Applied Physiology & Chemistry

1. Applied Physiology & Chemistry RT 210 Unit B

2. Mechanics of Ventilation: Ventilation & Respiration • Ventilation is air movement in and out of the lungs to allow external respiration to occur • Respiration is gas exchange across a permeable cellular membrane • External respiration is gas exchange between alveolar gas (air) and capillaries (blood) • Internal respiration is gas exchange between capillaries and the tissues

3. The Lung - Thorax Relationship • Two opposing forces • Lungs tend to collapse due to elasticity • Chest wall tends to spring out • Linked together by the pleura • Negative pressure -4 to -5 cm H2O • Parietal pleura lines chest wall • Visceral pleura covers lung • Potential space between with small amount of lubricant/pleural fluid between layers

4. Normal ventilation pressures • Inspiration, (intrapleural = -10 cm H2O, intrapulmonary -3 cm H2O) • Diaphragm contracts and flattens • Chest cavity expands • Negative intrapulmonary pressure • Negative transairway pressure • Gas flows in through the mouth

5. Normal ventilation pressures • Expiration, (intrapleural = -5 cm H2O, intrapulmonary = +3 cm H2O) • Diaphragm relaxes • Chest cavity recoils and decreases in size • Slight positive intrapulmonary pressure • Gas flows out through the mouth

6. Physics of Ventilation • Law of Laplace • P = 2 ST/r • surface tension tends to collapse alveoli • Surfactant allows different sized alveoli to be connected without smaller emptying into the larger alveoli and collapsing • Phospholipid • Decreases surface tension of the alveoli • Allows critical volume to be variable from alveoli to alveoli

7. Compliance-measures dispensability of the lung • Compliance of the Lung = change in volume divided by change in pressure

8. Compliance-measures dispensability of the lung • Total compliance = lung and thorax (lung is not measured out of thorax) • Pulmonary compliance = 0.2L/cm H2O • Thoracic compliance = 0.2L/cm H2O • Total compliance = 0.1 L/cm H2O

9. Compliance-measures dispensability of the lung • Pressure is peak pressure during gas flow

10. Compliance-measures dispensability of the lung • Decreased or less compliance seen in: • Pulmonary consolidation • Pulmonary edema • Pneumothorax • Abdominal distension • ARDS • Pulmonary fibrosis • Thoracic deformities • Complete airway obstruction

11. Compliance-measures dispensability of the lung • Compliance increases • Alveolar distension • Alveolar septal defect • Obstructive disorders-CBABE • C = Cystic Fibrosis • B = Bronchitis • A = Asthma • B = Bronchiectasis • E = Emphysema • Compliance is inversely related to elastance • Elastance is the property of resisting deformation

12. Resistance • Resistance =

13. Resistance • Laminar • Poiseuille’s Law states that flow rate varies directly with radius of a tube • Small changes in airway radius will dramatically affect flow and resistance • ½ decrease in diameter increases resistance by 16 times • Turbulent (non laminar or eddy flow) • The higher the flow the more resistance • Resistance is also directly proportional to gas density

14. Resistance • Transitional • Tracheobronchial tree has both laminar and turbulent flow caused in part by the directional changes in the conductive airway • Reynold’s number • Less than 2000 is laminar flow • 2000-4000 is laminar and turbulent or mixed flow • Greater than 4000 is turbulent flow

16. Resistance • Viscosity • Pressure Gradient • Bernoulli’s Principle • Coanda Effect

17. Lung Volumes • Relate to lung/thorax relationship, compliance and surface tension • Four volumes and four capacities • IRV - Inspiratory Reserve Volume • Maximum inhalation following quiet inhalation • Normally 3.1 L • VT - Tidal Volume • Volume inspired or expired during quiet breathing • Normally 0.5L

18. Lung Volumes • Four volumes and four capacities (cont) • ERV - Expiratory Reserve Volume • Maximum exhalation following quiet exhalation • Normally 1.2L • RV - Residual Volume • Gas remaining in lung after maximum exhalation • Normally 1.2L

19. Lung Volumes • Capacities - consist of 2 or more volumes or capacities • IC - Inspiratory Capacity • Made of IRV and VT • Maximum inhalation following quiet exhalation • Normally 3.6L • FRC - Functional Residual Capacity • Made of ERV and RV • Gas in lung following quiet exhalation • Normally 2.4L

