PULMONARY MECHANICS GAS TRANSPORT

Transcription

1 PULMONARY MECHANICS GAS TRANSPORT

2 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O 2 CO 2

3 FORCES PARTICIPATING IN RESPIRATION ACTIVE FORCES performed by respiratory muscles PASSIVE FORCES represented by: lungs elasticity chest elasticity QUIET RESPIRATION INSPIRATION - active forces of inspiratory muscles prevail EXPIRATION - passive (elastic) forces only 1

4 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O 2 CO 2

5 RESPIRATORY MUSCLES accessory muscles external intercostals INSPIRATORY diaphragm internal intercostals EXPIRATORY abdominal muscles 2a

6 INSPIRATORY muscles QUIET breathing diaphragm ( 80 % ) external intercostals ( 20 % ) FORCED breathing accessory inspiratory muscles (scalene muscles, ) EXPIRATORY muscles Only at FORCED breathing internal intercostals muscles of the anterior abdominal wall (abdominal recti, ) 2b

7 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O 2 CO 2

8 200 SALINE AIR DEFLATION VOLU UME (m ml) HYSTERESIS LOOP opening pressure INFLATION LUNGS ELASTICITY 1 kpa = 7.5 mm Hg INTRAPULMONARY PRESSURE (kpa) LUNGS ELASTICITY INHERENT TISSUE ELASTICITY (elastin and collagen fibres) SURFACE TENSION FORCES (physical properties of air-liquid interface) 3

9 LAW OF LAPLACE spherical structures r P = 2T r P? T P 1 P 2 P 1 > P 2 P distending pressure (transmural P) r radius T surface tension PATHOLOGY COLLAPSE OF ALVEOLI EXPANSION OF ALVEOLI ATELECTASIS BULLOUS EMPHYSEMA 4

10 SURFACTANT PHOSPHOLIPID dipalmitoyl fosfatidyl cholin surfactant cycle SURFACE TENSION LOWERING AGENT EFFECT MAINLY IN THE EXPIRED POSITION ALVEOLAR EPITHELIAL CELLS exocytosis of lamellar bodies surfactant TYPE II specialized granular epithelial cells PRODUCTION OF SURFACTANT macrofage TYPE I thin epithelial cells DIFFUSION OF GASSES fatty acids, choline, glycerol, amino acids, etc.) INFANT RESPIRATORY DISTRESS SYNDROME PATCHY ATELECTASIS AFTER CARDIAC SURGERY 5a

11 SALINE AIR DEFLATION VOL LUME (ml) HYSTERESIS LOOP opening pressure INFLATION ALVEOLAR PRESSURE (kpa) LAPLACE LAW (opening pressure of alveoli) Dynamic changes in the DENSITY OF SURFACTANT MOLECULES during inspiration and expiration Factors involved in HYSTERESIS LOOP 5b

12 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O 2 CO 2

13 COMPLIANCE (VOLUME STRETCHABILITY) STATIC MEASUREMENT IN CLOSED SYSTEM chan nge of th he volum me V ( l ) end of quiet expiration Müller s maneuver -50 relaxation pressure curve Valsalva s maneuver VC C V = V P FRC relaxation volume P P alveolar pressure P A (mm Hg) TOTAL RESPIRATORY SYSTEM (lungs and chest) RV V compliance is decreased stiffness of the tissue compliance is increased stiffness of the tissue 18

14 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O 2 CO 2

15 7 ELASTIC (STATIC) WORK W ELAST (J) CLOSED SYSTEM lu ung volu ume V V (l) elastic forces of the chest and lungs act in the same direction elastic force of the chest is zero TV 500 ml expiratory reserve volume relaxation pressure curve relaxation CHEST pressure curve P LUNGS PL P TP (P A -P PL ) PA relaxation pressure curve TOTAL SYSTEM elastic forces of the chest and lungs are in equilibrium? TOTAL SYSTEM intrapulmonary pressure P A LUNGS transpulmonary pressure P TP = P A - P PL CHEST intrapleural pressure P PL pressure P (mm Hg) +15

16 TOTAL ELASTIC (STATIC) WORK OF INSPIRATORY MUSCLES AT QUIET INSPIRATION (V ~ 500 ml) W TOTAL ELASTIC insp = W LUNG + (-W CHEST ) STRETCHING against elastic forces of the lungs ELASTIC RECOIL of the chest ELASTIC FORCES OF THE CHEST HELP inspiratory muscles to increase thoracic cavity 8a

17 ACTIVE AND PASSIVE (ELASTIC) FORCES IN RESPIRATORY SYSTEM F elast-chest F elast-lungs F muscle 0 0 P PL INSPIRATION V T P A P ATM air ways V T tidal volume at quiet inspiration (~500 ml) CHEST LUNGS STATES OF BALANCE RESPIRATORY SYSTEM (LUNGS and CHEST) RESPIRATORY SYSTEM: elastic forces of lungs and chest are balanced CHEST: elastic force of the chest alone is zero at V~ 1 l LUNGS: elastic force of the lungs is zero only when P PL = P ATM ( pneumothorax ) 8b

