Development and Disorders of the Lungs Flashcards
What are the precursors to the lungs and what do they form?
Endoderm - Epithelial linings
Splanchnic mesoderm - Structural components (walls): Smooth muscles/fibrous tissues
When does the lung become active?
Upon birth
Allows developmental delay, but must be ready to operate upon birth
What is first phase of development and when does it occur?
What two events characterize this event?
Embryonic Phase (Weeks 4-7) Lung primordium appearance and initial airway branching
How does the lung primordium appear?
Respiratory diverticulum part of the foregut
From a fold in the pharynx
Separates from esophagus (posterior)
What are the initial branching patterns during the embryonic phase?
First branches – Primary bronchi
Second branches – Lobar bronchi
3 on right, 2 on left
Tertiary branches follow after
What are possible anomalies during the embryonic phase?
Inadequate partitioning due to abnormal or insufficient development of tracheoesophageal septum
Anatomic anomalies: Absence of lungs, extra lobes, ectopic/absence of lobes, abnormal/insufficient branching, accessory lung, bronchogenic cysts, pulmonary vascular anomalies
What is the second phase of lung development?
When does it occur?
What is it characterized by?
What interactions govern it and what events occur?
Pseudoglandular Phase (Week 6-16): Airway branching continues
Epithelial/mesenchymal interactions
Pulmonary vasculature developing around the epithelium
Several generation of branches
What is the third phase of development, when?
What two major events occur?
Canalicular Phase (Week 16-26)
Capillary density increases
Alveolar cells begin to differentiate
What is the limit of etrauterine viability?
Week 22-24
What is the fourth phase of lung development?
What is it defined by?
Is the fetus now viable?
Terminal Sac Phase (Week 26 to Birth)
Distal airways dilate forming terminal sacs (primitive alveoli)
Viability is possible
What/when is the final phase of lung development?
What occcurs in this phase?
Alveolar Phase (32 weeks to 8 years of age)
Alveolar formation begins by subdivision of terminal sacs – Septation
Alveolar septum become thinner
When do the majority of alveoli form?
Post-natal (After birth)
Are these phases discrete events?
What direction does airway formation occur?
What interactions play a major role in development?
What is the relative speed of lung development?
No, phases blend to form a continuum of development
Proximal to distal
Epithelial-Mesenchymal
Slow formation
What does the prenatal lung contain?
What happens if it doesn’t have enough of this?
What kinds of prenatal respiratory movements exist?
What is the PVR of the prenatal lung?
Prenatal lung contains fluid
Insufficient fluid production leads to hypoplastic lungs
Respiratory movements exist, but shallow and episodic
Pulmonary vascular resistance is very high
What changes occur post-natally that allow for breathing?
Pulmonary changes – Fluid replaced by air
Circulatory changes – Cardiac shunts close, pulmonary vessels fill
Neural – Breathing, sympathetic activation (reduce secretions in epithelial lining)
What can problems in fluid removal result in?
Wet lung (Transient tachypnea) – usually a transient condition
What are characteristics of the new air/liquid interface within the alveoli postnatally?
Thin compliant wall
Subjected to surface tension
How and when does the lung adapt to surface tension?
What is the mechanism of this adaptation?
Pulmonary Surfactant Production – Type 2 Pneumocytes
Production begins toward the end of canlicular period
Significant increase in production at 35 weeks: General cut-off for viability without assistance
Functions of pulmonary surfactant: decrease surface tension, stabilize alveolar surface, decrease fluid transfer (Prevents the alveoli completely collapsing)
What is esophageal atresia?
What are the types of it mentioned in class?
Atresia in the esophagus with a possible fistula between esophagus and trachea
Esophageal atresia and distal esophageal-tracheal fistula (Most common)
Long gap atresia (no fistulas)
Basically any other permutation of positioning of the esophagus and the trachea can exist
How can esophageal atresia with fistula be diagnosed?
CXR - Air in stomach for fistula
Bronchoscope reveals fistula at bottom of trachea
How often do associated anomalies occur with esophageal atresia?
What major ones are there?
What associated risks are there?
Occur in 50% of patients
Cardiac (30%): VSD is the main one
Other include GI (12%), GU, Musculoskeletal
Poor birth weight is increased CV risk
What is the treatment for esophageal atresia?
Pre-op management: Patient head up, suck out secretions, check for associations
Operative approach for most common type
- Incision into right pleura
- Spread ribs apart
- Find the fistula
- Divide the fistula and close off the trachea
- Reconnect the esophagus
What is congenital cystic adenomatoid malformation?
What is the histology characterized by?
What classifications are there?
