Pulmonary Function Tests: Spirometry

Pulmonary Function Tests

Spirometry

• Measures lung function by assessing airflow and lung volumes
• Key measurements:
  • Forced Vital Capacity (FVC): total volume of air exhaled from the lungs
  • Forced Expiratory Volume (FEV1): volume of air exhaled in the first second
  • FEV1/FVC ratio: proportion of FVC exhaled in the first second
• Spirometry is used to:
  • Diagnose and monitor obstructive lung diseases (e.g., asthma, COPD)
  • Evaluate lung function in patients with respiratory symptoms
  • Monitor response to therapy

Lung Volumes

• Measures the total amount of air in the lungs
• Key components:
  • Total Lung Capacity (TLC): total volume of air in the lungs
  • Residual Volume (RV): volume of air remaining in the lungs after exhalation
  • Functional Residual Capacity (FRC): volume of air in the lungs at the end of normal exhalation
• Lung volume measurements are used to:
  • Diagnose restrictive lung diseases (e.g., pulmonary fibrosis)
  • Evaluate lung function in patients with respiratory symptoms
  • Monitor response to therapy

Diffusion Capacity

• Measures the ability of the lungs to transfer oxygen from the air into the blood
• Key measurement:
  • Diffusion Capacity of the Lung for Carbon Monoxide (DLCO): measures the rate of CO transfer from the air into the blood
• Diffusion capacity is used to:
  • Diagnose and monitor lung diseases that affect gas exchange (e.g., emphysema, pulmonary hypertension)
  • Evaluate lung function in patients with respiratory symptoms
  • Monitor response to therapy

Pulmonary Function Tests

Spirometry

• Assesses airflow and lung volumes to measure lung function
• Provides three key measurements:
• Forced Vital Capacity (FVC): total air volume exhaled from lungs
• Forced Expiratory Volume (FEV1): air volume exhaled in the first second
• FEV1/FVC ratio: proportion of FVC exhaled in the first second
• Used for:
• Diagnosing and monitoring obstructive lung diseases (e.g., asthma, COPD)
• Evaluating lung function in patients with respiratory symptoms
• Monitoring response to therapy

Lung Volumes

• Measures total air volume in the lungs
• Comprises three key components:
• Total Lung Capacity (TLC): total air volume in the lungs
• Residual Volume (RV): air volume remaining in the lungs after exhalation
• Functional Residual Capacity (FRC): air volume in the lungs at the end of normal exhalation
• Used for:
• Diagnosing restrictive lung diseases (e.g., pulmonary fibrosis)
• Evaluating lung function in patients with respiratory symptoms
• Monitoring response to therapy

Diffusion Capacity

• Measures the rate of oxygen transfer from air into the blood
• Key measurement:
• Diffusion Capacity of the Lung for Carbon Monoxide (DLCO): CO transfer rate from air into the blood
• Used for:
• Diagnosing and monitoring lung diseases affecting gas exchange (e.g., emphysema, pulmonary hypertension)
• Evaluating lung function in patients with respiratory symptoms
• Monitoring response to therapy

Interpreting ABG Results

Acid-Base Status

• pH level: normal range is 7.35-7.45
• Acidosis: pH level is less than 7.35
• Alkalosis: pH level is greater than 7.45

Identifying Primary Disorder

• Respiratory Acidosis:
  • Characterized by high pCO2 (>45 mmHg)
  • Low pH (<7.35) due to high pCO2
  • May be caused by hypoxia (oxygen saturation <95%)
• Respiratory Alkalosis:
  • Characterized by low pCO2 (<35 mmHg)
  • High pH (>7.45) due to low pCO2
• Metabolic Acidosis:
  • Characterized by low HCO3- (<22 mEq/L)
  • Low pH (<7.35) due to low HCO3-
• Metabolic Alkalosis:
  • Characterized by high HCO3- (>26 mEq/L)
  • High pH (>7.45) due to high HCO3-