Effect of marine heatwaves and warming on kelp microbiota influence trophic interactions

The range-expansion of tropical herbivores due to ocean warming can profoundly alter temperate reef communities by overgrazing the seaweed forests that underpin them. Such ecological interactions may be mediated by changes to seaweed-associated microbiota in response to warming, but empirical evidence demonstrating this is rare. We experimentally simulated ocean warming and marine heatwaves (MHWs) to quantify effects on two dominant temperate seaweed species and their microbiota, as well as grazing by a tropical herbivore. The kelp Ecklonia radiata's microbiota in sustained warming and MHW treatments was enriched with microorganisms associated with seaweed disease and tissue degradation. In contrast, the fucoid Sargassum linearifolium's microbiota was unaffected by temperature. Consumption by the tropical sea-urchin Tripneustes gratilla was greater on Ecklonia where the microbiota had been altered by higher temperatures, while Sargassum's consumption was unaffected. Elemental traits (carbon, nitrogen), chemical defences (phenolics) and tissue bleaching of both seaweeds were generally unaffected by temperature. Effects of warming and MHWs on seaweed holobionts (host plus its microbiota) are likely species-specific. The effect of increased temperature on Ecklonia's microbiota and subsequent increased consumption suggest that changes to kelp microbiota may underpin kelp-herbivore interactions, providing novel insights into potential mechanisms driving change in species' interactions in warming oceans.

Host genetics, phenotype and geography structure the microbiome of a foundational seaweed

Interactions between hosts and their microbiota are vital to the functioning and resilience of macro-organisms. Critically, for hosts that play foundational roles in communities, understanding what drives host-microbiota interactions is essential for informing ecosystem restoration and conservation. We investigated the relative influence of host traits and the surrounding environment on microbial communities associated with the foundational seaweed Phyllospora comosa. We quantified 16 morphological and functional phenotypic traits, including host genetics (using 354 single nucleotide polymorphisms) and surface-associated microbial communities (using 16S rRNA gene amplicon sequencing) from 160 individuals sampled from eight sites spanning Phyllospora's entire latitudinal distribution (1,300 km). Combined, these factors explained 54% of the overall variation in Phyllospora's associated microbial community structure, much of which was related to the local environment (~32%). We found that putative "core" microbial taxa (i.e., present on all Phyllospora individuals sampled) exhibited slightly higher associations with host traits when compared to "variable" taxa (not present on all individuals). We identified several key genetic loci and phenotypic traits in Phyllospora that were strongly related to multiple microbial amplicon sequence variants, including taxa with known associations to seaweed defence, disease and tissue degradation. This information on how host-associated microbial communities vary with host traits and the environment enhances our current understanding of how "holobionts" (hosts plus their microbiota) are structured. Such understanding can be used to inform management strategies of these important and vulnerable habitats.

Is the Intestinal Bacterial Community in the Australian Rabbitfish Siganus fuscescens Influenced by Seaweed Supplementation or Geography?

We recently demonstrated that dietary supplementation with seaweed leads to dramatic improvements in immune responses in S. fuscescens, a candidate species for aquaculture development in Asia. Here, to assess whether the immunostimulatory effect was facilitated by changes to the gut microbiome, we investigated the effects of those same seaweed species and four commercial feed supplements currently used in aquaculture on the bacterial communities in the hindgut of the fish. Since we found no correlations between the relative abundance of any particular taxa and the fish enhanced innate immune responses, we hypothesised that S. fuscescens might have a core microbiome that is robust to dietary manipulation. Two recently published studies describing the bacteria within the hindgut of S. fuscescens provided an opportunity to test this hypothesis and to compare our samples to those from geographically distinct populations. We found that, although hindgut bacterial communities were clearly and significantly distinguishable between studies and populations, a substantial proportion (55 of 174 taxa) were consistently detected across all populations. Our data suggest that the importance of gut microbiota to animal health and the extent to which they can be influenced by dietary manipulations might be species-specific or related to an animals’ trophic level.

Seaweed dietary supplements enhance the innate immune response of the mottled rabbitfish, Siganus fuscescens

Disease is one of the major bottlenecks for aquaculture development, costing the industry in excess of US $6 billion each year. The increase in pressure to phase out some traditional approaches to disease control (e.g. antibiotics) is pushing farmers to search for alternatives to treat and prevent disease outbreaks, which do not have detrimental consequences (e.g. antibiotic resistance). We tested the effects of eleven seaweed species and four established fish immunostimulants on the innate immune response (cellular and humoral immunity) of the rabbitfish Siganus fuscescens. All supplements including different seaweeds from the three groups (Chlorophyta, Phaeophyta and Rhodophyta) were included in the fish pellet at 3% (by weight) and had variably positive effects across the four innate immune parameters we measured compared to control fish. Diets supplemented with the red seaweed Asparagopsis taxiformis and the brown seaweed Dictyota intermedia led to the largest boosts in humoral and cellular innate immune defences, including particularly significant increases in haemolytic activity. Diets supplemented with Ulva fasciata also led to promising positive effects on the fish innate immune responses. We conclude that dietary seaweed supplements can boost the immune response of S. fuscescens and thus the top three species highlighted in this study should be further investigated for this emerging aquaculture species and other fish species.

