Respiratory Physiology - A

RESPIRATORY RESPIRATORY PHYSIOLOGYPHYSIOLOGY

Agaton T. Panopio, Jr., MD, MHPEdAgaton T. Panopio, Jr., MD, MHPEd

Lung PressuresLung Pressures

Intrathoracic PressureIntrathoracic Pressure

Pressure within the pleural cavityPressure within the pleural cavity

Intrapulmonic PressureIntrapulmonic Pressure

Pressure within the pulmonary alveoliPressure within the pulmonary alveoli

Transpulmonary PressureTranspulmonary Pressure

Pressure across lung parenchymaPressure across lung parenchyma

Transthoracic PressureTransthoracic Pressure

Pressure across the chest wallPressure across the chest wall

Normally subatmospheric at rest, due to Normally subatmospheric at rest, due to inward elastic recoil of the lungs and inward elastic recoil of the lungs and outward elastic recoil of chest walloutward elastic recoil of chest wallPressure is more negative at upper thorax Pressure is more negative at upper thorax

due to gravity and posturedue to gravity and postureBecomes more negative during quiet Becomes more negative during quiet inspiration, less negative during quiet inspiration, less negative during quiet expirationexpiration


Intrathoracic (Intrapleural) Pressure Intrathoracic (Intrapleural) Pressure

Initially equal to atmospheric pressure Initially equal to atmospheric pressure at restat restDuring inspiration, it becomes negative, During inspiration, it becomes negative, causing entry of air into alveolicausing entry of air into alveoliAlveolar pressure returns to zero and air Alveolar pressure returns to zero and air flow stopsflow stopsAt expiration, alveolar wall recoils, alveolar At expiration, alveolar wall recoils, alveolar gas is compressed, and pressure rises gas is compressed, and pressure rises above above atmospheric pressure atmospheric pressure


Intrapulmonic (Alveolar) PressureIntrapulmonic (Alveolar) Pressure

During inspiration, as intrathoracic During inspiration, as intrathoracic pressure becomes more negative, pressure becomes more negative, transpulmonary pressure increases transpulmonary pressure increases and and alveoli expandalveoli expand

During expiration, as intrathoracic pressure During expiration, as intrathoracic pressure becomes less negative, transpulmonary becomes less negative, transpulmonary pressure decreases and alveoli recoilpressure decreases and alveoli recoil


Transpulmonary (Transmural) PressureTranspulmonary (Transmural) Pressure

A measure of the elastic recoil of the A measure of the elastic recoil of the thoraxthorax


Transthoracic PressureTransthoracic Pressure

Quiet InspirationQuiet Inspiration

Inspiratory muscles contractInspiratory muscles contract

Chest wall expandsChest wall expands

Thoracic volume increasesThoracic volume increases

Intrathoracic pressure becomes more negativeIntrathoracic pressure becomes more negative

Quiet InspirationQuiet Inspiration

Alveolar transmural pressure gradient increasesAlveolar transmural pressure gradient increases

Alveoli expandAlveoli expand

Alveolar pressure falls below atmospheric Alveolar pressure falls below atmospheric pressurepressure

Air flows into the alveoliAir flows into the alveoli

Quiet ExpirationQuiet Expiration

Inspiratory muscles recoilInspiratory muscles recoil

Thoracic volume decreasesThoracic volume decreases

Intrathoracic pressure becomes less negativeIntrathoracic pressure becomes less negative

Alveolar transmural pressure gradient Alveolar transmural pressure gradient decreasesdecreases

Quiet ExpirationQuiet Expiration

Increased alveolar elastic recoilIncreased alveolar elastic recoil

Alveolar pressure rises above Alveolar pressure rises above atmospheric pressureatmospheric pressure

Air flows out of the alveoliAir flows out of the alveoli

Amount of air that moves in and out of Amount of air that moves in and out of the lungs during normal resting the lungs during normal resting ventilationventilation

Usually 500-600 mlUsually 500-600 ml

Lung Volumes and CapacitiesLung Volumes and Capacities

Tidal VolumeTidal Volume

The amount of air that can be inhaled The amount of air that can be inhaled maximally after a normal inhalationmaximally after a normal inhalation

About 2.5 litersAbout 2.5 liters


Inspiratory Reserve VolumeInspiratory Reserve Volume

The amount of air than can be exhaled The amount of air than can be exhaled maximally after a normal maximally after a normal

exhalationexhalation



Expiratory Reserve VolumeExpiratory Reserve Volume

Amount of air that remains in the lungs Amount of air that remains in the lungs after a maximal exhalationafter a maximal exhalation



Residual VolumeResidual Volume

The amount of air that can be inhaled The amount of air that can be inhaled maximally after a normal maximally after a normal

exhalationexhalation

About 3 litersAbout 3 liters


Inspiratory CapacityInspiratory Capacity

Amount of air that remains in the lungs Amount of air that remains in the lungs after a normal exhalationafter a normal exhalation



