The Effects of Different Flow Settings on Lung Impedance: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effects of Different Flow Settings on Lung Impedance (NCT06228703), a randomized na study. The primary outcome is Change in End-expiratory Lung Impedance From Baseline Measured by Electrical Impedance Tomography (EIT).

2. Clinical Question

3. Trial Design

This was a prospective, randomized crossover study of healthy volunteers, sponsored by Rush University Medical Center. The registry lists the study as completed, with enrollment of 26. The recorded start date is 2024-05-19, and the primary completion date is 2024-10-15. The phase is listed as not applicable.

In a crossover design, participants receive or experience multiple study conditions, allowing measurements under different conditions to be compared within the same person. This can reduce the influence of stable differences between participants when estimating condition contrasts. Random allocation can help determine the order in which conditions are experienced, but the registry record does not describe the allocation sequence, condition order, or procedures used to conceal allocation. Masking is listed as none.

The conditions cover Airvo 3 and HFT 750 at flow settings of 20 L/min, 40 L/min, and 60 L/min. The study summary describes measuring peak inspiratory flow with a mask connected to a respiratory monitor before treatment, then monitoring it during high-flow nasal cannula treatment. The primary outcome concerns lung aeration, represented by change in end-expiratory lung impedance. Other questions in the summary concern device differences, comfort, and the relationship between peak inspiratory flow measurements from the mask and high-flow nasal cannula.

The record does not describe a washout period, the time allowed between conditions, or how potential order or carryover effects were addressed. Those details matter when interpreting crossover comparisons because a participant's measurement in one condition may be affected by the sequence of conditions. The registry record also does not report the statistical plan or condition-specific outcome results.

4. Participant Flow and Accounting

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

Before assignment: Adult healthy volunteers were recruited at a single academic medical center through posted study invitations and direct approach. Individuals expressing interest were screened for eligibility, and those who met inclusion criteria provided written informed consent prior to participation

Device A - Flow Setting 1

Device A - Flow Setting 2

Device A - Flow Setting 3

Device B - Flow Setting 1

Analysis population for the primary outcome, as defined in the registry: All enrolled participants (n=26) were included in this baseline analysis.

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 in End-expiratory Lung Impedance From Baseline Measured by Electrical Impedance Tomography (EIT), measured over Up to 4 hours.

The primary endpoint is change in end-expiratory lung impedance (EELI) from baseline, measured continuously using electrical impedance tomography (EIT). For each flow-setting condition, the description says EELI values were averaged over a stable 1-minute period. The outcome is expressed in arbitrary impedance units and interpreted as change relative to that participant's baseline measurement before intervention. Positive values indicate an increase in end-expiratory lung volume relative to baseline; negative values indicate a decrease.

EIT impedance units are dimensionless and device-specific. They are used to represent relative changes in ventilation and lung volume, rather than a direct measurement in a standard volume unit. In general, a baseline-referenced endpoint can describe how a measurement shifts during an intervention condition while accounting for the participant's own starting value. That makes the endpoint relevant to the study's question about changes in lung aeration across device and flow conditions.

The endpoint description specifies a mean and standard deviation and gives a timeframe of up to 4 hours. It does not report the condition-specific means, standard deviations, or estimated differences. Those results, along with their uncertainty, are not reported in the registry record, so the endpoint definition alone cannot show the size or precision of any condition effect.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

Randomization is intended to reduce systematic differences in how study conditions are assigned. In a crossover study, randomized condition order can help prevent one condition from consistently occurring earlier or later than another. The registry identifies the study as randomized but does not report the sequence-generation method, allocation procedures, or the details of condition order. It lists masking as none, so participants and study personnel were not described as masked to the conditions.

Why use a crossover design?

In general, crossover designs compare measurements from the same participant under multiple conditions. Each participant can serve as their own reference, which may reduce the influence of stable characteristics that differ across people. The statistical analysis must account for this repeated-measure structure; treating all condition measurements as independent would generally fail to represent their within-person relationship. The registry record does not identify the model or method used for repeated measurements, and it does not report how period, sequence, or carryover effects were assessed.

What does the endpoint represent?

The primary outcome is mean change in EELI from baseline, measured by EIT and reported in arbitrary units. The study description says EELI was measured continuously and averaged over a stable 1-minute period for each flow-setting condition. In general, averaging a measurement over a defined stable interval can reduce short-term fluctuation in the recorded signal. The resulting value is still a relative, device-specific impedance measure, not a direct measure in a standard volume unit. The stated direction is positive for an increase and negative for a decrease in end-expiratory lung volume relative to baseline.

