2 Lung Volumes and Capacities PFT tracings have:Four Lung volumes: tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volumeFive capacities:, inspiratory capacity, expiratory capacity, vital capacity, functional residual capacity, and total lung capacityAddition of 2 or more volumes comprise a capacity.
3 Lung VolumesTidal Volume (TV): volume of air inhaled or exhaled with each breath during quiet breathing (6-8 ml/kg)Inspiratory Reserve Volume (IRV): maximum volume of air inhaled from the end-inspiratory tidal position.( ml)Expiratory Reserve Volume (ERV): maximum volume of air that can be exhaled from resting end-expiratory tidal position.( ml).
4 Lung Volumes Residual Volume (RV): Volume of air remaining in lungs after maximium exhalation (20-25 ml/kg) ( ml)Indirectly measured (FRC-ERV)It can not be measured by spirometry
5 Lung CapacitiesTotal Lung Capacity (TLC): Sum of all volume compartments or volume of air in lungs after maximum inspiration (4-6 L)Vital Capacity (VC): TLC minus RV or maximum volume of air exhaled from maximal inspiratory level. (60-70 ml/kg) ( ml)Inspiratory Capacity (IC): Sum of IRV and TV or the maximum volume of air that can be inhaled from the end-expiratory tidal position. ( ml).Expiratory Capacity (EC): TV+ ERV
6 Lung Capacities (cont.) Functional Residual Capacity (FRC):Sum of RV and ERV or the volume of air in the lungs at end-expiratory tidal position.(30-35 ml/kg) ( ml).Measured with multiple-breath closed-circuit helium dilution, multiple-breath open-circuit nitrogen washout, or body plethysmography.It can not be measured by spirometry)
7 VOLUMES, CAPACITIES AND THEIR CLINICAL SIGNIFICANCE TIDAL VOLUME (TV):VOLUME OF AIR INHALED/EXHALED IN EACH BREATH DURING QUIET RESPIRATION.N – 6-8 ml/kg.TV FALLS WITH DECREASE IN COMPLIANCE, DECREASED VENTILATORY MUSCLE STRENGTH.INSPIRATORY RESERVE VOLUME (IRV):MAX. VOL. OF AIR WHICH CAN BE INSPIRED AFTER A NORMAL TIDAL INSPIRATION i.e. FROM END INSPIRATION PT.N ml ml.
8 CONTINUED……… 3) EXPIRATORY RESERVE VOLUME (ERV): MAX. VOLUME OF AIR WHICH CAN BE EXPIRED AFTER A NORMAL TIDAL EXPIRATION i.e. FROM END EXPIRATION PT.N- 700 ml – 1000 ml4) INSPIRATORY CAPACITY (IC) :MAX. VOL. OF AIR WHICH CAN BE INSPIRED AFTER A NORMAL TIDAL EXPIRATION.IC = IRV + TVN-2400 ml – 3800 ml.
9 CONTINUED……….. 4) VITAL CAPACITY: COINED BY JOHN HUTCHINSON. MAX. VOL. OF AIR EXPIRED AFTER A MAX. INSPIRATION .MEASURED WITH VITALOGRAPHVC= TV+ERV+IRVN L. OR ml/kgVC IS COSIDERED ABNORMAL IF ≤ 80% OF PREDICTED VALUE
10 FACTORS INFLUENCING VC PHYSIOLOGICAL :physical dimensions- directly proportional to ht.SEX – more in males : large chest size, more muscle power, more BSA.AGE – decreases with increasing ageSTRENGTH OF RESPIRATORY MUSCLESPOSTURE – decreases in supine positionPREGNANCY- unchanged or increases by 10% ( increase in AP diameter In pregnancy)
11 CONTINUED……… PATHOLOGICAL: DISEASE OF RESPIRATORY MUSCLES ABDOMINAL CONDITION : pain, dis. and splinting
13 5) Depression of respiration : opioids/ volatile agents 6) Abdominal splinting – abdominal binders, tight bandages, hip spica.7)Abdominal pain – decreases by 50% & 75% in lower & upper abdominal Surgeries respectively.8) Posture – by altering pulmonary Blood volume.
