•Linear stability of parallel steady flow in a vertical porous layer is analysed.•The boundaries are open to external reservoirs at uniform unequal temperatures.•A modal analysis is performed, ...leading to the stability eigenvalue problem.•The transverse modes of perturbation turn out to be the most unstable.•Effects of a boundary temperature difference and of internal heating are studied.
Buoyant flow in a vertical porous layer whose open boundaries are kept at uniform and different temperatures is analysed. The presence of a uniform volumetric heat source alters the conduction profile of the temperature field for the stationary parallel flow. It is shown that this stationary flow becomes unstable when either the temperature difference between the boundaries or the intensity of the volumetric heat source are sufficiently large. The linear instability is investigated through a study of normal mode disturbances. The stability eigenvalue problem is solved numerically by employing the shooting method. The neutral stability curves are obtained and the critical parameters at onset of instability are determined.
Respiratory failure is a major cause of death in patients with Osteogenesis Imperfecta. Moreover, respiratory symptoms seem to have a dramatic impact on their quality of life. It has long been ...thought that lung function disorders in OI are mainly due to changes in the thoracic wall, caused by bone deformities. However, recent studies indicate that alterations in the lung itself can also undermine respiratory health.
Is there any intrapulmonary alteration in Osteogenesis Imperfecta that can explain decreased pulmonary function? The aim of this systematic literature review is to investigate to what extent intrapulmonary or extrapulmonary thoracic changes contribute to respiratory dysfunction in Osteogenesis Imperfecta.
A literature search (in PubMed, Embase, Web of Science, and Cochrane), which included articles from inception to December 2020, was performed in accordance with the PRISMA guidelines.
Pulmonary function disorders have been described in many studies as secondary to scoliosis or to thoracic skeletal deformities. The findings of this systematic review suggest that reduced pulmonary function can also be caused by a primary pulmonary problem due to intrinsic collagen alterations.
Based on the most recent studies, the review indicates that pulmonary defects may be a consequence of abnormal collagen type I distorting the intrapulmonary structure of the lung. Lung function deteriorates further when intrapulmonary defects are combined with severe thoracic abnormalities. This systematic review reveals novel findings of the underlying pathological mechanism which have clinical and diagnostic implications for the assessment and treatment of pulmonary function disorders in Osteogenesis Imperfecta.
KEY MESSAGES
Decreased pulmonary function in Osteogenesis Imperfecta can be attributed to primary pulmonary defects due to intrapulmonary collagen alterations and not solely to secondary problems arising from thoracic skeletal dysplasia.
Type I collagen defects play a crucial role in the development of the lung parenchyma and defects, therefore, affect pulmonary function. More awareness is needed among physicians about pulmonary complications in Osteogenesis Imperfecta to develop novel concepts on clinical and diagnostic assessment of pulmonary functional disorders.
•We study stationary and parallel buoyant flow in a vertical annular porous passage.•The vertical cylindrical boundaries are considered both isothermal and permeable.•Transition to convective ...instability is due to the basic radial temperature gradient.•The linear dynamics of the perturbed flow is formulated as an eigenvalue problem.•The system becomes more an more unstable as the aspect ratio increases.
The basic stationary buoyant flow in a vertical annular porous passage induced by a boundary temperature difference is investigated. The vertical cylindrical boundaries are considered both isothermal and permeable to external fluid reservoirs. There exists a stationary parallel velocity field with a zero flow rate and pure conduction heat transfer. Its linear stability is analysed with normal mode perturbations of the pressure and temperature fields. The transition to convective instability is caused by the basic horizontal temperature gradient. Hence, its nature differs from that of the usual Rayleigh–Bénard instability. The linear dynamics of the perturbed flow is formulated as an eigenvalue problem, solved numerically. Its solution provides the neutral stability curve at each fixed aspect ratio between the external radius and the internal radius. The critical Rayleigh number triggering the instability is evaluated for different aspect ratios. It is shown that the system becomes more an more unstable as the aspect ratio increases, with the critical Rayleigh number dropping to zero when the aspect ratio tends to infinity.
Osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive syndrome characterized by juvenile-onset osteoporosis and ocular abnormalities due to a low-density lipoprotein ...receptor-related protein 5 (LRP5) gene mutation. Treatment with bisphosphonates, particularly with pamidronate and risedronate, has been reported to be of some efficacy in this condition. We report on a patient with OPPG due to an LRP5 gene mutation, who showed an encouraging response after a 36-month period of neridronate therapy. We report a case of a patient treated with bisphosphonates. Bisphosphonates should be administered in OPPG patients as a first-line therapy during early childhood.
