Hypoxic Pulmonary Vasoconstriction Pilot Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Hypoxic Pulmonary Vasoconstriction Pilot Study (NCT03733470), a non-randomized phase 4 study. The primary outcome is Perfused Blood Volume Assessed for a Change in Lung Inflammation Pre and Post Dose Sildenafil Administration.

2. Clinical Question

In practical statistical terms, the endpoint is a before-and-after imaging measure following drug administration, considered in two smoker susceptibility groups. The registry does not report a formal hypothesis about the difference in change between those groups, nor does it identify a randomized contrast. Thus, the study description supports a question about measured change after dosing, but not a causal comparison of sildenafil against an independent control condition. The meaning of any observed pre-post change would depend on the measurement process, the analysis population, and the handling of repeated observations; those analysis details are not reported in the registry record.

3. Trial Design

The registry describes NCT03733470, titled “Hypoxic Pulmonary Vasoconstriction Pilot Study,” as a Phase 4, nonrandomized, unmasked, single-group study. Its official title is “Pilot Study for Perfusion Heterogeneity: a Mechanistic Image-Based Emphysema Phenotype.” The status is completed. The recorded enrollment is 22, and the condition is emphysema. The record gives a start date of 2011-06-29 and a primary completion date of 2014-01-13.

Two smoker cohorts are described: Nonsusceptible Smokers (NS) and Susceptible Smokers (SS). The respective arm descriptions list 8 and 11 subjects. Each description includes non-contrast imaging at TLC and 20% VC, and contrast DECT to assess perfused blood volume. The intervention is sildenafil at 20 mg, followed by repeat scanning one hour after administration. The registry's single-group model and nonrandomized allocation matter when interpreting those cohort labels: the descriptions do not establish a randomized control group or a like-for-like treatment comparison.

The intervention is unmasked. Masking is listed as none. The precise definitions used to assign susceptibility, the eligibility criteria, recruitment procedures, and the relationship between recorded enrollment and the analysis population are not reported in the registry record. The record also does not report whether every enrolled participant completed both scans, or how the imaging observations were processed.

This is described as a pilot, mechanistic imaging study rather than a trial with a reported randomized efficacy contrast. Its central design feature is measurement before and after sildenafil within the stated one-hour period. That arrangement can describe temporal change, but without a separate control condition it cannot by itself distinguish a drug-associated change from other explanations such as measurement variation or changes over time. The exact statistical plan for separating these possibilities 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.

Before assignment: Of 22 subjects, 3 were eliminated because of blood pressure or asthma medications leaving 8NS and 11SS subjects.

Overall Study

Reasons for not completing this period:

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: 2 subjects were eliminated after scanning because of mis-matched pre and post sildenafil lung volumes, leaving 7NS and 10SS subjects.

6. Primary Endpoint

The registry lists the primary outcome as Perfused Blood Volume Assessed for a Change in Lung Inflammation Pre and Post Dose Sildenafil Administration, measured over Change of perfused blood volume from baseline at one hour after sildenafil administration..

The primary outcome is titled “Perfused Blood Volume Assessed for a Change in Lung Inflammation Pre and Post Dose Sildenafil Administration.” The listed measurement is perfused blood volume, expressed as a coefficient of variation. The registry specifies the mean as the summary parameter and standard deviation as the dispersion measure. It describes CT measurement at two time points, before and after sildenafil, with the timeframe defined as change from baseline at one hour after administration.

In general, perfused blood volume is an imaging measure of blood volume reaching lung regions, while a coefficient of variation summarizes relative variability across measurements. A variability summary is relevant to a study motivated by perfusion heterogeneity because it describes how unevenly a measured quantity is distributed, rather than only its overall level. This is a general explanation of the measure; the registry does not provide a detailed imaging-processing definition or a clinical threshold for interpreting the coefficient of variation.

