Elsevier

Biological Psychology

Volume 56, Issue 2, June 2001, Pages 131-150
Biological Psychology

Analysis of twenty-four hour heart rate variability in patients with panic disorder

https://doi.org/10.1016/S0301-0511(01)00074-6Get rights and content

Abstract

Growing evidence suggests that alterations in autonomic function contribute to the pathophysiology of panic disorder (PD). This retrospective study employed 24-h heart rate variability (HRV) analysis of Holter records to compare autonomic function in PD patients (n=38) with healthy, age- and gender-matched controls. Both time and frequency domain measures were calculated, and a circadian rhythm analysis was performed. The SDNN index, 5-min total power, very low frequency (VLF) and low frequency (LF) power were significantly lower in panic patients relative to controls over the 24-h period. Hourly means were significantly lower during some of the waking hours as well as the latter part of the sleep cycle. In contrast, the mean RR interval, RMSSD and high frequency (HF) power were comparable in patients and controls. Results suggest that sympathetic activity is depressed in PD patients under usual life conditions, leading to a relative predominance of vagal tone. Findings of low HRV in PD patients are consistent with the high rate of cardiovascular morbidity and mortality in this population, as well as with the emerging view of panic as a disorder involving reduced flexibility and adaptability across biological, affective and behavioral dimensions.

Introduction

The high prevalence and severe impact on quality of life of panic disorder (PD) make this condition one of the most studied psychological disorders in the US (Weissman, 1991). Patients with panic disorder experience recurrent panic attacks, which are characterized by episodes of intense anxiety accompanied by a range of alarming somatic symptoms including chest pain, heart pounding, tachycardia, shortness of breath, sweating and dizziness. Collectively, these responses are suggestive of autonomic nervous system (ANS) dysfunction.

A number of recent investigations have sought to illuminate the autonomic underpinnings of PD using the analysis of heart rate variability (HRV), a noninvasive, sensitive and dynamic indicator of autonomic regulation of the heart. Low heart rate variability is found in individuals with a wide range of pathologies and is considered a powerful predictor of heart disease, increased risk of sudden death, as well as all-cause mortality (Öri et al., 1992, Tsuji et al., 1994, Tsuji et al., 1996, Dekker et al., 1997). Recently, measurements of HRV have also been increasingly applied to investigate autonomic regulation in affective disorders, and aberrant HRV patterns have been observed in various conditions including anxiety and major depression (Dalack and Roose, 1990, Rechlin et al., 1994, Thayer et al., 1996).

The majority of studies of HRV in panic disorder patients have focused on short-term resting recordings and/or autonomic responses to short-term challenges, such as cold pressor, postural change, sodium lactate infusion and various pharmacological treatments. Generally, this body of research indicates reduced overall HRV, diminished vagal tone and relative sympathetic dominance in PD patients under these types of conditions (Yeragani et al., 1990, Yeragani et al., 1991, Yeragani et al., 1993, Yeragani et al., 1994, Friedman et al., 1993, Klein et al., 1995, Friedman and Thayer, 1998a, Friedman and Thayer, 1998b, Hamada et al., 1998). However, with regard to the specific findings of these investigations, some inconsistencies do exist. For example, lowered high frequency (HF) power in panic patients as compared to control subjects in supine or standing postures was demonstrated in some cases (Klein et al., 1995, Seier et al., 1997) but not in others (Yeragani et al., 1993, Middleton et al., 1994, Rechlin et al., 1994). One short-term study showed panic patients to have increased very low frequency (VLF) power relative to controls in the supine posture (Rechlin et al., 1994); another demonstrated no difference in power in this frequency range in the supine condition but found decreased VLF power in patients as compared to controls while standing (Yeragani et al., 1993). One investigation demonstrated decreased short-term low frequency (LF) power in patients (Middleton et al., 1994) while others found no significant difference in power in the LF range between patients and controls (Yeragani et al., 1993, Rechlin et al., 1994). Further, one group reported a decrease in both HF and LF power in PD patients as compared to controls in response to lactate infusions (Seier et al., 1997), whereas other investigators demonstrated a significant decrease only in HF power (Yeragani et al., 1994). Still other research has shown normal autonomic responsivity to a broad range of challenges in PD patients (Stein and Asmundson, 1994).

While short-term HRV recordings can provide relevant data on autonomic function under specific controlled conditions, an informative contrast to these data can be achieved through the analysis of 24-h ambulatory ECG (Holter) records, which provides a window on individuals’ autonomic nervous system activity and balance in the context of their normal day-to-day activities. Advantages of ambulatory monitoring include a longer recording period, monitoring of the ECG in the subject's usual surroundings, the availability of sleep and circadian rhythm data, and a frequency resolution that includes the ultra low frequency (ULF) range. To our knowledge, only one study by Yeragani and colleagues has provided a full analysis of 24-h HRV in panic disorder patients. These authors reported decreased total, ULF and VLF power in PD patients as compared to healthy controls. Patients were found to have normal HF power, which reflects parasympathetic activity (Yeragani et al., 1998).

The present study provides further data on 24-h HRV in PD patients, using a larger sample size and employing time domain as well as frequency domain analysis methods. We also provide a circadian rhythm analysis of the hourly variations in HRV measures during the waking hours and during sleep. The overall aim of this investigation is to add to the existing body of data on autonomic nervous system function and balance in panic disorder, in an effort to characterize possible alterations in autonomic regulation that may underlie a vulnerability to panic attacks.

Section snippets

Subjects

In this retrospective study, we analyzed Holter records obtained from 38 patients with panic disorder (mean age 38 years, S.D.=7.65; age range 24–54 years; 20 females and 18 males), and 38 healthy control subjects (mean age 38 years, S.D.=7.86; age range 22–54 years). Written informed consent for the use of Holter information was obtained from all study participants.

Patients were diagnosed with panic disorder by a psychiatrist on the basis of DSM-IV criteria (American Psychiatric Association,

Twenty-four hour HRV measures

Table 1 and Fig. 1 compare mean values for all time and frequency domain HRV measures over the total 24-h recording period for PD patients and healthy age- and gender-matched controls.

Discussion

Overall, the results of this study are in accordance with previous reports indicating decreased HRV in individuals with panic disorder. PD patients had significantly lower 5-min total power, VLF and LF power as compared to healthy age and gender-matched controls over a 24-h period. The SDNN index, which correlates to the frequency domain measures of 5-min total power and VLF power, was also significantly lower in the patients, while the SDNN was significantly lower in the patients during sleep

Acknowledgements

The authors gratefully acknowledge Student Research Fellows Colette N. Meyer and Hayes H. Stuppy for the collection, compilation and verification of the patient records and data from which this paper was generated.

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