PubMed Health⌕ Search

Biomedical subjects

K Behbehani

Publications and source records attributed to K Behbehani.

At least 19 recordsLinked to original sources
PubMed2001

Dynamic regulation of heart rate during acute hypotension: new insight into baroreflex function.

UNLABELLED: To examine the dynamic properties of baroreflex function, we measured beat-to-beat changes in arterial blood pressure (ABP) and heart rate (HR) during acute hypotension induced by thigh cuff deflation in 10 healthy subjects under supine resting conditions and during progressive lower body negative pressure (LBNP). The quantitative, temporal relationship between ABP and HR was fitted by a second-order autoregressive (AR) model. The frequency response was evaluated by transfer function analysis. RESULTS: HR changes during acute hypotension appear to be controlled by an ABP error signal between baseline and induced hypotension. The quantitative relationship between changes in ABP and HR is characterized by a second-order AR model with a pure time delay of 0.75 s containing low-pass filter properties. During LBNP, the change in HR/change in ABP during induced hypotension significantly decreased, as did the numerator coefficients of the AR model and transfer function gain. CONCLUSIONS: 1) Beat-to-beat HR responses to dynamic changes in ABP may be controlled by an error signal rather than directional changes in pressure, suggesting a "set point" mechanism in short-term ABP control. 2) The quantitative relationship between dynamic changes in ABP and HR can be described by a second-order AR model with a pure time delay. 3) The ability of the baroreflex to evoke a HR response to transient changes in pressure was reduced during LBNP, which was due primarily to a reduction of the static gain of the baroreflex.

Acute Disease↗
PubMed1998

A sleep laboratory evaluation of an automatic positive airway pressure system for treatment of obstructive sleep apnea.

STUDY OBJECTIVES: This paper compares the performance of an experimental nasal positive airway pressure device that automatically adjusts the level of applied pressure (APAP) with the performance of a conventional continuous positive airway pressure (CPAP) in a sleep laboratory study. DESIGN: In a randomized sequence, conventional CPAP therapy was applied for 1 night (CPAP night) and APAP therapy the following night (APAP night). SETTING: The study was conducted in an accredited sleep disorders center. PATIENTS OR PARTICIPANTS: Twenty-six men and 5 women between the ages of 35 to 73 (51 +/- 9.6) years with body mass index 35.82 +/- 8.35 (kg/m2) who were diagnosed (using standard nocturnal polysomnography [NPSG] methods) as having OSA syndrome were studied. The subjects were treated with conventional CPAP for approximately 8 (7.79 +/- 3.16) weeks at home prior to their participation in this study. MEASUREMENTS AND RESULTS: All standard polysomnography data and nasal mask pressures were recorded using a computer-based data acquisition system. Sleep and respiratory data were scored by a registered polysomnographer. The mean apnea-hypopnea index (AHI) for subjects for the NPSG night was 55.2 +/- 33.7. It dropped to 4.2 +/- 3.8 for the CPAP night and to 5.4 +/- 5.4 for the APAP night. There was no significant (p = 0.05) difference between mean AHI indices, sleep stages, sleep stage shifts, and snore arousals for CPAP night and APAP night. However, all the measures showed significant (p = 0.05) improvement over NPSG night. The mean of APAP applied pressure (8.4 +/- 3.3 cm H2O) was significantly (p = 0.05) lower than the prescribed pressure (11.5 +/- 3.1 cm H2O), but there was no significant (p = 0.05) difference between the maximum APAP applied pressure (12.8 +/- 4.3 cm H2O) and the prescribed pressure (11.5 +/- 3.1 cm H2O). All mean comparison tests were carried out using two-tailed statistics. CONCLUSIONS: APAP appears to be as effective as CPAP in treating OSA patients. APAP delivers the same level of therapy as CPAP, but it reduces the average airway pressure while providing needed peak pressures.

Adult↗
PubMed1998

In vivo evaluation of a closed loop monitoring strategy for induced paralysis.

