A spirometer measures the volume and speed of air during inhalation and exhalation, while a full PFT machine includes advanced modules for lung volumes and gas exchange. You’ll find that a handheld spirometer is suitable for basic asthma monitoring, but a complete station provides a comprehensive view of respiratory health. These larger systems utilise body plethysmography or nitrogen washout to determine Functional Residual Capacity, which is vital for diagnosing restrictive lung diseases.