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PubMed2003

Amotosalen: Allogeneic Cellular Immunotherapies system, INTERCEPT Plasma System, INTERCEPT Platelet System, S 59.

Adis CommentsCerus Corporation is developing a variety of pathogen-inactivation systems, based on its Helinx technology. Three of the systems include amotosalen [S 59] as the inactivation compound. Amotosalen is a light-activated, DNA-, RNA-crosslinking psoralen compound, which is used to neutralise pathogens. The systems that utilise amotosalen are called the INTERCEPT Platelet System, the INTERCEPT Plasma System and the Allogeneic Cellular Immunotherapies (ACIT) system. The INTERCEPT Platelet System and INTERCEPT Plasma System are two of the systems that make up Cerus' INTERCEPT Blood Systems. The other system is the INTERCEPT Red Blood Cell System, which contains S 303 as the inactivation compound rather than amotosalen. Cerus' Helinx technology is able to prevent replication of DNA or RNA that is present in pathogens but not in the blood components being treated (e.g. platelets and plasma). When added to the blood components, the inactivation agent (in this case amotosalen) crosses the membrane or cell wall of the pathogen. When activated by light, amotosalen binds to the nucleic acid of the pathogen and prevents replication. This process prevents infection. INTERCEPT Platelet System: Cerus developed its INTERCEPT Platelet System, in collaboration with Baxter Healthcare, for use in blood centres. Platelets are an essential component of the coagulation process and may be required by patients undergoing surgery, cancer chemotherapy, transplantation or with bleeding disorders. The system is made up of an illuminator device, a compound absorption device and a processing kit containing amotosalen. In October 2002, the two companies announced that CE Mark approval had been received for the illuminator device for the INTERCEPT trade mark Blood System. Application of this technology to platelets is the first to be approved. As it is a new technology, the system is currently undergoing process validation in accordance with European Blood Bank GMP requirements. This validation process is currently being conducted in Denmark, France, Germany, Sweden and the UK. Marketing approval applications for the INTERCEPT Platelet System have also been submitted in Australia and Canada. In addition, the regulatory submission process has begun in the US. A phase III trial (EuroSPRITE) has been conducted in 103 patients in Europe with pooled random donor platelets. The platelets were collected using the buffy coat process. Another two 20-patient clinical trials have also been conducted in Europe, as well as a 40-patient trial using platelets collected by an apheresis collection system. Cerus has also conducted a phase III trial (SPRINT) in the US. The trial was conducted in 671 patients and used platelets collected by Baxter's apheresis collection system. INTERCEPT Plasma System: Cerus is also developing the INTERCEPT Plasma System in collaboration with Baxter Healthcare. The system also combines amotosalen, an illumination device and a compound absorption device. The two companies are currently preparing regulatory applications for the INTERCEPT Plasma System for the US. This application will be followed by a submission for CE Mark designation in Europe. Patients undergoing surgery, or transplantation, or with bleeding disorders, may require transfusions of plasma, often to control bleeding. The type of plasma is stored in frozen form and is called fresh frozen plasma (FFP). The INTERCEPT Plasma System is currently in phase IIIc development in the US. Patient enrolment in the trial is still ongoing. The trial is comparing INTERCEPT trade mark Plasma System treated versus untreated FFP in 30 patients with thrombotic thrombocytopenic purpura. Allogeneic Cellular Immunotherapies system: Cerus is also investigating the potential of its Helinx technology to improve the outcome of bone marrow transplantation procedures (used to treat leukaemia and lymphoma) through the treatmatment for many forms of leukaemia and is most effective when the donor is very closely matched to the patient for the major human leucocyte antigen (HLA) groups. As part of the transplant procedure, patients receive donor T cells to improve engraftment of the bone marrow transplant and strengthen the patient's immune system. However, donor T cells expose the patient to a high risk of contracting graft-versus-host disease (GVHD) caused by the proliferation of donor T cells, which attack the patient's healthy tissue. GVHD has a high mortality rate. Cerus' ACIT system has been developed to decrease the stringency of matching donors to patients and to inhibit the ability of donor T cells to cause GVHD. Light-activated amotosalen binds and permanently crosslinks DNA, preventing replication and thus stopping proliferation of donor T cells. Phase I development is currently being conducted in this area in the US using amotosalen as the neutralising agent. Cerus completed a phase I study investigating the safety and tolerability of its ACIT system in 2001. The study was conducted in patients receiving closely matched allogeneic bone marrow transplants for leukaemia. The company is currently collaborating with the National Marrow Donor Program in order to conduct further clinical studies in patients receiving bone marrow transplants from unmatched donors. Cerus has development, manufacturing and marketing agreements with Baxter covering the INTERCEPT Blood Systems, which includes the INTERCEPT Platelet system, the INTERCEPT Plasma System, and the INTERCEPT Red Blood Cell System. Under the terms of the agreements the two companies usually share the very early development activities. Cerus then conducts preclinical and clinical trials, while Baxter is responsible for the development of the systems disposables and devices. Following commercialisation Cerus will supply amotosalen and Baxter will supply the other components of the system and market, sell and distribute the system In January 2001, Cereus announced that it has entered into a collaborative agreement with the Pharmaceutical Division of Kirin Brewery in Japan to develop and market products for stem cell transplantation based on Cerus' proprietary Helinx technology. Under terms of the agreement, Cerus and Kirin will jointly develop the products. Cerus has received an initial license fee of US dollar 1 million. In addition it may receive up to US dollar 11 million in future payments upon achievement of development milestones. Kirin will also fund all development expenses for the Asia-Pacific region and a portion of Cerus' development activities aimed at obtaining product approval in the US. Kirin will market the products in the Asia-Pacific region, including Japan, China, Korea and Australia, and Cerus will receive a specified share of product revenues. Cerus will retain marketing rights in the rest of the world, including the US and Europe.

