2,361 research outputs found
The effect of gag reflex on cardiac sympatovagal tone
Objectives: Heart velocity may be influenced by gagging. The medulla oblongata receives the afferents of gag reflex. Neuronal pools of vomiting, salivation and cardiac parasympathetic fibers are very close in this area. So, their activities may be changed by spillover from each other. Using the heart rate variability (HRV) analysis, the effect of gagging on cardiac sympatovagal balance was studied. Methods: ECG was recorded from 9 healthy nonsmoker volunteer students for 10 minutes in the sitting position between 10 and 11 AM. Gagging was elicited by tactile stimulation of the posterior pharyngeal wall. At 1 kHz sampling rate, HRV was calculated. The mean of heart rate at low and high frequencies (LF: 0.04-0.15; HF: 0.15-0.4 Hz) were compared before and after the stimulus. Results: The mean of average heart rate, LF and HF in normalized units (nu) and the ratio of them (LF/HF) before and after the gagging were 89.9 ± 3 and 95.2 ± 3 bpm; 44.2 ± 5.8 and 21.2 ± 4; 31.1 ± 5.3 and 39.4 ± 3.8; and 1.7 ± 0.3 and 0.6 ± 0.2 respectively. Conclusion: Gagging increased heart velocity and had differential effect on two branches of cardiac autonomic nerves. The paradoxical relation between average heart rate and HRV indexes of sympatovagal tone may be due to unequal rate of change in autonomic fiber activities which is masked by 5 minutes interval averaging. © OMSB, 2012
S-Restricted Compositions Revisited
An S-restricted composition of a positive integer n is an ordered partition
of n where each summand is drawn from a given subset S of positive integers.
There are various problems regarding such compositions which have received
attention in recent years. This paper is an attempt at finding a closed- form
formula for the number of S-restricted compositions of n. To do so, we reduce
the problem to finding solutions to corresponding so-called interpreters which
are linear homogeneous recurrence relations with constant coefficients. Then,
we reduce interpreters to Diophantine equations. Such equations are not in
general solvable. Thus, we restrict our attention to those S-restricted
composition problems whose interpreters have a small number of coefficients,
thereby leading to solvable Diophantine equations. The formalism developed is
then used to study the integer sequences related to some well-known cases of
the S-restricted composition problem
Constraints on stable equilibria with fluctuation-induced forces
We examine whether fluctuation-induced forces can lead to stable levitation.
First, we analyze a collection of classical objects at finite temperature that
contain fixed and mobile charges, and show that any arrangement in space is
unstable to small perturbations in position. This extends Earnshaw's theorem
for electrostatics by including thermal fluctuations of internal charges.
Quantum fluctuations of the electromagnetic field are responsible for
Casimir/van der Waals interactions. Neglecting permeabilities, we find that any
equilibrium position of items subject to such forces is also unstable if the
permittivities of all objects are higher or lower than that of the enveloping
medium; the former being the generic case for ordinary materials in vacuum.Comment: 4 pages, 1 figur
Ageing and ankle pulse pressure
Background: Pulse pressure (PP) is a marker of arterial stiffness. Ageing of the arterial
system is accompanied by atherosclerosis of coronary arteries and atherosclerosis of popliteal
artery. However, severe impairment of the brachial artery is rare. This study investigates
whether there is any significant inter-limb (brachial/ankle) PP difference.
Methods: Blood pressure was measured in a group of young and a group of old non-smoking
men; all were free from medication and disease with a mean age of 22 ± 1.3 and 59 ± 2 years
respectively. The blood pressure was taken while they were in a supine position on three separate
occasions. Lower limb pressure was measured by placing the cuff on the calf muscle. For auscultation
of Korotkoff sounds the stethoscope was placed on the posterior surface of the internal
malleolus. The mean of the second and third readings were rounded off and used for analysis.
Results: Significant differences were found between brachial and ankle PP in both groups
(p < 0.01). The ratio of brachial PP to ankle PP in the young men was greater than 1. In the
old men it was less than 0.15. There was no significant difference between the brachial PP in
the two groups, but on both sides the ankle PP was significantly greater in the old men (p < 0.01).
Conclusions: With the ageing of the arterial system, raised PP is more prominent in the
lower limb (e.g. ankle). Cuff measurement of blood pressure at this site may be a useful index
of peripheral PP changes with ageing. (Cardiol J 2010; 17, 2: 163-165
A Complete Online Solution of Harmonic Elimination PWM Method Using Modified-Equilibrium Optimizer-Levenberg- Marquardt Algorithm
A Comparison of Fuzzy Membership Kriging and Indicator Kriging for Predicting Land Suitability
Structure Space of Model Proteins --A Principle Component Analysis
We study the space of all compact structures on a two-dimensional square
lattice of size . Each structure is mapped onto a vector in
-dimensions according to a hydrophobic model. Previous work has shown that
the designabilities of structures are closely related to the distribution of
the structure vectors in the -dimensional space, with highly designable
structures predominantly found in low density regions. We use principal
component analysis to probe and characterize the distribution of structure
vectors, and find a non-uniform density with a single peak. Interestingly, the
principal axes of this peak are almost aligned with Fourier eigenvectors, and
the corresponding Fourier eigenvalues go to zero continuously at the
wave-number for alternating patterns (). These observations provide a
stepping stone for an analytic description of the distribution of structural
points, and open the possibility of estimating designabilities of realistic
structures by simply Fourier transforming the hydrophobicities of the
corresponding sequences.Comment: 14 pages, 12 figures, Conclusion has been modifie
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