Physiology of Respiratory Signs ✅ Flashcards
What is normal tidal volume proportional to?
Weight
Why is the respiratory rate in higher in young children?
Because energy requirements and therefore oxygen demand and carbon dioxide production are relatively higher in younger children
What modulates the breathing pattern in an awake child?
Various baseline physical activities
Under what control is breathing pattern in an awake child?
Conscious control
What happens to breathing pattern during sleep?
Physiological changes occur that vary with sleep state
What are the changes that occur to breathing pattern during sleep influenced by?
Maturational changes in respiratory mechanics and control of breathing
What can happen to the breathing pattern during sleep in infants?
Pauses and gaps in breathing of up to 15 seconds during sleep are common
When might the pauses and gaps in breathing in infants be exaggerated?
In illness
Describe the response to hypoxia in infants
Biphasic, with an initial increase in respiratory rate followed by a decrease, often in association with apnoea
What happens to minute ventilation during sleep in well children?
It falls by 15% during sleep
What happens to breathing during REM sleep?
There is an automatic decrease in accessory muscle activity, accompanied by an increase in upper airway resistance
Why is there an increase in upper airway resistance in REM sleep?
As the muscles supporting the upper airway relax
How much do newborn infants sleep?
Approx 2/3 of the time
What % of new-born infants sleep is REM?
60%
How much do children sleep by 6 months of age?
11-14 hours per day
What proportion of a 6 month old child’s sleep is REM?
1/3
How much does the typical adult sleep?
8 hours a day
What % of an adults sleep is REM?
20%
Why do the airways and lungs not collapse completely during expiration?
It would be inefficient
Why would it be inefficient for the airways and lungs to collapse completely during expiration?
As re-inflation requires much more energy than widening/expanding a partially closed airway
What opposes airway closure under normal circumstances?
Maintenance of functional residual capacity (FRC) at a level above the point at which the airways collapse
What increases airway collapse?
- Surfactant deficiency
- Bronchiolitis
- Pneumonia
When does FRC reduce?
- When lying supine
- Anaesthesia
- Sleep
What factors affect FRC?
- Elastic recoil of the lungs
- Time allowed for expiration
- Expiratory flow rate
What happens to the elastic recoil of the lungs with age?
It increases
What is the result of the elastic recoil of the lungs increasing with age?
Older children are less susceptible to complete airway closure
How do younger children oppose airway collapse?
By having higher respiratory rates, thus reducing the time allowed for expiration
What happens if having a higher respiratory rate is insufficient to maintain FRC in infants?
They will attempt to reduce expiratory flow rates using partial closure of the glottis and upper airway
What does partial closure of the glottis and upper airway result in?
Grunting
When is grunting seen?
In neonates with respiratory distress
How does grunting prevent airway collapse?
It maintains a positive expiratory pressure but reduces expiratory flow
What does reflex or voluntary coughing require?
Co-ordination of a complex series of events
How does coughing begin?
With opening the glottis and a short inspiration to increase lung volume
Why is recruitment of lung volume essential in coughing?
To maximise expulsion
Why does the recruitment of lung volume in coughing maximise expulsion?
It allows elastic recoil of the lung to assist muscular contractions
What happens after the opening of the glottis and short inspiration in coughing?
The glottis closes and respiratory muscles contract
What is the effect of the glottis closing and the respiratory muscles contracting in coughing?
It generates high intra-thoracic pressures
What happens to the glottis shortly after closure in coughing?
It re-opens
What happens when the glottis re-opens in coughing?
Rapid decompression of the airways and high velocity expulsion of gas
What do the rapid shifts in airway volume cause in coughing?
A degree of small airway closure and compression
What is the effect of airway closure and compression in coughing?
It physically squeezes mucus and other intraluminal contents into the larger proximal airways
What happens as expired air flows from the alveoli to the mouth in coughing?
Pressure within the airway falls
What is the effect of airway obstruction on coughing?
