Multi-time scale perspective in analyzing cardiovascular data.

Cardiovascular dynamic and variability data are commonly used in experimental protocols involving cognitive challenge. Usually, the analysis is based on a sometimes more and sometimes less well motivated single specific time resolution ranging from a few seconds to several minutes. The present paper aimed at investigating in detail the impact of different time resolutions of the cardiovascular data on the interpretation of effects. We compared three template tasks involving varying types of challenge, in order to provide a case study of specific effects and combinations of effects over different time frames and using different time resolutions. Averaged values of hemodynamic variables across an entire protocol confirmed typical findings regarding the effects of mental challenge and social observation. However, the hemodynamic response also incorporates transient variations in variables reflecting important features of the control system response. The fine-grained analysis of the transient behavior of hemodynamic variables demonstrates that information that is important for interpreting effects may be lost when only average values over the entire protocol are used as a representative of the system response. The study provides useful indications of how cardiovascular measures may be fruitfully used in experiments involving cognitive demands, allowing inferences on the physiological processes underlying the responses.

Individual stability of orthostatic tolerance response.

We studied individual stability of orthostatic tolerance as well as presyncopal signs and symptoms across four runs in subjects undergoing combined head-up tilt (HUT) and lower body negative pressure (LBNP). Ten healthy young males were subjected to HUT+ LBNP, to achieve a presyncopal end-point. Four test runs were separated by two week intervals. Hemodynamic variables and orthostatic tolerance were measured. From supine control to presyncope, heart rate increased while mean arterial blood pressure and stroke index decreased significantly. Individual orthostatic tolerance ranged from 7.2 to 30.0 min. Repetitions from the 1st to the 4th trial increased orthostatic tolerance by about 3 min, from 15+/-6 (trial 1) to 18+/-7 min (trial 4) but not significantly (p>0.05). Additionally, specific signs and symptoms as subjects approached presyncope were not always identical in the same persons. While considerable difference existed in tolerance times between healthy young men, orthostatic tolerance within subjects was similar, with little individual variability. However, as the reasons for termination of the tests were not always identical in the same subjects, and many subjects showed presyncopal symptoms rather than signs, close attention must be given to monitoring not only the signs but also the symptoms in subjects reaching presyncope.

Frequency, clinical and dermoscopic features of benign papillomatous melanocytic naevi (Unna type).

BACKGROUND: Most previous studies on melanocytic naevi have not distinguished between the different types of naevi, except for some studies trying to define atypical naevi. No large, population-based studies on papillomatous or Unna-type melanocytic naevi have been performed. OBJECTIVES: To investigate the dermoscopic and clinical features of papillomatous naevi and to study some of the factors which could potentially influence their development. METHODS: Seven hundred and seven caucasians aged 1-82 years participated in a screening campaign at open-air recreation facilities in Austria. The volunteers underwent a total body examination by experienced dermatologists and answered a questionnaire. Clinical and dermoscopic images of one representative papillomatous naevus per person were taken. RESULTS: Twenty-nine per cent of the volunteers exhibited papillomatous naevi, the highest frequency being found in young adults. No correlation between the frequency of papillomatous naevi and gender, skin type, sunburns, sunbed use or hormonal factors was found. Most lesions were brown papules (median diameter 5.0 mm), located on the trunk. Dermoscopy showed a predominance of homogeneous and globular pattern, multifocal hypo/hyperpigmentation and comma vessels. Of the papillomatous naevi, 9.8% showed suspicious scores with dermoscopic algorithms. CONCLUSIONS: The lack of exogenous influencing factors and the predominance of globular dermoscopic pattern strengthen the hypothesis that papillomatous naevi belong to the same spectrum as small congenital melanocytic naevi. As the role of papillomatous naevi as precursors of melanoma remains unclear and they are frequently not recognized by the patients, one should perform dermoscopy of papillomatous naevi during skin cancer screening.

Magnetic induction tomography: hardware for multi-frequency measurements in biological tissues.

Magnetic induction tomography (MIT) is a contactless method for mapping the electrical conductivity of tissue. MIT is based on the perturbation of an alternating magnetic field by a conducting object. The perturbation is detected by a voltage change in a receivercoil. At physiologically interesting frequencies (10 kHz-10 MHz) and conductivities (< 2 S m(-1)) the lower limit for the relative voltage change (signal/carrier ratio = SCR) to be resolved is 10(-7)-10(-10). A new MIT hardware has been developed consisting of a coil system with planar gradiometers and a high-resolution phase detector (PD). The gradiometer together with the PD resolves an SCR of 2.5 x 10(-5) (SNR = 20 dB at 150 kHz, acquisition speed: 100 ms). The system operates between 20 and 370 kHz with the possibility of extending the range up to 1 MHz. The feasibility of measuring conductivity spectra in the beta-dispersion range of biological tissues is experimentally demonstrated. An improvement of the resolution towards SCR = 10(-7) with an SNR of > or = 20 dB at frequencies > 100 kHz is possible. On-line spectroscopy of tissue conductivity with low spatial resolution appears feasible, thus enabling applications such as non-invasive monitoring of brain oedema.