David G. Fleming

FOOD INTAKE STUDIES IN PARABIOTIC RATS

The physiological regulation of food intake may be viewed as a multi-dimensional problem. The dimensionality becomes apparent when one considers that the role played by this regulatory process is to provide an approximate balance between the food intake and nutrient need. This functional relationship holds through the mammalian life cycle and varies as a function of growth, maturation, aging, gestation, lactation, activity, and environmental factors. The inherent complexity of the phenomenon raises the question of how to identify the basic properties of such a system. No one experimental approach or conceptual framework currently in use can do more than contribute a small fraction of the total functional structure. The studies described in this paper were initiated to examine the relationship between humoral factors involved in food intake regulation and the central neural integrating mechanisms. The experimental procedures developed for this work involve the use of parabiotic rats selected from a large standardized population of these animals. The investigations themselves were conducted ( 1 ) to evaluate the effect of differential time feeding on parabiotic rats; (2) to determine the rate at which glucose crosses from one to the other, and ( 3 ) to examine the effects of hypothalamic lesions in one animal on the food intake of its partner. Current concepts of the control of appetite and satiety include both neural and humoral factors. It was first reported in 1943 by Brobeck et a/.’ that bilateral lesions of the medial nuclei of the hypothalamus will result in hyperphagia and subsequent obesity. Anand and Brobeck2 observed that lesions lateral to the hypothalamic satiety areas would produce an aphagic animal. Subsequent investig a t o r ~ ~ have concluded that the hyperphagia is the product of depressed satiety rather than increased appetite. Kennedy4 found that hyperphagia became less pronounced when rats became obese and that food consumption eventually approached normal levels. He suggested that other signals become regulatory and limit food intake of these animals. Peripheral metabolic states may be correlated with the onset of hunger and the appearance of satiety. Mayer5 proposes “that the influence of the metabolic state on feeding behavior and its role in regulating food intake were mediated through the rate of passage of glucose into the cells of the ventral medial hypothalamic areas.” The rate of glucose entering the cells may be correlated with the peripheral utilization of glucose. According to Mayer, a small difference between capillary and venous glucose levels indicates hunger, whereas large capillary venous differences signify fullness (satiety). In addition, the administration of gold thioglucose will produce hyperphagic animals and in these animals lesions

Spectrophotometric Investigation of Pulsatile Blood Flow for Transcutaneous Reflectance Oximetry

A new method to estimate arterial oxygen saturation is suggested based on the presence of the plethysmographic pulse. A prototype skin reflectance oximeter system utilizing a miniature solid state optical transducer has been constructed. Preliminary data collected from a group of volunteers indicated good quantitative correlation between skin reflectance and arterial oxygen saturation as determined by an earlobe oximeter. We are now investigating the dependency of the measurements on various physiological conditions and skin characteristics in order to determine appropriate calibration procedures. This study has demonstrated for the first time that arterial hemoglobin oxygen saturation can be measured quantitatively using transcutaneous reflectance techniques. However, more extensive work is needed to further develop this technique into a viable clinical tool.

ADAPTIVE PROPERTIES OF THE EYE‐TRACKING SYSTEM AS REVEALED BY MOVING‐HEAD AND OPEN‐LOOP STUDIES*

The ability to fix ones eye on a moving or stationary object is an essential property of the overall visual system. One important role subserved by this mechanism is to position selected images at the center of the retinal field, where visual acuity is maximum. A second function of the eye-movement system is to scan the visual field by generating a succession of rapid eye movements called saccades. A third attribute of the oculomotor control system is its ability to stabilize the visual field during head or combined body-head movements. From the standpoint of systems analysis, the visual-tracking system presents an almost unique opportunity for studying the behavior of a neuromuscular control system on an input-output basis. Studies of eye movements have long been used in conjunction with other methods to explore problem-solving behavior and other cognitive processes. For example, there is extensive literature on the relationship of eye movements to the development of reading skills, on human factor studies of pilots during flight maneuvers, and on other situations involving man-machine interaction. Experimental approaches, however, have often been constrained by the objectives of the study or limited by the instrumentation available. The primary objective of the research presented in the body of this paper was to formulate and execute a set of procedures that would be useful in establishing the functional structure of the visual-tracking system. Such a description, however, would have little meaning unless it was framed in the context of the role of the eyes as part of an informationprocessing system. This consideration was important in our decision to discard the linear control system approach in favor of other techniques of systems analysis more suited to the complexities of vision.

