Respiration Xia Qiang, PhD Department of Physiology Zhejiang University School of Medicine Email: [email protected].

Respiration

Xia Qiang, PhDDepartment of PhysiologyZhejiang University School of MedicineEmail: [email protected]

The major parts of the “airways,” along which air movements (ventilation) occur during breathing.

The relaxation/contractionof circular smooth musclelining these “airways’” determines how easily airflow can occur(bronchodilation vs.bronchoconstriction).

Most gas exchange occurs in the~8,000,000 alveolar sacs.

Respiratory process

External respiration

Internal respiration

Pulmonary ventilationPulmonary ventilation

Definition: The

process of moving

air into and out of

the lungs

Thorax & respiratory muscleThorax & respiratory musclePrimary muscles of respiration: external intercostals & diaphragm

Breathing is an active processBreathing is an active processTo inhale– Contraction of external intercostal muscles elevation

of ribs & sternum increased front- to-back dimension of thoracic cavity lowers air pressure in lungs air moves into lungs

– Contraction of diaphragm diaphragm moves downward increases vertical dimension of thoracic cavity lowers air pressure in lungs air moves into lungs

Breathing is an active processBreathing is an active process

To exhale– Relaxation of external intercostal muscles &

diaphragm return of diaphragm, ribs, & sternum to resting positionrestores thoracic cavity to preinspiratory volume increases pressure in lungs air is exhaled

Pattern of respirationPattern of respiration

EupneaEupnea

Forced breathingForced breathing

Intrapulmonary pressureIntrapulmonary pressure

The Heimlich maneuverincreases the alveolar pressure (Palv) by supplementingthe upward movement of the diaphragm, thus compressing the thoracic cavity to dislodge foreign objects in the airways.

Pleural pressurePleural pressurePleural cavityPleural cavity– Pleural cavity is the closed space between Pleural cavity is the closed space between

parietal pleura & lungs covered with visceral parietal pleura & lungs covered with visceral pleurapleura

Pleural pressurePleural pressurePleural pressure is the pressure within Pleural pressure is the pressure within pleural cavity pleural cavity

Measurement of intrapleural Measurement of intrapleural pressurespressures

Direct method Direct method

Measurement of intrapleural Measurement of intrapleural pressurespressures

Indirect method Indirect method

Inspiration is the result ofthe expansion of the thoraciccage in response to skeletalmuscle contraction.

The expansion reduces alveolar pressure (Palv) belowatmospheric pressure (Patm),so air moves into the lungs.

Expiration is the result ofreducing the volume of thethoracic cage; in a restingperson, this occurs in response to skeletalmuscle relaxation.

The volume reduction increases alveolar pressure (Palv) aboveatmospheric pressure (Patm),so air moves out of the lungs.

Formation of intrapleural pressureFormation of intrapleural pressure

Fetus lungFetus lung

Formation of intrapleural pressureFormation of intrapleural pressure

Air in lungs after Air in lungs after deliverydelivery

Intrapleural pressureIntrapleural pressurePressures involvedPressures involved– Atmospheric (760 mmHg) pressureAtmospheric (760 mmHg) pressure

=Intrapulmonary pressure=Intrapulmonary pressure– Elastic recoil Elastic recoil – Intrapleural pressure Intrapleural pressure

Intrapleural pressureIntrapleural pressure

Physiological significance of Physiological significance of

intrapleural negative pressureintrapleural negative pressure

– Allow expansion of the lungsAllow expansion of the lungs

– Facilitate the venous & lymphatic returnFacilitate the venous & lymphatic return

PneumothoraxPneumothoraxAir escapes from Air escapes from the lungs or leaks the lungs or leaks through the chest through the chest wall and enters the wall and enters the pleural cavitypleural cavity

Lateral Bilateral

Compliance of the lungsCompliance of the lungs

Compliance: the extent to which the Compliance: the extent to which the

lungs expand for each unit increase lungs expand for each unit increase

in pressurein pressure

C=ΔV/ΔP (L/cmHC=ΔV/ΔP (L/cmH22O)O)

Compliance varies within the lung according to the degree of inflation. Poor compliance is seen at low volumes (because of difficulty with initial lung inflation) and at high volumes (because of the limit of chest wall expansion), with best compliance in the mid-expansion range

Lung compliance is ameasure of the lung’s “stretchability.”

When compliance is abnormally high, the lungs might fail to hold themselves open, and are prone to collapse.

When compliance is abnormally low, the work of breathing is increased.

Elasticity of lungsElasticity of lungs

DefinitionDefinition

– Tendency to return to initial structure after Tendency to return to initial structure after

being distended being distended

Elastic force (R)Elastic force (R)

C=1/RC=1/R

Elastic forces of the lungsElastic forces of the lungs

– 1/3 Elastic forces of the lung tissue itself1/3 Elastic forces of the lung tissue itself

– 2/3 Elastic forces caused by 2/3 Elastic forces caused by surface surface

tensiontension of the fluid that lines the inside of the fluid that lines the inside

walls of the alveoli walls of the alveoli

Surface tensionSurface tension

DefinitionDefinition– Tension of a liquid's Tension of a liquid's

surface. Due to the surface. Due to the

forces of attraction forces of attraction

between moleculesbetween molecules

Effect of detergent

Pierre Simon Laplace(1749 - 1827)

Laplace’s law: P=2T/r

Effect of size of sphere

Alveolar surfactantAlveolar surfactant

Surfactant is a complex mixtureSurfactant is a complex mixture– Several phospholipids Several phospholipids

(dipalmitoylphosphatidylcholine)(dipalmitoylphosphatidylcholine)

– Proteins (apoproteins)Proteins (apoproteins)

– Ions (calcium)Ions (calcium)

Secreted by type II alveolar epithelial Secreted by type II alveolar epithelial cellscells

Type II alveolar epithelial cellsType II alveolar epithelial cells

Alveolar surfactantAlveolar surfactant

Physiological effect of surfactantPhysiological effect of surfactant

Reduces surface tensionReduces surface tension

– Maintains the stability of the alveoli in different Maintains the stability of the alveoli in different

sizesize

– Keeps the dryness of the alveoliKeeps the dryness of the alveoli

– Eases expansion of lung (increases Eases expansion of lung (increases

compliance)compliance)

By reducing the surfacetension of water, surfactant helps prevent alveolar collapse.

