Mechanics Of Breathing Flashcards
What is the definition of breathing?
The bodily function that leads to ventilation of the lungs, also known as external respiration
What is the definition of ventilation?
The process of moving gases in (inspiration) and out (expiration) of the lungs
What are obstructive diseases?
Diseases that obstructs airflow in the lungs
What are restrictive diseases?
Diseases that cause the loss of elasticity in the lung tissue, chest wall or the thorax
What are examples of obstructive conditions affecting ventilation?
- asthma
- chronic obstructive pulmonary disease
- lung cancer
What are examples of restrictive conditions affecting ventilation?
- intrinsic e.g. pulmonary fibrosis
- extrinsic e.g. pneumothorax, disorders of the thoracic skeleton
What pressure differences are required for inspiration
Inspiration when barometric pressure is greater than alveolar pressure
What pressure differences are required for expiration?
Expiration when barometric pressure is less than alveolar pressure
What is Boyle’s law for pressure changes occurring secondarily to thoracic volume changes
P is inversely proportional to the volume of an enclosed space
P ∝ 1/V
Which inspiratory muscles are used in quiet breathing ?
- diaphragm flattens
- external intercostals contract to stabilise ribcage, moving it up and out to increase the lateral and antero-posterior diameter of the thorax
- internal intercostals relaxed
Which inspiratory muscles are used in breathing with increased effort?
- diaphragm
- external intercostals move ribcage up and out
- accessory muscles (neck muscles and shoulder girdle muscles). Neck muscles pull the ribcage up, pectoralis major and latissimus dorsi pull the ribcage outwards
- Sternocleidomastoids elevate the sternum, scalenus major and minor muscles elevate the first two ribs and sternum
Describe the diaphragm
- Thin, dome shaped layer of muscle and tendon that separates the abdominal cavity from the chest cavity
- Attaches at the costals in the lower ribcage, high in the front of the sternum and deeply in the back of the spine
- Also attaches at the central tendon, uses central tendon and attachments to leverage itself during inhalation
What are the expiratory muscles used in quiet breathing?
elastic recoil of tissues, diaphragm relaxes, external intercostal muscles relax
What are the expiratory muscles used in breathing with increasing effort?
- internal intercostals contract
- oblique, transversus and rectus abdominis muscles pull the ribcage downwards
- contraction of the abdominal muscles also increase intra-abdominal pressure and pulls the ribcage downwards and medially in forced expiration.
How is the diaphragm innervated?
Phrenic nerves - nerves that come from the cervical = C3, C4, C5
How are the intercostals innervated?
segmental thoracic nerves from the relevant levels of the thoracic spinal cord
How is the level of injury of the spinal cord nerves relevant to which mechanism works?
Everything above the nerves which are injured still function but the muscles below would be paralysed
(if injury is C5 and above, the diaphragm will not function)
e.g. if thoracic nerves were injured, the muscles below would stop working
During inspiration what happens to the alveolar and intrapleural pressure?
alveolar pressure goes up and intrapleural pressure goes down (difference increases)
During expiration what happens to the alveolar and intrapleural pressure?
Alveolar pressure goes down and intrapleural pressure goes up (difference decreases)
What is pneumothorax? How do you recognise it on a chest scan?
- air gets into the pleural space and the lung collapses
- increased blankness, no white striations showing blood vessels in lung area
- organs pushed to other side more
What is a tension pneumothorax?
Increase in pressure pushes heart and stops the heart from filling with blood so there is not enough to pump around the body
What is pleural effusion? How is it recognised on a chest scan?
- Fluid leaks into the pleural space which can be caused by heart failure
- costodiaphragmatic recess
How could you clinically assess if there is a pneumothorax or pleural effusion?
Can use hands to find magnitude of chest expansion, one side of the chest moves more than the other when breathing
How can the volume of air moving in and out of the lungs be measured?
Using a spirometer (traditional or modern)
Modern apparatus has a head which measures flow of air and is converted by a connected computer
What is the definition of tidal volume?
The volume of air moved in or out of the lungs during normal breathing
What are the typical values of tidal volume at rest and during exercise?
At rest: 6-7 ml/kg
During exercise : 15ml/kg
*However all lung volumes are dependant on age, sex and height
What is the definition of inspiratory reserve volume?
- After a normal expiration, the measurement of the volume taken after maximal inspiration.
- measured from end inspiration to max vol of inspiration
What is the typical value of inspiratory reserve volume for a 70kg male?
3,000 ml
What is the definition of expiratory reserve volume?
- After normal inspiration, the maximal expired breath
- measured from end expiration to maximal volume of expiration
What is the typical value of expiratory reserve volume for a 70kg male?
1,500ml
What is the definition of residual volume?
The air remaining in the lungs after maximal expiration
Why is there residual air left after maximal expiration?
The thorax is rigid in nature and the pleural attachments of the lungs to the chest prevent complete emptying of the lungs
What is a typical measure of the residual volume in a 70kg male?
1,000 ml
How can residual volume be measured?
(Cannot be measured by spirometry)
- Air contains a fixed concentration of N2 that is neither absorbed or produced by the body, if all N2 is washed out and volume is measured, the volume of air that was in the lungs can be estimated
- To wash N2 from lungs, subject breathes O2 (N2 free) and breathes out through a turbine volume-flow meter for a few minutes
- 2 minutes required in healthy adult but longer with people with asthma or emphysema
- expired gas collected and N2 concentration measured and volume determined
What is the equation used to calculate residual volume using N2 measurements?
Volume of gas in the lung (V) x concentration of N2 in the lung = volume of gas exhaled x concentration of N2 in gas exhaled