This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Short-term Cardiovascular Benefits of Wearing Particulate-filtering Respirators (NCT02238028), a randomized na study. The primary outcome is Heart Rate Variability-LF Power,HF Power,VLF Power.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02238028 |
| Phase | NA |
| Condition | Autonomic Nervous System Imbalance, Blood Pressure, Inflammation |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | Single |
| Enrollment | 28 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Fudan University |
| Results posted | Yes |
2. Clinical Question
Population
The trial concerns healthy young adults. The registry record describes recruited healthy subjects and gives an enrollment of 28. It does not provide further eligibility details, such as age limits or other inclusion and exclusion criteria.
Intervention
Participants wore a high-efficiency particulate-filtering respirator as much as possible during a continuous 48-hour intervention period. The study was intended to assess short-term cardiovascular effects of reducing personal air-pollution exposure by wearing the respirator. Actual adherence and measured personal exposure are not reported in the registry record.
Comparator
The comparison condition was usual behavior without wearing the respirator. The randomized groups exchanged their roles after a three-week interval, making this a crossover design in which participants experienced both conditions according to the registry description.
Primary question
The primary outcome is described as heart-rate variability (HRV) low-frequency, high-frequency, and very-low-frequency power, measured in ms^2, with a timeframe of up to 24 hours. The clinical question is whether these cardiovascular measurements differ during short-term respirator use compared with usual behavior in healthy young adults. The registry record does not report the numerical results or a single summary comparison for these measures, so the direction and precision of any observed difference cannot be established from the posted record.
3. Trial Design
This was a randomized, single-masked, crossover trial. The registry record lists Fudan University as the sponsor and describes an intervention study among healthy young adults. Enrollment was 28. The record lists the study as completed, with a start date of 2014-03 and primary completion in 2014-10.
In each intervention period, one group wore a high-efficiency respirator as much as possible for a continuous 48-hour period, while the other group behaved as usual. After a three-week interval, the groups exchanged roles. Thus, the intended comparison was within a crossover structure: the same participants were assigned to experience both respirator use and usual behavior. The registry does not report the sequence assigned to each group or details of how the randomization was generated or concealed.
The record labels masking as single, but does not identify which people were masked or describe how masking was maintained. Masking participants to whether they were wearing a respirator may be difficult, but the record does not explain masking procedures, so the masked role cannot be inferred.
Heart-rate variability was assessed using a Holter monitor on the second day of each 48-hour intervention period. The primary outcome description lists LF, HF, and VLF power and gives a timeframe of up to 24 hours. It also describes eight HRV parameters overall, including four time-domain indices and four frequency-domain indices. The registry lists eight outcome measures and two analyses, but does not report the analysis model or explain how the multiple measures were handled. The rationale for the three-week interval, adherence procedures, and sample-size justification 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.
Overall Study
| Stage | Wearing Respirator First,Then Not Wearing Respirator | Not Wearing Respirator First,Then Wearing Respirator |
|---|---|---|
| STARTED | 14 | 14 |
| COMPLETED | 12 | 12 |
| NOT COMPLETED | 2 | 2 |
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.
| Characteristic | Unit | All Study Participants |
|---|---|---|
| Participants analysed | 24 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 24 |
| Age, Categorical: >=65 years | Participants | 0 |
| Age, Continuous | years | 23 (SD 2) |
| Sex: Female, Male: Female | Participants | 11 |
| Sex: Female, Male: Male | Participants | 13 |
| Region of Enrollment: China | participants | 24 |
| BMI | kg/m^2 | 22 (SD 4) |
| systolic pressure | mmHg | 108 (SD 8) |
| diastolic pressure | mmHg | 70 (SD 5) |
6. Primary Endpoint
The registry lists the primary outcome as Heart Rate Variability-LF Power,HF Power,VLF Power, measured over up to 24 hours.
| Element | Registry entry |
|---|---|
| Result type | Geometric Mean |
| Measure of spread | Standard Deviation |
| Unit | ms^2 |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is described as heart-rate variability (HRV) power in the low-frequency (LF), high-frequency (HF), and very-low-frequency (VLF) bands, with measurements expressed in ms^2 and a timeframe of up to 24 hours. HRV quantifies variation in the timing between successive normal heartbeats. The registry describes it as a marker used to estimate cardiac autonomic function and control.
