Dyspnea is a frightening and debilitating experience. It attracts less attention than pain ('dyspnea invisibility'), possibly because of its non-universal nature. We tested the impact of self-induced ...experimental dyspnea on medical residents.
During a teaching session following the principles of experiential learning, emergency medicine residents were taught about dyspnea theoretically, observed experimental dyspnea in their teacher, and personally experienced self-induced dyspnea. The corresponding psychophysiological reactions were described. Immediate and 1-year evaluations were conducted to assess course satisfaction (overall 0-20 grade) and the effect on the understanding of what dyspnea represents for patients.
Overall, 55 emergency medicine residents participated in the study (26 men, median age 26 years). They were moderately satisfied with previous dyspnea teaching (6 5-7 on a 0-10 numerical rating scale NRS) and expressed a desire for an improvement in the teaching (8 7-9). Immediately after the course they reported improved understanding of patients' experience (7 6-8), which persisted at 1 year (8 7-9, 28 respondents). Overall course grade was 17/20 15-18, and there were significant correlations with experimental dyspnea ratings (intensity: r = 0.318 0.001-0.576, p = 0.043; unpleasantness: r = 0.492 0.208-0.699, p = 0.001). In multivariate analysis, the only factor independently associated with the overall course grade was 'experiential understanding' (the experimental dyspnea-related improvement in the understanding of dyspneic patients' experience). A separate similar experiment conducted in 50 respiratory medicine residents yielded identical results.
This study suggests that, in advanced medical residents, the personal discovery of dyspnea can have a positive impact on the understanding of what dyspnea represents for patients. This could help fight dyspnea invisibility.
Whether dyspnea is present before starting a spontaneous breathing trial (SBT) and whether it may affect the outcome of the SBT is unknown. Mechanical Ventilation-Respiratory Distress Observation ...Scale (MV-RDOS) has been proposed as a reliable surrogate of dyspnea in non-communicative intubated patients. In the present study, we sought (1) to describe the evolution of the MV-RDOS during a SBT and (2) to investigate whether MV-RDOS can predict the outcome of the SBT.
Prospective, single-center study in a twenty-two bed ICU in a tertiary center. Patients intubated since more 48 h who had failed a first SBT were eligible if they meet classical readiness to wean criteria. The MV-RDOS was assessed before, at 2-min, 15-min and 30-min (end) of the SBT. The presence of clinically important dyspnea was inferred by a MV-RDOS value ≥ 2.6.
Fifty-eight patients (age 63 51-70, SAPS II 66 51-76; med IQR) were included. Thirty-three (57%) patients failed the SBT, whose 18 (55%) failed before 15-min. Twenty-five (43%) patients successfully passed the SBT. A MV-RDOS ≥ 2.6 was present in ten (17%) patients before to start the SBT. All these ten patients subsequently failed the SBT. A MV-RDOS ≥ 2.6 at 2-min predicted a SBT failure with a 51% sensibility and a 88% specificity (AUC 0.741 95% confidence interval CI 0.616-0.866, p = 0.002). Best cut-off value at 2-min was 4.3 and predicted SBT failure with a 27% sensibility and a 96% specificity.
Despite patients met classical readiness to wean criteria, respiratory distress assessed with the MV-RDOS was frequent at the beginning of SBT. Measuring MV-RDOS before to initiate a SBT could avoid undue procedure and reduce patient's exposure to unnecessary mechanical ventilation weaning failure and distress.
In critically ill patients receiving mechanical ventilation, dyspnoea is frequent, severe and associated with an increased risk of neuropsychological sequelae. We evaluated the efficacy of sensory ...interventions targeting the brain rather than the respiratory system to relieve dyspnoea in mechanically ventilated patients.
Patients receiving mechanical ventilation for ≥48 h and reporting dyspnoea (unidimensional dyspnoea visual analogue scale (Dyspnoea-VAS)) first underwent increased pressure support and then, in random order, auditory stimulation (relaxing music
pink noise) and air flux stimulation (facial
lower limb). Treatment responses were assessed using Dyspnoea-VAS, the Multidimensional Dyspnea Profile and measures of the neural drive to breathe (airway occlusion pressure (
) and electromyography of inspiratory muscles).
