Dries Testelmans

Increased duration of mechanical ventilation is associated with decreased diaphragmatic force: a prospective observational study

IntroductionRespiratory muscle weakness is an important risk factor for delayed weaning. Animal data show that mechanical ventilation itself can cause atrophy and weakness of the diaphragm, called ventilator-induced diaphragmatic dysfunction (VIDD). Transdiaphragmatic pressure after magnetic stimulation (TwPdi BAMPS) allows evaluation of diaphragm strength. We aimed to evaluate the repeatability of TwPdi BAMPS in critically ill, mechanically ventilated patients and to describe the relation between TwPdi and the duration of mechanical ventilation.MethodsThis was a prospective observational study in critically ill and mechanically ventilated patients, admitted to the medical intensive care unit of a university hospital. Nineteen measurements were made in a total of 10 patients at various intervals after starting mechanical ventilation. In seven patients, measurements were made on two or more occasions, with a minimum interval of 24 hours.ResultsThe TwPdi was 11.5 ± 3.9 cm H2O (mean ± SD), indicating severe respiratory muscle weakness. The between-occasion coefficient of variation of TwPdi was 9.7%, comparable with data from healthy volunteers. Increasing duration of mechanical ventilation was associated with a logarithmic decline in TwPdi (R = 0.69; P = 0.038). This association was also found for cumulative time on pressure control (R = 0.71; P = 0.03) and pressure-support ventilation (P = 0.05; R = 0.66) separately, as well as for cumulative dose of propofol (R = 0.66; P = 0.05) and piritramide (R = 0.79; P = 0.01).ConclusionsDuration of mechanical ventilation is associated with a logarithmic decline in diaphragmatic force, which is compatible with the concept of VIDD. The observed decline may also be due to other potentially contributing factors such as sedatives/analgesics, sepsis, or others.

Intermittent spontaneous breathing protects the rat diaphragm from mechanical ventilation effects

Objective:Short-term mechanical ventilation has been proven to reduce diaphragm force and fiber dimensions. We hypothesized that intermittent spontaneous breathing during the course of mechanical ventilation would minimize the effects of mechanical ventilation on diaphragm force and expression levels of transcription factors (MyoD and myogenin). Design:Randomized, controlled experiment. Setting:Animal basic science laboratory. Subjects:Male Wistar rats, weighing 350–500 g. Interventions:Anesthetized and tracheotomized rats were submitted to either 24 hrs of spontaneous breathing (SB, n = 5), 24 hrs of continuous controlled mechanical ventilation (CMV, n = 7), or controlled mechanical ventilation with intermittent spontaneous breathing: 60 mins every 5 hrs of mechanical ventilation repeated four times (ISB60, n = 8) or 5 mins every 5 hrs 55 mins of mechanical ventilation repeated four times (SB5, n = 9). They were compared with control animals free from intervention (C, n = 5). Measurements and Main Results:The profile of the diaphragm force-frequency curve of the controls and SB group was significantly different from that of the ISB and CMV groups; especially, the mean asymptotic force was less in the ISB and CMV compared with controls and SB. CMV resulted in a significant decrease in the diaphragm type I (−26%, p < .05 vs. C) and type IIx/b (−39%, p < .005 vs. C and SB) cross-sectional area, whereas this was not observed in the ISB groups. Diaphragm MyoD protein expression was significantly decreased after ISB60 (−35%, p < .0001 vs. C and SB) and even more after CMV (−73%, p < .0001 vs. others). The same pattern was observed with myogenin protein levels. Positive relationships between diaphragm MyoD and myogenin protein levels and diaphragm force were observed. Conclusions:The data demonstrated that intermittent spontaneous breathing during the course of mechanical ventilation may minimize the deleterious effect of controlled mechanical ventilation on diaphragm force, fiber dimensions, and expression of transcription factors.