14 DIFFERENT POSTURES AFFECTING VC POSITIONTRENDELENBERGLITHOTOMYPRONERT. LATERALLT. LATERALDECREASE IN VC14.5%18%10%12%
15 VC CONTINUED…….VC correlates with capability for deep breathing and effective cough.So in post operative period if VC falls below 3 times VC– artificial respiration is needed to maintain airway clear of secretions.
16 CONTINUED……. 6) TOTAL LUNG CAPACITY : Maximum volume of air attained in lungs after maximal inspiration.N- 4-6 l or ml/kgTLC= VC + RV7) RESIDUAL VOLUME (RV):Volume of air remaining in the lungs after maximal expiration.N – 2100 ml OR 20 – 25 ml/kg.
17 CONTINUED…… 8) FUNCTIONAL RESIDUAL CAPACITY (FRC): Volume of air remaining in the lungs after normal tidal expiration, when there is no airflow.N L OR ml/kg.FRC = RV + ERVDecreses under anaesthesiawith spontaneous Respiration – decreases by 20%With paralysis – decreases by 16%
18 FACTORS AFFECTING FRC FRC INCREASES WITH Increased height Erect position (30% more than in supine)Decreased lung recoil (e.g. emphysema)FRC DECREASES WITHObesityMuscle paralysis (especially in supine)Supine positionRestrictive lung disease (e.g. fibrosis, Pregnancy)AnaesthesiaFRC does NOT change with age.
19 FUNCTIONS OF FRC Oxygen store Buffer for maintaining a steady arterial po2Partial inflation helps prevent atelectasisMinimise the work of breathingMinimise pulmonary vascular resistanceMinimised v/q mismatch - only if closing capacity is less than frcKeep airway resistance low (but not minimal
20 Pulmonary Function Tests The term encompasses a wide variety of objective tests to assess lung functionProvide objective and standardized measurements for assessing the presence and severity of respiratory dysfunction.
21 GOALS To predict the presence of pulmonary dysfunction To know the functional nature of disease (obstructive or restrictive. )To assess the severity of diseaseTo assess the progression of diseaseTo assess the response to treatmentTo identify patients at increased risk of morbidity and mortality, undergoing pulmonary resection.
22 To wean patient from ventilator in icu. GOALS, CONTINUED……..To wean patient from ventilator in icu.Medicolegal- to assess lung impairment as a result of occupational hazard.Epidemiological surveys- to assess the hazards to document incidence of diseaseTo identify patients at perioperative risk of pulmonary complications
23 INDICATIONS OF PFT IN PAC TISI GUIDELINES FOR PREOPERATIVE SPIROMETRYAge > 70 yrs.Morbid obesityThoracic surgeryUpper abdominal surgerySmoking history and coughAny pulomonary disease
24 INDICATIONS FOR PREOPERATIVE SPIROMETRY ACP GUIDELINES FOR PREOPERATIVE SPIROMETRYLung resectionH/o smoking, dyspnoeaCardiac surgeryUpper abdominal surgeryLower abdominal surgeryUncharacterized pulmonary disease(defined as history of pulmonary Disease or symptoms and no PFT in last 60 days)
25 BED SIDE PFT Sabrasez breath holding test: Ask the patient to take a full but not too deep breath & hold it as long as possible.>25 SEC.-NORMAL Cardiopulmonary Reserve (CPR)15-25 SEC- LIMITED CPR<15 SEC- VERY POOR CPR (Contraindication for elective surgery)SEC ml VC20 – 25 SEC ml VCSEC ml VCSEC ml VCSEC ml VC
26 BED SIDE PFT 2) Single breath count: After deep breath, hold it and start counting till the next breath.N COUNTIndicates vital capacity
27 BED SIDE PFT3) SCHNEIDER’S MATCH BLOWING TEST: MEASURES Maximum Breathing Capacity.Ask to blow a match stick from a distance of 6” (15 cms) with-Mouth wide openChin rested/supportedNo purse lippingNo head movementNo air movement in the roomMouth and match at the same level
28 BED SIDE PFT Can not blow out a match Able to blow out a match MBC < 60 L/minFEV1 < 1.6LAble to blow out a matchMBC > 60 L/minFEV1 > 1.6LMODIFIED MATCH TEST:DISTANCE MBC9” >150 L/MIN.6” >60 L/MIN.3” > 40 L/MIN.
