the respiratory system - rcst.or.thrcst.or.th/userfiles/the respiratory system .pdf · lung volumes...
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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
ระบบหายใจ
การหายใจเกิดขึ้นที่ 2 ระดับคือ
• External respiration• Internal respiration หรือ cellular respiration
External Respiration
External Respiration
Internal Respiration
• Pulmonary ventilation
• Diffusion
• Transportation
• Diffusion
ระบบหายใจ
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
Respiratory MembraneRespiratory Membrane
Respiratory MembraneRespiratory Membrane
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
Pulmonary Circulation
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
Pulmonary Circulation
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
Passive control of the circulation
Passive control of the circulation
Passive control of the circulation
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
ความสัมพันธระหวางการกระจายของเลือดและอากาศในปอด
ความสัมพันธระหวางการกระจายของเลือดและอากาศในปอด
ความสัมพันธระหวางการกระจายของเลือดและอากาศในปอด
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.
การขนสงออกซิ เจน
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.
การขนสงออกซิ เจน
• 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