Static Mechanics of Breathing

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1 Static Mechanics of reathing สรช ย ศร ส มะ พบ., Ph.D. ภาคว ชาสร รว ทยา คณะแพทยศาสตร ศ ร ราชพยาบาล มหาว ทยาล ยมห ดล ผ ป วยถ กม ดแทงท ทรวงอกข างขวา ม เล อดจากแผลพอสมควร แพทย ตรวจพบม ช พจรส งปานกลาง หายใจหอบ ไม ม ไข ฟ ง เส ยงหายใจด วยห ฟ ง (stethoscope) พบเส ยงหายใจลดลง ในทรวงอกข างขวาเม อเท ยบก บข างซ าย

3 Learning Objectives Define the, volume, force and their changes in magnitude and direction of all components of breathing (airway, airspace, pleura) during inspiration and expiration Describe the muscles of respiration, their roles and functions as well as nerve supplies Determine the distensibility of all components of breathing using -volume relationships and effects of its alteration Understand the concept of surface tension and interdependence Outline (สร รว ทยา 2, p ) Lung volumes Driving Static in airway, airspace, pleural space Transmural, distending Elastic recoil Muscles of respiration Respiratory cycle ompliance: Lung, hest wall, Total respiratory system Surface tension, Laplace law lveolar interdependence

4 Spirometry and Lung Volumes Generation of a Pressure Gradient between ompartments: Flow of Fluids ir, like other fluids, moves from a region of higher to one of lower For example in the lungs and atmosphere, air moves into or out of the lungs, a gradient must be established between origin and destination If there is no gradient, no flow will occur

5 Pressure Gradient between tmosphere and lveoli: Inspiration 760 mmhg tmosphere gradient Mouth/Nose Upper irway Lower irway lveoli Pressure Gradient between tmosphere and lveoli: Inspiration Inspiration is accomplished by causing alveolar to fall below atmospheric tmospheric (760 mmhg) is conventionally referred to as ZERO cmh 2 O Lowering alveolar below atmospheric is known as negative- breathing Increase in the volume of alveoli lowers the alveolar according to oyle s law

6 Pressure Gradient between tmosphere and lveoli: Inspiration 0 cmh 2 O tmosphere gradient Mouth/Nose Upper irway Lower irway lveoli Pressure Gradient between tmosphere and lveoli: Expiration 0 cmh 2 O tmosphere gradient Mouth/Nose Upper irway Lower irway lveoli

7 Generation of a Pressure Gradient between ompartments: Expansion pleural space resting chest wall alveoli airway inspiration chest wall pleural space alveoli airway Generation of a Pressure Gradient between ompartments: Expansion inspiration chest wall pleural space alveoli airway There are forces acting on chest wall, alveoli and airway by pulling out or expanding them of resting position during inspiration This force generates NEGTIVE in pleural cavity allowing the expansion of alveoli

8 Intrapleural Pressure During inspiration, intrapleural must be smaller than intra-alveolar, allowing the expansion of alveoli arometric bsolute s: mmhg 760 Relative s: cm H 2 O 0 arometric intra-alveolar intrapleural Intrapleural Pressure arometric bsolute s: mmhg intra-alveolar Relative s: cm H 2 O 0-5 arometric intrapleural Intrapleural is less than barometric (P), that is, the intrapleural space is a relative vacuum Intrapleural space is the virtual space between the visceral and parietal pleural membranes, a space that usually contains only a thin layer of fluid, allowing the pleural layers to slide past one another as the lungs change volume

9 Intrapleural Pressure Intrapleural reflects the in several other regions of the chest cavity the virtual space between the chest wall/ diaphragm and the parietal pleura the virtual space between the lung and the visceral pleura the interstitial space surround the airways in the lungs around the heart and great vessels around and inside the esophagus (not engaged in peristalsis) Transmural Pressure Transmural = Pressure inside Pressure outside or surrounding tissue bsolute s: mmhg Relative s: cm H 2 O arometric arometric intra-alveolar intrapleural Transpulmonary = intra-alveolar intrapleural = (-2.5) (-5) = 2.5 cm H 2 O distension of alveoli, no collapse

10 Elastic Property of Tissue and Elastic Recoil Force End of inspiration chest wall pleural cavity alveoli airway Expiration pleural cavity alveoli airway Elastic Property of Tissue and Elastic Recoil Force The recoil of the tissue due to tissue stretching Elastic fibers have elastic relationships of length and tensile force and can be extended to ~2.3 times resting length rubber band of tissue ollagen fibers are stiff, contributing the steel wire framework

