Biomedical subjects

Tarek Sharshar

Publications and source records attributed to Tarek Sharshar.

25 records · Page 2Linked to original sources

PubMed2003

Effect of voluntary facilitation on the diaphragmatic response to transcranial magnetic stimulation.

We assessed recruitment curves of the surface diaphragm motor-evoked potential (MEP) after transcranial magnetic stimulation during relaxation and at three different levels of facilitation (20, 40, and 60% of maximal inspiratory esophageal pressure) in 10 healthy subjects (six young and four elderly). MEP amplitude recruitment curves varied between individuals during relaxation and at each level of facilitation. Amplitude recruitment curves during relaxation were reproducible in individual subjects. Inspiratory maneuvers caused a decrease in motor threshold and latency and an increase in MEP amplitude, positively correlated to the intensity of facilitation. These changes were similar in young and elderly subjects. The best fit for MEP amplitude recruitment curves for each condition was obtained with a Boltzmann model. The performance of repeated submaximal inspiratory maneuvers did not affect the amplitude recruitment curves of the relaxed diaphragm. We conclude that the recruitment curve of the diaphragm with transcranial magnetic stimulation is repeatable and changes consistently with facilitation and will, therefore, be a robust experimental tool for the investigation of supraspinal pathways to the diaphragm.

Adult↗

PubMed2003

Air leaks during mechanical ventilation as a cause of persistent hypercapnia in neuromuscular disorders.

OBJECTIVE: This study investigated whether air leaks from the upper airway during assisted ventilatory support are associated with persistent hypercapnia (PaCO(2) >45 mmHg) in patients with neuromuscular disorders. SETTING: A rehabilitation hospital. PATIENTS: The study was performed in 95 neuromuscular patients; 52 were tracheostomized with a cuffless tracheostomy tube (invasive ventilation), and 43 received noninvasive ventilation. MEASUREMENTS AND RESULTS: The volume of air leaked (VL) and arterial carbon dioxide (PaCO(2)) were routinely measured during mechanical ventilation; PaCO(2) was also measured during spontaneous breathing. VL, expressed as a percentage of tidal volume, was higher in the hypercapnic group (32+/-14%, n=20) than the nonhypercapnic group ( vs. 20+/-14%). PaCO(2) during mechanical ventilation was correlated with both VL and the duration of ventilatory support per day; PaCO(2) during spontaneous breathing was correlated only with the volume of air leaked. In stepwise multiple regression analysis, air leaks contributed to 8% of the variance in PaCO(2) during mechanical ventilation, and daily duration of ventilatory support contributed 5%. In addition, reduction in VL with normalization of PaCO(2) was achieved in five of the noninvasively ventilated patients with persistent hypercapnia by using a chin strap. CONCLUSIONS: Air leaks during wakefulness are an important cause of persistent hypercapnia in both invasively and noninvasively ventilated neuromuscular patients. However, simple practical measures to reduce the volume of air leaks improve the efficacy of ventilation in these patients.

Adult↗

PubMed2003

Early predictors of mechanical ventilation in Guillain-Barré syndrome.

OBJECTIVE: Although mechanical ventilation is required in 30% of patients with Guillain-Barré syndrome, early predictors of this treatment remain unknown. DESIGN: Analysis of two cohorts of patients enrolled in two multicenter randomized clinical trials. SETTING: French intensive care and neurologic units. MEASUREMENTS: Demographic, neurologic, and biologic data; vital capacity; and time of onset, admission, and endotracheal mechanical ventilation were collected. RESULTS: Amid 722 consecutive adults not ventilated at admission, endotracheal mechanical ventilation was required in 313 (43%) patients. Multivariate analyses identified six predictors of endotracheal mechanical ventilation: time from onset to admission of <7 days (odds ratio, 2.51), inability to cough (odds ratio, 9.09), inability to stand (odds ratio, 2.53), inability to lift the elbows (odds ratio, 2.99) or head (odds ratio, 4.34), and liver enzyme increases (odds ratio, 2.09). In the 196 (27%) patients whose vital capacity was measured, time from onset to admission of <7 days (odds ratio, 5.00), inability to lift the head (odds ratio, 5.00), and vital capacity <60% (odds ratio, 2.86) predicted endotracheal mechanical ventilation. CONCLUSIONS: Patients with at least one of these predictors should be monitored in an intensive care unit. Mechanical ventilation was required in >85% of patients with at least four predictors from the first multivariate model and in 85% of patients with all three predictors from the second multivariate model. In these patients at high risk of respiratory failure, the value of early mechanical ventilation may deserve investigation.

Analysis of Variance↗

PubMed2003

Circulating vasopressin levels in septic shock.

OBJECTIVE: To assess the frequency of vasopressin deficiency in septic shock. DESIGN: Prospective cohort study. SETTING: Intensive care unit at Raymond Poincaré University Hospital. PATIENTS: A cohort of 44 patients who met the usual criteria for septic shock for < 7 days. A second cohort of 18 septic shock patients were enrolled within the first 8 hrs of disease onset. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: General demographics, severity scores, vital signs, standard biochemical data, and circulating vasopressin levels were systematically obtained at baseline in the two cohorts. Vasopressin deficiency was defined by a normal plasma vasopressin level in the presence of a systolic blood pressure of <100 mm Hg or in the presence of hypernatremia. Baroreflex sensitivity was systematically evaluated in patients of the first cohort when vasopressin deficiency was noted. In the second cohort of patients, plasma levels of vasopressin were obtained at baseline, 6, 24, 48, and 96 hrs after shock onset. In the first population, plasma vasopressin levels were inversely correlated to the delay from shock onset. Fourteen patients had relative vasopressin deficiency: 12 patients had systolic blood pressure <100 mm Hg, with impaired baroreflex sensitivity in four, and three patients had hypernatremia. In the second population, only two patients had relative vasopressin deficiency. The plasma levels of vasopressin significantly decreased over time (p < 10-3). CONCLUSIONS: Plasma vasopressin levels are almost always increased at the initial phase of septic shock and decrease afterward. Relative vasopressin deficiency is seen in approximately one-third of late septic shock patients.

