Biomedical subjects

Hakan Johansson

Publications and source records attributed to Hakan Johansson.

4 recordsLinked to original sources

PubMed2003

Neuropeptide Y induces ischemic angiogenesis and restores function of ischemic skeletal muscles.

Previously we showed that neuropeptide Y (NPY), a sympathetic vasoconstrictor neurotransmitter, stimulates endothelial cell migration, proliferation, and differentiation in vitro. Here, we report on NPY's actions, receptors, and mediators in ischemic angiogenesis. In rats, hindlimb ischemia stimulates sympathetic NPY release (attenuated by lumbar sympathectomy) and upregulates NPY-Y2 (Y2) receptor and a peptidase forming Y2/Y5-selective agonist. Exogenous NPY at physiological concentrations also induces Y5 receptor, stimulates neovascularization, and restores ischemic muscle blood flow and performance. NPY-mediated ischemic angiogenesis is not prevented by a selective Y1 receptor antagonist but is reduced in Y2(-/-) mice. Nonischemic muscle vascularity is also lower in Y2(-/-) mice, whereas it is increased in NPY-overexpressing rats compared with their WT controls. Ex vivo, NPY-induced aortic sprouting is markedly reduced in Y2(-/-) aortas and spontaneous sprouting is severely impaired in NPY(-/-) mice. NPY-mediated aortic sprouting, but not cell migration/proliferation, is blocked by an antifetal liver kinase 1 antibody and abolished in mice null for eNOS. Thus, NPY mediates neurogenic ischemic angiogenesis at physiological concentrations by activating Y2/Y5 receptors and eNOS, in part due to release of VEGF. NPY's effectiveness in revascularization and restoring function of ischemic tissue suggests its therapeutic potential in ischemic conditions.

Animals↗

PubMed2003

Muscle strength assessment from functional performance tests: role of body size.

The aim of the study was to test the hypothesis that the body size plays an important role in assessment of muscle ability to exert force by standard functional performance tests. Twenty-one male students were tested on maximal isometric lift, one leg rising, vertical jump, and box lift tests, and the maximal isokinetic strength of hip and knee extensors was also recorded. When indices of the 4 functional performance tests were related to the strength of each of the 2 leg extensor muscle groups, only maximal isometric lift demonstrated positive correlation with knee extensors strength. When muscle strength was corrected for body mass, however, the aforementioned relationship became insignificant, but the 1 leg rising performance demonstrated a positive relationship with knee extensor strength. In addition, maximal isometric lift and 1 leg rising test performance provided positive and negative correlation, respectively, with body mass. The obtained findings were in line with the effects of scale applied on the tested performance. We generally conclude that the assessment of muscle capability to exert force based on some standard functional performance tests could be confounded by the body size effect.

Adult↗

PubMed2002

Muscle force and muscle torque in humans require different methods when adjusting for differences in body size.

Different methods for adjusting muscle strength ( S) to normalise for differences in various estimates of body size [such as body mass ( m) or, infrequently, some other anthropometrical measurements] have been either proposed or applied when presenting the results of muscle function tests in various medical, ergonomic, and sport related studies. However, the fact that the relationship between S and body size may differ when muscle torque (measured using a standard isokinetic apparatus) and muscle force (measured using a dynamometer) are recorded has not been taken into account. To address this problem, we tested both muscle force and muscle torque under isometric conditions in six different muscle groups. The relationship assumed between S and m was S=k.m(b) and, according to a simple mechanical model based on geometrical similarity we developed, the exponential parameter b would be expected to equal 1.00 and 0.67 for torque and force, respectively. The experimentally obtained values for the parameter b were higher for muscle torque than for muscle force in five out of the six muscle groups tested ( P=0.068; Wilcoxon matched pairs test). Despite a relatively wide scatter, the mean (SD) values were also close to those predicted, being b=0.67 (0.19) (corresponding to the allometric scaling method) and b=1.02 (0.34) (corresponding to the ratio standards method) for muscle force and for muscle torque, respectively. Therefore, we concluded that the ratio standards and allometric scaling should be employed to adjust S for body size when muscle torque and muscle force, respectively, are tested.

Adult↗

PubMed2001

Structure of joint variability in bimanual pointing tasks.

Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.

Adult↗