Human balance and posture control during standing and walking

The common denominator in the assessment of human balance and posture is the inverted pendulum model. If we focus on appropriate versions of the model we can use it to identify the gravitational and acceleration perturbations and pinpoint the motor mechanisms that can defend against any perturbation.

We saw that in quiet standing an ankle strategy applies only in the A/P direction and that a separate hip load/unload strategy by the hip abd/adductors is the totally dominant defence in the M/L direction when standing with feet side by side. In other standing positions (tandem, or intermediate) the two mechanisms still work separately, but their roles reverse. In the tandem position M/L balance is an ankle mechanism (invertors/evertors) while in the A/P direction a hip load/unloading mechanism dominates.

During initiation and termination of gait these two separate mechanisms control the trajectory of the COP to ensure the desired acceleration and deceleration of the COM. During initiation the initial acceleration of the COM forward towards the stance limb is achieved by a posterior and lateral movement of the COP towards the swing limb. After this release phase there is a sudden loading of the stance limb which shifts the COP to the stance limb. The COM is now accelerated forward and laterally towards the future position of the swinging foot. Also M/L shifts of the COP were controlled by the hip abductors/adductors and all A/P shifts were under the control of the ankle plantar/dorsiflexors. During termination the trajectory of both COM and COP reverse. As the final weight-bearing on the stance foot takes place the COM is passing forward along the medial border of that foot. Hyperactivity of that foot's plantarflexors takes the COP forward and when the final foot begins to bear weight the COP moves rapidly across and suddenly stops at a position ahead of the future position of the COM. Then the plantarflexors of both feet release and allow the COP to move posteriorly and approach the COM and meet it as quiet stance is achieved. The inverted pendulum model permitted us to understand the separate roles of the two mechanisms during these critical unbalancing and rebalancing periods.

During walking the inverted pendulum model explained the dynamics of the balance of HAT in both the A/P and M/L directions. Here the model includes the couple due to the acceleration of the weight-bearing hip as well as gravitational perturbations. The exclusive control of A/P balance and posture are the hip extensors and flexors, while in the M/L direction the dominant control is with the hip abductors with very minor adductor involvement. At the ankle the inverted pendulum model sees the COM passing forward along the medial border to the weight-bearing foot. The model predicts that during single support the body is falling forward and being accelerated medially towards the future position of the swing foot. The model predicts an insignificant role of the ankle invertors/evertors in the M/L control. Rather, the future position of the swing foot is the critical variable or more specifically the lateral displacement from the COM at the start of single support. The position is actually under the control of the hip abd/adductors during the previous early swing phase.

The critical importance of the hip abductors/adductors in balance during all phases of standing and walking is now evident. This separate mechanism is important from a neural control perspective and clinically it focuses major attention on therapy and potential problems with some surgical procedures. On the other hand the minuscule role of the ankle invertors/evertors is important to note. Except for the tandem standing position these muscles have negligible involvement in balance control.     

Familial persistent pulmonary hypertension of the newborn resulting from misalignment of the pulmonary vessels (congenital alveolar capillary dysplasia).

Misalignment of the pulmonary veins with congenital alveolar capillary dysplasia, although rare, has been reported as a cause of persistent pulmonary hypertension of the newborn. Reported cases have been mainly sporadic. Familial occurrence has been reported in only three instances. We present affected sibs with this condition. In addition to pulmonary abnormalities, urogenital abnormalities, including ureteric and urethral obstruction, seem to be common. Autosomal recessive inheritance is suggested.     

C3d binding to the circumsporozoite protein carboxy-terminus deviates immunity against malaria

The immunogenicity of recombinant protein or anti-viral DNA vaccines can be significantly improved by the addition of tandem copies of the complement fragment C3d. We sought to determine if the efficacy of a circumsporozoite protein (CSP)-based DNA vaccine delivered to mouse skin by gene gun was improved by using this strategy. Instead, we found that C3d suppressed the protective immunity against Plasmodium berghei malaria infection and deviated immunity, most notably by suppressing the induction of antibodies specific for the CSP C-terminal flanking sequence and by suppressing the induction of CSP-specific IL-4-producing spleen cells. We further showed that C3d bound to the C-terminal flanking sequence of the CSP, which may explain the immune deviation observed in CS/C3d chimeric antigen. We have thus identified C3d-mediated epitope masking and shifting of both the humoral and cellular immune responses as a potential novel escape mechanism, which plasmodia may use to divert the induction of protective immunity.     

Levels of stem cell factor and interleukin-3 in serum in acute Plasmodium falciparum malaria.