We included 46 patients (tracheotomy or intubation n=37; noninvasive ventilation n=9). Increasing pressure support decreased Dyspnoea-VAS by median 40 mm (p<0.001). Exposure to music decreased Dyspnoea-VAS compared with exposure to pink noise by median 40 mm (p<0.001). Exposure to facial air flux decreased Dyspnoea-VAS compared with limb air flux by median 30 mm (p<0.001). Increasing pressure support, but not music exposure and facial air flux, reduced
by median 3.3 cmH
O (p<0.001).
In mechanically ventilated patients, sensory interventions can modulate the processing of respiratory signals by the brain irrespective of the intensity of the neural drive to breathe. It should therefore be possible to alleviate dyspnoea without resorting to pharmacological interventions or having to infringe the constraints of mechanical ventilation lung protection strategies by increasing ventilatory support.
Human
mutations result in life-threatening sleep-related hypoventilation (congenital central hypoventilation syndrome, CCHS). Most patients retain ventilatory activity when awake through a ...respiratory-related cortical network. We hypothesised that this need to mobilise cortical resources to breathe would lead to breathing-cognition interferences during cognitive loading.
Seven adult CCHS patients (five women; median age 21) performed standard neuropsychological tests (paced auditory serial addition test - calculation capacity, working memory, sustained and divided attention; trail making test - visuospatial exploration capacity, cognitive processing speed, attentional flexibility; Corsi block-tapping test - visuospatial memory, short-term memory, working memory) during unassisted breathing and under ventilatory support. Ventilatory variables and transcutaneous haemoglobin oxygen saturation were recorded. Cortical connectivity changes between unassisted breathing and ventilatory support were assessed using electroencephalographic recordings (EEG).
Baseline performances were lower than expected in individuals of this age. During unassisted breathing, cognitive loading coincided with increased breathing variability, and decreases in oxygen saturation inversely correlated with an increasing number of apnoeic cycles per minute (rho -0.46, 95% CI -0.76 to -0.06, p=0.01). During ventilatory support, cognitive tasks did not disrupt breathing pattern and were not associated with decreased oxygen saturation. Ventilatory support was associated with changes in EEG cortical connectivity but not with improved test performances.
Acute cognitive loads induce oxygen desaturation in adult CCHS patients during unassisted breathing, but not under ventilatory support. This justifies considering the use of ventilatory support during mental tasks in CCHS patients to avoid repeated episodes of hypoxia.
Characterizing the breathing pattern in naturally breathing humans brings important information on respiratory mechanics, respiratory muscle, and breathing control. However, measuring breathing ...modifies breathing (observer effect) through the effects of instrumentation and awareness: measuring human breathing under true ecological conditions is currently impossible. This study tested the hypothesis that non-contact vibrometry using airborne ultrasound (SONAR) could measure breathing movements in a contactless and invisible manner. Thus, first, we evaluated the validity of SONAR measurements by testing their interchangeability with pneumotachograph (PNT) measurements obtained at the same time. We also aimed at evaluating the observer effect by comparing breathing variability obtained by SONAR versus SONAR-PNT measurements. Twenty-three healthy subjects (12 men and 11 women; mean age 33 years - range: 20-54) were studied during resting breathing while sitting on a chair. Breathing activity was described in terms of ventilatory flow measured using a PNT and, either simultaneously or sequentially, with a SONAR device measuring the velocity of the surface motion of the chest wall. SONAR was focused either anteriorly on the xiphoid process or posteriorly on the lower part of the costal margin. Discrete ventilatory temporal and volume variables and their coefficients of variability were calculated from the flow signal (PNT) and the velocity signal (SONAR) and tested for interchangeability (Passing-Bablok regression). Tidal volume (VT) and displacement were linearly related. Breathing frequency (BF), total cycle time (TT), inspiratory time (TI), and expiratory time (TE) met interchangeability criteria. Their coefficients of variation were not statistically significantly different with PNT and SONAR-only. This was true for both the anterior and the posterior SONAR measurements. Non-contact vibrometry using airborne ultrasound is a valid tool for measuring resting breathing pattern.
