Pressure-flow relationships measured in human plastinated specimen of both nasal cavities and maxillary sinuses were compared to those obtained by numerical airflow simulations in a numerical three-dimensional reconstruction issued from CT scans of the plastinated specimen. For experiments, flow rates up to 1,500 ml/s were tested using three different gases: HeO(2), Air, and SF(6). Numerical inspiratory airflow simulations were performed for flow rates up to 353 ml/s in both the nostrils using a finite-volume-based method under steady-state conditions with CFD software using a laminar model. The good agreement between measured and numerically computed total pressure drops observed up to a flow rate of 250 ml/s is an important step to validate the ability of CFD software to describe flow in a physiologically realistic binasal model. The major total pressure drop was localized in the nasal valve region. Airflow was found to be predominant in the inferior median part of nasal cavities. Two main vortices were observed downstream from the nasal valve and toward the olfactory region. In the future, CFD software will be a useful tool for the clinician by providing a better understanding of the complexity of three-dimensional breathing flow in the nasal cavities allowing more appropriate management of the patient's symptoms.

We have developed a discrete multisegmental model describing the coupling between inspiratory flow and nasal wall distensibility. This model is composed of 14 individualized compliant elements, each with its own relationship between cross-sectional area and transmural pressure. Conceptually, this model is based on flow limitation induced by the narrowing of duct due to collapsing pressure. For a given inspiratory pressure and for a given compliance distribution, this model predicts the area profile and inspiratory flow. Acoustic rhinometry and posterior rhinomanometry were used to determine the initial geometric area and mechanical characteristics of each element. The proposed model, used under steady-state conditions, is able to simulate the pressure-flow relationship observed in vivo under normal conditions (4 subjects) and under pathological conditions (4 vasomotor rhinitis and 3 valve syndrome subjects). Our results suggest that nasal wall compliance is an essential parameter to understand the nasal inspiratory flow limitation phenomenon and the associated increase of resistance that is well known to physiologists. By predicting the functional pressure-flow relationship, this model could be a useful tool for the clinician to evaluate the potential effects of treatments.

This paper describes a technique that combines radial MRI and phase contrast (PC) to map the velocities of hyperpolarized gases ( 3 He) in respiratory airways. The method was evaluated on well known geometries (straight and U-shaped pipes) before it was applied in vivo. Dynamic 2D maps of the three velocity components were obtained from a 10-mm slice with an in-plane spatial resolution of 1.6 mm within 1 s. Integration of the in vitro throughplane velocity over the slice matched the input flow within a relative precision of 6.4%. As expected for the given Reynolds number, a parabolic velocity profile was obtained in the straight pipe. In the U-shaped pipe the three velocity components were measured and compared to a fluid-dynamics simulation so the precision was evaluated as fine as 0.025 m s ؊1. Ventilation and particle-deposition studies are important parts of functional and physiological explorations of the lungs. Normal or altered geometries of the bronchial tree directly affect airflow distributions in the lungs (1). Particle deposition is involved in inhalation toxicology, and its study is motivated to achieve a better understanding of its effects and devise new therapies based on drug inhalation (2,3). Knowledge of flow patterns in large tracheobronchial airways is required to understand flow distribution, gas mixing, and inhaled particle deposition.Several experimental and numerical studies have focused on the velocity patterns in large airways. Experimentally, velocity fields in various airway models were obtained with the available techniques for measuring gas velocity, including hot-wire anemometry, laser Doppler anemometry, and particle-image velocimetry (4 -6). Numerical simulations were also performed with computational fluid dynamics (CFD) (2,6 -8). Both approaches independently yielded basic results that led to a better understanding of gas-flow dynamics in the bronchi. However, in vivo, functional respiratory tests provide only global information on the airflow, and some invasive techniques introduce sensors to probe flow properties locally but only at a few specific points (9). Nevertheless, noninvasive direct measurements of gas velocities have never been obtained in living subjects, since none of the abovecited measurement techniques are able to do so.Recently it was shown that ventilation dynamics in the lungs of small animals and humans can be monitored by hyperpolarized (HP) gas MRI (10) using EPI (11), fast gradient-echo (12), spiral (13,14), or radial sequences (15,16). However, quantifying the gas-flow rate from signal dynamics is not straightforward because it is difficult to separate flip angle and inflow effects (12,(17)(18)(19). Moreover, additional signal losses result from oxygen-dependent longitudinal relaxation times that become relevant over long acquisition times (20), and from short effective transverse relaxation times, while the gas diffuses through the magnetic field gradients within the airways (21,22).In proton MRI, phase contrast (PC) has been widely used to map blood v...

Nasal compliance is a measure related to the blood volume in the nasal mucosa. The objective of this study was to better understand the vascular response in vasomotor rhinitis by measuring nasal cross-sectional area and nasal compliance before and after mucosal decongestion in 10 patients with vasomotor rhinitis compared with 10 healthy subjects. Nasal compliance was inferred by measuring nasal area by acoustic rhinometry at pressures ranging from atmospheric pressure to a negative pressure of -10 cmH2O. Mucosal decongestion was obtained with one puff per nostril of 0.05% oxymetazoline. At atmospheric pressure, nasal cross-sectional areas were similar in the vasomotor rhinitis group and the healthy subject group. Mucosal decongestion did not induce any decrease of nasal compliance in patients with vasomotor rhinitis in contrast with healthy subjects. Our results support the hypothesis, already proposed, of an autonomic dysfunction based on a paradoxical response of the nasal mucosa in vasomotor rhinitis. Moreover, the clearly different behavior between healthy subjects and vasomotor rhinitis subjects suggests that nasal compliance measurement may therefore represent a potential line of research to develop a diagnostic tool for vasomotor rhinitis, which remains a diagnosis of exclusion.