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Biomedical subjects

R N Robertson

Publications and source records attributed to R N Robertson.

At least 37 records · Page 2Linked to original sources
PubMed1976

Interaction of apoprotein from porcine high-density lipoprotein with dimyristoly lecithin. 2. Nature of lipid-protein interaction.

The detailed molecular structure of the complex formed by the apoprotein from porcine high density lipoprotein and dimyristoly phosphatidylcholine (lecithin) has been investigated by a range of physical techniques. The complex, an oblate ellipsoid with major axis 11.0 nm and minor axis 5.5 nm (see the accompanying paper), is comprised of a section of lecithin bilayer with apoprotein at the surface. The main site of interaction between protein and lipid is in the lipid glycerophosphorylcholine group region; as with native high density lipoprotein the surface of the particle consists of a mosaic of lecithin polar groups and protein. The formation of this mosaic reduces the cooperativity of the lecithin chain motions and changes the curvature of the lipid-water interface, as compared to a bilayer. Otherwise, there are no major changes in lecithin motions indicating that no strong binding of lipid to protein occurs. The interaction involves the intercalation of amphipathic, 60% alpha-helical, apoprotein molecules among the lecithin molecules so that the protein residues at the lipid-water interface. The apoprotein has a high affinity for the lipid-water interface but specific lipid-protein interactions are not involved.

Amino Acid Sequence↗
PubMed1975

NMR studies of pig low- and high-density serum lipoproteins. Molecular motions and morphology.

1. NMR spectra of porcine high- and low density lipoproteins (d 1.120--1.210 and 1.019--1.070, respectively) and their extracted lipids were obtained as functions of temperature, frequency and solution viscosity, and from solutions to which paramagnetic species had been added. 2. About one-third of the N(CH3)3 groups in low-density lipoproteins are so immobile that they do not give a sharp resonance at any temperature up to 65 degrees C, unless the particles are disrupted with sodium dodecylsulphate. Most of the protein residues also undergo little segmental motion. 3. A marked restriction of motion of acyl chain terminal CH3 groups suggests that chain interdigitation occurs in low-density lipoprotein. Apart from this, there is a general ordering of the lipids without a decrease in the rate of rotation about bonds, suggesting that the protein organizes the lipids by controlling the molecular packing rather than by direct strong interactions. The lipids are more ordered in low-density than in high-density lipoprotein. 4. All phospholipids with mobile N(CH3)3 groups are at the particle surfaces, in patches separated by protein. In low-density lipoprotein the patches are raised proud of the protein, whereas in high-density lipoproteins the protein and lipid polar groups are coplanar. 5. The high-density lipoprotein results are consistent with literature models for the structure. The low-density lipoprotein results suggest a new model, which is basically a trilayer. The centre consists of a monolayer of phospholipid with tightly-packed polar groups in contact with a protein core. The outer monolayer of phospholipid contains the rest (most) of the protein; the central layer contains the neutral lipid (cholesterol esters and triglycerides), interdigitated into both the inner and outer monolayers. Unesterified cholesterol is distributed through all three layers.

Animals↗
PubMedDate not supplied

Wheelchair racing efficiency.

PURPOSE: For individuals with disabilities exercise, such as wheelchair racing, can be an important modality for community reintegration, as well as health promotion. The purpose of this study was to examine selected parameters during racing wheelchair propulsion among a sample of elite wheelchair racers. It was hypothesized that blood lactate accumulation and wheeling economy (i.e. oxygen consumed per minute) would increase with speed and that gross mechanical efficiency would reach an optimum for each athlete. METHOD: Twelve elite wheelchair racers with paraplegia participated in this study. Nine of the subjects were males and three were females. Each subject used his or her personal wheelchair during the experiments. A computer monitored wheelchair dynamometer was used during all testing. The method used was essentially a discontinuous economy protocol. Mixed model analysis of variance (ANOVA) was used to compare blood lactate concentration, economy (minute oxygen consumption), and gross mechanical efficiency across the stages. RESULTS: The results of this study show that both economy and blood lactate concentration increase linearly with speed if resistance is held constant. The subjects in this study had gross mechanical efficiencies (gme) of about 18%, with the range going from 15.222.7%. The results indicate that at the higher speeds of propulsion, for example near race speeds, analysis of respiratory gases may not give a complete energy profile. CONCLUSION: While there is a good understanding of training methods to improve cardiovascular fitness for wheelchair racers, little is known about improving efficiency (e.g. technique, equipment), therefore methods need to be developed to determine efficiency while training or in race situations.

Adult↗
PubMedDate not supplied

Upper limb nerve entrapments in elite wheelchair racers.