Genomic vulnerability of a dominant seaweed points to future-proofing pathways for Australia's underwater forests

Globally, critical habitats are in decline, threatening ecological, economic and social values and prompting calls for 'future proofing' efforts that enhance resilience to climate change. Such efforts rely on predicting how neutral and adaptive genomic patterns across a species' distribution will change under future climate scenarios, but data is scant for most species of conservation concern. Here, we use seascape genomics to characterise genetic diversity, structure and gene-environmental associations in a dominant forest-forming seaweed, Phyllospora comosa, along its entire latitudinal (12° latitude), and thermal (~14°C) range. Phyllospora showed high connectivity throughout its central range, with evidence of genetic structure and potential selection associated with sea surface temperatures (SSTs) at its rear and leading edges. Rear and leading-edge populations harboured only half the genetic diversity of central populations. By modelling genetic turnover as a function of SST, we assessed the genomic vulnerability across Phyllospora's distributional range under climate change scenarios. Despite low diversity, range-edge populations were predicted to harbour beneficial adaptations to marginal conditions and overall adaptability of the species may be compromised by their loss. Assisted gene flow from range edge populations may be required to enhance adaptation and increase resilience of central and leading-edge populations under warming oceans. Understanding genomic vulnerability can inform proactive restoration and future-proofing strategies for underwater forests and ensure their persistence in changing oceans.

Application of omics research in seaweeds with a focus on red seaweeds

Targeted 'omics' research for seaweeds, utilizing various computational and informatics frameworks, has the potential to rapidly develop our understanding of biological processes at the molecular level and contribute to solutions for the most pressing environmental and social issues of our time. Here, a systematic review into the current status of seaweed omics research was undertaken to evaluate the biological diversity of seaweed species investigated (red, green and brown phyla), the levels to which the work was undertaken (from full genome to transcripts, proteins or metabolites) and the field of research to which it has contributed. We report that from 1994 to 2021 the majority of seaweed omics research has been performed on the red seaweeds (45% of total studies), with more than half of these studies based upon two genera Pyropia and Gracilaria. A smaller number of studies examined brown seaweed (key genera Saccharina and Sargassum) and green seaweed (primarily Ulva). Overall, seaweed omics research is most highly associated with the field of evolution (46% of total studies), followed by the fields of ecology, natural products and their biosynthesis, omics methodology and seaweed-microbe interactions. Synthesis and specific outcomes derived from omics studies in the red seaweeds are provided. Together, these studies have provided a broad-scale interrogation of seaweeds, facilitating our ability to answer fundamental queries and develop applied outcomes. Crucial to the next steps will be establishing analytical tools and databases that can be more broadly utilized by practitioners and researchers across the globe because of their shared interest in the key seaweed genera.

Kelp forests

Vergés and Campbell introduce the kelp forest ecosystem.

Genomic, metabolic and phenotypic variability shapes ecological differentiation and intraspecies interactions of Alteromonas macleodii

Ecological differentiation between strains of bacterial species is shaped by genomic and metabolic variability. However, connecting genotypes to ecological niches remains a major challenge. Here, we linked bacterial geno- and phenotypes by contextualizing pangenomic, exometabolomic and physiological evidence in twelve strains of the marine bacterium Alteromonas macleodii, illuminating adaptive strategies of carbon metabolism, microbial interactions, cellular communication and iron acquisition. In A. macleodii strain MIT1002, secretion of amino acids and the unique capacity for phenol degradation may promote associations with Prochlorococcus cyanobacteria. Strain 83-1 and three novel Pacific isolates, featuring clonal genomes despite originating from distant locations, have profound abilities for algal polysaccharide utilization but without detrimental implications for Ecklonia macroalgae. Degradation of toluene and xylene, mediated via a plasmid syntenic to terrestrial Pseudomonas, was unique to strain EZ55. Benzoate degradation by strain EC673 related to a chromosomal gene cluster shared with the plasmid of A. mediterranea EC615, underlining that mobile genetic elements drive adaptations. Furthermore, we revealed strain-specific production of siderophores and homoserine lactones, with implications for nutrient acquisition and cellular communication. Phenotypic variability corresponded to different competitiveness in co-culture and geographic distribution, indicating linkages between intraspecific diversity, microbial interactions and biogeography. The finding of "ecological microdiversity" helps understanding the widespread occurrence of A. macleodii and contributes to the interpretation of bacterial niche specialization, population ecology and biogeochemical roles.