11 Elastic Property of Tissue and Elastic Recoil Force Elastic recoil of lungs chest wall lungs intrapleural space The lungs have a tendency to collapse, which is known as elastic recoil Forces acting in the opposite the direction must balance this elastic recoil to prevent lung collapse Elastic Property of Tissue and Elastic Recoil Force Elastic recoil of chest wall The chest wall has an elastic recoil that is opposite to that of the lungs, tending to pull the thoracic cage outward The chest cavity can maintain its normal volume only if an equal but opposite force pulls the chest wall inward

12 Elastic Property of Tissue and Elastic Recoil Force Muscles of Inspiration Muscles Nerve Primary Muscles of Inspiration Location of ell ody of Motor Neuron Diaphragm External intercostal muscles Phrenic nerve Intercostal nerves Phrenic motor nuclei in ventral horn of spinal cord, cervical 3-5 Ventral horn of thoracic spinal cord Secondary Muscles of Inspiration Larynx and Pharynx Tongue Vagus (ranial Nerve X) and Glossopharyngeal (N IX) nerves Hypoglossal nerve (N XII) Nucleus ambiguus Hypoglossal motor nucleus Sternocleidomastoid and Trapezius muscles ccessory nerve (N XI) Spinal accessory nucleus, 1-5 Nares Facial nerve (N VII) Facial motor nucleus

Muscles of Inspiration Inspiration is an TIVE process, needs neuro-muscular interaction The muscles of inspiration expand the chest increase elastic recoil of chest wall causing intrapleural more

13 Muscles of Inspiration Inspiration is an TIVE process, needs neuro-muscular interaction The muscles of inspiration expand the chest increase elastic recoil of chest wall causing intrapleural more negative enhancing intrapleural vacuum lungs passively expand The primary muscles of inspiration produce a quiet inspiration During a forced inspiration, the accessory or secondary muscles of inspiration come into play Muscles of Inspiration Diaphragm contraction vertical (rostrocaudal) diameter of thoracic cage

14 Muscles of Inspiration External Intercostal Muscles Water-pump handle effect anteroposterior diameter of thoracic cage ucket-handle effect transverse diameter

Expiration Relaxing the muscles of inspiration produces a quiet expiration quiet expiration is normally, PSSIVE process During a forced expiration or a patient with diseases of increasing airway

15 Expiration Relaxing the muscles of inspiration produces a quiet expiration quiet expiration is normally, PSSIVE process During a forced expiration or a patient with diseases of increasing airway resistance, the accessory or secondary muscles of expiration come into play Muscles Secondary Muscles of Expiration Internal intercostal muscles Nerve Intercostal nerves Location of ell ody of Motor Neuron Ventral horn of thoracic spinal cord bdominal muscles Spinal nerves Ventral horn of lumbar spinal cord Muscles of Expiration The accessory muscles of expiration make intrapleural more positive

16 Pressure Gradients in Respiratory System P =0 P TM = Pel = 5 Palv = 0 alveolus P = barometric = atmospheric P TM = transmural = transpulmonary Pel = elastic recoil Ppl= -5 pleural space Ppl = intrapleural = intrathoracic P TM = Palv Ppl = 0 (-5) = +5 cm H 2 O P alv = intra-alveolar Respiratory ycle P TM = 5 P =0 alveolus pleural space Palv = 0 Ppl= -5 P TM = 0 (-5) = +5 cm H 2 O +0.5 hange in lung volume ΔV L (liters) Intrapleural (cm H 2 O) TV FR Intraalveolar (cm H 2 O) Transpulmonary 6 (cm H 2 O) Time (seconds)

17 Respiratory ycle P TM = 5 P =0 alveolus pleural space Palv = 0 Ppl= -5 P TM = 0 (-5) = +5 cm H 2 O P =0 P TM = 6.25 Ppl= Palv = hange in lung volume ΔV L (liters) Intrapleural (cm H 2 O) TV FR P TM = -0.5 (-6.75) = Intraalveolar (cm H 2 O) Transpulmonary 6 (cm H 2 O) Time (seconds) Respiratory ycle P TM = 5 P =0 alveolus pleural space +0.5 hange in lung volume ΔV L (liters) TV Palv = 0 Ppl= -5 P TM = 0 (-5) = +5 cm H 2 O P =0 P TM = 6.25 Ppl= Palv = -0.5 Intrapleural (cm H 2 O) FR P TM = -0.5 (-6.75) = P =0 P TM = 7.5 Ppl= -7.5 Palv = 0 Intraalveolar (cm H 2 O) P TM = 0 (-7.5) = Transpulmonary 6 (cm H 2 O) Time (seconds)

