Pft volumes and capacities

Lung Volumes and Capacities

• Primary lung volumes include tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV).
• Lung capacities include: Total Lung Capacity (TLC), Vital Capacity (VC), Inspiratory Capacity (IC), and Functional Residual Capacity (FRC).

Primary Lung Volumes

Tidal Volume (VT)

• Amount of air entering or leaving the lungs during a single normal breath.
• Approximately 500 ml at rest, increases with activity.

Inspiratory Reserve Volume (IRV)

• Additional volume of air that can be maximally inspired beyond the normal tidal volume by forced inspiration.
• Approximately 3100 ml at rest.

Expiratory Reserve Volume (ERV)

• Additional volume of air that can be maximally expired beyond the normal tidal volume by forced expiration.
• Approximately 1200 ml at rest.

Residual Volume (RV)

• Volume of air still remaining in the lungs following a maximal forced expiration.
• Approximately 1200 ml at rest.

Lung Capacities

Total Lung Capacity (TLC)

• Total amount of air that the lungs can hold, or the amount of air in the lungs at the end of a maximal inspiration.
• TLC = VT + IRV + ERV + RV

Vital Capacity (VC)

• Maximum amount of air that can be moved out of the lungs after a person inhales as deeply as possible.
• VC = VT + IRV + ERV

Inspiratory Capacity (IC)

• Maximum amount of air that can be inhaled from a normal end-expiration.
• Performed by breathing out normally, then inhaling as much as possible.
• IC = VT + IRV

Functional Residual Capacity (FRC)

• Amount of air remaining in the lungs following a normal expiration.
• FRC = ERV + RV

Lung Ventilation Measures

• Measures evaluate air volume versus time.

Respiratory Frequency (f)

• Breathing rate.
• About 12 breaths per minute at rest.

Minute Volume (VE)

• Amount of air moved by the lungs in 1 minute.
• VE = VT x f

Forced Expiratory Volume (FEVt)

• Amount of air forcibly expired in t seconds.

Calculating FEV1

• Determined by the formula: (Volume/VC) x 100%

Normal FEV Measurements

• FEV1 = ~80% VC
• FEV2 = ~94% VC
• FEV3 = ~97% VC
• Index of air flow through the respiratory air passages.

Static Lung Volumes

• Lung volumes measured without airflow.

Helium Dilution

• Method uses helium in a closed system to measure FRC.

Technique

• Patient rebreathes a known concentration of helium (usually 10%) mixed with room air from a spirometer for up to 7 minutes.
• The helium distributes throughout the patient's lungs until helium concentration equilibrium is established between the lungs and the spirometer as the test progresses.
• The "switch-in" occurs at the end of a normal expiration, when only FRC is left in the lung.
• Initial and final helium concentrations are measured with a helium analyzer, values are used to calculate the patient's FRC.
• Requires a CO2 absorber in the circuit.
• Measured at ATPS and corrected to BTPS.
• Wait 10-15 minutes before repeating the procedure to allow clearance of helium from the lungs and the circuit.
• A small volume is subtracted from the FRC to account for helium absorbed by the blood, the dead space volume of the breathing valve must also be subtracted.
• The "End of Test" occurs when helium concentration changes by less than 0.02% over a 30 second interval.
• A consistent baseline should be maintained by adding small amounts of oxygen as the oxygen in the system is consumed and may be added manually or by automated function of equipment.
• ERV is obtained from the basic spirometry (VC) measurement, RV is calculated: FRC - ERV, TLC is calculated: RV + VC = TLC.

Helium Dilution Troubleshooting

• Failure to reach equilibrium indicates a leak.
• An increase in the patient's breathing pattern (rate and/or volume) indicates the CO2 absorber is exhausted and should be replaced.
• If the cylinder pressure is low at the start of the test (50 psi), the cylinder should be replaced.
• Saturated expired air which passes through soda lime and silica gel will result in a volume loss of approximately 5%.
• Dizziness and visual changes (dimming of the lights) may indicate hypoxemia.
• The technologist should check the gas concentration mixture as air leak will result in higher measured volumes..
• Check blower speed if slow equilibration times occur in subjects with normal lung function.
• Erroneously high measurements (out of proportion to clinical history or other values) may be the result of leaks (circuit, at the mouthpiece, no nose clips, etc.), ruptured eardrum (tympanic membrane).
• The "Switch-in" occurred at a point before end-expiration and/or failure of analyzers.

Nitrogen Washout

• Method measures FRC by replacing the nitrogen in the lungs with oxygen.