18 TOTAL WORK OF BREATHING (total work of respiratory muscles) ELASTIC (STATIC) WORK (65%) to overcome the elastic forces of the lungs and chest DYNAMIC WORK (35%) to overcome the resistance of air passages during the air movement AERODYNAMIC RESISTANCE (~ 28%) to overcome the friction during the mutual movement of inelastic tissues VISCOUS RESISTANCE (~ 7%) 9a

19 RESISTANCE OF AIR PASSAGES HAGEN-POISEUILLE S LAW (laminar flow Q) Q = P R Ohm s law R = 8ηl 4 πr l length r radius η viscosity LAMINAR FLOW Re < 2000 < TURBULENT FLOW REYNOLDS NUMBER Re 2 rρ v Re = η Critical velocity r radius v velocity ρ density η viscosity 9b

20 TOTAL WORK OF RESPIRATORY MUSCLES [J] DURING RESPIRATORY CYCLE AT QUIET BREATHING change in volum me (ml) ±W ELAST W DYN DYNAMIC PRESSURE-VOLUME DIAGRAM W INSPIR = W ELAST + W DYN insp W EXPIR = =-W ELAST +W+ W DYN DYN expir expir W DYN = W DYN insp + W DYN expir change in pressure P (mm Hg) DYNAMIC WORK W DYN is done to overcome aerodynamic resistance frictional (viscose) resistance W DYN is finally transformed into heat energy (loss of energy) 10

21 INCREASED RESISTANCE OF AIR PASSAGES CLINICAL IMPLICATION chan nge of vo olume (l) elastic work E I change in pressure (kpa) NORMAL LUNGS 1 kpa = 7.5 mm Hg OBSTRUCTIVE LUNG DISEASE (asthma bronchial) chan nge of vo olume (l l) 0 1 E additional work of expiratory muscles changes in pressure (kpa) Expiratory muscles are active to overcome the resistance of air passages I 11

22 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O O 2 CO 2

23 HAEMOGLOBIN γ β tetramer β γ Hb O 2 Hb 4 O 8 oxygenation DEOXY Fe 2+ HAEM OXY α α 1 nm N N N Fe N N porfyrin N N N N Fe N N O 2 fetal Hb Fe 3 + (methaemoglobin) oxidation polypeptide chain polypeptide chain 12

24 O 2 HAEMOGLOBIN DISSOCIATION CURVE CO O 2 satura ation of haem moglobi in (%) 100 a v 50 0 CO Hb P 50 steep portion plateau area ph, CO 2 BPG (2,3-bisphosphoglycerate) physiological range P CO O2 (mm Hg) temperature BOHR EFFECT ( ph, CO 2 ) deoxyhb - + H + H-Hb fetal Hb myoglobin methaemoglobin physically dissolved O 2 (1.4%) 13

25 I. PULMONARY MECHANICS RESPIRATORY MUSCLES LUNGS ELASTICITY COMPLIANCE WORK OF BREATHING II. TRANSPORT OF GASES O O 2 CO 2

26 TRANSPORT OF CO 2 CO 2 HAMBURGER CHLORIDE SHIFT HCO 3 - Cl - CA CO 2 + H 2 O H 2 CO 3 H + + HCO - 3 Cl - H-deoxyHb H + + deoxyhb - H 2 O CA carbonic anhydrase 14

27 CO 2 CO CO 2 CO 2 CO 2 CO 2 + H 2 O HCO 3 - Cl - HCO 3- + H + Na + K + KHCO 3 NaHCO 3 Hb.CO 2 O 2 O2 HbO 2 CO 2 physically dissolved (~5.3%) H 2 O 2 CO 2 + Hb-NH 2 Hb.NH-COO - (carbamino-hb) (~5.3%) 2 2 CO 2 + H 2 O HCO 3- + H + ~60% in plasma, ~29% in red blood cell 15

28 CO 2 DISSOCIATION CURVE tot tal CO 2 conten (mm mol/l) deoxygenated blood a 15 oxygenated blood 10 5 physically dissolved CO P CO2 (mm Hg) HALDANE EFFECT v? physiological values in arterial and venous blood 1 2 DEOXY-Hb Hb.NH.COO - Hb - + H + HHb deoxygenated blood in peripheral tissues oxygenated blood in the lungs CO 2 + H 2 O H 2 CO 3 H + + HCO 3 - TISSUES: DEOXY-Hb binds H + more readily (weaker acid) amount of chemically bound CO 2 LUNGS: H + is released from OXY-Hb amount of chemically bound CO 2 Hb - + H + HHb 16

29 PROCESSES UNDERLYING TRANSPORT O 2 AND CO 2 IN RED BLOOD CELLS OCCUR SIMULTANEOUSLY FACILITATE EACH OTHER TISSUES uptake of CO 2 by blood release of O 2 from Hb LUNGS binding of O 2 to Hb release of CO 2 from blood BOHR s AND HALDANE s EFFECTS 17

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