18 Respiratory ycle P TM = 5 P =0 alveolus pleural space +0.5 hange in lung volume ΔV L (liters) D TV Palv = 0 Ppl= -5 P TM = 0 (-5) = +5 cm H 2 O P =0 P TM = 6.25 Ppl= Palv = -0.5 Intrapleural (cm H 2 O) D FR P TM = -0.5 (-6.75) = P =0 P TM = 7.5 Ppl= -7.5 Palv = 0 Intraalveolar (cm H 2 O) D D P TM = 0 (-7.5) = +7.5 P =0 P TM = 6.25 Ppl= Transpulmonary 6 (cm H 2 O) D Palv = +0.5 P TM = 0.5 (-5.75) = Time (seconds) Respiratory ycle P TM = 5 P =0 alveolus pleural space +0.5 hange in lung volume ΔV L (liters) D TV Palv = 0 Ppl= -5 P TM = 0 (-5) = +5 cm H 2 O P =0 P TM = 6.25 Ppl= Palv = -0.5 Intrapleural (cm H 2 O) D FR P TM = -0.5 (-6.75) = P =0 P TM = 7.5 Ppl= -7.5 Palv = 0 Intraalveolar (cm H 2 O) D D P TM = 0 (-7.5) = +7.5 P =0 P TM = 6.25 Ppl= Transpulmonary 6 (cm H 2 O) D Palv = +0.5 P TM = 0.5 (-5.75) = Time (seconds)

19 ompliance P TM = 5 P =0 alveolus pleural space +0.5 hange in lung volume ΔV L (liters) D Palv = 0 Ppl= -5 0 P TM = 0 (-5) = +5 cm H 2 O P =0 P TM = 6.25 Ppl= Palv = -0.5 P TM = -0.5 (-6.75) = P =0 P TM = 7.5 Ppl= hange in lung volume ΔV L (liters) Transpulmonary (cm H 2 O) = ΔV L ΔP TM Palv = 0 D P TM = 0 (-7.5) = +7.5 P =0 P TM = 6.25 Ppl= Transpulmonary 6 (cm H 2 O) D Palv = +0.5 P TM = 0.5 (-5.75) = Time (seconds) ompliance ompliance defines change in the volume of a closed system to the change in the distending it OR the slope of the volume curve +0.5 hange in lung volume ΔV L (liters) = ΔV L ΔP TM Transpulmonary (cm H 2 O) = 0.5 liter (7.5 5) cm H 2 O = 0.2 liter/cm H 2 O

20 ompliance Lung ompliance 5 Vital capacity (L) TL Transmural (cm H 2 O) t high expanding s, the lung is stiffer, and its compliance is smaller, shown by the flatter slope of the curve

21 Reduced ompliance 5 Vital capacity (L) Normal TL TL Reduced ompliance Transmural Lung collapse (atelectasis) (cm H 2 O) Pulmonary edema Increase in fibrous tissue in the lung (pulmonary fibrosis) Obesity Diseases of chest wall Increased ompliance Vital capacity (L) Increased ompliance 5 TL 4 Normal TL TL Reduced ompliance Transmural (cm H 2 O) Is related to an alteration in elastic tissue in the lung Pulmonary emphysema = abnormal airspace enlargement lung tissue is destroyed, including fibrous and elastic tissue reduced elastic recoil of the lungs Normal aging lung

22 Specific ompliance The compliance of lung depends on size The compliance per unit volume of lung, or specific compliance is measured for intrinsic elastic properties of the lung tissue Specific compliance = compliance FR Elastance Elastance is the inverse term of compliance Elastance = 1 ompliance Elastance = ΔP ΔV The higher the elastance, the higher the stiffness of structure, the lower the compliance

23 ompliance of Total Respiratory System ompliance of the total respiratory system is less than the compliance of individual structure 1 rs = 1 L + 1 W Ers = EL + Ecw The compliance of lungs (L) is 0.2 L/cmH 2 O, the compliance of chest wall (cw) is 0.2 L/cmH 2 O = + rs rs = 0.1 L/cmH 2 O Pressure-Volume haracteristics of the Respiratory System

