Hypoglycemia and Autonomic Nervous System Function: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Hypoglycemia and Autonomic Nervous System Function (NCT01816893), a randomized na study. The primary outcome is Change in Baroreflex Sensitivity.

2. Clinical Question

3. Trial Design

This was a randomized, double-blind, crossover trial sponsored by Brigham and Women's Hospital. Its recorded status is completed, and the phase is listed as not applicable. The registry reports enrollment of 22 participants. In a crossover design, participants receive both conditions, making the within-person comparison central to the design; the record states that 20 participants completed both arms.

The two conditions were a hypoglycemic hyperinsulinemic clamp and a euglycemic hyperinsulinemic clamp. The primary outcome was measured at baseline on the day before a clamp and again 16 hours after the clamp. The reported change is the later measurement minus baseline. The registry does not report the order in which participants received the conditions, whether order was balanced, or the interval between conditions. These details matter when assessing possible period or carryover effects, but their absence does not establish that such effects occurred.

For the primary outcome, the record says that only 18 participants had change measurements for both arms. The arm summaries each have 18 participants. Secondary-outcome records use 20 participants per arm for the catecholamine measure. The registry names muscle sympathetic nerve activity as another secondary outcome, but numerical results for it are not reported in the registry record.

Three outcome measures are recorded, and there are no reported analyses in the registry. The original sample-size justification, statistical plan, treatment sequence, and approach to the crossover data are not reported in the registry record. Consequently, the arm summaries and posted contrast describe the available results, but do not establish how the trial's original analysis was conducted.

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.

Euglycemic Clamp/ Hypoglycemic Clamp

Washout Period

Reasons for not completing this period:

Hypoglycemic Clamp/ Euglycemic Clamp

Analysis population for the primary outcome, as defined in the registry: 20 subjects completed both arms, but only 18 had the change in BRS outcome for both arms.

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 Baroreflex Sensitivity, measured over 16 hours after euglycemic and hypoglycemic clamps as compared to baseline.

The primary endpoint is change in baroreflex sensitivity, measured in milliseconds per millimeter of mercury. Baroreflex sensitivity describes the relationship between changes in blood pressure and the body's reflex adjustment of heart rate. In general, it is used as a measure of cardiovascular autonomic regulation. That general physiological context explains why it is relevant to a study examining hypoglycemia and autonomic nervous system function; it does not by itself establish what a particular change means clinically.

The registry defines change as the measurement taken 16 hours after the clamp on day 3 minus the baseline measurement on day 1, which was obtained on the day before the clamp. A positive change therefore indicates a higher measured value at the later assessment than at baseline, while a negative change indicates a lower value. The outcome is summarized with means and standard deviations, appropriate descriptive statistics for a continuous measure.

Using a change score places each post-clamp measurement in relation to its own baseline rather than comparing post-clamp values alone. In a crossover design, the intended contrast is the difference between each participant's changes under the two clamp conditions. The registry reports that only 18 participants had the change outcome for both arms. It does not report whether the primary statistical analysis used a paired method or otherwise modeled the repeated observations, so the posted contrast should be read with that reporting limitation in mind.

7. Results Posted in the Registry

• Hypoglycemic Clamp: mean -1.60 versus 2.30 on control; difference -3.90 (95% CI -7.42 to -0.38), standardized effect d = -0.72; z-test p = 0.030.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Catecholamine Response to Lower-body Negative Pressure

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Hypoglycemic Clamp: mean 2.00 versus 3.00 on control; difference -1.00 (95% CI -1.16 to -0.84), standardized effect d = -3.92; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Hypoglycemic Clamp than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes address related aspects of autonomic function: muscle sympathetic nerve activity and catecholamine response to lower-body negative pressure. The detailed numerical results include the catecholamine measure, while numerical results for muscle sympathetic nerve activity are not reported in the registry record. The secondary result therefore offers a limited additional view rather than a complete account of every listed secondary outcome.

In broad terms, a secondary measure can help contextualize a primary result by asking whether related physiological measures show a compatible pattern. However, distinct outcomes capture distinct processes and can differ in measurement properties, timing, and variability. A pattern across endpoints is not proof that they measure the same biological response, and a result on one endpoint cannot fill in an unreported result on another.

The registry's secondary comparison is unadjusted, and no reported analyses describe a correction for testing multiple outcomes. When several outcomes are considered, isolated low p-values can be less persuasive than a result that was prespecified as primary and interpreted within a documented testing strategy. The record does not report such a strategy or an outcome hierarchy beyond identifying the primary endpoint.

