Effect of postextubation noninvasive ventilation with active humidification vs high-flow nasal cannula on reintubation in patients at very high risk for extubation failure: a randomized trial

PURPOSE

High-flow nasal cannula (HFNC) oxygen therapy was noninferior to noninvasive ventilation (NIV) for preventing reintubation in a heterogeneous population at high-risk for extubation failure. However, outcomes might differ in certain subgroups of patients. Thus, we aimed to determine whether NIV with active humidification is superior to HFNC in preventing reintubation in patients with ≥ 4 risk factors (very high risk for extubation failure).

METHODS

Randomized controlled trial in two intensive care units in Spain (June 2020‒June 2021). Patients ready for planned extubation with ≥ 4 of the following risk factors for reintubation were included: age > 65 years, Acute Physiology and Chronic Health Evaluation II score > 12 on extubation day, body mass index > 30, inadequate secretions management, difficult or prolonged weaning, ≥ 2 comorbidities, acute heart failure indicating mechanical ventilation, moderate-to-severe chronic obstructive pulmonary disease, airway patency problems, prolonged mechanical ventilation, or hypercapnia on finishing the spontaneous breathing trial. Patients were randomized to undergo NIV with active humidification or HFNC for 48 h after extubation. The primary outcome was reintubation rate within 7 days after extubation. Secondary outcomes included postextubation respiratory failure, respiratory infection, sepsis, multiorgan failure, length of stay, mortality, adverse events, and time to reintubation.

RESULTS

Of 182 patients (mean age, 60 [standard deviation (SD), 15] years; 117 [64%] men), 92 received NIV and 90 HFNC. Reintubation was required in 21 (23.3%) patients receiving NIV vs 35 (38.8%) of those receiving HFNC (difference -15.5%; 95% confidence interval (CI) -28.3 to -1%). Hospital length of stay was lower in those patients treated with NIV (20 [12‒36.7] days vs 26.5 [15‒45] days, difference 6.5 [95%CI 0.5-21.1]). No additional differences in the other secondary outcomes were observed.

CONCLUSIONS

Among adult critically ill patients at very high-risk for extubation failure, NIV with active humidification was superior to HFNC for preventing reintubation.

Animal evidence considered in determination of cannabis smoke and Δ9 -tetrahydrocannabinol as causing reproductive toxicity (developmental endpoint); Part I. somatic development

OBJECTIVES

On December 11, 2019, California's Developmental and Reproductive Toxicant Identification Committee (DARTIC) met to consider the addition of cannabis smoke and Δ⁹ -THC to the Proposition 65 list as causing reproductive toxicity (developmental endpoint). As the lead state agency for implementing Proposition 65, the Office of Environmental Health Hazard Assessment (OEHHA) reviewed and summarized the relevant scientific literature in the form of a hazard identification document (HID). Here we provide reviews based on the HID: shortened, revised, and reformatted for a larger audience.

METHODS

While the HID included both human and animal data, this set of three reviews will highlight the animal-derived data pertaining to somatic development (Part I), neurodevelopmental effects (Part II), and proposed neurodevelopmental mechanisms of action (Part III).

RESULTS

Endogenous cannabinoids (eCBs) and their receptors serve many critical functions in normal development. Δ⁹ -THC can interfere with these functions. Mechanistic studies employed techniques including: blocking Δ⁹ -THC binding to endocannabinoid (EC) receptors, inhibiting Δ⁹ -THC metabolism, and/or using animals expressing knockout mutations of EC receptors. Apical somatic effects of cannabis smoke or Δ⁹ -THC reported in whole animal studies included decreases in offspring viability and growth. Mechanistic studies discussed in Part I focused on Δ⁹ -THC effects on early embryos and implantation, immune development, and bone growth.

CONCLUSIONS

In reaching its decision to list cannabis and Δ⁹ -THC as a developmental toxicant under California's Proposition 65, the DARTIC considered biological plausibility and the consistency of mechanistic information with effects reported in human and whole animal studies.

Animal evidence considered in determination of cannabis smoke and Δ9 -tetrahydrocannabinol as causing reproductive toxicity (developmental endpoint): Part III. Proposed neurodevelopmental mechanisms of action

This review summarizes the most common potential pathways of neurodevelopmental toxicity due to perinatal exposure to Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC) that lead to behavioral and other adverse outcomes (AOs). This is Part III in a set of reviews highlighting the animal-derived data considered by California's Developmental and Reproductive Toxicant Identification Committee (DARTIC) in 2019. The Hazard Identification Document (HID) provided to the DARTIC included a summary of human, whole animal, and mechanistic data on the neurodevelopmental toxicity of cannabis smoke and Δ⁹ -THC. The literature search for mechanistic data has been updated through 2020. We focus on mechanistic pathways relating to behavioral and other neurodevelopmental outcomes of perinatal exposure to Δ⁹ -THC. The endocannabinoid system (EC system) plays a crucial role in many processes involved in neurodevelopment and exposure to Δ⁹ -THC can alter these processes. Whole animal studies report changes in cognitive ability, behavior, and motor function after prenatal exposure to Δ⁹ -THC. Findings from mechanistic studies add to this evidence and further provide information regarding the pathways leading to these outcomes. Neuromechanistic studies can bridge the gaps between molecular initiating events and apical neurodevelopmental endpoints caused by a chemical. They offer insight into potential alterations in the same pathways by other chemicals that can also result in AOs. Studies of cannabinoid receptor agonist-induced molecular alterations and provide deep biological plausibility at the mechanistic level for the cognitive, behavioral, and motor impairments observed in animal studies after perinatal exposure to Δ⁹ -THC.

Proposed Key Characteristics of Female Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Data in Hazard Assessment

BACKGROUND

Identification of female reproductive toxicants is currently based largely on integrated epidemiological and in vivo toxicology data and, to a lesser degree, on mechanistic data. A uniform approach to systematically search, organize, integrate, and evaluate mechanistic evidence of female reproductive toxicity from various data types is lacking.

OBJECTIVE

We sought to apply a key characteristics approach similar to that pioneered for carcinogen hazard identification to female reproductive toxicant hazard identification.