The endpoint title refers to lung inflammation, but the listed outcome itself is perfused blood volume assessed by CT. The registry does not describe a direct inflammation measurement among the primary outcome details. Nor does it report a numerical estimate of the pre-post change, a confidence interval, or a test result. Consequently, the endpoint definition clarifies what was intended to be measured, but the registry record does not report the observed magnitude or precision of change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical details recorded for this study are limited. The primary outcome is continuous, is summarized as a mean, and names the standard deviation as its dispersion measure. One outcome measure and one analysis are listed. The record does not describe the specific model, test, confidence-interval method, covariate adjustment, or analysis population used for the primary endpoint. The explanations below describe general statistical concepts and do not imply that a particular method was used in this study.

What does a mean represent?

In general, a mean summarizes the average value of a continuous measurement across the observations included in an analysis. For a change endpoint, the mean can describe the average within-participant difference between the post-dose and baseline measurements, if that is how change is defined and calculated. The registry identifies the mean as the summary parameter, but it does not specify whether the analysis uses individual changes, a model of repeated measurements, or another formulation. It also does not report the resulting mean or the number of observations used to estimate it.

For repeated measurements, accounting for the fact that two observations from the same participant are related is generally important. Treating those observations as independent can misstate uncertainty. A paired analysis or an appropriate repeated-measures model can account for within-participant dependence, but the registry record does not identify which approach, if any, was used. The description of pre-dose and post-dose scans establishes the repeated-measurement intent, not the details of the statistical analysis.

Why report a standard deviation?

In general, a standard deviation describes the spread of measurements around their mean. It helps show whether participant values are tightly clustered or widely dispersed. A standard deviation is not the same as a standard error: the standard deviation describes variability among observations, while the standard error describes uncertainty in an estimated quantity. The registry names standard deviation as the dispersion measure but does not provide an observed value or clarify whether it applies to individual measurements or changes.

The coefficient of variation is a relative measure of variability, conventionally relating spread to the mean. In this study, it is the stated unit for perfused blood volume. General interpretation of a coefficient of variation depends on how it is calculated, the scale of the measurement, and whether the mean is appropriate for that use. The registry does not provide the calculation details, data distribution, or reference range needed to assess those issues for this endpoint.

How should uncertainty be read?

In general, a confidence interval communicates uncertainty around an estimated effect. A narrow interval indicates greater precision under the model assumptions than a wide interval, while the interval's location indicates which effect values remain compatible with the data. A confidence interval does not establish clinical importance, and it does not correct for bias in study design or measurement. No interval for the primary outcome is reported in the registry record.

A hypothesis test, when used, evaluates how compatible the observed data are with a specified null hypothesis under its assumptions. A p-value does not measure the probability that the null hypothesis is true, and it does not convey the size or practical importance of an effect. The registry record does not report a p-value, test statistic, null hypothesis, or test procedure for the primary outcome. Statistical significance therefore cannot be assessed from the registry information.

What does nonrandomized mean for the comparison?

In general, random allocation helps balance measured and unmeasured characteristics between treatment groups in expectation. This study is identified as nonrandomized, unmasked, and single-group. The NS and SS labels denote cohorts in the arm descriptions, not a randomized treatment-versus-control allocation. A pre-post comparison can be informative about observed temporal change, but it is more vulnerable to alternative explanations than a randomized concurrent comparison. Lack of masking may also matter for study procedures or interpretation, although the registry does not report whether or how it influenced measurement or analysis.

The outcome timeframe is one hour after sildenafil administration. A short interval defines when the repeat scan was planned; it does not establish that the measured change is attributable to the intervention. The registry does not report a control condition, blinding procedures, adjustment for baseline differences, or methods addressing confounding. Those features should not be assumed.

What do the sample-size assumptions mean?

The registry's planning description specifies a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect. These are planning assumptions, not a description of the trial's own design or evidence about the precision of its observed result. The record does not report a sample-size justification for the trial or numerical planning outputs alongside these details.

In general, planning calculations estimate the number of participants needed to detect an assumed effect under chosen assumptions about variability, significance level, power, allocation, and analysis. A planning illustration based on an observed effect is sensitive to the effect estimate used: if that estimate is uncertain, the resulting planning value is uncertain too. Such calculations are not observed power and do not show that the completed study had a particular probability of detecting its true effect. The registry does not report the numerical effect estimate needed to evaluate any such illustration.

