Neurally adjusted ventilatory assist (NAVA).
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Electrodes↗
Biomedical subjects
C Sinderby
Publications and source records attributed to C Sinderby.
Electrical activity of the diaphragm during pressure support ventilation in acute respiratory failure.
We compared crural diaphragm electrical activity (EAdi) with transdiaphragmatic pressure (Pdi) during varying levels of pressure support ventilation (PS) in 13 intubated patients. With changing PS, we found no evidence for changes in neuromechanical coupling of the diaphragm. From lowest to highest PS (2 cm H(2)O +/- 4 to 20 cm H(2)O +/- 7), tidal volume increased from 430 ml +/- 180 to 527 ml +/- 180 (p < 0.001). The inspiratory volume calculated during the period when EAdi increased to its peak did not change from 276 +/- 147 to 277 +/- 162 ml, p = 0.976. Respiratory rate decreased from 23.9 (+/- 7) to 21.3 (+/- 7) breaths/min (p = 0.015). EAdi and Pdi decreased proportionally by adding PS (r = 0.84 and r = 0.90, for mean and peak values, respectively). Mean and peak EAdi decreased (p < 0.001) by 33 +/- 21% (mean +/- SD) and 37 +/- 23% with the addition of 10 cm H(2)O of PS, similar to the decrease in the mean and peak Pdi (p < 0.001) observed (34 +/- 36 and 35 +/- 23%). We also found that ventilator assist continued during the diaphragm deactivation period, a phenomenon that was further exaggerated at higher PS levels. We conclude that EAdi is a valid measurement of neural drive to the diaphragm in acute respiratory failure.
Acute Disease↗
Changes in respiratory effort sensation over time are linked to the frequency content of diaphragm electrical activity.
This study evaluated whether respiratory effort sensation (RES) changes over time when breathing is performed with constant contraction pattern, fixed diaphragm activation, and maintained pressure generation. Another aim was to assess whether there was any association between RES and the power spectrum center frequency of the diaphragm (CFdi) electrical activity. Six healthy subjects performed two 10-min periods targeting diaphragm electrical activation (EAdi) to 40% of maximum using (1) expulsive or Mueller maneuvers at FRC generating a mean transdiaphragmatic (Pdi) pressure of 55.0 +/- 22.7 cm H(2)O (+/- SD) and (2) inspiration to 71.2 +/- 14.1% of inspiratory capacity (IC) generating a Pdi of 21.4 +/- 5.2 cm H(2)O. The Pdi did not decrease over time during either maneuver. During both periods RES increased (p < 0.001) and CFdi decreased (p < 0.001) over time with higher Pdi levels producing larger decreases in CFdi (p = 0.003) and greater increases in RES (p = 0.008). Changes in CFdi and RES were related, and identical slopes were obtained during the two maneuvers. In conclusion, while breathing with a fixed pattern, constant diaphragm activation, and maintained pressure generation, RES increases over time and is associated with CFdi independent of the level of diaphragm pressure generated.
Adult↗
Diaphragm activation during exercise in chronic obstructive pulmonary disease.
Although it has been postulated that central inhibition of respiratory drive may prevent development of diaphragm fatigue in patients with chronic obstructive pulmonary disease (COPD) during exercise, this premise has not been validated. We evaluated diaphragm electrical activation (EAdi) relative to maximum in 10 patients with moderately severe COPD at rest and during incremental exhaustive bicycle exercise. Flow was measured with a pneumotachograph and volume by integration of flow. EAdi and transdiaphragmatic pressures (Pdi) were measured using an esophageal catheter. End-expiratory lung volume (EELV) was assessed by inspiratory capacity (IC) maneuvers, and maximal voluntary EAdi was obtained during these maneuvers. Minute ventilation (V E) was 12.2 +/- 1.9 L/min (mean +/- SD) at rest, and increased progressively (p < 0.001) to 31.0 +/- 7.8 L/min at end-exercise. EELV increased during exercise (p < 0.001) causing end-inspiratory lung volume to attain 97 +/- 3% of TLC at end-exercise. Pdi at rest was 9.4 +/- 3.2 cm H(2)O and increased during the first two thirds of exercise (p < 0.001) to plateau at about 13 cm H(2)O. EAdi was 24 +/- 6% of voluntary maximal at rest and increased progressively during exercise (p < 0.001) to reach 81 +/- 7% at end-exercise. In conclusion, dynamic hyperinflation during exhaustive exercise in patients with COPD reduces diaphragm pressure-generating capacity, promoting high levels of diaphragm activation.
