Respiratory Flashcards
Regions of the pharynx?
Pharynx = throat
1. Nasopharynx (nostrils to soft palate)
2. Oropharynx (soft palate to hyoid bone)
3. Laryngopharynx (hyoid bone to cricoid cartilage/oesophagus)
Impact of vocal cord movement on speech?
Cords adducted = high pitched sound
Cords abducted = lower pitch sounds
Difference between conducting zone and gas exchange zone of the lungs?
Conducting zone - terminal bronchioles, high resistance to airflow
Gas exchange zone - respiratory bronchioles/alveoli, very low resistance to airflow, pleural pressure more negative at apex (with bigger gradient in taller people)
Levels of the bronchial tree
Trachea -> primary bronchi -> secondary (lobar) bronchi -> tertiary (segmental) bronchi -> bronchioles -> terminal bronchioles -> respiratory bronchioles -> alveolar ducts -> alveolar sacs
What are the bronchopulmonary segments?
Each portion of lung supplied by each tertiary bronchus is called the bronco pulmonary segment
Overview of bronchioles
Continuations of airways that lack supportive cartilage
Each portion of lung ventilated by one bronchiole is a pulmonary lobule
Walls made of well-developed smooth muscle (ciliated cuboidal epithelium)
Anatomy of terminal bronchioles
50-80 branch from bronchioles
No mucous glands or goblet cells, but retain cilia
Last area of the CONDUCTING zone (conducts air)
Anatomy of respiratory bronchioles
First part of the RESPIRATORY zone
Narrowed airways of the lungs
Alveoli bud from walls
Not much smooth muscle or cilia
Anatomy oc alveolar ducts
2-10 from each respiratory bronchiole
Alveoli along walls
No cilia
Overview of alveoli
150million in the lungs
70m2 surface area for gas exchange
Types of cells include type 1, type 2 and alveolar macrophages
Type 1 alveoli
95% surface area
Squamous cells
Function for rapid gas exchange
Type 2 alveoli
5% surface area
Cuboidal and much more numerous than type 1 (although less surface area)
Function to repair alveolar epithelium and secrete surfactant
Surfactant = protein and phospholipid solution that coats alveoli and prevents collapse during exhalation due to reducing surface tension
Alveolar macrophages
Most numerous cells in the lung
In alveoli and surrounding connective tissue
Function to remove foreign matter and bacteria via phagocytosis
Respiratory membrane
= barrier between alveolar air and blood
Made up of squamous alveolar cells (type 1), basement membrane (shared) and squamous endothelial cell of capillary (pulmonary arterial supply)
Total thickness of 0.5micrometres
Pulmonary circulation MAP 10mmHg (allows gas exchange and keeps alveoli dry)
Oncotic pressure 25mmHg in alveolar capillaries, therefore keeps alveoli dry
Parietal pleura
Reflection of visceral pleura on the inner surface of the chest wall, mediastinum, diaphragm
Visceral pleura
Serous membrane covering the surface of lung to hilum
Pleural space
Refers to space between parietal and visceral pleura
Contains pleural fluid, is a potential space
Functions to reduce friction, create pressure gradient for ventilation, compartmentalisation to reduce spread of infection
What type of embryonal tissue does the respiratory system develop from?
Endoderm
Embryonic stage of lung development
Week 4-5 (other resource says week 3)
Lung buds originate from the primitive foregut
Pseudoglandular stage of lung development
Approx week 5-16
Airway branching begins, lobar structure apparent
By the end of this phase, all the conducting airways have been fully developed, and the vascular development is complete
Canalicular stage of lung development
Approx week 16-25
Bronchioles are produced, increasing number of capillaries
Type 1 and II alveolar cells form
Air-blood barrier forms
Saccular stage of lung development
Approx week 24-36 weeks
Alveolar ducts and air sacs are developed
Vascular expansion occurs
True alveoli seen by 32 weeks, recognisable by 36 weeks
Alveolar stage of lung development
Occurs from late gestation (32 weeks onwards) to childhood
Marked increase in the number and size of capillaries and alveoli
Most development is postnatal (85% of alveolarization occurs postnatally)
15 million alveoli at birth (term baby) -> 300-600 million as an adult (exponential increase until 2 years old)
Overview of lung development postnatally
Birth to 3 years: formation of true alveoli, further complexity of gas-exchange airways
3-8 years: increase size and complexity of alveoli, pores of Kohn (collateral ventilation)
Surfactant development and production
Type II alveolar cells present from 20-24 weeks
Surfactant secretion from 30 weeks
Neurological regulation of respiration
Central control centre = 2 groups of neurons
1. Brainstem (pons and medulla) = pre Botzinger complex
2. Cortex (voluntary control)
Brainstem regulation of respiration
Neurons in medulla and pons control inspiration (dorsal respiratory centre) and expiration (ventral respiratory group)
Pneumotaxic centre controls rate and pattern of breathing, limits inspiration
