Evaluation of wearing comfort of dust masks.

Dust masks are widely used to prevent the inhalation of particulate matter into the human respiratory organs in polluted air environments. The filter of a dust mask inherently obstructs the natural respiratory air flows, and this flow resistance is mainly responsible for the discomfort experienced when wearing a dust mask. In atmospheric conditions seriously contaminated with fine dust, it is recommended that common citizens wear a dust mask in their everyday lives, yet many people are reluctant to wear a dust mask owing to the discomfort experienced when wearing it for a long time. Understanding of physical reasons for the discomfort is thus crucial in designing a dust mask, but remains far from clear. This study presents a technique to quantify the wearing comfort of dust masks. By developing a respiration simulator to measure the pressure loss across a dust mask, we assessed the energy costs to overcome flow resistance when breathing through various types of dust masks. The energy cost for a single inhalation varies with the mask type in a range between 0 and 10 mJ. We compared the results with the survey results of 40 people about the wearing comfort of the dust masks, which revealed that the wearing comfort crucially depends on the energy cost required for air inhalation though the dust mask. Using the measured energy cost during inhalation as a parameter to quantify the wearing comfort, we present a comprehensive evaluation of the performance of dust masks in terms of not only the filtering performance but also the wearing comfort. Our study suggests some design principles for dust mask filters, auxiliary electric fans, and check valves.

Basilar artery angulation in association with aging and pontine lacunar infarction: a multicenter observational study.

AIM: Deep pontine lacunar infarction (DPLI) not involving the basal pial surface of the medial part of the pons, is known to be a small vessel disease in the territory of the basilar artery (BA). In the present study, we examined whether morphological features of the BA differ in individuals with an advanced age and may be associated with DPLI. METHODS: This study included 338 healthy subjects and 78 patients with DPLI treated at the stroke centers of three university hospitals in Korea. Time-Of-Flight magnetic resonance angiographic images were transported to a central lab and analyzed blind to obtain the clinical data. For the quantitative analysis, the BA was projected two-dimensionally in the anteroposterior and lateral views and perceived as triangles of the vertebrobasilar junction, angulation point and BA division. The angles and triangular areas were summated into angulation indexes and used to quantify the degree of BA tortuosity. RESULTS: The BA showed a more acute angle at the angulation point in the elderly patients than in the healthy subjects. Compared to the healthy subjects, the DPLI patients exhibited significantly larger angles at the vertebrobasilar junction, in addition to the acute angles noted at the angulation point. A unit increase in the BA angle indexes at the vertebrobasilar junction and angulation points for DPLI was found to have an odds ratio of 1.15 (95% confidence interval, 1.05-1.26) and 0.95 (95% CI, 0.91-0.99), respectively, even after adjusting for potential confounders. CONCLUSIONS: The angulation point of the BA becomes more acute in elderly individuals. In this study, the vertebrobasilar junction showed a larger angle in the patients with DPLI than in the healthy controls.

Geometric analysis and blood flow simulation of basilar artery.

AIM: The aim of this study was to find a region of low wall shear stress (WSS) in a basilar artery using 3-dimensional (3D) geometric analysis and blood flow simulation. METHODS: A 61-year-old patient who underwent follow-up time-of-flight magnetic resonance angiography (TOF-MRA) of the brain was recruited as the subject of the present study. In the basilar artery, the angle of the directional vector was calculated for the region of low WSS. The subject's 3D arterial geometry and blood flow velocity from a transcranial Doppler examination were used for a blood flow simulation study. The regions of low WSS identified by both geometric analysis and blood flow simulation were compared, and these methods were repeated for the basilar arteries of various geometries from other patients. RESULTS: Two distinct arterial angulations along the basilar artery were identified: lateral and anterior angulations on the anteroposterior and lateral TOF-MR views, respectively. A low WSS region was observed in the distal portion along the inner curvatures of both angulations in the basilar artery. The directional vectors of the region of low WSS calculated by geometric analysis and blood flow simulation were very similar (correlation coefficient= 0.996, p < 0.001). Follow-up MRA confirmed the progression of plaque in the region of low WSS. CONCLUSION: Detailed geometric analysis and blood flow simulation of the basilar artery identified lateral and anterior angulations which determined the low WSS region in the distal portion along the inner curvatures of the angulations.

Blood flow velocities of cerebral arteries in lacunar infarction and other ischemic strokes.

Blood flow velocity is an important determinant of vascular hemodynamics. The aim of the present study was to determine the mean flow velocities (MFVs) of cerebral arteries in patients with ischemic stroke, comparing lacunar and nonlacunar infarctions. 388 consecutive patients were examined for lacunar infarction, other subtypes of ischemic stroke, and the presence of underlying internal carotid artery steno-occlusion (ICS). MFVs were measured using transcranial Doppler along the full segments of each cerebral artery including both right and left middle cerebral arteries, basilar artery, and both of the vertebral arteries. The patients were categorized into two major groups: lacunar infarction, and nonlacunar infarction with or without underlying ICS. The characteristics of patients with lacunar infarction (n=83, 21.4%) were significantly different from those with nonlacunar infarctions: younger age, lower prevalence of type 2 diabetes, and lower concentration of plasma total homocysteine. The patients with lacunar infarction had lower MFVs in cerebral arteries than the patients with nonlacunar infarctions, especially in the posterior circulation vessels such as the basilar artery and both vertebral arteries. Different hemodynamics might be pathophysiologically associated with the lacunar infarction, compared with the other subtypes of ischemic stroke.

Competitive entry of sodium and potassium into nanoscale pores.

We have studied the competitive entry of potassium and sodium into carbon nanotubes using molecular dynamics simulations. Our results demonstrate how a combination of strong sodium hydration coupled with strong potassium-chlorine interaction leads to enhanced potassium selectivity at certain diameters. We detail the reasons behind this, and show how variation of nanotube diameter can cause a switch to sodium selectivity, or even cause a decrease in overall ion entry despite an increase in diameter. These results demonstrate the importance of considering inter-ion dependence in the theoretical study of pore selectivity and show that, with careful design, the practical separation of sodium and potassium is possible using diameter variation alone.