Charles M. Wiener

Impaired physiological responses to chronic hypoxia in mice partially deficient for hypoxia-inducible factor 1α

Chronic hypoxia induces polycythemia, pulmonary hypertension, right ventricular hypertrophy, and weight loss. Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding proteins that mediate adaptive responses to hypoxia, including erythropoietin, vascular endothelial growth factor, and glycolytic enzymes. Expression of the HIF-1alpha subunit increases exponentially as O2 concentration is decreased. Hif1a-/- mouse embryos with complete deficiency of HIF-1alpha due to homozygosity for a null allele at the Hif1a locus die at midgestation, with multiple cardiovascular malformations and mesenchymal cell death. Hif1a+/- heterozygotes develop normally and are indistinguishable from Hif1a+/+ wild-type littermates when maintained under normoxic conditions. In this study, the physiological responses of Hif1a+/- and Hif1a+/+ mice exposed to 10% O2 for one to six weeks were analyzed. Hif1a+/- mice demonstrated significantly delayed development of polycythemia, right ventricular hypertrophy, pulmonary hypertension, and pulmonary vascular remodeling and significantly greater weight loss compared with wild-type littermates. These results indicate that partial HIF-1alpha deficiency has significant effects on multiple systemic responses to chronic hypoxia.

Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients

OBJECTIVEnTo assess the safety and potential efficacy of a mechanical ventilation strategy designed to reduce stretch-induced lung injury in acute respiratory distress syndrome.nnnDESIGNnProspective, randomized, controlled clinical trial.nnnSETTINGnEight intensive care units in four teaching hospitals.nnnPATIENTSnFifty-two patients with acute respiratory distress syndrome.nnnINTERVENTIONSnTraditional tidal volume patients: tidal volume 10-12 mL/kg ideal body weight, reduced if inspiratory plateau pressure was > 55 cm H2O (7.3 kPa). Small tidal volume patients: tidal volume 5-8 mL/kg ideal body weight, to keep plateau pressure < 30 cm H2O (4.0 kPa).nnnMEASUREMENTS AND MAIN RESULTSnMean tidal volumes during the first 5 days in traditional and small tidal volume patients were 10.2 and 7.3 mL/kg, respectively (p < .001), with mean plateau pressure = 30.6 and 24.9 cm H2O (3.3 kPa), respectively (p < .001). There were no significant differences in requirements for positive end-expiratory pressure or FIO2, fluid intakes/outputs, requirements for vasopressors, sedatives, or neuromuscular blocking agents, percentage of patients that achieved unassisted breathing, ventilator days, or mortality.nnnCONCLUSIONSnThe reduced tidal volume strategy used in this study was safe. Failure to observe beneficial effects of small tidal volume ventilation treatment in important clinical outcome variables may have occurred because a) the sample size was too small to discern small treatment effects; b) the differences in tidal volumes and plateau pressures were modest; or c) reduced tidal volume ventilation is not beneficial.

Temporal, spatial, and oxygen-regulated expression of hypoxia-inducible factor-1 in the lung

Hypoxia-inducible factor (HIF)-1 is a basic helix-loop-helix transcription factor that transactivates genes encoding proteins that participate in homeostatic responses to hypoxia. Several of these downstream gene products, such as erythropoietin, vascular endothelial growth factor, heme oxygenase-1, and inducible nitric oxide synthase, may contribute to the pathogenesis of pulmonary hypertension. Previous studies demonstrated increased HIF-1 mRNA levels in rats and mice subjected to hypoxia. In this study, we have demonstrated spatial, temporal, and O2-dependent expression of HIF-1 protein. Immunoblot analysis revealed hypoxic induction of HIF-1 in all cultured pulmonary cell types assayed, including those derived from pulmonary arterial endothelium and smooth muscle, bronchial epithelium, alveolar macrophages, alveolar epithelium, and microvascular endothelium. In contrast to all other cell types, pulmonary arterial smooth muscle cells expressed HIF-1 under nonhypoxic conditions. Immunohistochemistry and immunoblot analysis of ferret lungs demonstrated pulmonary expression of HIF-1 in vivo. HIF-1 protein expression was induced maximally when lungs were ventilated with 0 or 1% O2 for 4 h. On reoxygenation, HIF-1 was rapidly degraded, with a half-life of <1 min. These findings demonstrate that HIF-1 expression is tightly coupled to O2 concentration in vivo and are consistent with the involvement of HIF-1 in the physiological and pathophysiological responses to hypoxia in the lung.Hypoxia-inducible factor (HIF)-1 is a basic helix-loop-helix transcription factor that transactivates genes encoding proteins that participate in homeostatic responses to hypoxia. Several of these downstream gene products, such as erythropoietin, vascular endothelial growth factor, heme oxygenase-1, and inducible nitric oxide synthase, may contribute to the pathogenesis of pulmonary hypertension. Previous studies demonstrated increased HIF-1 mRNA levels in rats and mice subjected to hypoxia. In this study, we have demonstrated spatial, temporal, and O2-dependent expression of HIF-1 protein. Immunoblot analysis revealed hypoxic induction of HIF-1 in all cultured pulmonary cell types assayed, including those derived from pulmonary arterial endothelium and smooth muscle, bronchial epithelium, alveolar macrophages, alveolar epithelium, and microvascular endothelium. In contrast to all other cell types, pulmonary arterial smooth muscle cells expressed HIF-1 under nonhypoxic conditions. Immunohistochemistry and immunoblot analysis of ferret lungs demonstrated pulmonary expression of HIF-1 in vivo. HIF-1 protein expression was induced maximally when lungs were ventilated with 0 or 1% O2 for 4 h. On reoxygenation, HIF-1 was rapidly degraded, with a half-life of <1 min. These findings demonstrate that HIF-1 expression is tightly coupled to O2 concentration in vivo and are consistent with the involvement of HIF-1 in the physiological and pathophysiological responses to hypoxia in the lung.

