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PULMONARY FUNCTION TESTS

PULMONARY FUNCTION TESTS

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PULMONARY FUNCTION TESTS

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  1. PULMONARY FUNCTION TESTS Made by: MeenalAggarwal Moderator: Dr. Ajay Sood

  2. Lung Volumes & Capacities

  3. Respiratory minute volume (at rest): 6 L/min • Alveolar ventilation (at rest): 4.2L/min • Maximum voluntary ventilation: 125-170 L/min

  4. Pulmonary Function Tests : Introduction • Aim: to identify abnormal lung function in hope of altering patient’s outcome by reducing risk of intra/post op ventilatory impairments • Enables us to: • Assess the presence and severity of respiratory dysfunction • Follow the progression of impairment • Document the response to therapy • 2 major groups of tests: • To detect abnormalities of gas exchange • To assess mechanical ventilatory functions of lungs & chest wall

  5. Clinical Spirometry • Inventor: John Hutchinson Vital Capacity: • The largest volume measured after the subject inspires deeply and maximally to TLC and then exhales completely to RV • Normal values are lower in supine than in sitting • Abnormal: when <80% seen in restrictive ds: • Lung pathologies (pneumonia, atelectasis, pulmn fibrosis) • Loss of lung tissue (Following surgical resection) • Diminished effort (muscle paralysis, abdominal swelling, )

  6. Time Expired Spirogram • After a maximal inspiratory effort subject exhales as forcefully and rapidly as possible Forced Vital Capacity: • Exhaled volume if recorded with respect to time • Reflects flowresistive properties of the airways • Practice attempts given, 3 acceptable tracings required • Normal: Exhalation takes at least 4 sec, should not be interrupted by coughing, glottic closure or any mechanical obstruction FEV1 (Forced Expiratory volume in 1sec): • Either in Lt or FEV1/FVC percentage • Normal: 75-80 %

  7. Abnormal: Mild obst <70% Moderate obst <60% Severe obst <50% • Restrictive diseases: dec TLC, dec FVC, so dec FEV1 but ratio FEV1/FVC either normal or increased

  8. PEFR: (Peak Expiratory Flow Rate) • Maximum flow rate obtainable at any time during FVC maneuver • L/sec or L/min • Usually measured as the average flow of gas expired after initial 200ml (k/a FEF 200-1200 or MEFR) • Can be measured with a handheld flow meter (serves as a bed side test) or a pneumotachygraph • Markedly affected by obstruction of large airways • Responsive to bronchodilator therapy so used to monitor therapeutic response in acute asthma • N value: 500Lts/min or more • If < 200Lts/min, suggests impaired cough efficiency and likelihood of post op complications

  9. Also affected in muscle weakness • Variable as highly dependent on patient effort FEF25-75%: (a/k/a Forced Mid-Expiratory Flow) • Middle half of FVC doesn’t require high degree of efforts • k/a Effort independent (not truly as marked reductions in effort will reduce it) • Negative effort dependence: flow rates can actually decrease with truly maximum efforts compared from a slightly submaximal effort (d/t dynamic airway compression) • N value: 4.5 – 5 L/sec • Sensitive indicator of early obstruction in small distal airways • Reduced even in restrictive ds, but FEV1/FVC is Normal

  10. Maximum Breathing Capacity: • a/k/a MVV (Maximum Voluntary Ventilation) • Largest volume that can be breathed per minute by voluntary effort • Instructed to breathe as hard and fast as possible for 12 sec, and then extrapolated to 1min • Reduced in obstructive diseases • Other factors: elasticity of lungs, resp muscle strength, patient co-operation • Correlates well with FEV1 (MVV= FEV1 X 35) • Normal: 150-175L/min • < 80% indicates gross impairment in resp function