Anti-Infective Agents↗
PubMed1994

Palatally impacted canines: aetiology of impaction and the scope for interception. Report of cases outside the guidelines for interception.

Patients with palatally impacted canines have an increased incidence of missing or anomalous lateral incisors adjacent to the impacted canines. Their arches are often uncrowded and this, in part, is linked to the increased incidence of missing or anomalous lateral incisors. Other teeth are also more frequently missing. The present guidelines for the relief of palatally impacted canines by extraction of the deciduous canine require that the patient is aged between 10-13 years and that normal space conditions are present. Two successful case reports are presented which were outside the recommended guidelines. The technique of relieving a palatal impaction by extraction of the deciduous canine has wide application.

Adolescent↗
PubMed1996

Intercepting real and path-guided apparent motion targets.

Human subjects were instructed to intercept with a cursor real and apparent motion targets presented on a computer screen. Targets traveled counterclockwise (CCW) in a circle at one of five angular velocities (180, 300, 420, 480 and 540 deg/s), either smoothly (real motion) or in path-guided apparent motion. Subjects operated a computer mouse and were instructed to intercept targets at the 12 o'clock position; there were no constraints on when to initiate the response, which was a movement from the center of the screen towards and past 12 o'clock. We found the following: (a) for both motion conditions and all target velocities, subjects were late in intercepting the target, especially at higher target velocities; (b) for both motion conditions, the directional variability of the response increased as a linear function of the target velocity; (c) the directional variability of the response was systematically higher for the apparent than the real motion condition; there was no significant interaction between target velocity and target motion type; (d) the response time did not vary significantly with velocity, but was consistently longer for apparent than real motion targets; (e) the movement time was very similar for different target velocities; and (f) the moment of initiation of the interception movement was delayed appreciably at higher target velocities, relative to that dictated for perfect interception at a given target velocity. This delay was greater for the apparent motion target. These results demonstrated the following: (a) for both target motion conditions, interception was not fully predictive but lagged the target in spite of the constant target velocity and the unconstrained time allowed for initiating the interception movement; (b) subjects can intercept an apparent motion target but, compared with real motion, the performance is somewhat degraded overall; (c) the similarities in performance between the two target motion conditions, and the fact that target velocity influenced performance in a similar fashion, suggest that the motor system can access the visual information provided by the moving target; and (d) since movement time was similar for different target velocities, the strategy for interception relied on controlling the moment of initiation of the interception movement. This was successful for low target velocities but became unsuccessful at higher target velocities.

