A functional-structural model to understand cardiac autonomic nervous system (ANS) dysregulation in affective illness and to elucidate the ANS effects of antidepressive treatment.

Numerous studies provide evidence that major depression (MD) is associated with certain disorders of cardiac autonomic nervous system (ANS) function, in particular, with an autonomic neurocardiac imbalance characterized by a low cardiovagal modulation, a raised sympathetic nerve activity and a high resting heart rate. We assume that such MD-associated cardiac ANS disorders are mainly caused by functional-structural abnormalities within the central autonomic network (CAN), in particular, by well-defined abnormalities of hypothalamic structures in MD. In view of the well-known association between an autonomic neurocardiac imbalance and the risk for cardiac arrhythmias, we assume that MD-associated cardiac ANS disorders are at least partly responsible for the high cardiovascular mortality risk in MD. It is, however, still unclear whether antidepressive treatment will lower the risk for cardiovascular complications in MD. There is convincing evidence that a successful antidepressive treatment with electroconvulsive therapy, cognitive behavioral therapy, or pharmacotherapy with primarily non-antimuscarinergic antidepressants can improve an initially disturbed cardiac ANS function in MD. These studies correspond well to our findings that treatment with both, nefazodone or reboxetine, can induce a reduction of central sympathetic nerve activity and an increase of the initially lowered cardiovagal modulation depending on the improvement of depressive symptoms after treatment. Since both effects occured obviously independent from the primarily serotonergic or noradrenergic action of the antidepressants, our findings suggest the existence of a generally supraordinate and uniform mechanism underlying the ANS effects of antidepressive treatment with drugs inhibiting serotonin- or noradrenaline reuptake.

[Does acupuncture influence the cardiac autonomic nervous system in patients with minor depression or anxiety disorders?]. / Beeinflusst Akupunktur die autonom kardiale Regulation bei Patienten mit leichten depressiven Episoden oder Angststörungen? Eine randomisierte, plazebokontrollierte Verlaufsstudie.

We undertook this study to evaluate the effects of needle acupuncture on cardiac autonomic nervous system (ANS) function in patients with minor depression or anxiety disorder. Patients (n = 36) were randomly distributed into a verum acupuncture (VA) group (needles were applied at classical acupuncture points, e. g. He7, Pe6, Du20, Bl62, Ex6) or a placebo (PL) group (needles were applied only epidermal at non-acupuncture points). Both groups underwent standardized measurements of the 5-minute resting heart rate variability (HRV), which were performed before the first and after the 9th acupuncture session of an acupuncture series, and also three times (before the start and 5, respectively, 15 minutes after needle application) during the third acupuncture session. Demographic data between the VA and PL group did not differ. Before the start of acupuncture there were also no significant differences in HRV data between these groups. Compared to PL the VA group showed a significant decrease of the mean resting heart rate both, 5 and 15 minutes after needle application, combined with a trend towards an increase of the high frequency (HF; 0.15 - 0.4 Hz) and a decrease of the low frequency (LF; 0.04 - 0.15 Hz) spectral power. The latter effects resulted in an overall significant decrease of the mean LF/HF ratio in VA compared to PL treated patients. This pattern of findings suggests that in patients with minor depression or anxiety only verum acupuncture 1.) leads to a relative increase of cardiovagal modulation of heart rate and 2.) facilitates the physiological regulatory ANS function in response to alterations of external or internal environment. Clinical implications of these findings are discussed.

In-flight radiation measurements on STS-60.

A joint investigation between the United States and Russia to study the radiation environment inside the Space Shuttle flight STS-60 was carried out as part of the Shuttle-Mir Science Program (Phase 1). This is the first direct comparison of a number of different dosimetric measurement techniques between the two countries. STS-60 was launched on 3 February 1994 in a nearly circular 57 degrees x 353 km orbit with five U.S. astronauts and one Russian cosmonaut for 8.3 days. A variety of instruments provided crew radiation exposure, absorbed doses at fixed locations, neutron fluence and dose equivalent, linear energy transfer (LET) spectra of trapped and galactic cosmic radiation, and energy spectra and angular distribution of trapped protons. In general, there is good agreement between the U.S. and Russian measurements. The AP8 Min trapped proton model predicts an average of 1.8 times the measured absorbed dose. The average quality factor determined from measured lineal energy, y, spectra using a tissue equivalent proportional counter (TEPC), is in good agreement with that derived from the high temperature peak in the 6LiF thermoluminescent detectors (TLDs). The radiation exposure in the mid-deck locker from neutrons below 1 MeV was 2.53 +/- 1.33 microSv/day. The absorbed dose rates measured using a tissue equivalent proportional counter, were 171.1 +/- 0.4 and 127.4 +/- 0.4 microGy/day for trapped particles and galactic cosmic rays, respectively. The combined dose rate of 298.5 +/- 0.82 microGy/day is about a factor of 1.4 higher than that measured using TLDs. The westward longitude drift of the South Atlantic Anomaly (SAA) is estimated to be 0.22 +/- 0.02 degrees/y. We evaluated the effects of spacecraft attitudes on TEPC dose rates due to the highly anisotropic low-earth orbit proton environment. Changes in spacecraft attitude resulted in dose-rate variations by factors of up to 2 at the location of the TEPC.