Technique

• Patient breathes 100% oxygen for up to 7 minutes or until the N2% is less than 1% to "washout" the nitrogen from the lungs (final fractional expired nitrogen concentration 0.01).
• A patient with normal lung function should washout in 3 minutes or less. Patients with obstructive lung disease (emphysema) may not washout completely even after 7 minutes or more.
• The "switch-in" should be at the end of a normal expiration.
• The exhaled gases are collected in a spirometer or bag, the final %N2 is used to calculate the FRC.
• The RV and TLC are calculated as with the helium dilution technique/
• A rapid nitrogen analyzer breath-by-breath analysis is possible.
• Utilizes an open-circuit method that does not require a CO2 absorber because no rebreathing occurs.
• Measured at ATPS and corrected to BTPS.

Nitrogen Washout Troubleshooting

• Troubleshooting is similar to helium dilution.
• If %N2 does not drop after several minutes, there is air leaking into the system (Room air = 79% N2).
• Replace the oxygen tank if the pressure is 50 psig or less.

Body Plethysmography/Body Box

• Method measures static volumes.
• FRC requires measurement of the patient's weight.
• Thoracic gas volume is the volume of gas contained in the thorax measured at end-expiration.
• The method includes measurement of air trapped in the thorax which is not in communication with airways.
• VTG is normally equal to FRC.
• Measures RV and TLC.
• Calculating the RV/TLC ratio: divide residual volume by total lung capacity and multiplying by 100 to get a percentage.
• Measures airways resistance (Raw).

Body Box Technique

• Patient breathes normally for several breaths.
• At end-expiration, the shutter closes and the patient pants (no airflow during this step.)
• Mouth pressure approximates alveolar pressure when the shutter is closed because there is no airflow.
• A pressure transducer measures the pressure at the mouth, which is equal to alveolar pressure when there is no airflow.
• A second pressure transducer measures the pressure in the box, which is equal to the volume of gas in the thorax.
• Boyle’s Law is used to calculate thoracic gas volume.
• Mouth pressure (alveolar pressure) is plotted on the vertical axis of the oscilloscope.
• Box pressure (volume change) is plotted on the horizontal axis.

Body Plethysmography Assessment

• Measures gases that are trapped and otherwise excluded from FRC measurement by helium dilution and nitrogen washout.
• In a patient with normal lung function, the FRC measurements should be similar regardless of the method used.
• In patients with emphysema, the VTG will be higher than the FRC measured by the helium dilution and nitrogen washout.
• Requires careful instruction by a technologist.
• The angle of the pressure-volume loop should be 45 degrees.
• A flattened pressure-volume curve displaced downward indicates restrictive lung disease, such as pulmonary fibrosis.

Body Plethysmography Troubleshooting

• If the volume changed during the procedure but the pressure did not, the mouth pressure transducer line was not connected.

Radiologic Technique

• Chest X-rays are taken at total lung capacity from both posterior-anterior (PA) and lateral views.
• Standard points are marked on the image, and measurements and planar geometric formulas are used to calculate static lung volumes.
• Radiologic measurements are similar in accuracy to body box measurements.
• In patients with obstructive lung disease (air trapping), TLC, RV, and FRC measured by this method will result in higher values than those measured by gas techniques (helium dilution, nitrogen washout) and are more accurate in these patients.
• In a patient with normal lung function, the results from radiologic methods should be similar to those obtained from other methods.
• Useful in patients who are unable to perform other tests (i.e. patients with a tracheostomy, severe obstructive lung disease).
• Diseases or conditions in which air is replaced with fluid or solid (pneumonia, atelectasis, lung tumors, etc.) will result in a lower than actual thoracic gas volume measurement.

Significance of Results

• TLC, FRC, & RV increase with obstructive disease & decrease with restrictive impairment.
• Normal tidal volume is 500 to 700 ml (5 to 8 ml/kg of predicted body weight); VT measurement alone not helpful.
• Normal TLC is about 6 L.
• Normal VC is about 4.8 L in adults and results vary with age, gender, height, and ethnicity.

Functional Residual Capacity (FRC)

• Defined as the volume of gas remaining in the lungs at the end-expiratory level.
• Measured with a spirometer and a recording device.
• Reported in liters or milliliters, corrected to BTPS.
• Typical value = 2400 mL or 2.4 L.
• Decreased with restrictive lung disease, increased with obstructive lung disease (COPD, emphysema)because of air trapping.
• FRC = ERV + RV or FRC = TLC - IC

Residual Volume (RV)

• Defined as the volume of gas in the lungs at the end of maximum expiration.
• Measured with a spirometer and recording device.
• Reported in liters or milliliters, corrected to BTPS.
• Typical value = 1200 mL or 1.2 L.
• Decreased with restrictive lung disease, increased with obstructive lung disease.
• RV = FRC – ERV or RV = TLC – VC

