Jugular Venous Flow Healthy Volunteers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Jugular Venous Flow Healthy Volunteers (NCT02002494), a registered phase not stated study. The primary outcome is Internal Jugular Venous (IJV) Cross Sectional Area.

2. Clinical Question

The registry hypothesis predicts reduced internal jugular venous flow in the park bench position compared with supine, with a greater reduction on the dependent side. It also predicts the same internal jugular venous flow in prone and supine positions. These are hypotheses, not reported findings. The registry record does not provide numerical outcome estimates with which to assess them.

3. Trial Design

This completed study, titled “Jugular Venous Flow Healthy Volunteers,” is a position-comparison ultrasound study in volunteers. The official title describes the topic as the effect of different surgical positions on cerebral venous drainage. The sponsor is University Health Network, Toronto. The record lists a start date of 2013-06 and a primary completion date of 2014-02, with enrollment of 27.

The design description compares measurements within the same volunteer rather than assigning separate groups to different positions. It lists bilateral internal jugular venous flow comparisons for supine versus prone, supine versus park bench, and prone versus park bench. The primary outcome description specifically identifies comparisons of both internal jugular veins’ cross-sectional area in supine and prone positions. The population description also mentions Doppler velocity and flow.

The registry record does not state how the order of positions was determined, whether position order was randomized or counterbalanced, how long participants remained in each position, or whether measurements were repeated. These details can matter in a within-volunteer study because measurement order and time can affect comparisons; whether they were addressed in the study is not reported in the registry record. The record labels the intervention “Different positions,” with type “OTHER.”

The record lists six outcome measures but does not include numerical results or analysis entries. The number of analyses listed is zero. It does not report a statistical analysis plan, a sample-size justification for the study, or details about recruitment and participant characteristics beyond the volunteer population and enrollment. The sample-size planning assumptions associated with the record are illustrations, not a description of the study’s actual allocation or observed results.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Twenty-seven volunteers were included in this study.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Twenty-seven volunteers were included in this study. Comparisons of right and left internal jugular vein (IJV) cross sectional area, Doppler velocity and flow between supine and prone position.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: Twenty-seven volunteers were included in this study. The mean (SD) age, height and weight of these participants were analyzed.

6. Primary Endpoint

The registry lists the primary outcome as Internal Jugular Venous (IJV) Cross Sectional Area, measured over 1 day.

The listed primary endpoint is internal jugular venous cross-sectional area, with the unit cm2. Cross-sectional area describes the size of the vein’s internal opening at the measurement site. The registry specifies a mean as the summary measure and standard deviation as the dispersion measure. Its primary-outcome timeframe is 1 day, and the description names comparisons of both jugular veins in supine and prone positions.

In general, a continuous measurement such as cross-sectional area can describe how a vein’s dimensions vary between positions. The mean gives a central summary, while the standard deviation describes the spread of individual measurements around that mean. In a within-volunteer comparison, the relevant contrast is the change in a participant’s measurement between positions; a group-level summary can then describe the pattern across participants. Whether the study analyzed participant-level changes in this way is not reported in the registry record.

The record also describes Doppler velocity and venous flow as measures of interest, and the study hypotheses focus largely on flow. These are related but distinct measurements: cross-sectional area describes vein size, while velocity and flow describe blood movement. The primary endpoint therefore addresses one aspect of venous drainage rather than capturing every aspect of the stated hypothesis. The registry record does not give numerical endpoint results, units for the other measures, measurement procedures, or estimates of variation beyond the listed standard deviation summary type.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary measure as a continuous outcome summarized by a mean and standard deviation. It also describes measurements from both jugular veins and comparisons made within the same volunteer. These details determine which statistical ideas are relevant, but the actual analysis methods are not reported in the registry record. The explanations below are general statistical context, not a description of a confirmed analysis in this study.

What does a mean describe?

For a continuous measure, the mean is a way to summarize the central level of the measurements. It can be useful for comparing average cross-sectional area between positions, but a mean alone does not show how much participants differ from one another. The standard deviation describes the spread of individual values around the mean. A large spread can make a group average less representative of any particular participant, while a small spread indicates measurements are more clustered. The record specifies these summary types but does not report their values.

Why does within-volunteer pairing matter?

When each volunteer is measured in multiple positions, the measurements from that person are linked. In general, a paired analysis evaluates each person’s change between two positions and then summarizes those changes. This can account for stable differences between people, such as one volunteer having larger measurements in every position than another. Treating all measurements as if they came from unrelated participants can misrepresent uncertainty because it ignores the relationship among measurements from the same person. The registry describes same-volunteer comparisons, but does not identify the analysis used or state how dependence between right and left sides was handled.

For a paired comparison, the distribution of within-person differences is especially relevant. A mean difference would describe the average direction and size of those changes; its standard error would help quantify uncertainty. The registry record gives neither such estimates nor the underlying participant-level measurements. It is therefore not possible to assess assumptions about the distribution of differences or to recalculate an interval or test.