Diaphragm↗
Expiratory muscle pressure and breathing mechanics in chronic obstructive pulmonary disease.
Expiratory muscle recruitment is common in stable chronic obstructive pulmonary disease (COPD) patients. Due to airway obstruction, there is little reason to believe that active expiration in COPD would be mechanically effective in lowering operating lung volume. The physiological significance of expiratory muscle recruitment in COPD, therefore, remains unknown. The purpose of this study was to assess, in COPD patients breathing at rest, the effect of expiratory muscle contraction on force generating ability of the diaphragm. The force generating ability of the diaphragm was evaluated from its pressure swing (Pdi) for a given diaphragm electrical activity (Edi), where Edi was normalized as % of its maximal value (Pdi/Edi/Edi,max). Phasic expiratory muscle contraction was measured as the total expiratory rise in gastric pressure (Pga,exp.rise). Nineteen seated patients with moderate to severe COPD, participated in the study and 10 exhibited phasic rise in Pga during expiration with a mean Pga,exp.rise of 1.91+/-0.89 cmH2O. The patients were thus divided into passive expiration (PE) and active expiration (AE) groups. There was no significant difference in various lung function and breathing pattern parameters between the two groups. Pdi/Edi/Edi,max was 0.63+/-0.07 and 0.54+/-0.07 cmH2O/% in PE and AE groups, respectively, and was not significantly different between each other. Compared with PE group, AE group not only recruited expiratory muscles, but also preferentially recruited inspiratory rib cage muscles and derecruited the diaphragm. The results do not support a significant improvement of the force-generating ability of the diaphragm by phasic contraction of expiratory muscles at rest in chronic obstructive pulmonary disease patients.
Aged↗
Respiratory response to exercise in postpolio patients with severe inspiratory muscle dysfunction.
OBJECTIVES: To evaluate the limiting factors of exercise performance and to analyze the respiratory strategies adopted during exercise in postpolio patients with severe inspiratory muscle dysfunction. PATIENTS: Five patients with prior poliomyelitis associated with scoliosis and with respiratory muscle dysfunction (mean vital capacity, 1.74L [range, 1.1 to 2.4]) were studied at rest and during leg or arm cycle exercise. METHODS: Gas exchange was examined by arterial blood gases and mass spectrometry of expired air. Ventilatory mechanics were studied by measurement of esophageal and gastric pressures. RESULTS: Blood gases at rest were normal, except for subnormal PO2 levels in three patients. In all but one patient, ventilatory insufficiency was the limiting factor for exercise. A compensatory breathing pattern with abdominal muscle recruitment during expiration was present already at rest in three of the patients. The pressures generated by the diaphragm were below fatiguing margins, ie, levels that in healthy subjects can be sustained for at least 45 minutes. CONCLUSIONS: The extent of ventilatory dysfunction was not evident in blood gas values at rest; however, it was revealed by blood gas values during the exercise test. Diaphragm fatigue seems to be avoided at the cost of impaired blood gases.
Adult↗
Neural control of mechanical ventilation in respiratory failure.
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Animals↗
Influence of atracurium on the diaphragm mean action potential conduction velocity in canines.
