Wavelet analysis of autonomic outflow of normal subjects on head-up tilt, cold pressor test, Valsalva manoeuvre and deep breathing.

Non-invasive autonomic evaluation has used fast Fourier transform (FFT) to assign a range of low (LF) and high frequencies (HF) as markers of sympathetic and parasympathetic influences, respectively. However, FFT cannot be applied to brief transient phenomena, such as those observed on performing autonomic tests where the acute changes of cardiovascular signals (blood pressure and heart rate) that represent the first and most important stage of the autonomic performance towards a new state of equilibrium occur. Wavelet analysis has been proposed as a method to overcome and complement information taken exclusively in the frequency domain. With discrete wavelet transform (DWT), a time-frequency analysis can be done, allowing the visualization in time of the contribution of LF and HF to the observed changes of a particular signal. In this study, we evaluate with wavelets the acute changes in R-R intervals and systolic blood pressure that are observed in normal subjects during four classical autonomic tests: head-up tilt (HUT), cold pressor test (CPT), deep breathing (DB) and Valsalva manoeuvre (VM). Continuous monitoring of ECG and blood presure was performed. Also LF, HF and LF/HF were calculated. Consistent with previous interpretations, data showed an increase of sympathetic activity in HUT, CPT and VM. On DB, results reflected an increase in parasympathetic activity and frequencies. In conclusion, when compared with FFT, wavelet analysis allows the evaluation of autonomic variability during short and non-stationary periods of time and may constitute a useful advance in the assessment of autonomic function in both physiological and pathological conditions.

Sympathetic sudomotor function and amyotrophic lateral sclerosis.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting motor neuron cells in the cerebral cortex, brain stem and spinal cord. Autonomic nervous system involvement is not a recognized feature of the disease; nonetheless, autonomic dysfunction has been reported in severely affected patients. The aim of this study was to evaluate sympathetic sudomotor function in ALS patients, employing the sweat imprint test. METHODS: Twenty-four ALS patients and 25 controls, matched for sex and age, were included. In total, 34 hands and 35 feet in controls, and 29 hands and 30 feet in the ALS population, were investigated. RESULTS: No inter-side difference was found in controls or in ALS patients. The mean number of sweat drops/cm2 was comparable in both populations. However, six ALS patients had a lower count on the hand than on the foot, which was never observed in controls. Furthermore, in the ALS population, five hands and three feet showed values below the lower limit of normal. The abnormalities were more frequent in very weak limbs, and could be ascribed to lack of use. CONCLUSION: Although significant sudomotor hypofunction does not occur in ALS, mild subclinical changes can be observed in weak limbs.

Allgrove syndrome in adulthood.

A 35-year-old man with a past history of achalasia developed progressive spastic tetraparesis, distal limb atrophy, dysarthria, and dysphagia. A clinical diagnosis of amyotrophic lateral sclerosis (ALS) was considered before neurophysiological investigation, which disclosed a polyneuropathy and a prolonged central conduction time. One year later, the patient developed dysautonomic symptoms. Following confirmation of adrenal insufficiency, a diagnosis of Allgrove syndrome was made. This is a rare case, and we emphasize its clinical similarity with ALS.