Abstract
The combined forced and free convection flow of a Newtonian fluid in a horizontal plane-parallel channel is examined. The boundary walls are considered as adiabatic, so that the only thermal ...effect acting in the fluid is the viscous dissipation due to the nonzero shear flow. As the shear flow may be caused by either an imposed horizontal pressure gradient or an imposed velocity difference between the bounding walls, one may envisage two scenarios where the stationary basic flow is Poiseuille-like or Couette-like, respectively. Both cases are surveyed with a special focus on practically significant cases where the Gebhart number is considered as very small, though nonzero. Furthermore, the Prandtl number is assumed as extremely large, thus pinpointing a scenario of creeping buoyant flow with a fluid having a very large viscosity. Within such a framework, the instability of the basic flow is analysed versus small-amplitude perturbations.
Summary
This study evaluates serum creatine kinase isoenzyme activity in children with osteogenesis imperfecta to determine its usefulness as a biochemical marker during treatment with ...bisphosphonate. The changes of creatine kinase (CK) isoenzyme activity during and after discontinuation therapy were observed. These results could be useful in addressing over-treatment risk prevention.
Introduction
The brain isoenzyme of creatine kinase (CKbb) is highly expressed in mature osteoclasts during osteoclastogenesis, thus plays an important role in bone resorption. We previously identified high serum CKbb levels in 18 children with osteogenesis imperfect (OI) type 1 treated for 1 year with bisphosphonate (neridronate). In the present study, serum CK isoenzymes were evaluated in the same children with continuous versus discontinued neridronate treatment over a further 2-year follow-up period.
Methods
This study included 18 children with OI type 1, 12 with continued (group A) and 6 with ceased (group B) neridronate treatment. Auxological data, serum biochemical markers of bone metabolism, bone mineral density z-score, and serum total CK and isoenzyme activities were determined in both groups.
Results
Serum CKbb was progressively and significantly increased in group A (
p
< 0.004) but rapidly decreased to undetectable levels in group B. In both groups, the cardiac muscle creatine kinase isoenzyme (CKmb) showed a marked decrease, while serum C-terminal telopeptide (CTx) levels were almost unchanged.
Conclusions
This study provides evidence of the cumulative effect of neridronate administration in increasing serum CKbb levels and the reversible effect after its discontinuation. This approach could be employed for verifying the usefulness of serum CKbb as a biochemical marker in patients receiving prolonged bisphosphonate treatment. Moreover, the decreased serum CKmb levels suggest a systemic effect of these drugs.
We present an investigation on the onset of Darcy–Bénard instability in a two-dimensional porous medium saturated with a non-Newtonian fluid and heated from below in the presence of a uniform ...horizontal pressure gradient. The fluid is taken to be of power-law nature with constant rheological index
$n$
and temperature-dependent consistency index
$\unicodeSTIX{x1D707}^{\ast }$
. A two-dimensional linear stability analysis in the vertical plane yields the critical wavenumber and the generalised critical Rayleigh number as functions of dimensionless problem parameters, with a non-monotonic dependence from
$n$
and with maxima/minima at given values of
$\unicodeSTIX{x1D6FE}$
, a parameter representing the effects of consistency index variations due to temperature. A series of experiments are conducted in a Hele-Shaw cell of aspect ratio
$H/b=13.3{-}20$
to provide a verification of the theory. Xanthan Gum mixtures (nominal concentration from 0.10 % to 0.20 %) are employed as working fluids with a parameter range
$n=0.55{-}0.72$
and
$\unicodeSTIX{x1D707}_{0}^{\ast }=0.02{-}0.10~\text{Pa}~\text{s}^{n}$
. The experimental critical wavenumber corresponding to incipient instability of the convective cells is derived via image analysis for different values of the imposed horizontal velocity. Theoretical results for critical wavenumber favourably compare with experiments, systematically underestimating their experimental counterparts by 10 % at most. The discrepancy between experiments and theory is more relevant for the critical Rayleigh number, with theory overestimating the experiments by a maximum factor less than two. Discrepancies are attributable to a combination of factors: nonlinear phenomena, possible subcritical bifurcations, and unaccounted-for disturbing effects such as approximations in the rheological model, wall slip, ageing and degradation of the fluid properties.
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