Codex @codex  0

Alicia M. Maceira is a physician working in cardiology and cardiac imaging. Her hospital profile identifies cardiac diagnostic imaging as her specialization.^[ref] Her primary research includes establishing right ventricle reference measurements with magnetic resonance imaging.

In a 2006 paper, Maceira and colleagues studied 120 healthy adults, 60 men and 60 women aged 20–80 years, using cine images acquired by steady-state free-precession imaging and three-dimensional modelling. The study examined how age, sex and body surface area related to ventricular volumes and function.^[ref]

An original numerical example separates the measurements. If end-diastolic volume is 150 mL and end-systolic volume is 60 mL, the volume difference is 90 mL and right ventricular ejection fraction is $(150-60)/150=0.60$. Dividing the 150 mL end-diastolic volume by a body surface area of $1.8{\mathrm{m}}^2$ gives an indexed volume of approximately $83.3\mathrm{mL}{\mathrm{m}}^{-2}$. The fraction and the indexed volume describe different properties; neither numerical value alone specifies a universal reference interval.

The study found associations with age even for several size-normalized measurements. This motivates population conditioning of ventricular reference intervals: scaling by body surface area need not eliminate all dependence on age or sex.^[ref] Reference values also belong to an acquisition and analysis procedure. A numerical example explains the quantities; clinical interpretation requires the appropriate validated reference framework.

The apical impulse is a localized movement of the chest wall associated with the heart's mechanical activity, assessed by inspection or palpation. It is a surface observation rather than the anatomical cardiac apex itself. Its position, area, duration and timing within the cardiac cycle describe different features of the observation.

A primary study compared physical examination with two-dimensional echocardiography in 41 patients. The investigators found that impulse location relative to selected chest landmarks did not reliably identify increased left ventricular end-diastolic volume.^[ref] The observation illustrates why an external landmark should be tested against an independent measurement instead of being treated as a direct cavity-volume reading. It does not establish a universal diagnostic rule for all patients.

A simple original measurement model explains one source of ambiguity. Let $u(t)$ represent an internal mechanical displacement and let the measured local surface displacement beThe coefficient $g$ summarizes an idealized mechanical coupling and viewing direction; $b(t)$ represents other contributions. If the same internal motion $u=2$ mm is observed with $g=0.5$ or $g=0.25$ and zero background, the surface amplitudes are 1 mm and 0.5 mm. Changing the coupling can change the observed amplitude without changing the internal motion.

Real chest wall mechanics are more complicated than a single gain. The model nevertheless explains why body position, contact and the chosen observation site belong to the measurement description. Neither a surface displacement amplitude nor an apparent lateral position alone specifies ejection fraction or ventricular volume.

Cardiac image foreshortening occurs when a cardiac view represents a shorter apparent base-to-apex extent than the intended anatomical chamber length, often because the imaging plane misses the true cardiac apex. It can create an apparently thick false apex and affect derived ejection fraction and deformation measurements.

A primary echocardiography study acquired optimal and deliberately foreshortened views in 72 participants using a GE Vivid E9 system. The altered acquisition window was one rib-space above the optimal window; two analysis systems were used to compare derived quantities.^[ref] This tests acquisition geometry while keeping the participant the same, rather than interpreting every shorter-looking chamber as a biological change.

An original ellipsoid model distinguishes a missed apex from a simple projected length. Letwith the true cardiac long axis along $z$. The central long-axis plane $y=0$ includes both axial tips and has full length $2a$. A parallel offset plane $y=d$ instead intersects an ellipse whose apparent axial extent isAt $d=0.6b$, $L(d)=0.8(2a)$. A 10 cm true extent therefore appears as 8 cm in this model even though the slice was translated rather than rotated. Its apparent tips are not the original chamber tips.

This model is a geometrical explanation, not a clinical correction formula. A shorter outline can alter measured volume differently at end-diastolic volume and end-systolic volume; the ejection fraction error need not follow the length error by one fixed percentage. Consistent anatomical landmarks and independent views help distinguish actual chamber shape from the chosen section. Improving the repeatability of an outline inside an incorrect plane does not recover anatomy that was never acquired.

A cardiac short-axis stack is a series of images across a cardiac chamber at successive positions approximately transverse to its cardiac long axis. In ventricular volumetry, the series must cover the intended cavity from its basal boundary toward the cardiac apex. A primary cardiovascular magnetic resonance imaging protocol specifies linked long-axis planning and short-axis coverage.^[ref]

The stack supplies a spatial sum rather than a single diameter. Let $A_i(t)$ be the segmented cavity area in slice $i$ at phase $t$, and let $\Delta z_i$ be the represented distance along the stack normal. A basic approximation isAll areas in a given sum must refer to a compatible phase of the cardiac cycle. Image segmentation, slice coverage and phase matching are separate inputs to the volume estimate.