Adult↗
PubMed2000

Interceptive orthodontics in the real world of community dentistry.

OBJECTIVE: To test the applicability and effectiveness of interceptive orthodontics in a community field trial. DESIGN: Prospective screening for suitable malocclusions, implementation of treatment and analysis of outcomes 12 months later. SETTING: Community dentistry in urban and rural areas of Northern Ireland, 1996-98. SUBJECTS AND METHODS: The initial sample consisted of 2002 children (1014 boys, 988 girls) who were screened in routine community dental inspections. One thousand and sixty (523 aged 9 years, 537 aged 11 years) were domiciled in the urban area of greater Belfast and 942 (479 aged 9 years, 463 aged 11 years) in the rural area of Enniskillen and Omagh, Co. Tyrone. INTERVENTIONS: Interceptive orthodontic treatment. OUTCOME MEASURES: Dental health component of the Index of Orthodontic Treatment Need (IOTN) and specially devised local indices of treatment outcomes. RESULTS: With the use of an interception gauge, orthodontic screening was included in the community dental inspections without difficulty. Thirty-three per cent of children were in need of interceptive treatment. Only 20% of those in need both attended for recall and underwent treatment. Compliance was better in the rural area but the need, with particular reference to extraction of carious first molars, was greater in the urban area. The numbers of children in IOTN grades 4 and 5 fell from 69% at the beginning of the study to 42% at the end. The outcome judged by local indices was 94% in the range of complete success to minimal improvement with only 2% showing deterioration. CONCLUSIONS: One in three children screened in community dental inspections at age 9 and 11 years would benefit from interceptive orthodontics. Parents and children seem reluctant to accept offers of interceptive orthodontics and to having the treatment carried out. Among those complying fully, the interceptive measures are very successful. Not only does community interceptive orthodontics improve the condition being treated but also reduces the need for further treatment.

Chi-Square Distribution↗
PubMed2003

Interception of real and apparent motion targets: psychophysics in humans and monkeys.

Human subjects and monkeys intercepted real (RM) and apparent (AM) moving targets that traveled through a low contrast circular path. The subjects intercepted the targets at 6 o'clock by applying a net force pulse on a semi-isometric joystick which controlled a cursor on the screen. Eight target speeds (180-560 degrees/s) were used. The starting points of the moving target were systematically placed around the circle in order to determine the effect of the target travel time and velocity on the decision to initiate the interception movement and on the interception accuracy. It was found that the probability of interception in the first revolution varied as a function of the target travel time, which followed an S-shaped psychometric curve. The minimum processing time (MPT) was defined as the target travel that corresponded to a 75% probability of interception in the first revolution on the psychometric curve. The MPT decreased slightly as a function of target speed and was larger in AM than RM. In addition, the interception accuracy increased when the target travel time was above the MPT, and the angular error was smaller in RM than in AM. Finally, the interception movement was initiated at different target locations and time-to-contacts, depending on the target speed and the motion condition. Interestingly, similar findings were observed in human subjects and monkeys. These results suggest that the neural mechanisms engaged in extracting the visual motion information and in the implementation of the response are more efficient during RM than AM, and that such mechanisms need less processing time when the target is moving faster.

Adult↗
PubMed1998

Nonrandom sequence of slope-intercept estimates in longitudinal gompertzian analysis suggests biological relevance.