What does a confidence interval add?

In general, a confidence interval presents uncertainty around an estimated quantity, such as a mean difference between positions. A narrower interval indicates greater precision under the chosen model and assumptions; a wider interval indicates less precision. An interval also helps readers distinguish a small, precisely estimated contrast from a large but uncertain one. No confidence interval for a primary or secondary outcome is reported in the registry record.

A p-value, when reported, addresses compatibility between the data and a null hypothesis under a statistical model. It is not a measure of effect size, and it does not tell readers the probability that the null hypothesis is true. The registry record lists no analyses and no p-values. Neither statistical significance nor a lack of statistical significance can be inferred from the stated hypotheses, enrollment, or completion status.

How should multiple comparisons be considered?

The study description names comparisons among three positions, bilateral measurements and several types of measurement, including area, velocity and flow. In general, testing multiple outcomes or contrasts creates a multiplicity issue: the more opportunities there are to identify an apparently unusual result, the more important it is to know which comparisons were primary and how they were handled. A prespecified primary outcome can clarify the main question, but additional analyses still need transparent interpretation. The record identifies a primary outcome but does not report a multiplicity strategy or analysis hierarchy.

What does over-dispersion mean?

Over-dispersion is a general concern when data vary more than a statistical model expects. It is most often discussed for outcomes such as counts, where an assumed variance may be too small; it is not automatically the central issue for a continuous cross-sectional-area measure. For continuous outcomes, the variance structure and within-person correlation still need to be represented appropriately. The record provides no numerical data or model details with which to assess variance assumptions, outliers or model fit.

The record’s planning assumptions describe a sample-size illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation and an effect defined as a stated fraction of the observed effect. For non-time-to-event outcomes, the illustration is expressed as participants per arm. These are planning assumptions, not observed findings or the study’s documented design. The registry describes comparisons within the same volunteer, while the illustration assumes equal allocation between two arms; it should not be read as evidence that the volunteers were assigned to two independent groups. The record does not provide numerical planning results or the endpoint estimates underlying the illustration. Such calculations are not observed power and do not establish what the completed study detected.

10. Multiplicity, Missing Data and Analysis Populations

The registry names six outcome measures and describes multiple comparisons across supine, prone and park bench positions. It also identifies bilateral measurements and refers to cross-sectional area, Doppler velocity and flow. The primary endpoint is cross-sectional area in supine and prone positions, but the record does not explain how the other outcomes or position contrasts were ordered or prioritized for analysis. Whether any adjustment for multiple testing was planned or used is not reported in the registry record.

In general, multiplicity matters when several outcomes or contrasts are examined because repeated testing can increase the chance of at least one apparently unusual result. Prespecifying a primary question and distinguishing confirmatory from exploratory analyses can help readers interpret a collection of findings. Here, the registry identifies a primary measure, but numerical analyses and a multiplicity method are not listed. No conclusion about the handling of multiple comparisons can be drawn.

Missing-data procedures and the extent of missing measurements are not reported in the registry record. Although enrollment is 27 and the primary-outcome description refers to twenty-seven volunteers, that wording does not establish that all measurements were available for every outcome and position. The record does not state whether any participants or measurements were excluded, how missing values were handled, or whether sensitivity analyses were performed.

The analysis population is also not specified beyond the description of volunteers included in the study. There is no reported distinction among enrolled, measured and analyzed participants, and no analysis entries are listed. The registry record does not report an intention-to-treat framework, which is generally relevant to randomized treatment assignment and is not established for these within-volunteer position comparisons. These omissions limit assessment of how complete and representative the analyzed measurements were.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event record lists 27 volunteers at risk for serious adverse events, 0 affected by serious adverse events and 0 deaths. It also lists 27 at risk for other adverse events and 0 affected. No serious adverse-event terms are listed.

These figures describe what the registry record reports; they do not establish that no event of any kind occurred or that every possible event was captured. The record does not provide further detail about safety definitions, collection procedures, observation periods for adverse events, or whether events were assessed separately by position. The listed primary outcome has a timeframe of 1 day, but that does not by itself specify the safety-monitoring period.

In general, a count of zero recorded events is interpreted in the context of the number of participants, the duration and completeness of monitoring, and the way events were defined and collected. The registry figures should therefore be read as no serious or other adverse events recorded among the listed group, not as proof that risk is absent. These volunteers and positional measurements are not described as a randomized comparison of treatment groups, so the record does not support a comparative safety estimate between positions.

12. What the Result Does, and Does Not, Mean

The study addresses a focused physiological question: whether internal jugular measurements differ when the same volunteers are placed in supine, prone and park bench positions. Its primary endpoint is cross-sectional area, and its broader hypotheses concern venous flow and side-to-side differences. This design can be relevant to understanding positional variation in ultrasound measurements, but the registry record does not report the measurements or analyses needed to determine what patterns were observed.

