Time course analysis of mechanical ventilation-induced diaphragm contractile muscle dysfunction in the rat.

Controlled mechanical ventilation (CMV) plays a key role in triggering the impaired diaphragm muscle function and the concomitant delayed weaning from the respirator in critically ill intensive care unit (ICU) patients. To date, experimental and clinical studies have primarily focused on early effects on the diaphragm by CMV, or at specific time points. To improve our understanding of the mechanisms underlying the impaired diaphragm muscle function in response to mechanical ventilation, we have performed time-resolved analyses between 6 h and 14 days using an experimental rat ICU model allowing detailed studies of the diaphragm in response to long-term CMV. A rapid and early decline in maximum muscle fibre force and preceding muscle fibre atrophy was observed in the diaphragm in response to CMV, resulting in an 85% reduction in residual diaphragm fibre function after 9-14 days of CMV. A modest loss of contractile proteins was observed and linked to an early activation of the ubiquitin proteasome pathway, myosin:actin ratios were not affected and the transcriptional regulation of myosin isoforms did not show any dramatic changes during the observation period. Furthermore, small angle X-ray diffraction analyses demonstrate that myosin can bind to actin in an ATP-dependent manner even after 9-14 days of exposure to CMV. Thus, quantitative changes in muscle fibre size and contractile proteins are not the dominating factors underlying the dramatic decline in diaphragm muscle function in response to CMV, in contrast to earlier observations in limb muscles. The observed early loss of subsarcolemmal neuronal nitric oxide synthase activity, onset of oxidative stress, intracellular lipid accumulation and post-translational protein modifications strongly argue for significant qualitative changes in contractile proteins causing the severely impaired residual function in diaphragm fibres after long-term mechanical ventilation. For the first time, the present study demonstrates novel changes in the diaphragm structure/function and underlying mechanisms at the gene, protein and cellular levels in response to CMV at a high temporal resolution ranging from 6 h to 14 days.

Impact of post-synaptic block of neuromuscular transmission, muscle unloading and mechanical ventilation on skeletal muscle protein and mRNA expression.

To analyse mechanisms of muscle wasting in intensive care unit patients, we developed an experimental model where rats were pharmacologically paralysed by post-synaptic block of neuromuscular transmission (NMB) and mechanically ventilated for 9+/-2 days. Specific interest was focused on the effects on protein and mRNA expression of sarcomeric proteins, i.e., myosin heavy chain (MyHC), actin, myosin-binding protein C (MyBP-C) and myosin-binding protein H (MyBP-H) in fast- and slow-twitch limb, respiratory and masticatory muscles. Muscle-specific differences were observed in response to NMB at both the protein and mRNA levels. At the protein level, a decreased MyHC-to-actin ratio was observed in all muscles excluding the diaphragm, whereas at the mRNA level a decreased expression of the dominating MyHC isoform(s) was observed in the hind limb and intercostal muscles, but not in the diaphragm and masseter muscles. MyBP-C mRNA expression was decreased in the limb muscles, but it otherwise remained unaffected. MyBP-H conversely increased in all muscles. Furthermore, we found myofibrillar protein and mRNA expression to be affected differently when comparing NMB animals with peripherally denervated (DEN) ambulatory rats. We report that NMB has both a larger and different impact on muscle, at the protein and mRNA levels, than DEN has.

Carotid and aortic baroreflexes of the rat: I. Open-loop steady-state properties and blood pressure variability.