Measuring continuous compositional change using decline and decay in zeta diversity

Incidence, or compositional, matrices are generated for a broad range of research applications in biology. Zeta diversity provides a common currency and conceptual framework that links incidence-based metrics with multiple patterns of interest in biology, ecology, and biodiversity science. It quantifies the variation in species (or OTU) composition of multiple assemblages (or cases) in space or time, to capture the contribution of the full suite of narrow, intermediate, and wide-ranging species to biotic heterogeneity. Here we provide a conceptual framework for the application and interpretation of patterns of continuous change in compositional diversity using zeta diversity. This includes consideration of the survey design context, and the multiple ways in which zeta diversity decline and decay can be used to examine and test turnover in the identity of elements across space and time. We introduce the zeta ratio-based retention rate curve to quantify rates of compositional change. We illustrate these applications using 11 empirical data sets from a broad range of taxa, scales, and levels of biological organization-from DNA molecules and microbes to communities and interaction networks-including one of the original data sets used to express compositional change and distance decay in ecology. We show (1) how different sample selection schemes used during the calculation of compositional change are appropriate for different data types and questions, (2) how higher orders of zeta may in some cases better detect shifts and transitions, and (3) the relative roles of rare vs. common species in driving patterns of compositional change. By exploring the application of zeta diversity decline and decay, including the retention rate, across this broad range of contexts, we demonstrate its application for understanding continuous turnover in biological systems.

Future climate change is predicted to affect the microbiome and condition of habitat-forming kelp

Climate change is driving global declines of marine habitat-forming species through physiological effects and through changes to ecological interactions, with projected trajectories for ocean warming and acidification likely to exacerbate such impacts in coming decades. Interactions between habitat-formers and their microbiomes are fundamental for host functioning and resilience, but how such relationships will change in future conditions is largely unknown. We investigated independent and interactive effects of warming and acidification on a large brown seaweed, the kelp Ecklonia radiata, and its associated microbiome in experimental mesocosms. Microbial communities were affected by warming and, during the first week, by acidification. During the second week, kelp developed disease-like symptoms previously observed in the field. The tissue of some kelp blistered, bleached and eventually degraded, particularly under the acidification treatments, affecting photosynthetic efficiency. Microbial communities differed between blistered and healthy kelp for all treatments, except for those under future conditions of warming and acidification, which after two weeks resembled assemblages associated with healthy hosts. This indicates that changes in the microbiome were not easily predictable as the severity of future climate scenarios increased. Future ocean conditions can change kelp microbiomes and may lead to host disease, with potentially cascading impacts on associated ecosystems.

Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp

Some of the most profound effects of climate change on ecological communities are due to alterations in species interactions rather than direct physiological effects of changing environmental conditions. Empirical evidence of historical changes in species interactions within climate-impacted communities is, however, rare and difficult to obtain. Here, we demonstrate the recent disappearance of key habitat-forming kelp forests from a warming tropical-temperate transition zone in eastern Australia. Using a 10-y video dataset encompassing a 0.6 °C warming period, we show how herbivory increased as kelp gradually declined and then disappeared. Concurrently, fish communities from sites where kelp was originally abundant but subsequently disappeared became increasingly dominated by tropical herbivores. Feeding assays identified two key tropical/subtropical herbivores that consumed transplanted kelp within hours at these sites. There was also a distinct increase in the abundance of fishes that consume epilithic algae, and much higher bite rates by this group at sites without kelp, suggesting a key role for these fishes in maintaining reefs in kelp-free states by removing kelp recruits. Changes in kelp abundance showed no direct relationship to seawater temperatures over the decade and were also unrelated to other measured abiotic factors (nutrients and storms). Our results show that warming-mediated increases in fish herbivory pose a significant threat to kelp-dominated ecosystems in Australia and, potentially, globally.

Central and rear-edge populations can be equally vulnerable to warming

Rear (warm) edge populations are often considered more susceptible to warming than central (cool) populations because of the warmer ambient temperatures they experience, but this overlooks the potential for local variation in thermal tolerances. Here we provide conceptual models illustrating how sensitivity to warming is affected throughout a species' geographical range for locally adapted and non-adapted populations. We test these models for a range-contracting seaweed using observations from a marine heatwave and a 12-month experiment, translocating seaweeds among central, present and historic range edge locations. Growth, reproductive development and survivorship display different temperature thresholds among central and rear-edge populations, but share a 2.5 °C anomaly threshold. Range contraction, therefore, reflects variation in local anomalies rather than differences in absolute temperatures. This demonstrates that warming sensitivity can be similar throughout a species geographical range and highlights the importance of incorporating local adaptation and acclimatization into climate change vulnerability assessments.

Low latitude populations are often thought to be more vulnerable to climate change due to warmer ambient conditions. Here, Bennett et al. show that populations of seaweed from different areas of their range have distinct thermal-tolerance thresholds, but share remarkably similar thermal safety margins to warming.

Continental-scale variation in seaweed host-associated bacterial communities is a function of host condition, not geography

Interactions between hosts and associated microbial communities can fundamentally shape the development and ecology of 'holobionts', from humans to marine habitat-forming organisms such as seaweeds. In marine systems, planktonic microbial community structure is mainly driven by geography and related environmental factors, but the large-scale drivers of host-associated microbial communities are largely unknown. Using 16S-rRNA gene sequencing, we characterized 260 seaweed-associated bacterial and archaeal communities on the kelp Ecklonia radiata from three biogeographical provinces spanning 10° of latitude and 35° of longitude across the Australian continent. These phylogenetically and taxonomically diverse communities were more strongly and consistently associated with host condition than geographical location or environmental variables, and a 'core' microbial community characteristic of healthy kelps appears to be lost when hosts become stressed. Microbial communities on stressed individuals were more similar to each other among locations than those on healthy hosts. In contrast to biogeographical patterns of planktonic marine microbial communities, host traits emerge as critical determinants of associated microbial community structure of these holobionts, even at a continental scale.

