scholarly journals THE EFFECTS OF VARIATIONS IN THE CONCENTRATION OF OXYGEN AND OF GLUCOSE ON DARK ADAPTATION

1940 ◽  
Vol 24 (1) ◽  
pp. 69-98 ◽  
Author(s):  
R. A. McFarland ◽  
W. H. Forbes
Keyword(s):  
Blood Sugar ◽  
Dark Adaptation ◽  
Control Level ◽  
Light Sensitivity ◽  
Individual Variability ◽  
Similar Degree ◽  
Base Line ◽  
Low Oxygen ◽  
Experimental Conditions ◽  
The Subject

In this study we have analyzed the effects of variations in the concentrations of oxygen and of blood sugar on light sensitivity; i.e. dark adaptation. The experiments were carried out in an air-conditioned light-proof chamber where the concentrations of oxygen could be changed by dilution with nitrogen or by inhaling oxygen from a cylinder. The blood sugar was lowered by the injection of insulin and raised by the ingestion of glucose. The dark adaptation curves were plotted from data secured with an apparatus built according to specifications outlined by Hecht and Shlaer. During each experiment, observations were first made in normal air with the subject under basal conditions followed by one, and in most instances two, periods under the desired experimental conditions involving either anoxia or hyper- or hypoglycemia or variations in both the oxygen tension and blood sugar at the same time. 1. Dark adaptation curves were plotted (threshold against time) in normal air and compared with those obtained while inhaling lowered concentrations of oxygen. A decrease in sensitivity was observed with lowered oxygen tensions. Both the rod and cone portions of the curves were influenced in a similar way. These effects were counteracted by inhaling oxygen, the final rod thresholds returning to about the level of the normal base line in air or even below it within 2 to 3 minutes. The impairment was greatest for those with a poorer tolerance for low O2. Both the inter- and intra-individual variability in thresholds increased significantly at the highest altitude. 2. In a second series of tests control curves were obtained in normal air. Then while each subject remained dark adapted, the concentrations of oxygen were gradually decreased. The regeneration of visual purple was apparently complete during the 40 minutes of dark adaptation, yet in each case the thresholds continued to rise in direct proportion to the degree of anoxia. The inhalation of oxygen from a cylinder quickly counteracted the effects for the thresholds returned to the original control level within 2 to 3 minutes. 3. In experiments where the blood sugar was raised by the ingestion of glucose in normal air, no significant changes in the thresholds were observed except when the blood sugar was rapidly falling toward the end of the glucose tolerance tests. However, when glucose was ingested at the end of an experiment in low oxygen, while the subject remained dark adapted, the effects of the anoxia were largely counteracted within 6 to 8 minutes. 4. The influence of low blood sugar on light sensitivity was then studied by injecting insulin. The thresholds were raised as soon as the effects of the insulin produced a fall in the blood sugar. When the subjects inhaled oxygen the thresholds were lowered. Then when the oxygen was withdrawn so that the subject was breathing normal air, the thresholds rose again within 1 to 2 minutes. Finally, if the blood sugar was raised by ingesting glucose, the average threshold fell to the original control level or even below it. 5. The combined effects of low oxygen and low blood sugar on light sensitivity were studied in one subject (W. F.). These effects appeared to be greater than when a similar degree of anoxia or hypoglycemia was brought about separately. 6. In a series of experiments on ten subjects the dark adaptation curves were obtained both in the basal state and after a normal breakfast. In nine of the ten subjects, the food increased the sensitivity of the subjects to light. 7. The experiments reported above lend support to the hypothesis that both anoxia and hypoglycemia produce their effects on light sensitivity in essentially the same way; namely, by slowing the oxidative processes. Consequently the effects of anoxia may be ameliorated by giving glucose and the effects of hypoglycemia by inhaling oxygen. In our opinion, the changes may be attributed directly to the effects on the nervous tissue of the visual mechanism and the brain rather than on the photochemical processes of the retina.

Do word learners ignore ignorant speakers?