To characterize the baroreflex in central nervous system-intact neuromuscular-blocked rats, we measured the vascular and cardiac responses and compared direct stimulation of the aortic depressor nerve (ADN) with a capacitance electrode (differentially activating either A or A + C fibers) to carotid sinus pressure with a micro-balloon (SINUS). One-thousand-two-hundred-ninety-seven open-loop measurements of systolic blood pressure (SBP), heart rate, venous pressure (VBP), and mesenteric (msBF), femoral (fmBF), and skin (skBF) blood flow were completed; the linear range of the effects was determined for each response and stimulus mode. The rats were sinoaortic denervated (SAD). The open-loop stimulation effect was very stable; e.g., the mean effect of 790 ADN stimulations during >7 days was -9.8 mmHg, with an average drift of +0.001 mmHg/h. In contrast, there was large variability of the SBP baseline (e.g., SD = +/-10.9), which was due to SAD (+/-6.3 to +/-16.3 mmHg, t = -13. 9, df = 4, P < 0.0002) and was reversed by ganglionic block (+/-10.8 to +/- 2.9 mmHg, t = -12.9, df = 3, P < 0.001). The ADN stimuli produced larger depressor responses than sinus stimuli (-66 vs. -45 mmHg); all component responses paralleled the magnitude of the SBP effect, except interbeat interval (IBI), for which the ADN DeltaIBI was approximately 10 times that of SINUS. For all stimuli, fmBF increased and msBF did not. Mesenteric and femoral vascular conductance both increased, whereas VBP decreased and skBF followed SBP. We found that for all baroreflex response components, with the exception of SINUS-elicited DeltaIBI, there was an orderly, substantially linear, relationship between stimulus strength and response magnitude.

Carotid and aortic baroreflexes of the rat: II. Open-loop frequency response and the blood pressure spectrum.

To determine the relationship between blood pressure (BP) variability and the open-loop frequency domain transfer function (TF) of the baroreflexes, we measured the pre- and postsinoaortic denervation (SAD) spectra and the effects of periodic and step inputs to the aortic depressor nerve and isolated carotid sinus of central nervous system-intact, neuromuscular-blocked (NMB) rats. Similar to previous results in freely moving rats, SAD greatly increased very low frequency (VLF) (0.01-0.2 Hz) systolic blood pressure (SBP) noise power. Step response-frequency measurements for SBP; interbeat interval (IBI); venous pressure; mesenteric, femoral, and skin blood flow; and direct modulation analyses of SBP showed that only VLF variability could be substantially attenuated by an intact baroreflex. The -3-dB frequency for SBP is 0.035-0.056 Hz; femoral vascular conductance is similar to SBP, but mesenteric vascular conductance has a reliably lower and IBI has a reliably higher -3-dB point. The overall open-loop transportation lag, of which

Introduction and commentary to: M.I. Mityushov (1954) "Conditioned reflex secretion of insulin".

Recent research on the role of classical conditioning in homeostatic regulation (Dworkin, 1993; Siegel, Krank & Hinson, 1987) has underscored the potential importance of the work of earlier Eastern-European work on physiological conditioning. The present article is a translation and discussion of a paper on blood glucose conditioning, first published in 1954 by the Russian physiologist M.I. Mityushov. Mityushov was able to demonstrate conditioned hypoglycemia in humans and dogs after using an injection procedure as the CS and intravenous glucose as the UCS. The translation is preceded by a general introduction and followed by a reanalysis and discussion of Mityushov's results.

Pruritus in chronic hepatitis C: association with high serum bile acids, advanced pathology, and bile duct abnormalities.

Pruritus is a common symptom of chronic cholestatic liver diseases but is considered rare in chronic hepatitis. We observed pruritus to be an unusually common complaint in patients with advanced chronic hepatitis C. We reviewed the records of 175 chronic hepatitis C patients to identify patients with severe, diffuse, unexplained pruritus; 12 consecutive prospective patients undergoing liver biopsy for chronic hepatitis C served as controls. Assessment included laboratory biochemical tests and assessment of liver pathology by stage, grade, hepatic activity index, and a bile duct score. Pruritus was present in nine (5.1%) patients. Serum AST, ALT, alkaline phosphatase, GGTP, total bilirubin, and ferritin were similar in pruritics and controls. Pruritics had higher serum bile acids (2028.4 +/- 223.1 mmol/liter vs 423.1 +/- 194.3, P < 0.001), higher transferrin saturation (57.5 +/- 6.8% vs 33.2 +/- 3.3, P < 0.01), and lower HCV RNA by bDNA (24.5 +/- 12.7 x 10(5) vs 172.7 +/- 54.1 x 10(5), P < 0.05). Pathology revealed cirrhosis in 6/9 (66.6%) pruritics vs 1/12 (8.3%) controls (P < 0.01). Pruritics had higher pathologic stage (3.7 +/- 0.2 vs 2.2 +/- 0.4, P < 0.01), grade (4.4 +/- 0.2 vs 2.1 +/- 0.2, P < 0.001), activity index (14.3 +/- 1.9 vs 8.6 +/- 1.9, P < 0.025), and bile duct score (7.6 +/- 0.6 vs 4.7 +/- 0.4, P < 0.01). Of eight pruritics treated with IFN-alpha2b, two had complete ALT response and one relapsed. Pruritus followed a relapsing course and only three patients partially responded despite a variety of interventions. In conclusion, pruritus is a common complication of advanced CHC. Its presence is associated with high serum bile acids, advanced pathology and bile duct abnormalities. The clinical course of pruritus is relapsing and response to therapy is inconsistent. These features suggest that pruritus in CHC has a pathogenesis that may vary from that of chronic cholestatic diseases.

