Mechanical Factors in Breathing

Mechanical Factors in Breathing Patmos Air flows from region of high pressure to region of low pressure Flow = (P1 – P2)/R 1/r = k Flow = K(P1 – P2) Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv 25-Feb-19 Respiratory Movements

Mechanical Factors in Breathing Patmos Two ways of producing the necessary pressure differences Alveolar pressure can be lowered below atmospheric pressure Natural negative pressure breathing Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv 25-Feb-19 Respiratory Movements

Mechanical Factors in Breathing Patmos Atmospheric pressure can be increased above alveolar pressure Positive pressure breathing Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv 25-Feb-19 Respiratory Movements

Respiratory Movements Natural Breathing Accomplished by Active contraction of inspiratory muscles Thoracic volume increases Intrathoracic pressure decreases Pulls on the lungs Enlarges the alveoli Increase in thoracic volume decrease intrathoracic pressure 25-Feb-19 Respiratory Movements

Respiratory Movements Natural Breathing Expands alveolar gas Decreases its pressure below atmospheric pressure Air at atmospheric pressure Flows into lungs Increase in thoracic volume decrease intrathoracic pressure 25-Feb-19 Respiratory Movements

Respiratory Movements Respiratory Muscles Inspiratory muscles Diaphragm,external intercostals Others Scaleni, sternocleidomastoid, pectoralis minor Expiratory muscles Internal intercostals Abdominal recti 25-Feb-19 Respiratory Movements

Respiratory Movements Respiratory Muscles Have no inherent rhythm Do not contract if they do not receive motor impulses Motor impulses originate from Higher centers, respiratory centers, spinal cord 25-Feb-19 Respiratory Movements

Muscles of Inspiration Diaphragm Most important muscle of inspiration In quite breathing May be the only active inspiratory muscle Its motor nerve leaves the spinal cord C3,4,5 Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration When the diaphragm move down Abdominal contents are forced downward Increase the vertical dimension of the thorax Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration In quite breathing Diaphragm moves down by about 10mm (1 cm) In forceful inspiration It can move down by 10 cm Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration The area of the diaphragm About 250 cm2 During normal tidal breathing It increases the thoracic volume by 250 x 1 = 250 cm3 Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration During forceful inspiration It increases the thoracic volume by 250 x 10 = 2500 cm3 Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration External intercostals Lift sternum upwards and forwards AP diameter External intercostals Connect adjacent ribs Slope downwards & forwards When they contract Ribs are lifted upwards Causing an increase in AP diameter “Pump handle” Diaphragm Abdominal content 25-Feb-19 Respiratory Movements

Muscles of Inspiration When the external intercostals contract Ribs are lifted upwards In addition they are also moved outwards “Bucket handle” effect This increases the transverse diameter Bucket handle effect 25-Feb-19 Respiratory Movements

Respiratory Movements Overall Effects Of inspiratory muscles Increase the thoracic volume Increase lung volumes Decrease in intrapulmonary pressure Influx of air From region of high pressure To region of low pressure 25-Feb-19 Respiratory Movements

Respiratory Movements Expiration During quite breathing Passive After inspiratory muscles relax Elastic recoil of lungs and chest wall Cause movement of air from lungs to atmosphere 25-Feb-19 Respiratory Movements

Respiratory Movements Expiration During exercise Expiration is by active process Contraction of expiratory muscles Internal intercostals muscles Assist active expiration by Pulling ribs downwards and inwards 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax Trachea Lungs are separated from the rib cage by Parietal & visceral pleura Between these there is Pleural fluid Lubricant film 20 m thick Pleural space Bronchi Alveoli Diaphragm 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax Trachea The thoracic cage Has a tendency to expand The lungs Have a tendency to collapse Held together by the of pleural fluid Pleural space Bronchi Alveoli Diaphragm 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax Trachea Intrathoracic (intra pleural) pressure Normally = -5 mm Hg At the end of expiration during quiet breathing During inspiration it is = -8 to –10 mm Hg It is a measure of elastic recoil of the stretched lungs and the compressed thoracic cage Pleural space Bronchi Alveoli Diaphragm 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax P atmos Alveolar pressure Pressure of the air inside the lung alveoli When glottis is open & no air flowing into or out of the lung This pressure is equal to atmospheric pressure P alv Alveolus 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax P atmos To cause inward flow of air into alveli during inspiration Pressure falls to values below atmospheric (-1 cm of water) This is enough to cause 0.5 liters of air move into lungs P alv Alveolus 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax P atmos During expiration Alveolar pressure increases (+1 cm of water) Enough to cause movement of 0.5 liters of air out of the lung P alv Alveolus 25-Feb-19 Respiratory Movements

Pressure Changes in the Lungs and Thorax Inspiration Expiration Trans-pulmonary pressure Pressure difference between alveolar pressure and pleural pressure It is a measure of elastic forces in the lungs that tend to collapse the lungs Recoil pressure Alveolar pressure +2 Trans-pulmonary pressure -2 -4 -6 Pleural pressure -8 25-Feb-19 Respiratory Movements

Respiratory Movements Elastic Resistance Lung tissue is elastic Natural un-stretched volume is 1 liter Elastic element neither stretched nor compressed Human lung at the end of expiration Volume = 2.5 liters Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax 25-Feb-19 Respiratory Movements

