Anat/Develop/Physiology/Ix Flashcards
EMBRYOLOGY
What are the 5 phases of lung development?
What are some conditions that result from disordered/abnormal lung development?
Five phases of lung development:
- Embryonic (26 days to 6 weeks gestation)
- Pseudoglandular (6 to 16 weeks gestation)
- Canalicular (16-28 weeks gestation)
- Saccular (28-36 weeks gestation)
- Alveolar (36 weeks through to infancy)
Extremely premature infants (≤28 weeks gestation) have an immature lung, that is susceptible to insults resulting from medical treatments, causing dysmorphic growth and interrupted maturation in the canalicular to early saccular phase, with the risk of developing bronchopulmonary dysplasia (BPD)
- Week 4 - Lung bud from primitive foregut
- Pharyngeal arches 4&6 –> larynx, developed by Week 12
- Lung bud –> lung and tracheam stages PCSA
- Type II alveolar cells - 20-24 weeks
- Surfactant secretion - 30 weeks
SPIROMETRY/PFTs
FEV1
FEV1 reflects mechanical properties of both the large airways and medium-sized airways. In a normal flow-volume loop, the FEV1 occurs at about 75% of the FVC. This parameter is reduced in both obstructive and restrictive disorders. In obstructive diseases, FEV1 is reduced disproportionately to the FVC and is an indicator of flow limitation. In restrictive disorders, the FEV1, FVC, and total lung volume are in proportion.
Forced Expiratory Flow Rate (FEFR 25% - 75%):
This is defined as the maximum flow rate between 25 and 75 percent of the volume expired (FVC). It is also called the maximum mid-expiratory flow rate (MMFR). It is effort-independent, because it occurs late in the forced vital capacity maneuver, where airflow is mainly dependent on the elastic recoil pressure of the lung. Expressed in litres per second.
The FEF25-75% reflects the function of small airways. It is a more sensitive parameter and not as reproducible as the others. It reflects early airway obstruction it will be affected before FEV, hence it is a more sensitive indicator of mild airway obstruction than the FEV1/FVC ratio.
Forced Vital Capacity (FVC):
The maximum volume of air in litres that can be forcibly and rapidly exhaled following a maximum inspiration. Specifically, the FEV1/FVC ratio is a useful index of obstruction.
Peak Expiratory Flow Rate (PEFR):
Is the greatest flow that can be sustained by forced expiration starting from full inflation of the lungs. It is measured in litres per minute. It reflects and measures only the rate of flow from the large airways, and is affected by the strength of the thoracic and abdominal muscles, and the degree of muscular effort generated by the patient. The PEF measured by spirometry is far less reproducible and seems to have a wider range of normal values than other parameters such as FEV1 and FVC.
When peak expiratory flow is measured repeatedly over a period and plotted against time (e.g. by asthmatic patients), the pattern of the graph can be very important in identifying particular aspects of the patient’s disease. Typical patterns are the fall in PEF during the week with improvement on weekends and holidays which occurs in occupational asthma; and the ‘morning dipper’ pattern of some asthmatic patients due to a fall in PEF in the early morning hours. A downward trend in PEF and an increase in its variability can identify worsening asthma and can be used by the doctor or patient to modify therapy. PEF monitoring is particularly useful in the substantial number of asthmatic people with poor perception of their own airway calibre. Response to asthma treatment is usually accompanied by an increase in PEF and a decrease in its variability.
Intrathoracic gas volume (ITGV)
FRC when measured by whole-body plethysmography is called as the intrathoracic gas volume (ITGV). It describes the volume of gas in the lungs at the end of an average expiration. This resting end-expiratory volume includes the volume of gas contained in non communicating spaces such as blebs or bullae that the FRC measured by gas dilution techniques will not measure.