The use of a mouthpiece to measure ventilatory flow with a pneumotachograph (PNT) introduces a major perturbation to breathing ("instrumental/observer effect") and suffices to modify the respiratory ...behavior. Structured light plethysmography (SLP) is a non-contact method of assessment of breathing pattern during tidal breathing. Firstly, we validated the SLP measurements by comparing timing components of the ventilatory pattern obtained by SLP vs. PNT under the same condition; secondly, we compared SLP to SLP+PNT measurements of breathing pattern to evaluate the disruption of breathing pattern and breathing variability in healthy and COPD subjects. Measurements were taken during tidal breathing with SLP alone and SLP+PNT recording in 30 COPD and healthy subjects. Measurements included: respiratory frequency (R
), inspiratory, expiratory, and total breath time/duration (Ti, Te, and Tt). Passing-Bablok regression analysis was used to evaluate the interchangeability of timing components of the ventilatory pattern (R
, Ti, Te, and Tt) between measurements performed under the following experimental conditions: SLP vs. PNT, SLP+PNT vs. SLP, and SLP+PNT vs. PNT. The variability of different ventilatory variables was assessed through their coefficients of variation (CVs). In healthy: according to Passing-Bablok regression, Rf, TI, TE and TT were interchangeable between measurements obtained under the three experimental conditions (SLP vs. PNT, SLP+PNT vs. SLP, and SLP+PNT vs. PNT). All the CVs describing "traditional" ventilatory variables (R
, Ti, Te, Ti/Te, and Ti/Tt) were significantly smaller in SLP+PNT condition. This was not the case for more "specific" SLP-derived variables. In COPD: according to Passing-Bablok regression, Rf, TI, TE, and TT were interchangeable between measurements obtained under SLP vs. PNT and SLP+PNT vs. PNT, whereas only Rf, TE, and TT were interchangeable between measurements obtained under SLP+PNT vs. SLP. However, most discrete variables were significantly different between the SLP and SLP+PNT conditions and CVs were significantly lower when COPD patients were assessed in the SLP+PNT condition. Measuring ventilatory activity with SLP preserves resting tidal breathing variability, reduces instrumental observer effect and avoids any disruptions in breathing pattern induced by the use of PNT-mouthpiece-nose-clip combination.
Although compelling evidence has demonstrated considerable neuroplasticity in the respiratory control system, few studies have explored the possibility of altering descending projections to phrenic ...motoneurons (PMNs) using noninvasive stimulation protocols. The present study was designed to investigate the immediate and long-lasting effects of a single session of transcutaneous spinal direct current stimulation (tsDCS), a promising technique for modulating spinal cord functions, on descending ventilatory commands in healthy humans. Using a double-blind, controlled, randomized, crossover approach, we examined the effects of anodal, cathodal, and sham tsDCS delivered to the C3-C5 level on (1) diaphragm motor-evoked potentials (DiMEPs) elicited by transcranial magnetic stimulation and (2) spontaneous ventilation, as measured by respiratory inductance plethysmography. Both anodal and cathodal tsDCS induced a progressive increase in DiMEP amplitude during stimulation that persisted for at least 15 min after current offset. Interestingly, cathodal, but not anodal, tsDCS induced a persistent increase in tidal volume. In addition, (1) short-interval intracortical inhibition, (2) nonlinear complexity of the tidal volume signal (related to medullary ventilatory command), (3) autonomic function, and (4) compound muscle action potentials evoked by cervical magnetic stimulation were unaffected by tsDCS. This suggests that tsDCS-induced aftereffects did not occur at brainstem or cortical levels and were likely not attributable to direct polarization of cranial nerves or ventral roots. Instead, we argue that tsDCS could induce sustained changes in PMN output. Increased tidal volume after cathodal tsDCS opens up the perspective of harnessing respiratory neuroplasticity as a therapeutic tool for the management of several respiratory disorders.
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