1 / 40

Ventilation

Ventilation. Intro: why do we breathe?. Key Terms. Ventilation : Movement of air into and out of the lungs Gas exchange : Movement of gases across membranes according to pressure gradients Pressure gradients : Determined by the partial pressure of the gas

chidi
Download Presentation

Ventilation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ventilation

  2. Intro: why do we breathe?

  3. Key Terms • Ventilation: Movement of air into and out of the lungs • Gas exchange: Movement of gases across membranes according to pressure gradients • Pressure gradients: Determined by the partial pressure of the gas • Gases: Oxygen necessary for cellular respiration; Carbon dioxide is a volatile acid

  4. Breathing, ventilation and respiration • Used synonymously • Used to think respiration occurred in the lung • Ventilation: movement of air • Respiration: cellular utilization of O2

  5. Ventilation • Pulmonary minute ventilation (VE) • The rate of expired ventilation • Usually expressed in L/min • VE = VT x f • Expired ventilation and inspired essentially the same, may differ in transition from rest to exercise .

  6. Environmental influences • Temperature, pressure, water vapor all impact gas volumes • Gas laws • Boyle’s law: Pressure and volume inversely related; P1V1=P2V2 • So, as pressure goes up, volume goes down and vice versa • Charles’ law: Temp and volume directly related; V1/T1 = V2/T2 • So, as temperature goes up, volume goes up and vice versa • Dalton’s law: The total P of a gas is determined by the partial pressures of all the constituent gases • STPD • Standard temperature, pressure, dry • ST=0°C, P=760 mmHg, 0 mmHg H2O vapor pressure (PH2O) • BTPS • Body temperature, pressure, saturated • Body temperature, P= ambient pressure, PH20=47 mmHg at 37°C • ATPS • Ambient temperature, pressure, saturated • T=ambient, P=ambient, PH20=47 mmHg at 37°C • Typically you collect at ATPS and convert to BTPS (ventilation) or STPD (Vo2, Vco2); allows comparison across studies

  7. Entry of O2 into the blood

  8. Entry of O2 into the blood • Determined Entirely by pressure gradients • Partial pressure • Pressure exerted by each gas in a composition • Atmospheric pressure (PAtm): 760 mmHg • Partial pressure of O2 (Po2): 159 mmHg (.2094 x 760) • Rest is nitrogen, some argon and very little CO2 • When air reaches alveoli, Po2 falls, why? • Think of gas laws

  9. Entry of O2 into the blood 1) Water vapor • Gas is fully humidified, so at normal body temp, water vapor pressure is 47 mmHg 2) Co2 is also higher in the alveoli • Thus, Po2 of alveoli about 100-105 mmHg • 760 – 47 = 713 or the pressure of the air in the lung • Dalton’s Law • 713 x .2094 = 149 (inspired pressure of O2; PiO2) • PAO2 = PiO2 – (PACO2/RER) • Alveolar gas equation • PAO2 = 149 – (40/.85) or 149-47 = 102 • RER = respiratory exchange ratio or Vco2/Vo2 • Usually about 0.85 at rest with mixed diet

  10. Entry of O2 into the blood • Once O2 gets into alveoli it diffuses into the blood • Due to favorable oxygen gradient (~100 to 40 mmHg) • Most binds with Hb (~97%) • Some dissolved in plasma (3%) • Oxygen content of blood (CaO2) CaO2=1.34*[Hb]*(%sat of Hb) + 0.003 * PaO2 CaO2 = 1.34 * (15mg/dl)*(.98) + 0.003* (100mmHg) CaO2 = ~20 ml/dl [Hb]= hemoglobin concentration PaO2 = partial pressure of oxygen

  11. Diffusion of gases: Lung

  12. Pulmonary diffusion • Diffusion of gases through tissues (gel) • Major determinants • Partial pressure difference (major) • Solubility of the gas (minor) • Gases of lower solubility typically have greater partial pressure gradients

  13. Rate of diffusion • Determined by • Area available • Thickness • Partial pressure gradient (P1-P2) • Diffusion coefficient • Determined by solubility and molecular weight