The significance of intersections in age-specific mortality rate distributions could be attributed to a fundamental statistical relationship between estimates of slope and intercept. A strong negative correlation between estimates of slope and intercept is often observed in simple linear regression problems. The net result is that the family of lines generated by repetitive estimates of slope and intercept in a static experimental situation will tend to intersect at a common point. This statistical relationship between slope and intercept, however, should be random with respect to the time-ordered sequence of slope and intercept estimates. Annual paired slope and intercept estimates derived using the method of longitudinal Gompertzian analysis of age-specific mortality rates for men and women in the United States from 1900 to 1988 were analyzed to determine if they varied randomly. The probability that the observed sequence in these annual paired slope-intercept estimates was random is less than 10(-50) for both men and women. This finding essentially excludes the possibility that intersections in age-specific mortality rate distributions reflect a fundamental statistical relationship between slope and intercept and further suggests biological relevance for the method of longitudinal Gompertzian analysis.

Female↗
PubMed2001

Motor cortical activity during interception of moving targets.

The single-unit activity of 831 cells was recorded in the arm area of the motor cortex of two monkeys while the monkeys intercepted a moving visual stimulus (interception task) or remained immobile during presentation of the same moving stimulus (no-go task). The moving target traveled on an oblique path from either lower corner of a screen toward the vertical meridian, and its movement time (0.5, 1.0, or 1.5 sec) and velocity profile (accelerating, decelerating, or constant velocity) were pseudorandomly varied. The moving target had to be intercepted within 130 msec of target arrival at an interception point. By comparing motor cortical activity at the single-neuron and population levels between the interception and no-go tasks, we tested whether information about parameters of moving target is represented in the primary motor cortex to generate appropriate motor responses. A substantial number of neurons displayed modulation of their activity during the no-go task, and this activity was often affected by the stimulus parameters. These results suggest a role of motor cortex in specifying the timing of movement initiation based on information about target motion. In addition, there was a lack of systematic relation between the onset times of neural activity in the interception and no-go tasks, suggesting that processing of information concerning target motion and generation of hand movement occurs in parallel. Finally, the activity in the most motor cortical neurons was modulated according to an estimate of the time-to-target interception, raising the possibility that time-to-interception may be coded in the motor cortical activity.

Animals↗
PubMed2003

Development of interception of moving targets by chimpanzees (Pan troglodytes) in an automated task.

The experiments investigated how two adult captive chimpanzees learned to navigate in an automated interception task. They had to capture a visual target that moved predictably on a touch monitor. The aim of the study was to determine the learning stages that led to an efficient strategy of intercepting the target. The chimpanzees had prior training in moving a finger on a touch monitor and were exposed to the interception task without any explicit training. With a finger the subject could move a small "ball" at any speed on the screen toward a visual target that moved at a fixed speed either back and forth in a linear path or around the edge of the screen in a rectangular pattern. Initial ball and target locations varied from trial to trial. The subjects received a small fruit reinforcement when they hit the target with the ball. The speed of target movement was increased across training stages up to 38 cm/s. Learning progressed from merely chasing the target to intercepting the target by moving the ball to a point on the screen that coincided with arrival of the target at that point. Performance improvement consisted of reduction in redundancy of the movement path and reduction in the time to target interception. Analysis of the finger's movement path showed that the subjects anticipated the target's movement even before it began to move. Thus, the subjects learned to use the target's initial resting location at trial onset as a predictive signal for where the target would later be when it began moving. During probe trials, where the target unpredictably remained stationary throughout the trial, the subjects first moved the ball in anticipation of expected target movement and then corrected the movement to steer the ball to the resting target. Anticipatory ball movement in probe trials with novel ball and target locations (tested for one subject) showed generalized interception beyond the trained ball and target locations. The experiments illustrate in a laboratory setting the development of a highly complex and adaptive motor performance that resembles navigational skills seen in natural settings where predators intercept the path of moving prey.

Animals↗
PubMed1991

The y-intercept of the critical power function as a measure of anaerobic work capacity.