Anomalies of bronchioles and likely due to a single bronchiole stopping
Other airways overgrow instead forming mass of pulmonary tissue at the expense of alveolar development
Lined by combination of both respiratory and mucus-secreting epithelium with an adenomatoid lesion
Type I: Large macroscopic cysts
Type II: Small macroscopic cysts
Type III: Microscopic cysts
What are the characteristics of CCAM?
What is the presentation of CCAM?
What is the pathophysiology of CCAM?
Characterized by:
Single lobe typically
Communication with bronchial system
Progressive air trapping to distension (risk of pneumonia)
Presents as:
Respiratory distress (rare)
Recurrent pulmonary infections
Asymptomatic but detected radiographically (prenatal ultaround or chest radiograph)
Pathophysiology is:
Pulmonary hypoplasia, pulmonary hypertension, distortion of mediastinum and impaired venous return (Consequences of mass effect and timing of arrest of development)
Can result in hydrops, severe respiratory failure, pulmonary infection, or no symptoms
What is the therapeutic approach for CCAM?
- Respiratory distress as neonate – Emergent operation
- Thoractomy and lobectomy followed by stabilization
- For other cases, in the US excision is encouraged, elsewhere observation can be done instead
- Reduce recurrent infections, potential cancers
- Anatomic lobectomy – lung will compensate up to 7 yo
What are the clinical signs of respiratory distress?
Rapid breathing (> 60 BPM)
Flaring nostrils
Chest retractions
Expiratory grunt
Often cyanotic (blue)
Rapid HR
Anxious expression
What are the causes of respiratory distress?
Wet lung
Meconium Aspiration – First bowel movement
Pneumonia
Bilateral Choanal Atresia
Congenital Diaphragmatic Hernia
Hypoplastic Lung Development
Pulmonary Hemorrhage
Pneumothorax
Insufficient Pulmonary Surfactant
What is respiratory distress syndrome/hyaline membrane disease?
Clinical condition experience respiratory distress with thick hyaline coating in lungs
What is the cause and pathophysiology of RDS/HMD?
Inability to keep alveoli filled with air
Injury to type I alveolar cell injury results in :
- Breakdown air/capillary barrier
- Serum leaks into alveolar lumen
- Hyaline membrane forms inside of alveolus
Decreases in surfactant production results in:
- Poor compliance of lung tissue
- Atelectasis due to alveolar collapse
- Engorgement of pulmonary capillaries
- Formation of a hyaline membrane
What can premature infatns with RDS develop?
Bronchopulmonary dysplasia (chronic lung disease of infancy)
What are the risk factors for RDS/HMD?
Prematurity:
<28 weeks is 100% of RDS
28-34 has 33% chance
>34 weeks has 5%
Perinatal depression
Male predominance
Maternal diabetes
C-section: Ruins fluid expulsion
Multiple births
What is done to initially manage RDS/HMD patients?
How are they treated?
Positive Pulmonary Pressure Ventilation on birth
Move to ICU for observation
Oxygen supplementation Assisted ventilation (nCPAP) Mechanical ventilation (FiO2 \> 0.40) Fluid restriction Administer artificial surfactant (All neonates \< 29 in NICU receive, Neonates \> 29 weeks are case by case)
How can RDS be prevented?
What are the outcomes?
Antenatal metamethasone – Stimulate type II pneumocytes
Arrest of preterm labor
Peak severity 1-3 days
Recovery coincides with diuresis beginning at 72 hours
Severe cases evolved to bronchopulmonary dysplasia: Extreme prematurity, sepsis, chronic ventilation
How is RDS/HMD diagnosed? (Lab values, CXR, Specific tests)
Lab: Indication of respiratory acidosis, moderate hypoxia, delayed metabolic acidosis
CXR: Low lung volumes, diffuse atelectasis “ground glass opacities”, air bronchograms, difficult to distinguish from pneumonia
Lecithin (surfactant lipid)/Sphingomyelin Ratio
> 2.0: 98% OK
1.5-1.9: 50% RDS
<1.5: 73% RDS
Phosphatidylglycerol (surfactant lipid) is a more accurate indicator of lung maturity
What is transient tachypnea of the newborn? (TTN)
How long do the symptoms last?
What histology/morphology is observed?
What is a risk factor?
Tachypnea immediately after birth or within two hours, with other predictable signs of respiratory distress
Symptoms can last few hours to two days
Diffuse parenchymal infiltrates, a “wet silhouette” around heart, or intralobar fluid accumulation
More common in C-sections
What us meconium aspiration?
What is the incidence?
What is the “mechanism” of respiratory distress?
What is appearance on CXR?
How does it resolve?
Aspiration of first bowel movement resulting in significant respiratory distress, hypoxia
Incidence – 1.5-2% in term of post-eterm infants
Locally irritative, obstructive & medium for bacterial culture
CXR – Patchy atelectasis or consolidation
Will spontaneously resolve