29 BED SIDE TEST 4) COUGH TEST: DEEP BREATH F/BY COUGH ABILITY TO COUGH STRENGTHEFFECTIVENESSINADEQUATE COUGH IF: FVC<20 ML/KGFEV1 < 15 ML/KGPEFR < 200 L/MIN.VC ~ 3 TIMES TV FOR EFFECTIVE COUGH.A wet productive cough / self propagated paraoxysms of coughing – patient susceptible for pulmonary Complication.
30 BED SIDE TEST5) FORCED EXPIRATORY TIME: After deep breath, exhale maximally and forcefully & keep stethoscope over trachea & listen. N FET – 3-5 SECS. OBS.LUNG DIS. - > 6 SEC RES. LUNG DIS.- < 3 SEC
31 BED SIDE PFT6) WRIGHT PEAK FLOW METER: Measures PEFR (Peak Expiratory Flow Rate) N – MALES L/MIN. FEMALES L/MIN. <200 L/ MIN. – INADEQUATE COUGH EFFICIENCY. 7) DEBONO WHISTLE BLOWING TEST: MEASURES PEFR. Patient blows down a wide bore tube at the end of which is a whistle, on the side is a hole with adjustable knob. As subject blows → whistle blows, leak hole is gradually increased till the intensity of whistle disappears. At the last position at which the whistle can be blown , the PEFR can be read off the scale.
32 MEASUREMENT OF TV & MV8)Wright respirometer : measures tv, mv (15 secs times 4)Simple and rapidInstrument- compact, light and portable.Disadvantage: It under- reads at low flow rates and over- reads at high flow rates.Can be connected to endotracheal tube or face maskPrior explanation to patients needed.Ideally done in sitting pos.MV- instrument record for 1 min. And read directlyTV-calculated and dividing MV by counting Respiratory Rate.Accurate measurement in the range of l/min.(±10%)USES: 1)BED SIDE PFT2) ICU – WEANIG PTS. FROM Ventilation.
36 CATEGORIZATION OF PFT 2) GAS- EXCHANGE TESTS: A) Alveolar-arterial po2 gradientB) Diffusion capacityC) Gas distribution tests- single breathN2 test.- Multiple Breath N2 test- Helium dilution method.- Radio Xe scinitigram.D) ventilation – perfusion testsA) ABGB) single breath CO2 elimination testC) Shunt equation
37 CATEGORIZATION OF PFT 3) CARDIOPULMONARY INTERACTION: A) Qualitative tests:- History , examination- Abg- Stair climbing testB) Quantitative tests- 6 min. Walk test (gold standard)
38 STATIC LUNG VOLUMES AND CAPACITIES SPIROMETRY : CORNERSTONE OF ALL PFTs.John hutchinson – invented spirometer.“Spirometry is a medical test that measures the volume of air an individual inhales or exhales as a function of time.”Measures VC, FVC, FEV1, PEFR.CAN’T MEASURE – FRC, RV, TLC.
39 PREREQUISITIES Prior explanation to the patient Not to smoke /inhale bronchodilators 6 hrs prior or oral bronchodilators 12hrs prior.Remove any tight clothings/ waist belt/ denturesPt. Seated comfortablyIf obese, child < 12 yrs- standing
40 PREREQUISITES Nose clip to close nostrils. Exp. Effort shld last ≥ 4 secs.Should not be interfered by coughing, glottic closure, mechanical obstruction.3 acceptable tracings taken & largest value is used.
41 SPIROMETERDouble walled cylinder with water to maintain water tight sealInverted bell (9 l) attached to pulley which carries a counterweight and pen – moves up and down as volume of bell changesBREATHING ASSEMBLY i.E. Unidirectional breathing valves with mouth piece.