Inputs from peripheral sensors, can be overridden by cortex
Automatic rhythmic inspiratory stimuli and sometimes expiratory
Major output is to the phrenic nerves
Cortex regulation of respiration
Cerebral motor cortex and limbic structure, voluntary control
Receives sensory input from respiratory muscles via corticobulbar and corticospinal tracts
Respiration sensors
- Central chemoreceptors
- Peripheral chemoreceptors
- Lung and other receptors (pulmonary stretch, irritant receptors, J receptors, muscle receptors, arteriolar baroreceptors and pain/temperature receptors)
Overview of central chemoreceptors and regulation of respiration
Situated on ventral surface of medulla, surrounded by CSF
Respond to CSF [H+]
CSF [H+] is a reflection of CO2 in cerebral capillaries
Increased PaCO2 leads to increased CSF [H+], leads to increased ventilation
Does not respond to PaO2
Overview of peripheral chemoreceptors and regulation of respiration
Situated in carotid bodies at bifurcation of common carotid arteries in neck, and aortic bodies around arch of aorta
Rapid response
Respond to decreased PaO2, decreased pH, increased PaCO2, leading to increased ventilation
Overview of pulmonary stretch receptors
Located in airway smooth muscle of bronchi, bronchioles and visceral pleura
Function to respond to inflation of lungs (reduce RR in response to inhibition of inspiratory muscle activity)
Input to the dorsal respiratory group via the vagus nerve
Herring-Breuer reflex
What is the Herring-Breuer reflex?
Excessive inflation of the lungs triggers this reflex, which is protective to further inflation as it inhibits inspiratory neurons
Overview of irritant receptors
Found in epithelial cells of the airway
Stimulated by smoke, dust, pollen, chemicals, cold air, mucous
Inputs to the dorsal respiratory group via vagus nerve
Results in bronchiole smooth muscle effects = bronchoconstriction, shallow breathing, apnoea, cough
What are J receptors?
At justacapillary location
Stimulated by interstitial and alveolar oedema
Trigger shallow breaths and tachypnoea
Function of muscle receptors for regulation of respiration?
Sense stretch of diaphragmatic/intercostal muscles
Impact of REM sleep on respiration
Marked suppression of postural muscle tone
Chest wall is more compliant which can affect air flow
Relaxation of upper airway muscles can cause obstruction
Predominant sleep pattern in preterm infants, full term newborn has for 50% of sleep
How does a fetus/newborn/young infant respond to hypoxemia?
Will hyperventilate in response to hypoxemia (after a brief period of hyperventilation)
Improves as carotid chemoreceptors mature
Muscles are also more easily fatigueable
What is elastance?
Property that opposes deformation of stretching
Overview of compliance
Compliance = change in volume / change in pressure
Compliance is the distensibility of a substance
Reciprocal of elastance
Compliant lungs expand easily, a less compliant lung does not
What is elastic recoil?
Property of a substance that enables it to return to original state, after it is no longer subjected to pressure
What is resistance?
Amount of pressure required to generate flow of gas across the airways
Infants have smaller airways therefore prone to marked increase in resistance from inflammation/secretions
What is the time constant?
Time constant = compliance x resistance
Refers to the amount of time required for alveoli to equilibrate with atmospheric pressure (airway pressure)
Reduced compliance (pneumonia, pulmonary oedema, atelectasis) and impact on time constant/ventilation
Shorter time constant therefore less time for alveolar inflation and deflation
- would need to ventilate with shorter inspiratory times, smaller tidal volumes and faster rates
Increased resistance (asthma, bronchiolitis, MAS) and impact on time constant/ventilation
Prolonged time constant, therefore more time for alveolar inflation and deflation
- would need to ventilate with slower rates and larger tidal volumes to enable gas exchange with equilibration of gas and avoid inadvertent PEEP due to inadequate expiratory time
Boyle’s law
Pressure of given quantity of gas is inversely proportional to volume (assuming constant temperature)
Henry’s law
At this air-water interface, the amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in air (assuming constant temperature)
Charles’s law
The volume of the given quantity of gas is directly proportional to absolute temperature (assuming constant pressure)
Dalton’s law
Total pressure of a gas mixture is equal to the sum of the partial pressures of its individual gases
Poiseuille’s equation
Describes relationship between diameter and resistance to flow
Resistance = L / R^4
? (8 x length) / R^4
Laplace’s law
The larger the surface tension, the greater the pressure within alveoli
The smaller the radius, the greater the pressure within alveoli
P = surface tension / radius
Most common colonising pathogen in children with CF?
