Spirometry and Lung Function Testing

Spirometry

• Measures airflow into and out of the lungs.
• Low-risk procedure taking 15–20 minutes.
• Determines most, but not all, lung volumes and capacities.
• Results are evaluated against normal/predicted values.
• Requires at least three acceptable spirograms for valid, reproducible results.
• Cannot measure residual volume (RV), functional residual capacity (FRC), or total lung capacity (TLC).

Forced Vital Capacity (FVC)

• Total amount of air forcibly exhaled after maximal inspiration.
• Patient inhales to total lung capacity, then exhales quickly, forcefully, and completely.
• Measures the volume of air exhaled in this manner.

Forced Expiratory Volume in 1 second (FEV1)

• Volume of air exhaled during the first second of the FVC maneuver.
• Measures maximal exhaled air volume in one second following full inspiration.

FEV1/FVC Ratio

• Ratio of FEV1 to FVC.
• Represents the percentage of FVC expired in the first second.
• Helps determine if a patient has obstructive, restrictive, or normal lung function.
• A low ratio indicates an obstructive defect.

Arterial Blood Gases (ABGs)

• Measures blood's acid/base status and oxygenation.
• Useful for indicating the source of acid/base disturbances.
• Assesses response to treatment.
• Uses arterial blood (reflects lung gas exchange).

pH

• Measures hydrogen ion concentration in the blood.
• 7.35–7.45 (7.4 is neutral).
• Low pH = acidosis, high pH = alkalosis.

Partial pressure of oxygen (PaO2)

• Partial pressure of oxygen in arterial blood.

Percent of oxygen saturated hemoglobin (SaO2)

• Percent of oxygen saturated hemoglobin in arterial blood.

Partial pressure of carbon dioxide (PaCO2)

• Partial pressure of carbon dioxide in arterial blood.
• 35–45 mmHg.
• Increased in respiratory acidosis, decreased in respiratory alkalosis.
• Reflects lung gas exchange.

Bicarbonate (HCO3)

• Concentration of bicarbonate in the blood.
• 22–26 mEq/L.
• Decreased in metabolic acidosis, increased in metabolic alkalosis.
• Part of the carbonic acid-bicarbonate buffer system.

Pulse Oximetry

• Non-invasive, continuous method measuring arterial oxygen saturation.
• Measures oxygen saturation of blood (SpO2).
• Greater than 95% at rest, less than 5% desaturation with exercise considered normal.
• Less accurate than ABGs; affected by factors like nail polish, cold hands, smoking, and skin pigmentation.
• Used in perioperative settings, impact of treatment evaluation, and identifying need for mechanical ventilation.

Peak Flow Meter

• Measures maximal exhaled airflow rate.
• Used to self-monitor airflow obstruction in asthma.
• Effort-dependent; proper technique is critical.
• Patients establish a "personal best" for comparison.
• Peak flow readings indicate worsening asthma control.
• Measurements should be taken 2–4 times daily for 2–3 weeks to establish personal best. The highest of three readings is recorded , and the same meter should be used each time.
• Not a preferred diagnostic tool, spirometry is preferred.

This quiz covers the principles of spirometry, including methods for measuring airflow and lung volumes. It focuses on key metrics such as Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1), and their significance in assessing lung health. Test your understanding of these essential respiratory measurements.