Frequency-domain HRV methods group variation in heartbeat intervals into frequency bands. The record gives HF as 0.15 to 0.4 Hz, LF as 0.04 to 0.15 Hz, and VLF as 0.003 to 0.04 Hz. It notes that parasympathetic activity is a major contributor to HF. It also cautions against treating LF as a straightforward measure of sympathetic activity: LF includes both sympathetic and vagal influences.
These measurements are used as physiological indicators of autonomic modulation, not as direct measures of a clinical event. The endpoint description reports a geometric mean and standard deviation as the summary format. It does not give the observed values, estimated contrast between respirator use and usual behavior, confidence intervals, or a statistical test. The posted record therefore identifies what was measured and why HRV is relevant, but does not establish the size or precision of any condition difference.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes the question and design, but it does not provide numerical primary outcome results. In particular, it does not report the HRV values under respirator use or usual behavior, an estimated within-participant contrast, a confidence interval, or a p-value. The primary outcome is listed across multiple frequency-domain measures, and the record does not reduce those categories to one comparison. Consequently, the posted information does not establish the direction, magnitude, or statistical precision of a difference in LF, HF, or VLF power.
The crossover design is relevant to interpretation because each participant was intended to experience both conditions. In general, a crossover analysis can compare measurements within the same participant, thereby accounting for stable differences between people. That benefit depends on an analysis that respects the paired structure and considers possible period or sequence effects. The registry record does not report how the two periods were modeled, whether carryover was assessed, or how the three-week interval was treated analytically. It is therefore not possible to determine from the record whether those design features were incorporated into the reported analysis.
The endpoint is physiological and short-term: HRV was measured with a Holter monitor on the second day of each 48-hour intervention period, with a stated timeframe of up to 24 hours. Such measurements address autonomic modulation during the study conditions. They are not, by themselves, a report of longer-term health outcomes. The registry description itself emphasizes that LF has both sympathetic and vagal influences, so an LF change should not be given a simple one-direction interpretation as a change in sympathetic activity.
The record identifies geometric means and standard deviations for the primary outcome, but provides no numerical estimates to assess variability. A confidence interval, if reported, would convey the range of effect sizes compatible with the data under the analysis assumptions; no such interval is reported in the registry record. Likewise, the absence of reported primary outcome values is not evidence that the conditions were equivalent, and it is not evidence that there was no difference. It means the magnitude and uncertainty cannot be evaluated from this record.
The study lists eight outcome measures and two analyses. The registry record does not state which analysis corresponds to each endpoint or whether any outcome was designated as the principal inferential comparison beyond the primary outcome label. It also does not report a multiplicity adjustment. Without numerical results and an explicit account of the analysis, neither statistical significance nor the strength of evidence across the HRV measures can be assessed. The record supports a description of the trial structure and endpoints, not a conclusion about the effect of respirator use on HRV.
9. Statistical Methods Explained
What does the crossover design mean?
In a crossover trial, participants receive or experience more than one study condition in sequence. Here, the registry describes randomized groups that exchanged respirator and usual-behavior roles after a three-week interval. The intended comparison can therefore use information from both conditions within the same participant. In general, within-participant comparisons can reduce the influence of stable characteristics that differ between people, because each person can serve as their own comparison.
A crossover trial also requires attention to the order in which conditions occur and to effects that might persist from one period into another. Period effects are changes associated with timing or study period rather than the intervention itself. Carryover refers to an effect of an earlier condition that remains during a later condition. These are general considerations for crossover designs; the registry record does not report whether such effects were assessed or how they were addressed. It also does not state the assigned sequences or provide the statistical model used for the crossover comparison.
What do geometric means and standard deviations describe?
The primary outcome description specifies a geometric mean and standard deviation. In general, a geometric mean summarizes positive measurements on a multiplicative scale and can be useful when values are distributed asymmetrically. A standard deviation describes the spread of observations around a mean-based summary, although interpretation depends on the scale and analysis used. These are general statistical properties, not a claim about the distribution of HRV values in this trial. The registry record does not provide the observed summaries or explain whether data were transformed before analysis.
For a trial contrast, a point estimate would describe the estimated difference or other contrast between the study conditions, while a confidence interval would communicate uncertainty around that estimate. The record does not report a contrast or confidence interval for LF, HF, or VLF. Without those values, neither the estimated size of a condition difference nor its precision can be evaluated. No p-value for the primary outcome is reported in the registry record.
Why does measurement timing matter?