OBJECTIVE: Reliable closed loop infusion systems for regulating paralysis level can be a great convenience to the anesthesiologists in automating their task. This paper describes the in vivo performance evaluation of a self-tuning controller that is designed to accommodate large variations in patient drug sensitivity, drug action delays and environmental interfering noise. METHODS: The infusion system was evaluated in six adult mongrel dogs. Following the manual induction of paralysis by an anesthesiologist, the controller regulated the infusion of vecuronium to maintain a desired level of paralysis. The integrated EMG response of the hypothenar muscle to a train-of-four stimulation of the ulnar nerve quantified the depth of paralysis. The controller's robustness was tested by contaminating the sensed twitch signal with electrocautery noise and electrode disconnection. RESULTS: The controller reached the initial level of paralysis of 100% in about 4.0 minutes and arrived at the desired level of 90% with an overshoot of 6.38% (+/-6.82). It maintained the desired level of paralysis with a 2.04% (+/-1.20) mean offset at 90% and 0.4% (+/-0.5) mean offset at 80% steady state level, respectively. The mean infusion rate to sustain 90% and 80% paralysis were 2.70 (+/-2.05) and 2.15 (+/-2.57) ((mg/kg)/min), respectively. CONCLUSIONS: The system adapted to a large variation in the sample subject drug sensitivity. It remained stable despite large amplitude disturbances and maintained the paralysis at the desired level following the removal of the disturbances.

Animals↗
PubMed1998

Candidate parasitic diseases.

This paper discusses five parasitic diseases: American trypanosomiasis (Chagas disease), dracunculiasis, lymphatic filariasis, onchocerciasis and schistosomiasis. The available technology and health infrastructures in developing countries permit the eradication of dracunculiasis and the elimination of lymphatic filariasis due to Wuchereria bancrofti. Blindness due to onchocerciasis and transmission of this disease will be prevented in eleven West African countries; transmission of Chagas disease will be interrupted. A well-coordinated international effort is required to ensure that scarce resources are not wasted, efforts are not duplicated, and planned national programmes are well supported.

Africa↗
PubMed1998

Efficacy and safety of liposomal amphotericin B (AmBisome) for visceral leishmaniasis in endemic developing countries.

Reported are the results of a study to determine the efficacy and safety of liposomal amphotericin B (AmBisome) for treating visceral leishmaniasis (kala-azar) in several developing countries where the disease is endemic (Brazil, India, and Kenya). At each study site, sequential cohorts of 10 patients each were treated with AmBisome at a dose of 2 mg.kg-1.day-1 (2 MKD). The first cohort received regimen 1:2 MKD on days 1-6 and day 10 (total dose: 14 mg/kg). If the efficacy with this regimen was satisfactory, a second cohort received regimen 2:2 MKD on days 1-4 and 10 (total dose: 10 mg/kg); and a third cohort received regimen 3:2 MKD on days 1, 5, and 10 (total dose: 6 mg/kg). In India, regimens 1, 2, and 3 (which were studied concurrently) each cured 100% of 10 patients. In Kenya, regimen 1 cured all 10 patients, regimen 2 cured 90% of 10 patients, but regimen 3 cured only 20% of 5 patients. In Brazil, regimen 1 was only partially curative: 5 of 13 patients (62%). Therefore, 15 patients were administered regimen 4 (2 MKD for 10 consecutive days; total dose, 20 mg/kg) and 13 patients were cured (83%). These results suggest that for the treatment of kala-azar the following doses of AmBisome should be administered: in India and Kenya, 2 mg/kg on days 1-4 and day 10; and in Brazil, 2 mg/kg on days 1-10.

Adolescent↗
PubMed1997

Pharyngeal wall vibration detection using an artificial neural network.

An artificial-neural-network-based detector of pharyngeal wall vibration (PWV) is presented. PWV signals the imminent occurrence of obstructive sleep apnoea (OSA) in adults who suffer from OSA syndrome. Automated detection of PWV is very important in enhancing continuous positive airway pressure (CPAP) therapy by allowing automatic adjustment of the applied airway pressure by a procedure called automatic positive airway pressure (APAP) therapy. A network with 15 inputs, one output, and two hidden layers, each with two Adaline-nodes, is used as part of a PWV detection scheme. The network is initially trained using nasal mask pressure data from five positively diagnosed OSA patients. The performance of the ANN-based detector is evaluated using data from five different OSA patients. The results show that on the average it correctly detects the presence of PWV events at a rate of approximately 92% and correctly distinguishes normal breaths approximately 98% of the time. Further, the ANN-based detector accuracy is not affected by the pressure level required for therapy.