24 Pressure-Volume haracteristics of the Respiratory System Pressure-Volume haracteristics of the Respiratory System

25 Pressure-Volume haracteristics of the Respiratory System ompliance of Respiratory System From Pressure-Volume Relationships, at any given volume, the value of transmural to Respiratory system is the sum of PTM acting on chest wall and lung PTMrs = PTML + PTMcw = ΔV L ΔP TM ΔVrs rs = ΔVL L + ΔVW W t any given volume, so all ΔV are similar (Look at the graph) 1 = rs 1 L + 1 W

26 Elastic Recoil of the Lungs The lungs have inward elasticity. This works towards decreasing the lung volume. The larger the lung volume, the larger the elastic force. Elastic recoil or elastic resistance of the lungs is composed of 1. Stretching of collagen/elastic fibers 2. lveolar surface tension Surface Tension

27 Surface Tension It is an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet It is caused by the attraction between the molecules of the liquid by various intermolecular forces In the bulk of the liquid each molecule is pulled equally in all directions by neighboring liquid molecules, resulting in a net force of zero t the surface of the liquid, the molecules are pulled inwards by other molecules deeper inside the liquid, but there are no liquid molecules on the outside to balance these forces Surface Tension Thus the liquid squeezes itself together until it has the locally lowest surface area possible It is measured as the force along a line of unit length perpendicular to the surface, or work done per unit area (dyne/cm, newton/m)

28 Pressure-Volume Relationships in Excised Lungs saline Von Neergaard, 1929 air volume (ml) Transmural (cm H 2 O) When the lungs are inflated and deflated with air, two different curves are obtained During inflation, a higher transmural is required to achieve any given lung volume compared with deflation This separation of the inflation and deflation limbs of the -volume curves is termed hysteresis When the lungs are inflated with saline, a different P-V curve is generated that does not demonstrate hysteresis Pressure-Volume Relationships in Excised Lungs saline air volume (ml) Transmural (cm H 2 O) The reason for hysteresis and differences in compliance that occur with air versus saline inflation relates to surface tension forces that exist in the alveoli The alveolar surface is lined with a liquid, which forms an airliquid interface with alveolar gas Surface tension at the air-liquid interface tends to increase the lung elastic recoil generated at any lung volume Only the elastic structural elements contribute to the lung recoil in the lung inflated with saline

29 Young-Laplace Law Surface tension (T) =2 Surface tension (T) =2 r=2 P = 2T r r=1 r =radius or size Pressure (P) =2 Pressure (P) =4 The difference is dependent on the size of object and surface tension The smaller the object, the higher the What would happen to multiple bubbles with an airliquid interface of different sizes that are connected? The small bubbles would empty into the larger bubbles

30 Reducing Surface Tension to Maintain the Size of Objects Surface tension (T) =2 Surface tension (T) =1 r=2 P = 2T r r=1 r =radius or size Pressure (P) =2 Pressure (P) =2 Why do soap bubbles last longer? The soap in water solution reduces surface tension in the bubble and reduces the difference inside and outside the bubble

Surfactant r alveoli P = 2T r P surfactant T liquid lining Surfactant is produced by alveolar epithelium type 2 It has the lowest surface tension of any biological substance ever measured Surfactant

31 Surfactant r alveoli P = 2T r P surfactant T liquid lining Surfactant is produced by alveolar epithelium type 2 It has the lowest surface tension of any biological substance ever measured Surfactant It is a phospholipid, dipalmitoylphosphatidyl choline is the main constituent Its molecule has a hydrophobic and hydrophilic end It lowers surface tension in alveoli increases lung compliance during inspiration reduces work of breathing (PxΔV) stability of the alveoli during expiration prevent lung collapse or atelectasis It prevents an increase in the interstitial hydrostatic outside capillary by surface tension prevent fluid transudation keep alveoli dry

onsequences of Loss of Surfactant normal alveoli Infant respiratory distress syndrome The lungs of premature baby are too immature to produce enough pulmonary surfactant Surfactant is first

32 onsequences of Loss of Surfactant normal alveoli Infant respiratory distress syndrome The lungs of premature baby are too immature to produce enough pulmonary surfactant Surfactant is first detectable in the fetal lung at weeks of gestation Surfactant levels increase rapidly after week 30 and are low in babies with the infant respiratory distress syndrome Interdependence intrapleural

33 Interdependence

4/18/12 MECHANISM OF RESPIRATION. Every Breath You Take. Fun Facts

4/18/12 MECHANISM OF RESPIRATION. Every Breath You Take. Fun Facts Objectives MECHANISM OF RESPIRATION Dr Badri Paudel Explain how the intrapulmonary and intrapleural pressures vary during ventilation and relate these pressure changes to Boyle s law. Define the terms