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Background: Lipid A is the highly immunoreactive endotoxic center of lipopolysaccharide (LPS). It anchors the LPS into the outer membrane of most Gram-negative bacteria. Lipid A can be recognized by animal cells, triggers defense-related responses, and causes Gram-negative sepsis. The biosynthesis of Kdo2-lipid A, the LPS substructure, involves with nine enzymatic steps., Results: In order to elucidate the evolutionary pathway of Kdo2-lipid A biosynthesis, we examined the distribution of genes encoding the nine enzymes across bacteria. We found that not all Gram-negative bacteria have all nine enzymes. Some Gram-negative bacteria have no genes encoding these enzymes and others have genes only for the first four enzymes (LpxA, LpxC, LpxD, and LpxB). Among the nine enzymes, five appeared to have arisen from three independent gene duplication events. Two of such events happened within the Proteobacteria lineage, followed by functional specialization of the duplicated genes and pathway optimization in these bacteria., Conclusions: The nine-enzyme pathway, which was established based on the studies mainly in Escherichia coli K12, appears to be the most derived and optimized form. It is found only in E. coli and related Proteobacteria. Simpler and probably less efficient pathways are found in other bacterial groups, with Kdo2-lipid A variants as the likely end products. The Kdo2-lipid A biosynthetic pathway exemplifies extremely plastic evolution of bacterial genomes, especially those of Proteobacteria, and how these mainly pathogenic bacteria have adapted to their environment.

Lipopolysaccharide (LPS) (a.k.a., endotoxin) is an essential component of the outer leaflet of the outer membrane of gram-negative bacteria and is a potent activator of the innate immune system of animals. Lipid A, the glycolipid core of LPS, is the agent responsible for disease and death from gram-negative sepsis, an important cause of human mortality and morbidity. Although it is generally accepted that lipid A is restricted to the prokaryotes, recent efforts to purify molecules from green algae with structural features unique to lipid A have met with success. Furthermore, the vascular plant Arabidopsis thaliana has been found to contain genes that encode all of the enzymes of the biosynthetic pathway for lipid A. It is not known whether vascular plants synthesize lipid A or where lipid A might be located in the tissues. For the present study, we used affinity reagents for lipid A to probe green alga and tissues of the garden pea for a light microscopic localization of lipid A in these eukaryote cells. We find staining for lipid A in free-living and endosymbiotic green algae and in the chloroplasts of vascular plants, indicating that this molecule is not restricted to prokaryotes, but is found also in select eukaryotes.

Lipopolysaccharide (LPS, endotoxin) is a component of Gram-negative bacteria and is the principal indicator to the innate immune systems of higher animals of a Gram-negative bacterial invasion. LPS activates the blood clotting system of the American horseshoe crab, Limulus polyphemus. By stimulating blood cell degranulation, LPS triggers the release of the proteins of the clotting system from the cells, and by activating a protease cascade that converts coagulogen, a soluble zymogen, to coagulin, the structural protein of the clot, LPS triggers the production of the fibrillar coagulin blood clot. Although originally thought to be restricted to the Gram-negative bacteria and the cyanobacteria, LPS, or a very similar molecule, has recently been described from a eukaryotic green alga, Chlorella. Here we show that, like LPS from Gram-negative bacteria, the algal molecule stimulates exocytosis of the Limulus blood cell and the clotting of coagulin. The coagulin clot efficiently entraps the cells of Chlorella in a network of fibrils. Invasion and erosion of the carapace by green algae is an important cause of mortality of Limulus, and it is suggested that the cellular response to aLPS may contribute to defense against this pathogen.

We report on the influence of an LPS-like molecule (aLPS) from the pathogenic alga, Prototheca (strain 289) on insect and murine innate immune reactions. Insect innate reactions to infection include nodule formation, a process of entrapping bacterial cells in aggregates of hemocytes. We recorded eicosanoid-dependent, dose-related nodulation reactions to aLPS in hornworms (Manduca sexta). The insect reaction was attenuated by pre-incubating the aLPS with polymyxin-B. Conversely, the murine macrophages reacted to challenge with Escherichia coli LPS by secreting cytokines, but did not react to aLPS. We infer that, while highly conserved with respect to intracellular mechanisms of interaction, insect and mammalian immune surveillance systems differ in recognition of LPS molecular types.

A 37-year-old man developed persistent hemoptysis after sustaining a gunshot wound to the right shoulder and lung. A right upper lobectomy was performed, in which Aspergillus species microorganisms were identified within retained bullet fragments. The role of infected bullet fragments in the pathogenesis of hemoptysis in this patient is discussed.

Nodulation, which begins with the formation of cellular microaggregates, is the predominant cellular defense reaction to bacterial infections in insects. We suggested that these reactions to bacterial infections are mediated by eicosanoids. The lipopolysaccharide (LPS) component of some bacterial cells stimulates defense reactions in mammals and insects. Here, we report on experiments designed to test the hypothesis that eicosanoids mediate microaggregation reactions to LPS. Injections of LPS (purified from the bacterium, Serratia marcescens) into larvae of the tenebrionid beetle, Zophobas atratus, stimulated microaggregation reactions in a dose-dependent manner. Treatments with eicosanoid-biosynthesis inhibitors immediately prior to LPS challenge sharply reduced the microaggregation responses. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase and lipoxygenase reduced microaggregation, supporting our view that microaggregate formation involves lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 30min after injection, and microaggregation was significantly reduced, relative to control insects, over the following 90min. The dexamethasone effects were reversed by treating LPS-injected insects with the eicosanoid precursor, arachidonic acid. These findings indicate that cellular defense reactions to a specific component of bacterial cells are mediated by eicosanoids, and open up new possibilities for dissecting detailed hemocytic actions in insect immune reactions to bacterial infections.