METHODS

A working group of international experts was convened to discuss mechanisms associated with chemical-induced female reproductive toxicity and identified 10 key characteristics of chemicals that cause female reproductive toxicity: 1) alters hormone receptor signaling; alters reproductive hormone production, secretion, or metabolism; 2) chemical or metabolite is genotoxic; 3) induces epigenetic alterations; 4) causes mitochondrial dysfunction; 5) induces oxidative stress; 6) alters immune function; 7) alters cell signal transduction; 8) alters direct cell–cell interactions; 9) alters survival, proliferation, cell death, or metabolic pathways; and 10) alters microtubules and associated structures. As proof of principle, cyclophosphamide and diethylstilbestrol (DES), for which both human and animal studies have demonstrated female reproductive toxicity, display at least 5 and 3 key characteristics, respectively. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), for which the epidemiological evidence is mixed, exhibits 5 key characteristics.

DISCUSSION

Future efforts should focus on evaluating the proposed key characteristics against additional known and suspected female reproductive toxicants. Chemicals that exhibit one or more of the key characteristics could be prioritized for additional evaluation and testing. A key characteristics approach has the potential to integrate with pathway-based toxicity testing to improve prediction of female reproductive toxicity in chemicals and potentially prevent some toxicants from entering common use. https://doi.org/10.1289/EHP4971.

Optimal Piecewise Linear Function Approximation for GPU-Based Applications

Many computer vision and human-computer interaction applications developed in recent years need evaluating complex and continuous mathematical functions as an essential step toward proper operation. However, rigorous evaluation of these kind of functions often implies a very high computational cost, unacceptable in real-time applications. To alleviate this problem, functions are commonly approximated by simpler piecewise-polynomial representations. Following this idea, we propose a novel, efficient, and practical technique to evaluate complex and continuous functions using a nearly optimal design of two types of piecewise linear approximations in the case of a large budget of evaluation subintervals. To this end, we develop a thorough error analysis that yields asymptotically tight bounds to accurately quantify the approximation performance of both representations. It provides an improvement upon previous error estimates and allows the user to control the tradeoff between the approximation error and the number of evaluation subintervals. To guarantee real-time operation, the method is suitable for, but not limited to, an efficient implementation in modern graphics processing units, where it outperforms previous alternative approaches by exploiting the fixed-function interpolation routines present in their texture units. The proposed technique is a perfect match for any application requiring the evaluation of continuous functions; we have measured in detail its quality and efficiency on several functions, and, in particular, the Gaussian function because it is extensively used in many areas of computer vision and cybernetics, and it is expensive to evaluate.

We think you can dance! A pilot randomised controlled trial of dance for nursing home residents with moderate to severe dementia

OBJECTIVES

To evaluate the feasibility of a dance program for people with moderate to severe dementia living in nursing homeswith regards to recruitment and retention, assessment tools, intervention safety, attendance and engagement.

DESIGN

Pilot randomised controlled trial with assessments at weeks 0, 16 and 32.

SETTING

A nursing home in Sydney, Australia.

INTERVENTIONS

Experienced dance teachers conducted dance groups (intervention) or music appreciation and socialisation groups (control) for 45min, three times a week for 16 weeks.

MAIN OUTCOME MEASURES

Descriptive statistics for recruitment and retention, adverse events and attendance and engagement.

RESULTS

Recruitment was smooth, attrition was17% over 32 weeks. Engagement during the sessions was high, and no serious falls or behavioural incidents occurred. Average attendance was poorer than anticipated for dance groups (67%) in comparison to music groups (89%). A ceiling effect on the Severe Impairment Battery and the logistical challenges of the Clinical Global Impression of Change meant they may not be optimal tools.

CONCLUSIONS

It is feasible to conduct a study of group dance for people with moderate to severe dementia in residential care. Choice of attention control condition should be reconsidered.

Pulmonary thromboembolism presenting as asthma

When a patient presents with wheezing, pulmonary embolism is not usually considered as a possible cause. However, undoubtedly bronchoconstriction can be caused by pulmonary emboli and occasionally wheezing may be so obvious as to suggest a diagnosis of bronchial asthma. Eleven cases are reported in which wheezing was attributable to recurrent pulmonary emboli and one in which it was a clamant feature after a single embolic incident.

Respiratory muscle pressures in non-CF bronchiectasis: Repeatability and reliability

Background: Respiratory muscle strength is used diagnostically in clinical practice and as an outcome measure in clinical trials in various chronic lung diseases. There is limited data on its repeatability in people with non-CF bronchiectasis. The aim of the present study was to assess the repeatability of maximal inspiratory (P Imax) and expiratory pressures (PEmax) in a group of patients with stable, moderate-to-severe non-CF bronchiectasis. Methods: Twenty participants with stable moderate-to-severe non-CF bronchiectasis were recruited. Respiratory muscle strength measurements (three maximal inspiratory and expiratory pressures) were made on 2 separate days. A standard protocol was used, including practice tests, before obtaining three technically acceptable and reproducible readings with a difference of 10% or less between values. Clinical trial registration number: ClinicalTrials.gov: NCT00487149. Results: The mean (SD) age of the non-CF bronchiectasis group was 63 (9) years. Maximal inspiratory pressures were repeatable with mean (SD) for highest PImax, Test 1 and Test 2, 75.90 (20) and 79.40 (19) cmH2O, and limits of agreement (mean difference ± 2SD) —3.50 ± 20 cmH2O, (p = 0.14). Maximal expiratory pressures differed significantly with mean (SD) for highest PEmax, Test 1 and Test 2, 102.25 (27) and 112.30 (32) cmH 2O, and limits of agreement (mean difference ± 2SD) —10.10 ± 35 cmH2O, (p = 0.02). The intraclass correlation coefficient (95% CI) for highest PImax and PEmax was 0.93 (95% CI 0.82 to 0.97) and 0.90 (95% CI 0.76 to 0.96), respectively. Conclusion: Maximal inspiratory pressure measurements were repeatable during a period of clinical stability in moderate-to-severe non-CF bronchiectasis, suggesting this may be a useful outcome measure in non-CF bronchiectasis. Once a baseline has been established, a second visit is not required. PEmax was not a repeatable measure and further study is necessary to ascertain how much practice testing is required to obtain an accurate value.

Physical training for cystic fibrosis

BACKGROUND

Physical training may form an important part of the care package for people with cystic fibrosis.

OBJECTIVES

To determine whether a prescribed regimen of physical training produces improvement or prevents deterioration in physiological and clinical outcomes in cystic fibrosis compared to no training.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register which comprises references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. Date of the most recent search: September 2007.

