Study to Test Sensitivity and Specificity of Passive Wave Pressure Device in Determining Ischemic Stroke: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study to Test Sensitivity and Specificity of Passive Wave Pressure Device in Determining Ischemic Stroke (NCT01643525), a registered phase not stated study. The primary outcome is Number of Participants With Device Related Adverse Events.

2. Clinical Question

3. Trial Design

This was a nonrandomized, multicenter study of the Nautilus NeuroWaveTM System. The registry title describes a non-significant-risk study using a noninvasive passive pressure-wave method to develop a diagnostic algorithm for cerebral ischemia and test the algorithm’s sensitivity and specificity for determining ischemic stroke. Enrollment was 29, and the record lists the study status as terminated. The study start is recorded as 2012-06, and primary completion as 2012-12.

The registry describes two cohorts: subjects with stroke symptoms who presented to hospital and were evaluated for stroke, and a normal cohort of subjects not being evaluated for stroke who were confirmed to have no cerebrovascular disease. It does not report the number assigned to either cohort. Allocation is not stated, and the record cautions that this was not a randomized comparison and that the arms are not a like-for-like control comparison.

The intervention is the Nautilus NeuroWaveTM System, categorized as a device. CT appears in the brief summary as the reference for the stated sensitivity comparison. However, the record does not give a detailed CT comparison protocol, explain how diagnoses were adjudicated, or report results for sensitivity or specificity. The listed primary outcome instead concerns participants with device-related adverse events.

The primary outcome timeframe is recorded as “2-3 days, at subject exit,” with variation in exit date depending on when radiology imaging was obtained to confirm ischemic stroke. The registry does not report additional design details such as the allocation process, cohort-specific enrollment targets, masking, or a statistical analysis plan. The study’s termination reason is 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.

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.

Population: This number reflects all subjects enrolled in study and is not different from the assignment in the Participant Flow.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Device Related Adverse Events, measured over 2-3 days, at subject exit (variation of subject exit date depended on when subject obtained their radiology imaging to confirm ischemic stroke).

The listed primary endpoint is the number of participants with device-related adverse events. Its unit is participants, and the outcome is a count of people who experienced an event rather than a measure of how many events each person experienced. The timeframe is recorded as “2-3 days, at subject exit,” with the exit date varying according to when radiology imaging to confirm ischemic stroke was obtained.

A participant-level count is useful for describing how many people in the exposed group had a safety event during the stated observation period. It is distinct from a diagnostic-performance endpoint: it does not indicate how often the device correctly identifies stroke, how often it misses stroke, or how often it indicates stroke in someone without the condition. Those questions would require diagnostic classifications and an appropriate reference diagnosis. Although the registry’s study description discusses sensitivity and specificity, it does not report an analysis of those measures.

The record lists one outcome measure, but the analysis count is zero. The adverse-event summary reports 29 participants at risk in the Nautilus NeuroWave Recording Arm, with zero affected in the serious and other adverse-event categories. Those entries describe the posted safety counts; they do not establish the completeness of follow-up or provide a diagnostic result. The registry does not report additional details about how device-related events were defined or assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods help connect a study’s question, its recorded outcomes, and the strength of any conclusions. For this study, the registry describes a diagnostic objective but lists a participant-count safety endpoint as the primary outcome. It reports no analysis records. Consequently, statistical concepts can clarify what would be needed to answer the diagnostic question, but they cannot supply missing results.

What do sensitivity and specificity describe?

General explanation: Sensitivity describes how often a diagnostic method identifies the condition among people who truly have it. Specificity describes how often it identifies the absence of the condition among people who do not have it. Both require participants to be classified by the device and by a reference method or diagnosis. A comparison with CT, as stated in the brief summary, would need a defined comparison procedure and reported classifications to support estimates. The registry does not report those classifications, sensitivity, specificity, or their uncertainty.

Diagnostic performance is not summarized by a safety event count. The primary endpoint counts participants with device-related adverse events; it does not classify test results as true positives, false negatives, true negatives, or false positives. Without those diagnostic categories and an account of the reference diagnosis, the record cannot show how often the device detected ischemic stroke or produced a positive indication in its absence.

What does a confidence interval add?

General explanation: A confidence interval describes the statistical uncertainty around an estimated quantity under a specified method. For diagnostic measures, intervals help readers assess how precise estimates of sensitivity or specificity are. For an event count or event rate, an interval can communicate uncertainty that remains even when few or no events are observed. A point estimate alone does not describe that uncertainty. No confidence intervals for diagnostic performance or the adverse-event counts are reported in the registry record.

Why does the design matter?

