New Finding
What is the central question of this study?
Transition to supine posture induces an inspiratory load associated with cortical activation in awake healthy subjects. Some obstructive sleep ...apnoea patients exhibit this cortical activity in the sitting position contributing to the arousal‐dependent compensation of their upper airway abnormalities. Does a transition to the supine posture in awake obstructive sleep apnoea patients increase this cortical activity?
What is the main finding and its importance?
The transition to supine posture induces a reduction in the cortical activity despite evidence of an increase in genioglossus activity, suggesting that genioglossus activation is not driven by cortical activity.
The anatomy and mechanical properties of the upper airway (UA) depend on posture. Lying in a supine position causes cephalad fluid shift to the neck, thus narrowing the UA and predisposing the individual to obstructive sleep apnoea (OSA). Increased UA dilator muscle activity during wakefulness prevents the UA collapse but the underlying mechanism has not yet been elucidated. In the sitting position during wakefulness, some OSA patients exhibit preinspiratory cortical activity (preinspiratory potential, PIP) probably related to UA abnormalities. The aim of this study was to investigate changes in the preinspiratory cortical activity and UA dilator muscle in OSA patients during postural challenge. An electroencephalogram was used to detect PIP, and the genioglossus electromyographic activity and ventilation were analysed in 17 awake, male OSA patients while they were sitting, just after lying down, and then in response to leg positive pressure to enhance cephalad fluid shift. The prevalence of PIP decreased from 53% (sitting) to 12% (supine) (P = 0.002) in association with increased genioglossus activity (tonic from median (25th, 75th centiles) 2.3 (1.8, 2.8)% to 3.6 (1.7, 5.0)% of voluntary deglutition, P = 0.019; phasic from 2.3 (1.9, 2.8)% to 3.7 (2.0, 6.1)%, P = 0.024), and with increased transcutaneous carbon dioxide pressure (from 43.0 (42.4, 44.2) to 44.6 (43.5, 45.2) mmHg). No change was observed during leg‐positive‐pressure application. Moving from the sitting position to the supine position reduces respiratory‐related premotor cortical activity in awake OSA patients. The concomitant increase in genioglossus activity, therefore, is not driven by cortical respiratory activity.
New Findings
What is the central question of this study?
Moving to supine induces upper airway modifications and a fluid shift to the neck, which represent inspiratory load that predisposes to upper ...airway collapse. Is there cortical participation in the response to the load induced by transition to a supine posture in awake healthy subjects?
What is the main finding and its importance?
Moving to supine induces transient cortical activation in awake healthy subjects, with greater fluid shift, supporting possible cortical participation in the response to upper airway load induced by transition to a supine posture. Our findings open new perspectives in the understanding of the pathogenesis of obstructive sleep apnoea.
Moving from sitting upright to lying supine causes anatomical modifications and a fluid shift to the neck, which represent inspiratory loads that predispose to upper airway collapse. The pre‐inspiratory potential (PIP) corresponds to the cortical activity observed during inspiratory load. In the sitting position during wakefulness, some obstructive sleep apnoea patients exhibit PIP, probably in relationship to upper airway abnormalities. The aim of this study was to investigate whether moving to the supine position induces respiratory‐related cortical activation (PIP) in awake healthy subjects. The ECG was analysed to detect PIP, and EMG activity of the genioglossus muscle and ventilation were measured in the sitting position, immediately after moving to the supine position, and during application of leg positive pressure in the supine position to promote fluid shift, which was measured by bioelectrical impedance. Twenty‐four subjects were included. From sitting to lying, PIP prevalence increased from 1/24 to 11/24 (P = 0.002), and ventilation decreased with no change in genioglossus activity. The fluid shift from sitting to supine was higher in the subjects exhibiting PIP while supine compared with the subjects without PIP median (25th; 75th centiles) 440 (430; 520) versus 320 (275; 385) ml, P = 0.018, without any other differences. From before to during leg positive pressure, PIP disappeared (P = 0.006). These results indicate that moving from sitting to lying induces transient respiratory‐related cortical activity in awake healthy subjects with greater fluid shift, supporting possible cortical participation in the response to upper airway loading induced by moving from sitting upright to lying supine. This study offers new perspectives in the understanding of obstructive sleep apnoea pathogenesis.
Key points
Twitch transdiaphragmatic pressure elicited by cervical magnetic stimulation of the phrenic nerves is a fully non‐volitional method for assessing diaphragm contractility in humans, yet it ...requires invasive procedures such as oesophageal and gastric catheter balloons.