Rocuronium exacerbates mechanical ventilation-induced diaphragm dysfunction in rats

Objective:Nondepolarizing neuromuscular blocking agents are commonly used in the intensive care setting, but they have occasionally been associated with development of myopathy. In addition, diaphragmatic atrophy and a reduction in diaphragmatic force were reported after short-term controlled mechanical ventilation in animal models. We hypothesized that infusion of rocuronium, an aminosteroidal neuromuscular blocking agent, during 24 hrs of controlled mechanical ventilation would further alter diaphragm function and would enhance activation of the ubiquitin– proteasome pathway. Design:Randomized, controlled experiment. Setting:Basic animal science laboratory. Subjects:Male Wistar rats, 14 wks old. Interventions:Rats were divided into four groups: a control group, a group of anesthetized rats breathing spontaneously for 24 hrs, and two groups submitted to mechanical ventilation for 24 hrs, receiving a continuous infusion of either 0.9% NaCl or rocuronium. Measurements and Main Results:In vitro diaphragm force was decreased more significantly after 24 hrs of mechanical ventilation combined with rocuronium infusion than after mechanical ventilation alone (e.g., tetanic force, −27%; p < .001 vs. mechanical ventilation). Similarly, the decrease in diaphragm type IIx/b fiber dimensions was more pronounced after mechanical ventilation with rocuronium treatment than with saline treatment (−38% and −29%, respectively; p < .001 vs. control). Diaphragm hydroperoxide levels increased similarly in both mechanically ventilated groups. Diaphragm muscle RING-finger protein-1 (MURF-1) messenger RNA expression, an E3 ligase of the ubiquitin–proteasome pathway, increased after mechanical ventilation (+212%, p < .001 vs. control) and increased further with combination of rocuronium (+320%, p < .001 vs. control). Significant correlations were found between expression of MURF-1 messenger RNA, diaphragm force, and type IIx/b fiber dimensions. Conclusions:Infusion of rocuronium during controlled mechanical ventilation leads to further deterioration of diaphragm function, additional atrophy of type IIx/b fibers, and an increase in MURF-1 messenger RNA in the diaphragm, which suggests an activation of the ubiquitin–proteasome pathway. These findings could be important with regard to weaning failure in patients receiving this drug for prolonged periods in the intensive care unit setting.

Atrophy and hypertrophy signalling in the diaphragm of patients with COPD

We investigated whether atrophy and hypertrophy signalling were altered in the diaphragm of chronic obstructive pulmonary disease (COPD) patients. We studied diaphragm fibre dimensions and proportion, expression of markers of the ubiquitin-proteasome pathway, nuclear factor (NF)-κB pathways, muscle regulatory factors and myostatin in diaphragm biopsies from 19 patients with severe COPD and 13 patients without COPD. Type I proportion was significantly increased in the diaphragm of COPD patients while type II proportion was decreased. The cross-sectional area of all fibre types was reduced in the COPD patients. In addition, MAFbx mRNA was higher in the diaphragm of COPD patients while Nedd4 mRNA decreased. Cytoplasmatic levels of inhibitor protein IκBα and IκBβ were decreased in the COPD patients as was NF-κB p50 DNA-binding activity. MyoD mRNA and its nuclear protein content were decreased in the diaphragm of COPD patients and myogenin mRNA and protein levels remained unchanged. Myostatin mRNA was decreased but its protein levels in the nuclear and cytoplasmic fraction were significantly increased in the COPD patients. These data show that the ubiquitin-proteasome pathway, the NF-κB pathway and myostatin protein were up-regulated in the diaphragm of COPD patients while MyoD expression was reduced. These alterations may contribute to diaphragm remodeling in COPD.