Accordingly, the secondary information should be treated as contextual and exploratory rather than as independent confirmation of the primary finding. The registry does not provide enough detail to assess whether these outcomes were prespecified, how missing data were handled, or whether the analyses accounted for the crossover structure. Those uncertainties limit how strongly the secondary findings can reinforce or qualify the primary result.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Muscle Sympathetic Nerve Activity
• Catecholamine Response to Lower-body Negative Pressure

9. Statistical Interpretation

10. Statistical Methods Explained

The registry presents the primary endpoint as a continuous measure summarized by its mean and standard deviation. A mean describes the center of the observed values, while a standard deviation describes their spread around that center. These summaries help readers understand the direction and variability of measured changes, but do not show the full distribution of values or the pattern of within-person responses.

What does the mean difference represent?

The contrast is expressed as the hypoglycemic-clamp mean minus the euglycemic-clamp mean. The reported value is -3.9 ms/mmHg. A negative estimate means that the average change in the hypoglycemic condition was lower than the average change in the euglycemic condition, according to the reported contrast. This direction agrees with the posted arm means, 2.3 ms/mmHg and -1.6 ms/mmHg, respectively. The contrast is a difference in mean change, not a ratio or a percentage change.

In general, a mean difference retains the original measurement units, so readers can relate the estimate to the scale of the endpoint. Whether a difference is important in clinical or physiological terms requires a meaningful threshold or external context. Such a threshold is not reported in the registry record.

Why does the crossover structure matter?

In a crossover trial, the same participant experiences both conditions. A paired analysis can compare the two condition-specific changes within each participant and thereby use information about how that participant's measurements relate across conditions. The precision of a paired estimate depends in part on the within-person association between measurements. Separate arm summaries do not reveal that association.

The registry identifies the trial as crossover and reports that 20 participants completed both arms, but gives primary outcome changes for 18 participants in both arms. It does not describe the statistical model, the pairing method, or adjustment for treatment sequence or period. The posted mean difference and confidence interval therefore cannot be assumed to come from a particular paired model. In general, a method that ignores pairing can give a different standard error from one that uses the repeated measurements; the direction and size of that difference depend on the data.

What does the p-value say?

The unadjusted p-value for the primary contrast is 0.03. In general, a p-value measures how compatible the observed data are with a specified null hypothesis under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. Because the registry does not identify the test or model used, the assumptions behind this p-value are not reported in the registry record.

The word unadjusted is also consequential. It means the reported p-value is not presented as corrected for testing multiple outcomes or comparisons. When many hypotheses are examined, the chance of seeing at least one apparently unusual result can increase. Whether that issue affected the trial's original interpretation depends on its planned outcome hierarchy and analysis strategy, which are not reported.

Why do confidence intervals matter?

A confidence interval gives a range of estimates compatible with the data under the method used and its assumptions. In general, a narrower interval indicates greater statistical precision, while a wider interval leaves more uncertainty about the size of the contrast. The primary interval runs from -7.424 to -0.376 ms/mmHg. It is entirely negative, but covers estimates with different magnitudes. It should be interpreted together with the mean difference and the limitations of the unreported analysis method.

Confidence intervals do not guarantee that the true effect falls within a particular interval, nor do they incorporate sources of uncertainty omitted from the model. If the calculation does not account for the crossover pairing, for example, the interval may not reflect the precision of an appropriate paired analysis. The registry does not provide sufficient method details to assess that issue.

What is the role of standard deviation?

Standard deviations describe variability among observed values; they are not confidence intervals for the means. The primary arm standard deviations are 6.3 and 4.3 ms/mmHg. General statistical reasoning cautions against using these values alone to infer the variability of paired differences, because the correlation between a participant's measurements in the two conditions is also relevant. That correlation is not reported.

These methods explain how the posted summaries and contrast are commonly read, but they cannot reconstruct an unreported trial analysis. The registry contains no reported analysis entries, and the original protocol's statistical methods are not reported in the registry record. Thus, the most defensible reading distinguishes the recorded descriptive results from claims about the model or inferential procedure that generated them.

11. Confidence Intervals and Precision

The primary mean-difference estimate is -3.9 ms/mmHg, with a 95% confidence interval from -7.424 to -0.376 ms/mmHg. The interval is entirely below zero, indicating that the posted range of estimates is negative under the calculation used. Its endpoints nevertheless span a range of possible magnitudes, so the result does not pin down a single precise size of difference.

In general, a confidence interval communicates both direction and precision. A narrow interval would constrain the plausible values more tightly; a broad interval would leave greater uncertainty. The primary interval includes values relatively close to zero as well as more negative values. The registry does not provide a threshold for judging which values would be clinically or physiologically important, so statistical precision should not be confused with clinical interpretation.

The interval's interpretation depends on the statistical method and its assumptions. The record identifies a crossover design and says that 18 participants had primary outcome changes for both arms, but does not report the specific model, whether the comparison accounted for within-participant pairing, or how missing observations were handled. The registry also reports no analyses. Those omissions limit assessment of whether the reported interval represents the intended crossover analysis.

