Pulmonary Function Measurements Chapter 5

VOLUMES AND CAPACITIES TLC RV Vt VC IC IRV FRC ERV

Terminolgy 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 Results to determine disease FVC is best test to determine Restrictive disease Restrictive = Loss of volume

Examples PredictedActual FVC 4.75L 2.8L FEV1 4.06L/sec 2.65L/sec PredictedActual FVC 4.99L 3.48L FEV1 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 Fibrosis Bronchitis Asthma Bronchiectasis Emphysema

Terminology Resistance Elastance Compliance

LUNG AND CHEST MECHANICS RESISTANCE (Raw) AIRWAY RESISTANCE Normal Raw= cmH 2 O/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 (C L) OR C

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