SELECTION CRITERIA

All randomised and quasi-randomised controlled clinical trials in which a prescribed regimen of physical training is compared to no physical training in people with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed methodological quality and extracted data.

MAIN RESULTS

Of the 26 studies identified, seven studies which included 231 participants, met the inclusion criteria. This review does provide some limited evidence from both short- and long-term studies that aerobic or anaerobic physical training has a positive effect on primary outcomes (exercise capacity, strength and lung function) but improvements are not consistent between studies.

AUTHORS' CONCLUSIONS

Conclusions about the efficacy of physical training in cystic fibrosis are limited by the small size, short duration and incomplete reporting of most of the studies included in this review. Physical training is already part of the care package offered to most people with cystic fibrosis and there is a lack of evidence to actively discourage this. The benefits obtained from including physical training in a package of care may be influenced by the type of training programme. Further research is needed to assess comprehensively the benefits of exercise programmes in people with cystic fibrosis and the relative benefits of the addition of aerobic versus anaerobic versus a combination of both types of physical training to the care of people with cystic fibrosis.

Non-invasive ventilation for cystic fibrosis

BACKGROUND

Non-invasive ventilation (NIV) may be a means to temporarily reverse or slow the progression of respiratory failure in cystic fibrosis (CF).

OBJECTIVES

To compare the effect of NIV versus no NIV in people with CF.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings. We searched the reference lists of each trial for additional publications possibly containing other trials. Most recent search: October 2006.

SELECTION CRITERIA

Randomised controlled trials comparing a form of pressure preset or volume preset NIV to no NIV in people with acute or chronic respiratory failure in CF.

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed trials for inclusion criteria and methodological quality, and extracted data.

MAIN RESULTS

Fifteen trials were identified; seven trials met the inclusion criteria with a total of 106 participants. Six trials evaluated single treatment sessions only and one evaluated a six-week intervention. Four trials (79 participants) evaluated NIV for airway clearance compared with an alternative chest physiotherapy method and showed that airway clearance may be easier with NIV and people with CF may prefer it. We were unable to find any evidence that NIV increases sputum expectoration, but it did improve some lung function parameters.Three trials (27 participants) evaluated NIV for overnight ventilatory support. Lung function and nocturnal transcutaneous carbon dioxide were evaluated within two trials. Due to the small numbers of participants and statistical issues, there were discrepancies in the results between the RevMan and the original trial analyses. No clear differences were found between NIV compared with oxygen or room air except for exercise performance, which significantly improved with NIV compared to room air over six weeks.

AUTHORS' CONCLUSIONS

Non-invasive ventilation may be a useful adjunct to other airway clearance techniques, particularly in people with CF who have difficulty expectorating sputum. Non-invasive ventilation, when used in addition to oxygen, may improve gas exchange during sleep to a greater extent than oxygen therapy alone in moderate to severe disease. These benefits of NIV have largely been demonstrated in single treatment sessions with small numbers of participants. The impact of this therapy on pulmonary exacerbations and disease progression remain unclear. There is a need for long-term randomised controlled trials which are adequately powered to determine the clinical effects of non-invasive ventilation in CF airway clearance and exercise.

Incontinence in adult females with cystic fibrosis: a Northern Ireland survey

The objectives of this survey were to establish the prevalence, onset, severity and impact of incontinence and attitudes towards the availability of advice and treatment in female adults with cystic fibrosis (CF) in Northern Ireland. All female patients (n=59) at the Northern Ireland Regional Adult CF Centre were posted a questionnaire on incontinence. Leakage of urine occurred in 14/46 respondents. Leakage of urine occurred when chest was bad in 8/14 patients and when chest was good or bad in 3/14 patients. Patients reported that their bladder problem affected their ability to perform airway clearance or cough (13/14), and exercise (4/14). The main reason given for the patients who did not seek help for their incontinence (10/14) was that they were too embarrassed. This study highlights that patients with CF are reluctant to seek treatment for incontinence despite the impact this condition can have.

Non-invasive ventilation for cystic fibrosis

BACKGROUND

The use of non-invasive ventilation (NIV) has been proposed as a means to temporarily reverse or slow the progression of worsening respiratory failure in cystic fibrosis (CF).

OBJECTIVES

To compare the effect of NIV versus no NIV in people with CF.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings. The reference lists of each trial were searched for additional publications that may contain other trials. Date of most recent search: January 2002.

SELECTION CRITERIA

Relevant randomised controlled trials in which a form of pressure preset or volume preset NIV versus no NIV was used in people with acute or chronic respiratory failure in CF.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trials for inclusion criteria, methodological quality and data extraction.

MAIN RESULTS

Six trials were identified and four trials met the inclusion criteria with a total of 55 participants. All of these trials only evaluated single treatment sessions. Two trials (36 participants) evaluated the use of NIV for airway clearance compared with an alternative physiotherapy method. These trials showed that airway clearance may be easier and people with CF may prefer to use NIV for airway clearance. There was no evidence that NIV increases sputum expectoration or improves lung function. Two trials (19 participants) evaluated the use of NIV for overnight ventilatory support. Of the primary outcomes examined in this review, only lung function was evaluated within the two trials. Due to the small numbers of participants and the differing statistical techniques used within the review and the primary trials, there were discrepancies in the results obtained by the RevMan analysis and the original trial analysis. No clear differences were found between NIV compared with either oxygen or room air.

REVIEWER'S CONCLUSIONS

Non-invasive ventilation may be a useful adjunct to other airway clearance techniques, particularly in people with CF who have difficulty expectorating sputum. Non-invasive ventilation when used in addition to oxygen may improve gas exchange during sleep to a greater extent than oxygen therapy alone in moderate to severe disease. These benefits of NIV have only been demonstrated in single treatment sessions and its efficacy, safety and acceptability in the longer term are unknown. There is a need for long-term randomised controlled trials to determine the clinical effects of non-invasive ventilation in CF.

Improving linkage analysis in outcrossed forest trees - an example from Acacia mangium

Mapping in forest trees generally relies on outbred pedigrees in which genetic segregation is the result of meiotic recombination from both parents. The currently available mapping packages are not optimal for outcrossed pedigrees as they either cannot order phase-ambiguous data or only use pairwise information when ordering loci within linkage groups. A new package, OUTMAP, has been developed for mapping codominant loci in outcrossed trees. A comparison of maps produced using linkage data from two pedigrees of Acacia mangium Willd demonstrated that the marker orders produced using OUTMAP were consistently of higher likelihood than those produced by JOINMAP. In addition, the maps were produced more efficiently, without the need for recoding data or the detailed investigation of pairwise recombination fractions which was necessary to select the optimal marker order using JOINMAP. Distances between markers often varied from those calculated by JOINMAP, resulting in an increase in the estimated genome length. OUTMAP can be used with all segregation types to determine phase and to calculate the likelihood of alternative marker orders, with a choice of three optimisation methods.