In testing whether bacterial lipopolysaccharide (LPS) was a natural substrate for an esterase from the soil amebae Dictyostelium discoideum, we observed altered banding patterns of the LPS and changed protein mobility on sodium dodecyl sulfate (SDS) polyacrylamide gels after incubation of LPS with the enzyme. The initial interpretation of these results was that the enzyme had removed ester-linked acyl chains from the LPS, leading to a change in its migration on gels. However, esterase inactivated by treatment with either dithiothreitol (DTT), heat, or SDS generated the same mobility shifts. Bovine serum albumin (BSA) also induced the same change in the electrophoretic pattern. We conclude that the altered LPS patterns and protein mobility on SDS gels were caused by nonspecific interactions between LPS and protein.

The purpose of this study was to determine the regional and myofibrillar ATPase (M-ATPase) fibre type glycogen utilization patterns in response to increased ventilation induced by pre-exhaustive (Pre-Exh) and exhaustive (Exh) durations of swimming. Twenty-eight hamsters were studied: six controls (Con), 11 Pre-Exh (swam 82 min), 11 Exh (swam to exhaustion). We examined the optical density of PAS-stained fibres from the different regions of the diaphragm as a measure of glycogen remaining after the exercise or control period. The optical densities of PAS-stained fibres in most M-ATPase fibre types and diaphragmatic regions for the Pre-Exh and Exh groups was less than those in the Con hamsters except for the optical densities of all the M-ATPase fibre types in the sternal region. The optical densities of PAS-stained fibres in different regions and M-ATPase fibre types did not differ in the Exh and Pre-Exh groups. This data indicates that significant glycogen utilization occurred in all three M-ATPase fibre types in the costal, and both the thoracic and abdominal surface of the crural diaphragm in hamsters following pre-exhaustive and exhaustive durations of swimming. Glycogen utilization was greater in type 1 fibres of the thoracic surface of the crural region than in the type 1 fibres of the sternal region of the Pre-Exh group. Further, significant utilization of glycogen did not occur in any of the three M-ATPase fibre types of the sternal region of the diaphragm following prolonged durations of swimming. It would appear that glycogen is an important substrate in the hamster diaphragm during swimming.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of heart rate and oxygen uptake during incremental exercise and at maximal exercise is useful in evaluating mechanisms responsible for exercise limitation in patients with cardiopulmonary disease. Presently used prediction equations are based on relatively small groups of subjects in whom there was an uneven distribution of subjects with regard to age and sex or based on equations that were from extrapolated data. Our prediction equations are based on data from 231 men and women equally divided within decades between 20 and 80 years. Patients exercised to a symptom-limited maximum on a cycle ergometer while measurements of heart rate and oxygen uptake were recorded. The relationship between heart rate and oxygen uptake throughout exercise (HR:VO2) was determined using a statistical technique that included each data point from each subject. The HR:VO2 throughout incremental exercise was best described by separate equations for women younger than 50 years and older than 50 years and for men younger than 70 years and older than 70 years. Prediction equations for maximal heart rate (HRmax) and maximal oxygen uptake (VO2max) were developed by linear regression and were selected from all possible combinations of parameters. The HRmax was most accurately predicted by age alone for both sexes. Unlike the HR:VO2 relationship, the slope of the line relating heart rate to age was not different for the older women compared with the younger women so that a single equation was derived to predict HRmax. A single equation for the men was also sufficient since the slope of heart rate to age was the same for all ages. To most accurately predict VO2max, a separate equation was required for both the women and men that included age, height, and weight.