Ultrafast ultrasound enables a very high frame rate allowing the capture of transient events, such as muscle contraction elicited by nerve stimulation (twitch). Whether indices derived from ultrafast ultrasound can be used as an alternative to the invasive measurement of twitch transdiaphragmatic pressure is unknown.
Our findings demonstrate that maximal diaphragm tissue velocity assessed using ultrafast ultrasound following cervical magnetic stimulation is reliable, sensitive to change in cervical magnetic stimulation intensity, and correlates to twitch transdiaphragmatic pressure.
This approach provides a novel fully non‐invasive and non‐volitional tool for the assessment of diaphragm contractility in humans.
Measuring twitch transdiaphragmatic pressure (Pdi,tw) elicited by cervical magnetic stimulation (CMS) is considered as a reference method for the standardized evaluation of diaphragm function. Yet, the measurement of Pdi requires invasive oesophageal and gastric catheter‐balloons. Ultrafast ultrasound is a non‐invasive imaging technique enabling frame rates high enough to capture transient events such as evoked muscle contractions. This study investigated relationships between indices derived from ultrafast ultrasound and Pdi,tw, and how these indices might be used to estimate Pdi,tw. CMS was performed in 13 healthy volunteers from 30% to 100% of maximal stimulator intensity in units of 10% in a randomized order. Pdi,tw was measured and the right hemidiaphragm was imaged using a custom ultrafast ultrasound sequence with 1 kHz framerate. Maximal diaphragm axial velocity (Vdi,max) and diaphragm thickening fraction (TFdi,tw) were computed. Intra‐session reliability was assessed. Repeated‐measures correlation (R) and Spearman correlation coefficients (ρ) were used to assess relationships between variables. Intra‐session reliability was strong for Pdi,tw and Vdi,max and moderate for TFdi,tw. Vdi,max correlated with Pdi,tw in all subjects (0.64 < ρ < 1.00, R = 0.75; all P < 0.05). TFdi,tw correlated with Pdi,tw in eight subjects only (0.85 < ρ < 0.93, R = 0.69; all P < 0.05). Coupling ultrafast ultrasound and CMS shows promise for the non‐invasive and fully non‐volitional assessment of diaphragm contractility. This approach opens up the prospect of both diagnosis and follow‐up of diaphragm contractility in clinical populations.
Key points
Twitch transdiaphragmatic pressure elicited by cervical magnetic stimulation of the phrenic nerves is a fully non‐volitional method for assessing diaphragm contractility in humans, yet it requires invasive procedures such as oesophageal and gastric catheter balloons.
Ultrafast ultrasound enables a very high frame rate allowing the capture of transient events, such as muscle contraction elicited by nerve stimulation (twitch). Whether indices derived from ultrafast ultrasound can be used as an alternative to the invasive measurement of twitch transdiaphragmatic pressure is unknown.
Our findings demonstrate that maximal diaphragm tissue velocity assessed using ultrafast ultrasound following cervical magnetic stimulation is reliable, sensitive to change in cervical magnetic stimulation intensity, and correlates to twitch transdiaphragmatic pressure.
This approach provides a novel fully non‐invasive and non‐volitional tool for the assessment of diaphragm contractility in humans.
Patients with central respiratory paralysis can benefit from diaphragm pacing to restore respiratory function. However, it would be important to develop a continuous respiratory monitoring method to ...alert on apnea occurrence, in order to improve the efficiency and safety of the pacing system. In this study, we present a preliminary validation of an acoustic apnea detection method on healthy subjects data. Thirteen healthy participants performed one session of two 2-min recordings, including a voluntary respiratory pause. The recordings were post-processed by combining temporal and frequency detection domains, and a new method was proposed-Phonocardiogram-Derived Respiration (PDR). The detection results were compared to synchronized pneumotachograph, electrocardiogram (ECG), and abdominal strap (plethysmograph) signals. The proposed method reached an apnea detection rate of 92.3%, with 99.36% specificity, 85.27% sensitivity, and 91.49% accuracy. PDR method showed a good correlation of 0.77 with ECG-Derived Respiration (EDR). The comparison of R-R intervals and S-S intervals also indicated a good correlation of 0.89. The performance of this respiratory detection algorithm meets the minimal requirements to make it usable in a real situation. Noises from the participant by speaking or from the environment had little influence on the detection result, as well as body position. The high correlation between PDR and EDR indicates the feasibility of monitoring respiration with PDR.
