Spirometry Techniques and Measurements

Spirometry Techniques

• Spirometry is a technique used to measure lung volumes and capacities.
• Classic spirometry involves a device with a pen, bell, and counterweight in a water lock, while modern spirometry uses electronic devices.

Spirometry Measurements

• Inspiratory Reserve Volume (IRV) is the amount of air that can be forcefully inhaled after a normal tidal volume inhalation.
• Tidal Volume (TV or VT) is the amount of air inhaled or exhaled with each breath under resting conditions, typically 500 ml for both males and females.
• Expiratory Reserve Volume (ERV) is the amount of air that can be forcefully exhaled after a normal tidal volume exhalation.
• Residual Volume (RV) is the amount of air remaining in the lungs after a forced exhalation.
• Functional Residual Capacity (FRC) is the volume of air remaining in the lungs after a normal tidal volume expiration; FRC = ERV + RV.
• Vital Capacity (VC) is the maximum amount of air that can be expired after a maximum inspiratory effort; VC = TV + IRV + ERV, and should be 80% of TLC.
• Forced Expiratory Volume in 1 second (FEV₁) is the volume of air that can be forcibly expelled from maximum inspiration in the first second.
• Inspiratory Capacity (IC) is the maximum amount of air that can be inspired after a normal expiration; IC = TV + IRV.
• Total Lung Capacity (TLC) is the maximum amount of air contained in the lungs after a maximum inspiratory effort; TLC = TV + IRV + ERV + RV.
• Adult male average values: IRV is 3100 ml, ERV is 1200 ml, RV is 1200 ml, FRC is 2400 ml, VC is 4800 ml, and TLC is 6000 ml.
• Adult female average values: IRV is 1900 ml, ERV is 700 ml, RV is 1100 ml, FRC is 1800 ml, VC is 3100 ml, and TLC is 4200 ml.
• Normal FVC is approximately 5L for males and 3.5L for females
• Normal FEV₁ is approximately 3.6L for males and 2.7L for females
• FEV₁% greater than 72% is considered normal, while FEV₁% less than 72% may indicate obstructive disease.

Flow-Volume Loops

• Flow-volume loops graphically represent airflow rates during inspiration and expiration, and their shape can indicate different respiratory conditions.
• Obstructive diseases lead to a characteristic change in the shape of flow-volume loops, as do restrictive diseases.

Factors Causing Individual Variation in Lung Function

• Lung function varies based on individual factors such as height, effort, body type, body position, gender, age, and individual health.

Dead Space

• Anatomical dead space refers to the conducting zones of the respiratory system.
• Anatomical dead space is approximately 1 ml/lb of body weight.
• Physiological dead space includes areas where alveoli are not equally perfused by blood or have lost function due to disease.

Minute Ventilation Calculation

• Minute ventilation (AVR) is calculated by multiplying frequency (breaths/min) by the difference between tidal volume (TV) and dead space (DS) in ml/breath.
• Patients with obstructive disease should breathe in slow, deep breaths, while those with restrictive disease should take small, rapid breaths.

Conclusions

• Restrictive lung disease increases the work of breathing due to a loss of compliance.
• Obstructive lung disease results from a narrowing or obstruction of airflow.
• Lung volumes and capacities serve as indicators of respiratory health and are limited by the anatomy.
• Alveolar ventilation rate is determined from the respiratory rate and lung volumes.