The circulating leukocyte (WBC) count increases with exercise, because WBCs enter the circulation from the marginated pool. The lung is a major source of the demarginating cells, but it is unclear whether this occurs because of increased ventilatory movements, increased cardiac output, or both. The present study examined the mechanical effect of ventilation (VE) in six healthy men with three different protocols on three separate occasions. First, the subjects cycled for 5-min intervals at 50, 100, 150, and 200 W, and we measured heart rate (HR), minute ventilation (VE), tidal volume (VT), respiratory rate, and end-tidal CO2. Second, each subject reproduced his exercise VE by matching VT, respiratory rate, and end-tidal CO2 on a circuit designed for isocapnic hyperpnea (matched VE). The subjects then performed a hyperventilation (hyper-VE) protocol with a minimum VT of 1.5 liters and a respiratory rate of 20 breaths/min. Blood samples were drawn at rest and throughout each protocol for measurement of WBCs, hematocrit, and band cells. During cycling, VE increased (9 +/- 1 to 66 +/- 7 l/min), HR increased (71 +/- 7 to 172 +/- 10 beats/min), and WBCs increased (5.5 +/- 0.9 to 7.8 +/- 1.3 x 10(9)/l). During matched VE, VE increased (11 +/- 2 to 69 +/- 11 l/min), but neither HR nor WBCs increased (67 +/- 13 to 78 +/- 12 beats/min and 5.3 +/- 1.6 to 5.7 +/- 1.5 x 10(9)/l, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to define variability of the oxidative capacity and glycogen content between different fiber types and regions of the hamster diaphragm. Using histochemical and microphotometric techniques, the oxidative capacity (identified by nicotinamide-adenine dinucleotide tetrazolium reductase reaction end product) and glycogen levels (identified by the periodic acid-Schiff stain test) were examined in three myofibrillar ATPase (M-ATPase) fiber types and four diaphragmatic regions: sternal, anterior costal, thoracic surface of the crural (thor/crur), and abdominal surface of the crural (abd/crur). Most regional differences were found between the crus and the rest of the diaphragm. There were no differences in the oxidative capacity between diaphragmatic regions in the types 1 and 2a fibers, but the type 2b fibers in the thor/crur region had the greatest oxidative capacity and the 2b fiber in the sternal region had the lowest oxidative capacity. There were differences in glycogen content between diaphragmatic regions for all of the three M-ATPase fiber types. Variability in oxidative capacity between fiber types was demonstrated in all regions except the thor/crur region. Variation in glycogen content between fiber types was only demonstrated in the two surfaces of the crus. The type 2b fiber demonstrated the most differences from types 1 and 2a fibers in oxidative capacity and glycogen content in the different diaphragmatic regions, whereas the types 1 and 2a fibers demonstrated few differences from each other in these features across the different diaphragmatic regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the breathing pattern at maximal exercise in patients is limited because the range of ventilatory responses (minute ventilation; tidal volume; respiratory rate) at maximal exercise in normal humans is unknown. We studied 231 normal subjects (120 women; 111 men) equally distributed according to age from 20 to 80 years. Each subject performed a progressive incremental cycle ergometer exercise test to their symptom-limited maximum. Mean ventilation at the end of exercise (Vemax) was significantly higher in men (mean +/- SD, 97 +/- 25 L/min) than in women (69 +/- 22 L/min) (p less than 0.001). Minute ventilation at the end of exercise as a fraction of predicted maximal voluntary ventilation (Vemax/MVV) for all subjects was 0.61 +/- 0.14 (range, 0.28 to 1.02). There was no difference in Vemax/MVV between men (0.62 +/- 0.14) and women (0.59 +/- 0.14). Tidal volume at the end of exercise (Vtmax) was higher in men (2.70 +/- 0.48 L) than in women (1.92 +/- 0.41 L) (p less than 0.001). Any differences in Vtmax between men and women disappeared when Vtmax was corrected for baseline FVC. Respiratory rate at the end of exercise (RRmax) was 36.1 +/- 9.2 breaths per minute for all subjects. There was no difference in RRmax between men and women. The Vemax correlated best with carbon dioxide output at the end of exercise (r = 0.91; p less than 0.001) and with maximal oxygen uptake (r = 0.90; p less than 0.001) for all subjects. This study of a large group of subjects has demonstrated the wide range of possible breathing patterns which are adopted during exercise and has provided a wide range of "normal" responses which must be taken into consideration when maximal ventilatory data from exercise tests are analyzed.

Insufficient respiratory muscle endurance (RME) may be one of the factors limiting ventilation during peak athletic performance. Our purpose was to determine whether the RME of highly trained cyclists could be enhanced and if so, to determine the effects of improved RME on their maximal exercise performance. Ten male cyclists (maximal oxygen consumption (VO2max) greater than 60 ml/kg-1) began the study by performing 3 tests. These were VO2max, RME measured as maximal sustainable ventilatory capacity (MSVC) and maximal exercise endurance (tlim) measured by an endurance cycling test to exhaustion at 90% of their maximal power output. Five subjects then completed 4 weeks of isocapnic hyperpnea training (16 session) and 5 subjects were controls. Following this training interval, each subject repeated the initial tests. After the RME training, the MSVC increased from 155 +/- 11 to 174 +/- 12 l/min (p = 0.004) for the training subjects while there was no change in the controls (155 +/- 26 and 150 +/- 34 l/min). There were no changes for any of the 10 subjects in either the maximal exercise performance (VO2max = 66.1 +/- 4.7 to 66.5 +/- 4.8 ml.kg-1) or the maximal exercise endurance (tlim = 335 +/- 79 to 385 +/- 158 sec). In conclusion, 4 weeks of respiratory muscle endurance training increased respiratory muscle endurance but had no effect on the maximal cycling performance of highly trained cyclists.

Hemidiaphragmatic paralysis occurs in some patients following CAB surgery, possibly related to an intraoperative stretch or cold-induced phrenic injury. To determine the time and extent of recovery of phrenic nerve function, we studied five patients with left phrenic paresis or paralysis after CAB. The FVC, FEV1, Pmax and PEmax pressures, latency of conduction and amplitude of CDAP with phrenic nerve stimulation, and diaphragmatic excursion during fluoroscopy were measured for 12 months after CAB. Left phrenic paralysis was substantiated in four of five patients, and paresis was present in the other patient. Recovery of the left phrenic nerve occurred in all patients, complete in one and partial in four, but was delayed and continued for up to 12 months. We conclude that phrenic nerve recovery is delayed after CAB-associated injury and may be incomplete up to 14 months later, in keeping with rates of regeneration of other peripheral nerves.

