10. Lung Physiology And Image

Control of BreathingControl of Breathing

RESPIRATORYCENTRE (Medulla)

MEDULLARY &CAROTID

CHEMORECEPTORS

Higher Control Centres

RESPIRATORYREFLEXES

DRUG EFFECTS e.g.OPIATES & CAFFEINE

CRANIAL & SPINALMOTOR NEURONES

STRETCH & PROPRIOCEPTORSLUNGS & CHEST WALL

INSPIRATION

ChemoreceptorsChemoreceptors

Medulla Oblongata and Carotid BodyMedulla Oblongata and Carotid BodyRespond to changes in pH, CORespond to changes in pH, CO22 and O and O22

Resetting of carotid chemoreceptors Resetting of carotid chemoreceptors occurs at birth in response to oxygenationoccurs at birth in response to oxygenation

Not essential at initiation of respiration but Not essential at initiation of respiration but used for control of breathing used for control of breathing

Responses are weak in the immediate Responses are weak in the immediate newborn period and in preterm babiesnewborn period and in preterm babies

Response to HypoxiaResponse to Hypoxia

Breathing Efforts

+

-

Time in Minutes

Older Infant

Fetus

Preterm baby

Term baby

5 mins

Respiratory ReflexesRespiratory ReflexesHering-Breuer reflexesHering-Breuer reflexes

Lung inflation Lung inflation → inhibition of breathing→ inhibition of breathingProlonged inhalation → expiratory muscle contractionProlonged inhalation → expiratory muscle contractionRapid deflation → prolonged inspiratory responseRapid deflation → prolonged inspiratory response

Head’s paradoxical reflexHead’s paradoxical reflexRapid inflation Rapid inflation → diaphragmatic contraction (sigh)→ diaphragmatic contraction (sigh)

Intercostal phrenic inhibitory reflexIntercostal phrenic inhibitory reflexChest wall distortion Chest wall distortion → shallow inspiratory efforts→ shallow inspiratory efforts

Irritant reflexesIrritant reflexesUpper airway reflexesUpper airway reflexes

Nasal irritation/ suction Nasal irritation/ suction → apnoea→ apnoeaLiquid in larynx → apnoeaLiquid in larynx → apnoea

Lung MechanicsLung Mechanics

Total lung capacityTotal lung capacity Tidal volumeTidal volume Functional residual Functional residual

capacitycapacity Vital capacityVital capacity Inspiratory & expiratory Inspiratory & expiratory

reserve volumesreserve volumes Residual volume Residual volume

DefinitionsDefinitionsTidal volume = volume of gas each breathTidal volume = volume of gas each breath

5 - 7 mL/Kg in babies 5 - 7 mL/Kg in babies Minute volume = vol. of gas each minuteMinute volume = vol. of gas each minute

200 – 400 mL/kg/min200 – 400 mL/kg/min

Minute volume = Tidal volume x resp. rateMinute volume = Tidal volume x resp. ratePaCO2 inversely PaCO2 inversely MV MV

PaCO2 PaCO2 ↓↓ by by ↑ tidal volume or ↑ resp. rate↑ tidal volume or ↑ resp. rateDead Space = Vol. of lung not involved in Dead Space = Vol. of lung not involved in

ventilation (eg, airways and ET tubes)ventilation (eg, airways and ET tubes)

ComplianceCompliance Compliance is a measure of the distensibility of Compliance is a measure of the distensibility of

the lungthe lung

Compliance = Compliance = Change in Volume (L)Change in Volume (L)

Change in Pressure (cm HChange in Pressure (cm H22O)O)

Lung disease decreases complianceLung disease decreases compliance RDSRDS (Alveolar collapse)(Alveolar collapse) TTNTTN (Fluid in insterstitium)(Fluid in insterstitium) BPDBPD (Lung fibrosis)(Lung fibrosis) Pneumothorax (Lung compression)Pneumothorax (Lung compression)