BACKGROUND: It has been shown that progressive neuromuscular blockade (NMB) affects the electromyogram power spectrum and compound muscle action potential duration in skeletal muscle. These measures are linked to the mean muscle action potential conduction velocity (APCV), but no studies have confirmed a relation between the mean APCV and NMB. The aim of this study was to determine whether diaphragm mean APCV is affected by NMB. METHODS: The effects of NMB on diaphragm mean APCV were evaluated in five mongrel dogs. Progressive NMB was induced by slow intravenous infusion of atracurium. During spontaneous breathing, the diaphragm mean APCV was determined by electromyogram signals, in the time and frequency domains. The magnitude of NMB was quantified by the amplitude of the compound muscle action potential and by changes in muscle shortening during supramaximal stimulation of the phrenic nerve. RESULTS: Progressive NMB was associated with a decrease in diaphragm mean APCV. At approximately 70% reduction in the compound muscle action potential amplitude, diaphragm mean APCV had decreased more than 20%. Recovery after NMB was characterized by a restoration of the mean APCV to control values. CONCLUSION: This study shows that progressive NMB paralyzes motor units within the diaphragm in an orderly manner, and the blockade first affects muscle fibers with high APCV before it affects fibers with lower APCV.
Action Potentials↗
Crural diaphragm activation during dynamic contractions at various inspiratory flow rates.
The purpose of this study was to evaluate the influence of velocity of shortening on the relationship between diaphragm activation and pressure generation in humans. This was achieved by relating the root mean square (RMS) of the diaphragm electromyogram to the transdiaphragmatic pressure (Pdi) generated during dynamic contractions at different inspiratory flow rates. Five healthy subjects inspired from functional residual capacity to total lung capacity at different flow rates while reproducing identical Pdi and chest wall configuration profiles. To change the inspiratory flow rate, subjects performed the inspirations while breathing across two different inspiratory resistances (10 and 100 cmH2O . l-1 . s), at mouth pressure targets of -10, -20, -40, and -60 cmH2O. The diaphragm electromyogram was recorded and analyzed with control of signal contamination and electrode positioning. RMS values obtained for inspirations with identical Pdi and chest wall configuration profiles were compared at the same percentage of inspiratory duration. At inspiratory flows ranging between 0.1 and 1.4 l/s, there was no difference in the RMS for the inspirations from functional residual capacity to total lung capacity when Pdi and chest wall configuration profiles were reproduced (n = 4). At higher inspiratory flow rates, subjects were not able to reproduce their chest wall displacements and adopted different recruitment patterns. In conclusion, there was no evidence for increased demand of diaphragm activation when healthy subjects breathe with similar chest wall configuration and Pdi profiles, at increasing flow rates up to 1.4 l/s.
Adult↗
Effects of lung volume on diaphragm EMG signal strength during voluntary contractions.
The use of esophageal recordings of the diaphragm electromyogram (EMG) signal strength to evaluate diaphragm activation during voluntary contractions in humans has recently been criticized because of a possible artifact created by changes in lung volume. Therefore, the first aim of this study was to evaluate whether there is an artifactual influence of lung volume on the strength of the diaphragm EMG during voluntary contractions. The second aim was to measure the required changes in activation for changes in lung volume at a given tension, i.e., the volume-activation relationship of the diaphragm. Healthy subjects (n = 6) performed contractions of the diaphragm at different transdiaphragmatic pressure (Pdi) targets (range 20-160 cmH2O) while maintaining chest wall configuration constant at different lung volumes. The diaphragm EMG was recorded with a multiple-array esophageal electrode, with control of signal contamination and electrode positioning. The effects of lung volume on the EMG were studied by comparing the crural diaphragm EMG root mean square (RMS), an index of crural diaphragm activation, with an index of global diaphragm activation obtained by normalizing Pdi to the maximum Pdi at the given muscle length (Pdi/Pdimax@L) at the different lung volumes. We observed a direct relationship between RMS and Pdi/Pdimax@L independent of diaphragm length. The volume-activation relationship of the diaphragm was equally affected by changes in lung volume as the volume-Pdi relationship (60% change from functional residual capacity to total lung capacity). We conclude that the RMS of the diaphragm EMG is not artifactually influenced by lung volume and can be used as a reliable index of diaphragm activation. The volume-activation relationship can be used to infer changes in the length-tension relationship of the diaphragm at submaximal activation/contraction levels.
Adult↗
Voluntary activation of the human diaphragm in health and disease.