We studied six patients with type A botulism to determine the degree of initial respiratory compromise and to quantitate the time course and extent of recovery of the ventilatory and upper airway muscles and exercise performance. The VM weakness was identified in all patients early after botulism. Upper airway muscle weakness was also common, requiring intubation for airway protection in one patient. Recovery of VM and upper airway muscle strength occurred in all patients, predominantly over the first 12 weeks but continued up to one year in several. A similar time course of improvement was noted for exercise performance. Ventilatory limitation was an unusual cause for exercise limitation. By 12 months, lung function, VM and upper airway muscle strength and exercise performance had returned to normal in all but one patient. We conclude that VM and upper airway muscle weakness occurs in most patients with clinically significant type A botulism.

In this chapter, the different types of exercise tests and the indications for requesting a particular type of test have been discussed. The normal physiological responses to exercise have been reviewed and examples of the abnormal responses seen in a variety of disease states that have been discussed. The relatively small number of these responses limits the specificity of exercise tests in actually establishing a diagnosis, but can be helpful in narrowing the differential diagnosis. Perhaps exercise tests are most valuable in cases where the patient's symptoms are mainly limited to exercise and where investigations done at rest have failed to resolve a diagnostic question. When exercise testing is used under these circumstances, it serves a unique function in the diagnosis and management of pulmonary disease.

To examine the relationship between nutrition, pulmonary function, respiratory muscle strength, and respiratory muscle morphometry, we compared physiologic data and muscle morphometry obtained from internal intercostal, external intercostal, and latissimus dorsi muscle biopsies in 68 patients who were having a thoracotomy. We stained the biopsies for myosin ATPase and measured the proportions and diameters of the type 1 and type 2 fibers. There were more qualitative changes in the external intercostal muscles than in the other two, and some of these changes related to the incidence of malignancy. There were more type 1 fibers in the external intercostal (64 +/- 10 percent) and internal intercostal muscles (59 +/- 12 percent) than in the latissimus dorsi (44 +/- 13 percent) (p less than 0.005). The mean diameter of the type 2 fibers in the external intercostal muscles was less (44 mu +/- 7 mu) than the diameter in the latissimus dorsi (51 mu +/- 9 mu) and the internal intercostal muscles (52 mu +/- 8 mu) (p less than 0.01). The diameters of both fiber types were greater in men than in women. There was no significant relationship between measures of pulmonary function or respiratory muscle strength and muscle fiber proportions and diameters. There were significant correlations between the percentage of ideal body weight and type 1 and type 2 fiber diameters. We conclude that sex and nutrition influence respiratory muscle morphometry.

Dyspnea on exertion is a frequently reported symptom of thyrotoxicosis. In the majority of cases, there is no obvious cause of dyspnea, but as skeletal myopathy is also common in thyrotoxic patients, it has been postulated that increased dyspnea could be secondary to respiratory muscle weakness. We sought to determine whether thyrotoxic patients were in fact more dyspneic on exertion than age- and sex-matched controls, and if so, whether the increased dyspnea was secondary to respiratory muscle weakness. The study group consisted of 12 thyrotoxic patients and 12 control subjects matched for age and gender. We measured lung volumes, compliance, elastic recoil, respiratory muscle strength, maximal exercise performance, and the intensity of breathlessness (modified Borg scale) at various levels of exercise in all subjects. The respiratory muscles were weaker in patients than controls. This weakness improved in treated patients (p less than 0.05) with concomitant increases in VC, IC, and TLC (all p less than 0.05). Despite this, we found no differences in breathlessness intensity scores between patients and controls or in patients before and after successful antithyroid therapy.

Because of its potential relevance to heavy exercise we studied the ventilatory muscle function of five normal subjects before, during, and after shortterm near-maximal voluntary normocapnic hyperpnea. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made at four levels of ventilation: 76, 79, and 86% maximal voluntary ventilation (MVV) and at MVV. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made. The pressure-stimulation frequency relationship of the diaphragm obtained by unilateral transcutaneous phrenic nerve stimulation was studied in two subjects before and after hyperpnea. Decreases in maximal inspiratory (PImax) and transdiaphragmatic (Pdimax) strength were recorded posthyperpnea at 76 and 79% MVV. Decreases in the pressure-frequency curves of the diaphragm and the ratio of high-to-low frequency power of the diaphragm EMG occurred in association with decreases in Pdimax. Analysis of the pressure-time product (P X dt) for the inspiratory and expiratory muscles individually indicated the increasing contribution of expiratory muscle force to the attainment of higher levels of ventilation. Demonstrable ventilatory muscle fatigue may limit endurance at high levels of ventilation.

This study evaluated whether inspiratory muscle training (IMT) could increase inspiratory muscle strength and endurance and exercise performance in 11 patients with cystic fibrosis (CF) with moderately severe airflow limitation. The IMT consisted of breathing through an inspiratory resistance (IR) for 15 min twice daily for 4 wk, preceded or followed by a 4-wk control period. After IMT, there was an increase in inspiratory muscle strength measured by maximal inspiratory mouth pressure at functional residual capacity: 74 +/- 18 cmH2O before training to 81 +/- 12 cmH2O after training, mean +/- 1 SD, p less than 0.025, and in inspiratory muscle endurance measured by the maximal IR tolerated for 10 min. Limitation of performance in the progressive exercise test was related to increased airflow limitation and possibly to poor nutrition. Mean exercise performance during progressive or submaximal exercise testing did not change after training. It is concluded that this form of IMT improved inspiratory muscle strength and endurance, but had little effect on exercise performance in patients with CF.

