What is the clinical evidence from this study?

Study design: Cross-Sectional. Population: Severe mental illness (n=204). Intervention: Severe mental illness vs. Healthy controls. Primary outcome: Correlation between high-frequency heart rate variability (HF-HRV) and respiratory frequency (Pearson's r -0.29, 95% CI -0.52 to -0.03, p=0.03).

November 17, 2016Open Access

Resting-state high-frequency heart rate variability is related to respiratory frequency in individuals with severe mental illness but not healthy controls

Key Result

Resting-state high-frequency heart rate variability was significantly negatively correlated with respiratory frequency in individuals with severe mental illness (r = -0.29) but not in healthy controls.

Study Design

Type

Cross-Sectional (n=204)

Multicenter

Yes

Structured PICO

Population

204 adults without cardiovascular or metabolic diseases, comprising 55 individuals with severe psychiatric illness (schizophrenia spectrum n=34, bipolar spectrum n=21) recruited from 4 hospitals in the Oslo region, and 149 healthy controls from community census records. Mean age ~30 years.

Outcome

Correlation between resting-state high-frequency heart rate variability (HF-HRV) and respiratory frequencysurrogate

Resting-state high-frequency heart rate variability is significantly confounded by respiratory frequency in patients with severe mental illness, indicating that HRV research in this population must account for respiration.

Main Result

Effect estimate: Pearson's r -0.29 (95% CI -0.52 to -0.03)

Absolute Event Rate: -0.29% vs -0.04%

p-value: p=0.03

Limitations

Additional factors that influence HF-HRV, such as respiratory depth and central respiratory drive, were not collected.
Strain gauge around the chest may have offered less signal accuracy for participants who tend to breathe diaphragmatically.
Study sample size was not large enough to examine the link between HF-HRV and respiration in schizophrenia and bipolar disorder subtypes.
Measures of physical activity were not collected.
Pulse oximetry can make it difficult to identify cardiac dysrhythmia compared to ECG examination.

Abstract

Heart rate variability (HRV) has become central to biobehavioral models of self-regulation and interpersonal interaction. While research on healthy populations suggests changes in respiratory frequency do not affect short-term HRV, thus negating the need to include respiratory frequency as a HRV covariate, the nature of the relationship between these two variables in psychiatric illness is poorly understood. Therefore, the aim of this study was to investigate the association between HRV and respiratory frequency in a sample of individuals with severe psychiatric illness (n = 55) and a healthy control comparison group (n = 149). While there was no significant correlation between HF-HRV and respiration in the control group, we observed a significant negative correlation in the psychiatric illness group, with a 94.1% probability that these two relationships are different. Thus, we provide preliminary evidence suggesting that HF-HRV is related to respiratory frequency in severe mental illness, but not in healthy controls, suggesting that HRV research in this population may need to account for respiratory frequency. Future work is required to better understand the complex relationship between respiration and HRV in other clinical samples with psychiatric diseases.

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