PULMONARY FUNCTION

TESTINGAdditional Laboratory Assessment

If the spirometry results of a subject are normal, no further testing is needed.

If the results are abnormal, a physician may order further test to confirm the presence of restrictive lung disease or to assess the severity of either restrictive or obstructive lung disease.

The further tests must be done in a pulmonary function test laboratory.

DETERMINING LUNG CAPACITIES AND VOLUMES BODY PLETHYSMOGRAPH

Measures changes in volume and pressure in the thorax.

The patient sits in an airtight booth and breathes through a mouthpiece that is open to room air.

In-line are a pneumotachometer (a flow sensor), a pressure manometer, and a shutter that cuts off flow sensor transducer.

BODY PLETHYSMOGRAPHY The subjects pants against the closed

shutter, and mouth pressures and changes in the volume of air in the booth are measures.

The subject, with nose clips tightly in place and sitting in the booth with the door closed, breathes normally through the mouthpiece.

The subjects then puts and over the cheeks to prevent their expansion when panting against the closed shutter.

BODY PLETHYSMOGRAPHY Instruct the subject to pant ( in small

pants ) through the mouthpiece one ore two times per minute.

At end-exhalation, close the shutter, and tell the subject to try pant against the closed shutter.

The shutter is then opened, and the test is complete.

BODY PLETHYSMOGRAPHY Method of measuring FRC by measuring TGV

(thoracic gas volume).

RV is the difference between TGV and ERV, and TLC is the sum of RV and VC, or the sum of TGV and IC.

TLC 80 – 120 (normal) 70-79 mild 60 – 69 moderate < 60 moderately severe

RV 63 – 135

sRaw - ≤ 120

OTHER MEANS OF DETERMINING LUNG CAPACITIES AND VOLUMES

SLOW VOLUME CAPACITY – the same maneuver as for FVC, except the exhalation is slow rather than forceful.

VC, tidal volume, IRV, IC, and ERV are measured.

NITROGEN WASHOUT (OPEN CIRCUIT) The theory behind the nitrogen washout

test is that if all or most of the nitrogen is removed from the lung ad the volume of the nitrogen exhaled is measured, the FRC can be determined.

NITROGEN WASHOUT

HELIUM DELITION (CLOSED CIRCUIT) The theory behind the helium dilution

test is that if a known concentration of an inert gas is rebreathed by a subject until its concentration is the same on inhalation as it is on exhalation, the change in the concentration of the inert gas is due to dilution of the gas by the subjects FRC.

HELIUM DELUTION

DIFFUSING CAPACITY (SINGLE-BREATH MEATHOD) Most common test available to assess

lung diffusing capacity ( the rate at which oxygen diffuses from the alveoli to the capillaries).

A very low concentration of carbon monoxide is used.

The amount of CO that diffuses from the lung into the blood (DLCO) gives direct indication of the rate at which O2 diffuses from the lung into the blood.

DLCO With noseclips in place, the subjects

makes a tight lip seal around the mouthpiece and breathes normally.

Instruct the subject to exhale down to RV and then inhale up to TLC as quickly as possible. The gas inhaled is a special mixture containing 0.3% CO, 10% He, 21% O2, and balance N2.

The subject holds his or her breath at TLC for approximately 10 seconds and then exhales as quickly as possible.

BRONCHOPROVOCATION For detection if there is a presence of

airway-reactivity. Methacholine- a cholinergic agent and

Histamine – most common inhaled agents used.

Hyperventilation using cold air and room air may also be used.

For exercise induced bronchospasm (EIB), testing is done after exercise

BRONCHOPROVOCATION INDICATIONS When a subject has a symptoms of

bronchospasm but normal pulmonary function tests.

When there is a baseline study before occupational exposure.

Follow up testing to check for changes hyper-reactivity or severity.

METHACOLINE AND HISTAMINE PROCEDURE Prebronchoprovocation spirometry is

done. The FEV1 should be >60 to 70% of the predicted value

The subject is given nebulized normal saline, and the spirometry is repeated. If there is a 10% reduction in the FEV1, the test is positive for airway hyper-reactivity. No further testing should be done. Continue is the reduction is equal to or greater than 10%.

METHACOLINE AND HISTAMINE PROCEDURE At fixed intervals, increasing doses of

methacoline and histamine are given by nebulizer. A number of protocols for dosing are widely available. Spirometry is done at 30-90 seconds after each dose, and test procedure and results must met the current ATS acceptability guidelines. A 20% decrease in FEV1 is considered a postive test for airway hyper-reactivity, and at that time the testing is stopped. The dose after which this decrease occurs is the PD20 (the provocation dose resulting in a 20% or greater decrease in FEV1.

METHACOLINE AND HISTAMINE PROCEDURE A bronchodilator is administered te

reverse the bronchospasm. The reversal is documented by a return to bronchoprovocation values.