OBSTRUCTIVE AND RESTRICTIVE OF LUNG

DISEASE

HAMAD EMAD H. DHUHAYR

VALUES MEANING DESCRIPTION INTERPETITION

VC Vital Capacity Volume of air displaced by maximal exhalation or maximal inhalation maneuver Typically preserved in obstruction, but reduced in restriction.

FVC Forced vital capacity Volume forcefully exhaled from maximal inhalation (TLC) to maximal exhalation (RV), the FEVC maneuver 

Pattern similar to VC, although more likely to be reduced in obstruction than VC. Used to grade severity of restriction.

FEV1 Forced expiratory volume in one second

Volume exhaled in 1st second of FEVC maneuver Reduction typical of medium to large airways obstruction. Used to grade severity of obstruction

FEV1/FVC   Ratio of FEV1 to FVC Reductions indicative of airway obstruction

FEF25–75 Forced expiratory flow (25–75%) Mean expiratory flow rate in the middle half of FEVCmaneuver

Sensitive but nonspecific indicator of small airways obstruction. Poorly reproducible, varies with effort and time of expiration.

MVV Maximum voluntary ventilation Estimate of one minute’s maximal air displacement extrapolated from repeated inspiratory and expiratory efforts

Disproportionate reductions relative to FEV1 may indicate upper airways obstruction, muscle weakness, or poor performance.

PEF Peak expiratory flow Maximal sustained airflow achieved during the FEVCmaneuver

Worsening may correlate with asthma exacerbations. Sometimes helpful in assessing subject effort.

OBSTRUCTIVE AND RESTRICTIVE DISEASES:

OVERVIEW

• THE MAXIMUM INSPIRATORY FORCE: IS LIMITED AT TOTAL LUNG CAPACITY THAT CAN BE APPLIED BY THE INTERCOSTAL MUSCLES AND DIAPHRAGM

• IS OPPOSED EQUALLY BY:

THE INCREASING RECOIL FORCE OF THE LUNGS AS THEY ARE DISTENDED TO HIGHER VOLUMES

• SO, TLC IS LIMITED PRIMARILY BY THE ELASTIC PROPERTIES OF THE LUNGS, BECAUSE VARIATIONS IN MUSCLE STRENGTH HAVE ONLY A SMALL EFFECT ON TOTAL CHEST EXPANSION UNTIL WEAKNESS BECOMES QUITE MARKED.

• FACTORS THAT AFFECT TLS:

 

• 1-PARENCHYMAL RESTRICTIVE DISEASES REDUCE LUNG COMPLIANCE, SO GREATER DISTENDING PRESSURE IS REQUIRED TO ACHIEVE ANY VOLUME CHANGE AND, EVENTUALLY, LOWER TLC.

 

• 2-THE DISPLACEMENT OF INTRATHORACIC GAS VOLUME BY EFFUSIONS, EDEMA, INTRAVASCULAR VOLUME, AND INFLAMMATORY CELLS ALSO CONTRIBUTES TO A REDUCTION IN MEASURED LUNG GAS VOLUMES.

• * EXCEPT FOR PLEURAL EFFUSIONS, THESE QUANTITIES ARE RELATIVELY SMALL AND ARE OUTWEIGHED BY THE FREQUENTLY ASSOCIATED CHANGES IN LUNG ELASTIC PROPERTIES. THE MINIMUM LUNG VOLUME, OR RV, IS DETERMINED BY A COMBINATION OF TWO FACTORS. THE FIRST IS THE AMOUNT OF SQUEEZE THE CHEST WALL AND ABDOMINAL

• RESTRICTIVE DISEASE

RESTRICTIVE LUNG DISEASES ARE: THE DISEASES THAT CAUSE A SIGNIFICANT DECREASE IN TLC. 

• THE CHARACTERISTIC OF R.D: 

• 1- PARALLEL DECREMENTS IN FRC, RV, AND VC, ALTHOUGH A REDUCTION IN ONLY RV MAY BE SEEN IN EARLY STAGES OF DISEASE.

• 2- INCREASED TISSUE RECOIL DELAYS AIRWAY CLOSURE.  

• *OBESITY SHOWS A DIFFERENT PATTERN, IN THAT THE PRIMARY EFFECT IS ON THE RELAXED END-EXPIRATORY VOLUME OR FRC.

WHY??

THE LARGE ABDOMEN AND HEAVY CHEST WALL REDUCE THE OUTWARD RECOIL OF THE THORACIC CAGE, WHICH OPPOSES THE INWARD RECOIL OF THE LUNG PARENCHYMA AND MAINTAINS NORMAL FRC.  

• HOWEVER, RV IS DETERMINED BY AIRWAY CLOSURE AND IS LITTLE AFFECTED, AND THE TLC ACHIEVABLE BY USE OF MAXIMUM INSPIRATORY FORCE IS ONLY MINIMALLY REDUCED UNTIL OBESITY BECOMES EXTREME.  

OBSTRUCTIVE DISEASE

• OBSTRUCTIVE DISEASES CAUSE AIRWAY CLOSURE THAT STOPS EXHALATION AT A HIGHER LUNG VOLUME BECAUSE OF THE COMBINED EFFECTS OF AIRWAY INFLAMMATION AND LOSS OF TISSUE RECOIL ON LUMINAL CALIBER.

• THE CHARACTERISTIC OF R.D:

1- A PROGRESSIVE INCREASE IN RV, BECAUSE INCREASING AMOUNTS OF GAS ARE TRAPPED BEHIND CLOSED AIRWAYS.

2-THESE PATIENTS BREATHE AT AN INCREASED FRC

3- A DECREASE IN LUNG RECOIL FORCE FROM EMPHYSEMA

4- INCREASE LUMINAL CALIBER TO MINIMIZE THE RESISTIVE WORK OF AIRFLOW.

• ** THE TLC IS NORMAL TO HIGH, WHICH AGAIN REFLECTS THE LOSS OF LUNG RECOIL FORCES. BECAUSE RV INCREASES TO A GREATER EXTENT THAN DOES TLC, THE VC DECREASES WITH SEVERE AIRWAY OBSTRUCTION.