= Cardiologist
{tag=Cardiology}
A \b[cardiologist] is a <physician> with specialized training in identifying and treating disorders of the <heart> and <blood vessels>. The specialization is <cardiology>; it concerns the cardiovascular system's structure and function rather than only one instrument or one type of operation.<Cardiologist in the NCI Dictionary of Cancer Terms>[Definition]{ref}
The scientific work connects different observations to different physiological questions. <Electrocardiography> records electrical activity, <echocardiography> uses <ultrasound> to examine cardiac structures and motion, and flow measurements address the amount of <blood> transported per unit time. An electrical waveform, a chamber volume and a pressure reading are not interchangeable measurements of cardiac performance.
An original mean-flow example illustrates the <pressure-flow distinction in cardiovascular assessment>. In a simplified steady resistance model,
$$
Q=\frac{P_a-P_v}{R},
$$
where $Q$ is <cardiac output>, $P_a-P_v$ is the mean pressure difference and $R$ represents effective vascular <hydraulic resistance>. Stipulated pressures 90 and 5 mmHg with flow 5 L/min imply $R=17\,\mathrm{mmHg\,min\,L^{-1}}$. The same pressures with flow 2.5 L/min imply twice that resistance. A pressure observation alone therefore does not determine <cardiac output>. The model omits pulsatility and the distributed vascular geometry; it explains why complementary measurements are needed.
Another distinction concerns <right ventricular ejection fraction>: a fraction of chamber volume ejected per beat does not specify the number of beats per minute or the absolute volume transported. Interpreting a measurement requires its units, acquisition procedure and relationship to the physiological question. This quantitative reasoning is part of the specialty, alongside anatomical and clinical interpretation.
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