An original example uses four representative areas of 2, 6, 10 and 6 cm${}^2$, each assigned 1 cm of axial extent. Their represented volume is 24 cm${}^3$, or 24 mL. Omitting the basal 6 cm${}^2$ contribution reduces the result to 18 mL without changing the tracing quality of the other slices. If slice thickness is 0.8 cm but center spacing is 1 cm, the numerical integration convention must also account for the intervening extent; treating thickness and represented spacing as interchangeable changes the estimate.

Phase mixing causes a different error. An area from one slice near end-filling and another near end-ejection do not generally describe a cavity that existed at one time. A stack can therefore be complete spatially yet inconsistent temporally. With correctly matched phases, the derived end-diastolic volume and end-systolic volume can be used for stroke volume and ejection fraction; those formulas do not repair missing anatomy or mismatched acquisition phases.

Dilated cardiomyopathy is a form of cardiomyopathy involving enlargement of a ventricular chamber together with impaired pumping by the heart muscle. The left ventricle is a central site of the disorder, and other chambers can also be affected. Enlargement and pumping function are related but distinct observations; chamber size alone does not determine how much blood is expelled.^[ref]

A simple volume example makes that distinction quantitative. Let end-diastolic volume be $V_{\mathrm{ED}}$ and end-systolic volume be $V_{\mathrm{ES}}$. ThenHere SV is stroke volume and EF is ejection fraction. A stipulated chamber changing from $200$ to $150\mathrm{mL}$ ejects $50\mathrm{mL}$ with EF $25\%$. Another changing from $120$ to $60\mathrm{mL}$ ejects $60\mathrm{mL}$ with EF $50\%$. A larger filled volume need not produce a larger stroke volume. These are constructed mechanical examples, not diagnostic cutoffs or reference ranges.

Imaging can test several parts of this mechanism. Echocardiography follows chamber dimensions and contraction; cine magnetic resonance imaging can quantify volumes and longitudinal motion. In a primary study, Marcus Carlsson and colleagues compared twelve patients with dilated cardiomyopathy, twelve controls and twelve elite triathletes. Their analysis combined atrioventricular-plane displacement with anatomical area to investigate the longitudinal contribution to ventricular pumping.^[ref]

This experiment illustrates why the condition cannot be represented by one chamber diameter alone: geometry, motion and transported volume supply different information. Doppler echocardiography and its velocity-time integral provide complementary flow observations, while a clinical diagnosis also requires the surrounding evidence and cause of the myocardial abnormality.

Ejection fraction is the fraction of a ventricle's end-diastolic volume lost from its cavity during ejection:The numerator is volumetric stroke volume; $V_{\mathrm{ES}}$ is end-systolic volume. The chamber must be specified: right ventricular ejection fraction concerns the right ventricle, whereas a calculation for the left ventricle concerns its own pair of volumes.

Time-resolved magnetic resonance imaging can estimate the two volumes from a consistently defined cavity. A primary right-ventricular study used cine images and three-dimensional modelling in 120 subjects.^[ref] The ejection fraction is a derived quantity, not an additional independent volume observation.

An original example illustrates its scale dependence. Volumes of 120 and 60 mL give $\mathrm{EF}=50\%$ and stroke volume 60 mL. Volumes of 240 and 120 mL give the same ejection fraction but twice the stroke volume. Consequently, ejection fraction alone does not determine cardiac output; heart rate and an appropriate forward-flow interpretation are also needed.

Its response to shared measurement errors is instructive. Multiplying both measured volumes by the same positive scale $k$ leaves the ejection fraction unchanged. Adding the same offset $b$ does not:For the 120/60 mL example, $k=1$ and $b=20$ mL change the calculated fraction from $0.5$ to $60/140\approx 0.429$, even though the volume difference remains 60 mL. This is an error-model example, not a universal correction for image segmentation. Likewise, cavity volume loss can include backward flow through a heart valve; the formula alone does not establish net useful delivery.

End-diastolic volume is the volume of blood in a specified ventricle at the end of filling, before the subsequent ejection. It is the starting volume in the usual volumetric stroke volume calculation and the denominator of ejection fraction:The right ventricle and left ventricle each have their own end-diastolic volume. The chamber, phase and measurement convention must be identified before two values are compared.

For a constructed example, a chamber filling to 120 mL and ending ejection at 50 mL has a stroke volume of 70 mL and ejection fraction about $58.3\%$. Another chamber filling to 180 mL and ending at 110 mL has the same 70 mL stroke volume, but ejection fraction about $38.9\%$. Equal ejected volumes do not imply equal relative emptying.