When bouts of muscular work are performed to exhaustion at different intensities, the slope of the regression of maximal work (work limit) on maximal time (time limit) is referred to as critical power (CP). The y-intercept of this function is considered to represent anaerobic work capacity (AWC). The purpose of this investigation was to examine the relationship between the y-intercept from the critical power curve and measures of AWC (total work accomplished, maximal blood lactate and post-exercise venous blood pH) gained from repeated, maximal exercise. Nine male volunteers of moderately high training status (VO2 max 4.45 +/- 0.251/min) completed three cycle ergometer tests to exhaustion (at 300, 350 and 400 W) for the determination of CP. A second cycle ergometer task involved repeated maximal effort (against 0.075 N/kg body mass) over five 1 min periods. Five min of passive recovery separated each exercise bout, at the end of which capillary blood was collected for lactate analysis. On completion of the fifth bout, venous blood was sampled for the determination of blood pH. Total accumulated work provided a performance estimate of AWC which, together with blood lactate and pH, was compared to the y-intercept. Correlation analysis revealed a significant relation between the y-intercept and total work accomplished (r = 0.74; p less than 0.05), while post-exercise venous blood pH was positively related to both the y-intercept (r = 0.92; p less than 0.01) and the accumulated work recorded (r = 0.92; p less than 0.01). No significant correlation between peak blood lactate and work was found (r = 0.16; ns), although a relation between post-exercise venous blood pH and VO2 max was established (r = 0.84; p less than 0.05). The capacity for high intensity interval work was well represented by the y-intercept in active males. Furthermore, the relations between blood pH and both the y-intercept and accumulated work suggest that either improved buffering or a greater contribution of aerobic metabolism to the energy yield may have been responsible for the more successful performances in the interval exercise.

Acid-Base Equilibrium↗
PubMed1997

Applicability of interceptive orthodontics in the community.

The term interceptive orthodontics used in this paper is defined as the prompt treatment of unfavourable features of a developing occlusion categorized as local factors, crowding and displacements of the mandible in closing from the rest position. The aims of the study were to determine the best age or ages for interceptive orthodontics, to establish diagnostic cut-off points for self-correcting features of the developing occlusion which can be quantified, to investigate the reproducibility of treatment decisions and to make an initial estimate of the percentage of children suitable for interception. Based on material in the Belfast Growth Study, maximum or minimum measurements associated with spontaneous correction of quantifiable features were determined and incorporated into a disposable plastic gauge. Using the gauge, the available records of 278 Growth Study subjects at age 9 years and 272 at age 11 years were assessed for suitability for interception. Most of the conditions for interceptive treatments were present at age 9 years, but others were not present until 11 years. The majority of treatment decisions were highly reproducible. Approximately 50 per cent of the children in the Growth Study would have benefitted from interceptive orthodontics. A follow-up community study seems justified.

Age Factors↗
PubMed1997

Manual interception of moving targets. I. Performance and movement initiation.