  11. Respiratory Muscle Strength: • All Above parameters are affected by muscle strength • Evaluated by maximum static respiratory pressures (pressures generated against an occluded airway during a maximal forced inspiratory or expiratory effort) • Measured with Aneroid gauges (at FRC, to nullify effect of elastic recoil) • PImax (near RV) : -125cm H2O • If < -25 cm H2O, severe inability to take a deep breath • PEmax (near TLC) : +200 cm H2O • If < +40 cm H2O, severely impaired coughing ability • Useful in evaluating patients with Neuromuscular disorders

  12. Gauge

  13. Methods for Measuring Residual Volume • Body plethysmography • Helium dilution method

  14. Physiological Determinant of Maximum Flow Rates 3 factors: • Degree of effort (PEmax: at TLC, PImax: at RV) • Elastic recoil pressure of lungs (PL): Max at TLC: 25-30cm H2O Min at RV: 2-3 cm H2O Is opposed by elastic recoil of chest wall (Pcw) Net recoil Prs: PL + Pcw (zero at FRC) • Resistance to flow provided by airways (Raw): determined by size of airway, so min at TLC, max at RV Gaw (conductance, 1/ Raw, is related to lung volume linearly)

  15. Flow – Volume Relationships: • Useful as all determinants of flow are dependant on volume • During FVC, flow rises to a max at a volume close to TLC • Gradually: • In Obstructive ds, flows are decreased over full range

  16. Airway Compression & Flow Limitation: • Value in coughing

  17. Sites & Mechanisms of Decreased Airflow in Diseases: • D/t alterations in any 3 of the parameters (PEmax, PL, Raw)

  18. Measurement of Airway Obstruction Airway Resistance: (Raw) • Technique: patient pants once or twice per second through a mouth piece with a nose clip in place (to bypass max resistive areas-nose, nasopharynx) • Also panting maneuver keeps larynx dilated • Subject sits in a constant volume body plethysmograph (body box) • Lung volume & Raw can be measured using changes in the box pressure and volume (using Boyle’s law) • Normal Raw: 2cm H2O L/sec • Head flexion causes increased Raw (measured) as it reduces the caliber of hypopharynx, so be as errect as possible during maneuver

  19. Forced Expiratory Maneuvers (FVC, FEV1, PEFR): • Tells whether obstruction is present Flow-Volume loops: • Allows to discriminate b/w upper airway obstructive lesions • Subject inhales fully to TLC and then performs FVC maneuver, followed immediately by a max inspiration as quickly as possible to TLC • Whole inspiration and expiration near TLC are effort dependent (Normal = 1.0) • Mid VC ratio: ratio of expiratory flow to inspiratory flow at 50% VC

  20. Help to localize site & nature of obstruction • Upper airway obstruction: inspiratory flow reduced more than expiratory, so mid VC ratio >1 • Fixed airway obst : both inspiration and expiration reduced to same extent so plateaus of constant flow, so ratio = 1 • Variable obstruction: Lesion whose influence varies with the phase of respiration • Extrathoracic: l/t increased obst during forced inspiration, mid VC ratio >2 • Intrathoracic: Increased obstruction during forced inspiration, mid VC ratio is low

  21. Tests of Early Lung Dysfunction • Small airway disease, minimal airway dysfunction, early obstructive lung disease • It is a fore runner of chronic bronchitis & emphysema • Alveolar –Arterial Oxygen Tension Difference: • Detects regional V/Q mismatch • PaO2 =measured easily • PAO2 = PiO2 – PaCO2 / R • Difference : PAO2- PaO2 • Normal value at room air: 8 mm Hg • Increases with age (occurs d/t dec PaO2)

  22. Frequency Dependence of Compliance: • In normal lung: compliance not dependent on respiratory frequency • In small airway obstruction, d/t asynchronous behaviour of lung units where some areas of lung are moving out of phase with others, the compliance decreases with a high respiratory rate • If it falls to <80% : k/a compliance to be frequency dependent