The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts

Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to 'barrens' when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.

Spatial variability of microbial assemblages associated with a dominant habitat-forming seaweed

Macroalgal surfaces support abundant and diverse microorganisms within biofilms, which are often involved in fundamental functions relating to the health and defense of their seaweed hosts, including algal development, facilitation of spore release, and chemical antifouling. Given these intimate and important interactions, environmental changes have the potential to negatively impact macroalgae by disrupting seaweed-microbe interactions. We used the disappearance of the dominant canopy-forming fucoid Phyllospora comosa from the metropolitan coast of Sydney, NSW, Australia as a model system to study these interactions. We transplanted Phyllospora individuals from nearby, extant populations back onto reefs in Sydney to test whether bacterial assemblages associated with seaweed surfaces would be influenced by (i) the host itself, independently of where it occurs, (ii) the type of habitat where the host occurs, or (iii) site-specific differences. Analyses of bacterial DNA fingerprints (terminal fragment length polymorphisms) indicated that assemblages of bacteria on Phyllospora were not habitat-specific. Rather, they were primarily influenced by local, site-specific conditions with some evidence for host-specificity in some cases. This could suggest a lottery model of host-surface colonization, by which hosts are colonized by 'suitable' bacteria available in the local species pool, resulting in high variability in assemblage structure across sites, but where some species in the community are specific to the host and possibly influenced by differences in host traits.

Demographic consequences of disease in a habitat-forming seaweed and impacts on interactions between natural enemies

Diseases affecting natural ecosystems are increasing in frequency and severity, but unless obviously catastrophic, the consequences of disease outbreaks are often overlooked, relative to other ecological processes (e.g., predation, competition). Disease can have profound effects on individuals and can also strongly influence interactions between infected hosts and their natural enemies. We investigated whether a novel bleaching disease affected the survival or performance of a habitat-forming red seaweed, Delisea pulchra. In addition, we investigated bidirectional, multipartite interactions between this seaweed host, its pathogens, and consumers. Although we found no negative impacts of disease on survival of D. pulchra, bleaching had substantial, negative consequences for affected individuals, including a dramatic drop in fecundity and a significant decrease in size. In the first direct demonstration of bacterial disease-mediated herbivory of seaweeds, herbivores generally preferred to consume bleached tissue in feeding trials, and we also found higher densities of herbivores on bleached than co-occurring, healthy algae at sites where herbivores were abundant. In a conceptually reciprocal test of the effects of herbivores on infection, we showed that simulated herbivory increased susceptibility to bleaching when algae were also exposed to cultures of a bacterial pathogen. Given the high proportions of D. pulchra affected by bleaching during peak periods, the impacts of this disease are likely to have important implications at the population level. This work highlights complex interactions between habitat-forming organisms and their natural enemies and further emphasizes the need to consider disease in ecological research.

Chemical mediation of ternary interactions between marine holobionts and their environment as exemplified by the red alga Delisea pulchra

The need for animals and plants to control microbial colonization is important in the marine environment with its high densities of microscopic propagules and seawater that provides an ideal medium for their dispersal. In contrast to the traditional emphasis on antagonistic interactions of marine organisms with microbes, emerging studies lend support to the notion that health and performance of many marine organisms are functionally regulated and assisted by associated microbes, an ecological concept defined as a holobiont. While antimicrobial activities of marine secondary metabolites have been studied in great depth ex-situ, we are beginning to understand how some of these compounds function in an ecological context to maintain the performance of marine holobionts. The present article reviews two decades of our research on the red seaweed Delisea pulchra by addressing: the defense chemistry of this seaweed; chemically-mediated interactions between the seaweed and its natural enemies; and the negative influence of elevated seawater temperature on these interactions. Our understanding of these defense compounds and the functional roles they play for D. pulchra extends from molecular interactions with bacterial cell signaling molecules, to ecosystem-scale consequences of chemically-controlled disease and herbivory. Delisea pulchra produces halogenated furanones that antagonize the same receptor as acylated homoserine lactones (AHL)-a group of widespread intercellular communication signals among bacteria. Halogenated furanones compete with and inhibit bacterial cell-to-cell communication, and thus interfere with important bacterial communication-regulated processes, such as biofilm formation. In a predictable pattern that occurs at the ecological level of entire populations, environmental stress interferes with the production of halogenated furanones, causing downstream processes that ultimately result in disease of the algal holobiont.