Effects of Acute Administration of Corticosteroids during Mechanical Ventilation on Rat Diaphragm

RATIONALE Mechanical ventilation is known to induce ventilator-induced diaphragm dysfunction. Patients submitted to mechanical ventilation often receive massive doses of corticosteroids that may cause further deterioration of diaphragm function. OBJECTIVES To examine whether the combination of 24 hours of controlled mechanical ventilation with corticosteroid administration would exacerbate ventilator-induced diaphragm dysfunction. METHODS Rats were randomly assigned to a group submitted to 24 hours of controlled mechanical ventilation receiving an intramuscular injection of saline or 80 mg/kg methylprednisolone, a group submitted to 24 hours of spontaneous breathing receiving saline, or methylprednisolone and a control group. MEASUREMENTS AND MAIN RESULTS The diaphragm force-frequency curve was shifted downward in the mechanical ventilation group, but this deleterious effect was prevented when corticosteroids were administered. Diaphragm cross-sectional area of type I fibers was similarly decreased in both mechanical ventilation groups while atrophy of type IIx/b fibers was attenuated after corticosteroid administration. The mechanical ventilation-induced reduction in diaphragm MyoD and myogenin protein expression was attenuated after corticosteroids. Plasma cytokine levels were unchanged while diaphragm lipid hydroperoxides were similarly increased in both mechanical ventilation groups. Diaphragmatic calpain activity was significantly increased in the mechanical ventilation group, but calpain activation was abated with corticosteroid administration. Inverse correlations were found between calpain activity and diaphragm force. CONCLUSIONS A single high dose of methylprednisolone combined with controlled mechanical ventilation protected diaphragm function from the deleterious effects of controlled mechanical ventilation. Inhibition of the calpain system is most likely the mechanism by which corticosteroids induce this protective effect.

Gene Expression Profiling in Vastus Lateralis Muscle During an Acute Exacerbation of COPD

Background/aims: The molecular mechanisms leading to loss in muscle force during an acute exacerbation in COPD patients are unknown. A cross-sectional study was designed to compare the gene expression profile of the vastus lateralis muscle in patients with an acute COPD exacerbation and in stable COPD patients. Methods: Muscle biopsies were taken in 9 COPD patients with an exacerbation on day 4 of hospitalization and in 15 stable COPD patients. Micro-array was performed on an UniSet Human 20K Bioarray. Results: Gene Ontology and Gene Set Enrichment Analysis of the microarray data revealed enrichment of 1) the ubiquitin-dependent protein catabolism, the induction of apoptosis and anti-apoptosis and the response to reactive oxygen species in the upregulated transcripts, and 2) the aspartate catabolism and the mitochondrial respiratory chain in the downregulated transcripts. Real Time PCR data confirmed 1) increased expression of MuRF1 and MAFbx, markers of the ubiquitin dependent catabolism pathway, and 2) decreased expression levels of COX6C, a marker of mitochondrial respiration. Conclusions: The present study suggests that multiple pathways leading to muscle atrophy and mitochondrial dysfunction are altered in the muscle during an acute exacerbation. Strategies limiting the loss of muscle function during an acute exacerbation need to be developed.

A Novel Algorithm for the Automatic Detection of Sleep Apnea From Single-Lead ECG

Goal: This paper presents a methodology for the automatic detection of sleep apnea from single-lead ECG. Methods: It uses two novel features derived from the ECG, and two well-known features in heart rate variability analysis, namely the standard deviation and the serial correlation coefficients of the RR interval time series. The first novel feature uses the principal components of the QRS complexes, and it describes changes in their morphology caused by an increased sympathetic activity during apnea. The second novel feature extracts the information shared between respiration and heart rate using orthogonal subspace projections. Respiratory information is derived from the ECG by means of three state-of-the-art algorithms, which are implemented and compared here. All features are used as input to a least-squares support vector machines classifier, using an RBF kernel. In total, 80 ECG recordings were included in the study. Results: Accuracies of about 85% are achieved on a minute-by-minute basis, for two independent datasets including both hypopneas and apneas together. Separation between apnea and normal recordings is achieved with 100% accuracy. In addition to apnea classification, the proposed methodology determines the contamination level of each ECG minute. Conclusion: The performances achieved are comparable with those reported in the literature for fully automated algorithms. Significance: These results indicate that the use of only ECG sensors can achieve good accuracies in the detection of sleep apnea. Moreover, the contamination level of each ECG segment can be used to automatically detect artefacts, and to highlight segments that require further visual inspection.