  23. Multiple- Breath Nitrogen Washout: • Mild obstructive airway disease leads to uneven distribution of ventilation, measured by SBNW • Normal : lung behaves as a single compartment and produces a fast single exponential curve for N2 wash out • Abnormal : Lung appears to have more than one ventilatory compartment (d/t uneven dist of ventilation) • So different units have their N2 diluted at different rates, and so producing a tail on the washout curve • Very sensitive test, but requires computerization for analysis of curve

  24. Single Breath N2 Washout: • Described by Fowler in 1949 • Expired N2 conc was measured after inspiration of 1 L of O2 from FRC • The change in N2 concentration b/w 750-1250 ml of expired volume in seen • Modified method: Instead of just 1 L, patient makes a full inspiratory effort in 100% O2. the alveolar nitrogen slope with this method is less steep (as now whole lung is filled with O2, c/f 1L in which only lung bases are filled leading to an inc Apex base difference, so steeper slope) • The slope of alveolar nitrogen plateau is larger in old subjects (reflecting uneven evntilation) • <2% normal, Even Upto 10% in smokers

  25. Closing Volume: • Lung volume at which the airways in the dependent areas in the lungs begin to close • Occurs because lower portions of lungs are subject to Ppl pressure in excess of airway pressure, l/t closure of airways • Technique: tagging of these lung areas by giving them a different concentration of a tracer gas c.f. apex. • 2 methods: Bolus gas (uses He) • Resident gas (uses N2) • First a gradient is created, and then expiratory levels of gas are plotted. The volume at which phase 3 begins is known as closing volume • Closing capacity = closing volume + RV • Increases with age, in smokers

  26. Bed-Side PFT’s 1. Snider’s Match Blowing Test: • Mouth wide open • Match held at 15 cm distance • Chin supported • No head tilting • Match stick & mouth at same level • Cannot blow out a match: • MBC < 60 L/min • FEV1 <1.6 L • * Modified Snider’s test: • 3 inches: MBC >40 L/min • 6 inches: MBC >60L/min • 9 inches: MBC >150 L/min

  27. 2.Forced Expiratory Time: • FET < 3 sec (restrictive disease) • FET > 6 sec (obstructive disease) • 3. Seberese’s Single Breath Count: • Patient is asked to take a deep breath followed by counting, till the time he cannot hold breath • Shows trends of deteriorating/ improving lung functions • 4. Seberese’s Breath Holding Time: • Subject is asked to N tidal inspiration & hold breath • Normal >= 40 sec • < 15 sec C/I for surgery

  28. 5. Cough test: • Observe for ability to cough (strength & effectiveness) • Wet productive cough = prone for pulm complications • Inadequate cough= FVC < 20 ml/kg, FEV1 < 15ml/kg • 6. De Bono’s Whistle Test: • Wide bore tube with a whistle at end and an adjustable leak hole at the side, whistle blows only when air flow exceeds a certain value • 7. Wright’s Peak Flow Meter: • Normal males: 450- 700 l/min • Females: 300-500 l/min • Values< 200 l/min suggests impaired cough efficiency

  29. Peak flow meter

  30. Indications for PFT in Surgical Patients: • Patient factors: • Known Chronic pulmonary disease • Heavy smoker (>1 pack/day) • Chronic productive cough • Recent respiratory infections • Advanced age (>70 yrs) • Obesity (>30% over ideal wt) • Thoracic cage deformity (kyphoscoliosis) • Neuromuscular disease (MG) • Procedure: • Thoracic or upper abdominal surgery • Pulmonary resection • Prolonged anesthesia

  31. Pre-op Measures to Improve Lung Function: • Goal: to reduce intra/post op pulmonary complications • 4 basic modalities: • Smoking cessation: after 2-4 wk (reduced secretions, airway reactivity & improved mucociliary clearance) • Treatment of bronchospasm (Beta 2 agonists, antichol, theophylline) • Removal of secretions (AB therapy, adequate hydration, mucolytics, postural drainage, chest percussions) • Motivation & Stamina (incentive spirometry)

  32. Thank You