Keywords: cervical magnetic stimulation; contractility; diaphragm; phrenic nerves; skeletal muscle; ultrafast ultrasound imaging Article Note: Edited by: Scott Powers & Ken O'Halloran Linked ...articles: This is a reply to a Letter to the Editor by Beltrami. To read the Letter to the Editor, visit Poulard et al. To read the article, visit Jean-Luc Gennisson and Damien Bachansson contributed equally to this work. Byline: Thomas Poulard, Martin Dres, Marie-Cecile Nierat, Isabelle Rivals, Jean-Yves Hogrel, Thomas Similowski, Jean-Luc Gennisson, Damien Bachasson
The relationship between the diaphragm thickening fraction and the transdiaphragmatic pressure, the reference method to evaluate the diaphragm function, has not been clearly established. This study ...investigated the global and intraindividual relationship between the thickening fraction of the diaphragm and the transdiaphragmatic pressure. The authors hypothesized that the diaphragm thickening fraction would be positively and significantly correlated to the transdiaphragmatic pressure, in both healthy participants and ventilated patients.
Fourteen healthy individuals and 25 mechanically ventilated patients (enrolled in two previous physiologic investigations) participated in the current study. The zone of apposition of the right hemidiaphragm was imaged simultaneously to transdiaphragmatic pressure recording within different breathing conditions, i.e., external inspiratory threshold loading in healthy individuals and various pressure support settings in patients. A blinded offline breath-by-breath analysis synchronously computed the changes in transdiaphragmatic pressure, the diaphragm pressure-time product, and diaphragm thickening fraction. Global and intraindividual relationships between variables were assessed.
In healthy subjects, both changes in transdiaphragmatic pressure and diaphragm pressure-time product were moderately correlated to diaphragm thickening fraction (repeated measures correlation = 0.40, P < 0.0001; and repeated measures correlation = 0.38, P < 0.0001, respectively). In mechanically ventilated patients, changes in transdiaphragmatic pressure and thickening fraction were weakly correlated (repeated measures correlation = 0.11, P = 0.008), while diaphragm pressure-time product and thickening fraction were not (repeated measures correlation = 0.04, P = 0.396). Individually, changes in transdiaphragmatic pressure and thickening fraction were significantly correlated in 8 of 14 healthy subjects (ρ = 0.30 to 0.85, all P < 0.05) and in 2 of 25 mechanically ventilated patients (ρ = 0.47 to 0.64, all P < 0.05). Diaphragm pressure-time product and thickening fraction correlated in 8 of 14 healthy subjects (ρ = 0.41 to 0.82, all P < 0.02) and in 2 of 25 mechanically ventilated patients (ρ = 0.63 to 0.66, all P < 0.01).
Overall, diaphragm function as assessed with transdiaphragmatic pressure was weakly related to diaphragm thickening fraction. The diaphragm thickening fraction should not be used in healthy subjects or ventilated patients when changes in diaphragm function are evaluated.
Human breathing stems from automatic brainstem neural processes. It can also be operated by cortico-subcortical networks, especially when breathing becomes uncomfortable because of external or ...internal inspiratory loads. How the "irruption of breathing into consciousness" interacts with cognition remains unclear, but a case report in a patient with defective automatic breathing (Ondine's curse syndrome) has shown that there was a cognitive cost of breathing when the respiratory cortical networks were engaged. In a pilot study of putative breathing-cognition interactions, the present study relied on a randomized design to test the hypothesis that experimentally loaded breathing in 28 young healthy subjects would have a negative impact on cognition as tested by "timed up-and-go" test (TUG) and its imagery version (iTUG). Progressive inspiratory threshold loading resulted in slower TUG and iTUG performance. Participants consistently imagined themselves faster than they actually were. However, progressive inspiratory loading slowed iTUG more than TUG, a finding that is unexpected with regard to the known effects of dual tasking on TUG and iTUG (slower TUG but stable iTUG). Insofar as the cortical networks engaged in response to inspiratory loading are also activated during complex locomotor tasks requiring cognitive inputs, we infer that competition for cortical resources may account for the breathing-cognition interference that is evidenced here.
Introduction
Dyspnea is common and often severe symptom in mechanically ventilated patients. Proportional assist ventilation (PAV) is an assist ventilatory mode that adjusts the level of assistance ...to the activity of respiratory muscles. We hypothesized that PAV reduce dyspnea compared to pressure support ventilation (PSV).