  14. Rate of diffusion • CO2 is slightly larger than O2 (MW; 44 vs 32 g/mol) • CO2 has a much higher solubility coefficient (0.57 vs 0.024) • Thus, CO2 has a greater relative diffusion coefficient (~20 x higher) • Thus, O2 needs a larger pressure gradient to “force” itself across biological membranes

  15. Arterial blood gas homeostasis • Maintenance of blood gases (PaO2 and PaCO2) very important • Keep driving pressure for CO2 and O2 high • Driving pressure is the difference between arterial and venous pressure (PaO2-PvO2) • Note that gradients increase with exercise

  16. Oxygen transport • Oxygen content • CaO2 = 1.34[Hb]*(%sat) + 0.003 * PaO2 • Cardiac output (Qc) = HR * stroke volume • Thus, total oxygen transport capacity (or delivery) is Qc*CaO2 or Qo2 • Qo2 is a measure of how much oxygen is circulated around by the heart in one minute • So, if CaO2 = 20 ml/dl and Qc equals 30 L/min • Qo2 = 30 * 0.2 or • Qo2 = 6L/min

  17. Shifting of O2 dissociation curve • Remember: we noted that exercise increases the pressure gradients • How?: O2 dissociation curve shifts • Curve shows the relationship between Po2, CaO2 and % Hb saturation • Right shifting increases O2 unloading • Right shift called Bohr effect • What shifts the curve?

  18. Effects of Co2 and pH on O2 transport • The shape of the O2 dissociation curve is altered by 4 variables • pH • < 7.4 = right shift • >7.4 = left shift • Temperature • >38C = right shift • <38C = left shift • Co2 • >40 mmHg = right shift • <40 mmHg = left shift • 2,3 DPG (diphosphoglycerate) • Altitude increases this

  19. Co2 transport • Co2 must be transported from tissues to blood and lungs for removal • Carried in 3 ways • Bound to Hb (carbamino compounds) (15-20%) • Dissolved in plasma (5-10%) • As bicarbonate (HCO3-), ~70%

  20. Co2 transport • More Co2 dissolves (than O2) in plasma due to greater solubility • Binding of Co2 to Hb occurs at different site than O2 • Co2 combines with H2O to form bicarbonate

  21. Co2 content • Amount of Co2 carried in the blood depends upon Pco2 • Unlike oxygen, the Co2 curve is linear over a much greater range • Thus, as Co2 production increases • greater driving pressure (from tissue to blood) • As Co2 is extremely soluble, this increases Co2 transport (No upper limit)

  22. Effect of O2 on Co2 transport (and vice versa) • When Co2 increases in blood • Shifts O2 curve to right • Facilitates unloading of O2 at the tissues • Called Bohr effect • When O2 falls • Shifts Co2 curve up and right • Facilitates greater Co2 loading • Called Haldane effect • Thus, at the level of the tissue, high CO2 facilitates unloading of O2 which allows greater amount of CO2 to be carried in blood • At the lung, high O2 forces CO2 from Hb (and plasma) and it is then exhaled

  23. Arterial blood gases • Note how ventilation and PaCo2 inversely mirror each other • Note also the effect on pH • Major function of the ventilatory system is to rid the body of Co2 and control pH • VA = VCo2/PaCo2

  24. Buffering of metabolic acids • pH is a measure if the acidity of the blood • Several sources of acid are during exercise • Lactic acid (HLa) • Carbon dioxide • These cause a fall in pH • Bicarbonate is a very effective buffer • A buffer helps to prevent a change in pH pK: Dissociation constant. pH at which acid (or base) is 50% dissociated (50% acid and 50% base)

  25. Buffering of metabolic acids • Lactic acid produced • HLa → La- + H+ • H+ + HCO3- → H2CO3 → H2O + CO2 (exhaled) • Co2 produced • CO2 + H2O → H2CO3 → HCO3- + H+ (reverses at lung) • pH • Negative logarithm of the hydrogen concentration • pH = pk for HCO3-+ log [base/acid) • pH = 6.1 + log [HCO3-/(pCO2 *0.03)] (Henderson-Hasselbalch eq.) • pH = 6.1 + log [24 /1.2) • pH = 6.1 + 1.3 • pH = 7.4

