THE RESPIRATORY SYSTEM - rcst.or.thrcst.or.th/userfiles/THE RESPIRATORY SYSTEM .pdf · Lung Volumes • Tidal volume (V T) – air that moves into and out of the lungs with each breath

THE RESPIRATORY SYSTEM

The Physiologic Basis of Surgery

นพ. สัณฐิติ โมรากุลภาควิชาวิสญัญวีิทยา คณะแพทยศาสตรโรงพยาบาลรามาธิบดี มหาวิทยาลัยมหิดล

ระบบหายใจ

มีหนาที่หลักใน การหายใจ (Respiration)

O2+

FOOD

ENERGY

+

CO2

THE PROCESS BY WHICH THE BODY TAKES IN AND USES O2 AND REMOVES CO2


การหายใจเกิดขึ้นที่ 2 ระดับคือ

• External respiration• Internal respiration หรือ cellular respiration

External Respiration

External Respiration

Internal Respiration

• Pulmonary ventilation

• Diffusion

• Transportation

• Diffusion


สรุป กระบวนการทํางานของระบบหายใจ• Pulmonary ventilation• Diffusion• Transportation• Cellular respiration

Scope

• Structure and Function• Ventilation• Perfusion• Ventilation perfusion relationship• Mechanics of breathing• Transportation• Diffusion• Control of breathing

หนาที่อื่น ขๆองระบบหายใจ

• BEHAVIORAL• talking, laughing, singing, reading

• DEFENSE• humidification, particle expulsion (coughing,

sneezing), particle trapping (clots), immunoglobulins from tonsils and adenoids, a-1 antitrypsin, lysozyme, interferon, complement system

• SECRETIONS• mucus (goblet cells, mucus glands)

• METABOLIC• forms angiotensin II, prostacyclin, bradykinin,

serotonin and histamine

• ACID - BASE BALANCE• changes in ventilation ;e.g., acute acidosis of exercise

• MISCELLANAEOUS• lose heat and water, liquid reservoir for blood,force

generation for lifting, vomiting, defaecation and childbirth

หนาที่อื่น ขๆองระบบหายใจ

Structure and Function

Lung and Thoracic Cavity

Airways

•• Conducting ZoneConducting Zone•• Trachea Trachea ----> Terminal > Terminal

bronchiolesbronchioles

•• Respiratory ZoneRespiratory Zone•• Respiratory Bronchiole Respiratory Bronchiole ----> >

Alveolar Ducts Alveolar Ducts ----> > AlveoliAlveoli

Conducting Zone

Conducting Zone

•• Air transportAir transport• Anatomical dead space (150 ml.)

• Humidification and temperature regulation (conditioning the air)

• Filtration and removal of particles

Respiratory Zone

Respiratory Zone

•• Gas exchangeGas exchange•• Volume 3000 ml.Volume 3000 ml.

Respiratory Zone•• Airway BranchingAirway Branching

Respiratory MembraneRespiratory Membrane

• This air-blood barrier is composed of: • Alveolar and capillary walls• Their fused basal laminas

• Alveolar walls:• Are a single layer of type I epithelial cells• Permit gas exchange by simple diffusion• Secrete angiotensin converting enzyme

(ACE)• Type II cells secrete surfactant



Blood Supply to LungsBlood Supply to Lungs

2 circulations• Pulmonary circulation• Bronchial circulation

Pulmonary Circulation

• Pulmonary arteries – supply systemic venous blood to be oxygenated• Branch profusely, along with bronchi• Ultimately feed into the pulmonary capillary

network surrounding the alveoli

• Pulmonary veins – carry oxygenated blood from respiratory zones to the heart

Bronchial Circulation

• Bronchial arteries – provide systemic blood to the lung tissue• Arise from aorta and enter the lungs at the

hilus• Supply all lung tissue except the alveoli

• Bronchial veins anastomose with pulmonary veins

• Anatomical shunt

CHEST WALL

InspirationInspiration

• Diaphragm and external intercostal muscles contract

• The size of the thoracic cavity increases• External air is pulled into the lungs due to

an increase in intrapulmonary volume• Causes pressure to be less than atmospheric,

creating a vacuum, leading to air being sucked into the lungs

• Air flows until intrapulmonary pressure equals atmospheric pressure

InspirationInspiration

ExhalationExhalation

• Largely a passive process which depends on natural lung elasticity

• As muscles relax, rib cage compresses and lungs recoil to original shapes and air is pushed out of the lungs

• Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage (narrowing, disease)

