E-Cigarette Effects on Markers of Cardiovascular and Pulmonary Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for E-Cigarette Effects on Markers of Cardiovascular and Pulmonary Disease (NCT03863509), a registered phase not stated study. The primary outcome is Brachial Artery Flow-Mediated Dilation (FMD)- Pre Challenge.

2. Clinical Question

The study is titled E-Cigarette Effects on Markers of Cardiovascular and Pulmonary Disease and is also identified by its official title as CLUES, the Cardiac and Lung E-cig Smoking Study. Its stated aim is to relate acute and longer-term use of e-cigarettes and conventional cigarettes to cardiovascular and pulmonary disease biomarkers. The primary endpoint is a measure of artery dilation rather than a clinical cardiovascular event or pulmonary diagnosis. The question is therefore about a biomarker measured under the stated pre-challenge conditions, not directly about whether a product causes disease or changes clinical outcomes.

3. Trial Design

The registry describes three groups: exclusive smokers, exclusive e-cigarette users, and never-users. The study was designed to examine associations between acute and longer-term product use and validated cardiovascular and pulmonary biomarkers. Participants could expect up to 4 weeks of study participation. The registry lists an enrollment of 450 and a status of completed. The recorded start date is 2019-03-05, and the primary completion date is 2022-03-09.

The group descriptions specify use patterns rather than assignment by the study. Exclusive smokers are described as smoking daily, at least 5 cigarettes per day for the last 6 months. Exclusive e-cigarette users are described as using e-cigarettes at least 5 days per week for the last 3 months. Never-users are described as having used fewer than 100 cigarettes in their lifetime, none for more than 5 years, and fewer than 3 instances of e-cigarette use in their lifetime. These criteria define the groups in the record; further eligibility criteria are not reported in the registry record.

The primary measure is pre-challenge brachial artery flow-mediated dilation at visit V2, up to 4 weeks from the enrollment visit, while fasting. The registry also describes assessment before and after an acute exposure challenge, but the posted primary endpoint is explicitly the pre-challenge value. The study lists cigarettes and e-cigarettes as behavioral interventions. Random allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. This means the design should be read as a comparison of distinct product-use groups, not as a randomized treatment contrast.

The record lists 28 outcome measures and 91 analyses. It names several secondary outcomes, including heart rate, heart rate variability, systolic blood pressure, forced vital capacity, fractional exhaled nitric oxide, autonomic measures, arterial pulse wave analysis, and treadmill exercise capacity. Details of the protocol, recruitment procedures, follow-up completion, and analysis populations are not reported in the registry record.

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: Participants tested for Exhaled CO and urinary nicotine to determine if they qualified for either arm of the study. E-cigarette vapers exclusively (exhaled CO less than 5 ppm and nicotine in urine), cigarettes exclusively (CO more or equal 5 ppm, positive urine nicotine), and controls (CO less than 5 ppm, and negative nicotine in urine). NOTE: one participant was enrolled twice completing all study visits. Later, when this was noticed, we amended procedures, only his initial data was used.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: % FMD pre-challenge after 8 hours refraining from nicotine exposure. A higher % dilation is an indication of better endothelial function.

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: results are reported for only those participants who completed the final study visit, when outcome data was collected.

6. Primary Endpoint

The registry lists the primary outcome as Brachial Artery Flow-Mediated Dilation (FMD)- Pre Challenge, measured over V2 up to 4 weeks from enrollment visit, fasting.

The primary endpoint is brachial artery flow-mediated dilation before the acute exposure challenge. It is expressed as percent change from resting diameter. The registry describes an ultrasound assessment in which a forearm cuff is inflated to 250mmHg for 5 minutes; the artery diameter is measured 60 to 90 seconds after cuff release and compared with its resting diameter. The posted endpoint is a mean with standard deviation, and the stated timeframe is visit V2, up to 4 weeks from enrollment, fasting.

FMD is used as a biomarker of endothelial function. The registry explains that a higher percentage dilation indicates better endothelial function. Its stated population condition is pre-challenge measurement after 8 hours refraining from nicotine exposure. This context matters: the endpoint represents a vascular response measured under specified conditions, not a direct count of cardiovascular events or a diagnosis of cardiovascular disease.

