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Biophysics of Breathing

This text provides an overview of the biophysics of breathing, including the anatomy, mechanics, and physiology involved. It explores the role of respiratory muscles, the process of ventilation, gas exchange, and the relationship between respiratory and cardiovascular systems.

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Biophysics of Breathing

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  1. Biophysics of BreathingJan Jakuš

  2. Breathingis a vital function of the body, a periodic and rhythmic processof inspirationand expiration thatcovers the metabolic demands of bodyfor O2 and CO2.- must assure in adults the intake ofO2 250 ml/min,and the expenditure of CO2200 ml /min.- is governed involuntarily by “arespiratorycentre’’, localized within the brainstem-- can be interrupted orincreased voluntarily(from the cortex) (for more info look at a book: Jakus, Tomori Stran-sky: Neuronal Determinants of Breathing, Coughing and Related Motor Behaviours,2004, Wist, 335p.)

  3. Anatomy of Breathing Upper Airways - nose, nasopharynx, larynx Lower Airways - trachea, bronchial „tree“, Lungs (right + left)-alveoli Respiratory muscles

  4. Breathing(Respiration):-External(the air exchange at the level of lungs)-Internal(the O2 and CO2 exchange at the tissuelevel)

  5. External and Internal BreathingAtmosphere Lung Blood - Heart Extracel. liquid Cells Oxygen CO2

  6. Respiratory and Cardiovascular Relationships

  7. External Breathing:1. VENTILATION-cyclic air exchange during breathing caused by the respiratory „pump“ muscles - diaphragm, external and internal intercostals, abdominal,and auxiliary muscles (Jakus et al. book)2.DISTRIBUTION- mixing of inhaled air with an air that remains within the airwaysafter expiration (150 ml-death volume).3. DIFFUSION - transfer of O2 and CO2 through the alveol-ar-capilĺary membrane along the partial pressure gradients (Fick´s Law)4.PERFUSION- gas transport in blood between lungs and tissues by heart and vessels

  8. Ventilation - the role of respiratory musclesDiaphragm – moves downward at inspiration and upward during expiration (60% of volume changes in thorax )Intercostal muscles - external (inspiratory), and inte-rnal (expiratory) muscles Auxiliary musles (of neck, thorax, abdomen)- help to main respiratory muscles (Paralelogram- see Practicals)

  9. Ventilation- types (in adults) Minute ventilation(MV) =VT .fb =0.5.12= 6 (l/min) (VT – tidal volume (0.5 l), fb – breathing rate) Alveolar ventilation(AV)= 0.35.12 = 4.2 (l/min) Comparing to Minute ventilation, the value of Alveolar ventilation is reduced, because the death volume (0.15 l ) must be substracted from VT

  10. Origine of Breathing.Action potentials from respiratory centre drive respiratory muscles. These, in turn are contracted and create pressure changes. Pressure changes enable pressure gradient and this leads to a flow of air. Then lungs are filled (or emptied)with air volumes.(Hering´s model of breathing -see practicals)Remember these changes: A/ AT REST:QUIET INSPIRATION (active process): contraction of diaphragm + external intercostals fall of pleural pressure (PPl = - 0.8 kPa) fall of intrapulmonary(Pp = - 0.1 kPa )Pressure gradient inspiratory airflow (VI = + 0.4 l/s) inspiratory tidal volume (VT = 0.5 l)

  11. OUIET EXPIRATION( mostly passive process) : recoil forces (i.e elasticityof the thoracic wall and lung tissue + passive movement of the diaphragm upward  slightly negativePpl = - 0.1kP, and to slightly positive intrapulmonay pressure PP=+ 0.5 kPapressure gradientexpiratory airflow (VE= - 0.4 l/s)  expiratory volume(VT = 0.5 l )empties the lungsB/AT WORK: FORCEFUL INSPIRATION consists of the same processes as shown above + contraction of external intercostals + auxiliary muscles result in higher pressure gradients, and to higher values of Ppl, PP, VE and VT

  12. FORCEFULEXPIRATION(e.g. in cough, sneeze, strong voluntary expiration)It starts sudenly with contraction of abdominal muscles(expiratory), creating high abdominal pressure (PAB), very high PPl and PP pressures, also very high pressure gradient ,and thus extremely strong expiratory airflow (velocity like tornado) and very high expiratory volume

