Pulmonary Flashcards
Lung and Airway Development
- Derived from Endoderm
- Lung forms from ventral bud of esophagus
- Lung development dependent on : Fetal lung fluid, fetal breathing, peristalsis of airway
Lung Vascular Supply
- Arise from branches of 6 aortic a.
- Pre-acinar a.: adjacent to airways up to and including non resp bronchioles, developed by angiogenesis (from pre existing vessels); complete by 16 w
- Intra-acinar a: Adjacent to resp bronchioles and alveolar ducts; develop by vasculogenesis (de novo from mesoderm); growth continues until 8-10 y old
Development of Small Pulm Arteries
- Fetus: Proximal a. have completely encircling sm. muscle layer that changes to incomplete muscularization until distally disappears completely (intra acinar a. lack muscle)
- Near - Term: Half of resp bronchiolar vessels are muscularized or partially muscularized; intra acinar a. continue to lack
- 4-6 w.: Involution of medial sm. muscle layer and reduction in muscular wall thickness
- Adult: Extension of muscularization to include acinar arteries as well - only a thin layer of sm muscle
Alveolarization
- Continue development until 3-8 y.
- 50-150 million at term increasing to 200-600 million in adult
- Enhanced by: Vit A and thyroxine
- Delayed by: Postnatal Steroids, O2, nutritional deficiencies, Mechanical Vent, Insulin, Inflammation
Lung Development Stages
- Embryonic (0-5 w): Lung forms from ventral bud of Esophagus; bronchi established; 5 lobes of lung; pulm vasculature develops
- Pseudoglandular (5-15w): Continued branching, all large airway up to term bronchiole, AF production begins, pneumocyte precursors develop, vasculature of a and v, separation of thorax and peritoneal cavity
- Canalicular (15-25w): Canaliculi branch out of terminal bronchioles, prelim gas exchange, T II pneumocytes →T I
- Saccular (25-35w): Multiple sacs form from terminal bronchioles, gas exchange via alveolar-capillary membrane
- Alveolar and Vasculature (36+w- 8 y): Alveoli form from terminal sacs, alveoli increase in diameter, microvascular growth and maturation
Lung Stage Development-Specific Abnormalities
- Embryonic - BLTT: Bronchogenic Cysts, Laryngeal Cleft, Tracheal Stenosis, TEF
- Pseudoglandular - BCCCP: Branching Abnormalities, CDH, CLE, CPAM, Pulmonary lymphangiectasia,
- Canalicular - PSA: Pulm Hypoplasia, Surfactant Deficiency, Alveolar Capillary Dysplasia
- Saccular - PS: Pulm Hypoplasia, Surfactant Deficiency
- Alveolar - CPS: CLE, Pulm Hypertension, Surfactant Deficiency
TI v TII Pneumocyte
- Fried Egg Shape, Tight Jxn, thin and cover 90% surface but fewer # cells, GAS EXCHANGE, derived from TII
- Cuboidal shape, cover 10% surface but greater # cells, SURFACTANT Metab and secretion, Progenitor to TI
Fetal Lung Fluid
- During respiration, larynx opening allows minimal but steady FLF flow out that is swallowed or mixed with AF; larynx closure maintains distending pressure on lungs
- FLF maintains airway volume similar to FRC at birth 20-30 mL/kg
- Near term FLF production decreases to 4-5 mL/kg/h
- FLF production inhibited by Epinephrine and β agonists
- Prior to birth, resp epithelium changes from Cl secreting to Na absorbing membrane
FLF Clearance
- PRENATAL: ↓ Formation FLF, ↓Cl secretion concurrently with ↑ Na transport, ↑Lymph oncotic pressure and ↓ fetal alveolar protein →fluid movement to lymphatics
- LABOR: Mechanical Forces, Catecholamine surge ↑ Na transport, ↑ Cortisol and Tyroid Hormones that ↑ Na transport
- POSTNATAL (35% to still be cleared): Lung distension ↑ transpulmonary pressures, ↑Lymph oncotic pressure and ↓ fetal alveolar protein →fluid movement to lymphatics
Surfactant Composition
- 50% DPPC, 20% PC, 8% PG, 8% Surf Protein A, B, C,D, 8% Neutral Lipids
