= Pulmonologist
A \b[pulmonologist] is a <physician> specializing in diseases of the <lungs>, conducting <airways> and related respiratory function. The work connects clinical observations with <respiratory mechanics>, ventilation and <gas exchange>. The American Board of Internal Medicine's primary specialty standards include supervision and interpretation of pulmonary-function testing, ventilator-related skills and <bronchoscopy>.<Pulmonary Disease by the American Board of Internal Medicine>[Training and Procedure Requirements, pulmonary-function testing and bronchoscopy competencies]{ref}
The scientific question determines the measurement. <Spirometry> records gas moved at the mouth. <Lung compliance> relates volume to an internal pressure difference. <Gas exchange> also depends on the exchange surface and <blood flow>, so an expired-volume trace does not by itself measure every part of respiratory performance. A pulmonologist interprets these complementary observations alongside the clinical context rather than treating all breathing measurements as interchangeable.
An original ventilation example illustrates why this distinction matters. Let <tidal volume> be $V_T$, <respiratory rate> be $f$, and non-exchanging conducting-airway volume be $V_D$, representing <anatomical dead space>. In a simplified model where the remaining inspired gas reaches functioning exchange regions,
$$
\dot V_E=fV_T,\qquad \dot V_A=f(V_T-V_D).
$$
The first is total ventilation per minute; the second is the model's <alveolar ventilation>. OpenStax distinguishes conducting-airway dead space from gas available to alveolar exchange.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§22.3, Respiratory Volumes and Capacities, anatomical and alveolar dead space]{ref}
With stipulated $V_D=0.15$ L, twelve breaths per minute at $V_T=0.50$ L give total ventilation 6 L/min and alveolar ventilation 4.2 L/min. Thirty breaths per minute at $V_T=0.20$ L still move 6 L/min in total, but give only 1.5 L/min in this model. Equal total movement can therefore supply quite different amounts of fresh gas to exchange regions. These chosen numbers explain the quantities; they are not a breathing recommendation or a patient assessment.
Measurement quality is part of the specialty's scientific reasoning. The primary spirometry statement separately evaluates instrument response, maneuver acceptability and repeatability.<Standardization of Spirometry 2019 Update by Brian L. Graham and others>[Device Quality Assurance and FVC Maneuver]{ref} A precise measurement of one function can be informative while leaving the cause of an abnormal result unresolved. Combining anatomy, mechanics and exchange measurements makes those remaining questions explicit.
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