The record therefore does not establish that flow decreased in park bench compared with supine, that the dependent side had a greater reduction, or that flow was the same in prone and supine. Those statements are hypotheses in the study description. Likewise, the absence of posted estimates does not show that there was no difference. Without effect estimates and uncertainty intervals, the size and precision of any positional contrast remain unknown.

Even if results were available, their interpretation would be tied to the population and measurements studied. The record describes 27 healthy volunteers and ultrasound measurements of the internal jugular veins. It does not report a patient population, clinical outcomes, or evidence about consequences beyond the listed measurements. A change in cross-sectional area is not itself a direct estimate of a clinical benefit or harm.

The within-volunteer structure allows comparisons of positions in the same people, but interpretation depends on measurement procedures, position order, missing data and statistical handling of repeated and bilateral measurements. Those details are not reported. The completed status indicates the study record is marked completed; it does not mean that the results are available or that a hypothesis was confirmed.

The most defensible conclusion is about the limits of the record: it documents a planned and completed ultrasound comparison with enrollment of 27, but does not provide numerical outcome findings. It cannot support a claim that one position changes venous flow or area, that positions are equivalent, or that a difference is clinically important. Any such judgment would require results and analysis details not reported in the registry record.

13. Why This Trial Matters Statistically

This study is statistically interesting because its central comparisons are within the same volunteer. Repeated measurements can remove some between-person variation from a position contrast, but they also require methods that respect the dependence among observations from the same participant. The registry describes this paired structure clearly enough to identify the statistical issue, while leaving the actual analysis unreported.

The study also illustrates the distinction between a biological hypothesis and a reported statistical result. The registry sets out predictions about flow in different positions, yet no numerical results or analysis entries are listed. Readers need estimates and measures of uncertainty to assess direction, magnitude and precision; a hypothesis alone cannot answer those questions. A completed study status and an enrollment count do not substitute for those results.

There is also a useful distinction between the named primary endpoint and the broader set of measurements and comparisons. Cross-sectional area is the listed primary outcome, while the study description also discusses velocity and flow and several positional contrasts. This makes clear why a prespecified analysis plan and transparent treatment of multiple outcomes matter. Whether such methods were used is not reported in the registry record.

Finally, the planning assumptions associated with the record should be separated from the study’s observed evidence. A sample-size illustration is a planning exercise, not a result and not observed power. The assumptions describe a two-arm allocation even though the clinical comparison is described as measurements in the same volunteers. Keeping these roles distinct helps prevent planning calculations from being mistaken for proof of a finding.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The principal limitation for statistical interpretation is the absence of posted numerical results. The registry record does not report means, standard deviations, position contrasts, confidence intervals or p-values for the primary outcome, and it lists no analyses. Consequently, readers cannot assess effect size, direction, precision or statistical evidence.

The study description does not report details of measurement acquisition, such as the precise ultrasound protocol, measurement location, assessor procedures or reproducibility. It also does not state position order, time in position or whether order effects were considered. These details could affect interpretation of within-volunteer comparisons, but their handling is not reported in the registry record.

Participant information is limited. The record identifies 27 healthy volunteers but does not report demographic characteristics, eligibility criteria or recruitment methods. The number of volunteers alone does not indicate how representative the measurements are, and no numerical variability estimates are available to judge precision.

The analysis plan is not reported. In particular, the record does not explain how paired measurements, right and left sides, multiple outcomes or multiple position contrasts were handled. Missing-measurement counts, exclusions, analysis populations and missing-data procedures are also not reported. These gaps prevent assessment of whether the analyzed measurements, if any, differed from those planned.

Finally, the record describes a focused set of ultrasound measurements in volunteers. It does not report clinical outcomes or establish how the measured positional changes relate to outcomes beyond those measurements. The stated hypotheses should therefore remain distinct from findings, and no clinical conclusion can be drawn from the registry information alone.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Jugular Venous Flow Healthy Volunteers — NCT02002494.
• Registry record last updated 2020-06-04; status last verified 2020-05.
• Results first posted 2020-06-04.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT02002494 is a completed ultrasound study titled “Jugular Venous Flow Healthy Volunteers.” The official title describes an examination of different surgical positions and cerebral venous drainage in healthy volunteers. The sponsor is University Health Network, Toronto. The record lists a start date of 2013-06, a primary completion date of 2014-02 and enrollment of 27.

Volunteers were compared in supine, prone and park bench positions. The listed primary endpoint is internal jugular venous cross-sectional area in cm2, summarized as a mean with standard deviation, with a timeframe of 1 day. The record also discusses Doppler velocity and flow. Six outcome measures are listed, but no analysis entries or numerical outcome results are reported.

The record lists 0 volunteers with serious adverse events, 0 with other adverse events and 0 deaths among 27 at risk in each adverse-event category. It does not report the statistical analysis plan, missing-data procedures or multiplicity handling. The hypotheses about positional flow changes are not accompanied by results that would confirm or refute them.