Ch 17: Mechanics of BreathingCh 17: Mechanics of Breathing

Functional division of respiratory system:• respiratory zone• conducting zone

Key Topics:Key Topics:

Structure and function of Structure and function of respiratory pumpsrespiratory pumps

Gas exchangeGas exchange with blood with blood

Role of Role of surfactantsurfactant and and pressure differences on rate pressure differences on rate of exchangeof exchange

RegulationRegulation of respiration of respiration

Functions of the Respiratory System

Oxygen exchangeOxygen exchange Air to bloodAir to blood Blood to cells Blood to cells

Carbon dioxide exchange Carbon dioxide exchange Cells to bloodCells to blood Blood to airBlood to air

Regulation of body pHRegulation of body pH

Protection of alveoliProtection of alveoli

VocalizationVocalization

Lungs: – thin walled, Lungs: – thin walled, moist exchange moist exchange surface (75 msurface (75 m2 2 ) )

Ribs & skin protectRibs & skin protect

Respiratory muscles Respiratory muscles pump airpump air

Review AnatomyExternal R

espirationCellular RespirationFig 17-1

CDAnimation

Respiratory System: Anatomy Review

Pulmonary Circulation High-flow, low-pressure High-flow, low-pressure 5 Mio Americans suffer from CHF 5 Mio Americans suffer from CHF (read (read

clinical focus p. 565)clinical focus p. 565)

Gas Laws

Air is a mix of gases:Air is a mix of gases: Dalton’s lawDalton’s law Total P = Total P = Ps of individual gases Ps of individual gases Calculate Calculate partial pressure of Opartial pressure of O22 in dry air at sea level in dry air at sea level

Gases move down their pressure gradientsGases move down their pressure gradients

Pressure-volume relationship:Pressure-volume relationship: Boyle’s law:Boyle’s law: PP11VV11 = P = P22VV22

Ventilation= Breathing= Breathing

Pulmonary function tests use spirometerPulmonary function tests use spirometer

Measure lung volumes during ventilationMeasure lung volumes during ventilation

Covered in detail in lab

The Airways: Conduction of Air from Outside to Alveoli

3 upper airway functions: _______________3 upper airway functions: _______________ Mucociliary escalator depends on secretion of watery saline Mucociliary escalator depends on secretion of watery saline

– – note:note: ______________ ______________ (genetic disease)(genetic disease)

Effectiveness of nose vs. mouth breathing Effectiveness of nose vs. mouth breathing (Respirators!)(Respirators!)

Compare to Fig. 17.8

Breathing = VentilationAir flows due to pressure gradients Air flows due to pressure gradients (analogous to blood)(analogous to blood)

InspirationInspiration:: Contraction of diaphragm (60-75%) of volume changeContraction of diaphragm (60-75%) of volume change _______ intercostals and scalenes (25-40%) _______ intercostals and scalenes (25-40%)

ExpirationExpiration Relaxation of inspiratory musclesRelaxation of inspiratory muscles Elastic recoil of pleura and lung tissue reinforce muscle Elastic recoil of pleura and lung tissue reinforce muscle

recoilrecoil

Fig17-9/11

Po = Pi Po vs Pi ? Po vs Pi ?

Fig17-9

Pressure Changes During Ventilation

Fig17-11

Alveolar and Intrapleural Pressures

Lungs unable to expand and contract on their ownLungs unable to expand and contract on their own

During development, intrapleural pressure During development, intrapleural pressure becomes subatmosphericbecomes subatmospheric

Lungs “stuck” to thoracic cage by pleural fluid Lungs “stuck” to thoracic cage by pleural fluid bondbond

Pneumothorax ?Pneumothorax ?

Fig 17-12

Pneumothorax Therapy?

Fig 17-12

Tube thoracostomy

Lung Compliance and Elastance

Compliance:Compliance: ability of lungs to stretch ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive Low compliance in fibrotic lungs (and other restrictive

lung diseases) and when not enough surfactantlung diseases) and when not enough surfactant

ElasticityElasticity (= Elastance): ability to return to (= Elastance): ability to return to original shapeoriginal shape Low Elasticity in case of emphysema due to destruction Low Elasticity in case of emphysema due to destruction

of elastic fibers.of elastic fibers.

Normal lung is both compliant AND elasticNormal lung is both compliant AND elastic

Surfactant

Surface tension at all air-fluid boundaries due to?Surface tension at all air-fluid boundaries due to? Surface tension opposes alveolar expansionSurface tension opposes alveolar expansion SurfactantSurfactant = detergent like complex of proteins & = detergent like complex of proteins &

PL: Disrupts cohesive forces between water PL: Disrupts cohesive forces between water molecules molecules surface tension surface tension work of breathing

IRDSIRDS

Unequal attraction produces tension at liquid surface

Airways Resistance Also influences work of breathing.Also influences work of breathing. Primary determinant: airway diameterPrimary determinant: airway diameter Bronchiole diameter is adjustable Bronchiole diameter is adjustable Under nervous, hormonal and paracrine Under nervous, hormonal and paracrine

controlcontrol Parasympathetic:Parasympathetic: Sympathetic:Sympathetic: Epinephrine (Epinephrine (22 receptors): receptors): Histamine:Histamine: CO CO 22

Matching Ventilation with Alveolar Blood Flow (Perfusion)

Mostly local regulation Mostly local regulation Lung has collapsible capillaries Lung has collapsible capillaries Reduced Reduced

blood flow at rest in lung apex blood flow at rest in lung apex (reserve capacity (reserve capacity of body)of body)

[CO[CO22] in exhaled air ] in exhaled air bronchodilation bronchodilation

[O[O22] in ECF around pulmonary arterioles ] in ECF around pulmonary arterioles vasoconstriction of arteriole (blood vasoconstriction of arteriole (blood diverted) – diverted) – opposite of systemic circulation!opposite of systemic circulation!

Emphysema