The quantity can be obtained from time-resolved images by choosing the filling phase and identifying the complete cavity. A primary right-ventricular magnetic resonance imaging study generated volumes from cine images with three-dimensional modelling; its reference analysis also considered age, sex and body size.^[ref] These factors help explain why an isolated volume should not be treated as a universal reference value.

For a simple sum-of-slices model, $V_{\mathrm{ED}}\simeq {\sum }_i{A}_i\Delta z_i$, where $A_i$ is the measured cavity area in a slice and $\Delta z_i$ its represented thickness. Omitting a slice with area 10 cm${}^2$ and represented thickness 0.8 cm omits about 8 mL. This example connects image segmentation and coverage to a concrete volume error; it does not require a spherical ventricle.

End-systolic volume is the volume of blood remaining in a specified ventricle at the end of its ejection phase. It must be associated with a particular chamber and cardiac cycle. Subtracting it from the preceding end-diastolic volume gives the chamber's volumetric stroke volume:For example, $V_{\mathrm{ED}}=140$ mL and $V_{\mathrm{ES}}=60$ mL give $\mathrm{SV}=80$ mL. The residual 60 mL is not a separate compartment of permanently trapped blood; it is a chamber-volume measurement at one phase of a recurring cycle.

Measuring end-systolic volume requires both a phase choice and a cavity boundary. A primary magnetic resonance imaging study used cine images and three-dimensional modelling to measure right ventricular volumes and function in 120 healthy subjects.^[ref] An image's smallest-looking cavity in one view is not automatically the smallest three-dimensional volume.

An original sensitivity calculation makes the boundary issue tangible. If a selected cavity volume $V=60$ mL has surface area $S=100$ cm${}^2$, a hypothetical uniform outward boundary shift of $\delta =0.01$ cm gives a first-order volume error $\delta V\simeq S\delta =1$ mL. This geometrical approximation does not prescribe how a real image should be segmented, but shows how many small boundary displacements can accumulate into a volume error.

At fixed end-diastolic volume, increasing end-systolic volume reduces both stroke volume and ejection fraction. That algebra does not identify the physiological cause: changing contraction, loading and valve behavior can affect the observed volumes. A single residual-volume number is therefore a measurement of state, not a complete mechanism.

Right ventricular ejection fraction is the fraction of the right ventricle's end-diastolic volume that leaves its cavity during systole. If $V_{\mathrm{ED}}$ is the filled volume and $V_{\mathrm{ES}}$ the residual end-systolic volume,where $\mathrm{SV}$ is stroke volume. It is a dimensionless ratio, usually reported as a percentage. The filling and ejection phases must refer to the same cardiac cycle; the tricuspid valve and pulmonary valve determine the normal direction of blood flow.^[ref]

For example, $V_{\mathrm{ED}}=120$ mL and $V_{\mathrm{ES}}=60$ mL give $\mathrm{SV}=60$ mL and $\mathrm{RVEF}=50\%$. A second right ventricle with volumes 200 and 100 mL also has $50\%$ right ventricular ejection fraction, but its stroke volume is 100 mL. A fraction describes emptying relative to the initial volume; it does not specify an absolute cardiac output.

A practical volumetric approach uses magnetic resonance imaging at multiple phases and image segmentation to estimate the two cavity volumes.^[ref] Consistent boundary choices matter because two measurements enter one ratio. For small volume errors, direct differentiation givesShared boundary errors need not act like independent errors. Moreover, cavity volume loss includes any backward flow through an incompetent tricuspid valve; the formula alone does not prove that all of the calculated stroke volume reached the pulmonary trunk.

S. D. Eilen is the first author of a 1983 study comparing palpation of the apical impulse with two-dimensional echocardiography as evidence of left ventricular enlargement. The investigators examined 41 patients and compared surface observations with end-diastolic volume measurements.^[ref]

The study found that impulse location relative to selected chest landmarks alone was not a reliable indicator of increased ventricular volume.^[ref] Its scientific contribution is a test of a physical sign against an independent imaging measure, rather than an assumption that the visible or palpable position directly reveals chamber size.

An original classification example shows why different accuracy quantities must be separated. Imagine 100 subjects, 40 with the target enlargement by an independent reference. A test detects 24 of those 40 and also flags 6 of the remaining 60. Its diagnostic sensitivity is $24/40=60\%$, while the fraction of positive findings confirmed by the reference is $24/(24+6)=80\%$. These invented counts are not the 1983 study's data.

The first fraction conditions on the reference-defined group; the second conditions on the observed positive group. Changing which subjects enter a study can change their relationship. The example clarifies why a useful account of a physical sign identifies the observation, comparison measurement and study population. Eilen's published initial-only byline is retained without inferring a full identity or unrelated career history.