The registry states that participants wore a Holter monitor on the second day of each 48-hour intervention period and gives the primary outcome timeframe as up to 24 hours. Repeated physiological measurements can vary over time. In general, the selected measurement window and the way recordings are summarized affect what a comparison represents. The record does not describe the exact recording window, rules for processing the Holter data, or handling of unusable recordings. It is therefore not possible to determine those details from the posted information.
The outcome description includes frequency bands: HF from 0.15 to 0.4 Hz, LF from 0.04 to 0.15 Hz, and VLF from 0.003 to 0.04 Hz. The record explains that HF has a major parasympathetic contribution, whereas LF includes both sympathetic and vagal influences. This matters statistically as well as physiologically: a measurement can be estimated precisely without being uniquely attributable to one biological pathway. A narrow confidence interval, if one had been reported, would concern statistical uncertainty in the measurement or contrast, not settle every question about its physiological meaning.
How should multiple outcomes be considered?
The record describes eight HRV parameters, including four time-domain indices and four frequency-domain indices, and lists eight outcome measures and two analyses. In general, testing several outcomes creates multiple opportunities to observe an apparently notable result by chance. A prespecified primary endpoint and a clearly stated analysis plan can help readers understand which comparison is central and how other outcomes are interpreted. The registry record does not report a multiplicity strategy, the allocation of analyses to outcomes, or numerical test results. No multiplicity-adjusted or unadjusted inference can therefore be reconstructed from the record.
What can be inferred from the available statistical information?
The registry identifies the study as randomized and crossover, specifies the HRV summary format, and describes the measurement conditions. It does not report the detailed randomization method, the statistical model, the analysis population, missing-data procedures, or primary outcome estimates. In general, these details affect how a result should be interpreted: model choice determines which sources of variation are accounted for, and missing-data handling can affect the participants or observations contributing to an estimate. Because the record does not document these methods or give the numerical results, a reader cannot verify the treatment contrast or judge its precision from the registry record alone.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists eight outcome measures and two analyses. The primary outcome description covers LF, HF, and VLF power, while the broader HRV description states that eight parameters were analyzed, including four time-domain and four frequency-domain indices. The record does not identify the full relationship between the listed outcome measures and the two analyses, explain which comparisons were prespecified, or report a strategy for addressing multiplicity. In general, when multiple outcomes or comparisons are examined, interpretation should distinguish a designated primary comparison from exploratory analyses. No such inferential detail is reported.
The record does not report missing-data counts, reasons for missing observations, or procedures for handling incomplete Holter recordings or incomplete intervention periods. It also does not describe whether all randomized participants were included in each analysis, or define an analysis population. These omissions matter because crossover analyses depend on data from the relevant periods, and the available observations can affect both the estimate and its precision. No imputation or sensitivity-analysis method is reported in the registry record.
The enrollment is listed as 28, whereas the adverse-event information lists 24 at risk in each condition. The record does not explain this difference, and it should not be interpreted as an account of the HRV analysis population. The number contributing to each primary outcome analysis is not reported in the registry record. The statistical analysis plan, including any interim analyses or stopping rules, is also not reported. Thus, the posted information does not allow an assessment of multiplicity control, missing-data impact, or the exact population represented by any primary estimate.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Wear Respirator | 0 | 24 | 0.0% |
| Not Wear Respirator | 0 | 24 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Wear Respirator | 0 of 24 |
| Not Wear Respirator | 0 of 24 |
The adverse-event figures list 24 participants at risk in the Wear Respirator group and 24 at risk in the Not Wear Respirator group. The serious adverse event count is 0 in each group, and the other adverse event count is also 0 in each group. The registry record lists no serious adverse event terms. Deaths are recorded as not reported rather than as a numerical count.
These figures describe the adverse-event entries in the registry; they do not establish that no adverse event of any kind occurred outside the reported categories or observation period. The record does not define the collection window, event ascertainment procedures, or criteria used to classify seriousness. It also does not explain why the risk-set figures differ from the enrollment entry. Accordingly, the zero counts should be read narrowly as the posted event counts, not as proof of absence of risk or as a comprehensive safety assessment.
12. What the Result Does, and Does Not, Mean
The record establishes that a randomized crossover study of short-term respirator use was conducted among healthy young adults. It describes respirator use as wearing a high-efficiency device as much as possible for a continuous 48-hour period, compared with usual behavior, with the groups exchanging roles after a three-week interval. It also identifies HRV measurements as the primary outcome and explains the frequency bands and measurement context.