The unadjusted p-value is 0.03. It is related to the interval but answers a different question and does not measure precision or effect importance. It also does not account for possible multiplicity. Taken together, the estimate, interval, and p-value describe a negative posted contrast, while the absent analysis details and missing-data information leave uncertainty beyond the interval itself.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the trial's original design justification. For these continuous outcomes, the entries are participants per arm, not total events. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The planned effect to detect is set at the listed fraction of the observed effect. The original trial's sample-size assumptions are not reported in the registry record.

The 80% power column describes the number of participants per arm that the planning calculation estimates would give an 80% chance of detecting the specified effect if that effect were the true one and the assumptions held. The 90% power column gives the corresponding planning count for a 90% chance. Higher planned power generally requires more participants, all else held constant.

The rows consider planning for 100%, 75%, and 50% of the observed effect. The smaller the effect a future study aims to detect, the more participants it generally needs, because a modest signal is harder to distinguish from random variation. These figures are illustrative rather than recommendations: they inherit assumptions about effect size, allocation, significance level, and the normal approximation, and do not incorporate a documented crossover-specific design model.

This is not observed power. It is a forward-looking calculation using an effect estimated from the posted results. The curve should be read as a visual expression of how required enrollment changes with the assumed effect under the same planning framework; it does not describe what power the completed trial actually achieved.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -3.900; pooled standard deviation σ = 5.394.
2. n = 2 × (1.96 + 0.842)² × 5.394² / -3.900² = 30.0, rounded up to 31 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -3.9                      # observed difference in means
sigma <- 5.39351462406472                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1816893)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 31 (80% power), 41 (90% power)
 75% of observed effect: n per arm = 54 (80% power), 72 (90% power)
 50% of observed effect: n per arm = 121 (80% power), 161 (90% power)
power.t.test: 31 
Simulated power at n = 31 per arm: 0.795 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry identifies change in baroreflex sensitivity as the primary outcome and lists secondary outcomes, but does not report a multiplicity plan. It does not state whether the trial controlled the overall type I error across endpoints, used a hierarchy, or treated secondary tests as exploratory. The posted primary p-value is explicitly unadjusted. The secondary comparison is also unadjusted. With multiple outcomes, the interpretation of individual p-values depends on the analysis strategy, which is not reported in the registry record.

Missing outcome data are visible for the primary measure. The record states that 20 participants completed both arms, while 18 had the change in baroreflex sensitivity outcome for both arms. The reasons the other participants lacked that outcome, whether measurements were missing in one or both conditions, and whether any imputation or sensitivity analysis was performed are not reported. The primary arm summaries each include 18 participants.

The detailed catecholamine outcome uses 20 participants per arm. The registry also names muscle sympathetic nerve activity as a secondary outcome, but numerical results and analysis details for it are not reported in the registry record. The safety denominators differ between clamp groups, and the record does not explain the difference.

These gaps matter because the analysis population and missing-data assumptions affect what the estimated contrast represents. An available-case comparison describes those with usable outcome data; it does not automatically describe every participant enrolled or every participant who completed both arms. The record does not report an intention-to-treat definition, per-protocol population, missingness mechanism, or imputation method. Nor does it report interim analyses or stopping rules. No conclusion about these procedures should be inferred from their absence in the registry.

15. 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 registry reports zero serious adverse events and zero other adverse events in the euglycemic clamp group, with 22 participants at risk. For the hypoglycemic clamp group, it reports zero serious adverse events and zero other adverse events, with 20 participants at risk. Deaths are reported as zero in both groups, and no serious adverse-event terms are listed.

These are registry counts over the reported safety populations. They do not describe the kinds of events that were monitored, the observation period, the severity criteria, or how events were collected; those details are not reported in the registry record. The different numbers at risk also mean the group counts should be read with their recorded denominators rather than as identical observation sets.

A zero count in a registry entry means no events were recorded in that category for the stated group. It does not establish that no event could occur, nor does it provide a precise estimate of risk without additional information about surveillance and follow-up. The safety figures are descriptive and should not be extended beyond the populations and recording information reported.

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

The posted primary results describe a lower mean change in baroreflex sensitivity after the hypoglycemic clamp than after the euglycemic clamp among the 18 participants with change measurements for both arms. The estimated mean difference is -3.9 ms/mmHg, and the 95% confidence interval is from -7.424 to -0.376. The unadjusted p-value is 0.03. These numbers describe the direction, estimated size, and statistical uncertainty of the recorded contrast under the method used to calculate it.

They do not establish that the contrast is clinically important. The registry does not report a threshold for an important change, and a statistical difference is not automatically a meaningful physiological difference. The results also do not show whether any change persisted beyond the assessment 16 hours after the clamp. Longer-term outcomes are not reported in the registry record.