Total Lung Capacity (TLC)

• Defined as the volume of gas in the lungs following a maximum inspiration.
• Measured with a spirometer and recording device.
• Reported in liters or milliliters, corrected to BTPS.
• Typical value = 6000 mL or 6.0 L.
• Decreased with restrictive lung disease, increased with obstructive lung disease.
• TLC = IRV + VT + ERV + RV or TLC = IC + FRC or TLC = VC + RV

Typical Lung Values

• VC = 4800
• RV = 1200
• FRC = 2400
• TGV (VTG) = 2400
• TLC = 6000

Forced Vital Capacity (FVC)

• Take a deep breath as deep as you can, and say to the patient, "Now blow as hard and as fast as you can".
• Encourage the patient to blow faster and longer and say, blow, blow, keep it blowing.

Patient Information

• Physical factors, occupational and smoking history and medical background all influence pulmonary testing.

Physical Description

• Age influences testing, older persons have smaller predicted values.
• Height is a factor, in determining predicted values, taller have larger prediction. For patients with spinal deformities arm span is measured to derived height.
  • Measure from fingertip to fingertip. To convert inches to centimeters, multiply by 2.54.
• Females have smaller lung volumes than males of equal age and height, therefore it is a factor in calculating predicted values.
• Weight estimates static volumes (FRC, RV, TLC, VTG) and not a major factor in predicted values but a consideration in determining restrictive lung disease.
• Race/Ethnicity can be used for calculating predicted values.

Medical/Surgical Background

• Inquire about any chronic respiratory disease (asthma, tuberculosis, chronic bronchitis, etc.), recurrent colds, infections, or pneumonia.
• Record allergies or hay fever (allergic rhinitis).
• Record previous chest surgery particularly a pneumonectomy or lobectomy as it may aid test results.
• Note chronic cough including time of they day or year it is worst.

Smoking History

• Needed to differentiate between cigarettes, cigars, and pipe smoking and record smoking history in pack/years of the number of packs smoked per day multiplied years of smoking.
• A patient has smoked 2 packs of cigarettes per day for the last 20 years would document their smoking history as 2 x 20 = 40 pack/year smoking history.
• The technologist should note whether or not the patient still smokes and patients should avoid at least 1hr+ before testing.

Occupational History

• Assists in diagnosis. This may be the only thing the technologist has about the patient and the patients occupation is important to note: Mine quarry or foundry work.
• Mill work.
• Farming.
• Exposure to gas or fumes.
• Dusty environment, etc. (sarcoidosis, pneumoconiosis, histoplasmosis, etc.).

Respiratory Modalities

• Continuous oxygen may have difficulty completing the test without it and in this case should be removed at least 20 minutes prior to drawing an arterial blood gas.
• If the patient cannot be without O2 for that length of time the FO2 should be reported on the blood gas record.
• If the patient is taking aerosolized bronchodilators, hold the medication prior to testing but post bronchodilator should be the same as home administration.
• Serial pulmonary function tests can be performed to evaluate the effectiveness of a rehabilitation program.

Medications

Bronchodilators should be withheld:

• Short-acting B-2 agonist for 4hrs: Albuterol and levalbuterol.
• Long-acting B-2 agonist for 12hrs: Salmeterol, formoterol and arformoterol.
• Methylxanthines for 12hrs: Theophylline.
• Slow-release methylxanthines for 24hrs: Slo-Phyllin, Slo-BID.
• Atropine-like preparations for 8hrs: Ipratropium and tiotropium.
• Cromolyn Sodium for 8-12 hrs: Intal.
• Other medications are important to note, but do not need to be held prior to testing (inhaled steroids, cardiac medications, antibiotics, etc.)

Vital Signs

• Check Respirations with Normal range - 10-20 breaths per minute.
• Pattern and depth are important.
• Checking Pulse with a normal range of 60-100 bpm.
• Check pulse strength.
• Blood Pressure with a normal range of 120/80 mm Hg.
• May be a result of increased pressures in the thorax during forced expiratory maneuvers and the patient should be able to follow commands. .

Testing Conditions

• Patients who have any of the following should not perform the procedure: active hemoptysis in past 24 hours, unstable vital signs or an inability to cooperate/understand instructions.
• Patient should avoid: Consuming alcohol for at least 4 hours prior to testing, vigorous exercise at least 30 minutes prior to testing, wearing clothing which restrict movement of the chest, and eating a large meal within 2 hours of testing.
• Record the room temperature, barometric pressure and time of day, dentures should be kept in unless loose, use nose clips.
• Normal testing will is performed is sitting position with the following actions.Standard technique include inspire as deeply as possible and hold breath and exhale.