42 Flow-Volume Curves and Spirograms Two ways to record results of FVC maneuver:Flow-volume curve---flow meter measures flow rate in L/s upon exhalation; flow plotted as function of volumeClassic spirogram---volume as a function of time
44 Spirometry Interpretation: So what constitutes normal? Normal values vary and depend on:HeightAgeGenderEthnicityHeight varies directly with vcVC increases with age up to age 20 years then becomes inversely proportion to ageWomen usually with lower vc than men
45 Acceptable and Unacceptable Spirograms (from ATS, 1994)
46 Measurements Obtained from the FVC Curve FEV1---the volume exhaled during the first second of the FVC maneuverFEF 25-75%---the mean expiratory flow during the middle half of the FVC maneuver; reflects flow through the small (<2 mm in diameter) airwaysFEV1/FVC---the ratio of FEV1 to FVC X 100 (expressed as a percent); an important value because a reduction of this ratio from expected values is specific for obstructive rather than restrictive diseases
47 Spirometry Interpretation: Obstructive vs. Restrictive Defect Obstructive DisordersCharacterized by a limitation of expiratory airflow so that airways cannot empty as rapidly compared to normal (such as through narrowed airways from bronchospasm, inflammation, etc.)Examples:AsthmaEmphysemaCystic FibrosisRestrictive DisordersCharacterized by reduced lung volumes/decreased lung complianceExamples:Interstitial FibrosisScoliosisObesityLung ResectionNeuromuscular diseasesCystic Fibrosis
48 Normal vs. Obstructive vs. Restrictive (Hyatt, 2003)
49 Spirometry Interpretation: Obstructive vs. Restrictive Defect Obstructive DisordersFVC nl or↓FEV1 ↓FEF25-75% ↓FEV1/FVC ↓TLC nl or ↑Restrictive DisordersFVC ↓FEV1 ↓FEF 25-75% nl to ↓FEV1/FVC nl to ↑TLC ↓
50 Spirometry Interpretation: What do the numbers mean? FVCInterpretation of % predicted:80-120% Normal70-79% Mild reduction50%-69% Moderate reduction<50% Severe reductionFEV1Interpretation of % predicted:>75% Normal60%-75% Mild obstruction50-59% Moderate obstruction<49% Severe obstruction<25 y.o. add 5% and >60 y.o. subtract 5
51 Spirometry Interpretation: What do the numbers mean? FEF 25-75%Interpretation of % predicted:>79% Normal60-79% Mild obstruction40-59% Moderate obstruction<40% Severe obstructionFEV1/FVCInterpretation of absolute value:80 or higher Normal79 or lower Abnormal
52 What about lung volumes and obstructive and restrictive disease? (From Ruppel, 2003)
53 MEASUREMENTS OF VOLUMES TLC, RV, FRC – MEASURED USINGNitrogen washout methodInert gas (helium) dilution methodTotal body plethysmography
54 CONTINUED……….. 1) HELIUM DILUTION METHOD: Patient breathes in and out of a spirometer filled with 10% helium and 90% o2, till conc. In spirometer and lung becomes same (equilibirium).As no helium is lost; (as he is insoluble in blood)C1 X V1 = C2 ( V1 + V2)V2 = V1 ( C1 – C2)C2V1= VOL. OF SPIROMETERV2= FRCC1= Conc.of He in the spirometer before equilibriumC2 = Conc, of He in the spirometer after equilibrium
55 CONTINUED……… 2) TOTAL BODY PLETHYSMOGRAPHY: Subject sits in an air tight box. At the end of normal exhalation – shuttle of mouthpiece closed and pt. is asked to make resp. efforts. As subject inhales – expands gas volume in the lung so lung vol. increases and box pressure rises and box vol. decreases.BOYLE’S LAW:PV = CONSTANT (at constant temp.)For Box – p1v1 = p2 (v1- ∆v)For Subject – p3 x v2 =p4 (v2 - ∆v)P1- initial box pr. P2- final box pr.V1- initial box vol. ∆ v- change in box vol.P3- initial mouth pr., p4- final mouth pr.V2- FRC