What the record does not establish is whether respirator use changed LF, HF, or VLF power, how large any difference was, or how precise an estimate might be. Numerical primary outcome results, confidence intervals, and test statistics are not reported in the registry record. The absence of those results cannot be interpreted as evidence of no difference, equivalence, or benefit. It means the effect cannot be evaluated from the posted record.
The endpoint is a short-term physiological measurement, not a direct report of longer-term cardiovascular events or health outcomes. The registry describes HRV as a marker used to estimate autonomic function and notes that LF includes both sympathetic and vagal influences. Therefore, even a measured difference in HRV would need careful interpretation in relation to the particular index and the limits of what it represents.
The crossover structure could support comparisons within participants, but the record does not describe the statistical model, handling of period or carryover effects, analysis populations, or missing-data procedures. Those details and the numerical results are necessary to assess the estimated contrast and its uncertainty. The posted information is sufficient to characterize the research question and basic design, but not to reach a statistical conclusion about the primary outcome.
13. Why This Trial Matters Statistically
This trial is statistically notable for using a randomized crossover structure to study a short-term exposure-reduction intervention. When participants experience both conditions, a within-participant comparison can, in general, separate condition differences from stable differences between individuals. That design feature makes clear reporting of period, sequence, and carryover handling especially important. The registry describes the crossover but does not provide those analysis details.
The endpoint also illustrates why statistical precision and physiological interpretation are separate issues. HRV is used to estimate autonomic function, but the registry notes that LF includes both sympathetic and vagal influences. A numerical estimate could be precise while still requiring caution about what biological process it represents. In this record, the numerical estimates are not reported, so neither their precision nor their interpretation can be assessed.
The study description includes several HRV indices, yet the record does not explain how the multiple outcomes were handled or report a single comparison. That makes a transparent analysis plan important for distinguishing a primary inferential question from other measurements. The absence of reported outcome estimates also highlights the limits of relying on a registry description alone: design information can explain what investigators intended to measure, but it cannot substitute for results and uncertainty estimates.
Finally, the posted safety counts are limited to the recorded event entries and risk sets. They should be read alongside the absence of information about event collection and analysis populations. Taken together, the record is useful for understanding the structure of the question, while illustrating why numerical results, analysis methods, and clear reporting of outcomes are needed for statistical interpretation.
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 main limitation for interpreting the trial from the registry record is that numerical results for the primary HRV outcome are not reported. There are no reported condition-specific estimates, contrasts, confidence intervals, or test statistics for LF, HF, or VLF power. The magnitude, direction, and precision of a primary outcome difference therefore cannot be assessed.
The record gives only limited methodological detail. It does not report the randomization procedure, allocation concealment, identity of the masked party, or the statistical model. Although the design is crossover and includes a three-week interval between periods, the record does not explain the rationale for that interval or report how period, sequence, and possible carryover effects were considered.
The HRV description identifies the endpoint categories and measurement timing, but does not report detailed Holter processing, data-quality rules, adherence, or actual personal exposure. The record lists eight outcome measures and two analyses but does not describe how these map to one another or whether multiplicity was addressed. The analysis population, missing-data procedures, and number contributing to the primary analysis are not reported in the registry record.
The enrollment entry is 28, while the adverse-event entries list 24 at risk in each condition; the record does not explain the difference. The safety entries also lack a reported event-collection window and ascertainment details. These limitations do not establish that the trial was conducted improperly, but they restrict what can be concluded from the posted record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Short-term Cardiovascular Benefits of Wearing Particulate-filtering Respirators — NCT02238028.
- Registry record last updated 2016-05-06; status last verified 2016-04.
- Results first posted 2016-05-06.
- 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.
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18. Record Summary
The registry record describes a completed randomized, single-masked crossover trial sponsored by Fudan University, with enrollment of 28 and a study start of 2014-03. Healthy young adults wore a high-efficiency respirator as much as possible during a continuous 48-hour period or behaved as usual; the groups exchanged roles after a three-week interval.
The primary outcome was HRV power in LF, HF, and VLF bands, measured in ms^2, with a timeframe of up to 24 hours. Holter monitoring took place on the second day of each intervention period. The outcome description specifies geometric means and standard deviations and discusses the interpretation of the frequency bands.
Numerical primary outcome results and detailed statistical methods are not reported in the registry record. Adverse-event entries list zero serious and zero other adverse events in each condition, with 24 at risk per condition; deaths are not reported.