We investigated the capacities of human subjects to intercept moving targets in a two-dimensional (2D) space. Subjects were instructed to intercept moving targets on a computer screen using a cursor controlled by an articulated 2D manipulandum. A target was presented in 1 of 18 combinations of three acceleration types (constant acceleration, constant deceleration, and constant velocity) and six target motion times, from 0.5 to 2.0 s. First, subjects held the cursor in a start zone located at the bottom of the screen along the vertical meridian. After a pseudorandom hold period, the target appeared in the lower left or right corner of the screen and traveled at 45 degrees toward an interception zone located on the vertical meridian 12.5 cm above the start zone. For a trial to be considered successful, the subject's cursor had to enter the interception zone within 100 ms of the target's arrival at the center of the interception zone and stay inside a slightly larger hold zone. Trials in which the cursor arrived more than 100 ms before the target were classified as "early errors," whereas trials in which the cursor arrived more than 100 ms after the target were classified as "late errors." Given the criteria above, the task proved to be difficult for the subjects. Only 41.3% (1080 out of 2614) of the movements were successful, whereas the remaining 58.7% were temporal (i.e., early or late) errors. A large majority of the early errors occurred in trials with decelerating targets, and their percentage tended to increase with longer target motion times. In contrast, late errors occurred in relation to all three target acceleration types, and their percentage tended to decrease with longer target motion times. Three models of movement initiation were investigated. First, the threshold-distance model, originally proposed for optokinetic eye movements to constant-velocity visual stimuli, maintains that response time is composed of two parts, a constant processing time and the time required for the stimulus to travel a threshold distance. This model only partially fit our data. Second, the threshold-tau model, originally proposed as a strategy for movement initiation, assumes that the subject uses the first-order estimate of time-to-contact (tau) to determine when to initiate the interception movement. Similar to the threshold distance model, the threshold-tau model only partially fit the data. Finally, a dual-strategy model was developed which allowed for the adoption of either of the two strategies for movement initiation; namely, a strategy based on the threshold-distance model ("reactive" strategy) and another based on the threshold-tau model ("predictive" strategy). This model provided a good fit to the data. In fact, individual subjects preferred to use one or the other strategy. This preference was allowed to be manifested at long target motion times, whereas shorter target motion times (i.e., 0.5 s and 0.8 s) forced the subjects to use only the reactive strategy.

Adult↗
PubMed1998

Shoot structure, light interception, and distribution of nitrogen in an Abies amabilis canopy.

We studied the effects of variation in shoot structure and needle morphology on the distributions of light and nitrogen within a Pacific silver fir (Abies amabilis (Dougl.) Forbes) canopy. Specifically, we investigated the role of morphological shade acclimation in the determination of resource use efficiency, which is claimed to be optimal when the distribution of nitrogen within the canopy is directly proportional to the distribution of intercepted photosynthetically active radiation (PAR). Shoots were collected from different heights in the crowns of trees representing four different size classes. A new method was developed to estimate seasonal light interceptance (SLI, intercepted PAR per unit needle area) of the shoots using a model for the directional distribution of above-canopy PAR, measurements of shoot silhouette area and canopy gap fraction in different directions. The ratio SLI/SLI(o), where the reference value SLI(o) represents the seasonal light interceptance of a spherical surface at the shoot location, was used to quantify the efficiency of light capture by a shoot. The ratio SLI/SLI(o) doubled from the top to the bottom of the canopy, mainly as a result of smaller internal shading in shade shoots than in sun shoots. Increased light-capturing efficiency of shade shoots implies that the difference in intercepted light by sun shoots versus shade shoots is much less than the decrease in available light from the upper to the lower canopy. For example, SLI of the five most sunlit shoots was only about 20 times greater than the SLI of the five most shaded shoots, whereas SLI(o) was 40 times greater for sun shoots than for shade shoots. Nitrogen content per unit needle area was about three times higher in sun needles than in shade needles. This variation, however, was not enough to produce proportionality between the amounts of nitrogen and intercepted PAR throughout the canopy.

Journal Article↗
PubMed2000

Comparing light interception with stand basal area for predicting tree growth.

Empirical and process-based tree growth models have been developedconcurrently; however, their growth predictions have rarely been compared directly. A major difference between the model types is the explicit quantification of foliage biomass as a key variable in process-based models. The aim of this work was to test if this difference has a significant impact on model behavior, especially when simulating silvicultural practices such as intensive thinning. A method was developed to evaluate leaf area and light interception of the mean tree of an even-aged stand from yield table data for Norway spruce (Picea abies (L.) Karst.) in the northern French Alps. Two scenarios were analyzed: (1) a closed stand where leaf area was limited by a maximum leaf area index-represented by young, dense stands, and (2) an open stand where leaf area was limited by the height of the crown base-represented by old, sparse stands. Light interception was calculated based on interpolation between a closed stand (Beer-Lambert law) and an isolated tree (light interception proportional to leaf area). This approach was then used to build a growth model in which competition was described by the ratio of light intercepted by a mean tree of the stand to light intercepted by an isolated tree of the same size. This process-based model was compared with a simpler empirical model in which competition was described by stand basal area. Both models fit well to yield table diameter increment data, the simpler model being slightly better. Simulation of long-term growth, interspersed with thinning, revealed differences between the models. The empirical model was sensitive to thinning and simulated a discontinuous growth pattern, whereas the model based on light calculation showed a smoother growth response to thinning. Simulations of heavy thinning in a dense stand highlighted these differences. The empirical model simulated heavy thinning in a dense stand unrealistically: after thinning, trees immediately grew as fast as trees of similar diameter in an unthinned stand at the same density. In contrast, leaf area played a regulatory role in the model based on light interception: trees with short crowns, as a result of a previous period of growth at high density, benefited little from an increase in light following thinning. It is concluded that models based on physiological or ecological processes have qualitative behaviors different from those of classical empirical models. This is especially important when models are used to make extrapolations far from reference data, for example, to forecast the long-term effect of a new silvicultural strategy.