Analysis of Variance↗

PubMed2002

Paresis acquired in the intensive care unit: a prospective multicenter study.

CONTEXT: Although electrophysiologic and histologic neuromuscular abnormalities are common in intensive care unit (ICU) patients, the clinical incidence of ICU-acquired neuromuscular disorders in patients recovering from severe illness remains unknown. OBJECTIVES: To assess the clinical incidence, risk factors, and outcomes of ICU-acquired paresis (ICUAP) during recovery from critical illness in the ICU and to determine the electrophysiologic and histologic patterns in patients with ICUAP. DESIGN: Prospective cohort study conducted from March 1999 to June 2000. SETTING: Three medical and 2 surgical ICUs in 4 hospitals in France. PARTICIPANTS: All consecutive ICU patients without preexisting neuromuscular disease who underwent mechanical ventilation for 7 or more days were screened daily for awakening. The first day a patient was considered awake was day 1. Patients with severe muscle weakness on day 7 were considered to have ICUAP. MAIN OUTCOME MEASURES: Incidence and duration of ICUAP, risk factors for ICUAP, and comparative duration of mechanical ventilation between ICUAP and control patients. RESULTS: Among the 95 patients who achieved satisfactory awakening, the incidence of ICUAP was 25.3% (95% confidence interval [CI], 16.9%-35.2%). All ICUAP patients had a sensorimotor axonopathy, and all patients who underwent a muscle biopsy had specific muscle involvement not related to nerve involvement. The median duration of ICUAP after day 1 was 21 days. Mean (SD) duration of mechanical ventilation after day 1 was significantly longer in patients with ICUAP compared with those without (18.2 [36.3] vs 7.6 [19.2] days; P =.03). Independent predictors of ICUAP were female sex (odds ratio [OR], 4.66; 95% CI, 1.19-18.30), the number of days with dysfunction of 2 or more organs (OR, 1.28; 95% CI, 1.11-1.49), duration of mechanical ventilation (OR, 1.10; 95% CI, 1.00-1.22), and administration of corticosteroids (OR, 14.90; 95% CI, 3.20-69.80) before day 1. CONCLUSIONS: Identified using simple bedside clinical criteria, ICUAP was frequent during recovery from critical illness and was associated with a prolonged duration of mechanical ventilation. Our findings suggest an important role of corticosteroids in the development of ICUAP.

Aged↗

PubMed2002

Depletion of neurohypophyseal content of vasopressin in septic shock.

OBJECTIVES: To assess the mechanisms underlying the inappropriately low plasma vasopressin levels reported in septic shock. DESIGN: Prospective case series. SETTING: A 26-bed general medical intensive care unit at a university hospital. PATIENTS: Septic shock patients. MEASUREMENTS AND MAIN RESULTS: In three consecutive patients with septic shock, plasma vasopressin levels, circulating vasopressinase activity, baroreflex sensitivity, and neurohypophyseal vasopressin content were assessed. Plasma vasopressin concentration was unexpectedly within normal range in two patients (1.6 pg/mL and 1.8 pg/mL) and increased in one (16 pg/mL). In all cases, vasopressinase activity was undetectable, baroreflex sensitivity was decreased, and the high signal intensity of the posterior lobe of the pituitary gland on T1-weighted magnetic resonance images was absent. Magnetic resonance imaging and plasma vasopressin levels normalized after recovery from shock in the patient who survived. CONCLUSION: These data suggest that in septic shock, inappropriately low plasma levels of vasopressin are at least partly related to a depletion of vasopressin stores in the neurohypophysis.

Aged↗

PubMed2002

Multifocal necrotizing leukoencephalopathy in septic shock.

OBJECTIVE: Multifocal necrotizing leukoencephalopathy, characterized by multiple microscopic foci of necrosis involving the white matter of the pons, has been described mainly after chemotherapy or radiotherapy for brain cancer and in HIV infection. The role of circulating cytokines has been suggested but remains to be assessed. DESIGN: Prospective case series. SETTING: A 26-bed general medical intensive care unit at a university hospital. PATIENTS: Septic shock patients. MEASUREMENTS AND PATIENTS: In three patients who died from septic shock, careful postmortem examination of the brain was performed, including studies of neuronal apoptosis and cytokine expression. MAIN RESULTS: In one patient, typical lesions of multifocal necrotizing leukoencephalopathy were seen. As compared with control 1 and control 2 who did not have multifocal necrotizing leukoencephalopathy, marked lesions of the pons, including vacuolization, apoptosis, microglial activation, and expression of tumor necrosis factor-alpha and interleukin-1beta, were observed in the case. Simultaneously, case 1 had markedly increased circulating levels for tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, interleukin-8, interleukin-10, soluble tumor necrosis factor receptor II, and for interleukin-1 receptor antagonist. CONCLUSION: Septic shock is a newly described cause of multifocal necrotizing leukoencephalopathy, probably mediated by an excessive systemic inflammatory response.

Adult↗