Pulmonary function testing
Encyclopedia
Pulmonary Function Testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFT's are performed by a Pulmonary scientist
who typically hold credentialing as a Registered Pulmonary Function Technician, a Certified Pulmonary Function Technician
or a Registered Respiratory Therapist
.
are associated with gradual loss of muscle function over time. Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to atelectasis
(the ability of the lungs to gain oxygen) and an overall insufficency in lung strength. A combination of reduced lung compliance caused by generalized and widespread microatelectasis and chest wall deformity caused by increased chest wall compliance4 results in increased work of breathing and chronic respiratory insufficiency. Musculoskeletal deformities such as kyphoscoliosis contribute to restrictive lung disease.
Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.
Complications
Spirometry is a safe procedure however there is cause for concern regarding untoward reactions. The value of the test data should be weighed against potential hazards. Some complications have been reported such as; pneumothorax
, increased intracranial pressure, syncope, chest pain, paroxysmal coughing, nosocomial infection
s, oxygen desaturation, and bronchospasm
.
(VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). The four lung capacities are total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity
(FRC) and the vital capacity
(VC).
(DLCO) is a fast and safe tool in the evaluation of both restrictive and obstructive lung disease
.
, such as COPD or idiopathic pulmonary fibrosis
es (ABGs) are a helpful measurement in pulmonary function testing in selected patients. The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced COPD.
An elevated serum bicarbonate level, or chronic hypoxemia. ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.
, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.
and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.
s and decrease with restrictive impairment.
Pulmonary scientist
A Pulmonary Scientist is a health care occupation in the field of diagnostic studies related specifically to pulmonary function, the term Respiratory Scientist may also refer to a Pulmonologist who holds a medical degree and a doctoral degree...
who typically hold credentialing as a Registered Pulmonary Function Technician, a Certified Pulmonary Function Technician
Certified Pulmonary Function Technician
A Certified Pulmonary Function Technician is a technician who is at least a Certified Respiratory Therapist and at most a Registered Respiratory Therapist that has successuly passed the national certification exam. A pulmonary function technician assists a Registered Pulmonary Function Technician...
or a Registered Respiratory Therapist
Registered Respiratory Therapist
A Registered Respiratory Therapist is a cardiopulmonary therapist and specialist who is required to exercise considerable independent clinical judgment in the respiratory care of patients...
.
Indications
Pulmonary function testing is a diagnostic and management tool used for a variety of reasons.Pediatric neuromuscular disorders
Neuromuscular disorders such as Duchenne muscular dystrophyDuchenne muscular dystrophy
Duchenne muscular dystrophy is a recessive X-linked form of muscular dystrophy, which results in muscle degeneration, difficulty walking, breathing, and death. The incidence is 1 in 3,000 boys. Females and males are affected, though females are rarely affected and are more often carriers...
are associated with gradual loss of muscle function over time. Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to atelectasis
Atelectasis
Atelectasis is defined as the collapse or closure of alveoli resulting in reduced or absent gas exchange. It may affect part or all of one lung. It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.It is a very common finding in chest x-rays and other...
(the ability of the lungs to gain oxygen) and an overall insufficency in lung strength. A combination of reduced lung compliance caused by generalized and widespread microatelectasis and chest wall deformity caused by increased chest wall compliance4 results in increased work of breathing and chronic respiratory insufficiency. Musculoskeletal deformities such as kyphoscoliosis contribute to restrictive lung disease.
Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.
Other indications
- Chronic dyspneaDyspneaDyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
- Asthma
- Chronic obstructive pulmonary diseaseChronic obstructive pulmonary diseaseChronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...
- Restrictive lung disease
- Preoperative testing
- Impairment or disability
Spirometry
Spirometry includes the tests of pulmonary mechanics, the measurements of FVC, FEV1, FEF values, forced inspiratory flow rates (FIFs), and the MVV. Measuring pulmonary mechanics is assessing the ability of the lungs to move large volumes of air quickly through the airways to identify airway obstruction.Complications
Spirometry is a safe procedure however there is cause for concern regarding untoward reactions. The value of the test data should be weighed against potential hazards. Some complications have been reported such as; pneumothorax
Pneumothorax
Pneumothorax is a collection of air or gas in the pleural cavity of the chest between the lung and the chest wall. It may occur spontaneously in people without chronic lung conditions as well as in those with lung disease , and many pneumothoraces occur after physical trauma to the chest, blast...
, increased intracranial pressure, syncope, chest pain, paroxysmal coughing, nosocomial infection
Nosocomial infection
A nosocomial infection , also known as a hospital-acquired infection or HAI, is an infection whose development is favoured by a hospital environment, such as one acquired by a patient during a hospital visit or one developing among hospital staff...
s, oxygen desaturation, and bronchospasm
Bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release of substances from mast cells or basophils under the influence of anaphylatoxins...
.
Measurements
There are four lung volumes and four lung capacities. A lung capacity consists of two or more lung volumes. The lung volumes are tidal volumeTidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...
(VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). The four lung capacities are total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity
Functional residual capacity
Functional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...
(FRC) and the vital capacity
Vital capacity
Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inspiration. It is equal to the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume....
(VC).
Maximal respiratory pressures
Measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically. Maximal inspiratory pressure (MIP) is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece. Maximal expiratory pressure (MEP) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation. Repeated measurements of MIP and MEP are useful in following the course of patients with neuromuscular disorders.Diffusing capacity
Measurement of the single-breath diffusing capacity for carbon monoxideCarbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
(DLCO) is a fast and safe tool in the evaluation of both restrictive and obstructive lung disease
Obstructive lung disease
Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. It is generally characterized by inflamed and easily collapsible airways, obstruction to airflow, and frequent office visits and hospitalizations. Types of obstructive lung disease include; Asthma,...
.
Oxygen desaturation during exercise
The six-minute walk test is a good index of physical function and therapeutic response in patients with chronic lung diseaseChronic lung disease
Chronic lung disease could refer to one of the following topics:* Asthma* Chronic bronchitis* Chronic obstructive pulmonary disease* EmphysemaOther related topics may include:* Arterial blood gas* Pulmonary function testing...
, such as COPD or idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis is a chronic, progressive form of lung disease characterized by fibrosis of the supporting framework of the lungs...
Arterial blood gases
Arterial blood gasArterial blood gas
An arterial blood gas is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or...
es (ABGs) are a helpful measurement in pulmonary function testing in selected patients. The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced COPD.
An elevated serum bicarbonate level, or chronic hypoxemia. ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.
Helium Dilution
The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit. This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed spirometerSpirometer
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. It is a precision differential pressure transducer for the measurements of respiration flow rates. The spirometer records the amount of air and the rate of air that is breathed in and out over a...
, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.
Nitrogen Washout
The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.Plethysmography
The plethysmography technique applies Boyle's lawBoyle's law
Boyle's law is one of many gas laws and a special case of the ideal gas law. Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system...
and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.
Significance
Changes in lung volumes and capacities are generally consistent with the pattern of impairment. TLC, FRC and RV increase with obstructive lung diseaseObstructive lung disease
Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. It is generally characterized by inflamed and easily collapsible airways, obstruction to airflow, and frequent office visits and hospitalizations. Types of obstructive lung disease include; Asthma,...
s and decrease with restrictive impairment.