As a continuous measure, FMD can be summarized by group means and variability. A mean describes the central level of the measurement, while a standard deviation describes how dispersed individual measurements are around that mean. General statistical interpretation: these summaries do not alone establish whether groups differ beyond what might be expected from sampling variability. That assessment would require the analysis results and, for interpretation, information such as estimated contrasts and uncertainty intervals. Those primary outcome results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary measure: pre-challenge brachial artery flow-mediated dilation, expressed as percent change from resting diameter. General statistical context: continuous outcomes are commonly summarized with a mean and a measure of spread, such as the standard deviation. The record specifies those summary measures for the primary endpoint. A mean condenses the group’s measurements to a central value; a standard deviation indicates how much individual values vary around that mean. Neither quantity is reported for the primary outcome in the registry record.

What would a group contrast represent?

A statistical comparison of the groups would estimate how their average FMD measurements differ, under the analysis model used. General statistical context: the estimate describes the size and direction of a contrast, while a confidence interval describes a range of values compatible with the data and model at a chosen confidence level. A narrow interval indicates greater precision than a wide interval, though precision is not the same as freedom from bias. The registry does not report a primary contrast estimate or confidence interval, so the magnitude and precision of any difference cannot be assessed from this record.

Because group membership is based on product-use patterns and the comparison is not randomized, a group contrast should not automatically be interpreted as an effect caused by product use. General statistical context: randomization can help balance measured and unmeasured baseline characteristics on average, while nonrandomized groups can differ in characteristics related to both group membership and outcome. Statistical adjustment may address some measured differences, but cannot necessarily remove bias from unmeasured or poorly measured factors. The registry record does not state the allocation method, covariates, or adjusted analysis model.

Why does uncertainty matter?

An estimate is subject to sampling variability because it is based on observations from participants rather than every person in the target population. General statistical context: uncertainty intervals help distinguish a relatively precise estimate from one that remains compatible with a broad range of values. A p-value, when reported, addresses compatibility of data with a specified null model under assumptions; it does not measure the probability that the null hypothesis is true, the importance of an effect, or the probability that the finding will replicate. No primary confidence interval or p-value is reported in the registry record.

Interpretation also depends on the endpoint’s scale and measurement conditions. FMD here is a percent change from resting diameter, obtained after cuff occlusion and measured in the stated post-release window. The primary value is pre-challenge and is specified after 8 hours without nicotine exposure. These conditions define what the measurement represents. They do not make it interchangeable with other vascular measures, clinical events, or measurements taken under different conditions. The record states that a higher percentage dilation indicates better endothelial function, but does not report group results.

What is over-dispersion, and is it relevant?

General statistical context: over-dispersion means observed variability is greater than a statistical model expects. It is especially relevant for count outcomes or other outcomes whose model assumes a particular variance structure; ignoring it can make uncertainty appear too small. The primary endpoint is continuous and is summarized with a mean and standard deviation. The registry record does not describe an over-dispersion model or provide evidence that over-dispersion was assessed. This concept should not be used to infer a problem with the analysis in the absence of reported model details.

The registry lists 28 outcome measures and 91 analyses. General statistical context: multiplicity arises when many hypotheses or contrasts are considered. If each is assessed without an appropriate strategy, the overall chance of at least one false-positive finding may increase. Possible approaches include defining a hierarchy of outcomes, limiting confirmatory tests, or adjusting inference for a family of comparisons. Which analyses were prespecified, whether multiplicity was controlled, and how the 91 analyses relate to the listed outcomes are not reported in the registry record. The count of analyses is not itself evidence that a particular result is false or reliable.

How should planning illustrations be read?

The registry describes planning illustrations computed from the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect considered is a stated fraction of the observed effect. The record says that non-time-to-event illustrations are expressed as participants per arm, while time-to-event illustrations use total events. These are planning illustrations, not observed enrollment requirements or a retrospective measure of success. The observed effect and the calculated participant figures are not reported in the registry record. General statistical context: sample-size calculations depend on assumptions about the effect, variability, allocation, and statistical method. If those assumptions differ from the eventual analysis, the planning result may not describe the precision achieved. These illustrations are not observed power.

The trial enrollment is recorded as 450, but the registry does not report the number included in the primary analysis, outcome-specific missingness, or the handling of missing measurements. General statistical context: missing data can affect both precision and bias, depending on why values are missing and how the analysis handles them. A complete-case analysis, an imputation approach, or another method can lead to different assumptions and results. The analysis population and missing-data methods are not reported in the registry record. Consequently, enrollment alone cannot determine how many observations contributed to the primary estimate.