Physical training for bronchiectasis

BACKGROUND

The pathophysiology of bronchiectasis may result in the development of dyspnoea and decreased exercise tolerance, both of which can impact on a patient's quality of life and ability to perform activities of daily living. There is little information regarding the benefits of physical training in bronchiectasis: however it is probable that the benefits of physical training in bronchiectasis are at least comparable to benefits demonstrated in other respiratory conditions. There is also no information regarding the effects of non-adherence to prescribed physical training in bronchiectasis. However as in patients with COPD non-adherence may contribute to a deterioration in the patient's condition and conceivably the long term prognosis.

OBJECTIVES

The objective of this review is to determine whether a prescribed regime of physical training produces improvements or prevents deterioration in physiological and clinical outcomes in bronchiectasis compared to no physical training.

SEARCH STRATEGY

We searched the Cochrane Airways Group specialised register and the Cochrane Controlled Clinical Trials Register.

SELECTION CRITERIA

Randomised or quasi randomised controlled trials in which a prescribed regime of physical training are compared to no physical training in patients with bronchiectasis.

DATA COLLECTION AND ANALYSIS

Three studies were identified. One was did not meet the inclusion criteria and two appeared in abstract form only. More comprehensive data will be incorporated into this review once data from those two trials are published, and when further data is made available to the authors of this review.

MAIN RESULTS

Results from the two studies published in abstract showed that inspiratory muscle training compared to sham or no inspiratory muscle training improved endurance exercise capacity: Weighted Mean Difference (WMD) 264 metres (95% CI 16.4 to 512 metres). PiMax improved: WMD 25 cms H20 (95% CI 11.6 to 38.4 cms H2O )as did quality of life measured with the CRQ: WMD 12.4 units (95% CI 2.4 to 22.5 units).

REVIEWER'S CONCLUSIONS

This review only provides evidence of the benefits of inspiratory muscle training and provides no evidence of the effect of other types of physical training (including pulmonary rehabilitation) in bronchiectasis.

Physical training for cystic fibrosis

BACKGROUND

Physical training may form an important part of the care package for patients with cystic fibrosis.

OBJECTIVES

To determine whether a prescribed regime of physical training produces improvement or prevents deterioration in physiological and clinical outcomes in cystic fibrosis compared to no training.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group specialist trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Date of the most recent search: August 2001.

SELECTION CRITERIA

All randomised controlled clinical trials in which a prescribed regime of physical training is compared to no physical training in patients with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials for inclusion, assessed methodological quality and extracted data.

MAIN RESULTS

Of the sixteen trials identified six trials, which included 184 patients, met the inclusion criteria. Exercise tolerance in the short term, during an acute admission was improved in patients who received physical training. In a three year study there was no improvement in exercise tolerance at the end of the study period. Over three years there was a significantly greater mean annual rate of decline in FVC in the control group compared to the exercise group WMD 2.17 (95%CI 0.47, 3.87). Changes in other lung function parameters showed a similar trend, but these were not statistically significant.

REVIEWER'S CONCLUSIONS

Conclusions about the efficacy of physical training in cystic fibrosis are limited by the small size, short duration and incomplete reporting of most of the trials included in this review. Physical training is already part of the care package offered to most patients with cystic fibrosis and there is no evidence to actively discourage this. Further research is needed to assess comprehensively the net benefit of the addition of physical training to the care of cystic fibrosis patients.

Zonal expression of endothelial nitric oxide synthase in sheep and rhesus adrenal cortex

There is mounting evidence that nitric oxide (NO) may inhibit adrenal steroidogenesis by binding to the heme group of P450 enzymes, particularly the rate-limiting steps cholesterol side-change cleavage P450, aldosterone synthase P450, and 17 alpha-hydroxylase/C(17/20)-lyase P450. Using immunohistochemistry, nitrotyrosine was detectable throughout the ovine adrenal cortex, and endothelial NO synthase (eNOS) was further identified in zona glomerulosa (ZG) and at a higher level throughout the zona fasciculata, increasing toward the medulla. Caveolin-1, 90-kDa heat shock protein, ERK-1/2, and Akt, all known and proposed regulators of eNOS activity, were detected throughout the ovine adrenal cortex. Western immunoblotting confirmed the identity of these proteins as well as the absence of neuronal NOS, inducible NOS, caveolin-2, and caveolin-3. Through dual immunostaining we further identified for the first time a zona intermedia without strong staining for 17 alpha-hydroxylase/C(17/20)-lyase P450 or angiotensin II type 1 receptor, but positive for eNOS. Rhesus adrenals also stained positively for eNOS, but staining was seen only in the ZG and zona reticularis. We conclude that eNOS may play a role in controlling zone-specific aldosterone synthase vs. 11 beta-hydroxylase activities of the single CYP11B gene in sheep. In the rhesus monkey, NO may modulate ZG aldosterone synthase, but it is not needed for control of the distinct 11 beta-hydroxylase in the zona fasciculata. In the zona reticularis, however, eNOS may control C(19) steroid production at the level of 17 alpha-hydroxylase vs. 17,20-lyase activity otherwise unopposed by 3beta-hydroxysteroid dehydrogenase.