Journal Article↗
PubMed1988

The interrelationships among plant biomass, plant surface area and the interception of particulate deposition by grasses.

The interrelationships among plant biomass, plant surface area and interception fraction were determined for the interception by corn of 238Pu-bearing particles released to the atmosphere from the H-Area nuclear fuels chemical separations facility on the U.S. Department of Energy's Savannah River Plant in Barnwell County, South Carolina. The relationship between interception fraction and corn biomass was accurately approximated by a filtration model with an absorption coefficient of 3.60 m2 kg-1. A filtration model with an absorption coefficient of 2.91 m2 kg-1 accurately approximated the relationship between biomass and interception fraction for data compiled from the literature for a variety of grass species. A linear regression model accurately approximated the relationship between interception fraction and surface area, but was not a better predictor of interception fraction than the filtration model for biomass.

Air Pollutants↗
PubMed1990

Two zero-flow pressure intercepts exist in autoregulating isolated skeletal muscle.

The autoregulating vascular bed of the isolated canine extensor digitorum longus muscle was investigated for the possible existence of two positive zero-flow pressure axis intercepts, a tone-dependent one and a tone-independent one. An isolated preparation, perfused with autologous blood, was used to exclude effects of collateral flow and nervous and humoral regulation while autoregulation was left intact [mean autoregulatory gain 0.50 +/- 0.24 (SD)]. In a first series of experiments, the steady-state (zero flow) pressure axis intercept [mean 8.9 +/- 2.6 (SD) mmHg, tone independent] and the instantaneous (zero flow) pressure axis intercept [mean 28.5 +/- 9.9 (SD) mmHg, tone dependent] were determined as a function of venous pressure (range: 0-45 mmHg) and were independent of venous pressure until the venous pressure exceeded their respective values. Beyond this point the relations between the venous pressure and the steady-state and instantaneous pressure axis intercept followed the line of identity. The findings agree with the predictions of the vascular waterfall model. In a second series it was shown by means of administration of vasoactive drugs that the instantaneous pressure axis intercept is tone dependent, whereas the steady-state pressure axis intercept is not. It is concluded that there is a (proximal) tone-dependent zero-flow pressure at the arteriolar level and a (distal) tone-independent zero-flow pressure at the venous level.

Animals↗
PubMed1997

Gender Differences in Intercepting a Moving Target by Using a Throw or Button Press.

Humans are a throwing species just as much as a talking species (Calvin, 1982), but preadaptations for throwing remain largely unexplored. The ability of undergraduate students (N = 165) to intercept a stimulus with a thrown object was determined for 10 stimulus speeds, ranging from 2 to 5 m/s. The inclusion of a condition in which the moving stimulus was intercepted via button press allowed the role of the perceptual aspect of velocity estimation to be evaluated separately from the act of throwing. Gender differences were observed in both the button and the throwing intercept tasks: The men had smaller timing errors and higher accuracy than the women. Contrary to expectations, the male and female patterns of intercept errors as a function of stimulus speed were more similar in the throwing task than in the button intercept task.

gender differences↗