Liver function in early Lyme disease.

To evaluate the frequency, pattern, and severity of liver function test abnormalities in patients with Lyme disease associated with erythema migrans (EM), 115 individuals with no other identifiable cause for liver function test abnormalities who presented with EM between July 1990 and September 1993 were prospectively evaluated. For individuals with abnormal liver function tests, common causes of hepatitis, including hepatitis A, B, and C, were excluded. A local control group was used for comparison. Forty-six (40%) patients had at least one liver test abnormality, and 31 (27%) had more than 1 abnormality compared with 19 (19%) and 4 (4%) of controls, respectively (P < .01 for each comparison). gamma-Glutamyl transpeptidase (28%) and alanine transaminase (ALT) (27%) were the most frequently elevated liver function tests among Lyme disease patients. Anorexia, nausea, or vomiting was reported by 30% of patients, but did not occur more frequently in patients with elevated liver function tests compared with those with normal values. Patients with early disseminated Lyme disease were more likely to have elevated liver function studies (66%) compared with patients with localized disease (34%) (P = .002). After antibiotic treatment, elevated liver function tests improved or resolved in most patients. Liver function test abnormalities are common in patients with EM but were mild, most often not associated with symptoms, and improved or resolved by 3 weeks after the onset of antibiotic therapy in most patients.

Learning of physiological responses: II. Classical conditioning of the baroreflex.

The baroreflex can be classically conditioned. In neuromuscular blocked (NMB) rats, electrical stimulation of the aortic depressor nerve (ADN) and dopamine-produced blood pressure rise were effective unconditioned stimuli (UCS) for auditory discriminative classical conditioning. The conditioned response (CR) pattern (bradycardia, vasodilatation, and hypotension > 10 torr) closely resembled that of the unconditioned baroreflex. Conditioned stimulus (CS) specificity was demonstrated by discrimination of baroreflex-associated and nonassociated auditory stimuli, and also by elaborating depressor and pressor CRs to auditory CSs, which respectively had been associated with either baro-afferent (depressor) or tail-shock (pressor) UCSs. The conditioned-baroreflex-magnitude increased with trials. These findings support quantitative models in which CRs interact with and calibrate the gain and dynamic properties of natural reflexes.

The breakthrough phenomenon during alpha-interferon therapy of chronic hepatitis C: incidence, management, and outcome.