Interruption of estradiol signal transduction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through disruption of the protein phosphorylation pathway in adipose tissues from immature and mature female rats

At doses of 10-115 microg/kg, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) decreased body and adipose tissue weights of mature female rats. Doses below 10 microg TCDD/kg decreased body and adipose tissue weights of immature, but not mature females. Doses of 2 and 10 microg TCDD/kg decreased adipose tissue epidermal growth factor receptor (EGFR) binding activity 5 and 7 days later in immature and mature females, respectively. At these times, there was a decrease in the activities of tyrosine kinase (TK), mitogen-activated protein kinase (MAP2K), and protein kinase A (PKA). In mature females, estradiol (E2, 15 microg/kg) increased TK and PKA activities and decreased MAP2K activity. In immature females, E2 decreased TK and PKA activities but not MAP2K activity. TCDD abolished the stimulatory effect of E2 on TK and PKA in mature females, and in immature females TCDD potentiated the negative effect of E2 on all three kinases. TCDD decreased binding of [3H]E2 to cytosolic and nuclear estrogen receptors (ERs) of mature and immature females, and antagonized the stimulatory effect of E2 on ER binding activity. E2 increased DNA binding activity of the estrogen response element (ERE) and activator protein-1, and TCDD antagonized this effect. Geldanamycin, an inhibitor of Src tyrosine kinase, reduced the effects of TCDD on body and adipose tissue weights. Geldanamycin antagonized the effects of TCDD on EGFR binding activity and TK activity. In cell-free preparations, TCDD antagonized E2 action on TK activity in mature females, as well as E2 action on PKA activity in immature females. We hypothesize that TCDD antagonizes E2 action in female adipose tissues through disruption of common cytosolic signal transduction pathways.

Growth retardation in premenarchial female rhesus monkeys during chronic administration of GnRH agonist (leuprolide acetate)

Leuprolide acetate in depot form (0.75 mg/kg body weight/month, i.m.) was administered to four female rhesus monkeys from 18-30 months of age, a period that includes the premenarchial growth spurt. They were compared to eight age matched controls. As anticipated, sexual maturation was blocked in the Leuprolide group and menarche did not occur. Growth was also severely retarded; no weight gain occurred during the study in the Leuprolide group as compared to a 25% weight gain (P = .044) in the control group. The Leuprolide group also lost muscle mass. Food intake normalized for body weight was not affected. Linear growth averaged 35% less in the Leuprolide group. Serum IGF-1 concentrations increased from 486 +/- 84 to 965 +/- 47 ng/mL (P = .0025) in the Leuprolide group and from 838 +/- 139 to 3,006 +/- 545 ng/mL (P = .0016) in the control group. These data suggest that premenarchial pituitary/gonadal suppression results in a distinctive pattern of growth retardation in monkeys.

Mechanism of toxic action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in cultured human luteinized granulosa cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) caused a significant decrease in estradiol (E2) production when it was administered to human luteinized granulosa cells (hLGCs) in culture. We investigated the involvement of the epidermal growth factor receptor (EGFR) and protein tyrosine kinase (PTK) in this TCDD-induced toxicity. Upregulation in 125I-EGF binding to EGFR was measured after 24 h of TCDD treatment, while downregulation in EGFR binding was measured after 72 h of TCDD treatment. Upregulation of EGFR binding was associated with a significant decrease in postnuclear (7000 x g supernatant) PTK activity, but this activity was stimulated after 72 h of TCDD treatment. TCDD altered the level of tyrosine phosphorylation in proteins with molecular weights 35, 40, 43, 45, 60, and > 205 kDa. TCDD caused a significant increase in postnuclear cAMP-dependent protein kinase (PKA) after 24 h of treatment. The actions of TCDD on protein kinases were partially blocked by the protein synthesis inhibitor, cycloheximide. On the other hand, TCDD increased nuclear PTK and decreased nuclear PKA activity. E2 inhibited the postnuclear and nuclear activity of both PTK and PKA in control samples, but did not affect TCDD actions on either postnuclear or nuclear PTK activity. However, E2 abolished the stimulatory effect of TCDD on PKA activity in postnuclear protein. In the presence of insulin, TCDD did not induce any additional changes in postnuclear or nuclear PTK. Forskolin (FK) alone inhibited postnuclear PTK activity and stimulated its nuclear activity. The addition of TCDD 20 min after FK resulted in an increase in postnuclear PTK, but there was little change in nuclear PTK as compared to the effect of FK alone. The stimulatory effect of TCDD on postnuclear PKA activity was enhanced by insulin and TCDD reversed the negative effect of FK, but there was no effect of either insulin or FK on the inhibition by TCDD of nuclear PKA activity. TCDD decreased the activity of MAP2 kinase and reduced the binding activity of AP-1 DNA when given alone, and also blocked the E2 stimulation of MAP2K. These findings suggest that TCDD may interrupt the endocrine function of hLGCs through the blockage of the mitotic signal directly or indirectly through the interaction of PTK/MAP2K and PKA signaling.

Response of cynomolgus macaques to immunization against a synthetic peptide from the human zona pellucida

This study tested immunogenicity of a synthetic peptide hZP3(327-341) from a human zona pellucida (ZP) glycoprotein. After antibody response to various peptide-carrier conjugates was assessed in mice, two female cynomolgus macaques were immunized with the peptide conjugated to keyhole limpet hemocyanin (KLH). A control macaque was immunized with KLH. The peptide was immunogenic in both species, and included both B and T cell epitopes since low to moderate titers of peptide-specific antibodies and a T cell proliferative response were measured. Profiles of ovarian steroid metabolites indicated unchanged ovarian function in the macaques, but only the control conceived when bred. Ovarian histology was normal except that immunoglobulin was bound to ZP in follicles of the peptide-immune macaques. ZP from these females bound sperm and induced acrosome reactions at rates equal to those of an untreated control. The results support the feasibility of an immunocontraceptive vaccine based on autologous ZP peptides.

An evaluation of integrated cardiopulmonary exercise testing in a pulmonary function laboratory

Clinical exercise testing has been used mainly to assess the cardiac response to exercise. Integrative cardiopulmonary exercise tests (CPET) involving the measurement of the ventilatory, circulatory and metabolic response to exercise has largely been a research tool. We analysed the results of one hundred tests randomly chosen from a total of 472 exercise tests performed between January 1992 and June 1993 as clinical investigation in a pulmonary function laboratory. CPET was used (a) to identify the cause of effort limitation in patients where more than one illness could be relevant (26); (b) to obtain an objective measure of the exercise capacity of patients with respiratory or cardiac disease (31); (c) as monitor of response to treatment (11) and (d) in the investigation of unexplained dyspnoea (32). In 94 of the 100 cases CPET was able to provide an answer to the specific clinical question posed. In patients with unexplained dyspnoea (CPET identified a group who exhibit an inappropriate hyperventilatory response to exercise with no supportive evidence of cardiopulmonary disease. In a small minority of cases CPET gave non-specific results. We conclude that CPET is a useful investigation in the management of patients with cardiopulmonary disease and complements the various other investigations offered by a pulmonary function laboratory.