Temperature induced bacterial virulence and bleaching disease in a chemically defended marine macroalga

Host-pathogen interactions have been widely studied in humans and terrestrial plants, but are much less well explored in marine systems. Here we show that a marine macroalga, Delisea pulchra, utilizes a chemical defence - furanones - to inhibit colonization and infection by a novel bacterial pathogen, Ruegeria sp. R11, and that infection by R11 is temperature dependent. Ruegeria sp. R11 formed biofilms, invaded and bleached furanone-free, but not furanone-producing D. pulchra thalli, at high (24°C) but not low (19°C) temperatures. Bleaching is commonly observed in natural populations of D. pulchra near Sydney, Australia, during the austral summer when ocean temperatures are at their peak and the chemical defences of the alga are reduced. Furanones, produced by D. pulchra as a chemical defence, inhibit quorum sensing (QS) in bacteria, and this may play a role in furanone inhibition of R11 infection of furanone-free thalli as R11 produces QS signals. This interplay between temperature, an algal chemical defence mechanism and bacterial virulence demonstrates the complex impact environmental change can have on an ecosystem.

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

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.

Total head excursion and resting head posture: normal and patient comparisons

OBJECTIVE

To determine whether significant differences existed between normal and patient groups on three postural measurements: anterior-posterior total head excursion (THE), resting head posture in sitting (RHPsit), and resting head posture in standing (RHPstd).

SUBJECTS

Forty-two healthy subjects, 13 men and 29 women between the ages of 20 and 60 years, were matched to 42 patients according to gender and age.

DESIGN

Measurements of THE, RHPsit, and RHPstd were taken for each subject. Patients were measured during their initial evaluation and had neck pain as a primary or secondary complaint.

RESULTS

A two-way multivariate analysis of variance followed by two-way analyses of variance showed that normal subjects had a significantly (p<.05) greater THE than did the patients and that men (patients and controls) scored significantly higher (p<.05) than women (patients and controls) on both THE and RHPstd.

CONCLUSION

Clinical assessment of patients with cervical pain should focus on cervical mobility rather than resting head posture. Head/neck posture is different for males and females and they should not be judged by the same standard.

Brief upper airway dysfunction

We have analysed the clinical manifestations of nine patients with brief upper airway dysfunction (BUAD) who attended the thoracic department of a major teaching hospital between 1987 and 1991. Episodes of BUAD developed within 1-4 months of presentation in three patients but were undiagnosed for 2.5-12.5 years in six. The mean age at onset was 51 years ranging from 37 to 66 years. The episodes occurred at irregular intervals. They lasted approximately 1-5 min, were frightening and consisted of an initial phase of obstructive apneoa lasting a few seconds to 2 min and a second phase of respiratory distress with inspiratory stridor lasting 1-4 min. Daytime episodes occurred in all and at night in five, waking three of the patients from sleep. In most instances, throat irritability triggered the episodes which were often preceded by cough. Potential causes of throat irritability included respiratory tract infection, allergy, oesophageal reflux and obstructive sleep apnoea. After treatment of throat irritability BUAD has ceased for at least a year in six of the eight with adequate follow-up. In conclusion, BUAD has characteristics clinical features which should enable it to be recognized more frequently, ensuring successful management.

Brief upper airway (laryngeal) dysfunction

We describe in six men, recurrent episodes recurring over months or years, of sudden, brief complete obstruction to respiration followed by dyspnoea with loud inspiratory stridor lasting two to five minutes. Attacks occurred during wakefulness and/or sleep. In one patient an episode was witnessed endoscopically: the initial obstruction was seen to be caused by complete laryngeal closure. The false vocal cords then opened, but the vocal cords remained adducted and caused inspiratory stridor. The similarity of the attacks described by the other patients suggests that they were all caused by laryngeal closure. Furthermore, they could simulate the episodes by voluntarily adducting their vocal cords. The symptoms were usually preceded by a sensation of throat irritation and in four cases symptoms of upper respiratory infection were present. Associated features present in some of the patients included post-nasal discharge, snoring, sleep apnoea and gastro-oesophageal reflux. None was hypocalcaemic. Although stimulation of laryngeal receptors is known to produce reflex laryngeal closure, cough is the usual response during wakefulness. Treatment aimed at reducing upper airway irritation and voluntary inhibition of coughing appeared successful in reducing the incidence and severity of the episodes. Recognition of the condition is important as it may be confused with other causes of acute dyspnoea and it appears to respond to specific management.

Factors affecting the decline of ventilatory function in chronic bronchitis

Ninety six middle aged male patients with chronic bronchitis with relatively well preserved ventilatory function who were resident in Queensland, New South Wales, or Victoria took part in a prospective study to determine the relationship of various factors to the rate of decline of the FEV1. Thirty of the subjects withdrew, leaving 66 to be followed for four to six years. The mean rate of decline of the FEV1 was 58.6 (SD 51.4) ml/year. The subjects' ventilatory responses to bronchodilator and to methacholine (measures of bronchial lability) were significantly related to each other and to sputum eosinophilia. With a linear model for the data on 57 patients who had methacholine and skin tests the rate of decline of the FEV1 was found, after adjustment had been made for other variables, to be significantly related to State of residence, current smoking, response to bronchodilator, age, and occupational exposure to dust. Response to bronchodilator was interchangeable with response to methacholine. With the five variables in the model none of the following factors was related to the rate of decline of the FEV1:FEV1 on entry, FEV1% predicted normal, FEV1/VC%, skin test reaction, occupation on entry, history of sinusitis and rhinitis, and height. When data from all 66 subjects were introduced into the model, in addition to the five significant individual variables (FEV1/VC% X response to bronchodilator) was significantly related to the rate of decline of the FEV1. Of these prognostic indices, response to bronchodilator was independent of the initial FEV1, FEV/VC%, and FEV1% predicted. The difference between States, which was not explained by differences due to sampling or withdrawal of subjects, was due to a low rate of decline in Queensland.

