Do we “drive” dyspnoea?

Increasing Sweep Gas Flow Reduces Respiratory Drive and Dyspnea in Nonintubated Venoarterial Extracorporeal Membrane Oxygenation Patients: A Pilot Study

BACKGROUND

Data on assessment and management of dyspnea in patients on venoarterial extracorporeal membrane oxygenation (ECMO) for cardiogenic shock are lacking. The hypothesis was that increasing sweep gas flow through the venoarterial extracorporeal membrane oxygenator may decrease dyspnea in nonintubated venoarterial ECMO patients exhibiting clinically significant dyspnea, with a parallel reduction in respiratory drive.

METHODS

Nonintubated, spontaneously breathing, supine patients on venoarterial ECMO for cardiogenic shock who presented with a dyspnea visual analog scale (VAS) score of greater than or equal to 40/100 mm were included. Sweep gas flow was increased up to +6 l/min by three steps of +2 l/min each. Dyspnea was assessed with the dyspnea-VAS and the Multidimensional Dyspnea Profile. The respiratory drive was assessed by the electromyographic activity of the alae nasi and parasternal muscles.

RESULTS

A total of 21 patients were included in the study. Upon inclusion, median dyspnea-VAS was 50 (interquartile range, 45 to 60) mm, and sweep gas flow was 1.0 l/min (0.5 to 2.0). An increase in sweep gas flow significantly decreased dyspnea-VAS (50 [45 to 60] at baseline vs. 20 [10 to 30] at 6 l/min; P < 0.001). The decrease in dyspnea was greater for the sensory component of dyspnea (-50% [-43 to -75]) than for the affective and emotional components (-17% [-0 to -25] and -12% [-0 to -17]; P < 0.001). An increase in sweep gas flow significantly decreased electromyographic activity of the alae nasi and parasternal muscles (-23% [-36 to -10] and -20 [-41 to -0]; P < 0.001). There was a significant correlation between the sweep gas flow and the dyspnea-VAS (r = -0.91; 95% CI, -0.94 to -0.87), between the respiratory drive and the sensory component of dyspnea (r = 0.29; 95% CI, 0.13 to 0.44) between the respiratory drive and the affective component of dyspnea (r = 0.29; 95% CI, 0.02 to 0.54) and between the sweep gas flow and the alae nasi and parasternal (r = -0.31; 95% CI, -0.44 to -0.22; and r = -0.25; 95% CI, -0.44 to -0.16).

CONCLUSIONS

In critically ill patients with venoarterial ECMO, an increase in sweep gas flow through the oxygenation membrane decreases dyspnea, possibly mediated by a decrease in respiratory drive.

EDITOR’S PERSPECTIVE

Sensory interventions to relieve dyspnoea in critically ill mechanically ventilated patients

BACKGROUND

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.

METHODS

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 versus pink noise) and air flux stimulation (facial versus lower limb). Treatment responses were assessed using Dyspnoea-VAS, the Multidimensional Dyspnea Profile and measures of the neural drive to breathe (airway occlusion pressure (P 0.1) and electromyography of inspiratory muscles).

RESULTS

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 P 0.1 by median 3.3 cmH2O (p<0.001).

CONCLUSIONS

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.

Exertional Dyspnoea in Chronic Respiratory Diseases: From Physiology to Clinical Application

Dyspnoea is a complex, highly personalized and multidimensional sensory experience, and its underlying cause and mechanisms are still being investigated. Exertional dyspnoea is one of the most frequently encountered symptoms of patients with cardiopulmonary diseases, and is a common reason for seeking medical help. As the symptom usually progresses with the underlying disease, it can lead to an avoidance of physical activity, peripheral muscle deconditioning and decreased quality of life. Dyspnoea is closely associated with quality of life, exercise (in)tolerance and prognosis in various conditions, including chronic obstructive pulmonary disease, heart failure, interstitial lung disease and pulmonary hypertension, and is therefore an important therapeutic target. Effective management and treatment of dyspnoea is an important challenge for caregivers, and therapeutic options that attempt to reverse its underlying cause have been only partially successful This "review" will attempt to shed light on the physiological mechanisms underlying dyspnoea during exercise and to translate/apply them to a broad clinical spectrum of cardio-respiratory disorders.