Diaphragmatic paralysis in motor neurone disease: use of non-invasive investigative and therapeutic techniques

Two cases of bilateral diaphragmatic weakness are described in which the condition was the presenting feature of motor neurone disease. Inspiratory muscle strength was assessed by a non-invasive technique involving measurements of pressures generated within the mouth. One patient with severe inspiratory muscle weakness is being treated with domiciliary nasal ventilation and has returned to a good-quality life. The other patient with less severe weakness has thus far required no ventilatory support.

Luminescence luteinizing hormone/choriogonadotropin (LH/CG) bioassay: measurement of serum bioactive LH/CG during early pregnancy in human and macaque

Because of the microheterogeneities of gonadotropins, measurement of immunoreactivity of these glycoproteins does not necessarily reflect changes in their bioactivity. In addition, LH bioactivities in human samples analyzed by a rodent LH bioassay have been discordant with findings based on human granulosa-luteal cells. We have isolated a human LH/choriogonadotropin (CG) receptor cDNA and expressed the recombinant protein. Using 293 cells permanently transfected with the human LH receptor cDNA and a luciferase reporter gene driven by a cAMP-dependent promoter, we have developed a luminescence LH/CG bioassay. After cells were treated with human LH or CG for 20 h, luciferase activity was measured through use of a luminometer. Luciferase activity in the cells was increased in a dose-dependent manner. In contrast, treatment with FSH, thyroid-stimulating hormone, prolactin, growth hormone, adrenocorticotropin, insulin, prostaglandins, and several neurotransmitters had no effect. Because treatment with basic fibroblast growth factor (bFGF) caused significant increases in basal luciferase activity, a fixed amount of bFGF was included in all reactions. Incubation with 0.1 to 30 microliters serum from women during different physiological states stimulated the luciferase activity in parallel with the hCG standard curve. In 4 conception cycles, bioactive LH/hCG levels began to increase 2 wk after the midcycle LH surge, followed by a logarithmic increase from 22 days on. Due to the lack of a homologous RIA for measuring CG levels in monkeys, we analyzed serum bioactive monkey CG (mCG) in macaque during early pregnancy. Bioactive mCG was detected about 12 days after the midcycle LH surge and fertile mating and persisted until Days 21-23, followed by a decline.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a combined oxygen and carbon dioxide transcutaneous electrode in the estimation of gas exchange during exercise

BACKGROUND

Accurate and reliable measurement of gas exchange during exercise has traditionally involved arterial cannulation. Non-invasive devices to estimate arterial oxygen (O2) and carbon dioxide (CO2) tensions are now available. A method has been devised and evaluated for measuring gas exchange during exercise with a combined transcutaneous O2 and CO2 electrode.

METHODS

Symptom limited exercise tests were carried out in 24 patients reporting effort intolerance and breathlessness. Exercise testing was performed by bicycle ergometry with a specifically designed protocol involving gradual two minute workload increments. Arterial O2 and CO2 tensions were measured at rest and during exercise by direct blood sampling from an indwelling arterial cannula and a combined transcutaneous electrode heated to 45 degrees C. The transcutaneous system was calibrated against values obtained by direct arterial sampling before each test.

RESULTS

In all tests the trend of gas exchange measured by the transcutaneous system was true to the trend measured from direct arterial sampling. In the 140 measurements the mean difference between the O2 tensions estimated by direct sampling and the transcutaneous method was 0.08 kPa (0.62 mm Hg, limits of agreement 4.42 and -3.38 mm Hg). The mean difference between the methods for CO2 was 0.02 kPa (0.22 mm Hg, limits of agreement 2.20 and -1.70 mm Hg). There was no morbidity associated with the use of the transcutaneous electrode heated to 45 degrees C.

CONCLUSIONS

A combined transcutaneous O2 and CO2 electrode heated to 45 degrees C can be used to provide a reliable estimate of gas exchange during gradual incremental exercise in adults.

A five-year clinical experience with 112 Blalock-Taussig shunts

In spite of recent advances in neonatal open repair for complex cyanotic heart disease, some patients require palliation with a systemic-to-pulmonary artery shunt. We report a 5-year experience (1985-1990) with 112 Blalock-Taussig shunts. Forty-six of the 92 patients had some variant of tetralogy of Fallot, with a wide spectrum of diagnoses in the remainder. The median age at surgery was 3 months. A classic Blalock-Taussig shunt was done in 26% (group I), and a 4- or 5-mm PTFE graft was utilized in the remainder (group II). The technical aspects of each of the procedures are reviewed. There were three early deaths in the entire group, none of them related to Blalock-Taussig shunt function. There was no incidence of early shunt insufficiency, bleeding, infection, limb ischemia, or pulmonary artery distortion. There was a 21% incidence of clinical congestive heart failure, seen somewhat more commonly in group I. The overall need for reshunting/open repair was similar in both groups, but there was a statistically longer interval between the initial Blalock-Taussig shunt and the second procedure in group I (21.6 vs 12.4 months). The Blalock-Taussig shunt remains a safe, reliable, and effective means of increasing pulmonary flow.

Improving management of asthma: closing the loop or progressing along the audit spiral?

OBJECTIVE

To assess whether the management of asthma has improved from three consecutive surveys.

DESIGN

Retrospective case note survey of acute asthma admissions in 1983 and 1989; case notes selected from 1985-6 survey of prospectively identified patients to include only patients with a final discharge code of asthma.

SETTING

A large city teaching hospital. Patients--101 patients with acute asthma as the primary diagnosis in 1983; 85 in 1985-6; and 133 in 1989, 14 of whom were subsequently transferred elsewhere.

MAIN MEASURES

Conformity with a checklist of important aspects of the process of asthma management including initial assessment, treatment, supervision, and discharge and review arrangements.

RESULTS

All patient groups were similar in age, smoking habit, and stay in hospital and, as an objective guide to severity of asthma, had similar initial pulse rates. Major improvements occurred in management: by 1989, 119(90%) patients were treated with oral corticosteroids (69(68%), 67(79%) in 1983, 1985-6 respectively) and 109(82%) with oxygen (62(61%), 51(60%)) (both p < 0.001). 114(86%) had regular recording of peak flow measurements (53(52%), 54(64%); p < 0.001), and 103/119(86%) were discharged taking oral corticosteroids (66(65%), 63(74%); p < 0.01). Significantly fewer patients, however, had their regular inhaled corticosteroid treatment increased on discharge (38/119(32%) v 53(52%), 39(46%); p < 0.01), but more were receiving high dose inhaled treatment on admission.