OBJECTIVES: Some patients treated with alpha-interferon (alpha-IFN) for chronic hepatitis C (CHC) initially respond with normalization of ALT only to encounter a rise in ALT while still on the drug. This phenomenon is called breakthrough (BT). We reviewed our experience with BT to clarify its incidence, pathogenesis, management, and outcome. METHODS: Charts from 71 consecutive patients with CHC treated with alpha-IFN were reviewed. Forty of these patients were part of a study of 1-yr escalating dose alpha-IFN, initiated at 2 million units (MU) 3 times per week. Endpoints that were evaluated were: reachievement of normal ALT, complete response (CR) (defined as normal ALT at the end of therapy), and sustained CR maintained for 6 months after therapy. RESULTS: Twenty-one (29.5%) patients sustained 28 BT events. Thirteen (46.4%) BT events occurred during the first 6 months of a course of alpha-IFN therapy, and 15 (53.6%) occurred during months 7 through 12. Of patients experiencing BT, six (28.6%) completed their course of therapy with a CR, of which two (9.5%) were sustained. By comparison, of 22 patients who normalized ALT without BT, all completed their course with a CR by definition (p < 0.0001), and nine (40.9%, p < 0.05) had a sustained CR. Of 28 BT events, 13 (46.4%) were followed by reattainment of normal ALT. Of 16 BT events managed with continuation of the same dose of alpha-IFN, normal ALT was reachieved in seven (43.8%). Of 12 BT events managed with an escalation in alpha-IFN dose, six (50%) reachieved normal ALT. A full sequential series of hepatitis C virus RNA PCR from periods of elevated, normal, and again elevated ALT was available for 12 BT events. The pattern was +/+/+ in six, +/-/+ in five, and +/-/- in one. In one additional patient, an apparent BT was attributable to alpha-IFN-induced autoimmune hepatitis. CONCLUSIONS: BT is a common event that may occur at any point during alpha-IFN therapy of CHC. This may limit the benefits of maintenance strategies. After a BT event, normal ALT can be reestablished in about 50% of cases, although the chance of a sustained CR falls to less than 10%. No advantage was demonstrated for escalating the alpha-IFN dose after a BT event. Therefore, we recommend continuation of the same dose as the initial approach. We suspect that BT relates to nonspecific ALT fluctuation in some patients and to emergence of resistant hepatitis C virus strains in others. Other causes of ALT elevation must also be considered in patients with apparent BT.

Low-dose dexamethasone as adjunctive therapy for disseminated Mycobacterium avium complex infections in AIDS patients.

Five human immunodeficiency virus-infected patients with disseminated Mycobacterium avium complex infection had progressive weight loss and persistent fever despite multidrug antimycobacterial therapy. These patients were given daily low-dose oral dexamethasone (typically 2 mg/day) as adjunctive therapy. All had substantial and sustained weight gain (12 to 50% of pre-steroid treatment body weight [P < 0.03]), reduction in fever, and an improved sense of well-being. The serum albumin level increased during dexamethasone therapy (from 3.06 +/- 0.59 g/dl [mean +/- standard deviation] to 3.9 +/- 0.22 g/dl [P < 0.01]), while the serum alkaline phosphatase level fell (from 368 +/- 247 U/liter to 128 +/- 43.6 U/liter [P < 0.04]). Further studies of the potential role for corticosteroids in the management of disseminated M. avium complex infections in human immunodeficiency virus-infected patients are warranted.

Behavioral treatment of scoliosis and kyphosis.

A behavioral treatment of scoliosis and kyphosis was tested with 27 adolescent patients (19 scoliosis, eight kyphosis patients) to determine in which cases the conspicuous and restraining brace treatment could be replaced. In 22 compliant patients, posture biofeedback (PB) was highly effective compared to five non-compliant patients. Biologically more mature scoliosis patients (menarche at the beginning of treatment) seemed to profit more from PB. With kyphosis patients the PB treatment resulted in rapid straightening of the spine and removal of structural deformities of Scheuermann's disease. PB may serve as an unobtrusive yet effective treatment alternative for both juvenile scoliosis and kyphosis.

Open label study of long-term effectiveness of cisapride in patients with idiopathic gastroparesis.

Cisapride induces acetylcholine release in cells of the myenteric plexus, thus promoting gastrointestinal motility. We studied the effects of cisapride on 11 patients with idiopathic gastroparesis. All had negative gastrointestinal endoscopy, normal glucose, and took no drugs capable of influencing motility. Most (9/11) were prior metoclopramide treatment failures. Patients' symptoms were scored (0-60) for pain, satiety, bloating, nausea, vomiting, and heartburn. All underwent a solid gastric emptying study using a Technetium-99-labeled egg meal and received placebo prior to cisapride. There were 10 females and one male with a mean (+/- SE) age of 37.8 +/- 2.6 years. Disease duration was 7.9 +/- 2.8 years. The dose of cisapride was 30-60 mg/day and the duration of therapy was 12.6 +/- 2.6 months (range 2.5-25 months). The symptom score improved on cisapride from 30.9 +/- 3.6 to 14.4 +/- 2.7 (P < 0.002 signed rank test). Emptying half-time improved from 113 +/- 4 min to 94 +/- 6 min, and 46.9 +/- 2.4% food remaining at 120 min decreased to 35.5 +/- 3.6% (both P < 0.05). Emptying half-time in normals was 68 +/- 5 min with 16.9 +/- 2.9% remaining at 120 min. Nine of 11 patients gained weight, with a mean increase of 6.7 +/- 1.6 lb (range 2-12 lb). We conclude that cisapride significantly reduces gastrointestinal symptoms and promotes weight gain in patients with idiopathic gastroparesis and is associated with improvement in solid gastric emptying. The drug is useful in patients who previously failed metoclopramide.

