Annals of Biomedical Engineering

Járos, George; Guyton, Arthur; Coleman, Thomas

doi: 10.1007/BF02364660pmid: 7458022

In this article we present a detailed description of an analog-digital computer model of those aspects of the bone which are considered to be important in the short-term homeostasis of calcium ions in the body. Quantitative relationships for parameters and variables were obtained from the literature either directly or indirectly. The bone-calcium model was linked to a previously described model of the entire homeostatic system for calcium ions.

Longobardo, Guy; Cherniack, Neil; Damokosh-Giordano, Aniko

doi: 10.1007/BF02364661pmid: 6779678

The effect of respiratory controller gain on the speed of correction of disturbances in CO2 balance, and the energy used by the respiratory muscles during the correction period is explored using a mathematical model. As controller sensitivity is increased, CO2 balance is more rapidly restored, but there is a greater expenditure of energy in breathing. The relationship between speed of correction and energy expenditure rises to a maximum value near usual values for controller sensitivity to CO2 in normal human adults. With less efficient respiratory muscles or with higher resting levels of PCO2, maximum values for the ratio of speed to energy consumption occur at decreased levels of controller sensitivity. Increased cardiac output and functioning central and peripheral CO2 chemoreceptors improve speed of response without proportionate rises in energy use.

Walburn, Frederick; Stein, Paul

doi: 10.1007/BF02364662pmid: 6450558

The effects of unevenly distributed flow were investigated in a symmetrically branched tube with an angle of branching and branch-to-trunk area ratio that were comparable to the human descending aorta. Profiles of velocity were measured at the vertex of the bifurcation with a laser Doppler anemometer during pulsatile flow as well as steady flow. The mean Reynolds numbers were 500, 1000, and 1500. When flow in the branches was equal, reversals were present along the outer wall during the minimal phase of the flow cycle at a Reynolds number of 500. Such reversals were absent at higher Reynolds numbers. When flow in the branches was unequal, reversals occurred only in the branch with the lower flow. Such reversals occurred at all of the Reynolds numbers studied. Pulsatile flow separation, however, did not occur at any Reynolds number when the flow in the branches was equal. Pulsatile flow separation occurred in the partially occluded branch when flow in the branch was ≤8% of the total flow only at Reynolds numbers of 1000 and 1500. A prominent difference between pulsatile and steady flow was that reversals along the outer wall occurred during pulsatile flow at percentages that were prominently higher than the percentage of flow in the branch that produced reversals during steady flow. These observations may be pertinent to understanding the potential of characteristics of flow in the genesis of atherosclerosis in the region of the bifurcation of the aorta.

Barbenel, J.; Makki, S.; Agache, P.

doi: 10.1007/BF02364663pmid: 7458023

Normalised autocorrelation functions were used to assess the variability of the contour scans produced from replicas of the skin surface of normal subjects. Systematic errors due to the presence of abnormal scans were detected by the occurrence of low values associated with specific scans. Mean harmonic coefficients were calculated and shown, by using the correlation technique, to be reliable representations of the skin surface contours.