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Biomedical subjects

M Valach

Publications and source records attributed to M Valach.

16 recordsLinked to original sources
PubMed1998

Mean blood pressure and velocity for calculation of ventricular systolic work.

In physiology, the mean arterial pressure is defined as an average pressure during one or several cardiac cycles. When calculus is not used, the mean pressure is approximately calculated as the diastolic pressure plus one third of the pulse pressure. In this article it is demonstrated that, when ventricular systolic work is concerned, the above definition of mean pressure must be replaced by a weighted average during the ejection phase of the systole. This gives a formula, by which a much higher estimate of the mean pressure is obtained.

Blood Flow Velocity↗
PubMed1995

A technique for the evaluation of the left ventricle contraction.

A new method of left ventricle contraction evaluation using radiance is submitted. The reference point is not established a priori. It is the point where the function given by contraction variability and its magnitude has the minimum. This minimum can be considered as the contraction evaluating parameter.

Angina Pectoris↗
PubMed1984

Visual evoked responses to pattern-reversal: the signal-to-noise ratio.

Visual evoked responses (VERs) to checkboard-reversal photic stimuli were recorded in 30 healthy experimental subjects with a mean age of 32 years. In 20 cases the stimuli were presented monocularly and in 10 cases binocularly. The estimated mean signal-to-noise ratio (SNR) of the individual VERs was found to be 0.245 +/- 0.092 for monocular stimulation and 0.444 +/- 0.23 for binocular stimulation. The power-based SNR of the averaged VERs was 24.5 and 44.4 respectively. The SNR was raised the most effectively by a new selective averaging variant applied after latency correction of the individual VERs; in the case of monocular stimulation the SNR rose to a mean 58.94 and in binocular stimulation to a mean 87.42. The mean proportion of discarded single VERs was 24%.

Adolescent↗
PubMed1981

Averaging, selective averaging and latency-corrected averaging.

Although latency-corrected averaging and selective averaging represent frequency used alternatives to the time-locked averaging, little is known about the changes of the signal-to-noise ratio (SNR) associated with their application. For this reason, visual evoked responses (VERs) to blank and checkerboard patterned flashes of light (5.6 cd/m2) were recorded in 15 subjects using a referential (Oz - A1 + 2) and a bipolar (Oz - Pz) derivation, and interstimulus intervals (ISI) of 1.4s and 2.4s; SNRs were calculated for all combinations. With time-locked averaging (referential derivation) the mean SNR of single VERs was 0.35 to blank stimuli and 0.68 to patterned stimuli. With latency-corrected averaging, the means SNR rose to 0.56 (0.74), and with selective averaging it increased to 0.81 (1.00). A combined procedure of selective and latency-corrected averaging yielded the highest mean SNR values of single VERs: 0.98 (1.21). Increasing ISIs from 1.4 - 2.4s did not change the results; the mean SNR values were always higher in bipolar than in referential derivations. The selective, latency-corrected averaging produced higher SNRs, and the group mean number of detectable single VERs (62% of the single VERs to blank stimuli, and 74% of the single VERs to patterned stimuli) and the latency variability of the single VERs: -0.33 +/- 14.5 ms (blank stimulation) and -0.48 +/- 13.96 ms (patterned stimulation).

Adult↗