Use of ipratropium bromide in patients with severe airways obstruction

In ten adult patients with severe, partially reversible airflow obstruction due to asthma, with or without co-existent chronic bronchitis, the acute bronchodilator responses of ipratropium bromide (40 micrograms) and terbutaline (500 micrograms) from metered-dose inhalers, atropine methonitrate (2 mg) as a wet aerosol and placebo were compared in a double blind trial. Also the combination of ipratropium bromide and terbutaline aerosols was compared with both ipratropium and terbutaline alone in short-term and long-term studies. In the short-term study, all the drugs produced significant bronchodilatation compared with placebo. The responses to ipratropium bromide and terbutaline alone were not significantly different. The combination of ipratropium bromide with terbutaline did not produce significantly greater changes in the FEV1, SGaw or static lung volume than terbutaline alone. Atropine methonitrate however, produced significantly greater changes of the airway conductance (SGaw) and static lung volumes (TLC and RV) but not FEV1, when compared to ipratropium bromide. When administered over randomised periods of one month each there were no significant differences between the combination of ipratropium bromide and terbutaline and each drug alone in daily airflometer recordings, daily symptom scores or fortnightly spirometry and clinical assessment. It is concluded that ipratropium bromide, in the conventional dose of 40 microgramm by metered-dose inhaler produces safe, effective bronchodilatation. Its effect, however, did not significantly augment that of the beta adrenergic stimulant, terbutaline and was less than that of atropine methonitrate 2 mg by wet aerosol.

Comparison of inhaled atropine sulphate and atropine methonitrate

The bronchodilator potencies of inhaled atropine sulphate and atropine methonitrate have been compared either alone or in combination with fenoterol in a group of adult asthmatic patients. A cumulative dose response study showed that 2 mg of atropine sulphate produced near maximum bronchodilatation. A larger dose of 4 mg was used in comparing the potency of this drug with 2 mg of atropine methonitrate, a dose previously shown to produce optimum bronchodilatation. In a randomised double-blind fashion atropine methonitrate (2 mg), atropine sulphate (4 mg), fenoterol (400 μg), a combination of atropine methonitrate with fenoterol, a combination of atropine sulphate with fenoterol, and two placebos were administered by inhalation on separate days to eight stable adult asthmatics. Measurements of FEV₁ were made before administration of the drugs and at 20 minutes, one, two, four, and six hours afterwards. The two atropine drugs produced a similar peak effect but the bronchodilatation after atropine methonitrate was more prolonged. In combination the bronchodilatation achieved with both atropine drugs and fenoterol was greater than with either atropine or fenoterol alone, confirming that atropine and an adrenergic drug can have an additive effect. The response with atropine methonitrate and fenoterol showed a significant increase in the FEV₁ for six hours whereas with atropine sulphate and fenoterol the increase of FEV₁ was significantly greater than the placebo for only four hours. It was concluded that the atropine drugs produce useful bronchodilatation either alone or in combination with an adrenergic agent. Of the two atropine drugs, the methonitrate appears to be superior to the sulphate as an inhaled bronchodilator in adult asthmatics.

Dose response of ipratropium assessed by two methods

The dose-response relationships of ipratropium bromide were assessed by two different techniques in two groups of 10 male patients with partially reversible airways obstruction. In a randomised double-blind fashion on four days, 10 patients were given 40 μg, 80 μg, or 120 μg of ipratropium bromide or placebo from identical containers. Baseline FEV₁ and vital capacity were measured and the measurements repeated after 40 minutes, one, two, four, and six hours, and any symptoms were elicited. In the second study, each patient received cumulative doses of 40 μg, 80 μg, and 120 μg. Baseline FEV₁ was obtained and repeated 35 minutes after each dose. The peak increase of the FEV₁ was comparable in both studies. The FEV₁ was slightly greater after 120 μg than after 40 μg. Although this reached statistical significance only in the first study, it was concluded that the cumulative dose-response technique was suitable for determining the peak response. However, this technique was unsuitable for assessing duration of effect, which could be examined only in the first study. After 120 μg of ipratropium bromide, the FEV₁ was significantly greater than after 40 μg at each time interval and it was greater than 80 μg at six hours (p<0·05). No significant side effects were noted in either study. When prolonged effective bronchodilation is sought, a dose of 120 μg of ipratropium bromide may be preferable to the recommended dose of 40 μg.

