Abstract
Decreased heart rate variability (HRV) was shown for unmedicated patients with schizophrenia and their first-degree relatives, implying genetic associations. This is known to be an important risk factor for increased cardiac mortality in other diseases. The interaction of cardio-respiratory function and respiratory physiology has never been investigated in the disease although it might be closely related to the pattern of autonomic dysfunction. We hypothesized that increased breathing rates and reduced cardio-respiratory coupling in patients with acute schizophrenia would be associated with low vagal function. We assessed variability of breathing rates and depth, HRV and cardio-respiratory coupling in patients, their first-degree relatives and controls at rest. Control subjects were investigated a second time by means of a stress task to identify stress-related changes of cardio-respiratory function. A total of 73 subjects were investigated, consisting of 23 unmedicated patients, 20 healthy, first-degree relatives and 30 control subjects matched for age, gender, smoking and physical fitness. The LifeShirt®, a multi-function ambulatory device, was used for data recording (30 minutes). Patients breathe significantly faster (p<.001) and shallower (p<.001) than controls most pronouncedly during exhalation. Patients' breathing is characterized by a significantly increased amount of middle- (p<.001), high- (p<.001), and very high frequency fluctuations (p<.001). These measures correlated positively with positive symptoms as assessed by the PANSS scale (e.g., middle frequency: r = 521; p<.01). Cardio-respiratory coupling was reduced in patients only, while HRV was decreased in patients and healthy relatives in comparison to controls. Respiratory alterations might reflect arousal in acutely ill patients, which is supported by comparable physiological changes in healthy subjects during stress. Future research needs to further investigate these findings with respect to their physiological consequences for patients. These results are invaluable for researchers studying changes of biological signals prone to the influence of breathing rate and rhythm (e.g., functional imaging).
Highlights
Somatic consequences of chronic mental diseases have been brought into focus during the last years
In contrast to autonomic function in primary medical conditions, it has been suggested that decreased heart rate variability (HRV) in patients with schizophrenia is caused by a decreased interaction between prefrontal brain areas and subcortical structures, leading to arousal and an autonomic imbalance characterized by vagal withdrawal and sympathetic predominance [8,9]
First Experiment - Multivariate analysis of covariance (MANCOVA) of respiratory parameters and follow-up analysis of covariance (ANCOVA) of single parameters for all groups controlled for age
Summary
Somatic consequences of chronic mental diseases have been brought into focus during the last years. In contrast to autonomic function in primary medical conditions, it has been suggested that decreased HRV in patients with schizophrenia is caused by a decreased interaction between prefrontal brain areas and subcortical structures, leading to arousal and an autonomic imbalance characterized by vagal withdrawal and sympathetic predominance [8,9]. This autonomic pattern was demonstrated in unmedicated patients with schizophrenia by examining the heart, the pupil, the stomach or the cadio-respiratory system [6,10,11]. Another important player, namely the respiratory function, which is a key regulatory centre for body homeostasis [12], has very rarely been assessed in the disease, it might point to the central origin of the autonomic disturbance and might serve as an entrance to influence autonomic function directly by means of biofeedback interventions
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