In 7 normocapnic and 6 hypercapnic patients with chronic obstructive pulmonary disease (COPD), we confirmed the recently reported observation that hypercapnic and/or hypoxemic patients with COPD breathe with a shorter inspiratory time (TI) and a smaller tidal volume (VT) than normocapnic and/or normoxemic patients with COPD. Both hypercapnic and normocapnic groups were exposed to doubling concentrations of aerosolized histamine, and FEV1 was measured 30 and 90 s after each 2-min exposure. A provocative concentration (PC20) of histamine was defined as that which produced a 20% decrease in FEV1. At PC20, minute ventilation and VT decreased in both groups. The decrease in VT was significantly greater in the normocapnic patients. Inspiratory flow (VT/TI) did not change in either group. Although breathing frequency (f) and inspiratory time (TI) did not change in the hypercapnic group, f increased and TI decreased significantly in the normocapnic patients. The same results were obtained when patients were separated into hypoxemic and "normoxemic" groups. At PC20, therefore, the pattern of breathing of the hypercapnic and/or hypoxemic patients showed only small variations, whereas in the normocapnic and/or "normoxemic" patients, the breathing pattern showed greater changes, becoming similar to that of the hypercapnic and/or hypoxemic patients during control breathing. We speculated, therefore, that activation of histamine-sensitive receptors in the airways could be involved in the pathophysiology of the rapid shallow breathing present at rest in hypercapnic and/or hypoxemic patients with COPD.

To determine whether normal ventilatory muscles fatigue during short-term high-intensity exercise, we measured diaphragmatic electromyogram (EMG, esophageal electrode), and pleural (Ppl), gastric (Pga), and transdiaphragmatic (Pdi) pressures in seven normal young men. On separate days, the subjects performed exercise to exhaustion at a constant work load (80% maximum power output) inspiring air or 40% O2. Before and after exercise, Pdimax and maximum expiratory pressure at the mouth (PEmax) were measured. At 0.5-2 min postexercise, there was a decrease in Pdimax in both air (P less than 0.02) and O2 studies (P less than 0.05). There was some recovery in Pdimax from 2-5 min postexercise in air (P less than 0.05) and complete recovery 2-5 min postexercise in O2. PEmax did not change postexercise. During exercise in air, the EMG predicted diaphragmatic fatigue in five subjects using a 20% fall of the ratio of high-frequency (150-350 Hz) to low-frequency) (20-46 Hz) power (H/L) as the criterion. Further evidence of diaphragmatic fatigue during exercise in air in two subjects was the decrease in end-inspiratory Pdi toward end exercise. There was an increase in exercise time with O2 (P less than 0.05). The improved performance in O2 was associated with a delay in the fall in H/L and the absence of the decrease in end-inspiratory Pdi in those subjects in whom such changes were observed in air.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximum relaxation rate (MRR) and the time constant of relaxation (tau) of transdiaphragmatic pressure (Pdi) was measured in four male subjects and compared with the high-to-low frequency ratio (H/L) of the diaphragmatic electromyogram (EMG) as a predictor of diaphragmatic fatigue. Pdi and inspiratory time-to-total breath duration ratios (TI/TT) were varied, and TT and tidal volume were held constant; inspiratory resistances were used to increase Pdi. Studies were performed at various tension-time indices (TTdi = Pdi/Pdimax X TI/TT). Base-line MRR/Pdi was 0.0100 +/- 0.0004 (SE) ms-1, and baseline tau was 53.2 +/- 3.2 ms. At TTdi greater than 0.20, MRR and H/L decreased and tau increased, with maximum changes at the highest TTdi. At TTdi less than 0.20, there was no change in H/L, MRR, or tau. The time course of changes in H/L correlated with those of MRR and tau under fatiguing conditions. In this experimental setting, change in relaxation rate was as useful a predictor of diaphragmatic fatigue as fall in H/L of the diaphragmatic EMG.

Diaphragmatic weakness has been identified as one of the pulmonary manifestations of systemic lupus erythematosus. Whether this weakness results from a neuropathic or myopathic process has not been established. Thirty patients with SLE were screened for the presence of inspiratory muscle (IM) weakness. Detailed studies were performed in nine with IM weakness. All nine were found to have diaphragmatic weakness (mean +/- SD, maximal transdiaphragmatic pressure 50 +/- 12 cmH2O). Phrenic nerve latencies, evaluated using transcutaneous stimulation, were normal in all individuals excluding a demyelinating neuropathy. Compound diaphragm action potential (CDAP) with phrenic nerve stimulation was normal in six of these nine patients. Reduced CDAP in three of nine patients was consistent either with axonal degeneration of the phrenic nerve or diaphragm myopathy. Nerve conduction and electromyographic studies on peripheral nerves and muscles respectively failed to demonstrate an associated generalized neuropathy or myopathy. We conclude that diaphragmatic weakness in patients with SLE is both common and is very unlikely to be caused by a phrenic neuropathy.