In the absence of surfactant, the attraction between water molecules (H-bonds)can cause alveolar collapse.

Neonatal respiratory distress syndrome (NRDS):

lack of surfactant

cyanosis

retraction of soft tissue on inspiration (“seesaw”)

Non-elastic resistance Non-elastic resistance

Inertia resistanceInertia resistance

Viscosity resistanceViscosity resistance

Airway resistance: 80~90%Airway resistance: 80~90%

– R =ΔP/ VR =ΔP/ V

– RR1/r1/r44 (laminar flow) (laminar flow)

– RR1/r1/r55 (turbulent flow) (turbulent flow)

Regulation of the respiratory smooth Regulation of the respiratory smooth muscle muscle – Vagus nerve: Ach Vagus nerve: Ach M receptor M receptor

ContractionContraction

– Sympathetic nerve: NE Sympathetic nerve: NE 22-receptor -receptor Relaxation Relaxation

– Histamine, Bradykinin Histamine, Bradykinin Contraction Contraction– NE, E, Isoproterenol NE, E, Isoproterenol Relaxation Relaxation

AsthmaAsthma

Pathophysiology of asthma

Pulmonary volumes and capacitiesPulmonary volumes and capacities

SpirometerSpirometer

The tidal volume is the amount of air moved in (or out) of the airways in a single breathing cycle. Inspiratory and expiratoryreserve volumes, are, respectively, the additional volume thatcan inspired or expired; all three quantities sum to the lung’svital capacity. The residual volume is the amount of air that must remain in the lungs to prevent alveolar collapse.

Pulmonary volumesPulmonary volumes

Tidal volume (TV)Tidal volume (TV)– Volume of air inspired or expired with Volume of air inspired or expired with

each normal breatheach normal breath

Normal value: 400~500 mlNormal value: 400~500 ml

Inspiratory reserve volume (IRV)Inspiratory reserve volume (IRV)– Amount of air that can be inspired Amount of air that can be inspired

above and above and beyond TVbeyond TV

Normal value: 1500~2000 mlNormal value: 1500~2000 ml

Expiratory reserve volume (ERV)Expiratory reserve volume (ERV)– Amount of air that can be expired after Amount of air that can be expired after

a tidal expirationa tidal expiration

Normal value: 900~1200 ml Normal value: 900~1200 ml

Residual volume (RV)Residual volume (RV)– RV: the volume of air remaining in the RV: the volume of air remaining in the

lungs at the end of a maximal lungs at the end of a maximal exhalation exhalation

Normal value: M 1500 ml,Normal value: M 1500 ml, F 1000 mlF 1000 ml

Pulmonary capacitiesPulmonary capacities

Inspiratory capacityInspiratory capacity

=IRV+TV=IRV+TV

Functional residual capacityFunctional residual capacity

=ERV+RV=ERV+RV

Vital volumeVital volume

=TV+IRV+ERV=TV+IRV+ERV

Normal value: M 3500 ml, F 2500 mlNormal value: M 3500 ml, F 2500 ml

Pulmonary capacitiesPulmonary capacities

Total lung capacityTotal lung capacity

Pulmonary capacitiesPulmonary capacities

Forced expiratory volumeForced expiratory volume– The maximal volume of air that can be The maximal volume of air that can be

exhaled as fast as possible from the lungs exhaled as fast as possible from the lungs

following a maximal inspirationfollowing a maximal inspiration

– Normal value:Normal value:

1st sec. (FEV1) -- 831st sec. (FEV1) -- 83 ％％2nd sec. (FEV2) -- 962nd sec. (FEV2) -- 96 ％％3rd sec. (FEV3) -- 993rd sec. (FEV3) -- 99 ％ ％

Pulmonary ventilationPulmonary ventilation

Minute respiratory volume (MRV)Minute respiratory volume (MRV)

– The amount of air inspired (or expired) The amount of air inspired (or expired)

during one minuteduring one minute

– MRV = TV x breaths/min = 500 X12 = MRV = TV x breaths/min = 500 X12 =

6000 ml 6000 ml

Pulmonary ventilationPulmonary ventilation

Alveolar ventilation (VAlveolar ventilation (VAA))

– The amount of inspired air that is The amount of inspired air that is

available for gas exchange each minuteavailable for gas exchange each minute

– VVAA = (TV - dead space) x breaths/min = (TV - dead space) x breaths/min

= (500-150) X12 = 4200 ml = (500-150) X12 = 4200 ml

Dead spaceDead space– Anatomical dead spaceAnatomical dead space

Volume in respiratory passageways Volume in respiratory passageways which can not be exchangedwhich can not be exchanged

~150ml~150ml– Alveolar dead spaceAlveolar dead space

Alveoli which cease to function in gas Alveoli which cease to function in gas exchangeexchange

Normally ~0 Normally ~0

“Fresh” inspired air is diluted by the left over air remaining in the lungs from the previous breathing cycle.

End.End.