Surfactant Protein Origin (Made in ER and glycosylated in Golgi Bodies)
A. TII, Clara Cells, Chr 10, expressed 3rd tri
B. TII, Clara Cells, Chr 2, expressed end of 1st tri
C. TII, Chr 8, expressed end of 1st tri
D. TII, Nonpulm Cells, Chr 10, expressed last - 3rd tri
Surfactant Protein Characteristics
A. 28, 32 kDA, MOST ABUNDANT (~50%), induced by steroids, Hydrophilic, Collectin Member
B. 8 kDA, Hydrophobic, induced by steroids
C. 4 kDA, Hydrophobic, induced by steroids
D. 43 kDA, induced by steroids, Hydrophilic, Collectin Member
SP-A
- Assists with tubular myelin formation (w/ SP-B and Ca)
- Enhances phospholipid uptake and inhibits phospholipid secretion
- Place role in host defense: role in opsonization, phagocytosis, agglutination, reduction of viral infectivity, modulation of inflammation
SP-A Null: ↑ inflammation, ineffective pulm clearance, no tubular myelin
SP-A Deficient: ↑ RDS severity and CLD development
SP-B
- Critical for SURFACTANT Function
- Assists with tubular myelin formation (w/ SP-A and Ca)
- Promotes surface adsorption of phospholipids (w/ SP-C)
SP-B homozygote deficiency: Severe resp failure soon after birth, require lung transplant, AR inheritance
SP-B Partial Deficiency: CILD in childhood
SP-C
- Critical for SURFACTANT Function
- Promotes surface adsorption of phospholipids (w/ SP-B)
SP-C Null: Minimal Effect
SP-C Deficient: ILD at a few mo of age ranging from mild symptoms to requiring lung transplant, AD or sporadic inheritance
SP-D
- Place role in host defense: role in agglutination, reduction of viral infectivity, also involved in opsonization and modulation of inflammation
- Anti-oxidant
- Surfactant lipid homeostasis
SP-D null: altered surfactant homeostasis, susceptible to viral pathogens
SP-D Deficiency: No association
ATP-Binding Cassette Member A3 Deficiency
- Most common genetic cause of surfactant deficiency
- AR Inheritance
- lack DPPC and PG, ↓ Lamellar bodies
- term infant with resp distress soon after birth, may present later with FTT, clubbing and ILD
Surfactant Protein and Secretion
- TRANSPORT: SP-B & SP-C with surfactant lipids transported to multivesicular bodies
- LAMELLAR STORAGE
- SECRETION: SP-B & SP-C with surfactant lipids secreted into alveolar subphase and interact with SP-A to form tubular myelin reservoir
- ADSORPTION: Tubular myelin multi layers form a film and reduce surface tension at air-liquid interface
- TURNOVER: Endocytosis takes remnants by TII cells
- RECYCLING: Recycled into multivesicular and lamellar bodies; 95% secreted surfactant is recycled with 10 h turnover time
- CLEARANCE: Alveolar Macrophages clear and catabolize remnants
Accelerate Lung Maturation
- Pregnancy: cHTN, CV Dz, Placental Infarct, IUGR, PIH, PROM, Incompetent Cervix, Hemoglobinopathy, Chorio (yet higher CLD incidence)
- Other: Steroids, TH, TSH, TRH, cAMP, Methylxanthines, β agonists, Prolactin, Estrogens, Epidermal GF, Transforming GF α
Delayed Lung Maturation
- Pregnancy: DM, Rh Isoimmun w/ hydrops, 2nd born twin, Male, C/s, Prematurity
- Other: Insulin, Androgens, Transforming GF β
Immature V Mature Lung Surfactant Changes
- Immature: Large # glycogen lakes & Few Lamellar Bodies, Saturated PC/Total PD = 0.6, Low PG, 10% PI, Low SP-A
- Mature: No glycogen lakes & Many Lamellar Bodies, Saturated PC/Total PD = 0.7, 10% PG, 2% PI, 5% SP-A
Surfactant Component Changes during Development
- PI present before PG, increases until ~35 w then falls
- L/S increases with GA, sharply at ~ 35 w ; sphingomyelin decreases after 32 w; L/S = 2 at 35 w
- PG increases at 34-35w, not present in infants with RDS; certain bacteria produce PG leading to False +, not necessary for surfactant function
Fetal Lung Maturity Testing