This study demonstrated that there was interanimal and interregional variability of proportions and sizes of the muscle fiber types in the hamster diaphragm. Muscle fiber type proportions and sizes were determined for each side (right, left), surface (abdominal, thoracic), and region (sternal, anterior costal, posterior costal, crural) in six hamsters. There was marked regional and surface-to-surface variability and some interanimal variability in proportions and sizes of fiber type within the hamster diaphragm. The sternal and costal regions were relatively homogeneous. However, there were differences in both proportions and sizes of fiber types between the thoracic surface of the crural region and the abdominal surface of the crural region. These two surfaces of the crural region differed from the rest of the diaphragm. For muscle fiber type proportions, type 2a fibers demonstrated the most interanimal variability. Muscle fiber size varied little between animals.

The response of the ventilatory pump during exercise in health and in patients with COPD is reviewed. The authors' hope is that the pump's response to the stress of exercise will be seen to be efficiently matched to the demands placed on it, even though in disease or under some extreme circumstances in normal subjects it may be stretched to (or beyond) its capacity. From a review of the literature, suggestions are made for directions for future research.

We performed a two-minute incremental threshold loading test (incremental test) in ten normal subjects on three occasions, and having ascertained the maximum load (max load) against which they could inspire for two minutes, measured how long this load could be tolerated by these same subjects on three further occasions (tlim test). We compared the reproducibility of the two tests. There were no significant differences found in the mean max loads in the three incremental tests, or in the endurance times in the three tlim tests. However, the intraindividual coefficients of variation of max load in the incremental test (0 to 14 percent) were much smaller than the intraindividual coefficients of variation of endurance time in the tlim test (20 to 65 percent). We found that the large variability in endurance time in our tlim tests was most likely accounted for by variability in breathing pattern, inspiratory flow rate and breath-by-breath mouth pressure generation. Differences in these parameters did not, however, explain why in the tlim test a given subject could tolerate for 19 minutes a load only 100 g less than that which he was unable to tolerate for two minutes in the incremental test. These findings emphasize the differences between these two tests of respiratory muscle endurance. Since there was less intraindividual variability in the two-minute incremental threshold loading test, we suggest that this test may be more useful than the tlim test.

1. Hydra that maintain algal symbionts evidenced three modes of metabolism depending upon the nutritional state of the host and the photoperiodic conditions under which the animals were maintained. Animals either fed or fasted but maintained in the dark exhibited an RQ of 0.725 indicating fat metabolism. When they were fed Artemia nauplii and maintained in the light green hydra exhibited a mixed metabolism of carbohydrate and fat which gave an RQ of 0.862. Fasting green hydra, when maintained in the light, showed a pronounced carbohydrate metabolism typified by an RQ of 0.970. 2. Aposymbiotic hydra, whether fed or fasted, exhibited an RQ of 0.725 indicating a high degree of fat metabolism. 3. Symbiotic hydra which were fed and maintained in the light demonstrated a respiration rate of 14.4 microliter/day per hydra, which was 2.5 times greater than animals (symbiotic or aposymbiotic) maintained under any other condition of fasting or photoperiod. It is hypothesized that the enhanced respiration observed in these animals is due to the metabolic activities of the symbiotic algae associated with reproduction and development. 4. Calculations based on respiratory measurements and indirect calorimetry suggest that hydra consume approximately 0.0320 calories per day and that symbiotic algae may supply up to 69% of the host caloric requirements via the translocation of approximately 5 microgram of carbohydrate when the host is fasting and light is provided.

The relaxation rate of transdiaphragmatic pressure (Pdi) after voluntary contractions of the diaphragm slows with fatigue. We determined a range of values for the relaxation rate of mouth pressure (Pm) after voluntary contractions of the inspiratory muscles in 27 normal men and women at various lung volumes at rest. Values were similar for both sexes. The relaxation rates were similar at functional residual capacity (FRC) and below FRC, but were greater above FRC (p less than 0.05). In addition, we studied the effect of diaphragmatic fatigue induced by inspiratory resistive loading on the relaxation rates of Pdi and Pm with voluntary contractions of the inspiratory muscles in 6 subjects. With fatigue, the relaxation rates of Pdi and Pm both decreased by similar amounts, indicating that a decrease in the relaxation rate of Pm is as useful a predictor of inspiratory muscle fatigue as a decrease in the relaxation rate of Pdi has been shown to be for the diaphragm. The relaxation rate of Pm varies widely in normal subjects at rest, so isolated values do not indicate whether fatigue is present or developing. However, this may be predicted if relaxation rate decreases with serial measurements.

Inspiratory muscle function was assessed in a patient with the Lambert-Eaton myasthenic syndrome that developed in association with a bronchogenic carcinoma. Repetitive maximal inspiratory pressure measurements and the electromyographic response to phrenic nerve stimulation established involvement of the inspiratory muscles in general and the diaphragm specifically in this condition.