20. Lung Volumes • Capacity (cont) • VC - Vital Capacity • Made of IRV, VT, and ERV • Maximum exhalation following a maximum inspiration • Normally 4.8L • TLC - Total Lung Capacity • Made of IRV, VT, ERV and RV • Gas in the lung following maximum inhalation • Normally 6L

22. FRC and Lung Compliance • FRC is most consistent volume - diaphragm at rest • At FRC, equalization of opposing forces of pulmonary and thoracic elasticity • As elasticity changes, FRC changes • At FRC, intrapleural pressure is normal -5 cm H2O • At FRC, intrapulmonary pressure equals ambient pressure • With an increase in compliance, (decrease elasticity), an increase in ease of inspiration but difficulty in expiration • Decrease in compliance, decrease the ease of inspiration

23. Classification of Ventilation • VE = Minute Ventilation • The amount of gas moved in 1 minute • Calculated by VT times (*) f • Can be measured by a respirometer • Vane- Draeger, Wright • Volume bellows spirometer • Venticomp bag • Vortex principle- Boum’s LS 75 • Use a respirometer with a filter attached to demonstrate measuring VE

24. Classification of Ventilation • VD= Dead space • Part of min. ventilation is "wasted", does not reach alveoli where external respiration occurs • Anatomical (VDanat) • Fills space in the conductive airways • Alveolar (VDalv) • Alveoli that are not perfusion • Physiologic (VDphys) • All dead space combination of VDanat and VDalv

25. Classification of Ventilation • Dead space (cont) • Mechanical • Added dead space • Normally 1 cc per pound ideal weight (approx. 150cc) • Volume rebreathed

26. Classification of Ventilation • VA = Alveolar ventilation • Gas in perfused alveoli • Participates in external respiration • VA= (VT - VD)

27. Classification of Ventilation • Terms relating to dead space • Normal ventilation • Adequate ventilation to meet metabolic needs • Hypoventilation • Decreased alveolar ventilation • Can be caused by increased VD or decreased VT • Ventilation less than that necessary to meet metabolic needs; signified by a PCO2 greater than 45 mmHg in the arterial blood • Hyperventilation • Increased alveolar ventilation • Caused by decreased VD or increased VT • Ventilation more than necessary to meet metabolic needs, signified by a PCO2 less than 35 mmHg in the arterial blood

28. Ventilation and Perfusion • Ventilation = alveolar minute ventilation • VA = (VT - VD)* f • Perfusion = blood flow to the tissues

29. Ventilation and Perfusion • External respiration = gas exchange between the alveoli and capillaries • Carbon dioxide leaves blood • Oxygen enters the blood • Respiratory Quotient -unequal exchange of CO2 produced vs. oxygen uptake or utilization • 200 ml CO2 produced by 250 ml O2 used due to normal metabolism in the Kreb’s cycle (CARC page 154 & 389).

30. Gas exchange unit • Normal unit • Alveoli with capillary—relationship between ventilation and gas flow are relatively equal • Dead space unit • ventilation without or in excess of perfusion • Shunt • Perfusion without or in excess of ventilation • Silent unit • No perfusion, no ventilation

31. Regional Differences in Ventilation & Perfusion • More ventilation to the bases • 4 times more ventilation to bases than apices • Due to gravity’s effect on pleural pressures • On inspiration the transpulmonary pressure is greater at the bases • More perfusion to bases • Due to gravity • 20 times more perfusion to bases than apices • Ventilation/Perfusion ratio (V/Q) • V/Q = 4L alveolar minute volume 5L minute cardiac output • Overall for the lung is 4:5 or 0.8

32. Regional Differences in Ventilation & Perfusion • Diffusion • Whole Body Diffuision Gradients • Determinants of Alveolar Gas Tensions • Mechanism of Diffusion • Systemic Diffusion Gradients • Abnormalities • Impaired oxygen Delivery • Impaired Carbon Dioxide Removal

33. Shunting • Unoxygenated blood entering the left side of the heart • Anatomical shunt • Normally 2-5% of cardiac output • Bronchial veins drains bronchial circulation • Pleural veins drains pleural circulation • Thebesian veins drains heart circulation • Absolute capillary shunt • Alveoli perfused but not ventilated • “True Shunt” • Refractory to O2 therapy

