Biomedical subjects

C Sinderby

Publications and source records attributed to C Sinderby.

24 records · Page 2Linked to original sources

PubMed1995

Automatic assessment of electromyogram quality.

Power spectrum analysis of the diaphragm electromyogram (EMGdi) is time consuming, and no criteria have been developed to objectively quantify contamination of the signal. The present work describes a set of computer algorithms that automatically select EMGdi free of the electrocardiogram and numerically quantify the common artifacts that affect the EMGdi. The algorithms were tested 1) on human EMGdi (n = 5) obtained with esophageal electrodes positioned at the level of the gastroesophageal junction, 2) on EMGdi obtained in mongrel dogs (n = 5) with intramuscular electrodes in the costal diaphragm, and 3) on computer-simulated power spectra. For authentic and simulated power spectra, indexes were obtained by the algorithms and were able to quantify signal disturbances induced by noise, electrode motion, esophageal peristalsis (in humans), and non-QRS complex-related electrocardiogram activity. With the index inclusion thresholds set to levels that allowed for a high signal acceptance rate with relatively small artifact-induced fluctuations (10-15%) of the EMGdi center frequency, the computer algorithms were found to be as reliable as or more reliable than other methods, including careful visual selection of the time domain signals by experienced analysts. In conclusion, the frequency domain application of computer algorithms offers a reliable and reproducible means to objectively quantify the sources that contaminate the interference pattern EMG.

Algorithms↗

PubMed1994

An ATP-sensitive potassium channel blocker decreases diaphragmatic circulation in anesthetized dogs.

The goal of this study was to determine whether in the dog ATP-sensitive K+ channels blocked with glibenclamide affect diaphragmatic blood flow [phrenic arterial blood flow (Qpa)] during both spontaneous breathing at rest and increased diaphragmatic activity. A control group (no glibenclamide; n = 4) and an experimental group (50 mg/kg of glibenclamide; n = 5) were studied. During spontaneous breathing at rest, Qpa was 15.0 ml.min-1 x 100 g-1 and decreased by 5% in the presence of glibenclamide. Diaphragmatic pacing (30 min-1) generated by phrenic nerve pacing produced an initial diaphragmatic tension-time index of 0.25 in both groups. A 50% decay in transdiaphragmatic pressure was reached at 165 s in the experimental group compared with 421 s in the control group. Diaphragmatic pacing increased Qpa by 46% in the experimental group and 65% in the control group, yielding a 63% greater vascular resistance in the experimental group. Phrenic vein K+ content at rest was unchanged by the presence of glibenclamide, being 3.6 +/- 0.16 mmol/l compared with 3.5 +/- 0.19 mmol/l in the control group. Phrenic nerve pacing in the control group produced a 13% increase in phrenic vein K+ content, whereas in the experimental group a 16% decrease was observed. We suggest that ATP-sensitive K+ channels play an important role in the modulation of Qpa.

Adenosine Triphosphate↗

PubMed1994

The unweanable patient.

Inspiratory muscles can be exerted to their maximal limits during situations of: 1) high ventilatory demands, such as in exercise; and 2) during cases of high force demands, as in obstructive or restrictive diseases. In either circumstance, the level of sustainable activity (many hours) seems to be about half of the subject's maximal ventilatory capacity (MVC) or their maximal inspiratory pressure (MIP), respectively. The natural history of chronic hypercapnia in chronic obstructive pulmonary disease (COPD) or in neuromuscular disease suggests that spontaneous ventilation is set at a level below that which will trigger muscle fatigue, even if this lower level results in "chronic ventilatory failure". When this type of patient suffers a pathology that further decreases their global respiratory muscle function or increases their load, we have the makings of an unweanable patient; the mechanical ventilator ultimately replaces the lost inspiratory muscle function. Given time for the muscle to recover force and a reduction of the loads should, thus, be the therapeutic focus.

Humans↗

PubMed1992

Electromyographic registration of diaphragmatic fatigue during sustained trunk flexion in cervical cord injured patients.