  13. Mechanics of breathing-means concomitant changes of respiratorymuscles (diaphragm, intercostal and auxiliary muscles) creating particular Ppl and PP, pres-sures, inspiratory and expiratory airflows (V), and tidal volumes (VT), resultingin some Work of breathing (during inspirationand expiration).Work of breathing is affected by:Lung compliance, Airway resistance

  14. 1/ Lung compliance – distensibility (C)- is the ratio between Volume of air(VT) / Pressure( P).N = 2 (l . kPa-1)Lung fibrosis C - the lung tissue is thicker and thusits compliance (distensibility) is lowerLung emphysema C- lungtissue is thinner, andthuscompliance (distensibility)of the lungs is higher.LOOP OF LUNG COMPLIANCE

  15. 2/ Airway resistance Raw- is the relationship betweenPRESSURE (P) / AIR FLOW (V) (Unit is kPa/l/s)In a disease like bronchial asthma the airway resistance is high, because the contraction of smooth muscles within the lowerairways decreases the diameter of airways .Thus,the airflow is low, but Work of muscles and breathing is high. LOOP OF AIRWAY RESISTANCE

  16. The LungVolumes(Remember 4 main breathing volumes and 4 capacities).Tidal volume VT = 0.5 lInspiratory reserve volumeIRV = 2.5 lExpiratory reserve volume ERV = 1.5 lResidual volume RV = 1.2 l(consists ofcollapse volume = 0.4 l + minimal volume = 0.8 l)

  17. The Lung CapacitiesVital capacity VC= VT +IRV +ERVFunctional residual capacity FRC = ERV +RVInspiratory capacityIC= VT + IRVTotal capacity TC= VT + IRV +ERV+RV(See practicals)

  18. Morphology of Alveoli and Capillaries(Coupling of Respiratory and Cardiovascular Systems)

  19. Partial Pressure of Gases- a drive for diffusionATHMOSPHERICAIRis amixtureof21% of O2 + 0.04 % CO2 + 78% of N2 ,and other residual gases(e.g. Hellium, Neon, Argon) Partial pressures of particular gases depend on their % concentration within the air.(DALTON´S LAW).The higher is % of a gas within a gas mix-ture, the higher is its partial pressure (andvice versa).At normal value of barometric pressure = 101.3 kPa (760 torr,1atm)thepartial pressure of P02 is approx. 21 kPa and PCO2is 0.04 kPa

  20. Remember: UsingDALTON’S LAWone can count partial pre-ssure of a gas according to formula:PO2 = V% O2 x ( PB - PH2O) / 100PO2= 20.93 x (101.3 – 0.8) / 100 = 21.03 (kPa)PCO2 = 0.04 (kPa)PN2 = 79 (kPa) This formula can be used for calculations of parti-cular pressures of gases in the air, in the airways or within the arterial and venous blood. See next table.

  21. The values of GAS Volumes (in %) and their Partial pressures (kPa),in the Atmospheric air, Alveolar air, in the arterial and venous blood

  22. DIFFUSION– is a transfer of gases (O2...) through the Alveolar-capillary membrane along the partial pressuregradients of O2 and CO2 or N2being governed by :FICK’S LAWDiffusion rate: V= (P1 – P2) . A . ksP1 P2partial pressuresA=diffusion surface(70 m2)s = thickness of Alv.-capillary membrane(0.8 um)k= diffusive constant-depends on a membraneand gas propertiesDiffusion rate:VO2= 15 – 20 ml / min.Diffusion rate for VCO2is 20-times higher than forO2 (300-400 ml/ min)

  23. Diffusion through the alveolo-capillary membrane

  24. Dynamics of Diffusion

  25. PHYSICAL SOLUBILITYof O2 and CO 2 withinthe blood plasma is under HENRY’S LAW: VO2 =  x PO2 x 1000 = 3 mlO2/1l arterial bloodPBVCO2 = x PCO2 x 1000 = 27 ml CO2 / 1l arter. blood 101,  - coefficients for O2, and CO2 (respectively) PB - atmospheric (barometric) pressureSolubility of gases in liquids depends on their partial pressures. Gases in liquids are in two forms: physically disolvedin blood plasma, and chemically bounded on Hemoglobine of the red blood cells.1 l of arterial blood takes 200ml of O2. From this only 3 ml of O2 is physically dissolved in plasma, and 197 mlO2 binds chemically on Hemo-globine.

  26. Wishing You Pleasant Day

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