Patients and methods
Mechanically ventilated patients with clinically significant dyspnea were included. Dyspnea intensity was assessed by the Dyspnea—Visual Analog Scale (D-VAS) and the Intensive Care-Respiratory Distress Observation Scale (IC-RDOS) at inclusion (PSV-Baseline), after personalization of ventilator settings in order to minimize dyspnea (PSV-Personalization), and after switch to PAV. Respiratory drive was assessed by record of electromyographic activity of inspiratory muscles, the proportion of asynchrony was analyzed.
Results
Thirty-four patients were included (73% males, median age of 66 57–77 years). The D-VAS score was lower with PSV-Personalization (37 mm 20‒55) and PAV (31 mm 14‒45) than with PSV-Baseline (62 mm 28‒76) (
p
< 0.05). The IC-RDOS score was lower with PAV (4.2 2.4‒4.7) and PSV-Personalization (4.4 2.4‒4.9) than with PSV-Baseline (4.8 4.1‒6.5) (
p
< 0.05). The electromyographic activity of parasternal intercostal muscles was lower with PAV and PSV-Personalization than with PSV-Baseline. The asynchrony index was lower with PAV (0% 0‒0.55) than with PSV-Baseline and PSV-Personalization (0.68% 0‒2.28 and 0.60% 0.31‒1.41, respectively) (
p
< 0.05).
Conclusion
In mechanically ventilated patients exhibiting clinically significant dyspnea with PSV, personalization of PSV settings and PAV results in not different decreased dyspnea and activity of muscles to a similar degree, even though PAV was able to reduce asynchrony more effectively.
Purpose
In healthy humans, postural and respiratory dynamics are intimately linked and a breathing-related postural perturbation is evident in joint kinematics. A cognitive dual-task paradigm that is ...known to induce both postural and ventilatory disturbances can be used to modulate this multijoint posturo-ventilatory (PV) interaction, particularly in the cervical spine, which supports the head. The objective of this study was to assess this modulation.
Methods
With the use of optoelectronic sensors, the breathing profile, articular joint motions of the cervical spine, hip, knees and ankles, and centre of pressure (CoP) displacement were measured in 20 healthy subjects (37 years old 29; 49, 10 females) during natural breathing (NB), a cognitive dual task (COG), and eyes-closed and increased-tidal-volume conditions. The PV interaction in the CoP and joint motions were evaluated by calculating the respiratory emergence (REm).
Results
Only the COG condition induced a decrease in the cervical REm (NB: 17.2% 7.8; 37.2; COG: 4.2% 1.8; 10.0
p
= 0.0020) concurrent with no changes in the cervical motion. The CoP REm (NB: 6.2% 3.8; 10.3; COG: 12.9% 5.8; 20.7
p
= 0.0696) and breathing frequency (NB: 16.6 min-1 13.3; 18.7; COG: 18.6 min-1 16.3; 19.4
p
= 0.0731) tended to increase, while the CoP (
p
= 0.0072) and lower joint motion displacements (
p
< 0.05) increased.
Conclusion
This study shows stable cervical spine motion during a cognitive dual task, as well as increased postural perturbations globally and in other joints. The concurrent reduction in the PV interaction at the cervical spine suggests that this “stabilization strategy” is centrally controlled and is achieved by a reduction in the breathing-related postural perturbations at this level. Whether this strategy is a goal for maintaining balance remains to be studied.
Heart rate has natural fluctuations that are typically ascribed to autonomic function. Recent evidence suggests that conscious processing can affect the timing of the heartbeat. We hypothesized that ...heart rate is modulated by conscious processing and therefore dependent on attentional focus. To test this, we leverage the observation that neural processes synchronize between subjects by presenting an identical narrative stimulus. As predicted, we find significant inter-subject correlation of heart rate (ISC-HR) when subjects are presented with an auditory or audiovisual narrative. Consistent with our hypothesis, we find that ISC-HR is reduced when subjects are distracted from the narrative, and higher ISC-HR predicts better recall of the narrative. Finally, patients with disorders of consciousness have lower ISC-HR, as compared to healthy individuals. We conclude that heart rate fluctuations are partially driven by conscious processing, depend on attentional state, and may represent a simple metric to assess conscious state in unresponsive patients.
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•Narrative stimuli can synchronize fluctuations of heart rate between individuals•This interpersonal synchronization is modulated by attention and predicts memory•These effects on heart rate cannot be explained by modulation of respiratory patterns•Synchrony is lower in patients with disorders of consciousness
Stories affect our hearts and bind us together. Pérez et al. show that attention to narratives can synchronize fluctuations of heart rate between individuals. Heart synchronization predicts memory and cannot be explained by respiration. Finally, synchrony is lower in patients with disorders of consciousness and might inform prognosis.
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