Dynamics of hydrocephalus: a physical approach

“To sleep”, “to cough” and “to love’: Uncommon primary headaches

IntroductionThere are some physiological situations in which the individual may experience headache, such as to sleep, to cough and to love. In the first situation, "to sleep", the patient does not have headache when awake, but is awakened by pain during sleep; in the second, the act of "to cough" is a trigger for the onset of pain and finally, "to love," here, meaning sexual intercourse, can be a headache trigger.ObjectiveTo review the epidemiological, pathophysiological aspects and therapeutic management of headaches that arise when sleeping, coughing and having sexual intercourse.MethodA narrative review of literature including case reports and clinical trials were carried out. The articles were systematically obtained and assessed by the authors.ResultsThree primary forms considered rare were identified: hypnic headache, primary cough headache and primary headache associated with sexual activity. Hypnic headache occurs only during sleep, predominantly in women after 50 years of age. It was described in 1988 by Raskin, and has a prevalence ranging from 0.07% to 0.22%. Primary cough headache is triggered by coughing or another Valsalva maneuver and is more common in men over40 years of age. It was first described by Jules Tinel and has a prevalence of 0.4% to 1.2%. Primary headache associated with sexual activity occurs during sexual intercourse. It is more frequent in men after 40 years of age. It was described in the second century of the Christian era, by the Persian physician Avicenna. Its prevalence ranges from 0.9% to 1.6%.ConclusionPrimary headaches in the "to sleep", "to cough", and "to love" group are rare. They predominate in men, after 40 years of age, are of short duration, can be primary or secondary and have a therapeutic response to indomethacin.

Translating the Low Translaminar Cribrosa Pressure Gradient Hypothesis into the Clinical Care of Glaucoma

Glaucoma is an optic neuropathy with multiple known risk factors, including age, race, family history, and intraocular pressure. Unfortunately, the only currently modifiable risk factor in treating the disease is intraocular pressure (IOP). Recent studies have investigated intracranial pressure (ICP) and the translaminar cribrosa pressure gradient as a potential explanation for glaucomatous optic nerve vulnerability across a range of IOP values. The difference between these two pressures across the lamina cribrosa may have an effect on the optic nerve, which could provide another modifiable parameter in the battle against glaucoma. In order for modification of the translaminar pressure gradient to be considered in the treatment of glaucoma, noninvasive methods to accurately measure ICP need to be developed. The translaminar pressure gradient could be therapeutically adjusted by either further lowering the IOP or raising the ICP when it is pathologically low, if possible.

Dual-porosity poroviscoelasticity and quantitative hydromechanical characterization of the brain tissue with experimental hydrocephalus data

Hydromechanical brain models often involve constitutive relations which must account for soft tissue deformation and creep, together with the interstitial fluid movement and exchange through capillaries. The interaction of rather unknown mechanisms which produce, absorb, and circulate the cerebrospinal fluid within the central nervous system can further add to their complexity. Once proper models for these phenomena or processes are selected, estimation of the associated parameters could be even more challenging. This paper presents the results of a consistent, coupled poroviscoelastic modeling and characterization of the brain tissue as a dual-porosity system. The model draws from Biot's theory of poroviscoelasticity, and adopts the generalized Kelvin's rheological description of the viscoelastic tissue behavior. While the interstitial space serves as the primary porosity through which the bulk flow of the interstitial fluid occurs, a secondary porosity network comprising the capillaries and venous system allows for its partial absorption into the blood. The correspondence principle is used in deriving a time-dependent analytical solution to the proposed model. It allows for identical poroelastic formulation of the original poroviscoelastic problem in the Laplace transform space. Hydrocephalus generally refers to a class of medical conditions which share the ventricles enlargement as a common feature. A set of published data from induced hydrocephalus and follow-up perfusion of cats' brains is used for quantitative characterization of the proposed model. A selected portion of these data including the ventricular volume and rate of fluid absorption from the perfused brain, together with the forward model solution, is utilized via an inverse problem technique to find proper estimations of the model parameters. Results show significant improvement in model predictions of the experimental data. The convoluted and coupled solution results are presented through the time-dependent plots of the ventricular volume undergoing the perfusion experiment. The plots demonstrate the intricate interplay of viscous and poroelastic diffusive time scales, and their competition in reaching the steady state response of the system.