**5. Characteristic HRV profiles in depression**

**Figure 6** presents the characteristic HRV profiles at the baseline rest condition (Rest), during the task load (Task) and during the rest condition after the task (After) in the control healthy subjects, in the patients with major depressive disorder (MDD) and in the patients with a general anxiety disorder (GAD). The HRV profiles of MDD and GAD were used in the present chapter to represent that in depression and anxiety. The schematic diagrams are made based on our published data [13]. The data in each measurement condition are connected by lines to clarify the characteristic profiles. LF data are connected by dashed lines to indicate that the inter-subject differences are large not only in the healthy subjects but in the patients with MDD and GAD.

The healthy HF pattern takes the form of a V shape and the healthy LF/HF and HR patterns have inverted V shapes. HF decreases, and LF/HF and HR increase during Task, and they return to the original level at After. This indicates that the breathingrelated control of heart rate reflecting parasympathetic activity decreases during Tasks in healthy subjects. It is interesting that inhibition of parasympathetic activity during task load is observed in this paradigm. The parasympathetic inhibition during task load should be a healthy response of the autonomic system to stressful events. LF responses are not consistent. HF and LF react to stressful events differently. HR behaves similar to LF/HF.

#### **Figure 6.**

*Schematic diagrams of heart rate variability profiles in major depressive disorder (MDD) and generalized anxiety disorder (GAD). Detailed descriptions are found in the text.*

#### *Characteristic Profiles of Heart Rate Variability in Depression and Anxiety DOI: http://dx.doi.org/10.5772/intechopen.104205*

In depression, HF at the resting state is low, indicating the underactivity of parasympathetic system. Parasympathetic underactivity is found not only in depression but in cardiovascular, neurological, and other psychiatric disturbances. In ischemic heart disorder and diabetic neuropathy, the peripheral autonomic nerve function is disturbed. In dementia and epilepsy, organic changes of the brain lead to autonomic alteration. In depression, functional changes of the responsible brain areas should involve the central autonomic system to generate HRV changes.

In addition to baseline change of the parasympathetic activity reflected in low HF, response of HF to the task load is disturbed in depression, making Task/ Rest ratio high. Parasympathetic activity cannot be switched off during the task indicating the difficulty in modifying the autonomic activity in response to alteration of arousal level or attention. Unresponsiveness of HF is found not only in MDD [11] but in normal subjects with high depressiveness and anxiety [12]. Subjective scores for depressiveness and anxiety were correlated with Task/Rest ratio of HF in normal controls. Depressiveness and anxiety may be related to parasympathetic unresponsiveness to stress.

Depression is also accompanied by an increase of HF during the rest period after the task load. The rebound-like increase starts after the end of the task and lasts for several tens of seconds. The functional significance of this transient change of HF may be related to excessive excitation of the parasympathetic system after suppression during the task load. Overall, depression is accompanied by continuous suppression together with the uncontrollability of the parasympathetic system.

As for LF, a reduction in the baseline level is observed in depression. But the rebound-like increase is present at the resting state after the task load possibly because LF reflects both sympathetic and parasympathetic activity. LF/HF and HR are higher in depression than in control. Parasympathetic underactivity is also responsible for these changes. It is interesting to observe that LF/HF and HR increase in response to task load although HF and LF are unchanged during the task load. Individual differences during the task load may account for this discrepancy.

### **6. Characteristic HRV profiles in anxiety**

On the other hand, the patients with GAD show an elevation of both HF and LF when they are free of a panic attack or severe phobic symptoms. In contrast to the HRV profile in depression, the parasympathetic system is activated, and breathingrelated and blood pressure-dependent modulation of heart rate is enhanced. The elevation of HF and LF at the resting state may be considered as a regulation of autonomic activity to cope with anxiety-related changes. When the regulation does not work, panic attack may occur. During panic attacks and exacerbation of anxiety symptoms, HF decreases and LF/HF increases, reflecting parasympathetic inhibition [6]. But when the anxious state is ameliorated, HRV indices return to the original level [13].

The elevated HF in GAD reacts to the task load by decreasing as in the normal control. Reactivity of parasympathetic activity is maintained in anxiety patients. The elevated LF can contribute to the stabilization of blood flow when the fluctuation of blood flow is large. Such fluctuation would be present during the time of stress. LF elevation may be the sign of an increased control of stress-induced circulatory changes. HRV profiles in GAD can be the result of autonomic accommodation to the anxious state.
