الفهرس 
Nerve supply of the lungsOnly 14 pages are availabe for public view
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Abstract
Pulmonary function testing is a method of determining how well the lungs and the airways are working and how efficiently they transfer oxygen into the blood. The term of pulmonary function tests is a general term includes a broad range of tests for studying the different functions of the lungs separately.
Spirometry is the cornerstone of the PFTs; it is a simple computerized device that can measure how lungs exhale and it provides the results either as absolute values or percentage of normal range. Some devices are able to provide a graphic presentation of the flow of exhaled (and also inhaled) air against lung volumes in what is known by flow volume loop.
Spirometry measures all air that patient can blow out of the lungs, however, lungs can never be fully empty, and the volume of air remaining in the lungs after forced expiration can be measured by other several methods like body plethysmography or gas dilution technique.
For testing pulmonary ventilation, there are 3 groups of tests;
1. Static pulmonary function tests (static lung volumes): they are performed regardless to time. Changes in these volumes can permit the detection of many lung disorders especially restrictive lung diseases. The static function tests can be divided into 4 volumes and 5 capacities:
A. Lung volumes:
Tidal volume (Vt), Residual volume (RV), Expiratory reserve volume (ERV), and Inspiratory reserve volume (IRV).
B. Lung capacities:
Inspiratory capacity (IC), Vital capacity (VC), Inspiratory vital capacity (IVC), Functional residual capacity (FRC), and Total lung capacity (TLC).
2. Dynamic pulmonary function test: it is a spirometric study of the maximum volume of gas that can be expired into a spirometer as rapidly and as forcefully as possible after inspiration to TLC. This maneuver is called forced vital capacity FVC, in which the expired volume is plotted against time and so several other values can be detected from this curve such as:
• The volume expired in the 1st second, expressed either as an absolute value i.e. FVC, or as a percentage of the FVC i.e. FVC1\FVC%.
• The forced mid-expiratory flow rate (in the middle half of the FVC) (FEF25-75%).
• The forced expiratory flow rate after 1st 200 ml during FVC maneuvers (FEF200-1200).
• Peak expiratory flow rate (PEFR).
The information gathered during this maneuver is useful in diagnosis of certain disorders but most useful when assessing obstructive pulmonary diseases.
3. Flow volume loop: the shape of the loop differs and become characteristic for obstructive, restrictive lung diseases and different types of upper airway obstruction.
Testing the uneven distribution of ventilation using the N2 washout technique is a very sensitive test to the mild airway obstructive disorders.
Testing the diffusion capacity for carbon monoxide (DLCO) permits an estimate of how efficiently the lungs are able to transfer the oxygen from air into the blood stream.
Compliance can be measured for the lungs, the chest wall, or both together. This measurement can be obtained under static condition (static compliance Cst) or during rhythmic breathing (dynamic compliance Cdyn). The later is also dependent on the airways resistance. Normal lung compliance is 200 ml\cm and in normal individuals, Cdyn\Cst remains above 0.8. Decreased compliance is usually associated with restrictive pulmonary diseases while in obstructive pulmonary diseases, the compliance is usually increased.
Airway resistance (Raw) can be measured by the panting technique using a constant volume body plethysmography (body box) and the principle of the Boyle’s law. The upper limit of the normal Raw is about 2 cmH2O\sec. This value is increased in acute episode of bronchial asthma and in advanced cases of emphysema.
Testing of ventilation perfusion relationship can be done by using quantitative ventilation / perfusion lung scanning (split-function scanning) which is useful for predicting post-pneumonectomy lung function especially in patients with lung cancer.
Respiratory muscle strength measurement, Transdiaphragmatic pressure measurement, exercise test, and Methacholine challenge test are less commonly performed pulmonary function tests indicated in certain conditions.
The interpretation of PFTs usually involves comparing values measured in patients with reference values from studies of population of healthy non-smokers.
To simplify the interpretation of the spirogram, three steps can be followed:
1. Look at the time volume curve to determine the criteria for acceptability.
2. What is the FEV1?
i. > 80% is predicted normal. If FEV1\FVC < 80% and\or FEF25-75% < 50% think of early airway obstruction.
ii. < 80% is predicted abnormal, so what is the FEV1\FVC?
• > 80% of predicted for age = restriction, so get the lung volumes to confirm.
• < 80% of predicted for age = obstruction, so what is the FVC?
1. < 80% of predicted = pure obstruction, and the grading is based on the decrement in FEV1.
2. > 80% of predicted = possible concurrent restriction.
3- Look at flow-volume loop for upper airway obstructive pattern.
Although no general agreement exists as to which patient should be tested, the prime candidates are those in whom there is reasonable expectation of abnormal pulmonary function. This broad list has long included the following:
1. Patients with any evidence of chronic pulmonary diseases.
2. Heavy smokers with history of persistent cough.
3. Morbidly obese patients.
4. Elderly patients (>70 years of age).
5. Patients who chest wall and spinal deformity.
6. Patients who have to undergo upper abdominal surgery and thoracic surgery especially lung resection.
The optimal scheme for evaluating patients preoperatively is by means of arterial blood gas analysis and the FVC, FEV1, FEV1\FVC%, PEFR, and FEF 25-75%. Which can be obtained from single spirometric study, and benefits of these PFTs in surgical patient can be summarized as:
1. Supporting the clinical diagnosis.
2. Correlate lung pathology to the pulmonary dysfunction.
3. Determine the degree of dysfunction.
4. Differentiate between the obstructive and restrictive lung diseases.
5. Evaluate the response to lung therapy.
6. Predicted the postoperative pulmonary risk. Abnormalities in such spirometric tests seem to correlate with the incidence of postoperative pulmonary complication.