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Pulmonary Function Measurements

Pulmonary Function Measurements. CHAPTER 5 DR. CARLOS ORTIZ BIO-208. PULMONARY FUNCTION.

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Pulmonary Function Measurements

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  1. Pulmonary Function Measurements CHAPTER 5 DR. CARLOS ORTIZ BIO-208

  2. PULMONARY FUNCTION • PULMONARY FUNCTION REFERS TO THE ROLE OF THE LUNGS IN GAS EXCHANGE. TESTING PULMONARY FUNCTION IS A PRACTICAL APPLICATION OF RESPIRATORY PHYSIOLOGY AND NECESSARY FOR UNDERSTANDING ABNORMAL LUNG FUNCTION AND THE EFFECTS OF TREATMENT. • TESTS OF HEALTHY HUMANS HAVE IDENTIFIED FACTOR SUCH AS AGE, GENDER, HEIGHT, AND BODY SIZE PRODUCING NORMAL VARIATIONS IN LUNG FUNCTION. • PFT HELP DETERMINE THE SEVERITY OF FUNCTIONAL IMPAIRMENTS AND THE EXTENT TO WHICH TREATMENT RESTORES NORMAL FUNCTION. • ALTHOUGH PFT ARE DIAGNOSTIC, THEY ARE RARELY THE KEY FACTOR IN A DEFINITIVE DIAGNOSIS. • PFT REFLECT THE COMBINED FUNCTION OF THE AIRWAYS, ALVEOLAR CAPILLARY MEMBRANE, RESPIRATORY MUSCLES , AND NEURAL CONTROL MECHANISMS.

  3. STATIC LUNG VOLUMES • NORMAL VALUES AND INTERRELATIONSHIPS AMONG VOLUMES AND CAPACITIES ARE ILLUSTRATED IN THE FOLLOWING FIGURE. • NORMAL VALUES ARE PREDICTED FOR AN INDIVIDUAL BASED ON THESE PHYSICAL CHARACTERISTICS. FUNCTION IS GENERALLY CLASSIFIED AS NORMAL IF VALUES ARE WITHIN 20% OF THE PREDICTED VALUE (i.e., 80% TO 120 % OF THE PREDICTED VALUE)

  4. THEORETICAL BASIS FOR MEASUREMENT • BECAUSE THE RV CANNOT BE EXHALED, NEITHER IT NOR THE FRC, OR TLC, CAN BE MEASURED DIRECTLY WITH A SPIROMETER. THERE ARE INDIRECT TECHNIQUES TO MEASURE THESE LUNG VOLUMES • 1- HELIUM DILUTION • 2- NITROGEN WASHOUT • 3- BODY PLETHYSMOGRAPHY • ALL LUNG VOLUMES AND CAPACITIES MUST BE REPORTED UNDER BTPS CONDITIONS. VOLUMES MEASURED BY SPIROMETERS ARE AT ATPS CONDITIONS AND MUST BE ADJUSTED FOR THE TEMPERATURE DIFFERENCE. THIS ATPS TO BTPS ADJUSTMENT CAN INCREASE VOLUMES 5% TO 10%. • THESE TESTS ARE STARTED AT THE END OF A NORMAL EXPIRATION ( i.e., THE FRC LEVEL). • AS SHOWN IN THE PREVIOUS FIGURE, AFTER FRC IS DETERMINED, SPIROMETRIC MEASUREMENT OF THE ERV ALLOWS THE RV TO BE CALCULATED (RV= FRC - ERV)

  5. SIGNIFICANCE OF CHANGES IN FRC AND RV • CHANGES IN LUNG RECOIL AFFECT FRC BECAUSE FRC IS DETERMINED BY THE BALANCE POINT BETWEEN LUNG AND THORACIC RECOIL FORCES. • AN ABNORMALLY INCREASED FRC REPRESENT HYPERINFLATION, WHICH MAY BE CAUSED BY A LOSS OF ELASTIC RECOIL (NOT REVERSIBLE) OR PARTIAL AIRWAY OBSTRUCTION( REVERSIBLE). • FRC AND RV USUALLY INCREASE TOGETHER, REDUCING THE IC AND VC. • DISEASES INCREASING FRC AND RV ARE GENERALLY CLASSIFIED AS OBSTRUCTIVE. AN EXCEPTION IS NEUROMUSCULAR DISEASE IN WHICH FRC IS NORMAL BUT RV IS INCREASED BECAUSE OF WEAK EXPIRATORY MUSCLES. A WEAK, FORCED EXHALATION REDUCES THE ERV, INCREASING THE RV.