Adult↗
PubMed1997

Control of schistosomiasis--a global picture.

The control of schistosomiasis has been a challenging task for most endemic countries. Thus, despite the concerted efforts to date, schistosomiasis remains a major public health concern, second only to malaria in the tropics and subtropics. In this review, Lorenzo Savioli and colleagues highlight changes in schistosomiasis prevalence and distribution over the past decades, discuss the success and limitations of the various control strategies, and present possible control initiatives for the future.

Journal Article↗
PubMed1997

A noninvasive technique for detecting obstructive and central sleep apnea.

A new noninvasive method to detect obstructive and central sleep apnea [(OSA) and (CSA)] events is described. Data were collected from ten volunteer subjects with a previous diagnosis of OSA while they were titrated for continuous positive airway pressure (CPAP) therapy. Apneic events were identify by analyzing of estimated airway impedance determined from pressure and airflow signals delivered from CPAP. To enhance performance of this technique, a single-frequency (5 Hz with 0.5 cmH2O peak-to-peak amplitude) probing signal was superimposed on the applied CPAP pressure. The results indicated that estimated airway impedance during OSA (mean: 17.9, SD: 3.4, N = 50) was significantly higher then during CSA (mean: 4.1, SD: 1.7, N = 50). When the estimated impedance of OSA and CSA events were compared to a fixed threshold, 100% of all events can be correctly categorized. These results indicate that it may be possible to diagnose OSA and CSA noninvasively based upon this technique. The instrument and the algorithm required are relatively simple and can be incorporated in a home-based device. If this method was used for prescreening apnea patients, it could reduce cost, waiting time, and discomfort associated with traditional diagnostic procedures.

Airway Resistance↗
PubMed1997

Strategies and tools for the control/elimination of lymphatic filariasis.

Lymphatic filariasis infects 120 million people in 73 countries worldwide and continues to be a worsening problem, especially in Africa and the Indian subcontinent. Elephantiasis, lymphoedema, and genital pathology afflict 44 million men, women and children; another 76 million have parasites in their blood and hidden internal damage to their lymphatic and renal systems. In the past, tools and strategies for the control of the condition were inadequate, but over the last 10 years dramatic research advances have led to new understanding about the severity and impact of the disease, new diagnostic and monitoring tools, and, most importantly, new treatment tools and control strategies. The new strategy aims both at transmission control through community-wide (mass) treatment programmes and at disease control through individual patient management. Annual single-dose co-administration of two drugs (ivermectin + diethylcarbamazine (DEC) or albendazole) reduces blood microfilariae by 99% for a full year; even a single dose of one drug (ivermectin or DEC) administered annually can result in 90% reductions; field studies confirm that such reduction of microfilarial loads and prevalence can interrupt transmission. New approaches to disease control, based on preventing bacterial superinfection, can now halt or even reverse the lymphoedema and elephantiasis sequelae of filarial infection. Recognizing these remarkable technical advances, the successes of recent control programmes, and the biological factors favouring elimination of this infection, the Fiftieth World Health Assembly recently called on WHO and its Member States to establish as a priority the global elimination of lymphatic filariasis as a public health problem.

Adult↗
PubMed1995

Automatic control of airway pressure for treatment of obstructive sleep apnea.

Obstructive sleep apnea (OSA) occurs when airflow ceases because of pharyngeal wall collapse in sleep. Repeated apneic events results in the development of a pathological condition called OSA syndrome. We describe the methodology and design of a prosthetic device, named automatic positive airway pressure (APAP), for treatment of this syndrome. APAP applies a stream of air via a nasal mask at an initial pressure selected by the patient. By sensing specific pressure characteristics of air flow immediately preceding pharyngeal wall collapse, the APAP device automatically raises the applied pressure to maintain a patent upper airway and thus prevent apnea. Conversely, when such conditions are absent, pressure is lowered step wise until a preselected minimum pressure is reached. Performance evaluation of the APAP system in five OSA patients and five normal (asymptomatic for sleep apnea) subjects revealed that it effectively treated OSA syndrome. It lowered the apnea-hypopnea index without disturbing sleep and resulted in a lower mean airway pressure compared to the traditional continuous positive airway pressure (CPAP) therapy. The results also show that the pressure needed to prevent OSA varied significantly throughout the night. For OSA syndrome patients, this pressure ranged from 3 to 18 cm H2O. The mean airway pressure for these patients had a sample average of 6.80 cm H2O and a standard deviation of 3.17 cm H2O. In normal subjects, the device did not raise pressure except in response to Pharyngeal Wall Vibration events.