34. Shunting • Relative capillary shunt • V/Q mismatch • Areas where perfusion is in excess of ventilation • Physiological shunt • Sum of anatomical, absolute and relative shunts • Causes • Decrease in ventilation • An increase in perfusion (increased CO)

35. Dead Space • "Wasted" ventilation • Types • Anatomical • Conducting airways in tracheobronchial tree • Alveolar: Alveoli that have decreased perfusion • Physiological: Sum of anatomical and alveolar • Mechanical – added dead space • Causes • An increase in ventilation • A decrease in perfusion (decreased CO) • Effect • Increased VD will decrease VA if VE remains constant

38. Effects of exercise & of high pressure environs • Exercise • Increases CO2 production and O2 consumption • Aerobic versus anaerobic • Oxygen consumption correlates to alveolar ventilation • At rest 250ml rises to 3500ml/minute (untrained) to 5000ml/minute (trained athlete) • PaO2, PaCO2 and pH remain constant

39. Effects of exercise & of high pressure environs • Exercise (cont) • Circulation • Increased sympathetic impulses stimulates heart rate and perfusion to working muscles • Frank-Starling mechanism • Maximal heart rate • Muscle Work, Oxygen Consumption, and Cardiac Output Interrelationships • The Training Influence • Body Temperature: Cutaneous Blood Flow Relationship

40. Effects of exercise & of high pressure environs • High altitude • Acclimatization • Major cardiopulmonary responses • increased alveolar ventilation via peripheral chemoreceptor stimulation • Secondary polycythemia, increased RBC production due to low oxygen levels • Development of respiratory alkalemia, due to the increased alveolar ventilation and carbon dioxide elimination • Increased oxygen diffusion capacity in native high dwellers, due to increased lung size

41. Effects of exercise & of high pressure environs • Major cardiopulmonary responses (cont) • Increased alveolar arterial oxygen difference • Improved ventilation perfusion ratio • Increased cardiac output of non-acclimatized individuals • Increased pulmonary hypertension as a result of hypoxic vasoconstriction

42. Solutions • Definition • Concentration • Osmotic pressure • Quantifying solute content and activity • Calculating solute content • Quantitative classification of solutions

43. Electrolytic Activity and Acid Base Balance • Characteristics of acids, bases, and salts • Designation of acidity and alkalinity

44. Body Fluids and Electrolytes • Fluids • Electrolytes

45. Blood Gases • Define • Kreb’s [TCA] Cycle

46. Oxygen Transport • Dissolved • Henry's Law - weight of gas dissolving in liquid is proportional to the partial pressure of a gas • Bunsen solubility coefficient for O2 • 0.023ml of O2 can be dissolved in 1ml of plasma at 37°C and 760mmHg PO2 • This allows us to determine the amount of O2 (expressed in ml) dissolved in 1ml of plasma using the formula: 0.003 * PaO2 • (ex: PaO2 of 100 mmHg = 0.3ml of dissolved O2 in plasma)

47. Oxygen Transport • Graham's Law – rate of diffusion of a gas is directly proportional to its solubility coefficient and inversely proportional to the square root of its density • CO2 is 20 times more diffusible than O2 • CO is 200 times more diffusible than O2 • Hemoglobin’s affinity for CO is 200 times more than for oxygen.

48. Oxygen Transport • Combined with hemoglobin • Carries the most oxygen to the tissues • Doesn't exert a gas pressure • Calculate 1.34 * Hb * SaO2 • Total oxygen content is sum of dissolved and combined

49. Oxygen Transport • Oxyhemoglobin dissociation curve • Curve is sigmoidal due to Hb affinity for O2 at each of 4 binding sites • Last site has less affinity than 2nd & 3rd • In the steep portion minimal changes in PO2 will cause drastic changes in saturation and total O2 content • P50 is where Hb is 50% saturated with O2 and is normally a PaO2 of 27mm/Hg

50. Oxygen Transport • Oxyhemoglobin dissociation curve (cont) • A shift to right causes a decreased affinity for O2, resulting in decreased saturation but increased O2 to tissues • Factors causing shift to the right • Increased PCO2 • Increased H+ (decreased pH) • Increased 2, 3 DPG • Increased temperature