressure during inspiration
Pb (atmospheric pressure) is greater than alveolar pressure
Pressure during expiration
Aloveolar pressure (variable - Pa) is greater than the atmospheric pressure
Why does airway obstruction have a major effect on flow? describe in terms of the equation
flow = (k x delta PX r^4)/ (L)
As flow depends on the radius, airway obstruction would majorly affect it.
How is generation of Delta P brought about
atmospheric pressure is constant
therefore difference in pressure generation is dependent on the pressure changes in the chest
How does alveolar pressure changes related to thoracic volume
Change in pressure is inversely proportional to thoracic volume. The pressure is higher when the volume is low and vice versa
What are inspiratory muscles used in quiet breathing and when there is an increasing effort
quiet breathing: diaphragm
external intercostals stabilise rib cage
Increasing effort:
diaphragm
, external intercostals lift and expand rib cage, accessory muscles, neck muscles, shoulder girdle muscles
Expiratory muscles during quiet breathing and increasing effort
quiet breathing: elastic recoil of tissues
increasing effort: internal intercostals, abdominal wall muscles
what physical changes happen in inspiration
increased vertical diameter increase A-P diameter elevated rib cage external intercostals contracted internal intercostals relaxed neck muscles contract
Expiration: physical changes
abdominals contracted
Innervation of diaphragm and intercostals
phrenic nerve - C3,4,5
Intercostals: segmental thoracic nerves
What can a spinal cord injury cause
ventricular muscle paralysis
What are the pleura responsible in doing
transmitting thoracic cage expansion into lung volume expansion
thoracic cage expansion exerts an increasing negative pressure on the intrapleural space
What does a spirometer measure
Volume of air moving in and out of the lungs
What is tidal volume
the volume of air moved in or out of the lungs during normal breathing. at rest - 6-7 ml/kg during exercise - 15 ml/Kg Volumes dependent on age, sex and height typical value of an adult male is 500 ml
Inspiratory reserve volume
after normal expiration, take as deep a breath as possible
typical value for 70 kg male - 3000 ml
Expiratory reserve volume
after normal inspiration, breath out as deeply as possible
1,500 ml for 70 kg male
What is residual volume
even after maximal expiration, air remains in the lungs. this is because of rigid nature of thorax and pleural attachments of the lungs to the chest wall that prevent complete emptying.
this volume left is residual volume
cannot be measured by spirometry
typical value is 1000 ml
Lung capacities
combinations of lung volumes
Total lung capacity
TV+IRV+ERV+RV
Vital capacity
TV+IRV+ERV
Functional residual capacity
ERV+RV
What is vital capacity
after a maximal inspiration, make a maximal expiration
typical value - 5,000 ml
Examples of chest diseases affecting lung volumes and capactities
Restrictive lung diseases - pulmonary fibrosis - reduced Residual volume, FRC, VC, TLV
Obstructive - asthma, copd, emphysema,
increased RV, TLC may be reduced or increased
FRC increased in emphysema
what is measured clincally using a vitalograph spirometer
forced expiratory measurements
FVC, Forced expiratory volume in 1 second (FEV1)
What is a peak flow meter used to measure
peak expiratory flow rate
How do you distinguish between obstructive and restrictive clinically?
FEV1/FVC ratio
ratio below 0.7 - obstructive
ratio above 0.7 - restrictive
Peak expiratory flow rate
convenient way of measuring airways obstruction, not as good as spirometry for airflow limitation
can use it at home to monitor asthma or copd
wide diurnal variations - highest in the evenings and lowest in early hours
PEFR - less depenent on effort than FEV1
Reversibility of airflow limitation
In asthma, the airway constriction is reversible so that FEV1 and PEFR would be restored to normal after salbutamol.
when is airways constriction irreversible?
COPD
what provides additional information about pulmonary disease
flow-volume loops
What is FEV1?
The fraction of the vital capacity expired during the first second of forced respiration.
When can it be reduced even when vital capacity is normal?
in diseases like asthma when airway resistance is increased because of bronchial constriction.