Uncertainty sets associated with saccadic eye movements—basis of satisfaction control

Abstract Two types of uncertainty sets associated with visual target aquisition are described; one associated with the targets presentation time and another associated with the distance of the targets image from the fovea. The characteristics of the uncertainty sets are discussed in terms of anatomical and electrophysiological data. Also discussed are the relationships between the uncertainty sets and multiple saccades. Furthermore, it is argued that these sets form the basis for the “satisfaction” control action (versus optimization) of the saccadic system.

1179 ECHOCARDIOGRAPHIC EVALUATION OF RIGHT VENTRICULAR FUNCTION IN PATIENTS WITH CYSTIC FIBROSIS

Non-invasive evaluation of right ventricular (RV) function has been difficult in patients with cystic fibrosis (CF). Echographic recording of the pulmonary valve permits measurement of the phases of RV systole, and the ratio of the RV pre-ejection period to the RV ejection time (RPEP/RVET) correlates well with pulmonary artery pressure. RPEP/RVET and other echographic measurements including RV wall (RVW) and dimension (RVD) were compared with pulmonary function tests and clinical scores in 28 CF patients ranging in age from 4-35 years. RPEP/RVET correlated well with percent vital capacity (%VCA) r=-0.74, residual volume (%RVol) r=0.72, and clinical score r=-0.77. RVW and RVD correlated poorly (r<0.50) with %VCA, %RVol, and clinical score. Multilinear regression of RPEP/RVET and RVD improved correlations significantly for %RVol (r=0.82 and clinical score (r=0.84). Patients in right heart failure (RHF) exhibit significantly higher RPEP/RVET (mean 0.43) than those without RHF (mean=0.33) indicating higher pulmonary artery pressure or diminished RV contractility in patients with RHF. The use of digoxin did not significantly change this value. At the conclusion of the study satisfactory pulmonary valve echograms could be obtained in 2/3 of patients tested and success was independent of the severity of the pulmonary disease.

Monitoring infant respiration using an Eight-channel transthoracic impedance monitor

A special transthoracic electrical impedance infant respiration monitor that can sample eight pairs of electrodes has been used to measure breathing patterns in newborn infants. Quasi-simultaneous recordings have been made and used to determine the breath amplitude and duration of spontaneously occurring apneas during two-hour sessions. Preliminary results from eight infants have shown that breath amplitudes usually vary by factors of six to ten, cardiogenic artifact varies from 6 to 27% of mean breath amplitude for different electrode placements, and the apparent duration of apnea is often different for different electrode pairs.

Microprocessor-Controlled Memory for Cardiopulmonary Monitoring of High-Risk Infants

A semiconductor memory for delaying waveforms, operated in conjunction with commercially available vital signs monitors and recorders, has been developed to generate a concise record of apneic and bradycardic episodes during long-term monitoring of high-risk infants. The system is useful for quantitating the number, duration and nature of life-threatening episodes without resorting to continuous recording.

Chronic Monitoring of Intraventricular Pressure in Children Using Telemetry: Engineering and Physiologic Aspects

Acute monitoring of intracranial pressure via external ventricular drainage systems carries low risk when the implantation is for short periods of time (usually less than ten days) (Smith and Alksne 1976). As the length of time the device is used increases, the risk of infection increases (Rekate 1976). During the period of monitoring the patient is continuously restricted in movement by the drainage system. There are certain pathologic States in which prolonged monitoring of intracranial pressure would be clinically useful. These include hydrocephalus, some metabolic encephalopathies, and patients with brain tumors undergoing chemotherapy. For these purposes the Electronics Design Center of the School of Engineering is developing a device for the continuous monitoring of intraventricular pressure by telemetry. This report will deal with the development of, and clinical experience with, this device.

6 – Biological Receptors

Publisher Summary All cells are biological receptors in the sense that they receive messages from their extracellular environments and these messages affect intracellular responses. The output signal space of the receptor may be divided into two processes. The first yields a graded voltage, the receptor potential, that results directly from the effect of the stimulus on the receptor cell membrane. The second process leads to the generation of the action potential, which is then propagated to influence other cells in the nervous system synaptically. It is important to dichotomize these two aspects of receptor mechanism because they may not even occur within a single cell. However, all receptors considered in the chapter exhibit both these processes in the same cell. The chapter considers only those cells which sample the nonneural energy from their extracellular space and convert this energy to a form which is useful to the nervous system. It also discusses receptors and afferent process, mechanical filtering in the pacinian corpuscle, and the classification of receptors according to encoded quality or modality.