2003 ◽  
Vol 30 (4) ◽  
pp. 905-924 ◽  
Author(s):  
MARK A. SABBAGH ◽  
SYLWIA D. WDOWIAK ◽  
JENNIFER M. OTTAWAY
Keyword(s):  
Word Learning ◽  
Base Line ◽  
The Novel ◽  
Experimental Conditions ◽  
Knowledge States ◽  
Children First ◽  
Line Condition

Thirty-six three- to four-year-old children were tested to assess whether hearing a word-referent link from an ignorant speaker affected children's abilities to subsequently link the same word with an alternative referent offered by another speaker. In the principal experimental conditions, children first heard either an ignorant or a knowledgeable speaker link a novel word with one of three toys. The first speaker's labelling episode was followed by a second in which a different speaker used the same novel label but for a different toy. There was also a Base-line condition which was the same as the experimental condition involving the ignorant speaker except that she did not associate the novel label with a referent. When tested for comprehension of the novel label, children selected the FIRST speaker's toy at high levels when the first speaker was knowledgeable, but selected the SECOND speaker's toy when the first speaker was ignorant. These findings suggest that children's experience with the ignorant speaker did not affect their abilities to learn a subsequently presented alternative word-referent link. These findings are discussed in terms of understanding the mechanisms by which children adapt their word-learning in line with speakers' knowledge states.

Altered osmotic thresholds for vasopressin secretion and thirst in human pregnancy

1984 ◽  
Vol 246 (1) ◽  
pp. F105-F109 ◽  
Author(s):  
J. M. Davison ◽  
E. A. Gilmore ◽  
J. Durr ◽  
G. L. Robertson ◽  
M. D. Lindheimer
Keyword(s):  
Plasma Osmolality ◽  
Late Pregnancy ◽  
Base Line ◽  
Urinary Volume ◽  
Human Pregnancy ◽  
Slow Infusion ◽  
Vasopressin Secretion ◽  
The Subject ◽  
The Mean ◽  
Plasma Arginine

Osmoregulation was studied in eight women during late pregnancy and again 8-10 wk postpartum. Base-line plasma osmolality (Posmol) was significantly lower during (280.9 +/- 2.1 mosmol/kg, SD) than after (289.4 +/- 2.1 mosmol/kg) pregnancy yet 24-h urinary volume and plasma arginine vasopressin (PAVP) measured in vasopressinase-inactivated blood was similar in both groups (pregnancy, 1.39 +/- 0.56 pg/ml; postpartum, 1.25 +/- 0.62 pg/ml). After 12 h of dehydration PAVP rose similarly and significantly both during (2.25 +/- 0.81 pg/ml) and after (2.89 +/- 1.19 pg/ml) gestation, and Uosmol was similar on both occasions (pregnancy, 779 +/- 121 mosmol/kg; postpartum, 784 +/- 102 mosmol/kg). When Posmol was increased by the slow infusion of 5% saline PAVP increased as soon as body tonicity did both during and after pregnancy. PAVP correlated significantly with Posmol in each subject (range of r, 0.75-0.99) and the mean regression lines [pregnancy, PAVP = 0.32 (Posmol; -279), r = 0.79; postpartum, PAVP = 0.38 (Posmol, -285), r = 0.86] demonstrated that the apparent osmotic threshold for AVP secretion was 6 mosmol/kg lower during than after gestation. Similarly the Posmol at which the subject experienced a conscious desire to drink was lower in pregnant (287 +/- 1.6 mosmol/kg) compared with postpartum subjects (298 +/- 2.0 mosmol/kg; P less than 0.001). These data demonstrate decreased osmotic thresholds for AVP release and thirst during human pregnancy and explain why gravidas can maintain their new lower Posmol within narrow limits.

Contralateral coordination and retargeting of limb movements during scratching in the locust

1998 ◽  
Vol 201 (13) ◽  
pp. 2021-2032 ◽  
Author(s):  
T Matheson
Keyword(s):  
Nerve Cord ◽  
Tactile Stimulation ◽  
Schistocerca Gregaria ◽  
Limb Movements ◽  
Single Cycle ◽  
Experimental Conditions ◽  
The Subject ◽  
The Common ◽  
Peripheral Sensory ◽  
Stimulus Site