The prevalence of upper limb nerve injuries has been reported to be as high as 73% in individuals who rely on manual wheelchairs for mobility. Many authors hypothesize that the repetitive trauma to carpal canal structures caused by propelling a wheelchair is the reason for this high prevalence. The purpose of this study was to determine the prevalence of nerve conduction abnormalities in a group of elite wheelchair racers whose wrists are exposed to additional propulsion-related trauma during training and competition. We performed bilateral upper limb nerve conduction studies on each athlete (n = 12). The racers pushed their chairs an average of 56 miles a week for training purposes. Fifty percent of the athletes (n = 6) had evidence of median mononeuropathy by nerve conduction. Of these 6 racers, 5 had evidence of mononeuropathy bilaterally, making a total of 11 positive hands of the 23 tested. Twenty-five percent of the athletes had evidence of ulnar mononeuropathy at the wrist, and 25% had evidence of ulnar mononeuropathy at the elbow. Seventeen percent of athletes had evidence of radial nerve injury. Years with a disability accounted for a significant amount of the variance in the mean median sensory amplitude (R2 = 0.511; P = 0.020) and the mean ulnar palmar amplitude (R2 = 0.605; P = 0.008). Variables not correlated with nerve conduction studies include age, hours per day in a wheelchair not spent training, years competing, and number of miles pushed in training. Despite the amount of time spent training these wheelchair athletes have a similar or lower prevalence of median mononeuropathy then reported in the general wheelchair-using population.

Adult↗
PubMedDate not supplied

Three-dimensional pushrim forces during two speeds of wheelchair propulsion.

Upper limb pain frequently occurs in manual wheelchair users. Analyzing the pushrim forces and hub moments occurring during wheelchair propulsion is a first step in gaining insight into the cause of this pain. The objectives of this study were as follows: to describe the forces and moments occurring during wheelchair propulsion; to obtain variables that characterize pushrim forces and are statistically stable; and to determine how these variables change with speed. Convenience samples (n = 6) of paralympic athletes who use manual wheelchairs for mobility and have unimpaired arm function were tested. Each subject propelled a standard wheelchair on a dynamometer at 1.3 and 2.2 m/s. Biomechanical data were obtained using a force- and moment-sensing pushrim and a motion analysis system. A number of variables that describe the force and moment curves were evaluated for stability using Cronbach's alpha. Those measures found to be stable (alpha > 0.8) at each speed were then examined for differences associated with speed. The tangential, radial, and medial-lateral forces were found to comprise approximately 55, 35, and 10% of the resultant force, respectively. In addition to duration of stroke and propulsion, the following variables were found to be stable and to differ with speed (1.3 m/s +/- SD; 2.2 m/s +/- SD): peak force tangential to the pushrim (45.9 +/- 17.9 N; 62.1 +/- 30 N), peak moment radial to the hub (9.8 +/- 4.5 N x m 13.3 +/- 6 N x m), maximum rate of rise of the tangential force (911.7 +/- 631.7 N/sec; 1262.3 +/- 570.7 N/sec), and maximum rate of rise of the moment about the hub (161.9 +/- 78.3 N x m/s; 255.2 +/- 115.4 N x m/s). This study found stable parameters that characterize pushrim forces during wheelchair propulsion and varied with speed. Almost 50% of the forces exerted at the pushrim are not directed toward forward motion and, therefore, either apply friction to the pushrim or are wasted. Ultimately, this type of investigation may provide insight into the cause and prevention of upper limb injuries in manual wheelchair users.

Adult↗
PubMedDate not supplied

A unified method for calculating the center of pressure during wheelchair propulsion.

The measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion. however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTwheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject's upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject's except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder.

Biomechanical Phenomena↗
PubMedDate not supplied

Effects of prophylactic knee bracing on lower extremity joint position and muscle activation during running.

The primary purpose of a prophylactic knee brace is to decrease injury potential without compromising joint function; however, the extent that these devices can alter knee muscle function is not clear. This study investigated effects of nonprescription prophylactic knee bracing on lower extremity joint position and muscle activation during running. Six healthy male college-aged recreational runners used a motor-driven treadmill under 6 conditions: fast or slow speeds, with and without wearing a prophylactic knee brace, and with and without wearing a weighted vest. Changes in hip, knee, and ankle joint position and electromyographic activity from 9 lower extremity muscles were monitored during the running cycle weightbearing phase. Results revealed significant changes (P < 0.05) in joint position and electromyographic activity for comparisons of slow versus fast, braced versus nonbraced, and weighted versus nonweighted conditions. From 83% to 89% of the braced and nonbraced comparisons generated significant differences in knee joint position while significant hip and ankle joint position changes occurred in 50% to 58% of comparisons. From 67% to 83% of braced and nonbraced comparisons for the 9 muscles produced significant differences in electromyographic activity. Findings suggest that neuromuscular control is altered when external prophylactic devices are applied.

Adult↗