General explanation: Random allocation can help create comparable groups when comparing assigned interventions, but this study is identified as nonrandomized and allocation is not stated. The registry describes a symptomatic stroke-evaluation cohort and a normal cohort that was not being evaluated for stroke. These distinct descriptions do not establish a like-for-like comparison. Differences in how participants enter the cohorts can affect the interpretation of a diagnostic comparison. The record itself cautions that the arms are not a like-for-like control comparison.

For a diagnostic study, the way participants are selected and how the reference diagnosis is established are important. A sample assembled from people already being evaluated for stroke and a separate normal cohort may not represent the same clinical spectrum. That is a general design consideration, not a finding about the participants in this study. The registry does not report enough detail about selection or diagnostic adjudication to assess how such factors affected the results.

What does the safety count represent?

General explanation: A participant count reports how many individuals experienced an event, whereas an event count may include multiple events in one person. The listed primary endpoint is a count of participants with device-related adverse events. The adverse-event summary separately reports participants at risk and participants affected for serious and other categories. Those summaries should not be converted into diagnostic-performance measures, and they do not describe the number of events per participant.

Exposure time and event ascertainment also matter in safety interpretation. The record gives an endpoint timeframe of “2-3 days, at subject exit,” with timing dependent on radiology imaging for confirmation. It does not report whether observation was complete for every participant, how events were solicited, or the operational definitions used. A zero affected count is therefore a statement about the posted record, not a general guarantee about risk.

What can planning calculations tell readers?

General explanation: Sample-size planning explores how many participants might be needed to detect a specified effect under stated assumptions. Such calculations depend on the outcome, effect size, variability, allocation, significance level, and statistical method. They are planning illustrations, not evidence that a study actually had a particular probability of detecting an effect. The registry record does not report the trial’s own sample-size justification, and it does not report diagnostic analyses from which a study-specific effect could be interpreted. Any planning illustration based on an observed effect should not be confused with an observed result or with observed power.

The record’s study description does not report an analysis plan, interim analyses, or a multiplicity strategy. Those absences limit assessment of how outcomes and comparisons were selected or adjusted. General statistical principles cannot establish which procedures investigators actually used. In particular, without a reported analysis, there is no basis for evaluating model assumptions, adjustment methods, or the handling of missing diagnostic results.

Finally, statistical precision and clinical interpretation are different questions. Precision concerns uncertainty around an estimate; interpretation concerns what the estimate represents and how the design supports a conclusion. Here, diagnostic estimates and their precision are not reported. The adverse-event counts describe the recorded safety categories, but the registry’s limited details do not resolve uncertainty about event ascertainment, follow-up, or diagnostic performance.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Nautilus NeuroWave Recording Arm")
n      <- c(29)
events <- c(0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Nautilus NeuroWave Recording Arm  29  0  0.0  0.0  11.9  0.0  11.7  0.1  11.6

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several outcomes, comparisons, or analyses are tested. When many statistical tests are conducted, the chance of at least one apparently notable result can increase unless the analysis plan addresses that issue. This is a general statistical concern, not a claim that such testing occurred in this study. The registry lists one outcome measure and zero analysis records. It does not report a multiplicity adjustment or an analysis plan, so the approach to multiple outcomes or comparisons is not reported in the registry record.

The record also does not report how missing data were handled. For a diagnostic evaluation, missing device readings, unavailable reference diagnoses, or participants without complete follow-up can affect which people contribute to estimates. The registry does not state whether any such data were missing or how they would have been treated. It would be inappropriate to assume either complete data or a particular imputation or exclusion method.

Analysis populations are not described. The record gives total enrollment of 29 and describes symptomatic and normal cohorts, but does not provide cohort-specific counts or state which participants were included in any analysis. Since no analysis records are reported, the registry does not identify a diagnostic analysis population or a population used for the primary safety endpoint.

These reporting gaps do not establish that particular procedures were or were not conducted outside the registry record. They mean that the registry does not allow readers to assess multiplicity control, missing-data handling, or analysis-population definitions.

12. Safety Results

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

Other (non-serious) adverse events

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

The registry’s adverse-event summary lists the Nautilus NeuroWave Recording Arm with 29 participants at risk for serious adverse events and 0 affected. It also lists 29 at risk for other adverse events and 0 affected. These are participant counts, not event rates, and the two categories should be read separately. The registry lists no serious adverse-event terms.

The primary endpoint is described as the number of participants with device-related adverse events, with a timeframe of “2-3 days, at subject exit.” Exit timing depended on when radiology imaging to confirm ischemic stroke was obtained. The registry does not report the event definitions, assessment procedures, or whether all participants had complete observation through the stated timeframe. It also does not report deaths in the registry record.

The zero affected counts describe what the registry reports; they do not establish that the device has no safety risk. They also do not answer the diagnostic-performance question. Safety interpretation depends on how events were collected and how long participants were observed, and those details are not reported in the registry record. The terminated status does not explain the reason the study ended.

