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Maximal Flow (maximal + flow)

Distribution by Scientific Domains

Medical Sciences	60%

Selected Abstracts

Maximizing residual flow under an arc destruction

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2001
Y. P. Aneja
Abstract In this paper, we consider two problems related to single-commodity flows on a directed network. In the first problem, for a given s , t flow, if an arc is destroyed, all the flow that is passing through that arc is destroyed. What is left flowing from s to t is the residual flow. The objective is to determine a flow pattern such that the residual flow is maximized. We provide a strongly polynomial algorithm for this problem, called the maximum residual flow problem, and consider various extensions of this basic model. In the second problem, known as the "most vital arc" problem, the objective is to remove an arc so that the maximal flow on the residual network is as small as possible. Results are also derived which help implement an efficient scheme for solving this problem. © 2001 John Wiley & Sons, Inc. [source]

Lung Function Tests in Neonates and Infants with Chronic Lung Disease: Forced Expiratory Maneuvers

PEDIATRIC PULMONOLOGY, Issue 3 2006
Sooky Lum PhD
Abstract This fourth paper in a review series on the role of lung function testing in infants and young children with acute neonatal disorders and chronic lung disease of infancy (CLDI) addresses measurements of forced expiration using rapid thoraco-abdominal compression (RTC) techniques and the forced deflation technique. Following orientation of the reader to the subject area, we focus our comments on the areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. All studies on infants and young children with CLDI using forced expiratory or deflation maneuvers demonstrated that forced flows at low lung volume remain persistently low through the first 3 years of life. Measurement of maximal flow at functional residual capacity (V,maxFRC) is the most commonly used method for assessing airway function in infants, but is highly dependent on lung volume and airway tone. Recent studies suggested that the raised volume RTC technique, which assesses lung function over an extended volume range as in older children, may be a more sensitive means of discriminating changes in airway function in infants with respiratory disease. The forced deflation technique allows investigation of pulmonary function during the early development of CLDI in intubated subjects, but its invasive nature precludes its use in the routine setting. For all techniques, there is an urgent need to establish suitable reference data and evaluate within- and between-occasion repeatability, prior to establishing the clinical usefulness of these techniques in assessing baseline airway function and/or response to interventions in subjects with CLDI. Pediatr Pulmonol. © 2005 Wiley-Liss, Inc. [source]

Association of tobacco smoke exposure and respiratory syncitial virus infection with airways reactivity in early childhood

PEDIATRIC PULMONOLOGY, Issue 6 2001
Alan Adler MD
Abstract Exposure to infectious agents and environmental tobacco smoke are thought to induce bronchial hyperresponsiveness (BHR). This study was undertaken to determine the effects of passive exposure to tobacco smoke and respiratory syncitial virus (RSV) lower respiratory infection (LRI) during infancy on the occurrence of BHR in the first 2 years of life. Eighty-six cases of documented RSV (mean age, 188 days) and 78 controls (mean age, 162 days) were enrolled from the clinic and in-patient service of a single hospital. None had a history of prior LRI. Subjects were studied at 6-month intervals up to 19 months of age with a standardized respiratory illness and parental smoking questionnaire, partial expiratory flow-volume curves by the "hug" (rapid thoracic compression) technique, and methacholine challenge. Exposure to maternal and paternal cigarette smoking, maternal history of asthma, and mold exposure were associated with decreased levels of length-corrected maximal flow at functional residual capacity (V,maxFRC). RSV-LRI was not related to V,maxFRC. After adjustment of V,maxFRC for these factors, V,maxFRC was a significantly and positively correlated with a methacholine concentration provoking a 40% fall in V,maxFRC (PC40) and negatively correlated with dose-response slope. After adjustment for V,maxFRC, there were no independent effects of tobacco smoke exposure or RSV-LRI on methacholine responses. These data do not support a role for RSV as a risk factor for airways reactivity in childhood and indicate that exposure to tobacco smoke affects airways reactivity through its effects on airways. Pediatr Pulmonol. 2001; 32:418,427. © 2001 Wiley-Liss, Inc. [source]

Flow,volume curve changes in patients with obstructive sleep apnoea and brief upper airway dysfunction

RESPIROLOGY, Issue 1 2000
Alastair H Campbell
Objective: Patients with obstructive sleep apnoea (OSA) and those with brief upper airway dysfunction (BUAD) have been reported to have abnormalities of maximal flow,volume curves. This study was designed to assess the ability of flow,volume curves to predict the presence of OSA or BUAD. Methodology: Four maximal flow,volume manoeuvres performed by 33 OSA patients and 16 BUAD patients were compared with those of 36 normal subjects. Flow,volume indices, their variability, saw-toothing in the curve and an algorithm based on the flow ratios and shape of the curves were assessed. Results: When the confounding factors, body mass index (BMI), age, gender and smoking status were taken into account, there was no significant difference in a variety of indices derived from the flow,volume curves between OSA and normal subjects. No BUAD patient had normal flow,volume curves as determined with the algorithm. After BMI, age, gender and smoking status were accounted for, decreased forced expiratory volume in 1 s (FEV1), and increased variability of peak expiratory flow (PEF)/peak inspiratory flow (PIF) and FEV1/PEF remained significantly associated with BUAD. Conclusions: These findings suggest that flow,volume curve indices have no value in predicting OSA. Some abnormalities are found in patients with BUAD; a normal flow,volume curve makes the diagnosis of BUAD unlikely. [source]

Human cutaneous reactive hyperaemia: role of BKCa channels and sensory nerves

THE JOURNAL OF PHYSIOLOGY, Issue 1 2007
Santiago Lorenzo
Reactive hyperaemia is the increase in blood flow following arterial occlusion. The exact mechanisms mediating this response in skin are not fully understood. The purpose of this study was to investigate the individual and combined contributions of (1) sensory nerves and large-conductance calcium activated potassium (BKCa) channels, and (2) nitric oxide (NO) and prostanoids to cutaneous reactive hyperaemia. Laser-Doppler flowmetry was used to measure skin blood flow in a total of 18 subjects. Peak blood flow (BF) was defined as the highest blood flow value after release of the pressure cuff. Total hyperaemic response was calculated by taking the area under the curve (AUC) of the hyperaemic response minus baseline. Infusates were perfused through forearm skin using microdialysis in four sites. In the sensory nerve/BKCa protocol: (1) EMLA® cream (EMLA, applied topically to skin surface), (2) tetraethylammonium (TEA), (3) EMLA®+ TEA (Combo), and (4) Ringer solution (Control). In the prostanoid/NO protocol: (1) ketorolac (Keto), (2) NG -nitro- l -arginine methyl ester (l -NAME), (3) Keto +l -NAME (Combo), and (4) Ringer solution (Control). CVC was calculated as flux/mean arterial pressure and normalized to maximal flow. Hyperaemic responses in Control (1389 ± 794%CVCmax s) were significantly greater compared to TEA, EMLA and Combo sites (TEA, 630 ± 512, P= 0.003; EMLA, 421 ± 216, P < 0.001; Combo, 201 ± 200, P < 0.001%CVCmax s). Furthermore, AUC in Combo (Keto +l -NAME) site was significantly greater than Control (4109 ± 2777 versus 1295 ± 368%CVCmax s). These data suggest (1) sensory nerves and BKCa channels play major roles in the EDHF component of reactive hyperaemia and appear to work partly independent of each other, and (2) the COX pathway does not appear to have a vasodilatory role in cutaneous reactive hyperaemia. [source]