Intersubject comparison of the crural diaphragm electromyogram, as measured by an esophageal electrode, requires a reliable means for normalizing the signal. The present study set out 1) to evaluate which voluntary respiratory maneuvers provide high and reproducible diaphragm electromyogram root-mean-square (RMS) values and 2) to determine the relative diaphragm activation and mechanical and ventilatory outputs during breathing at rest in healthy subjects (n = 5), in patients with severe chronic obstructive pulmonary disease (COPD, n = 5), and in restrictive patients with prior polio infection (PPI, n = 6). In all groups, mean voluntary maximal RMS values were higher during inspiration to total lung capacity than during sniff inhalation through the nose (P = 0.035, ANOVA). The RMS (percentage of voluntary maximal RMS) during quiet breathing was 8% in healthy subjects, 43% in COPD patients, and 45% in PPI patients. Despite the large difference in relative RMS (P = 0.012), there were no differences in mean transdiaphragmatic pressure (P = 0.977) and tidal volumes (P = 0.426). We conclude that voluntary maximal RMS is reliably obtained during an inspiration to total lung capacity but a sniff inhalation could be a useful complementary maneuver. Severe COPD and PPI patients breathing at rest are characterized by increased diaphragm activation with no change in diaphragm pressure generation.
Adult↗
Diaphragm interference pattern EMG and compound muscle action potentials: effects of chest wall configuration.
The effect of chest wall configuration on the diaphragm electromyogram (EMGdi) was evaluated in five healthy subjects with an esophageal electrode for both interference pattern EMGdi (voluntary contractions) and electrically evoked diaphragm compound muscle action potentials (CMAPs). Diaphragm CMAPs (both unilateral and bilateral) were evaluated for the baseline-to-peak amplitude (Ampl), the time from the onset of the CMAP to first peak (T1), root mean square (RMS), and center frequency (CF) values of the CMAP power spectrum. CF values from the interference pattern EMGdi power spectrum were also calculated. For CMAPs obtained at an electrode position least influenced by variations induced by electrode positioning, Ampl increased with diaphragm shortening from functional residual capacity (FRC) to total lung capacity (TLC) by 101 and 98% (unilateral and bilateral, respectively). Bilateral CMAP RMS values increased 116% from FRC to TLC. CMAP T1 values decreased with diaphragm shortening from FRC to TLC by 1.1 and 2.1 ms for the unilateral and bilateral stimulations, respectively, and CF increased for the bilateral diaphragm CMAPs with diaphragm shortening. CF values from the interference pattern EMGdi did not show any consistent change with chest wall configuration. Thus CF values of the interference pattern EMGdi obtained with an esophageal electrode can be considered reliable for physiological interpretation, at any diaphragm length (if electrode positioning and signal contamination are controlled for), contrary to the diaphragm CMAPs, which are sensitive to changes in chest wall configuration. It is speculated that the different results (over the effects of chest wall configuration on interference pattern EMGdi and diaphragm CMAPs) amy be because of summation properties of the signals and how these influence the EMG power spectrum.
Action Potentials↗
Effects of diaphragm shortening on the mean action potential conduction velocity in canines.
1. The present study was designed to test if the mean muscle fibre action potential conduction velocity (VAPC) in the costal diaphragm changes with muscle length, in spontaneously breathing mongrel dogs. 2. VAPC was determined by the electromyogram (EMG) power spectrum 'dip' method, which is based on the bipolar electrode transfer function. A bipolar EMG electrode with a 20 mm fixed interelectrode distance was sutured to the costal diaphragm in the fibre direction, and in a region with a low density of motor endplates. Diaphragm length was measured with piezoelectric crystals positioned next to the EMG electrode. Seven dogs were vagotomized and spinally anaesthetized in order to increase diaphragmatic shortening, reduce velocity of shortening and abolish possible cross-talk signals from adjacent muscles. 3. Our results showed that VAPC in the canine costal diaphragm was 3.4 m s-1 and was not significantly related to diaphragmatic shortening.
Action Potentials↗
Electromyographical evidence for exercise-induced diaphragm fatigue in patients with chronic cervical cord injury or prior poliomyelitis infection.
