Pulmonary Function Measurements

Chapter 5

VOLUMES AND CAPACITIES

• TLC• RV• Vt• VC• IC• IRV• FRC• ERV

Term in o lgy

• TLC- (DOES NOT MEAN TENDER LOVING CARE !!)- IS THE AMOUNT OF GAS THE LUNG CONTAINS AFTER A MAXIMAL INSPIRATORY EFFORT. ALL OTHER LUNG VOLUMES ARE A NATURAL SUBDIVISION OF THE TLC (page 50)

• RV- RESIDUAL VOLUME- AMOUNT OF GAS THAT CANNOT BE EXHALED EVEN WITH THE GREATEST EXPIRATORY EFFORT

• THE RIGID RIB CAGE PREVENTS TOTAL LUNG DEFLATION. RV MUST BE MEASURED INDIRECTLY THROUGH OTHER TECHNIQUES

• Vt- TIDAL VOLUME- THE AMOUNT OF AIR INHALED AND EXHALED WITH EACH BREATH

• VC- VITAL CAPACITY- THE MAXIMUM LIMITS OF A SINGLE BREATH. MAXIMUM INHALATION WITH MAXIMUM EXHALATION

• IC- INSPIRATORY CAPACITY- THE AMOUNT OF MAXIMUM GAS POSSIBLE ON INHALATION AFTER A NORMAL TIDAL VOLUME

• FRC- FUNCTIONAL RESIDUAL CAPACITY- THE AMOUNT OF AIR IN THE LUNGS AT THE POINT OF VENTILATORY MUSCLE RELAXATION, ALSO KNOWN AS THE RESTING LEVEL, OR END-TIDAL EXHALATION LEVEL. ABDOMINAL MUSCLE CONTRACTION IS REQUIRED TO EXHALE ANY PORTION OF THE FRC.

• ERV- EXPIRATORY RESERVE VOLUME- THE TOTAL PORTION OF THE FRC THAT CAN BE ACTIVELY EXHALED. ( THE REMAINDER, RV, NEEDS A SPECIAL CALCULATION TO BE MEASURED)

• MIP/MEP- MAXIMUM INSPIRATORY PRESSURE/ MAXIMUM EXPIRATORY PRESSURE- THESE PRESSURE ARE MEASURED UNDER STATIC CONDITIONS WHILE A PATIENT INHALES OR EXHALES WITH MAXIMUM EFFORT AGAISNT AN OCCLUDED TUBE ATTACHED TO A PRESSURE GAUGE. MIP IS GREATEST AT RV (MUSCLES ARE MAXIMALLY LENGTHENED)

• MEP IS GREATES AT TLC (EXPIRATORY MUSCLES ARE MAXIMALLY CONTRACTED)

SVC vs FVC

• FVC

• The first second of the FVC = FEV1

Predicted and Actual Resultsto determine disease

• FVC is best test to determine Restrictive disease

• Restrictive = Loss of volume

ExamplesPredicted Actual

FVC 4.75L 2.8LFEV1 4.06L/sec 2.65L/sec

Predicted ActualFVC 4.99L 3.48LFEV1 4.2L/sec 2.1L/sec

Factors that can hinder air in the lungs

Airway Resistance (Loss of lung volume) Parenchymal Disease

“CBABE” (Flow is slow) Airway Disease

Cystic FibrosisBronchitisAsthmaBronchiectasisEmphysema

Terminology

• Resistance• Elastance• Compliance

LUNG AND CHEST MECHANICS

•RESISTANCE (Raw) AIRWAY RESISTANCE

Normal Raw= .5-1.5 cmH2O/L/sec•P. 63 BEACHEY•Clinically – accepted <2.0 cmH2O/L/sec•Obstructive Diseases have increased Resistance

Airway vs. Lung Parenchyma

•Airway Resistance = Obstruction

Elastance

•The lung parenchyma

•Stiff

•Strong Recoil

•AKA Elastic Resistance

•How compliant are the airways?

•How compliant is the lung parenchyma/alveoli?

•Airway Compliance = degree of obstruction

•“Lung” Compliance = degree of recoiling

Compliance

COMPLIANCE•LUNG COMPLIANCE (CL)

OR C

•

Static Pressure-Volume Relationships

Static Pressure-Volume Relationships

Terminology

• Resistance– Airway Obstruction

• Elastance– Recoiling– Restrictive Patients have High elastance; high recoiling.

“Stiff Lung”• Compliance

– “Lung Compliance” refers to Parenchyma. Restrictive disease = low lung compliance

– “Airway Compliance” refers to airways Obstructive disease = low airway compliance

Putting it together

Obstructive• High airway resistance • Low airway compliance

Restrictive• High airway elastance • Low lung compliance

Why is it difficult to inflate a restrictive lung?

• Alveolar Damage

• Alveoli produced surfactant

• Surfactant reduces surface tension

• Reduced Surface Tension allows alveoli to say open

SURFACE TENSION

•WATER

•ALVEOLI

•CRITICAL •PRESSURES

SURFACTANT

•COMPOSITION

•PURPOSE