Finally, statistical significance, if reported elsewhere, would not by itself determine scientific or clinical importance. General statistical context: interpretation considers the estimated magnitude, uncertainty, measurement quality, study design, and relevance of the endpoint. Here, the record defines the biomarker and its measurement but does not give its observed values or inferential results. The information in the registry therefore supports an explanation of the intended statistical question, not a conclusion about the result.

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("Exclusive Smokers", "Exclusive E-Cig Users", "Never Users")
n   <- c(113, 164, 114)
m   <- c(4.25, 4.89, 5.31)
sp  <- c(3.17, 2.92, 3.43)
sd  <- sp      # posted standard deviations
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  Exclusive Smokers  113  4.250  3.170  3.659  4.841
CARM  Exclusive E-Cig Users  164  4.890  2.920  4.440  5.340
CARM  Never Users  114  5.310  3.430  4.674  5.946

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 28 outcome measures and 91 analyses. It identifies pre-challenge FMD as the primary outcome, and names secondary measures that include cardiovascular, pulmonary, autonomic, and exercise-related assessments. General statistical context: testing multiple outcomes and contrasts creates multiplicity concerns because the chance of a seemingly notable result can increase when many questions are examined. A prespecified primary outcome can help distinguish the main question from exploratory analyses, but it does not by itself explain how secondary tests were handled.

The registry record does not report a multiplicity adjustment, a hierarchy of tests, the prespecification status of individual analyses, or how the listed analyses were grouped. It also does not report the statistical analysis plan. The total number of analyses cannot establish which findings were confirmatory or whether any particular adjustment was appropriate.

Missing-data details are also not reported in the registry record. There is no account of missing primary measurements, reasons for missingness, or methods used to handle incomplete observations. The analysis populations are not reported, so the record does not clarify whether all enrolled participants, participants with available outcome measurements, or another defined group contributed to each analysis. The enrollment of 450 is not enough to establish the outcome-specific analyzed sample size.

General statistical context: missingness can reduce precision and may bias an estimate if the likelihood of an outcome being observed is related to participants’ characteristics or results. Different missing-data methods rely on different assumptions. Without the analysis method and amount of missing data, the direction or size of any such impact cannot be evaluated. The registry record also does not report interim analyses or stopping rules; their presence or absence should not be inferred.

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.

Most frequent non-serious adverse event terms

The registry reports serious adverse event counts separately for the three groups. For exclusive smokers, 117 were at risk and 0 were affected by a serious adverse event; deaths were 0. For exclusive e-cigarette users, 164 were at risk and 0 were affected by a serious adverse event; deaths were 0. For never-users, 114 were at risk and 0 were affected by a serious adverse event; deaths were 0. The record lists no top serious adverse event terms.

The registry also reports other adverse events: 0 among the 117 exclusive smokers at risk, 1 among the 164 exclusive e-cigarette users at risk, and 1 among the 114 never-users at risk. These are distinct from the serious adverse event counts and should not be conflated with them. The figures are counts as recorded; they do not establish that group risks are equivalent or that an event was caused by a product.

General statistical context: safety counts need to be interpreted in light of the event definitions, observation period, completeness of reporting, and the number of participants contributing follow-up. Those details are not fully reported in the registry record. The listed counts should therefore be read as the registry’s reported events, not as a comprehensive estimate of comparative safety.

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

The registry record establishes the study’s stated question and the primary biomarker measurement: pre-challenge brachial artery FMD, expressed as percent change from resting diameter, after 8 hours refraining from nicotine exposure. It describes the assay and explains that higher dilation indicates better endothelial function. It also gives group definitions, the study’s completed status, enrollment of 450, and an intended participation period of up to 4 weeks.

The record does not report the primary outcome values or statistical comparisons. It therefore does not show whether the groups’ FMD measurements were similar or different, how large any difference was, or how precisely it was estimated. It does not report a confidence interval or p-value for the primary endpoint. A completed study status cannot fill those gaps, and the planning illustrations based on an observed effect do not substitute for posted results.

Even if group contrasts are available from another source, their interpretation should respect the design. The registry says the comparison is not randomized, allocation is not stated, and the arms are not a like-for-like control comparison. General statistical context: observed differences between nonrandomized groups can reflect both the exposure pattern and other differences between the groups. Statistical adjustment may help with measured characteristics but does not automatically eliminate all confounding.

FMD is a biomarker, not a direct measure of cardiovascular or pulmonary disease events. A biomarker finding would not alone establish a change in future clinical outcomes. Nor do the listed adverse event counts provide a definitive comparison of safety: the registry reports no serious events and one other adverse event in each of the e-cigarette-user and never-user groups, while none are reported in the smoker group, but does not provide all details needed to assess event ascertainment or comparative risks.