How should uncertainty be assessed?

A confidence interval is a statistical range that conveys uncertainty around an estimated effect under the assumptions of the analysis. In general, a narrow interval indicates greater precision than a wide interval, while the interval's location helps indicate which effect sizes remain compatible with the data. A p-value, when reported, addresses how compatible the data are with a specified null model; it does not measure the size or clinical importance of an effect. The registry record reports no estimated effects, confidence intervals, or p-values for the primary endpoint, so none can be interpreted.

Why might repeated measurements need special handling?

Measurements from the same participant are often correlated. A suitable analysis accounts for that dependence rather than assuming each observation is unrelated to every other observation. In general, the choice of method may also depend on whether the scientific target is a change from baseline, a comparison among conditions, or both. The record provides the endpoint definition but does not report the statistical model, variance assumptions, adjustment method, or planned contrasts. It is therefore not possible to assess whether the posted analysis used an approach suited to the crossover structure.

What does over-dispersion mean in general?

Over-dispersion occurs when variation in the observed data is greater than a statistical model expects. It is particularly relevant to some count-data models, where underestimating variability can make uncertainty appear too small. The primary endpoint in this study is described as a continuous measure summarized by a mean and standard deviation, not as a count outcome. The registry record does not identify a model or report a dispersion assessment, so over-dispersion is not a reported feature of this analysis.

Can a new sample-size calculation be interpreted as trial power?

No. A planning illustration based on an observed effect is not the same as the trial's original design justification and is not observed power. In general, such an illustration depends on assumptions about the target effect, significance level, allocation, and statistical model. The registry record gives general assumptions for planning illustrations, but it does not report a trial-specific sample-size justification or the underlying effect estimate needed to interpret a recalculation. There are no primary outcome results in the record from which to assess the observed effect. The trial's original sample-size justification is not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The study includes multiple conditions and several research questions. The primary outcome concerns change in EELI. The registry's secondary-outcome list names changes in respiratory rates compared with baseline and subject comfort. The study summary also describes questions about lung aeration by device and the correlation between peak inspiratory flow measured by high-flow nasal cannula and by a mask connected to a respiratory monitor.

When several outcomes or contrasts are tested, the chance of obtaining at least one apparently notable result can increase. In general, a prespecified multiplicity strategy may limit that risk, for example by prioritizing a primary comparison or adjusting interpretation across a family of tests. The statistical plan, the intended set of primary contrasts, and any multiplicity adjustment are not reported in the registry record. No inferential analyses are posted, so it is not possible to determine whether or how multiplicity was addressed.

The record describes all enrolled participants as included in the baseline analysis of the primary outcome. It does not report the number of measurements available for each condition, the handling of incomplete measurements, or any missing-data method. It also does not state whether all enrolled participants contributed data to every secondary outcome. In general, missing observations can affect both the analysis population and the interpretation of condition comparisons, especially when missingness differs by condition or relates to the measurement being studied. The registry record does not provide enough information to assess those possibilities.

The analysis populations and any exclusions after enrollment are not reported in the registry record. The record also does not describe interim analyses, and no statistical analysis plan is reported. These omissions do not establish that such procedures were absent; they mean their use cannot be evaluated from the registry record.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The safety record lists 26 participants at risk for serious adverse events and 0 affected by serious adverse events. It also lists 26 at risk for other adverse events and 0 affected by other adverse events. Deaths are reported as 0. These are the posted counts for the total study population.

In general, a count of zero means that no event was recorded in the category during the period and under the definitions used for the registry entry. It does not prove that an event is impossible, nor does it show that the study could rule out uncommon harms. The registry record does not report the safety-monitoring period, event definitions, severity criteria for other adverse events, or a breakdown by device or flow condition. Without those details, the counts cannot be used to compare safety across conditions.

These figures describe reported events in this study population; they do not establish a general safety profile. The record does not provide further narrative about safety events or explain the assessment procedures. Interpretation should therefore remain limited to the posted counts and the information recorded about their denominators.

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

This registry record documents a completed randomized crossover study in healthy volunteers examining lung impedance during high-flow nasal cannula treatment at different device and flow-setting conditions. It defines the primary endpoint as change in EELI from baseline measured by EIT, and explains how positive and negative values relate to baseline. It also records secondary questions about respiratory rate and comfort, while the study summary describes additional interests in device comparisons and peak inspiratory flow measurement.