Central effects of baroreceptor activation in humans: attenuation of skeletal reflexes and pain perception.

Activating the arterial baroreceptors blunts pain sensation and produces other forms of central nervous system inhibition in animals. These effects may be important to blood pressure regulation but have not been rigorously verified in humans. We describe (i) a noninvasive behaviorally unbiased method for baroreceptor stimulation and (ii) the application of this method to measurement of baroreceptor-mediated attenuation of pain perception and of the Achilles tendon reflex. The findings are relevant to basic mechanisms of blood pressure stabilization and cardiovascular reactivity and may also have implications for noncompliance with antihypertensive medications and for the pathophysiology of essential hypertension.

Selenium deficiency in HIV infection and the acquired immunodeficiency syndrome (AIDS).

UNLABELLED: Selenium is required for activity of the enzyme glutathione peroxidase, and selenium deficiency may be associated with myopathy, cardiomyopathy and immune dysfunction including oral candidiasis, impaired phagocytic function and decreased CD4 T-cells. We assessed selenium status in 12 patients with AIDS compared to normals and found significantly low plasma and red blood cell levels. Plasma selenium in AIDS was 0.043 +/- 0.01 microgram/ml vs 0.095 +/- 0.016 in controls (P < 0.001). Selenium status correlated with serum albumin (r = 0.77; P < 0.001) and 60% had documented GI malabsorption as determined by abnormal D-Xylose tests. In a subsequent study blood selenium and glutathione peroxidase were diminished in 12 AIDS and 8 ARC patients compared with normals (all P < 0.001). For glutathione peroxidase the mean levels were decreased by 45% in AIDS and 27% in ARC versus controls (P < 0.001). Both plasma selenium and glutathione peroxidase significantly correlated with total lymphocyte counts (r = 0.65; P < 0.001; glutathione peroxidase and lymphocyte counts). This occurred in both homosexuals and drug users with AIDS and irrespective of the presence or absence of diarrhea or GI malabsorption. To determine if tissue levels of selenium were also depleted we studied cardiac selenium levels in autopsy AIDS hearts compared to age and sex matched controls. Cardiac selenium in AIDS was 0.327 +/- 0.082 micrograms/g dry weight versus 0.534 +/- 0.184 in controls (P < 0.01). Two cases had histologic cardiomyopathy pathologically consistent with the cardiomyopathy described in Keshan disease associated with low selenium blood levels. To further assess mechanisms of nutrient and selenium deficiency in AIDS we studied dietary intake in outpatients and inpatients with various stages of HIV infection. Inadequate selenium intake based on a computer (Nutritionist 3) analysis of 72 h diet records was present in only 17% of clinically stable HIV positive outpatients and 71% of inpatients with AIDS. CONCLUSIONS: Selenium deficiency is common in HIV positive patients as documented by low plasma and red blood cell levels of selenium, diminished activity of glutathione peroxidase, and low cardiac selenium levels in AIDS hearts. Patients with AIDS tend to have more severe deficits than those with earlier stages of HIV infection. The selenium deficit in blood does correlate with serum albumin levels and total lymphocyte counts. Poor dietary intake and malabsorption could lead to this condition which has important implications for both cardiac and immune functions in HIV positive patients.

Sensory effects of baroreceptor activation and perceived stress together predict long-term blood pressure elevations.

Activating the arterial baroreceptors in animals has been shown to blunt pain sensation and provide other forms of central nervous system inhibition. This study tested the hypothesis that, among human subjects, a tonic increase in blood pressure (BP) could be a learned response to environmental stressors among subjects in whom the baroreceptor inhibitory mechanism is active. In a sample of 96 healthy, normotensive men and women, amount of pain-reduction produced by baroreceptor stimulation predicted an increase in resting BP 20 months later: the increase was proportional to self-assessed daily life stress. Among the subjects reporting the greatest amount of stress, the pain inhibition effect accounted for more than 80% of the BP variance. These results support the hypothesis that the reduction in perceived stress produced by baroreceptor stimulation may reward learned increases in BP.