A comparative study of atropine methonitrate, salbutamol, and their combination in airways obstruction

Dose-response relationships of the cholinergic antagonist, atropine methonitrate, and the beta-adrenergic agonist, salbutamol, were examined by cumulative dose techniques. A wet aerosol, 1.5 mg atropine methonitrate produced a maximum response. The response to 200 microgram of salbutamol from a pressurised aerosol was close to maximum. Secondly, the bronchodilator response of salbutamol microgram was compared with atropine methonitrate 2 mg and placebo in 18 asthmatic patients in a randomised crossover study. In 11 of them the bronchodilator response of the combination of salbutamol and atropine methonitrate was evaluated. Atropine methonitrate produced a similar peak bronchodilator effect to salbutamol, but its effect was more prolonged, the response being significantly greater at four and six hours than with salbutamol. The combination of drugs produced a significantly greater and more lasting bronchodilatation than either of the drugs alone. Despite mild side effects, atropine methonitrate, either alone or in combination with an adrenergic drug, appears to have a place in the treatment of sever reversible airway obstruction not adequately controlled by conventional treatment.

Acute changes of lung volumes and lung mechanics in asthma and in normal subjects

Lung volumes, pulmonary mechanics, and specific airway conductance (sGaw) were studied before and 15 minutes after 200 microgram of aerosol salbutamol in nine asthmatics undergoing mild spontaneous exacerbations of their disease and in five normal subjects. In addition, three of the normal subjects were studied after voluntarily breathing at high lung volumes for one minute. The normal subjects and four of the asthmatics showed no overall changes in lung volumes or pressure-volume (PV) curves after salbutamol, even though airway dilatation was produced in the asthmatic subjects. In another five asthmatics, salbutamol induced a significant fall in the total lung capacity (TLC) in three, and in the residual volume and functional residual capacity in all five. There was a significant displacement of the PV curve downwards and to the right in all five, with increased lung compliance (Cl stat) in two. The fall in TLC could be accounted for by the increase in lung elasticity. There is reason to believe that this change in lung mechanics could be due to the reversal of asthma-induced stress relaxation. Sustained breathing at high lung volume is known to cause stress relaxation of the lung. However, this breathing pattern did not alter the PV curve or TLC in two of three normal subjects, which is consistent with stress relaxation being rapidly reversible. The other normal subject had an acute shift of the PV curve upwards and to the left after breathing at high lung volume. It has been concluded that stress relaxation is usually rapidly reversed but that in some individuals it may only be slowly reversed. This more persistent form of stress relaxation may contribute to the acute changes of TLC found in some asthmatics.

Sputum eosinophilia in chronic bronchitis and asthma

The occurrence of sputum eosinophilia was investigated in 115 patients with chronic bronchitis and asthma. They were clinically divided into four groups; those with asthma only, those with asthma of equal or greater duration than chronic bronchitis, those with chronic bronchitis recently complicated by asthma and those with chronic bronchitis only. Although sputum eosinophilia was more common in the asthmatic groups there was no significant difference between the groups in the degree of sputum eosinophilia. When the groups were subdivided on the basis of methacholine and isoprenaline response (asthma subgroup, greater than or equal to 20% response to isoprenaline or greater than or equal to 40% response to methacholine; chronic-bronchitis subgroup, less than 10% response to isoprenaline plus less than 20% response to methacholine), there was a significant difference between the groups in the degree of sputum eosinophilia. However, sputum eosinophilia still occurred in the chronic bronchitics. In the asthmatic patients, there appeared to be no difference in the degree of sputum eosinophilia in those with positive skin tests, or on steroid medication, compared with those with negative skin tests or not on steroids.¿

Follow-up of past tuberculosis, its value and limitations

Recently the policy of life-long follow-up of tuberculous patients has been questioned, particularly for those who have taken adequate chemotherapy. To assess the value of follow-up at a chest clinic, the relapse rate of approximately 3000 male patients was examined and found to be 0.51 percent annually during the last eight years. It was 0.46 percent amongst those treated prior to the introduction of prolonged chemotherapy, 0.55 percent anually amongst those prescribed at least 18 months chemotherapy. No relapses would have been missed if all the patients had been followed for five years after ceasing chemotherapy and only selected groups subsequently. The selected groups included, those not prescribed adequate chemotherapy in the past, those suspected of irregularity of drug intake, alcoholics and those with atypical or resistant organisms. It was concluded that patients adequately treated with chemotherapy need not be followed up after five years.

Respiratory mechanics in airways obstruction associated with inspiratory dyspnoea

Inspiratory muscle strength and the flow and elastic pressure opposing inspiration were measured in seven patients with severe airways obstruction who found inspiration difficult at rest. A comparison was made of measurements obtained from seven normal subjects and five patients with airways obstruction not experiencing inspiratory dyspnoea at rest. Measurements were also obtained when inspiratory dyspnoea was induced in the normal subjects by adding an inspiratory resistance or by voluntarily increasing lung volume. Compared with the controls the inspiratory muscle strength of the patients was reduced but was not significantly less than that of the patients without inspiratory dyspnoea. The pressure required to produce inspiratory flow was significantly greater when inspiratory dyspnoea was present (P = 0-01). However, there was considerable overlap in the pressures of those with and without inspiratory dyspnoea. A better relationship was obtained when muscle strength was considered. The ratio of inspiratory muscle strength to the pressure required to produce flow was 0-24 +/- 0-07 (mean +/- SD) in patient with inspiratory dyspnoea, 0-10 +/- 0-03 in patients without inspiratory dyspnoea, and 0-033 +/- 0-019 in normal subjects. There was no overlap between the two patient groups. The ratios of the normal subjects were increased when inspiratory dyspnoea was induced and, with the exception of two cases, were all above those obtained when inspiratory dyspnoea was absent. Inspiratory dyspnoea was experienced with lower ratios in the normals than in the patients with airways obstruction.

