Endothelial Function in Lower Extremity Bypass Grafts: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Endothelial Function in Lower Extremity Bypass Grafts (NCT00759707), a na na study. The primary outcome is Change From Baseline in Saphenous Vein Bypass Graft Vasodilation.

2. Clinical Question

3. Trial Design

The registry record describes a completed, single-group study titled Endothelial Function in Lower Extremity Bypass Grafts. It lists the condition as peripheral arterial disease, enrollment as 19, and phase as NA. Allocation is listed as NA, masking as SINGLE, and the study model as SINGLE GROUP. These entries describe the registry classification; they do not establish details beyond what the record states.

The recorded study dates are start 2006-04 and primary completion 2009-12. The study status is COMPLETED. The timeframe for the primary measure is a single visit study. No separate parallel control arm or randomized allocation is described. The arm description combines ultrasound imaging after an ischemic stimulus with sublingual nitroglycerin and intravenous L-NMMA. The record does not state the purpose or timing of each drug relative to every measurement beyond the procedure details given for the primary outcome.

The primary outcome is continuous and reported as a mean, with standard error identified as the dispersion measure. The registry lists one outcome measure and zero analyses. Although it gives a detailed description of the cuff-based measurement, it does not include a numerical outcome estimate or an inferential result. Statistical analysis methods beyond the general planning assumptions recorded for sample-size illustrations are not reported in the registry record.

As a single-group physiological assessment, the design can describe the measured graft response under the recorded procedure. It cannot, on its own, separate that response from changes that might occur over time, procedural influences, or other explanations that a concurrent comparison might help assess. The registry record does not report a protocol-level account of these design considerations.

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.

Overall Study

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.

6. Primary Endpoint

The registry lists the primary outcome as Change From Baseline in Saphenous Vein Bypass Graft Vasodilation, measured over Single visit study.

The primary endpoint is change from baseline in saphenous vein bypass graft vasodilation. Its unit is vein bypass graft size increase (%), and the measure is specified as a continuous outcome summarized by a mean with standard error. The description defines flow-mediated, endothelium-dependent vasodilation by comparing baseline graft diameter with the diameter measured after release of an ischemic stimulus.

For that stimulus, a 2.5-inch wide sphygmomanometric cuff was inflated to suprasystolic pressure for 5 minutes. The cuff was not placed directly over the graft. Images were acquired 1 minute after cuff deflation. These details identify the intended measurement occasion and procedure; they do not provide the resulting diameter change.

In general, a flow-mediated response is used to characterize how a vessel changes after blood flow increases. A graft diameter response can therefore serve as a physiological measure relevant to the study’s question about endothelial function. This is a measurement rationale, not evidence that the response was present or that it predicts a clinical outcome. The registry gives no numerical endpoint value, standard error, confidence interval, or analysis result, so the magnitude and precision of the endpoint cannot be judged from the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods must be interpreted in light of what the registry record actually reports. It identifies a continuous primary measure summarized by a mean and standard error, but lists zero analyses and provides no numerical outcome estimate. The concepts below explain the statistical meaning of the recorded measure and design in general; they do not imply that a particular analysis was conducted.

What does a mean describe?

In general, a mean represents the average value of a continuous measurement in the observations included in an analysis. Here, the registry identifies the primary measure as change from baseline in graft vasodilation and gives graft size increase (%) as its unit. The record does not state the numerical mean or the number of observations used to obtain it. Consequently, neither the average response nor the distribution of individual responses can be reconstructed from the registry entry.

How is a standard error different from a standard deviation?

In general, a standard deviation describes the spread of individual observations around their mean. A standard error describes uncertainty in an estimated mean and is used to indicate how precisely that mean is estimated. They answer different questions: a dataset can show substantial variation among observations while still yielding a relatively precise mean, depending on the amount of information available. The record names standard error as the dispersion measure but does not report its value. It also does not report a standard deviation. No conversion between those quantities is possible from the information in the registry record.

What does a baseline comparison establish?

The primary outcome description compares baseline graft diameter with diameter after cuff deflation. In general, a paired or within-unit comparison can account for the fact that measurements taken from the same unit are related, if the analysis uses that structure. It can describe a change from a reference measurement. But a baseline is not a concurrent control group: it does not show what would have happened at the same time without the stimulus or procedure. The registry record does not report the statistical method used to quantify the change, whether paired observations were analyzed, or how any repeated measurements were handled.

Why does the single-group design matter?

In general, a single-group physiological study can characterize measurements under specified conditions, but causal interpretation is limited when there is no independent comparison group. Differences between baseline and a later measurement may reflect the stimulus, measurement variability, procedural effects, or other influences. A controlled design can help distinguish explanations, though its success depends on its conduct and analysis. The record classifies this study as SINGLE GROUP and allocation as NA; it does not report a randomized comparison.