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

The registry record establishes that a nonrandomized, multicenter study of the Nautilus NeuroWaveTM System enrolled 29 participants and was terminated. It describes a symptomatic stroke-evaluation cohort and a normal cohort, as well as an intended diagnostic algorithm for cerebral ischemia. Its brief summary states an aim to assess sensitivity for hyper acute ischemic stroke relative to CT. These are descriptions of design and intent, not evidence that the diagnostic aim was achieved.

The posted results report no analysis records. They do not provide sensitivity, specificity, diagnostic classifications, or a comparison with CT. Accordingly, the record cannot establish the device’s diagnostic accuracy from the information reported. It also cannot establish how precisely any diagnostic measure was estimated, because no estimate or confidence interval is reported.

The safety summary reports 0 affected participants in both the serious and other adverse-event categories, with 29 participants at risk in each. This is a descriptive account of the registry’s recorded safety information. The record does not provide enough detail about definitions, event collection, or completeness of follow-up to treat those counts as a comprehensive account of all possible risk.

The record’s limitations should not be replaced with assumptions. It does not state the reason for termination, cohort-specific enrollment, allocation, the analysis population, handling of missing data, or the statistical plan. These omissions leave important questions unanswered; they do not show what investigators may have done outside the registry record. The appropriate interpretation is therefore bounded: the posted record describes the study and its reported adverse-event counts, but does not report the diagnostic analyses required to answer its stated sensitivity and specificity question.

14. Why This Trial Matters Statistically

This trial is statistically notable because its stated diagnostic objective and its listed primary endpoint address different questions. The study description concerns developing and evaluating a method to identify ischemic stroke, including sensitivity and specificity. The primary endpoint, however, is the number of participants with device-related adverse events. Safety counts cannot substitute for diagnostic-performance analyses, so the distinction is essential when interpreting the record.

The study also illustrates why design descriptions matter. The registry identifies the study as nonrandomized, says allocation is not stated, and cautions that the arms are not a like-for-like control comparison. The symptomatic cohort and normal cohort have different descriptions. These features limit the interpretation of any direct comparison unless the selection process, reference diagnosis, and analysis are clearly specified. The registry does not report those details or diagnostic results.

Finally, the posted safety counts are easy to overread. Zero affected participants in the listed categories is a descriptive result, but its meaning depends on event ascertainment and observation. The registry records a limited timeframe and does not report all of the details needed to assess completeness. The case demonstrates a broader statistical principle: a count can be accurately reported while still leaving uncertainty about what it captures and how far it supports an inference.

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 study-specific limitations are apparent from the registry record. The study is terminated, but the reason for termination is not reported in the registry record. The record does not explain whether termination affected enrollment, follow-up, or analysis, so those possibilities should not be inferred.

Enrollment is 29, but cohort-specific counts are not reported. The registry describes a symptomatic cohort and a normal cohort, while also stating that this was not a randomized comparison and that the arms are not like-for-like controls. Allocation is not stated. These factors restrict assessment of the composition and comparability of the groups.

The stated diagnostic objective is not accompanied by reported sensitivity, specificity, diagnostic classifications, or results comparing the device with CT. The registry reports zero analysis records. Details of the reference diagnosis, device-result interpretation, and diagnostic analysis population are not reported in the registry record. The listed primary outcome measures adverse events rather than diagnostic performance.

Safety interpretation is also limited. The record lists zero participants affected in the serious and other adverse-event categories among 29 at risk, but does not report event definitions or ascertainment procedures. The observation timeframe is “2-3 days, at subject exit,” and exit timing varied with radiology imaging. Completeness of observation and deaths are not reported in the registry record. The analysis plan, missing-data handling, multiplicity approach, and sample-size justification are also not reported.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study to Test Sensitivity and Specificity of Passive Wave Pressure Device in Determining Ischemic Stroke — NCT01643525.
• Registry record last updated 2024-07-08; status last verified 2024-07.
• Results first posted 2015-06-19.
• 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 nonrandomized, multicenter device study of the Nautilus NeuroWaveTM System, intended to develop a cerebral-ischemia diagnostic algorithm and assess sensitivity and specificity for ischemic stroke. The brief summary states an intended sensitivity comparison with CT for hyper acute ischemic stroke. The study enrolled 29 participants, began in 2012-06, had primary completion in 2012-12, and is listed as terminated.

The primary outcome is the number of participants with device-related adverse events, assessed at “2-3 days, at subject exit,” with timing dependent on radiology imaging. The adverse-event summary lists 29 at risk and 0 affected for both serious and other adverse events. No analysis records are reported. Diagnostic-performance results, the reason for termination, and several design and analysis details are not reported in the registry record.