Locusts, Schistocerca gregaria, in common with many limbed vertebrates, can make directed scratching movements in response to tactile stimulation. For instance, stimulation of different sites on a wing elicits different movements that are accurately targeted so that the hindleg tarsus passes across the stimulus site. I have analysed these limb movements to define the ability of a locust to target stimulus sites correctly under a range of experimental conditions. In particular, I describe aspects of the behaviour that reveal possible neuronal pathways underlying the responses. These neuronal pathways will be the subject of further physiological analyses. Limb targeting during scratching is continuously graded in form; different patterns of movement are not separated by sharp transitions. The computation of limb trajectory takes into account the starting posture of the hindleg, so that different trajectories can be used to reach a common stimulus site from different starting postures. Moreover, the trajectories of the two hindlegs moving simultaneously from different starting postures in response to a single stimulus can be different, so that their tarsi converge onto the common stimulus site. Different trajectories can be used to reach a common stimulus site from the same start posture. Targeting information from a forewing is passed not only down the nerve cord to the ipsilateral hindleg but also across the nerve cord, so that the contralateral hindleg can also make directed movements. This contralateral transmission does not rely on peripheral sensory feedback. When the stimulus site moves during a rhythmical scratch, the targeting of subsequent cycles reflects this change. Both ipsilateral and contralateral hindlegs can retarget their movements. The trajectory of a single cycle of scratching directed towards a particular stimulus site can be modified after it has begun, so that the tarsus is redirected towards a new stimulus site.

scholarly journals Dark-adaptation in the eyes of a lake and a sea population of opossum shrimp (Mysis relicta): retinoid isomer dynamics, rhodopsin regeneration, and recovery of light sensitivity

2020 ◽  
Vol 206 (6) ◽  
pp. 871-889
Author(s):  
Tatiana Feldman ◽  
Marina Yakovleva ◽  
Martta Viljanen ◽  
Magnus Lindström ◽  
Kristian Donner ◽  
...  
Keyword(s):  
Dark Adaptation ◽  
Severe Depression ◽  
Light Sensitivity ◽  
Membrane Turnover ◽  
Low Light ◽  
Photoreceptor Membrane ◽  
Mysis Relicta ◽  
Opossum Shrimp ◽  
Exposure Levels ◽  
Photoreceptor Membranes

Abstract We have studied dark-adaptation at three levels in the eyes of the crustacean Mysis relicta over 2–3 weeks after exposing initially dark-adapted animals to strong white light: regeneration of 11-cis retinal through the retinoid cycle (by HPLC), restoration of native rhodopsin in photoreceptor membranes (by MSP), and recovery of eye photosensitivity (by ERG). We compare two model populations (“Sea”, Sp, and “Lake”, Lp) inhabiting, respectively, a low light and an extremely dark environment. 11-cis retinal reached 60–70% of the pre-exposure levels after 2 weeks in darkness in both populations. The only significant Lp/Sp difference in the retinoid cycle was that Lp had much higher levels of retinol, both basal and light-released. In Sp, rhodopsin restoration and eye photoresponse recovery parallelled 11-cis retinal regeneration. In Lp, however, even after 3 weeks only ca. 25% of the rhabdoms studied had incorporated new rhodopsin, and eye photosensitivity showed only incipient recovery from severe depression. The absorbance spectra of the majority of the Lp rhabdoms stayed constant around 490–500 nm, consistent with metarhodopsin II dominance. We conclude that sensitivity recovery of Sp eyes was rate-limited by the regeneration of 11-cis retinal, whilst that of Lp eyes was limited by inertia in photoreceptor membrane turnover.

scholarly journals A survey of mathematical models of human performance using power and energy

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Vijay Sarthy M. Sreedhara ◽  
Gregory M. Mocko ◽  
Randolph E. Hutchison
Keyword(s):  
Performance Optimization ◽  
Human Performance ◽  
Critical Power ◽  
Physical Exertion ◽  
Individual Variability ◽  
Health Performance ◽  
The Subject ◽  
Power And Energy ◽  
Two Parameter ◽  
Individual Training

AbstractThe ability to predict the systematic decrease of power during physical exertion gives valuable insights into health, performance, and injury. This review surveys the research of power-based models of fatigue and recovery within the area of human performance. Upon a thorough review of available literature, it is observed that the two-parameter critical power model is most popular due to its simplicity. This two-parameter model is a hyperbolic relationship between power and time with critical power as the power-asymptote and the curvature constant denoted by W′. Critical power (CP) is a theoretical power output that can be sustained indefinitely by an individual, and the curvature constant (W′) represents the amount of work that can be done above CP. Different methods and models have been validated to determine CP and W′, most of which are algebraic manipulations of the two-parameter model. The models yield different CP and W′ estimates for the same data depending on the regression fit and rounding off approximations. These estimates, at the subject level, have an inherent day-to-day variability called intra-individual variability (IIV) associated with them, which is not captured by any of the existing methods. This calls for a need for new methods to arrive at the IIV associated with CP and W′. Furthermore, existing models focus on the expenditure of W′ for efforts above CP and do not model its recovery in the sub-CP domain. Thus, there is a need for methods and models that account for (i) the IIV to measure the effectiveness of individual training prescriptions and (ii) the recovery of W′ to aid human performance optimization.

