= Palpation
\b[Palpation] is examination by touch with the hands or fingers. It uses physical contact to assess features such as an organ's apparent size, position, consistency and tenderness. The observed feature and the resulting <clinical diagnosis> are separate: feeling a moving or resistant region does not by itself identify the complete underlying anatomy or disease.<Palpation by MedlinePlus>[Information: definition and observed attributes]{ref}
The <force> applied during <palpation> is part of the measurement. In an original simplified indentation example, suppose a probe produces $2\,\mathrm{mm}$ of displacement under a $1\,\mathrm N$ load. The secant <stiffness> for that observation is
$$
k_{\rm sec}=\frac F\delta=0.50\,\mathrm{N/mm}.
$$
A second specimen requiring $2\,\mathrm N$ at the same displacement has twice this apparent <stiffness>. That ratio is not automatically a ratio of intrinsic <elastic modulus> values: contact geometry, specimen thickness, support and deformation rate can alter the <force-displacement curve>. Touch supplies a mechanical observation whose interpretation requires an appropriate model.
A clinical measurement study makes the distinction concrete. <S. D. Eilen> and colleagues compared precordial <palpation> with two-dimensional <echocardiography> in 41 patients. They compared the location and palpable diameter of the <apical impulse> with <left ventricle> end-diastolic volume. A lateral impulse location was sensitive but not specific for enlargement. Within the reported subgroup without ventricular hypertrophy, an impulse diameter above $3\,\mathrm{cm}$ in the left-lateral position had reported <diagnostic sensitivity> $92\%$ and <diagnostic specificity> $91\%$. Those are results for that study's condition and subgroup, rather than universal performance figures for touch.<Accuracy of precordial palpation for detecting increased left ventricular volume by S. D. Eilen and others>[Abstract, Annals of Internal Medicine99 (1983), pp.628–630: cohort, location result and subgroup diameter result]{ref}
A small probability example explains why both attributes matter. In a stipulated set with 20 enlarged and 80 non-enlarged hearts, a rule detecting 18 enlarged hearts but also flagging 24 non-enlarged hearts has <diagnostic sensitivity> $18/20=90\%$ and <diagnostic specificity> $56/80=70\%$. Only $18/42\simeq43\%$ of its positive results identify enlargement. These invented counts are not a reconstruction of the 41-patient study. They show why a palpable feature must be tested against an independent reference and interpreted with the population being examined.
Repeating a specified observation can assess reproducibility, while comparison with <echocardiography> assesses a different question: correspondence with the chosen anatomical reference. Holding body position and observation method consistent helps distinguish those sources of variation. A reliable description of what was felt is necessary evidence, but reproducibility alone does not establish the causal explanation.
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