What can a confidence interval contribute?

In general, a confidence interval gives an uncertainty range for an estimate under a specified statistical procedure. It helps readers consider both the estimated effect and the precision of that estimate, rather than relying only on whether a test crosses a threshold. Its interpretation depends on the model, assumptions, and data. The registry record does not report a confidence interval or a method for calculating one. It therefore cannot support a statement about the range of plausible values for the primary response.

Why can over-dispersion matter?

In general, over-dispersion means that variation in data is greater than a statistical model assumes. If a model underestimates variability, standard errors may be too small and inferential results may appear more precise than warranted. This concern is especially relevant when an analysis assumes a specific variance structure. The primary endpoint is continuous, and the record does not identify an analysis model or report a variance estimate, so there is no basis to claim that over-dispersion was assessed or present. This general issue should not be mistaken for a documented feature of this study.

How should the planning assumptions be read?

The record describes planning illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also describes planning for a stated fraction of the observed effect. These are assumptions for hypothetical sample-size calculations, not the study’s recorded design: the study is single-group. Any sample-size value derived under those assumptions is a planning illustration, not observed power. Observed power is not a substitute for an effect estimate and its uncertainty. The numerical planning outputs and the observed effect are not reported in the registry record, so their values cannot be interpreted.

The registry does not state the sample-size justification for the actual study, whether interim analyses were planned, or the statistical analysis plan. Those details are not reported in the registry record. The absence of an analysis result also means that no recalculated estimate can be compared with a sponsor analysis. If recalculated estimates and a discrepancy were reported elsewhere, the sponsor’s own analysis would take precedence when the discrepancy flag is true; no such comparison is described in this record.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Study Population")
n   <- c(19)
m   <- c(5.28)
sp  <- c(3.1)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Study Population  19  5.280  13.513  -1.233  11.793

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and zero analyses. It does not report a set of analyzed endpoints, repeated hypothesis tests, or a multiplicity adjustment. Whether multiplicity was considered in a protocol or analysis plan is not reported in the registry record. In general, when many outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase; methods such as prespecifying a primary outcome or adjusting inference can address that issue. The record does not establish that such methods were used or needed for the analyses, because no analysis is listed.

Missing-data handling is not reported in the registry record. The record does not say whether any primary measurements were missing, whether exclusions occurred, or whether imputation or another method was used. In general, missingness can affect an estimate if the observations available for analysis differ systematically from those not available. The number enrolled alone does not reveal how many contributed a usable outcome measurement.

The analysis population is also not described. There is no reported definition of which participants or measurements were included in an outcome analysis, and the registry lists zero analyses. No intention-to-treat, per-protocol, or other analysis population is specified in the record. These gaps limit assessment of how the endpoint was handled from measurement through reporting. They do not establish that missing data, multiplicity, or population-definition problems occurred; they mean the relevant methods are not reported in the registry record.

12. 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 entry lists a Study Population group with 19 at risk and 0 affected for serious events. It also lists 19 at risk and 0 affected for other events, and deaths are recorded as 0. No serious-event terms are listed. These are the registry’s reported figures, not a guarantee that no event could occur outside the recorded collection and reporting process.

The registry record does not specify the adverse-event ascertainment window, the procedures for collecting events, or whether the figures cover the entire study period or a particular visit. The primary study timeframe is described as a single visit study, but that does not by itself define the safety follow-up period. The record also does not provide event narratives, severity details beyond the serious-event category, or a breakdown by intervention exposure.

In general, a zero count in a registry entry means that no affected participants or events were recorded in that entry; it does not establish absence of risk. The recorded at-risk figures should not be treated as proof that every enrolled participant had complete safety follow-up, since the follow-up and analysis details are not reported. These safety figures should be read narrowly as registry-reported counts.

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

The registry record describes a study designed to measure whether saphenous vein bypass grafts in the leg dilate following an increase in blood flow. It identifies the cuff-based stimulus, the imaging timing, and the primary measure. It also records the study as completed and single-group. These details clarify the research question and how the physiological response was intended to be assessed.

What the record does not establish is the numerical size of the response. The primary endpoint mean and standard error are not reported in the registry record, and zero analyses are listed. Without an estimate, its uncertainty, or an analysis result, readers cannot determine whether a response was observed, how large it was, or how precisely it was estimated. The missing result should not be interpreted as a finding of no change.

Even if a within-graft change were reported, a change from baseline would not be equivalent to a controlled treatment effect. The study has no concurrent comparison group described in the registry record. In general, the observed difference across measurement conditions could reflect more than the intended physiological stimulus. A single-group assessment can provide descriptive evidence about a measurement under specified conditions, but causal claims require careful attention to design, measurement, and possible alternative explanations.