Staph aureus (25% will be MRSA)
Haemophilus and P aeruginosa are also very common
Overview of congenital diaphragmatic hernia
Can present within 24 hours of birth
Bowel in intrathroacic cavity causes pulmonary hypoplasia and displacement of mediastinum
Usually diagnosed antenatally, but should consider if mum has not had antenatal morphology scans
How is compliance calculated using the single-breath occlusion method?
The total exhaled volume divided by pressure at the airway opening recorded during occlusion:
- infant’s airway briefly occluded at end inspiratory part of tidal breath
- induction of Hering-Breuer reflex leads to respiratory system relaxation during occlusion and immediately after occlusion released
Compliance = change in volume / change in pressure
What is bronchiolitis obliterans?
Epithelial injury to the lower respiratory tract leading to obstruction and obliteration of distal airways
Injury can be due to infection or post-transplant
Commonly associated with adenovirus or mycoplasma
Clinical features of bronchiolitis obliterans?
Tachypnoea, dyspnoea, persistent cough, wheeze unresponsive to bronchodilators
Investigation findings in bronchiolitis obliterans?
LFT: airways obstruction with no significant bronchodilator response
CT: mosaic hyperinflation, bronchiectasis and vascular attenuation (pathognomonic)
Definitive diagnosis made with lung biopsy
What is dynamic tacheomalacia?
The dynamic collapse of the trachea during breathing, most lesions are intrathoracic leading to airway collapse during expiration
Overview of subglottic stenosis
Subglottis = narrowed portion of trachea, diameter 5-7mm at birth
Narrowing of 1mm = decrease in cross-sectional area by 75% and increase in airway resistance by 16x
Second most common cause of stridor (after laryngomalacia), with biphasic or usually inspiratory stridor
Usually present with URTI, recurrent croup common
Extrathoracic causes of obstruction
Acute: croup, epiglottitis, retropharyngeal abscess, diphtheria
Chronic: laryngomalacia (most common), tracheomalacia, vocal cord paralysis, subglottic stenosis
Intrathoracic causes of obstruction
Predominantly congenital - vascular rings, webs, external compression by tumours, lymph nodes
Overview of laryngomalacia
Collapse of supraglottic structures during inspiration (c/w tracheomalacia which is an abnormally compliant trachea)
Clinical features = low pitched stridor, loudest 4-8 months then resolve by 12-18 months, more intense with URTI/crying/feeding
The administration of which medication during an acute asthma exacerbation has been proven to reduce the duration of a hospital admission?
Oral prednisolone
The thymus becomes less visible on CXR at what age?
Becomes gradually less evident between the ages of 2-8 years, after which it cannot be visualised on the frontal CXR
What is minute volume?
Minute volume = tidal volume x respiratory rate
Higher minute volume will remove more CO2 and thus decrease arterial CO2 concentration, i.e. ventilation is primarily affected by minute volume
Oxygenation is primarily affected by which factors?
FiO2
Mean airway pressure
Lung volume
What type of noisy breathing will an extra thoracic narrowing of the trachea cause?
Inspiratory stridor
Clinical features of hypersensitivity pneumonitis?
Chronic cough, known antigen exposure, FTT, pulmonary hypertension (loud P2)
Most common cause in children is exposure to birds
Investigation findings in hypersensitivity pneumonitis?
CT findings of pneumonitis (centrilobular nodules, ground-glass opacities and air-trapping)
Polymorphonuclear leukocytosis with eosinophilia on bloods
Test for antigen specific serum precipitins = avian antigens are most common, also consider bacteria, fungi, mycobacteria, animal and plant proteins, chemicals and metals
What type of virus is COVID?
Positive sense single stranded RNA virus
Examples of negative sense single stranded RNA viruses?
Ebola, rabies
Examples of positive sense single stranded RNA viruses?
Dengue, MERS, SARS, rhinovirus, COVID
- these can be directly translated into viral proteins by the host cell
CF patient with cough, wheeze, reduced exercise tolerance, with elevated total serum IgE?
= allergic bronchopulmonary aspergillosis
A hypersensitivity reaction to a preceding fungal infection, clues are high IgE and wheeze
CT usually shows bronchiectasis with mucous plugging
Significance of nasal polyps in children under 10 years?
Red flag for cystic fibrosis, or less commonly primary ciliary dyskinesia, immunodeficiency or vasculitis
- particular concern for CF if associated with poor weight gain, lethargy and abdominal pain
Risk factors for benign nasal polyposis?
Recurrent infections, allergic rhinitis, tobacco smoke exposure, environmental pollution, reflux, foreign bodies
Most common airway abnormality in Down syndrome?
OSA: 50-97%
Laryngomalacia: 50%
Tracheomalacia: 33%
Lingual tonsil: 30%
Complete tracheal ring: 17%