CONGENITAL LUNG MALFORMATIONS Outline congenital malformations
Pulmonary sequestration - bronchopulmonary foregut malformation - males:females 4:1 - accessory lung tissue seperate from bronchial tree/arteries - abberant formation of lung tissue - systemic blood supply - intralobar (majority) - later - extralobar (minority) - neonatal - RDS, infection Bronchogenic cysts - form from foregut division - CCAM - pulmonary vascular supply
Anatomy of Resp tract
Conducting zone
- Generation 1 - terminal bronchioles
- High resistance to airflow
Gas exchange
- General 16 - alveolus
- Low resistance
- Primary bronchi - C- shaped cartilage, right larger more vertical - aspiration
- Secondary (lobar) bronchi - 2 Left, 3 right
- Tertiary (segmental) bronchi - portion supplied - bronchopulmonary segment
- Bronchioles - lack supportive cartilage, area supplied is pulmonary lobule
- Terminal bronchioles - last area of conducting zone (conductive air), no mucus glands or goblet cell, have cilia
- Respiratory bronchioles - first part of resp zone, alveoli bud from WALLS
- Alveolar ducts - alveoli on walls, no cilia
- Alveolar sacs - clusters of alveoli around central space (atrium)
Alveoli
- Type 1 - 95% surface area, squamous, rapid gas exchange
- Type 2 - 5% SA, cuboidal, repair alveolar epithelium and secrete surfactant
- Surfactant - protein and phospholipid solution that coats alveoli and prevents collape during exhalation due to decrease surfacte tension
- Alveolar macrophages - most numerous in lungs, alveoli and surrounding connective tissue
Blood supply
- Pulmonary artery - alveoli, supplies distally
- Bronchial artery - systemic supply from aorta
Resp membrane (blood gas barrier)
Pleura
- Parietal pleura - towards chest wall
- Visceral pleura - lining lung
- Pleural space - space between with pleural fluid
Outline lights criteria
lights - ratio of effusion : serum - LDH - albumin
Regulation/control of respiration physiology
Mechanics of breathing
Elastance
- Resists change/stretching etc, oppo
Compliance
- Distensibility, opposite of elastance, goes with stretching/change
- A more compliant lung expands more easily - Eg age - lung elastic tissue changes, asthma - unsure why
- A less compliant lung does not expand well - increased fibrous tissue, alveolar edema
- Conditions with decreased compliance (lung tissue/alveoli less able to expand (pneumonia, pul edema, atelectasis) - shorter time constant, less time alveolar inflation - ventilate with shorted inspiratory times, smaller tidal volume, faster rate
Elastic recoil
- Property of sustance that allows it to go back to natural/original state
Resistance
- Amount of pressure needed to overcome airway resistance
- Conditions with higher resistance (smaller radius) - asthma, bronchiolitis, MAS - ventilate with slower rate, large tidal volume (do don’t have to get over airway resistance each time)
Work of breathing
- Elastic work - work required to overcome lung and chest wall elastance - tidal volume. EG for diseases with decreased compliance - shallo rapid resp
- Resistive work - work required to overcome airway and tissue resistance - respiratory rate, EG disease with airway obstruction - deep slow respiration
Time constant
- Amount of time needed for alveoli to equilibrate with atmospheric pressure
Breathing Cycle
Inspiration - active (muscles contract)
- Chest muscles cause lung to expand, increase lung volume, decrease pressure in alveoli (greater pressure difference)
- Patmos > Palveoli - air moves into lungs
- Increased air inside alveoli increases pressure in alveoli
- Eventually, pressure in alveoli = pressure in atmosphere
- No more pressure difference to drive air into alveolus
Have to overcome 2 forces - elastic resistance and airway resistance
Elastic resistance (65%)
- Elastic recoil of lungs - tendency to recoil
- Pulmonary compliance - elasticity of lungs
Airway resistance (35%)
- Main factor is radius
Expiration - passive (elastic recoil)
- Chest muscle relax
- Allow lungs to spring back normal size - elastic recoil
- Elastic recoil causes decrease in alveoli volume, increased pressure
- P alveoli > P atmosphere
