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bioRxiv2019

Role of post-trial visual feedback on unintentional force drift during isometric finger force production tasks

Force produced during an isometric finger force production task tends to drift towards a lower magnitude when visual information is occluded. This phenomenon of drift in force without ones awareness is called unintentional drift. The present study used epilogue, a particular case of post-trial visual feedback, and compared the unintentional drift for two conditions, i.e., with and without the epilogue. For this purpose, fourteen healthy participants were recruited for the experiments and were instructed to produce fingertip forces using four fingers of the right hand with the target line at 15% MVC. A trial lasted for sixteen seconds, where for the initial eight seconds, there is visual feedback followed by the visual occlusion period. The results showed a significant reduction in unintentional drift for the condition involving epilogue when compared to no epilogue. This reduction in drift is due to the shift in the referent configuration parameter by the phenomenon of RC back coupling. Further, we also claim that there might be a distribution of {lambda}s or RCs, based on the history of tuning of the control parameter by the central controller. This distribution of {lambda}s selected by the central controller in a redundant environment based on the epilogue resulted in a reduction of unintentional drift.

neuroscience↗

bioRxiv2019

Blood pressure variability from intra-arterial recordings in humans

Systolic and diastolic blood pressures are reported as single point values by the non-invasive techniques used in clinical practice, while, in fact, they are highly varying signals. The objective of this study was to document the magnitude of variation of systolic and diastolic pressures over a few minutes by analysing intra-arterial pressure recordings made in 51 haemodynamically stable patients in an intensive care unit. Intra-arterial pressure data were acquired by a validated data acquisition system. Fast-Flush test was performed and the dynamic characteristics of the catheter transducer system namely natural frequency and damping co-efficient were calculated. Only those recordings with acceptable dynamic characteristics were included in the analysis. Power spectral calculation using the Discrete Fourier transform (DFT) of the pressure recording revealed two frequency peaks below the peak at heart rate. The lower and higher frequency peaks below the heart rate peak are referred to as Mayer and Traube waves in this study. Mayer wave peaks were observed in DFT spectra of 49 out of 51 patients. The Mayer wave frequency peaks ranged between 0.045 Hz to 0.065 Hz in 41 out of 51 patients. The frequency of Traube waves or the respiratory variations was more than 0.14 Hz. Three categories of systolic and diastolic pressure variabilities namely beat-to-beat variability, Respiratory variability (Traube wave amplitude) and Total magnitude of variation are reported for all 51 patients. The mean systolic and diastolic pressure variations (in a period of about 10 minutes) in the study sample were 21 {+/-} 9 mm Hg and 14 {+/-} 5 mm Hg respectively. Given the magnitude of systolic and diastolic pressure variations over a few minutes, the validity of reporting single point values for these pressures and using single point cut-offs for diagnosis and treatment of hypertension must be re-evaluated.

physiology↗