56 CONTINUED……… DIFFERENCE BETWEEN THE TWO METHODS: In healthy people there is very little difference.Gas dilution technique measures only the communicating gas volume.Thus,Gas trapped behind closed airwaysGas in pneumothorax=> are not measured by gas dilution technique, but measured by body plethysmograph
57 CONTINUED……… 3) N2 WASH OUT METHOD: Following a maximal expiration (RV) or normal expiration (FRC), Pt. inspires 100% O2 and then expires it into spirometer ( free of N2) → over next few minutes (usually 6-7 min.), till all the N2 is washed out of the lungs. N2 conc. of spirometer is calculated followed by total vol.of AIR exhaled. As air has 80% N2 → so actual FRC/RV is calculated.E.g. Total vol. collected = 50 L (as N2 makes 80% of FRC onroom air)Measured N2 = 5%vol. of N2 in bag = 50 x .05 = 2.5L2.5 L = X L.80 FRC FRCX = l (THIS IS PT’S FRC)
58 PROBLEMS WITH N2 WASH OUT METHOD Atelectasis may result from washout of nitrogen from poorly ventilated lung zones (obstructed areas)Elimination of hypoxic drive in CO2 retainers is possibleUnderestimates FRC due to underventilation of areas with trapped gas
59 MEASUREMENT OF DYNAMIC LUNG VOLUMES FEF25–75% = forced expiratory flow during expiration of 25 to 75% of the FVC; FEV1 = forced expiratory volume in the first second of forced vital capacity maneuver; FVC = forced vital capacity (the maximum amount of air forcibly expired after maximum inspiration).TIMED EXPIRED SPIROGRAMS
60 FORCED VITAL CAPACITY (FVC) Max vol. Of air which can be expired out as forcefully and rapidly as possible, following a maximal inspiration to TLC.Exhaled volume is recorded with respect to time.Indirectly reflects flow resistance property of airways.Normal healthy subjects have VC = FVC.Prior instruction to patients, practice attempts as it needs patient cooperation and effect.Exhalation should take at least 4 sec and should not be interrupted by cough, glottic closure or mechanical obstruction.
61 FORCED VITAL CAPACITY IN 1 SEC. (FEV1) Forced expired vol. In 1 sec during fvc maneuver.Expressed as an absolute value or % of fvc.N- FEV1 (1 SEC) % OF FVCFEV2 (2 SEC)- 94% OF FVCFEV3 (3 SEC)- 97% OF FVC
62 CONTINUED…… CLINICAL RANGE (FEV1) PATIENT GROUP 3 - 4.5 L 1.5 – 2.5 L NORMAL ADULTMILD – MOD.OBSTRUCTIONHANDICAPPEDDISABILITYSEVERE EMPHYSEMA
63 CONTINUED……FEV1 – Decreased in both obstructive & restrictive lung disorders. FEV1/FVC – Reduced in obstructive disorders. NORMAL VALUE IS 75 – 85 % (FEV1/FVC) < 70% OF PREDICTED VALUE – MILD OBST. < 60% OF PREDICTED VALUE – MODERATE OBST. < 50% OF PREDICTED VALUE – SEVERE OBST.
64 CONTINUED…… DISEASE STATES FVC FEV1 FEV1/FVC OBSTRUCTIVE NORMAL ↓ 2) STIFF LUNGS3 ) RESP. MUSCLE WEAKNESS
65 PEAK EXPIRATORY FLOW RATE (PEFR) It is the max. Flow rate during fvc maneuver in the initial 0.1 sec.-PEFR DETERMINED BY : 1) Function of caliber of airways2) Expiratory muscle strength3) Pt’s coordination & effort- Estimated by 1) drawing a tangent to steepest part of FVC spirogram (error prone)2) average flow during the litre of gas expired after initial 200 ml during fvc maneuver..