Functional Residual CapacityFunctional Residual Capacity

The maximum volume of air that can be The maximum volume of air that can be exhaled after the deepest possible exhaled after the deepest possible inspirationinspiration



Vital CapacityVital Capacity

Represents the total volume of air in the Represents the total volume of air in the lungs when maximally inflatedlungs when maximally inflated



Total Lung CapacityTotal Lung Capacity

Measurement of Lung Measurement of Lung Volumes and CapacitiesVolumes and Capacities

SpirometrySpirometry

Measures TV, IRV, ERV and VCMeasures TV, IRV, ERV and VC

Measurement of FRC, RV and TLCMeasurement of FRC, RV and TLC

Closed circuit method (helium dilution)Closed circuit method (helium dilution)

Open circuit method (nitrogen washout)Open circuit method (nitrogen washout)

Body plethysmographyBody plethysmography

HELIUM DILUTION

HELIUM DILUTION

NITROGEN WASHOUT

NITROGEN WASHOUT

Dead Air SpaceDead Air Space

Anatomic Dead Air SpaceAnatomic Dead Air Space

Volume of air in the non-gas Volume of air in the non-gas exchanging airways (conducting exchanging airways (conducting portion)portion)

About 150 mlAbout 150 ml

The portion of each inspiration that does The portion of each inspiration that does not equilibrate with gas in not equilibrate with gas in

pulmonary pulmonary capillary bloodcapillary blood


Physiologic Dead Air SpacePhysiologic Dead Air Space

The air in alveoli not perfused by The air in alveoli not perfused by pulmonary capillary bloodpulmonary capillary blood

The difference between physiologic and The difference between physiologic and anatomic dead air spaceanatomic dead air space


Alveolar Dead Air SpaceAlveolar Dead Air Space

Factors Affecting Anatomic Factors Affecting Anatomic Dead Air SpaceDead Air Space

AgeAgeAnatomic dead air space increases with age Anatomic dead air space increases with age due to loss of lung elasticitydue to loss of lung elasticity

Position of the headPosition of the headExtension of the neck increases dead air spaceExtension of the neck increases dead air space

DrugsDrugsBronchodilators increase dead air spaceBronchodilators increase dead air space

Snorkel breathingSnorkel breathingSnorkel increases dead air spaceSnorkel increases dead air space

Factors Affecting Alveolar Factors Affecting Alveolar Dead Air SpaceDead Air Space

Ventilation-Perfusion RelationshipsVentilation-Perfusion Relationships

An increase in ventilation without a An increase in ventilation without a corresponding increase in perfusion corresponding increase in perfusion

increases alveolar dead air spaceincreases alveolar dead air space

An increase in perfusion without a An increase in perfusion without a corresponding increase in ventilation corresponding increase in ventilation

decreases alveolar dead air spacedecreases alveolar dead air space

ComplianceCompliance

The volume of gas that can move into the The volume of gas that can move into the lungs for every unit of pressure changelungs for every unit of pressure change

It is a measure of elasticity of the It is a measure of elasticity of the bronchopulmonary systembronchopulmonary system

Determinants include:Determinants include:

Surface tensionSurface tension

Law of LaplaceLaw of Laplace

ElastanceElastance

The reciprocal of complianceThe reciprocal of compliance

The tendency for the bronchopulmonary The tendency for the bronchopulmonary system to oppose stretchsystem to oppose stretch

The ability of the bronchopulmonary The ability of the bronchopulmonary system to return to its original position system to return to its original position after removal of a distending forceafter removal of a distending force

It is a measure of recoilIt is a measure of recoil

Work of BreathingWork of Breathing

Mechanical WorkMechanical Work

Expressed in pressure change (cm Expressed in pressure change (cm water) x volume change water) x volume change (liter)(liter)

Metabolic WorkMetabolic Work

Refers to additional oxygen Refers to additional oxygen consumption x mechanical consumption x mechanical equivalent for oxygen consumptionequivalent for oxygen consumption

Dynamic Lung VolumesDynamic Lung Volumes

Maximal Voluntary VentilationMaximal Voluntary Ventilation

Maximum volume of a gas that can be Maximum volume of a gas that can be ventilated during a given periodventilated during a given period

Forced Expiratory Vital CapacityForced Expiratory Vital Capacity

Maximum volume of gas that can be forcibly Maximum volume of gas that can be forcibly and rapidly exhaledand rapidly exhaled

Forced Expiratory VolumeForced Expiratory Volume

Volume of gas exhaled at a specified timeVolume of gas exhaled at a specified time

T H A N K Y O U !

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Respiratory Physiology - A