Adult↗
PubMed1994

Accommodation of time delay variations in automatic infusion of sodium nitroprusside.

A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommodate variations in pure time delays, a problem that has not been addressed fully in previously proposed controllers. The control algorithm derivation is based on incorporating a self-tuning controller with an adaptive discrete time delay compensator. The derivation, however, is general and can potentially be applied to other pharmacological agents in addition to sodium nitroprusside. The a priori information required for implementation of the controller is the estimate of the order of the patient response transfer function and the range of the pure time delay. An attractive feature of the controller is its capability to optimize the level of the infused drug during the transient phase of the control without creating an output offset. This feature tends to reduce the overall level of the infused drug. Hence, it may be useful when the cost of a drug or its long-term administration side effects is of concern, such as in the case of sodium nitroprusside.

Algorithms↗
PubMed1992

Analysis of the in vitro lymphoproliferative responses and antibody levels to the arc-5 antigen in patients with cystic hydatid disease.

Using a commercially-available, purified, arc-5 antigen, we examined the in vitro proliferative responses of peripheral blood mononuclear cells from hydatid patients and from healthy controls. Antibody levels of different immunoglobulin classes were also measured against the same antigen, in sera of both groups. Our findings indicate that lymphocytes from healthy controls do not proliferate to the arc-5 antigen, whereas lymphocytes from the majority of patients do. The negative or weak responses observed among a few patients were not due either to increased release of prostaglandins in culture or to a lack of responsiveness to Interleukin-2. Antibodies of all three classes, G, M and A, measured by an ELISA, were elevated in sera of patients when compared with controls. However, only levels of specific IgG antibodies gave an excellent discrimination of the disease state and these were of diagnostic value. No direct or inverse correlations between lymphoproliferative responses and antibody levels were observed in either group, although a few patients with relatively low antibody titres demonstrated very high proliferative responses. The possible use of the proliferative assay as an adjunct to serology in the diagnosis of hydatid disease is indicated.

Adult↗
PubMed1991

A controller for regulation of mean arterial blood pressure using optimum nitroprusside infusion rate.

Automation of drug delivery for control of mean arterial blood pressure is highly desirable in a number of clinical applications. An integrating self-tuning control strategy for control of mean arterial blood pressure using sodium nitroprusside is presented. Next to robust performance, the most attractive feature of the controller is its capability to optimize the quantity of infused medication without introducing a bias in the blood pressure level; a problem that existed in some of the other adaptive control strategies that have been proposed previously. Further, the controller design requires only the knowledge of the pure delay and the order of the transfer function describing the patient's response to the medication; it does not require that the entire transfer function be specified. The derivation of the controller is not based on the patient response to sodium nitroprusside; indeed, it is a general adaptive control strategy for control of systems with transport delay. The controller performs robustly in the presence of variations in the patient response and successfully controls the pressure at the desired level. The ability of this strategy to reduce the amount of infused medication makes it potentially attractive for use in clinical applications, as large doses or long term use of sodium nitroprusside can adversely affect central nervous system and hematopoietic tissues.

Algorithms↗
PubMed1991

Antibody levels and in vitro lymphoproliferative responses to Streptococcus pyogenes erythrogenic toxin A and mitogen of patients with rheumatic fever.

We investigated the in vitro lymphoproliferative responses to a streptococcal mitogen and erythrogenic toxin A of children with acute rheumatic fever (ARF) and patients with chronic rheumatic heart disease (CRHD). Antibody levels to the streptococcal products were also analyzed in the sera of those with ARF or chronic rheumatic heart disease as well as in the sera of children with streptococcal pharyngitis or poststreptococcal glomerulonephritis. Our results demonstrated that the individuals had depressed lymphoproliferative responses during the active stage of rheumatic fever. The depressed responses were not found either to be induced by time-sensitive mitogen-specific suppressor cells or to be related to a dose-response phenomenon. On the other hand, antibody levels to the extracellular mitogens were significantly elevated in the sera of children with ARF compared with the levels in the rest of the groups. The hyperresponsiveness noted among children with ARF was found to be at a quantitative level and was not due to recognition of more epitopes, as determined by Western blotting (immunoblotting). The profile of immune responsiveness in children with ARF to the streptococcal extracellular mitogens is discussed in relation to the pathogenesis of disease.