CONCLUSIONS

The management of asthma improved significantly, and the normal practice of doctors has changed in an area of practice with longstanding problems.

The cellular immune response to immunization with zona pellucida antigens

The cellular immune response of mice to porcine and rat zona pellucida and cynomolgus macaques to porcine zona pellucida antigens was evaluated. Mice mounted a vigorous cellular response to both antigens, as determined by the T cell proliferation response in vitro. There was poor cross-reactivity to murine zonae by T cells or serum antibodies from mice immunized with rat zona pellucida. Nevertheless, ovaries from the mice immunized with rat zona had significantly fewer antral follicles than adjuvant-treated controls, suggesting that the immune response to the zona antigen disrupted follicular development. T cells from two macaques that had been immunized with porcine zona pelludica proteins proliferated in vitro in response to this antigen. Both macaques also had strong antibody responses. The patterns of urinary steroid metabolites in these animals provided clear evidence of ovarian malfunction following immunization. The data indicate that a significant cellular immune response is generated upon immunization of animals with zona pellucida antigens regardless of whether the antigens are cross reactive with the host zona antigens. Whether impaired ovarian function and follicular development are related to the cellular response must be determined in future studies.

Lung scanning for pulmonary embolism: clinical and pulmonary angiographic correlations

A group of 78 patients with suspected pulmonary embolism was studied by both ventilation perfusion lung scanning and pulmonary angiography. Symptoms and clinical signs were analysed using Bayesian techniques to produce pre-test odds for pulmonary embolism in individual patients. While, as a group, those with embolism could be discriminated from those without on this basis, major overlap existed between the groups, invalidating the use of this approach for individual patients. Strict diagnostic criteria for interpretation of lung scans were accurate using pulmonary angiography as the 'gold standard', but at the expense of a significant number of patients (38 per cent) in the indeterminate (non-diagnostic) group. In the 48 patients in whom the test yielded a diagnostic result, there was a sensitivity of 100 per cent (15/15) and a specificity of 97 per cent (32/33). In the series as a whole, the likelihood of lung scanning correctly diagnosing pulmonary embolism was 55 per cent (15/27) and of correctly excluding embolism, 63 per cent (32/51). By the use of strict criteria for interpretation of lung scanning, reliable information can be obtained on the presence or absence of pulmonary embolism in a large proportion of patients suspected of having the condition. Such information is more discriminating than clinical signs and symptoms.

Dopamine clearance in critically ill infants and children: effect of age and organ system dysfunction

To learn if there are age-related differences in the pharmacokinetic behavior of dopamine, plasma dopamine clearance was determined in 27 acutely ill infants and children who were receiving a continuous intravenous infusion of the drug. Steady-state clearance was calculated from dopamine concentration in arterial blood. Dopamine clearance was 60.7 +/- 28.1 ml/kg/min. The age of the patient exerted an effect on clearance of dopamine (r = -0.63; p less than 0.05), and dopamine clearance was nearly twice as rapid in children younger than 2 years as it was in older children (82.3 +/- 27.7 ml/kg/min versus 45.9 +/- 17.0 mg/kg/min). Conjugated bilirubin exerted an age-independent effect on clearance of dopamine; clearance was 44.8 +/- 28.6 ml/kg/min in children with abnormal conjugated bilirubin (greater than or equal to 0.9 mg/dl) and 70.1 +/- 2.56 ml/kg/min in children with normal conjugated bilirubin (less than 0.9 mg/dl). Clearance was lowest (29.8 +/- 5.7 ml/kg/min) in the four children who had both hepatic and renal dysfunction. Age is an important determinant of dopamine clearance, explaining in part the clinical observation that infants and young children require higher infusion rates.

Variation of breath sound and airway caliber induced by histamine challenge

Inspiratory breath sounds were recorded from the chest wall during histamine challenge in five subjects with mild asthma (baseline FEV1 greater than 60% of predicted normal). The median frequency of the power spectrum of the breath sounds was found to correlate with the percentage change in FEV1 induced by histamine and with FEF50. The analysis suggests that for a decrease in FEV1 of 20%, the median frequency of breath sound would increase by 80 Hz. Variation in airway caliber produced a consistent alteration in the distribution of energy in inspiratory breath sound in the absence of wheeze. Spectral analysis of breath sound may be a useful addition to conventional spirometry in identifying changes in airway diameter.

Diffuse meningeal thickening associated with pleural mesothelioma

A case of pleural mesothelioma with diffuse spinal meningeal thickening as shown by magnetic resonance imaging is reported.

Pulmonary abnormalities in Crohn's disease

Abnormalities of pulmonary function in Crohn's disease have been described, although the results are conflicting and anecdotal accounts of lung involvement are few. In this study we assessed the prevalence of lung function abnormalities in Crohn's disease, and the relative contributions of age, sex, smoking and past medical history, and Crohn's disease activity to the pulmonary abnormalities found. Twenty-nine patients with Crohn's disease and 29 age-, sex- and smoking-matched volunteer controls underwent detailed respiratory assessment. Airways obstruction due to chronic bronchitis and asthma was present in 13 patients with Crohn's disease, but was not more prevalent than in the control group. FEV1 was similar in both Crohn's disease and control subjects (84.2 +/- 21.2% predicted, mean +/- SD; 93.7 +/- 16.3%, respectively: n.s.). The vital capacity was significantly lower in the Crohn's disease patients than in controls (86.7 +/- 16.6%; 95.9 +/- 12.7%; P less than 0.01), but this may have been influenced by the higher prevalence of past or intercurrent medical illnesses affecting the chest in Crohn's disease patients. No patient had evidence of fibrosing alveolitis or bronchiectasis. The haemoglobin corrected transfer factor was significantly lower in the Crohn's disease patients than in controls (100.4 +/- 17.4%; 113.2 +/- 25.1: P less than 0.05) but the diffusing coefficient was not significantly different. There was a significant correlation (r = 0.44, P less than 0.05) between the residual volume and the Crohn's disease activity index but otherwise no close relationship was observed between Crohn's disease activity, extent or duration and the indices of lung function. These findings suggest that the lungs are relatively unaffected by Crohn's disease.

