Emphysema Diagnosis and Evaluation

Focusing on pulmonary function tests to measure air trapping and lung volume.

Pulmonology focuses on diagnosing and treating lung and airway conditions such as asthma, COPD, and pneumonia, as well as overall respiratory health.

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Emphysema: Diagnosis and Evaluation

Diagnosing emphysema requires a synthesis of clinical history, physical examination, and advanced physiological and imaging assessments. It is not enough to identify airflow obstruction; the clinician must define the extent of parenchymal destruction, the degree of hyperinflation, and the impact on gas exchange. At Liv Hospital, we utilize a multimodal approach not only to confirm the presence of the disease but also to quantify the extent of the destruction and its impact on the patient’s functional capacity. Because emphysema involves structural destruction, imaging plays a more central role in its specific diagnosis compared to chronic bronchitis. Early and accurate evaluation is paramount to implementing strategies that can slow disease progression and optimize symptom management.

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The Physical Examination Findings

The physical exam provides the first clues to the presence of emphysema. Clinicians look for specific signs of hyperinflation and airflow obstruction.

  • Inspection: The physician may observe a barrel chest, the use of accessory muscles in the neck (sternocleidomastoid) and shoulders for breathing, and a characteristic pursed-lip breathing posture. The patient may sit in a tripod position, leaning forward with the hands on the knees, to optimize diaphragm function.
  • Percussion: Tapping the chest wall typically produces a hyperresonant (drumlike) sound due to excess air trapped in the lungs. The liver dullness may be displaced downwards due to the flattened diaphragm.
  • Auscultation: Breath sounds are typically diminished or “distant” because airflow is weak, and the overinflated lung tissue dampens sound transmission. Wheezing may be present, particularly on forced exhalation. The heart sounds may also be distant due to the air filled lungs covering the heart.
  • Cyanosis and Clubbing: The physician checks for blue discoloration of the lips or nail beds. Digital clubbing is not typical of uncomplicated emphysema and should prompt a search for lung cancer or other causes.
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Spirometry: The Cornerstone of Diagnosis

Spirometry is the gold standard for diagnosing airflow limitation. It measures the volume and speed of air a patient can exhale.

  • FEV1 (Forced Expiratory Volume in 1 Second): This measures the volume of air exhaled in the first second of a forceful breath. In emphysema, this is reduced due to airway collapse. It is used to grade the severity of obstruction.
  • FVC (Forced Vital Capacity): The total amount of air exhaled. It may be reduced in severe emphysema due to air trapping (air that cannot be exhaled).
  • FEV1 FVC Ratio: A ratio of less than 0 point 70 confirms the presence of obstructive lung disease.
  • Flow Volume Loop: The flow-volume loop in emphysema shows a characteristic “scooped out” appearance on the expiratory limb, reflecting the sudden collapse of small airways during exhalation.

Lung Volume Measurement (Plethysmography)

While spirometry measures airflow, body plethysmography (body box) measures the volume of air in the lungs. This is crucial for quantifying hyperinflation, a hallmark of emphysema.

  • Total Lung Capacity (TLC): This is typically increased in emphysema as the lungs lose elasticity and over expand.
  • Residual Volume (RV): The amount of air left in the lungs after a complete exhalation is significantly increased due to air trapping.
  • RV TLC Ratio: An elevated ratio indicates severe air trapping and is a strong correlate of dyspnea during exertion.
  • Functional Residual Capacity (FRC): This is the volume of air in the lungs at the end of a normal breath, which is also increased, putting the respiratory muscles at a disadvantage.

Diffusing Capacity of the Lung for Carbon Monoxide (DLCO)

The DLCO test is the single most crucial physiological test to distinguish emphysema from chronic bronchitis and asthma. It measures the lungs’ ability to transfer gas from the alveoli into red blood cells.

  • Mechanism: The patient inhales a small amount of carbon monoxide. The test measures how much is absorbed.
  • Significance in Emphysema: Because emphysema destroys the alveolar capillary membrane (the surface area for gas exchange), the DLCO is significantly reduced. In chronic bronchitis or asthma, the alveolar units are intact, so DLCO is usually normal. A low DLCO correlates with exercise desaturation and the need for supplemental oxygen.

High Resolution Computed Tomography (CT)

CT imaging has revolutionized the evaluation of emphysema. Unlike a standard chest X ray, which is insensitive to early disease, a CT scan provides detailed visualization of the lung parenchyma.

  • Quantification: CT scans can quantify the percentage of lung tissue destroyed (low attenuation areas). Software analysis can measure lung density to track progression.
  • Phenotyping: It allows the radiologist to distinguish between centrilobular, panlobular, and paraseptal subtypes, which helps determine the etiology (smoking vs alpha-1).
  • Bullae Detection: It identifies the size and location of bullae, which are essential for surgical planning for procedures such as bullectomy or lung volume reduction.
  • Lung Cancer Screening: Because smokers are at high risk, CT scans are used to detect pulmonary nodules and masses.

Alpha 1 Antitrypsin Testing

Given the genetic implications, the World Health Organization recommends that all patients with a diagnosis of COPD or emphysema be screened once for Alpha 1 Antitrypsin Deficiency.

  • Serum Level: A blood test measures the level of the protein in the blood. Low levels suggest a deficiency.
  • Genotyping: If levels are low, genetic testing identifies the specific alleles (e.g., Z or S mutations) to confirm the diagnosis.
  • Family Screening: Identifying a patient with this deficiency triggers the screening of family members who may also be at risk.

Arterial Blood Gas (ABG) Analysis

In advanced disease, ABG analysis is performed to assess gas exchange efficiency.

  • Hypoxemia: Measures the partial pressure of oxygen (PaO2).
  • Hypercapnia: Measures the partial pressure of carbon dioxide (PaCO2). Emphysema patients are often “pink puffers” who maintain normal CO2 levels by hyperventilating until the very late stages of the disease, unlike chronic bronchitis patients who retain CO2 earlier.
  • Acid Base Balance: Assesses the pH to check for respiratory acidosis or compensation.

The 6 Minute Walk Test

Functional capacity is evaluated using the 6 minute walk test. This measures the distance a patient can walk in six minutes and monitors oxygen saturation during the activity.

  • Exertional Desaturation: Many patients have normal oxygen levels at rest but experience significant desaturation during walking due to increased demand and limited diffusion capacity. This test identifies the need for ambulatory oxygen therapy.
  • Prognosis: The distance walked is a strong predictor of mortality and hospitalization risk.

Echocardiography

Because emphysema damages the blood vessels in the lungs (by destroying the capillary bed), it can strain the heart. An echocardiogram is used to screen for pulmonary hypertension (high blood pressure in the lung arteries) and cor pulmonale (enlargement of the right side of the heart). Assessing proper ventricular function is critical for overall prognosis and management.

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FREQUENTLY ASKED QUESTIONS

Why do I need a body box test?

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CT scans do involve exposure to ionizing radiation, which carries a small theoretical risk of cellular damage over time. However, modern CT scanners use dose-modulation technology to minimize this exposure to the lowest level necessary for a diagnostic image. The benefit of an accurate and timely diagnosis for serious urological conditions typically far outweighs the minimal risk of radiation.

Many modern orthopedic implants are MRI-safe, although they may cause some image distortion. However, older pacemakers, defibrillators, and certain metal clips may be unsafe in the strong magnetic field. It is critical to inform the imaging team of any metallic implants so they can verify their safety compatibility or recommend an alternative test like a CT scan.

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