III—Interplanetary Navigation

1955 ◽  
Vol 8 (1) ◽  
pp. 35-40
Author(s):  
J. G. Porter
Keyword(s):  
Dead Reckoning ◽  
Difficult Problem ◽  
Base Line ◽  
The Sun ◽  
Space Navigation ◽  
Simple Matter ◽  
The Earth ◽  
The Subject ◽  
The One ◽  
Interplanetary Navigation

Most people know something about space ships nowadays, and probably think that navigation in space is quite a simple matter; at any rate, it is a subject that is glossed over very briefly in most books on the subject. In my view, space navigation is not a simple matter, and it has certainly not received the attention it deserves. Navigation on the Earth is easy, because of the one important fact that you are on the surface of the Earth. A couple of sights, measuring the angles from two stars down to the horizon, together with the azimuths of the stars and the distance from the centre of the Earth, will give an exact statement of position. But out in space there is no Earth, no horizon—in fact nothing whatever to use as a basis of measurement. Clearly then, two angles are not enough; a third one is needed, to give a sort of tripod of sights—two of the legs being anchored to two planets (or the Sun and a planet) because their positions in space at any time are known, and the distance between them can be used as a base-line. The solution of all the triangles involved is indeed a difficult problem, but there is also the impossibility of making three simultaneous observations. It might be thought that one could do as at sea and take one sight followed later by others, making allowance for the motion of the ship in the intervals. However, this involves the idea of dead reckoning, which, although a useful concept at sea, is quite impossible to apply in space, as the following example shows.

scholarly journals On the measurement of the dielectric constants of liquids, with a determination of the dielectric constant of benzene

1929 ◽  
Vol 123 (792) ◽  
pp. 664-685 ◽  
Keyword(s):  
Dielectric Constant ◽  
Physical Properties ◽  
Dielectric Constants ◽  
Experimental Conditions ◽  
The Past ◽  
A Value ◽  
The Subject ◽  
Important Indication

It has long been recognised that the dielectric constant of a substance gives an important indication of its constitution, and the classical papers of Nernst and Drude giving methods for the determination of dielectric constants, have been followed by a long series of papers giving the dielectric constants of several hundreds of pure liquids and solutions. Since the publication of Debye’s dipole theory in 1912, the literature of the subject has become even more voluminous than before. In surveying the mass of data one is struck by the very large discrepancies which exist in the values obtained by different observers for any one substance, and it is very difficult to decide whether they are due to the difficulty of pre­paring and purifying the substance, differences in experimental conditions such as frequency of the applied E. M. F., or errors in the methods of measure­ment. In order to make it possible to compare the results of different observers, and to provide a fundamental basis for new measurements, it is important that the value of at least one standard liquid should be known with unquestion­able accuracy. The object of the present investigation was to provide such a value. Benzene was chosen as the standard liquid since it has been very widely used in the past, and it is used as a standard in the measurement of other physical properties.

scholarly journals Optimisation of the prescription for trans-tibial (TT) amputees

1997 ◽  
Vol 21 (3) ◽  
pp. 168-174 ◽  
Author(s):  
A. Cortés ◽  
E. Viosca ◽  
J. V. Hoyos ◽  
J. Prat ◽  
J. Sánchez-Lacuesta
Keyword(s):  
Quantitative Method ◽  
Clinical Information ◽  
Normal Subjects ◽  
Individual Variability ◽  
Classification Criteria ◽  
The Other ◽  
Human Gait ◽  
Factors Influencing ◽  
The Subject

The great diversity of prosthetic mechanisms available nowadays leads to the question of which type of artificial foot would be the most advisable for a particular person. To answer correctly, it is necessary to establish, in an objective way, the performance of each type of prosthetic mechanism. This knowledge is obtained by means of the study of the subject-prosthesis interaction, both in static and dynamic conditions. This paper, based on the analysis of 8 transtibial (TT) amputees, presents a quantitative method for the study of human gait which allows the determination of the influence of four different prosthetic ankle-foot mechanisms (SACH, Single-axis, Greissinger and Dynamic) on gait. To do this, 1341 gait trials at different cadences were analysed (383 with normal subjects and 958 with amputees, using the four prosthetic feet under study). From all the variables available for study only those which offered interpretable clinical information were chosen for analysis. A total of 18 variables (kinetic, kinematic and time-related) were selected. A covariance analysis (ANOVA) of these variables was made, which showed that the factors influencing TT amputee gait were, in order of importance, cadence and leg studied (sound or prosthetic), inter-individual variability and, finally, the prosthetic mechanism used. When looking at the performance during gait of the 4 prosthetic mechanisms studied it can be observed that there are similarities in the kinetic study between SACH and Dynamic feet on one hand and Single-axis and Greissinger feet on the other. These results seem to support the classification criteria of articulated and non-articulated prosthetic mechanisms.