- Air moves out into atmosphere
Gas Exchange Physiology
A-a gradient
- PA02 (alveolar) - PaO2 (arterial)
- Alveolar gas equation
- O2 loaded from alveoli to pul blood
- CO2 loaded from pul blood into alveoli
Diffusion - Fick’s Law
- V (rate of diffusion) = Partial pressure alveolar sac (PA) - partial pressure in blood (Pa) x surface area x diffusion constant / wall thickness
Factors affecting diffusion:
- Pressure gradients of gases - want O2 to flow from alveolar to blood and CO2 from blood into alveoli
- Membrane thickness and surface area
- Ventilation and perfusion matching
- Gas co-efficient - weight and solubility of gases
Ventilation - Perfusion physiology
- Ventilation (V) - amount of gas going to alveoli
- Perfusion (Q) - amount of blood flow to alveoli
Hypoxemia - 5 causes
Hypoventilation
- Low alveolar ventilation
- Low alveolar ventilation - high alveolar CO2, increased arterial CO2
- Increased O2 concentation helps
- Eg - decreased resp drive, neuromuscular dysfunction, airway obstruction above carina
Diffusion limitation
- Not enough to adequate diffuse across gas barrier
- Eg - thickened blood- gas barrier, intersititial lung disease, extreme exercise (decreased transit time)
Shunt
- Shunt = blood entering arterial system without going through ventilated areas of lung
- Blood going to non ventilated areas of lung
- Does NOT improve with 100% O2 as shunted blood never exposed to increased O2
- Eg - pulmonary AV malformation, R-L cardiac shunt. Physiological - alveoli not ventilated but perfusion occurs - pulmonary, pul edema
V/Q mismatch (most common)
- Reduced efficacy of gas exchange as mismatch of perfusion/ventilation in lung areas
- O2 affected more than CO2
- Eg - neonatal RDS, mec asp, asthma, focal atelectasis, bronchiectasis, mucus plugging, bronchiolitis
Decreased PiO2
- Decreased partial pressure
- Eg - High altitude
Causes of hypercapnea
Hypoventilaion
V/Q mismatch
Oxygen binding/dissociation curve
- Hb 4 units and globin - bind O2. Positive co-operativity - once bound 1 O2, easier to bind remaining 3
Shift curve to right = more offloading of O2 in tissues, less affinity for Hb to O2
- Think running, exercise - need more O2
- Increased CO2, increased H, decreased pH, increased temperature
- increased 2-3 DPG
Shift curve to left = holding on to O2, higher affinity
- Decreased CO2, decreased H, increased pH
- Decreased DBP
- Fetal Hb - HbF
CO
- Hb binds CO more readily than O ++++
- Once saturated with CO, cannot bind O2
- Curve flattens depending where on amount bound to CO
Altitude
- Initial - resp alkalosis, increase pH, shift to left
- Metabolic comp - return pH to normal
- 2-3 days chronic hypoxia - increase 2-3 DPG - right shift
- After 1 week EPO, polycythemia
Site of obstruction to clinical signs
Extrathoracic (outside thorax, upper airway)
- Nose to thoracic inlet - eg choanal atresia, retropharyngeal abscess
- Below site of obstruction - negative pressure - collapse, worse obstruction
- Ex - inspiratory stridor and chest wall retraction
- Inspiration - much worse
- Expiration - ok
Intrathoracic - extra pulmonary
- Thoracic inlet to main stem bronchi - eg vascular ring, mediastinal tumour
- Ex - expiration much worse for obstruction
- Wheeze
Intrapulmonary
- Distal to main stem bronchi eg asthma, bronchiolitis
Parenchymal
- Lung tissue
- Grunting, tachypnoea, retractions
Lung volumes and capacities
Tidal volume (TV)
Amount of air moved in and out of the lungs during each breath (normal 6-7 ml/kg)
Inspiratory reserve volume (IRV)
Amount of air in excess of tidal volume that can be inhaled with maximum effort
Measures compliance
Expiratory reserve volume (ERV)
Amount of air exhaled by maximum expiratory effort after tidal expiration
- Effort dependent
Residual volume (RV)
Amount of air remaining lungs after maximum respiratory effort
- Effort dependent
Vital capacity (VC)
Amount of air moved in and out of the lungs with maximum inspiration an expiration
OR Amount of air exhaled following maximum inspiration
VC = ERV + TV + IRV
- Effort dependent
Inspiratory capacity (IC)
Amount of air inspired by maximum inspiratory effort after tidal expiration