It means the pressure drop when expired air flows form the alveoli to the mouth will be greater, with a tendency for more proximal airways to collapse
What causes the brassy sound that occasionally occurs during maximal forced expiration in healthy subjects?
Flow-related collapse
When is the brassy sound on maximal forced expiration more common?
If there is narrowing of the larger airways, or if they are less rigid than usual as in bronchomalacia
Why is it important to hear the cough when diagnosing?
It allows you to distinguish between dry and wet coughs, and wheezy or brassy coughs
What do wet coughs suggest?
Increased mucus in the airways
What does a wheezy cough suggest?
Smaller airway obstruction
What does a brassy or barking cough suggest?
Narrowing of the larger airways and/or a degree of bronchomalacia
What is the effect of muscular weakness on coughing?
Children with muscular weakness have a reduced ability to cough
How can you measure the force of coughing?
Asking the child to cough as hard as they can into a peak flow meter, either using the mouth piece or a mask
What cough expiratory flow predicts an adequate cough strength?
> 270L/min
What can assist airway clearance in children with inadequate cough strength?
Physiotherapy
How do cough assist devices work?
By generating a positive pressure followed by negative pressure upon initiation of cough, assisting complete expansion of the airways and chest
How does assisting with expansion of the airways and chest increase airway clearance?
As the natural elastic recoil rapidly empties the chest
How do cough assist devices apply negative pressure?
Via a tightly applied face mask
What is required for a cough assist device to be a useful aid?
Co-operation and practice
Is the cough reflex central or peripheral?
Has components of both
Where are cough receptors found?
Throughout the respiratory system
Where are irritant cough receptors found?
In the larynx and large airways
Where are stretch cough receptors found?
Within the lung parenchyma
What do irritant cough receptors respond to?
Mechanical irritation
What do stretch cough receptors respond to?
Over-distention of the lung
What does the cough pathway involve?
- Cough receptors
- Mediators of sensory nerves
- Afferent limb
- Vagus nerve
- Central cough centre
- Efferent limb
What are normal breath sounds described as?
Vesicular
Why is there little or no sound towards the end of expiration?
Dampening of the sound as it travels through normal lung tissue ensures that, as the lung deflates and flow diminishes, there is little to no sound towards the end of expiration
What happens to the lung parenchyma in pneumonia?
It becomes filled with inflammatory cells and fluid
What it the effect on the sound when the lung parenchyma is filled with inflammatory cells and fluid in pneumonia?
Sound is conducted from the central airways more efficiently, and so breath sounds on auscultation are harsher and similar to the airflow heard by listening over the trachea
What are crackles?
Discontinuous, non-musical additional respiratory sounds
What are the types of crackles?
- Course crackles
- Fine crackles/crepitations
What type of crackles are easier to hear?
Course crackles
What causes course crackles?
Collection of fluid or secretions in the large airways
What do course crackles sound like?
Coarse bubbling sounds
What can change the sound of course crackles?
Coughing or taking a deep breath
What do fine crackles sound like?
Higher pitched, explosive sounds
What causes fine crackles?
Small closed airways suddenly opening during inspiration
Why can fine crackles be hard to hear?
They are often obscured by other respiratory noises and are dampened by hyperinflation or the thicker chest wall of older children
When is wheeze primarily heard?
During expiration
What kind of sound is a wheeze?
Musical sound
What causes wheeze?
Flow limitation in the small intra-thoracic airways causing oscillation of the airway walls at the site of narrowing
When might wheeze be heard on inspiration?
In severe airway obstruction
What sounds can obstruction of extra thoracic airways result in?
- Stridor
- Stertor
When does obstruction of extra thoracic airways result in stridor?
When it is fixed
When does obstruction of extra thoracic airways result in stertor?
If it is intermittent
What can happens to stridor/stertor if obstruction becomes severe?
It may become biphastic
What happens to the volume fo stridor/stertor as the severity increases?
Flow reduces, and so do the abnormal noises
What might a silent chest indicate?
A very severe airway obstruction