When performing forward trunk flexion, cervical cord injured (CCI) patients exhibit continuous and high EMG activity in the diaphragm and elevated abdominal pressures. This study addressed the question whether the trunk flexion manoeuvres cause such a high force development in the diaphragm that this muscle shows EMG signs of fatigue. Six patients with complete cervical cord lesions were tested sitting in their own wheelchairs. The tension-time indices obtained when patients were sitting in a relaxed position were moderately to markedly higher than in normal subjects. The force developed during trunk flexion averaged 30% of the maximal transdiaphragmatic pressure and was accompanied by clear EMG findings of diaphragmatic fatigue in all patients except one. The acute diaphragmatic load in certain CCI patients may well produce ischaemia and increase the risk of tissue impairment. Therefore, there appears to be a need for differing strategies in the short and in the long term treatment of CCI patients; longitudinal evaluation of main diaphragmatic function may be useful for an adequate amount of respiratory muscle training.

Cervical Vertebrae↗

PubMed1992

The role of the diaphragm in trunk extension in tetraplegia.

Interest has been focused on the diaphragm as the all important respiratory muscle in tetraplegia for decades but its unique role as a trunk extension muscle has not been considered. This study set out to establish the relationship, if any, between the roles of the diaphragm during arm exercise and trunk flexion. Eight male complete cervical cord injuries (CCI) patients, sitting in their wheelchairs, were studied during rest, trunk flexion and start of arm cranking. The average flow, volume, oesophageal and gastric pressures (Poes and Pga) and the myoelectric activity of the diaphragm (EMGdi) were recorded. The EMGdi pattern changed from phasic activity at rest to continuous or almost continuous activity during trunk flexion. Patients were then either spontaneously holding their breath or breathing irregularly with rapid or shallow breaths. Also, the normalised EMGdi signal strength increased by an average of 150% and the mean Pga by about 3 kPa, while mean Poes decreased by about 0.5 kPa. At the start of exercise, patients with poor triceps function, less than MRC grade 3, exhibited similar ventilatory and EMGdi changes as had been seen in trunk flexion. In patients with better triceps function, only minor changes in these variables were observed. The findings suggest that the diaphragm acts both as a trunk extensor muscle and a respiratory muscle. During posture imbalance, the postural needs temporarily override the respiratory needs.

Adult↗

PubMedDate not supplied

Evaluation of diaphragm electromyogram contamination during progressive inspiratory maneuvers in humans.

The diaphragm electromyogram (EMGdi) is susceptible to contamination by non-diaphragm related electrical signals such as the ECG, electrode motion artifacts, and other sources of noise. It is difficult to distinguish between these contaminating signals and those that are representative of the non-contaminated EMGdi, especially during periods when the EMGdi amplitude is relatively small, as during mild contractions of the diaphragm. The aim of the present study was to evaluate how contaminating signals influence the EMGdi power spectrum center frequency (CF) during progressive inspiratory maneuvers. EMGdi and transdiaphragmatic pressure (Pdi) were measured via an esophageal electrode in eight patients with cervical cord injury performing inspiratory capacity (IC) maneuvers. The influence of the contaminating sources on CF was evaluated by two spectral deformation indices, one which is sensitive to both high and low frequency spectral deformation (omega index), and the other which is sensitive to high frequency deformation only (CF1000/CF500 index). The results indicated that EMGdi CF values scattered over a wide frequency range, particularly when the signals were obtained at Pdi levels less than 15% of Pdimax, or at lung volumes less than 30% of IC. When the spectral deformation indices were applied, the scattering in CF values was drastically reduced. This was expressed by a factor of 4 reduction in the coefficient of variation of the CF values. The majority of the excluded EMGdi signals (i.e. not satisfying the spectral deformation index inclusion levels), had low CF values mainly due to the presence of electrode motion artifacts. It was concluded that: 1) The majority of EMGdi power spectrums are deformed early on during unloaded inspirations, and their CF values should be carefully interpreted as being representative of diaphragm function. 2) The relative contribution of contaminating signals in the EMGdi decreases proportionally throughout the first two thirds of an inspiration to IC. 3) The use of visual inspection of the signal in the time domain is questionable as a method to discriminate non-contaminated signals. 4) Analysis of the signal in the frequency domain makes it possible to detect the influence of signal contamination.

Adult↗