• Abdominal muscle

ExhalationExhalation

VENTILATION

How Gas Gets to the Alveoli

Lung Volumes and CapacitiesLung Volumes and Capacities

Lung VolumesLung Volumes

• Tidal volume (VT) – air that moves into and out of the lungs with each breath

• Inspiratory reserve volume (IRV) – air that can be inspired forcibly beyond the tidal volume (2100–3200 ml)

• Expiratory reserve volume (ERV) – air that can be evacuated from the lungs after a tidal expiration (1000–1200 ml)

• Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml)

Lung CapacitiesLung Capacities

• Inspiratory capacity (IC) – total amount of air that can be inspired after a tidal expiration (IRV + TV)

• Functional residual capacity (FRC) – amount of air remaining in the lungs after a tidal expiration (RV + ERV)

• Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV)

• Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in males)

FRC

FRC

ปริมาตรสูญเปลาปริมาตรสูญเปลา (Dead Space)(Dead Space)

• Anatomical Dead Space• Alveolar Dead Space• Physiological Dead Space

Anatomical Dead SpaceDead Space

• Volume of the conducting respiratory passages (150 ml)• VT = 500 ml • Anatomical dead space = 150 ml • VD/VT 150/500 = 0.3 (0.25-0.35)

Alveolar Dead SpaceAlveolar Dead Space• ปริมาตรอากาศในถุงลมที่ ไ มมกีารแลกเปลี่ยนแกส • ถุงลมที่ ไ มไ ดรับเลือดมาเลี้ยง• ถุงลมที่ ไ ดรับเลือดมาเลี้ยงนอยลง

Physiological Dead SpacePhysiological Dead Space

• Normal lung• Physiological VD = Anatomical VD

Physiological VD = Alveolar VD + Anatomical VD

Physiological Dead SpacePhysiological Dead Space

VD = PaCO2 - PECO2

VT PaCO2

Normal ratio of VD/VT = 0.2-0.35 during resting breathing

Ventilation

การเขาออกของอากาศในระบบทางเดินหายใจ• Pulmonary ventilation• Alveolar ventilation

Pulmonary Ventilation

ปริมาตรอากาศที่หายใจเขาออกปกติใน 1 นาที

VT = 500ml RR= 15/min VE = VT x RR

= 500 x 15= 7500 ml/min

Alveolar VentilationAlveolar Ventilation

ปริมาตรอากาศที่ผ านเขาไปใน respiratory zone ตอ 1 นาทีเปนสวนหนึ่งของ pulmonary ventilation ที่มีการแลกเปลี่ยนแกส

VA = frequency X VT – VD

(ml/min) (breaths/min) (ml/breath)

Alveolar VentilationAlveolar Ventilation

Alveolar Ventilation and PaCOAlveolar Ventilation and PaCO22

No gas exchange occurs in the anatomic dead space

PaCO2 α VECO2

VA


Pressures within pulmonary blood vessels

• The walls of the pulmonary artery and its branch are remarkably thin and contain little smooth muscle.

• The systemic circulation where the arteries have thick wall and its have abundant smooth muscle.

• Low-pressure, low resistance system• Highly distensible• Contain little smooth muscle• Some bronchial venous blood drain

directly into pulmonary veins• PaO2 < PAO2


Clinical Measurement of Pulmonary Blood Pressure and Flow

Clinical Measurement of Pulmonary Blood Pressure and Flow

Pulmonary vascular resistance

• Vascular resistance of systemic blood vessels = Δ P/flow

• Pulmonary blood flow (CO) is about 6 liters/min

• PVR = (15-5)/6 =1.7 mmHg /liter/min.

Pulmonary Vascular Resistance(PVR)

PVR = MPAP – PAWPCO

Factors Affecting PVR

• Passive • Active

Active control of the circulation

• Hypoxic pulmonary vasoconstriction• Active response occurs when the Po2 of

alveolar gas is reduced.• Endothelium-derived vasoactive substances

• NO = endothelium-derived relaxing factor for blood vessels

• Endothelin = potent vasoconstrictor peptide

Active control of the circulation

• A low blood pH cause vasoconstriction, especially when alveolar hypoxia is present

• An increase in sympathetic outflow causing stiffening of the walls of the pulmonary arteries and vasoconstriction.

Passive control of the circulation





• The important determinant of PVR is lung volumelung volume

• They have high resistance when lung volume is low.

• The caliber of capillaries is reduced at large lung volumes because of stretching of the alveolar walls.

Pulmonary vascular resistance

• Role of smooth muscle in determining the caliber of the extra-alveolar vessels.