Cigarette smoking, blood lipids, and baroreceptor-modulated nociception.

Activation of arterial blood pressure has been shown to influence higher central nervous activity. In animals, induction of sleep-like states and increases of seizure and pain thresholds in response to baroreceptor stimulation have been reported. In certain human groups, mechanical stimulation of the carotid baroreceptors also increases pain thresholds. The present paper examines the hypothesis that smokers show baroreceptor dependent antinociception as compared to non-smokers. It is speculated that one effect which rewards smoking is the nicotine induced phasic blood pressure increase which leads to baroreceptor stimulation and dampens pain perception. One hundred and twenty subjects were investigated using a recently developed mechanical baroreceptor stimulation technique and an electrical pain stimulus. The group of heavy smokers showed the predicted effect: their pain thresholds were enhanced during conditions of increased baroreceptor activity as compared to the control condition. The group of medium, light and non-smokers, however, did not show this effect. Neither blood lipid levels nor diastolic or systolic blood pressure paralleled the group differences on baroreceptor dependent antinociception. In heavy smokers, the nicotine induced phasic blood pressure increases might have baroreceptor dependent pain dampening effects, which might be among the reinforcing qualities of smoking.

The safety and efficacy of gi endoscopy in patients with acute-leukemia - a review of 27 cases.

In the course of aggressive treatment for acute leukemia, the ensuing pancytopenia and intensive medical support may be accompanied by severe gastrointestinal (GI) complications. Therefore, to assess the safety and efficacy of GI endoscopy as a means of diagnosis, we analyzed the records of 16 patients undergoing 27 endoscopies a mean (+/-S.D.) of 18.4 +/- 11.9 days post chemotherapy. There were 6 procedures performed in patients with acute lymphocytic, 18 with acute myelogenous, including 3 with acute promyelocytic and 3 with blastic phase chronic myelogenous leukemia. 10/27 procedures were performed in patients with less than 1000 WBC/mm3 and 19/27 had less than 100,000 platelets. 15 patients had 25 upper endoscopies done for: bleeding (twenty-one), abdominal pain (two), and persistent vomiting (two). The principal bleeding sources were: esophagitis (eleven), Mallory Weiss tear (one), gastritis (three), gastric ulcer (one), duodenal ulcer (five). In the non-bleeding cases 2 exams were normal and the others had gastritis (one) and esophagitis (one). 15/25 procedures (64%) resulted in new diagnosis and 20/25 (80%) in additional therapies. 47% of patients undergoing upper GI endoscopy received specific new therapies as a result of that procedure. Nd: YAG laser photocoagulation was effective in stopping bleeding lesions in 4/6 cases. 10/12 bleeding patients had persistent or recurrent bleeding and 2 died from bleeding. None had surgery. Two patients underwent colonoscopy, both for colonic distention. One patient, who had been recently treated for Cl. difficile had submucosal petechiae. The other had non-specific colitis. No biopsies were done and both cases were successfully decompressed..No complications occurred from any GI endoscopy. We conclude that GI endoscopy can be safely performed in patients with acute leukemia, resulting in specific diagnoses and therapies. Esophagitis is a principal cause of GI bleeding in these patients. The role of therapeutic endoscopy in controlling bleeding is promising but requires further evaluation.

Verification of skeletal activity in tibial nerve recordings: a reply to Roberts (1991).

In Dworkin and Dworkin (1990), we described classically conditioned tibial nerve responses that were uncorrelated with vasomotor responses in the same limb. We pointed out that this finding conflicted with the persisting idea that skeletal and autonomic responses are permanently locked into fixed action patterns that can not be reorganized by learning (Cohen & Obrist, 1975). Roberts (1991) has doubted our interpretation. In this reply, we rebut his arguments and also describe new pharmacological and other recent data showing unambiguously that the nerve activity we measured was not of postganglionic sympathetic origin. We conclude that the nerve activity was most probably due to motoneurons and reiterate that the results of our experiment specifically failed to support a general assertion of obligatory central coupling between skeletal and autonomic mechanisms.