UNLABELLED: The purpose of this study was to determine, in exercising patients, how much diaphragm force increases before electromyographical evidence of diaphragm fatigue occurs. The study was performed in ten male patients with complete cervical cord injury (CCI) at the C5 to C8 levels, and five male patients with prior poliomyelitis infection (PPI) requiring chronic treatment with intermittent positive pressure ventilation (IPPV) at night. We studied the time course of the diaphragmatic tension-time index (TTdi), the centre frequency (CFdi) of the diaphragm electromyogram (EMGdi) power spectrum, and the ventilatory parameters, during steady-state submaximal arm/leg exercise. During exercise, early signs of diaphragm fatigue were present in seven out of 10 CCI patients and in four out of five PPI patients, as indicated by a reduction in CFdi. The increase in TTdi achieved before reductions in CFdi occurred was twofold in both the CCI and PPI patients. All patients except for the PPI patients, who demonstrated a reduction in CFdi, showed an increase in minute ventilation (VE), achieved by increasing both their tidal volume (Vt) and the breathing frequency (fb). The PPI patients demonstrating reductions in CFdi during exercise also increased their VE however, this was achieved by increasing fb while Vt remained constant. Following the reductions in CFdi, the CCI patients further increased their TTdi throughout the exercise test, while the PPI patients reduced their TTdi values. IN CONCLUSION: (1) During exercise, electromyographical evidence for diaphragmatic fatigue frequently occurred in the CCI and PPI patients studied; (2) Compared to the eightfold increase in TTdi seen in healthy subjects before reductions in CFdi occur, the TTdi values increased only two-fold before electromyographical evidence of diaphragm fatigue was present in these patients; (3) There is a clear discrepancy between the CCI and PPI patients who demonstrate electromyographical evidence of diaphragm fatigue, in terms of their ventilatory and TTdi responses.
Adult↗
Diaphragm function in patients with cervical cord injury or prior poliomyelitis infection.
Diaphragm function was evaluated in cervical cord injury patients (CCI), 1-3 years after injury (CCI(1-3)) and 10 years or more after injury (CCI(> or = 10)), as well as in a group of prior poliomyelitis infection patients (PPI), requiring intermittent positive pressure ventilation (IPPV) for about 6 h per night. Measurements included transdiaphragmatic pressure swings (delta Pdi) at rest, during maximal inspiratory efforts against closed airways (delta Pdi(max)) and during sniff manoeuvres (ie maximal inhalation through the nose, delta Pdi(sniff)), vital capacity normalized to age and height (VC(%pred)), tidal volume (Vt), relative inspiratory time (Ti/Ttot), breathing frequency (f(b)), and the tension-time index of the diaphragm (TTdi = delta Pdi/delta Pdi(max) x Ti/Ttot). The median VC(%pred) was 50% in the CCI(1-3) group and 57% in the CCI (> or = 10) group, but only 28% in the PPI group. Delta Pdi(max) values were similar for the CCI(1-3) (11.8 kPa) and CCI(> or = 10) (11.9 kPa) groups but were lower (71. kPa) in the PPI group. Due to the reduction in delta Pdi(max), the PPI group had higher delta Pdi/delta Pdi(max) values than the CCI groups, however, the TTdi was similar amongst the different groups studied. A submaximal exercise test in five cervical cord injury patients and in five polio patients with similar delta Pdi(max), delta Pdi(sniff) and TTdi values at rest revealed clear group differences with respect to force development, in that CCI patients showed significant increases in TTdi, while PPI demonstrated only minor changes. In CCI patients, an increase in ventilation was accompanied by an increase in delta Pdi/delta Pdi(max) while in contrast, the PPI patients showed no increase in delta Pdi/delta Pdi(max). We conclude that CCI patients, both recently and previously injured, have a similar maximal inspiratory force and are less impaired than the PPI patients. The TTdi at rest is similar in all groups, but the PPI patients react to inspiratory loads with little increases in TTdi, while the CCI patients increase their TTdi above fatiguing (0.15) levels. The different behaviours may be linked to loss of sensory pathways in the CCI patients.
Adult↗
Influence of bipolar esophageal electrode positioning on measurements of human crural diaphragm electromyogram.