• The drugs that cause vasoconstriction include serotonin,histamine and norepinephrine --> PVR

• The drugs that can relax smooth muscle in the pulmonary circulation include acethylcholine and isoproterenal --> PVR

Ventilation-perfusion Relationships

การกระจายของเลือดในปอด

การกระจายของอากาศในปอด

การกระจายของอากาศในปอด

ความสัมพันธระหวางการกระจายของเลือดและอากาศในปอด

Oxygen transport from air to tissues

• Level of PAO2 is determined by balance of• The rate of removal of O2 by the blood• The rate of replenishment of O2 by alveolar

ventilation




Alveolar-Arterial Oxygen pressure Difference (P(A-a)O2)

Alveolar gas equation

PAO2 = PIO2 – PACO2 + FR

= FiO2 (760-PH2O) – PaCO2

R

Abnormal Gas Exchange

• Hypoventilation• Absolute shunt• V/Q mismatch

Abnormal Gas Exchange

Cause P(A-a)O2 Response to O2

Example

Hypoventilation Normal Good Drug overdose

Shunt Increased Poor AtelectasisPneumonia

V/Q mismatch Increased Good Partial AW obstruction

Hypoventilation

• If alveolar ventilation is abnormally low• The alveolar Po2 fall, the Pco2 rises

• Cause of hypoventilation• Drugs which depress the central drive to the

respiratory muscles• Damage to the chest wall• Paralysis of respiratory muscles• High resistance to breathing

Hypoventilation

• The relationship between alveolar ventilation and Pco2

• PA CO2 =V CO2/ VA * K

Hypoventilation

• The relationship between the fall in Po2 and the rise in Pco2 can be calculated from

Alveolar gas equationPAo2 = PIo2 – PAco2 + F

RF = small collection factor ~ 2 mmHgR = respiratory exchange ratio ~ 0.8

Absolute Shunt

• Anatomical shunt• Normal เชน bronchial systemic vein• Abnormal เชน VSD

• Physiologic or intrapulmonary shunt

Clinical measurement of Shunt

• P(A-a)O2

• PaO2 / PAO2

• PaO2 /FiO2

Shunt Equation

Clinical Significance of Shunt

Shunt Fraction (%) Clinical Significance< 10% Clinical compatible with

normal lung10-19% Intrapulmonary abnormality20-29% Significant abnormality;

requires ventilatory support with PEEP

>30% Severe disease

การขนสงแกสในเลือด(Gas Transport between

The Lungs and Body Tissue)

การขนสงออกซิ เจน

1. ออกซิ เจนที่ ละลายในพลาสมา(dissolve oxygen)

= O2 solubility coefficient x So2

= 0.003 x PO2

= 0.003 x 100= 0.3 มล. O2 ตอเลือด 100 มล.


2. ออกซิ เจนที่ รวมกับฮีโ มโ กลบิน (oxyhemoglobin)= O2 capacity of Hb x Hb x SO2

= 1.34 x 15 x (98/100)= 19.7 มล./ เลือด 100 มล.


• Oxygen Content (CaO2)• ออกซิ เจนที่ รวมกับฮีโ มโ กลบิน• ออกซิ เจนที่ ละลายในพลาสมา• 19.7 + 0.3 = 20 มล. ตอ เลือด 100 มล.

Do2 = Q x CaO2

• Q = Cardiac output = 5000 ml/min• CaO2 = Oxygen Content = 20 ml/100ml of

blood• Do2 = Oxygen Delivery = 1000 ml/min

OXYGEN DELIVERY

OXYGEN CONSUMPTION

Vo2 = Q · ( CaO2 - CvO2)

= 250 ml/min

Q = Vo2 / ( CaO2 - CvO2) Fick principle

Oxygen Extract Ratio

• สัดสวนระหวางปริมาณของ O2 ที่ เซ ลรับไปใชใน 1 นาที ตอปริมาณของ O2 ในเลือดแดง

O2 Extract Ratio = (CaO2 - CvO2) / CaO2

• ในภาวะปกติ มคีาเท ากับ 20-15/20 = 0.25

Critical Illness

⇓ Do2

⇔ Vo2

Vo2 = ↓Q · ↑(CaO2 - ↓CvO2)

• Extraction Fraction

EF = (CaO2 - CvO2) / CaO2

Supply dependence of

Oxygen consumption

Extraction limitfor maintaining

aerobic metabolism

EFc

EFc = 0.67

Anaerobic metabolism↑ Lactic acid production

↑ L:P ratio↓ ATP

Pathologic Supply Dependence of Vo2

O2 Extraction Defect

↓ Do2 ↑ EFc < 0.67

SepsisImpair regulation of Q / Vo2 variance

• among various organ• within individual organ

Adequate aerobic metabolism

⇓ Vo2 ⇑Do2

⇑ Vo2 3 เทา ⇑ Do2 3 เทา EFc ปกติ

• ⇑ Vo2• Febrile pt. with burn, trauma ,sepsis• Acute respiratory failure with ↑ WOB