The purpose of the present study was to measure serum concentrations of stem cell factor (SCF) and interleukin-3 (IL-3) in patients with acute Plasmodium falciparum malaria. Serum samples from 15 patients were taken on day of admission and days 7, 14, 21, and 28. Anemia developed in 80% of patients. A transient increase in IL-3 could be observed at the beginning of the disease. It remains controversial whether the measured concentrations of IL-3 and SCF correlate with the grade of anemia. The possibly suppressed IL-3 and SCF production may contribute to the prolonged anemia in P. falciparum malaria, as has been shown for erythropoietin.     

A simple cardiac contractility computer

A single-purpose analogue-computing device is described for the online assessment of the contractile state of the human myocardium from the left ventricular pressure (P_lv) data available during routine cardiac catheterisation. Due attention has been paid to the design of the computer circuits so that they will not process pressure phenomena outside the isovolumic contractile period. Either a \(\left( {\frac{1}{{P_{lv} }}\frac{{dP_{lv} }}{{dt}}} \right)_{max} \) or a plain \(\left( {\frac{{dP_{lv} }}{{dt}}} \right)_{max} \) index is presented on a digitalvoltmeter display, thus obviating the need for any graphical extrapolation or additional computation.     

Velocardiofacial syndrome in a mother and daughter: variability of the clinical phenotype.

We report a mother and daughter with features of the velocardiofacial (VCF) syndrome and monosomy for 22q11 identified using molecular techniques. The mother had surgery as a child for a cleft palate and a congenital heart defect, and her facial features were consistent with the diagnosis. The daughter had developmental delay, absent speech, scoliosis, and similar facial features, but no cleft palate or congenital heart defect. These cases illustrate the considerable intrafamilial variability of the phenotype of VCF syndrome. The clinical and molecular diagnosis of this syndrome is discussed. The phenotypic variability of the VCF syndrome means that many cases may be undiagnosed.     

Direct comparison of umbilical cord blood versus bone marrow-derived endothelial precursor cells in mediating neovascularization in response to vascular ischemia.

Endothelial precursor cells (EPCs) cultured from adult bone marrow (BM) have been shown to mediate neovasculogenesis in murine models of vascular injury. We sought to directly compare umbilical cord blood (UCB)- and BM-derived EPC surface phenotypes and in vivo functional capacity. UCB and BM EPCs derived from mononuclear cells (MNC) were phenotyped by surface staining for expression of stromal (Stro-1, CXCR4, CD105, and CD73), endothelial (CD31, CD146, and vascular endothelial [VE]-cadherin), stem cell (CD34 and CD133), and monocyte (CD14) surface markers and analyzed by flow cytometry. The nonobese diabetic/severe combined immunodeficiency murine model of hind-limb ischemia was used to analyze the potential of MNCs and culture-derived EPCs from UCB and BM to mediate neovasculogenesis. Histologic evaluation of the in vivo studies included capillary density as a measure of neovascularization. Surface CXCR4 expression was notably higher on UCB-derived EPCs (64.29%+/-7.41%) compared with BM (19.69%+/-5.49%; P=.021). Although the 2 sources of EPCs were comparable in expression of endothelial and monocyte markers, BM-derived EPCs contained higher proportions of cells expressing stromal cell markers (CD105 and CD73). Injection of UCB- or BM-derived EPCs resulted in significantly improved perfusion as measured by laser Doppler imaging at days 7 and 14 after femoral artery ligation in nonobese diabetic/severe combined immunodeficiency mice compared with controls (P<.05). Injection of uncultured MNCs from BM or UCB showed no significant difference from control mice (P=.119; P=.177). Tissue samples harvested from the lower calf muscle at day 28 demonstrated increased capillary densities in mice receiving BM- or UCB-derived EPCs. In conclusion, we found that UCB and BM-derived EPCs differ in CXCR4 expression and stromal surface markers but mediate equivalent neovasculogenesis in vivo as measured by Doppler flow and histologic analyses.     

Blastogenic response of bovine lymphocytes to Brucella abortus lipopolysaccharide.

Brucella abortus lipopolysaccharide was tested in a blastogenesis assay with unfractionated and nylon wool-separated peripheral blood lymphocytes of Brucella-naive cattle and cattle immunized with B. abortus. Our results indicated that in cattle the lipopolysaccharide of B. abortus is not a B-cell mitogen. In immunized animals it stimulated predominantly nylon wool-adherent cells. The lipopolysaccharide of Escherichia coli O128:B12, in contrast, induced a substantially greater proliferative response in circulating lymphocytes, predominantly those adherent to nylon wool, of the Brucella-naive cattle.