Respiratory Movements Elastic Resistance Vol of lung Thus the elastic tissue is always under tension Tends to oppose expansion of the lungs 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax 25-Feb-19 Respiratory Movements

Respiratory Movements Elastic Resistance Vol of lung The natural un-stretched thoracic volume is 5 liters At end of expiration Volume of thorax is 2.5 liters The elastic tissues of thorax are compressed 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax 25-Feb-19 Respiratory Movements

Respiratory Movements Elastic Resistance Vol of lung Thus Lungs tend to contract Thorax tends to expand The lungs and thorax Held together by the integrity of the pleural cavity 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax 25-Feb-19 Respiratory Movements

Respiratory Movements Elastic Resistance Vol of lung If a gas is introduced in the pleural space Chest volume tends to expand Lung volume tend to decrease (collapse of the lungs) 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax 25-Feb-19 Respiratory Movements

Respiratory Movements Compliance Compliance Measure of the ability of the lung or chest cavity to be expanded The degree to which The lung volume can be changed By imposed intrapulmonary pressure Increased compliance V Volume in ml P decreased compliance Pressure cm H2O 25-Feb-19 Respiratory Movements

Respiratory Movements Compliance Compliance Change in volume (liters)/change in pressure (cm H2O) Compliance of Adult male = 0.09 to 0.26 L/ cm H2O Newborn = 0.005 l/cm H2O At 10 yrs = 0.06 L/ cm H2O Old age  compliance Increased compliance V Volume in ml P decreased compliance Pressure cm H2O 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Trachea Resistance offered to air as it flows through the respiratory airways Flow = (P1-P2)/R Vol of air that flow in/out of alveolar Directly proportional to pressure gradient Indirectly proportional to resistance Conducting zone 1 Bronchi 2 3 4 17 Respiratory bronchiole 18 19 Respiratory zone 20 Alveolar duct 21 22 23 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Trachea Conducting zone Airway resistance Frictional resistance Offered by the walls of tracheobronchial tree This is note evenly distributed 1 Bronchi 2 3 4 17 Respiratory bronchiole 18 19 Respiratory zone 20 Alveolar duct 21 22 23 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Trachea During quiet breathing with mouth closed Nose offers 50% of total resistance During mouth breathing Pharynx offers 25% of overall resistance This figure can increase up to 50% during exercise Conducting zone 1 Bronchi 2 3 4 17 Respiratory bronchiole 18 19 Respiratory zone 20 Alveolar duct 21 22 23 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Airway resistance VS airway generations Within the chest Trachea, lobar & segmental bronchi 0ffer 80% of the remaining resistance Small airways with diameter less than 2mm contribute 20% 0.08 0.06 Airway resist (cm H2O/L/S) 0.04 Segmental bronchi Terminal bronchi 0.02 5 10 15 20 Airway generations 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Airway resistance VS airway generations Cross section of individual peripheral airways are small Their large numbers Generate large overall cross section area Lowers the resistance 0.08 0.06 Airway resist (cm H2O/L/S) 0.04 Segmental bronchi Terminal bronchi 0.02 5 10 15 20 Airway generations 25-Feb-19 Respiratory Movements

Determinants of Airway Resistance Airway resistance VS lung volumes Lung volumes Greater tethering effect of lung parenchyma on airways Produce an increase in cross section area of each airway Results in reduced resistance 4 3 Airway resist (cm H2O/L/S) 2 1 2 4 6 8 Lung volumes (L) 25-Feb-19 Respiratory Movements

Determinants of Airway Resistance Others Resistance is proportional to Length of airway Physical properties of the gas Density, viscosity Resistance is inversely proportional to 4th power of radius of the airway 25-Feb-19 Respiratory Movements

Determinants of Airway Resistance Under normal condition Airways diameter “large” Interaction between gas molecules negligible Length of conducting tube relatively constant 25-Feb-19 Respiratory Movements

Determinants of Airway Resistance Resistance is largely controlled by radius Bronchial tree contain smooth muscle Under the influence of autonomic nerves Parasympathetic Sympathetic 25-Feb-19 Respiratory Movements

Determinants of Airway Resistance Parasympathetic activity causes Constriction of smooth muscles Reduction in cross section of airways Increased resistance Increased secretion of mucous glands Sympathetic activity Bronchodilatation Inhibition of mucous glad secretion Reduction in resistance 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Certain disease condition Increase airway resistance Asthma Contraction of bronchial smooth muscles Narrowing of airways Increased airway resistance 25-Feb-19 Respiratory Movements

Respiratory Movements Airway Resistance Chronic bronchitis Oedema of bronchial mucosa Excessive secretion by bronchial mucosa Increase airway resistance Intramural masses Bronchogenic carcinoma Occlude airways 25-Feb-19 Respiratory Movements

Respiratory Movements The Work of Breathing Breathing involves Application of force over distance Work is performed by respiratory muscles Stretching elastic tissues of chest wall & lungs Elastic work, compliance work Moving inelastic tissue (viscous resistance) Tissue resistance work 25-Feb-19 Respiratory Movements

Respiratory Movements Work of Breathing Work involved in moving air through the respiratory passages To overcome airway resistance Normally negligible But can be marked With increase in ventilation (turbulence) In asthma 25-Feb-19 Respiratory Movements