What the record does not provide is equally important: no condition-specific primary-outcome estimates, contrasts, confidence intervals, p-values, or analysis results are posted. The registry record therefore cannot show the observed size, direction, or precision of differences in EELI. It also cannot establish that conditions were equivalent, or that any difference was absent. Those conclusions require reported estimates and uncertainty, interpreted in light of the analysis method.

The endpoint is a relative, device-specific impedance measure expressed in arbitrary units. It should not be treated as a direct volume measurement in a standard physical unit. The study population is described as healthy volunteers, so the record does not directly provide results for other populations or clinical settings.

The safety entry reports no serious adverse events, other adverse events, or deaths in the posted counts. Those counts do not establish that risk is absent, and the record does not give enough detail to compare safety across settings. Overall, the registry record identifies the study question and design but leaves the principal outcome and statistical interpretation unavailable.

13. Why This Trial Matters Statistically

The study illustrates how a crossover design can address a measurement question across several device and flow conditions. Because participants can undergo multiple conditions, within-person comparisons may help separate condition-related variation from stable differences between people. That advantage depends on a suitable analysis of repeated measurements and attention to condition order and carryover. The registry identifies randomization and crossover structure but does not report the methods used to handle these issues.

The endpoint also raises an important measurement distinction. EIT-derived impedance is described as a device-specific, dimensionless indicator of relative changes in ventilation and lung volume. Interpreting the outcome correctly means distinguishing a change on that scale from an absolute volume measurement. Baseline-referenced values indicate direction relative to each participant's starting measurement, but the clinical meaning of a change would require evidence and context not reported in the registry.

For statistical interpretation, a study question and outcome definition are not substitutes for results. Effect estimates and their uncertainty are needed to understand whether observed condition differences are small or substantial and how precisely they are estimated. The absence of posted analyses means this registry record cannot answer the primary comparison, regardless of the completed status.

The record also shows why reporting analysis details matters in crossover studies. Condition order, repeated-measure modeling, missing measurements, multiplicity, and prespecified contrasts all shape what an estimate means. These details are not reported, limiting reproducibility and critical appraisal. The study is statistically relevant as a design and measurement question, but the record does not provide the outcome evidence needed to evaluate its findings.

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 central limitation of the registry record is the absence of posted primary-outcome results and statistical analyses. Although the endpoint is defined, the condition-specific mean changes, comparisons, and measures of uncertainty are not reported. The record therefore does not permit an assessment of the observed effect or its precision.

The crossover design makes details about condition sequence and timing important. The registry does not report the order of conditions, washout procedures, or how period and carryover effects were considered. It also does not identify the repeated-measure analysis method or planned comparisons. These gaps make it difficult to evaluate whether the analysis, if conducted, accounted for the structure of the design.

The primary outcome is measured in arbitrary, device-specific EIT impedance units. This supports relative interpretation as described in the record, but it limits direct interpretation as an absolute lung volume. The enrolled population is described as healthy volunteers, so the record does not establish how any findings would apply to people with health conditions.

The registry says all enrolled participants were included in the baseline analysis, but it does not report outcome-level availability by condition or how missing measurements were handled. The statistical plan, sample-size justification, and multiplicity strategy are also not reported in the registry record. Finally, safety counts are not broken down by condition, and the safety-monitoring period and event definitions are not described. These limitations concern what can be evaluated from the registry record; they do not establish what procedures were or were not used outside the record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Effects of Different Flow Settings on Lung Impedance — NCT06228703.
• Registry record last updated 2025-12-19; status last verified 2025-12.
• Results first posted 2025-12-19.
• 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.

18. Record Summary

The registry record describes a completed, randomized, unmasked crossover study sponsored by Rush University Medical Center, with enrollment of 26 healthy volunteers. It lists a start date of 2024-05-19 and a primary completion date of 2024-10-15.

The primary outcome is change in end-expiratory lung impedance from baseline, measured by electrical impedance tomography and summarized as a mean with standard deviation. Conditions use Airvo 3 or HFT 750 at flow settings of 20 L/min, 40 L/min, or 60 L/min. Secondary outcomes listed include respiratory-rate changes compared with baseline and subject comfort.

The registry record does not report primary-outcome estimates, statistical analyses, or a statistical analysis plan. It lists 0 serious adverse events, 0 other adverse events, and 0 deaths. Missing-data procedures, the analysis populations beyond the stated baseline population, and the sample-size justification are not reported in the registry record.