The appropriate conclusion from the record is limited: it describes a completed three-group biomarker study and its primary measurement, but does not post the primary results or analysis details needed to judge the observed FMD pattern. No treatment or health-effect conclusion follows from the information reported.

14. Why This Trial Matters Statistically

This study is statistically notable for framing product-use patterns as groups and evaluating a continuous vascular biomarker under stated measurement conditions. The endpoint is clearly named, its scale is specified, and the registry explains the physiological measurement and the direction in which the biomarker is interpreted. These details help readers understand what the primary question concerns before considering any statistical result.

The nonrandomized structure is also central to the interpretation. The registry explicitly cautions that the arms are not a like-for-like control comparison and does not state allocation. This makes it important to distinguish a comparison of observed groups from a randomized estimate of an intervention effect. General statistical context: design information is part of the evidence, not a technical footnote; it determines what causal language the analysis can support.

The record includes 28 outcome measures and 91 analyses, making transparent reporting of outcome priorities, analysis populations, missing data, and multiplicity especially relevant. Those details allow readers to understand which results answer the main question and how much weight to place on additional analyses. They are not reported in the registry record. The sample-size assumptions are described as planning illustrations, not as the trial’s design, and the associated observed effect and calculated sample-size values are not reported.

The registry also illustrates the distinction between a biomarker and a clinical outcome. FMD can characterize endothelial function, but the endpoint is not itself a diagnosis or event. Statistically, this matters because the meaning of an estimated contrast depends on both its measurement and its relationship to outcomes of interest. The record gives a useful description of the measure while leaving the results and the analysis details unavailable for evaluation. A careful reading can therefore identify the scientific question and its design limits without turning missing results into a conclusion.

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.

Several design and reporting limitations are specific to the information in this registry record. First, the groups are based on patterns of cigarette or e-cigarette use and never-use, rather than a stated randomized assignment. The registry says allocation is not stated and cautions that the arms are not a like-for-like control comparison. As a result, group differences, if reported elsewhere, should not automatically be treated as effects caused by product use.

Second, the registry does not report the primary FMD results, group-level summaries, contrast estimates, confidence intervals, or p-values. It is therefore not possible to evaluate the direction, magnitude, or precision of the primary result from this record. Although the trial is marked completed, completion does not supply the missing outcome results.

Third, the record lists 28 outcome measures and 91 analyses, but does not report the statistical analysis plan, multiplicity procedures, adjustment variables, or which analyses were prespecified. It also does not report missing-data amounts, handling methods, or the analysis populations. These omissions limit assessment of how the reported enrollment relates to the observations used for each outcome.

Fourth, the primary measure is a biomarker and not a clinical disease event. Its interpretation is bounded by the described pre-challenge conditions, including fasting and 8 hours refraining from nicotine exposure. The registry describes measurements before and after an acute exposure challenge as part of the study aim, but the primary endpoint listed is pre-challenge; other results are not reported in the registry record.

Finally, the record describes sample-size calculations as planning illustrations derived from the observed effect, not as the trial’s own design. The observed effect and calculated sample-size values are not reported. Details of interim analyses, protocol deviations, and outcome-specific follow-up are also not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: E-Cigarette Effects on Markers of Cardiovascular and Pulmonary Disease — NCT03863509.
• Registry record last updated 2023-08-21; status last verified 2023-08.
• Results first posted 2023-08-21.
• 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

NCT03863509 is a completed study titled E-Cigarette Effects on Markers of Cardiovascular and Pulmonary Disease, also identified as CLUES. The registry records enrollment of 450, a start date of 2019-03-05, and a primary completion date of 2022-03-09. Participants were described in three groups: exclusive smokers, exclusive e-cigarette users, and never-users, with participation of up to 4 weeks.

The primary outcome is pre-challenge brachial artery flow-mediated dilation, reported as percent change from resting diameter and intended as a measure of endothelial function. The registry lists 28 outcome measures and 91 analyses. It states that this was not a randomized comparison, allocation is not stated, and the arms are not a like-for-like control comparison.

The record does not report primary outcome values, statistical comparisons, analysis populations, missing-data methods, or multiplicity procedures. Serious adverse events and deaths are recorded as 0 in each group; other adverse events are recorded as 0 among exclusive smokers, 1 among exclusive e-cigarette users, and 1 among never-users.