Adolescent↗
PubMed1990

Cystic hydatid disease: aspects of the incidence in man in Kuwait, Arabian Gulf.

Cystic hydatid disease (CHD) is endemic in Kuwait, but the exact extent of the disease in man has yet to be determined. The incidence was calculated by serological testing of sera from patients with a presumptive clinical diagnosis of hydatidosis and follow-up until the final diagnosis was determined. During a one-year period, 123 sera were received from two District General Hospitals serving a population of approximately 500,000. Eighteen patients had confirmed CHD, 17 were serologically positive in two tests, indirect haemagglutination (IHA) and counterimmunoelectrophoresis (CIEP), while another positive patient was identified through surgery and histopathology. These cases represent an estimated incidence rate of 3.6 per 100,000. Various factors, however, indicate that this is an underestimation of the true incidence. The infection rate of camels with hydatid cysts and dogs harbouring the adult worm, a possible measure of the true incidence in man, is considered high. Because of the nature of the population structure, the majority of patients were, in fact, non-Kuwaitis. Kuwaitis, who form 40% of the population, constituted about 30% of the CHD patients. Females were in the majority, the 21 to 50 yr. age-group being the most symptomatic. Hydatid cysts were most commonly present in the liver. Finally, compared to other countries at the time when a control programme was instituted, the incidence rate in Kuwait is moderate to high. However, the number of individuals with CHD does not appear alarming as the available capacity of the medical services is adequate.

Adolescent↗
PubMed1990

Improved immunotherapy for pulmonary tuberculosis with Mycobacterium vaccae.

We previously demonstrated that a single intradermal injection of 10(9) irradiation-killed M. vaccae, given 1 month after starting chemotherapy, caused significant changes in responses to mycobacterial antigens. Amongst 38 patients with pulmonary tuberculosis, 29% had lymphocytes responding to common myocobacterial antigens after the injection, compared with only 11% of 49 similar patients after an injection of saline (p less than 0.03). To increase the proportion of responders to these antigens, six modifications of the potentially immunotherapeutic injection, randomized with injections of saline, have been assessed by biochemical, clinical, haematological, immunological and radiological criteria. Subsequent lymphocyte proliferation to mycobacterial antigens enabled the modifications to be ranked in order of efficacy. Tuberculin plus murabutide plus 10(9) irradiated M. vaccae (36% of 25), an autoclaved preparation of 10(9) M. vaccae (45% of 22), and 2 x 10(9) irradiated M. vaccae (75% of 12) were the most effective. Antibody responses in several IgG subclasses to mycobacteria, but not streptococci, were also significantly increased by the most effective modifications over the 8 weeks following injection. Detailed radiological study showed that use of the autoclaved bacilli was followed by a delay in clearing of consolidation, but by better closing of cavities than was found in the control group, suggesting enhanced, or altered, immunological activity around the lesions.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1990

An enzyme-linked immunosorbent assay using an arc 5 antigen for the diagnosis of cystic hydatid disease.

We report on an easily standardized enzyme-linked immunosorbent assay (ELISA) for the diagnosis of cystic hydatid disease. The antigen used is commercially available, and purified to elicit an arc 5 precipitation line by immunoelectrophoresis (IEP) with sera of patients harbouring hydatid cysts. The IgG-ELISA was highly sensitive and specific, and of diagnostic value compared to total Ig-ELISA, IgM-ELISA or IgA-ELISA. When compared to the indirect hemagglutination test and to counterimmunoelectrophoresis using an arc 5 antigen, minimal cross-reactions were observed in sera of patients with a presumptive diagnosis of hydatidosis but none were observed in those harbouring intestinal helminths, schistosomes or filarial parasites. The assay is of low cost, simple to perform, and highly reproducible. The IgG-ELISA provides an unequivocal laboratory diagnosis of hydatidosis. It is eminently suited for accurate and early identification of hydatid disease patients, for instance in mass surveys, who may benefit immediately from currently available anthelmintics, thereby obviating the need for surgery later.

Animals↗