  26. Control of pH • Co2 and pH (actually the H+) stimulate ventilation • Chemoreceptors • Carotid sinus • Centrally (medulla) • Sensitive to changes in Pco2 and H+ • Stimulate breathing to expel CO2 and partially compensate for the metabolic acidosis

  27. Ventilation • Gross Anatomy • Pharynx • Trachea • Bronchus • Alveolus

  28. Ventilation • Ventilation • Moves air into and out of lung • Two separate areas of lung • Conducting zone • Respiratory zone • Conducting zone • Network of tubes whose function is movement of air • Trachea and Bronchi • Respiratory zone • Large, thin area where gas exchange occurs • Respiratory bronchioles and alveolar ducts

  29. Ventilatory mechanics • Diaphragm • Main muscle of ventilation • Only skeletal muscle necessary for life • Accessory muscles • Intercostals • External • Inspiration • Internal • Expiration • Sternocleidomastoid, Scalenes • Inspiration • Abdominal muscles • Expiration

  30. Ventilatory volumes • Note how much ventilation can increase • Due to large increases in tidal volume and frequency • Increases in tidal volume (VT) largely due to accessory muscles • Increases in frequency (f) due to diaphragm

  31. Dead space and alveolar ventilation • Ventilation (VE) is the total amount of air moved in and out of the lungs • VE = VDS + VA • Dead space (VDS) • Anatomic dead space • Conducting zone • Physiologic dead space • Diseased areas • Dead space/tidal volume ratio • At rest ratio of VD/VT ~25-40% • With exercise VD/VT falls, why? • Alveolar ventilation • Ventilation of the gas exchange units

  32. Static lung volumes • Volumes and capacities • Volume: single measure • Residual volume (RV) • The amount of air in the lung after a maximal expiration • Expiratory reserve volume (ERV) • The amount by which you can increase expiration after a normal exhalation • Inspiratory reserve volume (IRV) • The amount by which you can increase inspiration after a normal inspiration • Tidal volume (VT) • The volume of a normal breath • Total lung capacity (TLC) • RV, ERV, VT and IRV • Vital capacity • ERV, VT and IRV • Functional residual capacity • RV, ERV • Where humans breath from • Inspiratory capacity • VT, IRV

  33. Composition of Alveolar gases Air breathing; no water or CO2 100% oxygen

  34. Movement of gas: diffusion

  35. Diffusion • Oxygen • Breathed into lungs • Diffuses across blood gas barrier • Binds with hemoglobin (97%) • Dissolved in plasma (3%) • Circulated to tissues • Diffuses into tissues • Binds with myoglobin • Keeps oxygen pressure homogeneous within tissues • Utilized in mitochondria Mb

  36. Transit time • Capillary blood volume (Vc) • The blood that is in the capillaries at one instant in time • Transit time • the ratio of VC/blood flow • VC =~70 ml • Qc = 100 ml/s • TT = 0.7 sec • More than adequate for equilibration of blood gases • Note that CO2 equillibrates MUCH faster than O2; why?

  37. Control of ventilation • Respiratory control center • Brainstem • Medulla • Pons • Feed forward • Central command • Feedback • Peripheral and central chemoreceptors

  38. Central and peripheral control • Feed forward • Sometimes called “central command” • Co-activation of cardiovascular, ventilatory and musculoskeletal systems • Central chemoreceptors • Sensitive to changes in pH • Caused by Co2 as H+ cannot cross Blood brain barrier • CO2 + H2O H2CO3 HCO3- + H+ • Peripheral chemoreceptors • Carotid sinus • Muscle metaboreceptors • Both sensitive to changes in pH, PCO2 and PO2 (particularly at high atltitude) • Peripheral mechanoreceptors • Sensitive to limb movement

  39. Feed forward 1 1 Peripheral3 Peripheral3 Central 2 3 & 4 Peripheral chemoreceptors and mechanoreceptors

More Related