Early use of non‐invasive ventilation prolongs survival in subjects with ALS

Non‐invasive positive pressure ventilation (NPPV) can improve survival in ALS patients with advanced respiratory impairment, but it is not known if it is beneficial earlier in the disease course. A retrospective cohort study of patients with ALS was performed comparing survival from time of diagnosis in subjects who started NPPV use when their FVC was ⩾65% predicted (Early NPPV) with subjects who started NPPV when their FVC was below 65% predicted (Standard NPPV). The Early group (n = 25) and the Standard group (n = 67) were similar except for pulmonary function (mean FVC in Early NPPV group = 74.3±10.1% predicted and 48.3±11.3 in Standard group, p<0.001). The median time from ALS diagnosis to death was significantly longer in the Early NPPV group (2.7 years vs. 1.8 years, p = 0.045). This remained significant after adjustment for potential confounding factors (H.R. = 0.55, 95% CI 0.31–0.98). Survival from time of diagnosis was nearly one year longer in the Early group. Until more definitive data are available from randomized trials, our findings suggest that clinicians either encourage earlier use of NPPV or use more sensitive tests for respiratory muscle impairment than upright FVC.

Amyotrophic lateral sclerosis: evaluation and treatment of respiratory impairment

Patients with amyotrophic lateral sclerosis (ALS) invariably develop respiratory muscle weakness and most die from pulmonary complications. There are numerous tests available to evaluate respiratory status in ALS and it is important to understand their various advantages and limitations. Forced vital capacity (FVC) is commonly used but can remain normal despite substantial inspiratory muscle weakness. Maximal pressures measured at the mouth are useful for excluding weakness if they are normal but are difficult to interpret if abnormal. Invasive testing, such as measurement of transdiaphragmatic pressure, provides an accurate measure of inspiratory strength but is not readily available and is not practical for serial measures. There are supportive respiratory techniques that have been shown to benefit patients with ALS. Clinicians should be familiar with these interventions, including mechanically assisted coughing, non-invasive ventilation and tracheostomy with mechanical ventilation. Observational studies have demonstrated improved survival and quality of life with noninvasive ventilation. Tracheostomy with long-term mechanical ventilation is not frequently used but can be an important component of care for ALS. This review describes an approach to respiratory evaluation and care of patients with ALS.

Pulmonary predictors of survival in amyotrophic lateral sclerosis: Use in clinical trial design

The rapidity of progression of amyotrophic lateral sclerosis (ALS) to death or respiratory failure impacts patients, clinicians, and clinical investigators. This study compared the abilities of various pulmonary function tests to predict tracheostomy‐free survival. We evaluated 95 ALS patients by determining upright and supine forced vital capacity (FVC), maximal inspiratory (MIP) and expiratory (MEP) pressures, arterial partial pressure of carbon dioxide (PaCO2), and transdiaphragmatic sniff pressures (Pdi‐sniff). Tracheostomy‐free survival time was measured from the date of spirometry. Supine FVC, upright FVC, MIP, MEP, and Pdi‐sniff were significantly associated with tracheostomy‐free survival after controlling for nonpulmonary factors, whereas PaCO2 was not. A normal supine FVC, MIP, or MEP was highly predictive for one‐year survival. These tests are well suited to predict survival for trial enrollment and patient counseling. Supine FVCs simplicity of use and availability to ALS investigators makes it a particularly attractive predictor of one‐year survival in ALS. Muscle Nerve, 2005

Use of noninvasive ventilation in patients with amyotrophic lateral sclerosis

INTRODUCTION: Noninvasive positive pressure ventilation (NIPPV) is associated with improved survival in amyotrophic lateral sclerosis (ALS) and has been widely recommended. The extent of NIPPV use in ALS patients and the factors associated with its use have not been studied. METHODS: A cross‐sectional study using the ALS Patient Care Database. Analyses were performed to assess the association of patient and care characteristics with use of ventilatory support. RESULTS: 1458 patients were studied. 15.6% used NIPPV and 2.1% used invasive mechanical ventilation. Patients who used NIPPV were significantly more likely to be male and have higher income than those who did not. They were also more likely to have a gastrostomy tube, lower vital capacity, more severe disease, bulbar involvement and poorer general health status as measured by the SF‐12 and Sickness Impact Profile. Multivariate analysis revealed that lower FVC, higher income and use of gastrostomy tube were independently associated with use of NIPPV. CONCLUSIONS: NIPPV is used more than seven times as frequently as invasive ventilation in ALS patients. Patients who use NIPPV have more severe disease than those who do not use any respiratory intervention. Patients with lower income are less likely to use NIPPV, which raises concerns about disparities in the care of patients with ALS.