Blunted perception of neural respiratory drive and breathlessness in patients with cystic fibrosis

The electromyogram recorded from the diaphragm (EMG_di) and parasternal intercostal muscle using surface electrodes (sEMG_para) provides a measure of neural respiratory drive (NRD), the magnitude of which reflects lung disease severity in stable cystic fibrosis. The aim of this study was to explore perception of NRD and breathlessness in both healthy individuals and patients with cystic fibrosis. Given chronic respiratory loading and increased NRD in cystic fibrosis, often in the absence of breathlessness at rest, we hypothesised that patients with cystic fibrosis would be able to tolerate higher levels of NRD for a given level of breathlessness compared to healthy individuals during exercise.

15 cystic fibrosis patients (mean forced expiratory volume in 1 s (FEV₁) 53.5% predicted) and 15 age-matched, healthy controls were studied. Spirometry was measured in all subjects and lung volumes measured in the cystic fibrosis patients. EMG_di and sEMG_para were recorded at rest and during incremental cycle exercise to exhaustion and expressed as a percentage of maximum (% max) obtained from maximum respiratory manoeuvres. Borg breathlessness scores were recorded at rest and during each minute of exercise.

EMG_di % max and sEMG_para % max and associated Borg breathlessness scores differed significantly between healthy subjects and cystic fibrosis patients at rest and during exercise. The relationship between EMG_di % max and sEMG_para % max and Borg score was shifted to the right in the cystic fibrosis patients, such that at comparable levels of EMG_di % max and sEMG_para % max the cystic fibrosis patients reported significantly lower Borg breathlessness scores compared to the healthy individuals. At Borg score 1 (clinically significant increase in breathlessness from baseline) corresponding levels of EMG_di % max (20.2±12% versus 32.15±15%, p=0.02) and sEMG_para % max (18.9±8% versus 29.2±15%, p=0.04) were lower in the healthy individuals compared to the cystic fibrosis patients.

In the cystic fibrosis patients EMG_di % max at Borg score 1 was related to the degree of airways obstruction (FEV₁) (r=−0.664, p=0.007) and hyperinflation (residual volume/total lung capacity) (r=0.710, p=0.03). This relationship was not observed for sEMG_para % max.

These data suggest that compared to healthy individuals, patients with cystic fibrosis can tolerate much higher levels of NRD before increases in breathlessness from baseline become clinically significant. EMG_di % max and sEMG_para % max provide physiological tools with which to elucidate factors underlying inter-individual differences in breathlessness perception.

Patients with CF can tolerate higher levels of NRD before breathlessness becomes clinically significanthttp://ow.ly/Xp2q3

Measuring Dyspnea and Perceived Exertion in Healthy Adults and with Respiratory Disease: New Pictorial Scales

Background

Dyspnea or perceived exertion during exercise is most commonly measured using Borg or visual analog scales, created for use in adults. In contrast, pictorial scales have been promoted for children due to skepticism concerning applicability of the said scales in pediatrics. We sought to validate our newly created, pictorial Dalhousie Dyspnea and Perceived Exertion Scales in adult populations and compare ratings with the Borg scale.

Methods

Dyspnea and perceived exertion ratings obtained with both modified Borg CR-10 and Dalhousie scales during maximal cycle exercise were compared in 24 healthy adults and 17 with various pulmonary disorders. Scale ratings for perceived exertion were plotted against work while ratings for dyspnea were plotted against ventilation using previously developed alternative models to simple power law. Goodness of fit was determined by lowest root-mean-square error or by corrected Akaike information criterion.

Results

Pictorial ratings of dyspnea and perceived exertion measured by both scale ratings rose as expected with increasing exercise intensity, and individual trajectories obtained by either scale were virtually superimposable in 90 % of subjects. In general, the lowest root-mean-square error or corrected Akaike information criterion was found with models which incorporated a time delay, defined as the fraction of maximum work or ventilation at which point a clear increase in ratings above resting level was reported.

Conclusions

The Dalhousie Dyspnea and Exertion Scales offer an equally good alternative to the Borg scale for measuring dyspnea and perceived exertion in adults.