Surfactant improves compliance Surfactant improves compliance (beware over distension)

Airways ResistanceAirways ResistanceMeasure of the pressure gradient needed Measure of the pressure gradient needed

for gas to flow through a tubefor gas to flow through a tubeAirway resistance = Airway resistance = Pressure differencePressure difference

(R(RAWAW)) Gas flowGas flow

• Poiseuilles’ equationPoiseuilles’ equation• RRAWAW airway length airway length

• RRAWAW 1/ radius 1/ radius44

• Small & long ET tubesSmall & long ET tubes• Subglottic stenosisSubglottic stenosis

Work of BreathingWork of BreathingEnergy required to produce change in lung Energy required to produce change in lung

volumevolume Increases with decreased complianceIncreases with decreased compliance Increases with increased resistanceIncreases with increased resistance

If energy required to breath exceeds If energy required to breath exceeds capacity to supply oxygen to provide that capacity to supply oxygen to provide that energy then respiratory failure develops energy then respiratory failure develops requiring mechanical ventilationrequiring mechanical ventilation

Pressure Volume CurvesPressure Volume Curves(Lung hysteresis loops)(Lung hysteresis loops)

PRESSURE

VOLUME

INSP

EXP

Pressure Volume CurvesPressure Volume Curves(Lung hysteresis loops)(Lung hysteresis loops)

PRESSURE

VOLUME

LOW COMPLIANCE

HIGH COMPLIANCE

Pressure Volume CurvesPressure Volume Curves(Lung hysteresis loops)(Lung hysteresis loops)

PRESSURE

VOLUME

LOWERRESISTANCE

HIGHERRESISTANCE

Questions on Anatomy Questions on Anatomy & Physiology& Physiology

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Neonatal respiratory diseaseNeonatal respiratory diseaseAims:-Aims:-

Overview of neonatal respiratory diseaseOverview of neonatal respiratory diseasePathophysiologyPathophysiologyClinical presentationClinical presentationAetiologyAetiologyX-ray appearancesX-ray appearancesTreatmentsTreatments

Hyaline membrane diseaseHyaline membrane diseaseClinical:-Clinical:-

Usually pretermUsually pretermTachypnoea > 60Tachypnoea > 60 Indrawing/ retraction/ recessionIndrawing/ retraction/ recessionGruntingGruntingNasal flaringNasal flaringCyanosis in airCyanosis in airPresents within a few hours of lifePresents within a few hours of life

HMD - AetiologyHMD - Aetiology

Surfactant deficiencySurfactant deficiencyStructurally immature lungsStructurally immature lungs

HMD - TreatmentHMD - Treatment

OxygenOxygenCPAPCPAPMechanical ventilationMechanical ventilationSurfactant replacementSurfactant replacement

TTNTTNClinical:-Clinical:-

Usually close to termUsually close to termTachypnoea 100-120/minTachypnoea 100-120/minOverinflated chestOverinflated chestNo grunting/ retractionNo grunting/ retractionSettles within 24-48 hoursSettles within 24-48 hours

TTN - AetiologyTTN - Aetiology

Delayed fetal lung fluid clearanceDelayed fetal lung fluid clearanceCaesarean section - no squeeze of thorax Caesarean section - no squeeze of thorax

at birthat birthMum not in labour - no catecholamine Mum not in labour - no catecholamine

surge to promote absorption of fetal lung surge to promote absorption of fetal lung fluidfluid

TTN - treatmentTTN - treatment

Prevention - avoid early elective Prevention - avoid early elective caesarean sections at termcaesarean sections at term

Oxygen supplementation and IV fluids until Oxygen supplementation and IV fluids until resolutionresolution

Airleak SyndromesAirleak Syndromes

PneumothoraxPneumothoraxPneumomediatinumPneumomediatinumPneumopericardiumPneumopericardiumPulmonary interstitial emphysemaPulmonary interstitial emphysema