Blood pressure regulation during cardiac autonomic blockade: effect of fitness

1988 ◽  
Vol 65 (4) ◽  
pp. 1789-1795 ◽  
Author(s):  
M. L. Smith ◽  
D. L. Hudson ◽  
H. M. Graitzer ◽  
P. B. Raven
Keyword(s):  
Blood Pressure ◽  
Vascular Resistance ◽  
Blood Pressure Control ◽  
Cardiovascular Responses ◽  
Pressure Control ◽  
Blood Pressure Regulation ◽  
Base Line ◽  
Adrenergic Blockade ◽  
Pressure Regulation ◽  
Experimental Conditions

The purpose of this study was to determine the role of the autonomic nervous system's control of the heart in fitness-related differences in blood pressure regulation. The cardiovascular responses to progressive lower-body negative pressure (LBNP) were studied during unblocked (control) and full blockade (experimental) conditions in 10 endurance-trained (T) and 10 untrained (UT) men, aged 20-31 yr. The experimental conditions included beta 1-adrenergic blockade (metoprolol tartrate), parasympathetic blockade (atropine sulfate), or complete blockade (metoprolol and atropine). Heart rate, blood pressure, forearm blood flow, and cardiac output were measured at rest and -16 and -40 Torr LBNP. Forearm vascular resistance, peripheral vascular resistance, and stroke volume were calculated from these measurements at each stage of LBNP. Blood pressure was maintained, primarily by augmented vasoconstriction, equally in T and UT subjects during complete and atropine blockade. The fall in systolic and mean pressure from 0 to -40 Torr was greater (P less than 0.05) in the T subjects during the unblocked and metoprolol blockade conditions. This reduced blood pressure control during unblocked condition was attributable to attenuated vaso-constrictor and chronotropic responses in the T subjects. We hypothesize that an autonomic imbalance (elevated base-line parasympathetic activity) in highly trained subjects restricts reflex cardiac responses, which accompanied by an attenuated vasoconstrictor response, results in attenuated blood pressure control during a steady-state hypotensive stress.

Age-related effects of digoxin on myocardial contractility and Na-K pump in sheep

1982 ◽  
Vol 243 (4) ◽  
pp. H517-H522
Author(s):  
T. J. Hougen ◽  
W. F. Friedman
Keyword(s):  
Active Transport ◽  
Monovalent Cation ◽  
Left Ventricular ◽  
Rate Of Change ◽  
Control Group ◽  
Base Line ◽  
Experimental Conditions ◽  
Adult Sheep ◽  
Age Related ◽  
Age Dependent

The age-dependent effects of an acute nontoxic, positively inotropic dose of digoxin on myocardial monovalent cation active transport were determined in fetal, newborn, and adult sheep. Thirty-five lightly sedated, closed-chest animals were instrumented to record electrocardiogram, left ventricular (LV) pressure, and rate of change of LV pressure (LV dP/dt). Ouabain-inhibitable uptake of Rb+ (86Rb+) was measured in both right ventricular (RV) and LV slices from control animals and in animals infused with [3H]digoxin (0.04 mg/kg) sufficient to cause an increase in LV dP/dt without toxicity. Sixty minutes after digoxin, LV dP/dt increased 123% over base-line values in fetuses, 131% in newborns, and 165% in adult animals. RV and LV myocardial digoxin concentrations were similar in all groups. Rb+ active transport was significantly reduced in both RV and LV tissue from all animals 60 min after digoxin. Control animals showed no significant changes in contractility or Rb+ active transport among the control group of fetal, newborn, or adult sheep. Acute infusions of digoxin increased LV contractility in each age group and was accompanied by digoxin-induced inhibition of myocardial Rb+ active transport. No age-related differences in the extent of Rb+ active transport among control or among digoxin-treated animals were observed under these experimental conditions. These studies suggest that the differential response to the therapeutic and toxic effects of digoxin in sheep of various ages does not reside in an age-dependent response of the myocardial sodium pump to digoxin.

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