66 Normal value in young adults (<40 yrs)= 500l/min Measured with pneumotachograph / Wright peak flow meterWright peak flow meter - valuable tool in identifying gross pulmonary Disability at bedside.-Less unpleasant & lessExhaustiveClinical significance - values of <200/l- impaired coughing & hence likelihood of post-op complication
67 FORCED MID-EXPIRATORY FLOW RATE (FEF25%-75%): Maximum Mid expiratory Flow rateMax. Flow rate during the mid-expiratory part of FVC maneuver.Effort independentMisnomer, as FEF25-75% decreased by1) marked reduction in exp. Effort2)submaximal inspiration b4 maneuver → ↓FVC → ↓ FEF25-75%It may decrease with truly max. Effort as compared to slightly submaximal effort as dynamic airway compression occurs with maximal effort.N value – l/sec. Or 300 l/min.Upto 2l/sec- acceptable.CLINICAL SIGNIFICANCE: SENSITIVE & IST INDICATOR OF OBSTRUCTION OF SMALL DISTAL AIRWAYS
68 MAXIMUM BREATHING CAPACITY: (MBC/MVV) MAX. VOLUNTARY VENTILATIONLargest volume that can be breathed per minute by voluntary effort , as hard & as fast as possible.N – l/min.Estimate of max. Ventilation available to meet increased physiological demand.Measured for 12 secs – extrapolated for 1 min.MVV = FEV1 X 35
70 RESPIRATORY MUSCLE STRENGTH Evaluated by measuring max. Static resp. Pressure with anaeroid gaugePressures are generated against occluded airway during a max. Forced insp/exp. EffortMAX STATIC INSP. PRESSURE: (PIMAX)-Measured when inspiratory muscles are at their optimal length i.e. at RVPI MAX = -125 CM H2OCLINICAL SIGNIFICANCE:IF PI MAX< 25 CM H2O – Inability to take deep breath.
71 CONTINUED……. MAX. STATIC EXPIRATORY PRESSURE (PEMAX): Measured after full inspiration to TLCN VALUE OF PEMAX IS =200 CM H20PEMAX < +40 CM H20 – Impaired cough abilityParticularly useful in pts with NM Disorders during weaning
72 PHYSIOLOGICAL DETERMINANTS OF MAX. FLOW RATES 1)DEGREE OF EFFORT- driving pressure generated by muscle contraction (PEmax & PI max)ELASTIC RECOIL PRESSURE OF LUNG: (PL)Tendency to recoil or collapse d/t PLPL increases from RV (2-3) to TLC (20-30)Opposed by Pcw (recoil pr. Of chest wall)Prs=Pl + Pcw = 0 at FRC-resting state(Prs-recoil pr.of resp.system)3) AIRWAY RESISTANCE: (Raw):Determined by the calibre of airwaysDecreases as lung vol increases (hyperbolic curve)Raw high at RV & low at TLC
73 Continued…… DISEASE MSL. STRENGTH Raw PL N-M WEAKNESS ↓ N EMPHYSEMA ASTHMA/BRONCHITIS↑PERIPHERAL AIRWAY DIS.
74 MEASUREMENT OF AIRWAY RESISTANCE 1) Raw- Body plethysmography2) Forced expiratory maneuvers:Peak expiratory flow (PEF)FEV13) Response to bronchodialtors (FEV1)
75 Spirometry Pre and Post Bronchodilator Obtain a flow-volume loop.Administer a bronchodilator.Obtain the flow-volume loop again a minimum of 15 minutes after administration of the bronchodilator.Calculate percent change (FEV1 most commonly used---so % change FEV 1= [(FEV1 Post-FEV1 Pre)/FEV1 Pre] X 100).Reversibility is with 12% or greater change.
76 AIRWAY PARTITIONING AND BEHAVIOUUR UPPER (EXTRATHORACIC)Surrounding soft tissue unsupportingCollapses during inspirationExpands during expirationINTRATHORACICOuter surface exposed to pleural pressureExpands during inspirationCollapses during expirationDISTAL (PULMONARY)Intimately related to lung tissueCollapses as expiration proceeds
77 FLOW VOLUME LOOPSDo FVC maneuver and then inhale as rapidly and as much as able.This makes an inspiratory curve.The expiratory and inspiratory flow volume curves put together make a flow volume loop.