Over-dispersion is a general issue when data vary more than a statistical model assumes. If variability is understated, standard errors and intervals can be too small and tests can be anticonservative. Conversely, an appropriate model should reflect the data structure and distribution. The registry does not report enough information about the outcome distribution or model to assess over-dispersion or determine whether it was relevant.

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("Nonsusceptible Smokers (NS)", "Susceptible Smoker (SS)")
n   <- c(7, 10)
m   <- c(0.37, 0.42)
sp  <- c(0.03, 0.09)
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  Nonsusceptible Smokers (NS)  7  0.370  0.030  0.342  0.398
CARM  Susceptible Smoker (SS)  10  0.420  0.090  0.356  0.484

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and one analysis. This does not establish that only one outcome or analysis was conducted, nor does it describe how the primary outcome was selected. The record does not report a multiplicity adjustment, a prespecified testing hierarchy, or whether additional subgroup or sensitivity analyses were planned. Without those details, the effect of multiple testing on interpretation cannot be assessed.

Missing-data handling is not reported in the registry record. It does not state how missing baseline or post-dose scans were handled, whether participants with incomplete imaging were excluded, or whether any imputation method was used. The number contributing to the primary endpoint analysis and the analysis population definition are also not reported. The enrollment figure and cohort descriptions do not establish how many participants had usable paired observations.

In general, missing observations can affect both the estimated change and its uncertainty, particularly if the probability of missingness is related to participant characteristics or outcomes. Complete-case analysis, imputation, and likelihood-based approaches rely on different assumptions; none should be attributed to this study without a reported analysis plan or results. Similarly, subgroup findings require a clear specification of the subgroup definition and analysis, neither of which is detailed for the susceptibility classification.

The registry record does not report an analysis protocol describing the primary model, handling of outliers, covariate adjustment, or sensitivity analyses. Thus, the listed single outcome and analysis provide a basic record structure but do not resolve multiplicity or missing-data concerns. These omissions limit assessment of whether the reported analysis, if available, would be robust to alternative reasonable choices.

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.

For Nonsusceptible Smokers (NS), the registry lists 8 at risk for serious adverse events and zero affected; it also lists 8 at risk for other adverse events and zero affected. For Susceptible Smokers (SS), it lists 11 at risk for serious adverse events and zero affected; it also lists 11 at risk for other adverse events and zero affected. Deaths are listed as zero for both groups. No top serious adverse event terms are listed.

These figures describe the recorded counts, not a comparative estimate of safety. The registry does not report event definitions, the length of safety follow-up, how events were collected, or whether the at-risk population corresponds to all enrolled participants. Zero recorded events should not be interpreted as evidence that the underlying risk is zero. In general, the interpretation of adverse-event counts depends on exposure and observation time, the completeness of reporting, and the size and characteristics of the group observed. No event-rate calculation or between-group safety test is reported in the registry record.

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

The record establishes that a pilot imaging study was completed and specifies a planned primary measure: mean perfused blood volume coefficient of variation, assessed before and one hour after sildenafil. It also describes CT imaging in two smoker cohorts and records adverse-event counts. Those details show the intended measurement framework and the study's mechanistic focus.

The record does not state the observed primary outcome values. Consequently, it does not show whether the coefficient of variation increased, decreased, or remained similar after administration, or how large or precise any change was. No confidence interval or inferential test result is reported. It is therefore not possible to characterize the primary finding as statistically significant or not, or to judge its clinical importance.

The design also limits what a pre-post observation could mean. In general, change after an intervention is not equivalent to a treatment effect when there is no randomized control group. The record identifies the study as nonrandomized, unmasked, and single-group. The NS and SS cohorts are not described as randomized comparators, and the registry does not report a formal between-cohort contrast. Any observed difference would need cautious interpretation in light of possible time effects, measurement variability, and differences between participant groups.

The study's stated mechanistic rationale concerns hypoxic pulmonary vasoconstriction and smoking-associated inflammation in emphysema. A perfused blood volume measure can be used to investigate perfusion patterns, but the registry's primary outcome description does not itself report a direct measurement of the proposed biological mechanism or establish why a change occurred. No mechanistic conclusion can be drawn from the endpoint definition alone.