L/S >2.0 = RDS <0.5%
L/S<1.0 = RDS 100%
PG present = RDS <0.5%
L/S >2.0, no PG = RDS >80 %
L/S >2.0, + PG = RDS 0 %
L/S >2.0, +DM or Rh Iso = RDS 13 %
Foam Test : AF+ethanol→Foam = Mature lung
Lamellar Body Solubilization Test: Unraveling or solubilization of lamellar bodies in mature lung
AF Appearance: Measure OD 650 nm of AF
Natural Surfactant - all contain DPPC and SP-B & C
Survanta/Beractant: Minced Bovine lung
Infasurf/Calfactant: Bovine lung lavage, most SP-B
Curosurf/Porctant Alpha :Minced Porcine lung
Alveofact/Bovactant: Bovine lung lavage
Synthetic Surfactant - all DPPC
Exosurf: Synthetic lipids mixture, Hexadecanol, tyloxapol, no SP
ALEC: PG, no SP
Surfaxin: DOPG, SP-B
LAPLACE’s Law
P=2T/r
- ↓ alveolus size = ↑ surf conc → ↓ Surface Tension further preventing air from leaving
- ↑ alveolus size = thinly spread surf and less conc → ↑ Surface Tension and lung recoil pressure
- As lung INflates, Surface Tension INcreases and as it DEflates, Surface Tension DEcreases
- Decreased Tension INCREASES Compliance
- Decreases Tension prevents transudation of fluid from capillaries into alveoli
↓ PVR during extrauterine Pulm Transition
- Lung inflation activating stretch receptors leading to Pulmonary Vasodilation
- Gas Exchange leading to ↑O2 resulting in Pulmonary Vasodilation
- Vasoactive mediators (NO, endothelin-1)
Factors leading to Delayed Fluid Resorption
- Maternal: Excessive analgesia, excessive maternal IV fluids
- Delivery: C/s, breech, DCC
- Fetal/Infant: perinatal depression, polycythemia, Inadequate Epi surge
Factors leading to Failure of ↓ PVR
- Airway obstruction and atelectasis → lack of oxygenation, minimal alveolar ventilation
- Inflammatory Conditions (PNA, Sepsis) → ↑ leukotrienes, thromboxane, PAF
- Pulm Hypoplasia (CDH) → abnormal pulm vasculature
- Defects of PG or NO synthesis
- Maternal Meds (Indomethacin, Aspirin)
Boyle’s Law
P1V1=P2V2
Control of Breathing
Inspiration: Insp muscles of Chest and diaphragm contract causing thorax expansion and greater neg intrapleural pressure that causes intra alveolar pressure to ↓ with corresponding ↑ in alveolar volume. As barometric pressure > alveolar pressure, air moves into lungs.
Expiration: Resp muscles relax. Lung recoil pressure results in positive alveolar pressure (intra pleural pressure approaches baseline) resulting in gas leaving lungs
Hering-Breuer Inflationary Reflex
Prevents overinflation
Pulm stretch receptors send afferent neural input to medulla causing vagal nerve to inhibit further inspiration and/or promote expiration limiting i time.
With associated ↑ e time, resp frequency ↓ = apnea potential
Progressive ↑ in reflex as lung volume ↑ above FRC
Reflex ↑ with GA, strongest in first few mo after birth and weak in adults
Hering-Breuer Deflation Reflex
Reacts to abrupt deflation
↑ RR with abrupt delation, assoc with periodic deep breaths (‘sighs’) to prevent atelectasis
Important to maintain FRC in setting of compliant chest wall and large lung recoil
Paradoxical Reflex of Head
Inhibits Hering-Breuer reflex and extends inspiration
Important in first few breaths after delivery to inflate fluid filled lungs
Causes ‘sigh” breaths that reverse lung preference to collapse during quiet breathing
Control of Respiration
- CSF: ↑ in H+ (most sens!), ↑ in paCO2 act on central chemoreceptors in medulla
- Blood: ↓ in paO2 (most sens!), ↑ in paCO2, H+ acting on peripheral chemoreceptos on carotid and aortic bodies
Response to CO2 Δ
- CO2 Δ dependent on CHEMORECEPTORS on ventrolateral surface of MEDULLA that sense H+ ion conc of ECF
- ↑ in paCO2 leads to ↑ in H+ ion conc and ↑ in RR
- Sensitivity to chemoreceptors is reduced in preterm infants and increases with GA
Minute Ventilation x Alveolar PCO2 graph