The rate of relaxation of the diaphragm after stimulated (4 subjects) and voluntary (8 subjects) contractions was compared in normal young men. Stimulated contractions were induced by supramaximal unilateral phrenic nerve stimulation and voluntary contractions by short, sharp sniffs of varying tensions against an occluded airway. The rate of relaxation of the diaphragm was calculated from the rate of decline of transdiaphragmatic pressure (Pdi). In both conditions the maximum relaxation rate (MRR) was proportional to the peak transdiaphragmatic pressure (Pdi), whereas the time constant (tau) of the later exponential decline in Pdi was independent of Pdi. The mean +/- SE rate constant of relaxation (MRR/Pdi) was 0.0078 +/- 0.0002 ms-1 and the mean tau was 57 +/- 3.8 ms for stimulated contractions. The rate of relaxation after sniffs was not different, and it was not affected by either the lung volume at which occluded sniffs were performed (in the range of residual volume to functional residual capacity + 1 liter) or by the relative contribution gastric pressure made to Pdi. After diaphragmatic fatigue was induced by inspiring against a high alinear resistance there was a decrease in relaxation rate. In the 1st min postfatigue MRR/Pdi decreased (0.0063 +/- 0.0003 ms-1; P less than 0.005) and tau increased (83 +/- 5 ms; P less than 0.005). Both values returned to prefatigue levels within 5 min of the end of the studies. We conclude that the sniff may prove to be clinically useful in the detection of diaphragmatic fatigue.

The application of skeletal muscle training principles to the respiratory muscles is a relatively new field. Strength and endurance training of the respiratory muscles can be achieved in normal humans and in patients with neuromuscular and chronic obstructive pulmonary diseases. Careful monitoring is required throughout a training program to ensure that the respiratory muscles are, in fact, being trained. This is a promising area, although further research is necessary to determine the indications for respiratory muscle training. Furthermore, it is still necessary to determine the optimal mode of training.

Diaphragmatic weakness implies a decrease in the strength of the diaphragm. Diaphragmatic paralysis is an extreme form of diaphragmatic weakness. Diaphragmatic paralysis is an uncommon clinical problem while diaphragmatic weakness, although uncommon, is probably frequently unrecognized because appropriate tests to detect its presence are not performed. Weakness of the diaphragm can result from abnormalities at any site along its neuromuscular axis, although it most frequently arises from diseases in the phrenic nerves or from myopathies affecting the diaphragm itself. Presence of diaphragmatic weakness may be suspected from the complaint of dyspnea (particularly on exertion) or orthopnea; the presence of rapid, shallow breathing or, more importantly, paradoxical inward motion of the abdomen during inspiration on physical examination; a restrictive pattern on lung function testing; an elevated hemidiaphragm on chest radiograph; paradoxical upward movement of 1 hemidiaphragm during fluoroscopic imaging; or reductions in maximal static inspiratory pressure. The diagnosis of diaphragmatic weakness is confirmed, however, by a reduction in maximal static transdiaphragmatic pressure (Pdimax). The diagnosis of diaphragmatic paralysis is confirmed by the absence of a compound diaphragm action potential on phrenic nerve stimulation. There are many causes of diaphragmatic weakness and paralysis. In this review we outline an approach we have found useful in attempting to determine a specific cause. Most frequently the cause is either a phrenic neuropathy or diaphragmatic myopathy. Often the neuropathy or myopathy affects other nerves or muscles that can be more easily investigated to determine the specific pathologic basis, and, by association, it is presumed that the diaphragmatic weakness or paralysis is secondary to the same disease process.

Nine anesthetized dogs breathed against an expiratory threshold load (ETL) applied by switching the expiratory circuit into a column of H2O to a depth of 20-30 cm. Arterial blood gas tensions were maintained in the normal range by placing the dogs under arteriovenous bypass to avoid any uncontrolled chemostimulation. There was an increase in integrated electromyogram activity of the diaphragm with the ETL. This was rarely observed after cold block of the vagus nerves which also reduced the evoked expiratory activity. The ventilatory response to hypercapnia was greatly depressed under loaded breathing whether vagal afferents were intact or blocked by cold. Both inspiratory drive and ventilatory timing were affected, suggesting that the central integration of chemosensitive afferents was altered. Proof of supraspinal projections of proprioceptive inputs from abdominal muscles was provided by the demonstration of changes in ventilatory timing during selective activation of muscle spindles in abdominal muscles by high-frequency mechanical vibration applied to the linea alba. Thus these observations suggest that during ETL breathing, a possible interaction exists between chemoreflex drive and proprioceptive afferents.

The capacity to sustain an increase in ventilation (VE) sufficient to decrease the end-tidal partial pressure of carbon dioxide (PETCO2) by about 10 mm Hg was studied in six hypercapnic patients with moderate to severe chronic airflow limitation (CAL). Patients could continue such an increased VE for a finite time (range 5 to 54 minutes). During hyperventilation (H), ventilation was approximately doubled and represented 77.1 +/- 8.4 (mean +/- SE) percent of maximum voluntary ventilation, mean oxygen consumption (VO2) increased 44 percent (p less than 0.005) and mean inspiratory pleural pressure (Ppl) swings were 43.8 +/- 10.5 percent of maximum Ppl. Four patients achieved reductions of PETCO2 less than 10 mm Hg, and two patients achieved or exceeded the target decrease in PETCO2. The decrease in PaCO2 was correlated with the wasted ventilation ratios (VD/VT) during H, the greatest decrease in PaCO2 being related to the lowest VD/VT (p less than 0.05). Electromyographic (EMG) evidence of inspiratory muscle fatigue developed in four of the six patients during H. Five normal subjects achieved an equal or greater decrease in PETCO2, and none showed EMG evidence of inspiratory muscle fatigue. We conclude that, although impaired gas exchange limits the capacity to voluntarily reduce the PaCO2, the development of respiratory muscle fatigue in some patients with CAL may also contribute by limiting the capacity to sustain the substantial increase in respiratory muscle work done in the attempt.