The safety counts record no serious or other adverse events and no deaths in the listed groups. They do not establish absence of risk, particularly without reported follow-up duration and event-collection details. Overall, the registry record describes the question and methods more fully than the results. It supports neither a conclusion about the primary outcome's direction nor a causal claim about sildenafil.

14. Why This Trial Matters Statistically

This study is statistically informative as an example of how a mechanistic imaging question differs from a conventional randomized treatment comparison. It focuses on perfusion heterogeneity, using a continuous CT-based measure before and after administration. The repeated-measure structure can make within-participant change a natural quantity of interest, because each participant has a baseline observation. At the same time, the absence of random allocation and a concurrent control condition constrains causal interpretation.

The distinction between two smoker cohorts and randomized arms is especially important. NS and SS are meaningful labels in the study description, but the registry identifies a nonrandomized, single-group model. Comparisons between those cohorts may be affected by baseline differences or other factors, and the record does not report a formal adjusted comparison. A within-cohort change and a between-cohort difference in change are different statistical questions; the registry does not report results for either.

The endpoint also illustrates why a measure's definition and its interpretation should be separated. The registry names a coefficient of variation for perfused blood volume and gives the imaging timeframe, but does not provide the calculation details, observed values, uncertainty, or a clinical threshold. Without those elements, readers can understand what was intended to be measured but cannot evaluate the size, precision, or practical relevance of the finding.

Finally, the record demonstrates the importance of distinguishing trial completion from result reporting. Study status and design details do not substitute for an estimate and uncertainty interval. The registry lists safety counts, but those counts also need context about follow-up and ascertainment. Transparent reporting of analysis populations, missing observations, and statistical methods would be needed to fully assess the evidential strength of a pilot imaging study.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary limitation of interpretation is that the registry record does not report numerical results for the primary endpoint. It gives no mean change, standard deviation value, confidence interval, or test result. Without those, the magnitude and precision of the outcome cannot be assessed. The analysis population and number of participants with complete paired scans are also not reported.

The design is nonrandomized, unmasked, and identified as single-group. Although NS and SS cohorts are described, they are not a randomized comparison and do not provide an established control condition. This limits causal interpretation of any before-and-after change and makes a cohort contrast vulnerable to differences between groups. The registry does not report methods for addressing confounding, baseline imbalance, or measurement bias.

Additional limitations include unreported definitions for susceptibility and detailed eligibility criteria; no reported imaging-processing or coefficient-of-variation calculation details; and no stated clinical threshold for interpreting the endpoint. The primary outcome title refers to lung inflammation, while the listed measurement is perfused blood volume assessed by CT. The record does not describe a direct inflammation measure in the primary outcome details.

The statistical plan is not described in sufficient detail to assess the model, assumptions, missing-data approach, multiplicity handling, or sensitivity analyses. Safety interpretation is also constrained because event definitions, observation period, and ascertainment procedures are not reported. These omissions do not establish that the methods were inadequate; they mean those aspects cannot be evaluated from the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Hypoxic Pulmonary Vasoconstriction Pilot Study — NCT03733470.
• Registry record last updated 2019-10-01; status last verified 2019-08.
• Results first posted 2019-10-01.
• 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

NCT03733470 is a completed Phase 4, nonrandomized, unmasked, single-group pilot study concerning emphysema and perfusion heterogeneity. It describes NS and SS smoker cohorts, sildenafil at 20 mg, and repeat CT imaging one hour after administration. The primary endpoint is the mean coefficient of variation for perfused blood volume, with standard deviation named as the dispersion measure.

The registry record reports enrollment of 22 and lists 8 NS subjects and 11 SS subjects in the arm descriptions. It records zero serious adverse events, zero other adverse events, and zero deaths for each named group. The numerical primary endpoint result, uncertainty estimates, statistical test, analysis population, and detailed missing-data and multiplicity methods are not reported in the registry record. The design does not describe a randomized control group, so a pre-post change would not by itself establish a causal treatment effect.