PneumothoraxPneumothoraxClinical:-Clinical:-

May be asymptomaticMay be asymptomaticMay be life threateningMay be life threateningSudden deterioration in gas exchangeSudden deterioration in gas exchangePoor colourPoor colourHypotension and tachycardiaHypotension and tachycardiaUnilateral overexpanded thoraxUnilateral overexpanded thorax

Pneumothorax - aetiologyPneumothorax - aetiology

Uneven alveolar ventilationUneven alveolar ventilationAir trapping and high pressure swingsAir trapping and high pressure swingsTracking of air from pulmonary interstitial Tracking of air from pulmonary interstitial

emphysemaemphysema

Pneumothorax - predisposing Pneumothorax - predisposing factorsfactors

Spontaneous in 1% of all babiesSpontaneous in 1% of all babies Increases with mechanical ventilationIncreases with mechanical ventilation Increased x 4 with HMDIncreased x 4 with HMD Increased x 16 with CPAPIncreased x 16 with CPAP Increased x 34 with IPPVIncreased x 34 with IPPV

Pneumothorax - preventionPneumothorax - preventionEarly surfactant therapyEarly surfactant therapyAvoid overdistensionAvoid overdistension

Volume guaranteeVolume guaranteeLow PIPLow PIP

Short inspiratory timeShort inspiratory timeFaster ventilation rates - entrainmentFaster ventilation rates - entrainmentHFOVHFOVTrigger ventilation - no proven benefitTrigger ventilation - no proven benefitParalysis - no proven benefitParalysis - no proven benefit

Pneumothorax - TreatmentPneumothorax - Treatment

None if asymptomaticNone if asymptomaticNitrogen washout technique - high FiO2 in Nitrogen washout technique - high FiO2 in

term babies onlyterm babies onlyChest drain if tension pneumothorax or on Chest drain if tension pneumothorax or on

mechanical ventilationmechanical ventilationEmergency needle thoracocentesisEmergency needle thoracocentesis

Pulmonary interstitial Pulmonary interstitial emphysemaemphysema

Mainly occurs in preterm babies ventilated Mainly occurs in preterm babies ventilated for HMDfor HMD

Gas trapping in perivascular sheathsGas trapping in perivascular sheaths Increased incidence at lower gestationsIncreased incidence at lower gestations

PIE - Clinical featuresPIE - Clinical features

Severe hypoxaemia and CO2 retentionSevere hypoxaemia and CO2 retentionDeteriorating clinical conditionDeteriorating clinical condition

X- RayX- RayOverinflation with gross cystic changesOverinflation with gross cystic changes

PIE - TreatmentPIE - Treatment

Lower PEEP and PIPLower PEEP and PIPParalysisParalysisHigh rate low pressure ventilationHigh rate low pressure ventilation? HFOV? HFOV? Selective bronchial intubation? Selective bronchial intubation

Persistent pulmonary Persistent pulmonary hypertension of the newbornhypertension of the newborn

Clinical featuresClinical features

Severe hypoxaemia (cyanosed in 100% O2)Severe hypoxaemia (cyanosed in 100% O2)No severe lung diseaseNo severe lung diseaseEvidence of R to L shunt (pre vs. postductal)Evidence of R to L shunt (pre vs. postductal)Structurally normal heartStructurally normal heart

PPHN - Aetiology and PPHN - Aetiology and predisposing factorspredisposing factors

Failure of NO synthaseFailure of NO synthaseAsphyxia/ acidosisAsphyxia/ acidosis InfectionInfectionDiaphragmatic herniaDiaphragmatic herniaAlveolar capillary dysplasiaAlveolar capillary dysplasiaMeconium aspiration syndromeMeconium aspiration syndrome