79 How is a flow-volume loop helpful? Helpful in evaluation of air flow limitation on inspiration and expirationIn addition to obstructive and restrictive patterns, flow-volume loops can show provide information on upper airway obstruction:Fixed obstruction: constant airflow limitation on inspiration and expiration—such as in tumor, tracheal stenosisVariable extrathoracic obstruction: limitation of inspiratory flow, flattened inspiratory loop—such as in vocal cord dysfunctionVariable intrathoracic obstruction: flattening of expiratory limb; as in malignancy or tracheomalacia
80 TESTS FOR GAS EXCHANGE FUNCTION 1) ALVEOLAR-ARTERIAL O2 TENSION GRADIENT:Sensitive indicator of detecting regional V/Q inequalityN value in young adult at room air = 8 mmhg to upto 25 mmhg in 8th decade (d/t decrease in PaO2)AbN high values at room air is seen in asymptomatic smokers & chr. Bronchitis (min. symptoms)PAO2 = PIO2 – PaCo2R
81 CONTINUED…….. 2) DYSPNEA DIFFENRENTIATION INDEX (DDI): To d/f dyspnea due to resp/ cardiac d’sDDI = PEFR x PaCO21000DDI- Lower in resp. pathology
82 CONTINUED……3) DIFFUSING CAPACITY OF LUNG: defined as the rate at which gas enters into bld. divided by its driving pr. DRIVING PR: gradient b/w alveoli & end capillary tensions. Fick’s law of diffusion : Vgas = A x D x (P1-P2) T D= diffusion coeff= solubility √MW
83 CONTINUED……. DL IS MEASURED BY USING CO, COZ: High affinity for Hb which is approx. 200 times that of O2 , so does not rapidly build up in plasmaUnder N condition it has low bld conc ≈ 0Therefore, pulm conc.≈0
84 SINGLE BREATH TEST USING CO Pt inspires a dilute mixture of CO and hold the breath for 10 secs.CO taken up is determined by infrared analysis:DlCO = CO ml/min/mmhgPACO – PcCON range ml/min./mmhg.DLO2 = DLCO x 1.23
85 Emphysema, lung resection, pul. Embolism, anaemia DLCO decreases in-Emphysema, lung resection, pul. Embolism, anaemiaPulmonary fibrosis, sarcoidosis- increased thicknessDLCO increases in:(Cond. Which increase pulm, bld flow)Supine positionExerciseObesityL-R shunt
86 TESTS FOR CARDIOPLULMONARY INTERACTIONS Reflects gas exchange, ventilation, tissue O2, CO.QUALITATIVE- history, exam, ABG, stair climbing testQUANTITATIVE- 6 minute walk test
87 CONTINUED……. 1) STAIR CLIMBING TEST: 2) 6 MINUTE WALK TEST: If able to climb 3 flights of stairs without stopping/dypnoea at his/her own pace- ↓ed morbidity & mortalityIf not able to climb 2 flights – high risk2) 6 MINUTE WALK TEST:Gold standardC.P. reserve is measured by estimating max. O2 uptake during exerciseModified if pt. can’t walk – bicycle/ arm exercisesIf pt. is able to walk for >2000 feet during 6 min pd,VO2 max > 15 ml/kg/minIf 1080 feet in 1 min : VO2 of 12ml/kg/minSimultaneously oximetry is done & if Spo2 falls >4%- high risk
88 EVALUATION OF PT. FOR LUNG RESECTION GOALS:1) to identify pts at risk of increased post-op morbidity & mortality2) to identify pts who need short-term or long term post-op ventilatory support.Lung resection may be f/by – inadequate gas exchange, pulm HTN & incapacitating dyspnoea.
89 CONTINUED…..Removal of entire lung is likely to be tolerated if pre-op pulm function meets the following criteria:A) FEV1 > 2 L or FEV1/FVC of atleast 50%B) MVV > 50% of predicted valueC) RV/ TLC < 50%If any of these criteria is not full filled – go for more invasive & sophisticated, split lung function tests.
90 CONTINUED……A predicted post op FEV1 Of atleast 800ml is required to perform pneumonectomyIf not- risk of significant resting CO2 retention & dyspnoea is high.IF Sx inevitable – invasive tests : Pulmonary artery occlusion testIf after occlusion of pulm artery of segment to be resected is not followed by pulm Htn ( mean pulm art pr > 35 mmhg) AND hypoxemia(PaO2 <45 mmhg) – Assure that remaining lung can accommodate entire C.O.