Superoxide and endothelium‐dependent constriction to flow in porcine small pulmonary arteries

The aim of this study was to determine the response of porcine small pulmonary arteries to intralumenal flow and to identify the cellular mechanisms and potential mediators involved in the response. Porcine small pulmonary arteries were isolated from a branch of the main intrapulmonary artery of the lower lung lobe and studied in a perfusion myograph system that allowed independent control of transmural pressure and intralumenal flow. At a transmural pressure of 20 mmHg, the baseline internal diameter (BID) of the arteries was 251.2±16.1 μm (n=16). Under quiescent conditions or during constriction with U46619 to ∼60% of BID, intralumenal flow caused reversible constriction in arteries with endothelium (in the presence of U46619, flow decreased diameter from 60.0±2.5% to 49.5±3.0% BID at 10 μl min−1, n=16, P<0.05) but no change in diameter of arteries without endothelium. In the presence of superoxide dismutase (SOD, 150 u ml−1), the response to flow was converted from constriction to vasodilatation (in presence of U46619 and SOD, flow increased diameter from 54.2±3.4% to 76.7±4.5% BID at 10 μl min−1, n=10, P<0.05). Inhibition of NO synthase with L‐NAME (3×10−5 M) abolished the flow‐induced vasodilatation occurring in the presence of SOD and the flow‐induced constriction occurring in the absence of SOD. In arteries with endothelium, L‐NAME (3×10−5 M) caused significant vasoconstriction, whereas SOD did not alter vasomotor tone. Acetylcholine (10−8 to 10−6 M) caused endothelium‐dependent relaxation of small pulmonary arteries that was not significantly affected by SOD (150 u ml−1) but was inhibited by L‐NAME (3×10−5 M). These results suggest that in small, porcine, isolated pulmonary arteries, intralumenal flow increases the production of NO but this is obscured by the generation of superoxide which causes vasoconstriction.

Western Lessons/Eastern Perspectives: Combining Neurology and Psychiatry in Preclinical Medical Student Education in Malaysia

Designated the “Decade of the Brain,” the 1990s was a time of increased public and political awareness of neuroscience and brought a renewed vigor and inspection to the interplay between the brain and themind. Coming after several decades of abundant research in the field, the end of the twentieth century marked significant changes in the understanding of the pathology and etiology of many psychological and neurologic diseases. In light of increasing public awareness, new technologies, and changing perceptions of psychiatric disease etiology, a growing number of practitioners within the fields have identified a need for more collaboration and interaction between psychiatrists and neurologists and a redesigning of the way medical students are taught about the brain and the mind. Notable neuroscientists, educators, and physicians argue that “the education of future psychiatrists and neurologists should be redesigned” [1].

Transcriptional Responses Mediated by Hypoxia-Inducible Factor 1

Hypoxia-inducible factor 1 (HIF-1) is a basic helix-loop-helix protein that activates transcription of hypoxia-inducible genes, including those encoding erythropoietin, vascular endothelial growth factor, heme oxygenase-1, inducible nitric oxide synthase, and the glycolytic enzymes aldolase A, enolase 1, lactate dehydrogenase A, phosphofructokinase L, and phosphoglycerate kinase 1. Hypoxia response elements from these genes consist of a HIF-1-binding site as well as additional DNA sequences that are required for function, which in some elements include a second HIF-1-binding site. HIF-1 is a heterodimer: the HIF-lα subunit is unique to HIF-1, while HIF-1β (ARNT) can dimerize with other proteins. Cotransfection of HIF-1α and HIF-1β (ARNT) expression vectors and a reporter gene containing a wild-type hypoxia response element resulted in increased transcription in nonhypoxic cells and a superinduction of transcription in hypoxic cells, whereas HIF-1 expression vectors had no effect on transcription of reporter genes containing a HIF-1 binding-site mutation. In HeLa cells, HIF-lα and HIF-1β protein levels and HIF-1 DNA-binding activity increased exponentially as oxygen tension decreased, with maximum values at 0.5% oxygen and half-maximal values at 1.5%–2% oxygen. HIF-lα and HIF-1β (ARNT) mRNAs were detected in all human and rodent organs assayed. HIF-lα protein levels were induced in vivo when animals were subjected to anemia or hypoxia.