The record also does not demonstrate whether the measured physiological response predicts graft performance, patient outcomes, or the effect of a clinical intervention. Those are separate questions requiring appropriate outcome data and design. The registry’s endpoint is graft vasodilation, not a reported clinical outcome. Accordingly, the available information supports a description of study intent and measurement, not a clinical conclusion about benefit, lack of benefit, or individual care.

The adverse-event entry records zero affected for serious and other events and zero deaths. Those counts are limited to what the registry reports and do not establish that risk is absent. Overall, the record is informative about the protocol’s measurement approach but incomplete for evaluating the primary result, its precision, and its safety context.

14. Why This Trial Matters Statistically

This study raises a useful statistical distinction between measuring a physiological response and establishing a causal effect. The endpoint compares graft diameter at baseline with a measurement after a defined cuff stimulus. That can frame a focused question about flow-mediated vasodilation. Yet without a concurrent control group, the resulting change would not automatically isolate the effect of the stimulus from other influences. The design classification is therefore central to interpreting any estimate.

It also illustrates why a result needs both an effect estimate and information about precision. A mean alone would describe the average response in the analyzed observations, while a standard error or confidence interval would help show how precisely that mean was estimated. The registry names a mean and standard error as the intended summary but does not report their values. No analysis is listed, so the principal statistical evidence needed to evaluate the study’s question is missing from the record.

The endpoint is a continuous measurement, and the record gives useful procedural detail: the cuff was not placed over the graft, it was inflated to suprasystolic pressure for 5 minutes, and images were acquired 1 minute after release. Such details help define what was measured and when. They do not replace outcome reporting, a clear analysis population, or a description of missing-data handling.

Finally, the record’s planning assumptions provide a reminder that sample-size calculations belong to a design context. The stated illustrations assume equal allocation between two arms, although this study is recorded as single-group. Those assumptions should not be read as the actual study design or as evidence of observed power. Careful separation of the measurement protocol, analysis plan, and hypothetical planning calculations is necessary for a sound statistical reading.

15. 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 most immediate limitation is the absence of a numerical primary outcome result. Although the registry identifies the endpoint, unit, summary measure, and dispersion measure, it does not report the mean change or standard error. It also lists zero analyses. The magnitude, direction, and precision of the primary response therefore cannot be evaluated using the registry record.

The design is single-group, with allocation listed as NA and no concurrent control comparison described. A baseline measurement provides a reference but cannot serve as a simultaneous control for all influences on the post-stimulus measurement. The record does not report additional design features that might address alternative explanations, nor does it describe a statistical model for the endpoint.

The registry does not report how many enrolled participants contributed analyzable measurements, how missing observations were handled, or how the analysis population was defined. It also does not report a protocol-level sample-size justification or an interim-analysis plan. These omissions prevent assessment of whether the available data and analysis matched the intended design. They should not be taken as evidence that data were missing or that an interim analysis occurred.

The procedure is described as a single-visit assessment, but the registry does not explain the timing of all procedures relative to one another or provide further details about measurement reproducibility. It does not report how observer or instrument variability was evaluated. Masking is recorded as SINGLE, but the record does not identify who was masked or how masking was implemented.

Safety reporting is also limited: the event counts are recorded, but the ascertainment period and collection methods are not. Finally, the study’s endpoint is a physiological measure; the registry record does not report clinical outcomes or establish how this measure relates to them. These limitations restrict interpretation to the stated measurement question and prevent broader conclusions about clinical effects.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Endothelial Function in Lower Extremity Bypass Grafts — NCT00759707.
• Registry record last updated 2017-05-16; status last verified 2017-04.
• Results first posted 2017-04-06.
• 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.

19. Record Summary

The registry record describes a completed single-group study of endothelial function in lower extremity saphenous vein bypass grafts. It lists peripheral arterial disease as the condition, enrollment of 19, masking as SINGLE, and a single-visit timeframe. The recorded intervention is intravenous L-NMMA, and the arm description also includes ultrasound imaging after an ischemic stimulus and sublingual nitroglycerin.

The primary endpoint is change from baseline in graft vasodilation, expressed as vein bypass graft size increase (%), with a mean and standard error specified. The cuff-based measurement procedure is described, but the numerical endpoint result is not reported in the registry record. The record lists one outcome measure and zero analyses.

Serious events, other events, and deaths are recorded as 0 affected or deaths, with the listed at-risk figures. The safety follow-up details are not reported in the registry record. The entry defines the study question and measurement procedure, but does not permit assessment of the primary result or its statistical precision.