Biomedical subjects

Kenneth H Norwich

Publications and source records attributed to Kenneth H Norwich.

5 recordsLinked to original sources

PubMed2006

Computational model of the movement of the human muscles of mastication during opening and closing of the jaw.

Muscle fibre bundles comprising the four major muscles of mastication in the human being were studied in cadavers. Markers were placed along each muscle fibre bundle by means of serial dissections. The 3D coordinates of each marker were tabulated and imported to Cinema 4D, a software animation program. Origins and insertions of each fibre bundle were also digitized and imported, as were the coordinates of the surface of the skull, the mandible and temporomandibular joint. It was then possible to visualize the movement of all relevant fibre bundles during the passive motions of the mandible. An animated film depicts the positions of all relevant muscle fibres during passive movement of the mandible. The properties of the masseter muscle were documented as a prototype for the eventual study of all the muscles of mastication. One can now proceed to study the inverse problem, namely the forces within each fibre bundle that actively generate mandibular motion. It is hoped that these studies will aid in the management of conditions affecting the temporomandibular joint.

Aged↗

PubMed2005

Human sulfate kinetics.

Electrospray tandem mass spectrometry was used to determine steady-state serum and urinary inorganic sulfate and sulfate ester kinetic profiles of nine normal men after intravenous injection of the stable isotope sodium [34S]sulfate. Sulfate ester appearance was traced by eliminating inorganic sulfate from samples, followed by hydrolysis of sulfate esters to inorganic sulfate for analysis. Whole body inorganic sulfate turnover in steady state was calculated using standard tracer techniques. Rate of appearance and disappearance of inorganic sulfate was 841 +/- 49 micromol/h. Average urinary inorganic sulfate excretion was 609 +/- 41 micromol/h, and the whole body sulfation rate (total rate of disappearance minus rate of urinary excretion) was 232 +/- 36 micromol/h. Tracer-labeled sulfate esters appeared in serum and urine within 1 h of tracer injection. The kinetics of inorganic sulfate and sulfate esters were linked by means of a compartmental model. The appearance and excretion of sulfate esters accounted for approximately 50% of the total sulfation rate. These results indicate that human whole body sulfation accounts for approximately 27% of inorganic sulfate turnover and that extracellular inorganic sulfate is an important pool for intracellular sulfation. A substantial fraction of newly synthesized sulfate esters promptly enters the extracellular space for excretion in the urine.

Fasting↗

PubMed2005

Physical entropy and the senses.

With reference to two specific modalities of sensation, the taste of saltiness of chloride salts, and the loudness of steady tones, it is shown that the laws of sensation (logarithmic and power laws) are expressions of the entropy per mole of the stimulus. That is, the laws of sensation are linear functions of molar entropy. In partial verification of this hypothesis, we are able to derive an approximate value for the gas constant, a fundamental physical constant, directly from psychophysical measurements. The significance of our observation lies in the linking of the phenomenon of "sensation" directly to a physical measure. It suggests that if the laws of physics are universal, the laws of sensation and perception are similarly universal. It also connects the sensation of a simple, steady physical signal with the molecular structure of the signal: the greater the number of microstates or complexions of the stimulus signal, the greater the magnitude of the sensation (saltiness or loudness). The hypothesis is currently tested on two sensory modalities.

Entropy↗

PubMed2004

Time response of interstitial fluid pressure measurements in cervix cancer.

Increased interstitial fluid pressure (IFP) is a common finding in malignant tumors as a result of the abnormal tumor vasculature and a lack of functional lymphatics. A recent clinical study by Milosevic et al. [Cancer Res. 61 (2001) 6400] reported a link between elevated IFP and survival in patients with cancer of the cervix. Patients with high IFP were more likely to have recurrence of tumors even after radiotherapy and were also more likely to die of progressive disease, independent of other prognostic factors. In this complementary study, using human data, we analyze 152 cervical tumor pressure IFP measurements from 42 patients with clinically diagnosed cancer of the cervix, randomly selected from the sample of 102 patients involved in the original study. We propose a simple biophysical model, based on flow through porous media, to explain the time response of the measured pressure curves in human cervical tumors. The response of IFP was governed by a time-constant tau(IFP) = 14 +/- 1 s averaged over multiple tumor sites. Interstitial hydraulic conductivity was computed to be approximately equal to 4.3 x 10(-6) cm(2)/mm Hgs.

Biophysical Phenomena↗

PubMed2002

Deriving the loudness exponent from categorical judgments.

The power function exponent for loudness is traditionally determined by means of a process of magnitude estimation. It is demonstrated in this paper that the exponent can also be obtained by using the procedure of absolute identification of sound intensity. It has been shown that subjects' responses to tones of a given intensity are distributed in a normal distribution whose variance depends on the range, R, over which the tones are distributed. By means of a standard statistical transformation, the normal density in log space is converted to the corresponding probability density in linear space. The power function exponent can then be obtained directly from the linear probability density. We also suggest that there is a direct relationship between the information calculated from experiments on absolute identification of sound intensity and the neurophysiological, poststimulus histogram measured in a nerve fiber in the auditory nerve.

Humans↗