PPHN - treatmentPPHN - treatment

Minimal handlingMinimal handling Inotropic supportInotropic supportVentilation - maintain low normal CO2Ventilation - maintain low normal CO2ParalysisParalysisHyperventilation - ? Risk of PVLHyperventilation - ? Risk of PVLHFOVHFOVNitric OxideNitric OxidePulmonary vasodilators Pulmonary vasodilators

Tolazoline/ Prostacyclin/ MgSO4Tolazoline/ Prostacyclin/ MgSO4

Meconium aspiration syndromeMeconium aspiration syndromeClinical:Clinical:

Meconium passage prior to deliveryMeconium passage prior to deliveryMeconium in pharynx and tracheaMeconium in pharynx and tracheaRespiratory distress post delivery with Respiratory distress post delivery with

typical X-ray changestypical X-ray changes

MAS - AetiologyMAS - Aetiology

Asphyxia and intrauterine stressAsphyxia and intrauterine stressPassage of meconium + gasping Passage of meconium + gasping

movementsmovements Inhalation usually prior to deliveryInhalation usually prior to delivery

MAS - effects of meconiumMAS - effects of meconium

Ball valve effect - air trappingBall valve effect - air trappingChemical irritation and pneumonitisChemical irritation and pneumonitisSuperinfection with bacteriaSuperinfection with bacteriaSurfactant inhibitionSurfactant inhibition

MAS - ManagementMAS - Management

Prevention in delivery suitePrevention in delivery suiteMinimal handlingMinimal handlingMaintain normoxaemiaMaintain normoxaemiaMay need ventilation + ? ParalysisMay need ventilation + ? ParalysisSurfactant lavageSurfactant lavageAntibioticsAntibiotics

Pulmonary haemorrhagePulmonary haemorrhageClinicalClinical

Sudden deteriorationSudden deteriorationCopious bloody secretions from airwayCopious bloody secretions from airwayHypotensionHypotensionPallorPallorHypoxaemiaHypoxaemia

Pulmonary haemorrhage -Pulmonary haemorrhage -AetiologyAetiology

Usually pretermUsually pretermHMD with PDAHMD with PDAPost surfactant therapyPost surfactant therapyCoagulopathyCoagulopathyCongestive cardiac failureCongestive cardiac failure

Pulmonary haemorrhage - Pulmonary haemorrhage - TreatmentTreatment

Ventilation with high PEEPVentilation with high PEEPSurfactantSurfactant Indomethacin for PDAIndomethacin for PDATreat coagulopathyTreat coagulopathy

Chronic lung diseaseChronic lung diseaseClinicalClinical

Protracted respiratory insufficiency and Protracted respiratory insufficiency and oxygen requirement beyond 28th day or oxygen requirement beyond 28th day or 36th week post conceptional age36th week post conceptional age

Very preterm with early ventilation for Very preterm with early ventilation for HMDHMD

CLD - AetiologyCLD - Aetiology

VentilationVentilationOxygen toxicityOxygen toxicityPROMPROMChorioamnionitisChorioamnionitis InflammationInflammationProteolytic enzymesProteolytic enzymes

CLD - preventionCLD - prevention

Minimise ventilation and oxygen exposureMinimise ventilation and oxygen exposureHFOVHFOVEarly surfactantEarly surfactantCorticosteroids Corticosteroids Early extubationEarly extubation

CLD treatmentCLD treatment

Minimise ongoing barotraumaMinimise ongoing barotraumaNutritionNutritionPermissive hypercapniaPermissive hypercapniaDiureticsDiureticsBronchodilatorsBronchodilatorsCorticosteroids - controversialCorticosteroids - controversialHome oxygen therapyHome oxygen therapy

SummarySummary Knowledge of respiratory anatomyKnowledge of respiratory anatomy Physiology of adaptation at birthPhysiology of adaptation at birth SurfactantSurfactant Gas exchangeGas exchange Gas transportGas transport Lung mechanicsLung mechanics

Application of knowledge to the clinical Application of knowledge to the clinical management of babies with respiratory diseasemanagement of babies with respiratory disease