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The strong electric currents used for heating purposes in welding and steel industries set up related magnetic fields (generally 0.1--10 mT and 50 Hz). Such fields 10--50 Hz, 0--40 mT) were used to induce visual light phenomena, magnetophosphenes. Threshold values for magnetophosphenes were determined as a function of magnetic field frequency as well as colour and intensity of the background illumination. A typical sensitivity maximum was found at 20--25 Hz. Differences between volunteers with normal colour vision and colour defective ones were observed. The frog retina was exposed to the same type of fields. Retinal activity, induced by the fields, was registered from the ganglion cell layer by means of microelectrode technique. The results indicate that magnetophosphenes are generated in the retina and in the same channels that are normally propagating signals induced by light of different qualities. The findings may be of guidance when formulating threshold limit values for extremely low frequency electromagnetic fields in industry.

The adhesion between the eye and a contact lens was recorded when influenced by water with varying salt concentrations. Both active removal and spontaneous loss of hard and soft contact lenses applied to the eye were investigated. In environments with saline less than 9 0/00 the risk of a soft contact lens falling out from the eye is almost negligible. In environments with saline greater than or equal to 9 0/00 the risk increase since adhesion in active removal decreased considerably. In reality, based upon the investigations of spontaneous loss of contact lenses in an underwater environment, well fitted soft lenses still do not however fall out of the eye. It should therefore be possible to use well fitted soft contact lenses without any significant risk even in working conditions which may include splashing of water upon the eye and regardless of the various salt concentrations of naturally occurring water in Sweden. For hard contact lenses, independent of salt concentration, adhesion in the underwater environment is extremely low and such lenses cannot therefore be used on an unprotected eye in conjunction with, for example, swimming. The risk of them falling out under splashing with water upon the eye is clearly greater than for soft lenses.

Using a method described in a previous article the transepidermal water loss (TEWL) was studied in 10 healthy newborn infants at rest and during activity. On the average TEWL was 37% higher during activity than during rest although no sweating was observed. In 9 infants placed in incubators with an ambient temperature slightly above the thermoneutral range measurements were made as the body temperature rose. TEWL was almost constant until a temperature of 37.1 degrees C was reached whereupon the water loss suddenly increased as the infant started sweating.

The long-term properties of commercially available ECG-electrodes were studied by investigating the parameters: polarization potential, electrical impedance, adhesion, and skin reactions during a period of 7 days. As expected, the most stable polarization potentials were obtained for Ag/AgCl electrodes. Certain simple disposable electrodes showed large polarization potential variations. The most stable electrode impedance was obtained for disposable electrodes with stable adhesion and equipped with an electrode cup or similar. Unchanged adhesion and mechanical properties during the test period were shown by the disposable electrodes with a large self-adhesive collar.

In order to investigate whether sweating and cutaneous vasodilatation. induced by a warm environment, is inhibited by central cold-stimulation, the evaporation rate and skin blood flow were studied by non-invasive techniques before and after the feeding of cold glucose to 17 fullterm appropriate for gestational age infants, born by elective Caesarean section, on their first day after birth. In newborn infants who were visibly sweating and had an increased skin blood flow at a body temperature above 37.1 degrees C, such central cold-stimulation quickly inhibited sweating and decreased skin blood flow. In infants with almost the same body temperature but with no sweating, this stimulation caused no change in evaporation rate or skin blood flow. The regulation of body temperature in fullterm newborn infants can thus be disturbed by central cold-stimulation, resulting in a decreased heat loss to the environment even though the body temperature is elevated.

Localized neural control of renal cortical blood flow was observed in five chloralose-anaesthetized baboons. Renal artery blood flow was measured with an electromagnetic flowmeter, while superficial renal cortical blood flow was measured with a laser Doppler flowmeter. Stimulation of all renal nerve bundles isolated produced significant reductions in total renal blood flow, but reduced the superficial renal cortical blood flow only in localized areas. Systemic arterial blood pressure did not vary significantly, which suggests that the changes in renal cortical blood flow were neurally mediated and not the result of autoregulation. The renal cortical blood flow response was delayed 1-4 s with respect to the total renal blood flow response. The localization of flow control is consistent with the neuroanatomy of the kidney, and the delayed renal cortical blood flow response is consistent with the vascular anatomy of the kidney and with previous measurements of red cell transit times through the renal cortex.

A method has been worked out by which one of the closed control circuits in the blood-pressure-regulating system of the dog can be reversibly opened and closed again with the aid of an on-line analog computer. This makes it possible to study the regulatory properties of the carotid-sinus reflex, as regards the baroreceptor function, in the regulation of the systemic blood pressure. Proportional characteristics in the analog produce marked instability in the blood-pressure regulation, while with increasing proportional-plus-derivative characteristics the stability is increased. The electronic analog can be given characteristics that produce the same step-function response in the systemic pressure as the biological reflex.

Oberg, P. A. and U. Sjostrand, Studies of blood-pressure regulation. III. Dynamics of arterial blood pressure on carotid-sinus nerve stimulation. Acta physiol. scand. 1971. 81. 96–109. An analysis of the properties of the blood pressure regulatory system has been made by means of carotid-sinus nerve stimulation. The method used involves analog simulation of the nonlinear properties of this reflex. The analysis gives the gain-frequency and the gain-phase shift curves characterizing the system under study. A resonance frequency for the system is mostly found in the frequency range 0.03–0.06 Hz. Modulation of the control signal decreases the systemic bandwidth. Non-linear simulation indicates that the mammalian blood pressure regulating system has some of the characteristics of a sampled regulatory system. The afferent information in the carotid-sinus baroreceptor reflex stabilizes the systemic blood pressure by means of its pulsating nature. Transfer functions characterizing the system under study are given. The data presented are relevant to the functional characteristics of baropacer systems.

Oberg, P. A. and U. Sjostrand. Simulator for demonstration of some bioelectric properties of “biological transducers”. Acta physiol. scand. 1968. 72. 1–5. An electronic simulator demonstrating some of the properties of biological transducers is described. It is possible to simulate the “nerve activity” and its relation to “generator potential” and the “adaptation phenomenon” for some different kinds of biological receptors.