Respiratory muscle weakness occurs commonly at presentation in patients with botulism. Although clinical improvement occurs over several months, symptoms such as fatigue and dyspnea persist in many patients in the long term. To determine whether continued respiratory muscle weakness might contribute to these symptoms, we compared lung function tests, respiratory muscle strength, and exercise performance in 13 patients 2 years after type B botulism. We found that residual symptoms including dyspnea and fatigue were common in botulism patients at 2 years postintoxication. Lung function tests had returned to normal in all patients. Maximal inspiratory and expiratory pressures were similar between botulism patients and control subjects. Evaluation of individual results showed evidence of inspiratory muscle weakness in four of 13 patients with botulism (Plmax less than 65% predicted). Maximal oxygen consumption and maximal workload during exercise were reduced in botulism patients in comparison to control subjects. During exercise, botulism patients had a more rapid and shallow breathing pattern and a higher dyspnea score at a given minute ventilation in comparison to control subjects. Reasons for premature exercise termination in botulism patients were multifactorial. Although respiratory muscle weakness may have been contributory in some patients, most appeared to be limited by reduced cardiovascular fitness, leg fatigue, or reduced motivation.

We measured cardiac output (Q), at rest and during graded exercise, in 68 women and 41 men over the age of 55 yr, using a CO2 rebreathing method. Mean (+/- SD) age was 66 +/- 5 yr in women and 66 +/- 6 yr in men. Only subjects with no history or physical examination findings of pulmonary, cardiac, neuromuscular, or endocrine disease and normal electrocardiography and spirometry were studied. We found a linear relationship between Q and oxygen uptake (VO2) in males and females. The regression equation expressing this relationship in males was Q = 2.9 + 5 VO2 1.min-1 (SEE 2.8) and, in females, Q = 2.9 + 4.6 VO2 1.min-1 (SEE 2.8). This is similar to the relationship previously estimated for elderly males using the direct Fick method and concurs with other reports in the literature which show that, while the Q-VO2 relationship in the elderly has a slope similar to that in younger groups, the Q-VO2 intercept is lower. This means that the absolute level of cardiac output for a given level of work is lower in the elderly than in younger populations. This may reflect an age-related decrease in active metabolic tissue in the elderly and/or altered metabolic regulation with increased oxygen extraction from blood.

To determine if a relationship exists between maximal static respiratory pressures measured at the mouth and age greater than 55 yr, and if so, whether regression equations can be derived that accurately reflect this, we measured maximal inspiratory (Plmax) and expiratory (PEmax) pressures in 64 normal women and 40 normal men older than 55 yr of age. We found no relationship between PImax and PEmax and age greater than 55 yr (all r squared values less than 0.14). We tested the reproducibility of our measurements of PImax and PEmax in 13 and 12 subjects, respectively, on three separate occasions. Repeated measures analysis showed no significant differences in these measurements. Using the measurements obtained in this large study, we calculated 95% confidence limits for PImax and PEmax values in men and women older than 55 yr of age. The 95% confidence limits for PImax in men were 55 to 161 cm H2O, and 26 to 124 cm H2O in women. The 95% confidence limits for PEmax in men were 90 to 256 cm H2O, and 46 to 184 cm H2O in women. We conclude that given the large interindividual variation, a cross-sectional study such as this or other previous studies may not be able to reveal age-dependent changes unless very large numbers are used, and even then potential for bias exists. However, with the small intraindividual coefficients of variation in repeated measurements of PImax and PEmax, a longitudinal study may provide more pertinent information.

The freshwater hydra, Hydra viridis is normally associated with Chlorella-like, algal symbionts which inhabit the host's digestive cells. Under experimental conditions bleached hydra will reassociate with algae harvested from green hydra, but not from our cultures of wild type Chlorella or strain NC64A which when originally isolated from Paramecium bursaria was symbiotically competent. Because of its demonstrated selectivity, the reassociation process is hypothesized to involve a recognition interface whose active participants are the algae cell wall and the digestive cell membrane. The data presented here confirm the hypothesis and suggest some potential molecular characteristics of the interacting partners. Concanavalin A (Con A), a plant lectin, used widely for similar studies in other systems totally inhibits reassociation; Wheat Germ Agglutinin (WGA), ricin and Lens culinaris lectin do so to a lesser degree. These results are consistent with the hypothesis that glycoproteins on the cells' peripheries are involved in cell-cell recognition in this system.

In 11 anesthetized dogs placed under extracorporeal circulation, the vagal feedback was tested by electrical stimulation of the vagus nerves with cold block of their caudal part and by passive lung hyperinflation. The apneic response to such vagal stimulation progressively disappeared during expiratory threshold load breathing but then returned to control values some minutes after the load was removed. This suppression of the inhibitory response to stimulation of the vagus nerves was usually observed when vagal afferents were intact or blocked by cold. However, it was not observed whether no evoked activity continued in expiratory muscles after the cold block, or after suppression of all proprioceptive muscular afferents after transection of the spinal cord at C6 level. These results strongly suggest that enhancement of proprioceptive inputs to the respiratory centers counteracts the vagally mediated inspiratory "off-switch" mechanisms.