Objectives:



?Conduct spirometry tests and make calculations from raw test results.

?Interpret results in light of published norms.

?Basic spirometry and terminology

?Tidal volume (TV): volume of air inhaled or exhaled in one normal breath.

?Inspiratory reserve volume (IRV): maximal amount of air that can be inhaled following a normal inhalation.

?Expiratory reserve volume (ERV): maximal volume of air that can be exhaled following a normal exhalation.

?Inspiratory Capacity (IC): maximal amount of air a subject can inhale following a normal exhalation.

?Vital capacity (VC): maximal amount of air that a subject can exhale after a maximal inhalation.

?Volumes not easily measured with spirometer

?Residual volume (RV): volume of air remaining in lungs after maximal inhalation.

?Functional residual capacity (FRC): volume of air left in lungs after a normal exhalation.

?Total lung capacity (TLC): total volume of air the lungs can hold.

?Calculated forced volumes and flows

?Forced vital capacity (FVC): total volume of air expired after a maximal inhalation when the subject is attempting to exhale as rapidly and forcefully as possible. In healthy subject, FVC = SVC.

?Forced expiratory volume - one second (FEV1.0): the amount of air exhaled in the first one second of FVC maneuver.

?Forced expiratory flow from 25-75% (FEF25-75) or Maximal Mid-Expiratory Flow (MMEF): the flow rate during the middle 50% of the FVC maneuver (from 25% to 75% of expired volume).

?Maximal voluntary ventilation (MVV): the maximal amount of air that a person can breathe in or out in a short period of time - usually 10, 12, or 15 seconds.

Use of Data:

?Deviations from normal indicators of pulmonary disease

?Asthma - constriction - restricts flow

?Emphysema - destruction of alveoli and trapping of air - inability to rapidly exhale and increase in residual volume.

?Smoking and air pollution effects on lungs

?Residual volume important in body composition measurements.

?FEV, FEV1.0, best predictors of disease.

?FEV/FEV1.0 also used to detect disease

?MVV sometimes used to evaluate respiratory muscle weakness.

Pulmonary Function Issues Related to Measured Values:

?Overinflation of Lungs

?Emphysema - COPD - Permanently

?Asthma - Acutely

?? RV + Ratio RV/TLC

?FEV1/ FVC ratio falls below 80% - Also flow rates fall

? With age (lungs less compliant)

? Falls with obstructive diseases; e.g. asthma/bronchitis

?Asthma - obstructive disease ? increased collapsing force of large airways

? obstruction to expiratory flow ? lung volume

? bronchodilators may return flow to normal

?Early COPD - characterized by irreversible ? in small airway resistance that reduces expiratory flow

? not very responsive to dilators

?Severe COPD - ? small & large airway resist

? severe flow limitations ? bronchodilators ? little help

? chronic bronchitis and emphysema

?Emphysema - loss of elastic recoil ? ? small airway collapse during expiration, thereby ? resistance

? Max Expiratory Flow ?

? Bronchodilators have no effect

? ? FRC + TLC

Training:

?In general, lung volumes and capacities ? little with training. VC may ? slightly. TLC doesn't change much, slightly ? possible

?MVV may ? considerably

?Due to ? TV and ? rate of respiration

Procedure Notes:

?Conversion to Body Temperature Pressure Saturated (BTPS)

?Body Temp ? 37o C

?Saturation with water vapor = 100%

?All pulmonary function values reported in BTPS, but measurements taken at Ambient Temperature Pressure Saturated (ATPS)

?Conversion (Ref: CCJ, p. 50)

VBTPS = VATPS * BTPSCF

Where:

BTPSCF = TB(?C) + 273 X PB ? PH2O at room temp

TR(?C) +273 PB ? PH2O at body temp

TB = body temp in degrees Celsius (? 37? C)

TR = room (or spirometer) temp in degrees Celsius

273 = factor to convert Celsius to Kelvin

PB = barometric pressure

PH2O = water vapor pressure at room and body temp (CCJ,p. 50)

?FRC by Nitrogen Washout - Breathing Pure Oxygen (Source: West, Respiratory Physiology, pp. 146-147)

?General Formula

V1 * C1 = (V1 * C3) + (V2 * C2)

Where:V1 = Lung Volume

V2 = Volume of gas exhaled over washout procedure

C1 = [N2] in lungs before washout (atmospheric ? 80%)

C2 = [N2] of exhaled gas over washout ([N2] in V2)

C3 = [N2] left in lungs after washout measured at

end-expiration

?Solve for unknown V1:

(V1 * C1) - (V1 * C3) = V2 * C2

V1 * (C1 - C3) = V2 * C2

V1 = V2 * C2)

C1 ? C3

Remember general constants given for atmospheric air:

? Pb at sea level = 760 mm Hg

? FIO2 = 0.2093 (or 20.93%)

? FICO2 = 0.0004 (or 0.04%)

? FIN2 = 0.7903 (or 79.03%)

? ?PIO2 = 0.2093 x 760 = 159 mm Hg

? PICO2 = 0.0004 x 760 = 0.3 mm Hg

? PIN2 = 0.7903 x 760 = 600 mm Hg

Assumption: since atmosphere is composed almost entirely of N2, O2, and CO2, then:

N2% = 100 - O2% - CO2%

Calculate residual volume as: (Ref. Wilmore, MSSE, 1980):

RV (L) = VO2bag (L) * (b-a) ? (c-d)

Where:RV = residual volume in liters

VO2bag = volume of oxygen in liters added to bag

(usually 3-5 L)

a = % nitrogen impurity in original oxygen (assume

to be 0.0 for practical purposes)

b= % nitrogen in rebreathing bag after subject completes breathing maneuver

c= % nitrogen in alveolar air at beginning of test (assume 80.0%)

d= % nitrogen in alveolar air during last maximal breath (assume 0.2% nitrogen higher than equilibrium %, I.e., b + 0.2% nitrogen)

Simplified (CCJ, p. 49):

RV = VO2bag * b or VO2bag * b

8.0.0 ? (b + 0.2) 79.8 - b

Where:

VO2bag= volume of O2 in bag at start

b = percent of N2 in bag after rebreathing

N2 = 100% - %O2 - % CO2

NOTE: If nitrogen analyzer is available, bag nitrogen concentration can be measured directly from the bag.