Mortality from asthma and bronchodilator aerosols

The mortality rate from asthma in Australia had a transcient rise between 1960 to 1967. There was a remarkably high correlation between the sales of pressurized adrenergic aerosols in each of the four most populated States and the corresponding asthma mortality rate for two triennia, 1961 to 1963 and 1964 to 1966. This relationship was not found after 1966. From 1965 to 1966, Australians were warned repeatedly of the possible dangers of over-usage of the adrenergic aerosols. The sales pattern of the aerosols altered, showing a slackening of the rate of increase of sales in 1966 and 1967. This and other evidence suggests that the warnings may have reduced the prevalence of over-usage of the aerosols and that before this, over-usage of the adrenergic aerosols could have caused the epidemic of asthma deaths.

Relationship of constitutional factors and cigarette smoking to decrease in 1-second forced expiratory volume

A 5-year prospective survey of 34 subjects with mild chronic bronchitis revealed marked individual variation in the annual rate of decrease in the forced expiratory volume in 1 sec. The mean annual decrease in the 1-sec forced expiratory volume was 0.046 +/- 0.057 liter. Although the annual decrease in the 1-sec forced expiratory volume was greater among smokers (0.056 +/- 0.061 liter per year) than non- and ex-smokers (0.016 +/- 0.021 liter per year; P less than 0.005), differences in tobacco consumption did not account for the individual variation. This variation was related, instead, to 3 phenomena believed to indicate the presence of host susceptibility to chronic bronchitis. These phenomena were bronchial reactivity to methacholine, ventilatory responsiveness to isoproterenol, and sputum eosinophilia. The correlation between the rate of decrease in 1-sec forced expiratory volume and the degree of methacholine reactivity was 0.76 (P less than 0.001); the correlation between the decrease in 1-sec forced expiratory volume and ventilatory responsoveness to isoproterenol was 0.45 (P less than 0.01). Deterioration of 1-sec forced expiratory volume was appreciably greater among those with sputum eosinophilia (0.062 +/- 0.06 liter per year) than among thse without eosinophilia (0.017 +/- 0.033 liter per year P less than 0.01). The progression of abnormality appeared to depend on an interaction between cigarette smoking and individual susceptibility. Even minimal tobacco consumption led to serious ventilatory deterioration when methacholine reactivity was high, whereas heavy smoking produced little effect on the decrease in 1-sec forced expiratory volume when methacholine reactivity was slight.

Increased upper airway resistance in patients with airway narrowing

The mean air flow resistance of the orolaryngeal (upper) airway was significantly increased in 7 of 11 patients with chronic airway obstruction, when compared with 6 controls. All the patients had noisy respiration with harsh breath sounds audible by auscultation over the larynx. The increase in resistance was greater during expiration than during inspiration. Since 4 patients had normal upper airway resistance, the signs were not invariably associated with upper airway narrowing and presumably could arise also in the chest. When increased, upper airway resistance was usually more than half the total airway resistance. It is suggested that this increase could only be due to narrowing of the glottis, probably by muscle activity. This narrowing may have had the same function as expiration through pursed lips. On the other hand, when present, the increased resistance through the upper airway during inspiration is unlikely to have had a useful function.

The effect of chest physiotherapy upon the FEV1 in chronic bronchitis

Chest physiotherapy, including posturing the patient head downwards while the chest is percussed and vibrated, was used in the treatment of patients with an exacerbation of chronic bronchitis. In seven patients the mean FEV declined from 1.38 litres plus or minus 0.39 to 1.25 litres plus or minus 0.37 after postural drainage and percussion (P less than 0.001). Twenty minutes later the FEV rose to 1.37 litres plus or minus 0.33. The mean decline in the FEV1 was prevented by prior administration of salbutamol. The fall in the FEV1 did not occur in 10 patients who received the postural tipping without chest percussion. Also it was not induced by coughing every two minutes during posturing. It was considered that the fall in FEV1 after chest physiotherapy was due to bronchoconstriction caused by the chest percussion or vibration, particularly in patients with bronchoconstriction under basal conditions. The induced bronchoconstriction counter-balanced any improvement of the FEV due to freeing the airways of sputum, but in two patients with moderate to copious sputum an improvement of the FEV1 was repeatedly obtained in measurements made 20 minutes after the physiotherapy when the bronchoconstriction had presumably subsided. Although the immediate decline in FEV1 was not large, it is considered inadvisable to employ chest percussion and vibration in sick patients unless a bronchodilator is administered previously.