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Insulin resistance and circadian rhythm of cardiac autonomic modulation
Sol M Rodríguez-Colón1, Xian Li, Michele L Shaffer
1Department of Public Health Sciences, Penn State University College of Medicine, 600 Centerview Dr, Suite 2200, A210, Hershey, PA, USA.
Insights
Insulin resistance (IR) impairs cardiac autonomic modulation (CAM) mean levels in non-diabetics, but not its circadian timing. In type 2 diabetes, IR adversely affects all CAM circadian parameters.
Area of Science:
- Cardiology
- Endocrinology
- Chronobiology
Background:
- Insulin resistance (IR) is linked to cardiovascular diseases (CVD).
- Heart rate variability (HRV) reflects cardiac autonomic modulation (CAM) and is associated with CVD outcomes.
- Limited data exist on IR's impact on CAM's circadian patterns.
Purpose of the Study:
- To investigate the association between IR and circadian oscillations of CAM.
- To examine how IR affects the daily rhythm of cardiac autonomic function.
Main Methods:
- Assessed IR using Homeostasis Model Assessment (HOMA-IR), insulin, and glucose levels.
- Measured CAM via 24-hour electrocardiogram (ECG) HRV analysis.
- Employed two-stage modeling: individual cosine modeling of HRV data and random-effects meta-analysis.
Main Results:
- In non-diabetics, elevated log HOMA-IR was associated with significantly lower mean HRV indices (M) (P < 0.05).
- IR was not significantly associated with the amplitude (Â) or acrophase (θ) of HRV indices in non-diabetics.
- In type 2 diabetics, higher HOMA-IR showed larger adverse effects on M, Â, and θ.
Conclusions:
- In non-diabetics, IR impairs overall CAM levels but not its circadian rhythmicity.
- In type 2 diabetes, characterized by more severe IR, adverse effects extend to all aspects of CAM's circadian parameters.
- Findings highlight differential impacts of IR on cardiac autonomic control based on diabetes status.
Background:
Insulin resistance (IR) has been associated with cardiovascular diseases (CVD). Heart rate variability (HRV), an index of cardiac autonomic modulation (CAM), is also associated with CVD mortality and CVD morbidity. Currently, there are limited data about the impairment of IR on the circadian pattern of CAM. Therefore, we conducted this investigation to exam the association between IR and the circadian oscillations of CAM in a community-dwelling middle-aged sample.
Method:
Homeostasis models of IR (HOMA-IR), insulin, and glucose were used to assess IR. CAM was measured by HRV analysis from a 24-hour electrocardiogram. Two stage modeling was used in the analysis. In stage one, for each individual we fit a cosine periodic model based on the 48 segments of HRV data. We obtained three individual-level cosine parameters that quantity the circadian pattern: mean (M), measures the overall average of a HRV index; amplitude (Â), measures the amplitude of the oscillation of a HRV index; and acrophase time (θ), measures the timing of the highest oscillation. At the second stage, we used a random-effects-meta-analysis to summarize the effects of IR variables on the three circadian parameters of HRV indices obtained in stage one of the analysis.
Results:
In persons without type diabetes, the multivariate adjusted β (SE) of log HOMA-IR and M variable for HRV were -0.251 (0.093), -0.245 (0.078), -0.19 (0.06), -4.89 (1.76), -3.35 (1.31), and 2.14 (0.995), for log HF, log LF, log VLF, SDNN, RMSSD and HR, respectively (all P < 0.05). None of the IR variables were significantly associated with  or θ of the HRV indices. However, in eight type 2 diabetics, the magnitude of effect due to higher HOMA-IR on M, Â, and θ are much larger.
Conclusion:
Elevated IR, among non-diabetics significantly impairs the overall mean levels of CAM. However, the  or θ of CAM were not significantly affected by IR, suggesting that the circadian mechanisms of CAM are not impaired. However, among persons with type 2 diabetes, a group clinically has more severe form of IR, the adverse effects of increased IR on all three HRV circadian parameters are much larger.
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