Mortality among United States Coast Guard marine inspectors

Work history records and fitness reports were obtained for 1,767 marine inspectors of the U.S. Coast Guard between 1942 and 1970 and for a comparison group of 1,914 officers who had never been marine inspectors. Potential exposure to chemicals was assessed by one of the authors (RP), who is knowledgeable about marine inspection duties. Marine inspectors and noninspectors had a deficit in overall mortality compared to that expected from the general U.S. population (standardized mortality ratios [SMRs = 79 and 63, respectively]). Deficits occurred for most major causes of death, including infectious and parasitic diseases, digestive and urinary systems, and accidents. Marine inspectors had excesses of cirrhosis of the liver (SMR = 136) and motor vehicle accidents (SMR = 107), and cancers of the lymphatic and hematopoietic system (SMR = 157), whereas noninspectors had deficits for these causes of death. Comparison of mortality rates directly adjusted to the age distribution of the inspectors and noninspectors combined also demonstrated that mortality for these causes of death was greater among inspectors than noninspectors (directly adjusted ratio ratios of 190, 145, and 198) for cirrhosis of the liver, motor vehicle accidents, and lymphatic and hematopoietic system cancer, respectively. The SMRs rose with increasing probability of exposure to chemicals for motor vehicle accidents, cirrhosis of the liver, liver cancer, and leukemia, which suggests that contact with chemicals during inspection of merchant vessels may be involved in the development of these diseases among marine inspectors.

A retrospective survey of asthma management in hospital

A retrospective survey of asthma admissions to general medical units during 1983 is described. 127 cases occurred, of whom 52 were males (44%). The average age was 45.2 years. Forty-eight per cent were receiving inhaled steroids or cromoglycate before admission and 16% regular oral steroids. Initial assessment seldom included peak flow measurement although these were made subsequently in 57%. No steroids were used in 32% of cases. No oxygen was given in 48% of cases and when used was usually at low flow rates. Apart from a reducing course of steroids, 46% of cases were discharged with no increase in pre-admission maintenance treatment and although follow-up was planned for 76% it was for an average 4.9 weeks later. This survey suggests a tendency to under-treatment and undersupervision of asthma patients admitted to acute general medical wards which may well be a cause of unnecessary morbidity.

Management of asthma in hospital: a prospective audit

In a prospective study of management of asthma in hospital patients with acute asthma admitted to a single hospital over a calendar year were surveyed. Altogether 157 out of 194 admissions (81%) were studied. The patients (16 of whom had been admitted twice and one three times) were interviewed at home about two weeks after discharge, and their hospital records were reviewed. When interviewed an appreciable proportion of patients said that their asthma had been poorly controlled after their discharge from the hospital: 54 reported regular sleep disturbance due to wheeze, 78 tightness of the chest in the morning, and 77 wheeze after climbing one flight of stairs. Patients had been described on admission as having had symptoms of deteriorating asthma for a median of three days. Closer questioning of 71 patients, however, elicited that 50 had had regular symptoms indicating poor control for weeks or months. Most patients did not know how their drugs worked, and many did not have an appropriate plan of action in the event of a further attack. In all the cases studied 114 patients were treated with oral corticosteroids, only 70 had had their previous maintenance treatment increased at the time of discharge, and 107 had a follow up appointment booked for an average of three and a half weeks after discharge. These findings show that undersupervision and undertreatment of patients with asthma are common and not confined to those dying of the condition.

Differences in hospital asthma management

Asthma management was audited prospectively for one year in a large teaching hospital. Full details were available on 77% of all patients admitted, or readmitted, with asthma during that year (150 of 195 admissions). 64 patients were admitted to general wards with a special interest in respiratory medicine, and 86 to general wards without this specialist interest. Cases in the two groups were similar in terms of age, previous severity of asthma, previous treatment, and initial pulse rate. Fewer cases in the non-specialist group were treated with oral corticosteroids (67%, vs 83%), had regular peak flow recordings (42%, vs 73%), or were given return appointments (56%, vs 92%); and fewer had their regular inhaled therapy increased after discharge (28%, vs 55%). At interview 13 days later, more patients from the non-specialist group reported sleep disturbance (41%, vs 23%), morning chest tightness (55%, vs 37%), ow wheeze on 1 flight of stairs (58%, vs 34%). 20% of first admissions in the non-specialist group were readmitted within the year, compared to 2% of the group treated on wards with a specialist interest in respiratory medicine. These data suggest that the intensive management of asthmatic patients, practised in respiratory units, prevents much unnecessary morbidity.

Finding complex oscillatory phenomena in biochemical systems. An empirical approach

Starting with a model for a product-activated enzymatic reaction proposed for glycolytic oscillations, we show how more complex oscillatory phenomena may develop when the basic model is modified by addition of product recycling into substrate or by coupling in parallel or in series two autocatalytic enzyme reactions. Among the new modes of behavior are the coexistence between two stable types of oscillations (birhythmicity), bursting, and aperiodic oscillations (chaos). On the basis of these results, we outline an empirical method for finding complex oscillatory phenomena in autonomous biochemical systems, not subjected to forcing by a periodic input. This procedure relies on finding in parameter space two domains of instability of the steady state and bringing them close to each other until they merge. Complex phenomena occur in or near the region where the two domains overlap. The method applies to the search for birhythmicity, bursting and chaos in a model for the cAMP signalling system of Dictyostelium discoideum amoebae.

Dynamics of a biochemical system with multiple oscillatory domains as a clue for multiple modes of neuronal oscillations

We analyze the behavior of a two-variable biochemical model in conditions where it admits multiple oscillatory domains in parameter space. The model represents an autocatalytic enzyme reaction with input of substrate both from a constant source and from non-linear recycling of product into substrate. This system was previously studied for birhythmicity, i.e. the coexistence between two stable periodic regimes (Moran and Goldbeter 1984), and for multi-threshold excitability (Moran and Goldbeter 1985). When two distinct oscillatory domains obtain as a function of the substrate injection rate, the system is capable of exhibiting two markedly different modes of oscillations for slightly different values of this control parameter. Phase plane analysis shows how the multiplicity of oscillatory domains depends on the parameters that govern the underlying biochemical mechanism of product recycling. We analyze the response of the model to various kinds of transient perturbations and to periodic changes in the substrate input that bring the system through the two ranges of oscillatory behavior. The results provide a qualitative explanation for experimental observations (Jahnsen and Llinas 1984b) related to the occurrence of two different modes of oscillations in thalamic neurones.