Profile of circulating cytokines: Impact of OSA, obesity and acute cardiovascular events

Obstructive sleep apnea (OSA) is inducing oxidative stress and consequently promotes systemic inflammation and cardiovascular morbidity. The respective impact of obesity, sleep apnea and acute cardiovascular events on the profile of inflammatory cytokines has not been extensively evaluated. We examined the profile of circulating cytokines in a case-control study comparing nonobese or obese patients with or without sleep apnea and with or without an acute cardiovascular event. Patients were assessed by sleep studies and inflammatory (hs-CRP, Leptin, RANTES, MCP1, IL6, IL8, TNF-α) and anti-inflammatory (adiponectin, IL1-Ra) cytokines profile. A cardiovascular phenotyping was performed including carotid intima-media thickness, pulse wave velocity and 24h blood pressure monitoring. In comparison with patients without sleep apnea or without comorbidities, patients with the combination of an acute cardiovascular event and pre-existing sleep apnea showed a higher burden of systemic inflammation with significant increase in serum levels of hs-CRP, IL1-Ra, IL-8, IL-6, TNF-α, Rantes and sICAM. Rantes and sICAM serum levels were independently associated with AHI after an acute cardiovascular event. Serum levels of different inflammatory markers were significantly increased in patients with the combination of sleep apnea and an acute cardiovascular event. Since these biomarkers could be associated with worsened cardiovascular outcome, diagnosing and treating associated sleep apnea is potentially important in patients after an acute cardiovascular event.

Noninvasive ventilation improves sleep in amyotrophic lateral sclerosis: a prospective polysomnographic study.

STUDY OBJECTIVE To evaluate the effects of noninvasive ventilation (NIV) on sleep in patients with amyotrophic lateral sclerosis (ALS) after meticulous titration with polysomnography (PSG). METHODS In this prospective observational study, 24 ALS patients were admitted to the sleep laboratory during 4 nights for in-hospital NIV titration with PSG and nocturnal capnography. Questionnaires were used to assess subjective sleep quality and quality of life (QoL). Patients were readmitted after one month. RESULTS In the total group, slow wave sleep and REM sleep increased and the arousal-awakening index improved. The group without bulbar involvement (non-bulbar) showed the same improvements, together with an increase in sleep efficiency. Nocturnal oxygen and carbon dioxide levels improved in the total and non-bulbar group. Except for oxygen saturation during REM sleep, no improvement in respiratory function or sleep structure was found in bulbar patients. However, these patients showed less room for improvement. Patient-reported outcomes showed improvement in sleep quality and QoL for the total and non-bulbar group, while bulbar patients only reported improvements in very few subscores. CONCLUSIONS This study shows an improvement of sleep architecture, carbon dioxide, and nocturnal oxygen saturation at the end of NIV titration and after one month of NIV in ALS patients. More studies are needed to identify the appropriate time to start NIV in bulbar patients. Our results suggest that accurate titration of NIV by PSG improves sleep quality. COMMENTARY A commentary on this article appears in this issue on page 511.

Robust artefact detection in long-term ECG recordings based on autocorrelation function similarity and percentile analysis

Artefacts can pose a big problem in the analysis of electrocardiogram (ECG) signals. Even though methods exist to reduce the influence of these contaminants, they are not always robust. In this work a new algorithm based on easy-to-implement tools such as autocorrelation functions, graph theory and percentile analysis is proposed. This new methodology successfully detects corrupted segments in the signal, and it can be applied to real-life problems such as for example to sleep apnea classification.