  6. SIGNIFICANCE OF CHANGES IN FRC AND RV • PULMONARY OF EXTRAPULMONARY FACTORS MAY DECREASE RV AND FRC. • FIBROTIC LUNG DISEASES INCREASE LUNG ELASTIC RECOIL, SHRINKING ALL VOLUMES AND CAPACITIES. INCREASED ALVEOLAR-CAPILLARY MEMBRANE PERMEABILITY, CHARACTERISTIC OF ARDS, DISRUPTS SURFACTANT SYNTHESIS AND INCREASES ALVEOLAR SURFACE TENSION. THIS DECREASES FRC AND RV BY CAUSING WIDESPREAD ALVEOLAR COLLAPSE. • EXTRAPULMONARY RESTRICTION OF LUNG EXPANSION BY SKELETAL DEFORMATIES ALSO REDUCES ALL LUNG VOLUMES AND CAPACITIES. REGARDLESS OF THE MACHANISMS INVOLVED,REDUCED FRC AND HIGH LUNG RECOIL INCREASE THE WORK OF BREATHING. DISEASES DECREASING FRC AND RV ARE GENERALLY CLASSIFIED AS RESTRICTIVE

  7. SIGNIFICANCE OF CHANGES IN FRC AND RV • IN OBSTRUCTIVE DISEASE THE TLC IS OFTEN NORMAL, OR IT MAY BE MODERATELY INCREASED IN SEVERE EMPHYSEMA. • THE MAJOR FEATURE OF OBSTRUCTIVE DISEASE IS A REDUCED MAXIMAL EXPIRATORY FLOW RATE. • THE MAJOR FEATURE IN RESTRICTIVE DISEASE ARE REDUCED LUNG VOLUMES AND CAPACITIES. THIS REDUCTION IS NORMALLY ACCOMPANIED BY NORMAL EXPIRATORY FLOW RATES. • NEUROMUSCULAR DISEASES ARE UNIQUE IN THAT THEY ARE CLASSIFIED AS RESTRICTIVE, ALTHOUGH LUNG AND THORACIC COMPLIANCE MAY BE NORMAL.HOWEVER THEY PRESENT A RESTRICTIVE PULMONARY FUNCTION PATTERN BECAUSE MUSCLE WEAKNESS LIMITS INSPIRATORY AND EXPIRATORY VOLUMES.

  8. SIGNIFICANCE OF CHANGES IN FRC AND RV • THE NORMAL RV/TLC RATIO IS 20% TO 25% IN HEALTHY ADULTS UP TO AGE 49. • IN PEOPLE OVER 50 YEARS OF AGE THE RV-TLC RATIO MAY RANGE AS HIGH AS 35%, REFLECTING A NORMAL LOSS OF ELASTIC RECOIL WITH AGING. • ABNORMALLY INCREASED RV/TLC RATIOS GENERALLY INDICATE HYPERVENTILATION, ALTHOUGH RV/TLC MAY BE INCREASED IN SOME RESTRICTIVE DISEASES IN WHICH THE VC (AND THUS THE TLC) IS REDUCED MORE THAN THE RV.

  9. DINAMIC PULMONARY MECHANICS MEASUREMENTS • DYNAMIC MEASUREMENTS REFLECT THE ABILITY OF THE LUNGS TO MOVE AIR RAPIDLY, ALLOWING THE DETECTION OF AIRWAY OBSTRUCTION. • MEASURING PULMONARY MECHANICS MAINLY INVOLVES MEASURING EXPIRATORY FLOWS WITH RESPECT TO TIME OR VOLUME. • THE ABILITY TO GENERATE HIGH FLOW RATES DEPENDS ON MUSCULAR STRENGTH, AIRWAY PATENCY, AND NEUROMUSCULAR FUNCTION.

  10. VOLUME-TIME MEASUREMENTS • FORCED VITAL CAPACITY. • FVC MEASUREMENT REQUIRES THE PERSON TO EXHALE THE VC AS FORCEFULLY AND RAPIDLY AS POSSIBLE. • THE FVC IS THE MOST FREQUENTLY PERFORMED PFT BECAUSE IT PROVIDES MUCH INFORMATION ABOUT LARGE AND SMALL AIRWAY FUNCTION. • IT IS EFFORT-DEPENDENT TEST, REQUIRING THOROUGH PATIENT INSTRUCTION, UNDERSTANDING, AND MAXIMAL EFFORT. • VALIDITY IS ASSUMED IF THE PERSON CAN REPEAT THREE FVC MANEUVERS WITH A VARIATION NO GREATER THAN 5%. • SOME PEOPLE WITH AIRWAY OBSTRUCTION MAY HAVE A NORMAL FVC, BUT THE TIME REQUIRED TO EXHALE IT IS LONGER THAN NORMAL. NORMAL PEOPLE CAN EXHALE THE FVC IN 4 TO 6 SECONDS.

  11. MEASUREMENT OF FVC AND FEV1

  12. VOLUME-TIME MEASUREMENTS • FORCED EXPIRATORY VOLUMES. • MEASURING THE AMOUNT OF FVC THAT CAN BE EXHALED WITHIN A GIVEN TIME INTERVAL PROVIDES ADDITIONAL INFORMATION ABOUT AIRWAY OBSTRUCTION. • THE MOST COMMON ASSESSED FORCED EXPIRATORY VOLUME (FEV) INTERVAL IS THE FEV1, THE AMOUNT OF FVC EXHALED IN I SECOND. • PEOPLE WITH OBSTRUCTIVE DISEASE CAN NOT EXHALE MUCH OF THE FVC IN A GIVEN TIME PERIOD, REDUCING THE FEV1 . • THE FEV1 COMPARED WITH THE FVC (FEV1/FVC)IS IMPORTANT IN DIFFERENTIATING OBSTRUCTIVE AND RESTRICTIVE CAUSES OF LOW FEV1 . • THE FEV1 IS AN INDEX OF SEVERITY IN COPD. THE ABILITY TO WORK AND LIKELIHOOD OF DYING RESPIRATORY DISEASE ARE STATISTICALLY CORRELATED WITH THE FEV1 .

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