The findings should not be treated as a complete account of the trial's original analysis. Although the design is crossover, the record does not describe the inferential model or whether it accounted for within-person pairing, treatment order, or period effects. It also does not explain why primary outcome data were unavailable for some participants who completed both arms. These missing details constrain interpretation of the estimate and interval.

Nor do the results establish a mechanism. The trial's stated goal was to determine effects of hypoglycemia on the autonomic nervous system, but the posted outcomes are measurements, not a direct demonstration of a causal pathway. A relationship between the clamp condition and an observed endpoint cannot by itself identify the underlying biological process.

The secondary outcome information is limited, multiplicity procedures are not reported, and the registry contains no reported analyses. The appropriate conclusion is therefore narrow: the posted summaries show a negative primary contrast at the stated follow-up time, with uncertainty and analysis limitations that remain important. The record does not support broader claims about treatment benefit, clinical outcomes, or effects outside the measured conditions.

17. Why This Trial Matters Statistically

This trial raises several statistical issues that are especially visible in a small crossover study. Because participants undergo both clamp conditions, the central comparison is naturally within-person. That design can make each participant their own comparator, but the statistical analysis needs to reflect the repeated measurements. The registry identifies the crossover design without describing how the posted contrast handles pairing. This makes reporting of the analysis model essential for readers who want to evaluate precision.

The difference between completion and outcome availability is also important. Twenty participants completed both arms, but only 18 had the primary change outcome for both. This highlights why enrollment, completion, and endpoint-specific analysis counts should not be treated as interchangeable. Without reasons for missing measurements and a stated missing-data approach, readers cannot determine how well the observed results represent all participants who completed the conditions.

The primary estimate is accompanied by a confidence interval and an unadjusted p-value, which are useful but incomplete without the model and multiplicity plan. A p-value alone cannot communicate effect size, and an interval cannot correct for a method that may not account for the design. The registry also lists a secondary outcome without numerical results, illustrating how selective availability of endpoint information can limit assessment of consistency across outcomes.

Finally, the sample-size illustrations are based on the observed effect rather than the trial's documented original design assumptions. They can help explain how planning changes when a smaller effect is targeted, but they cannot establish that the trial was adequately planned or that its observed findings have a particular level of power. Together, these points show why transparent reporting of design-specific analyses, missing data, and outcome plans is central to statistical interpretation.

18. 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 limitations specific to this record constrain interpretation. First, the crossover design is identified, but the registry does not report treatment sequence, period structure, washout interval, or a model for repeated measurements. These details are relevant when evaluating whether the comparison appropriately uses within-participant information and whether order or carryover could matter. Their absence means those possibilities cannot be assessed, not that they necessarily affected the findings.

Second, only 18 participants had primary change measurements for both arms, although 20 completed both arms and enrollment was 22. Reasons for the missing primary outcomes and their handling are not reported. The available summaries therefore represent the recorded endpoint population, and the record does not establish how it relates to all enrolled or completing participants.

Third, the registry reports no analyses and does not document the statistical test, adjustment strategy, or prespecified multiplicity approach. The posted unadjusted comparison should not be assumed to match an original protocol analysis. No sample-size justification for the original trial is reported; the planning illustrations are based on observed effects and are not evidence of the design's original rationale.

Finally, the registry names muscle sympathetic nerve activity as a secondary outcome but does not provide numerical results for it. It also does not report a clinical-importance threshold for the primary measure, broader participant characteristics, or follow-up beyond the stated measurement time. These limitations narrow the conclusions to the available endpoint summaries and prevent fuller assessment of generalizability, clinical significance, and robustness.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Hypoglycemia and Autonomic Nervous System Function — NCT01816893.
• Registry record last updated 2018-04-02; status last verified 2018-03.
• Results first posted 2018-03-06.
• 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.

22. Record Summary

NCT01816893 is a completed randomized, double-blind crossover trial of hypoglycemic and euglycemic hyperinsulinemic clamps, sponsored by Brigham and Women's Hospital. The primary outcome was change in baroreflex sensitivity measured 16 hours after each clamp relative to baseline on the day before the clamp.

The registry reports a mean change of 2.3 ms/mmHg for the euglycemic clamp and -1.6 ms/mmHg for the hypoglycemic clamp. The posted mean difference is -3.9 ms/mmHg, with a 95% confidence interval from -7.424 to -0.376 and an unadjusted p-value of 0.03. Eighteen participants had primary outcome changes for both arms; 20 completed both arms.

The record does not report the analysis model, missing-data method, multiplicity plan, or original sample-size justification. Secondary numerical information is incomplete, and safety entries report no recorded serious or other adverse events in either group.