We aimed to describe how the human diaphragm electromyogram (EMGdi) is filtered at different positions within the esophageal hiatus, i.e., in the close proximity of the diaphragm, when obtained with an array of bipolar electrode pairs mounted on an esophageal catheter. We defined the electrically active crural diaphragm musculature that covers the esophagus as the electrically active region of the diaphragm (EARdi) and its center as the EARdi center. EMGdi signals were obtained via a multiple-array esophageal catheter consisting of seven sequential electrode pairs with three different electrode configurations. Subjects (n = 5) performed voluntary contractions of the diaphragm at functional residual capacity. Visual inspection of the signals revealed reversal of signal polarity on either side of the EARdi center. Extreme correlation values (r values close to -1 at 0-ms time offset) were observed for the correlation of signals on either side of the EARdi center. The root mean square (RMS) was reduced at the EARdi center; moving peripherally from the EARdi center (caudally and cephalad), the RMS increased to a peak (range of 2.1-4.1 dB for the different electrode configurations) and then decreased for the most peripheral electrode pairs. From a position where the RMS values peaked, center frequency values increased at the EARdi center (range of 26-29 Hz for the different electrode configurations). Computer simulation yielded similar data to the experimental results. We conclude that electrode positioning within the EARdi severely influences center frequency and RMS values and that the center of the EARdi can be identified via cross-correlation analysis.
Diaphragm↗
Chest wall muscle cross talk in canine costal diaphragm electromyogram.
The present paper describes the influence of cross talk from the abdominal and intercostal muscles on the canine diaphragm electromyogram (EMG). The diaphragm EMG was recorded with bipolar surface electrodes placed on the costal portion of the diaphragm (abdominal side), aligned in the fiber direction, and positioned in a region with a relatively low density of motor end plates. The results indicated that cross talk may occur in the diaphragm EMG, especially during conditions of loaded breathing and light general anesthesia. The cross-talk signals showed characteristics that were entirely different from the diaphragm EMG. Although the diaphragm EMG was typical for signals recorded with electrodes aligned in the fiber direction, the cross-talk signals were characteristic of those obtained with electrode pairs not aligned in the direction of the muscle fibers. Alterations in electrode positioning, interelectrode distance, and/or electrode surface area cannot guarantee the elimination of cross-talk signals, whereas spinal anesthesia at a high thoracic level will paralyze the sources of the cross talk and hence eliminate the cross-talk signals. By taking advantage of the differences in EMG signal characteristics for the diaphragm EMG and cross-talk signals, an index that has the capability to detect cross talk was developed.
Abdominal Muscles↗
Effects of muscle-to-electrode distance on the human diaphragm electromyogram.
It has been suggested that esophageal recordings of the diaphragm electromyogram (EMGdi) are influenced by changes in chest wall configuration. Whether the changes are of physiological or artifactual origin is unclear. For example, the distance between the esophageal electrode and the diaphragm is likely to alter with chest wall configuration and may lead to misinterpretations of EMGdi. The aims of this study were 1) to evaluate and quantify the effect of the muscle-to-electrode (ME) distance filter on EMGdi, as obtained with a multiple-array esophageal electrode, 2) to take advantage of the ME distance filter to locate the position of the diaphragm with respect to the electrode, and 3) to evaluate the influence of lung volume and chest wall configuration on EMGdi center frequency (CF) while controlling for the ME distance filter and signal quality. Five subjects performed six static contractions of the diaphragm at each of seven chest wall configurations, as evaluated by the method of K. Konno and J. Mead (J. Appl. Physiol. 22: 407-422, 1967). EMGdi was measured with seven pairs of electrodes mounted on an esophageal catheter. The pair of electrodes whose EMGdi power spectra were the least filtered by the ME distance was assumed to be closest to the diaphragm. The results of the study indicated that 1) EMGdi power spectra were strongly affected by the distance between the diaphragm and the electrodes. CF decreased by approximately 1 Hz/mm displacement away from the electrode pair closest to the diaphragm; and 2) no systematic relationship was found between changes in chest wall configuration and CF, when CF was measured from the electrode pair closest to the diaphragm. We conclude that the EMGdi CF can be reliably measured with a multiple-array esophageal electrode that covers the span of diaphragmatic excursion and by selecting the pair of electrodes that is the closest to the diaphragm.
Diaphragm↗