IC = TV + IRV
- Effort dependent
Functional residual capacity (FRC)
Amount of air left in the lungs after tidal expiration;
FRC = RV + ERV
- Effort independent
- See further detail below
Total lung capacity (TLC)
Volume of air occupying lungs after maximum inhalation;
TLC = RV + VC
- Effort dependent
Forced parameters and interpretation
Forced expiratory volume - FEV1
- Volume of air blown out in 1 second of expiration (after max inhalation)
- Normal: 08-1.2
- Decreased in obstructive disease (more gas trapping, harder to get out)
- Decreased in restrictive disease (volume at start of expiratory manouvres in lower)
- FEV normal values:
- Mild > 70%, mod >50%, Severe > 35%, very severe <35%
- Correlates well with severity of obstructive disease
- Most useful long term measure of disease progression in obstructive airways disease
- Key outcome measure in CF - routinely used to monitor rate of progression of lung disease, need for interventions such as Abx, effectiveness of interventions
- In CF, FEV1 <30% = 50% 2 year survival - consider transplant
Forced vital capacity - FVC
- Maximum amount of air blown out after full inspiration
- 0.8-1.2
- Obstructive - normal or decreased due to gas trapping and hyperinflation
- Restrictive - decreased, less total volum e
- Duchennes DMD - FVC <20% daytime resp failure
FEV1/FVC
- Ratio
- Normal is > 0.7
- Obstructive - decreased as FVC decreased more than FEV1
- Restrictive - normal or decreased, FEV1 decreased and FVC decreased (reduced in proportion)
Forced expiratory flow (FEF)
- Forced expiratory flow during middle portion of forced expiration
- Usually measured 25, 50 and 75% of FVC
FEF25-75%
- Forced expiration at 25-75% of FVC
- >0.62
- Decreased in obstructive
- Represents flow in smaller conducting airways - more sensitive measure of small airway disease than FEV1
- Highly variable in repeat
- Most sensitive in children with small airway disease
PEFR
- Max flow during FVC
- Obstructive - decreased
PIFR
- Max flow in inspiration
FIF
- Forced inspiratory flow
- Upper airway obstruction
Obstructive
Eg asthma
- Decreased FEV1
- Decreased FVC
- Decreased FEV1/FVC
Restrictive
- FEV1 - decreased or normal
- FVC - decreased
- FEV1/FVC - normal
Forced parameters and interpretation
Forced expiratory volume - FEV1
- Volume of air blown out in 1 second of expiration (after max inhalation)
- Normal: 08-1.2
- Decreased in obstructive disease (more gas trapping, harder to get out)
- Decreased in restrictive disease (volume at start of expiratory manouvres in lower)
- FEV normal values:
- Mild > 70%, mod >50%, Severe > 35%, very severe <35%
- Correlates well with severity of obstructive disease
- Most useful long term measure of disease progression in obstructive airways disease
- Key outcome measure in CF - routinely used to monitor rate of progression of lung disease, need for interventions such as Abx, effectiveness of interventions
- In CF, FEV1 <30% = 50% 2 year survival - consider transplant
Forced vital capacity - FVC
- Maximum amount of air blown out after full inspiration
- 0.8-1.2
- Obstructive - normal or decreased due to gas trapping and hyperinflation
- Restrictive - decreased, less total volum e
- Duchennes DMD - FVC <20% daytime resp failure
FEV1/FVC
- Ratio
- Normal is > 0.7
- Obstructive - decreased as FVC decreased more than FEV1
- Restrictive - normal or decreased, FEV1 decreased and FVC decreased (reduced in proportion)
Forced expiratory flow (FEF)
- Forced expiratory flow during middle portion of forced expiration
- Usually measured 25, 50 and 75% of FVC
FEF25-75%
- Forced expiration at 25-75% of FVC
- >0.62
- Decreased in obstructive
- Represents flow in smaller conducting airways - more sensitive measure of small airway disease than FEV1
- Highly variable in repeat
- Most sensitive in children with small airway disease
PEFR
- Max flow during FVC
- Obstructive - decreased
PIFR
- Max flow in inspiration
FIF
- Forced inspiratory flow
- Upper airway obstruction
Obstructive
Eg asthma
- Decreased FEV1
- Decreased FVC
- Decreased FEV1/FVC
Restrictive
- FEV1 - decreased or normal
- FVC - decreased
- FEV1/FVC - normal