• ⇓ Vo2• Muscle relaxation• Artifitial respiration• Cooling

Lactic acidosis in high Do2

• Anaerobic Metabolism

• Hypovolemic, Cardiogenic shock ⇑ L:P ratio

• Septic shock ⇑ ⇑ Pyruvate

The Oxygen Dissociation Curve

In normal pH, PaO2, Temp

CaO2 = 1.34 x Hb x SO2 + 0.003 x PaO2

O2 sat PaO2

50% 27

75% 40

90% 55

100% >100

P50

PvO2

CaO2 = 1.34 x Hb x O2Sat + 0.003 x PaO2

At O2Sat = 100%Hb 1 gm O2 1.34 mlHb 15 g/dl O2 20ml /100 ml of blood

O2 solubility in plasma = 0.003ml/mmHg/100 ml of blood

PaO2 100 mmHg CaO20.3 ml/100 ml of bloodPaO2 650 mmHg CaO22.0 ml/100 ml of blood

↓ O2affinity↑O2affinity

Anemia

CO Poisoning

↓ Hb (7.5) ↓ CaO2 (10)

↔VO2(5)

↓ CvO2 (5)↓ PvO2 (27)

Tissue Hypoxia

↑QT

ANEMIA

COHb (50%) ↓ CaO2 (10)↑ Affinity

↔Vo2(5)

↓ CvO2 (5)↓↓ PvO2 (15)

↑FiO2 ↑Elimination CO

CO Poisoning

An approach to inadequateblood transport of O2

Vo2 = QT · C (a - v) O2↓ QT

↓ PaO2 & SaO2 ↓PvO2

↓ Hb

Rx ↑CaO2 (↑Hb or ↑ SaO2)↑ QT

Anaerobicmetabolism

↑ Dissolved O2

PaO2 650 mmHg ↑ CaO21.7 ml/100ml of bl.

CvO2 10 --------- 11SvO2 50 --------- 58PvO2 27 ----------34

Anaerobic

Aerobic

↓ Vo2

• ↓ WOBMuscle relaxantPPV

• Cooling

Hyperventilation

• Shift ODC to the left

• Same PaO2 ↑O2Sat ↑CaO2

• ↑ CaO2 > ↑CvO2

Mechanics of

The Respiratory System

ความตานทานตอการหายใจ

• Elastic resistance• 1/C หรือ P/V

• Airway resiatance• ΔP/F

• Tissue resistance

(Compliance)

Dynamic and Static Relationships between Respiratory Pressures and Volumes

Mechanics

• Force• Δ P

(Applied pressure)

• Motion• Δ V(volume change)• V (Flow rate)• V (volume

acceleration)

Equation of Motion

ΔP = Pel+ Pr + Pacc

ΔP = ΔV⋅Ers + V⋅Rrs + V⋅Irs

Pel= Elastic pressureErs= Elastance

Pacc= Accelerative pressureIrs = Inertia

Pr= Resistance pressureRrs= Resistance

↓↓↓ Irs ↓↓↓Pacc

ΔP = Pel + Pr

ΔP = ΔV⋅Ers + V⋅RrsFlow = 0 ; Pr = 0

ΔP = Pel (static)ΔP = ΔV⋅Ers Ers= ΔP/ ΔV

Plateau pressure

Time

Pres

sure

• On ventilatorPpeak = Ppl+Pr

• Inflation hold• Flow (V)=0• ΔP = Pel

• Ers = ΔP/ ΔV=10/0.5= 20

• Pr = ΔP – Pel

= 20-10= 10

• Rrs = Pr/flow= 10

• Pulmonary edema• ARDS• Pneumonia

↑ Ers

↔ VT

↑Pr,↑Pel

↔Rrs

Static P-V curve

MeasurementOf

Intrinsic PEEP

Scope

Structure and FunctionVentilationPerfusionVentilation perfusion relationshipMechanics of breathingTransportation

• Diffusion• Control of breathing

THE RESPIRATORY SYSTEM - rcst.or.thrcst.or.th/userfiles/THE RESPIRATORY SYSTEM .pdf · Lung Volumes • Tidal volume (V T) – air that moves into and out of the lungs with each breath

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