Feasibility of intercostal blood flow measurement by echo-Doppler technique in healthy subjects

The Influence of Minor Aortic Branches in Patient-Specific Flow Simulations of Type-B Aortic Dissection

Type-B aortic dissection (TBAD) is a disease in which a tear develops in the intimal layer of the descending aorta forming a true lumen and false lumen (FL). Because disease outcomes are thought to be influenced by haemodynamic quantities such as pressure and wall shear stress (WSS), their analysis via numerical simulations may provide valuable clinical insights. Major aortic branches are routinely included in simulations but minor branches are virtually always neglected, despite being implicated in TBAD progression and the development of complications. As minor branches are estimated to carry about 7-21% of cardiac output, neglecting them may affect simulation accuracy. We present the first simulation of TBAD with all pairs of intercostal, subcostal and lumbar arteries, using 4D-flow MRI (4DMR) to inform patient-specific boundary conditions. Compared to an equivalent case without minor branches, their inclusion improved agreement with 4DMR velocities, reduced time-averaged WSS (TAWSS) and transmural pressure and elevated oscillatory shear in regions where FL dilatation and calcification were observed in vivo. Minor branch inclusion resulted in differences of 60-75% in these metrics of potential clinical relevance, indicating a need to account for minor branch flow loss if simulation accuracy is sought.

Intercostal muscle oxygenation and expiratory loaded breathing at rest: Respiratory pattern effect

In patients with airway obstruction, an increase in breathing frequency at rest is commonly associated with a dynamic hyperinflation (DH). In such a situation, intercostal muscle oxygenation may be disturbed. This hypothesis was examined in a context of simulated airway obstruction in healthy subjects. After a control period of 5 min, twelve participants (20 ± 2 years) breathed at rest through a 20-cmH₂O expiratory threshold load, either by increasing or reducing their respiratory rate (_ETLF⁺ or _ETLF). Tissue saturation index (TSI) and concentration changes in oxyhaemoglobin (oxy[Hb+Mb]) were measured as well as cardiorespiratory variables. Inspiratory capacity was decreased in _ETLF⁺ (p < 0.001) and correlated with dyspnea. An increase in oxy[Hb+Mb] occurred in _ETLF⁺ that was higher than in _ETLF (p < 0.01). TSI was not different between conditions. In healthy subjects at rest, an increase in respiratory rate during a simulated obstruction with an expiratory threshold load resulted in paradoxical response with DH emergence while intercostal muscle oxygenation was preserved.

Effect of expiratory loaded breathing during moderate exercise on intercostal muscle oxygenation

BACKGROUND

In patients with obstructive lung disease, maintaining adequate ventilation during exercise may require greater contraction of the respiratory muscles, which may lead to a compression of muscle capillaries. Furthermore, dynamic hyperinflation (DH) is frequent during exercise in these patients, as it allows to reach higher expiratory flows and to satisfy respiratory demand. However, in such situation, intercostal muscles are likely to be stretched, which could affect the diameter of their capillaries. Thus, in a context of high level of expiratory resistance, intercostal muscle oxygenation may be disturbed during exercise, especially if DH occurs.

METHODS

Twelve participants (22±2 years) performed two sessions of moderate exercise (20 min) by breathing freely with and without a 20-cmH2O expiratory threshold load (ETL). Tissue saturation index (TSI) and concentration changes from rest (Δ) in oxygenated ([O2Hb]) and total haemoglobin ([tHb]) were measured in the seventh intercostal space using near-infrared spectroscopy. Respiratory, metabolic and cardiac variables were likewise recorded.

RESULTS

Throughout exercise, dyspnea was higher and TSI was lower in ETL condition than in control (p<0.01). After a few minutes of exercise, Δ [O2Hb] was also lower in ETL condition, as well as Δ [tHb], when inspiratory capacity started to be reduced (p<0.05). Changes in [O2Hb] and dyspnea were correlated with changes in expiratory flow rate (Vt/Te) (r = -0.66 and 0.66, respectively; p<0.05).

CONCLUSION

During exercise with ETL, impaired muscle oxygenation could be due to a limited increase in blood volume resulting from strong muscle contraction and/or occurrence of DH.

Intercostal muscle oxygenation during expiratory load breathing at rest

BACKGROUND

During acute bronchial obstruction, despite a higher work of breathing, blood supply and oxygen availability may be reduced in intercostal muscles because of mechanical constraints. This hypothesis was assessed in healthy subjects breathing with and without expiratory load (ETL).

METHODS

Eleven men (24 ± 2 years) breathed at rest for 5 min in unloaded condition and for 20 min through a 20-cmH₂O ETL. Tissue saturation index (TSI) and changes (Δ) in concentration of total and oxy-haemoglobin ([tHb] and [O₂Hb]) were measured in the seventh intercostal space by near-infrared spectroscopy.

RESULTS

[tHb] and [O₂Hb] decreased with ETL (-5.16 μM and -3.54 μM; p < 0.05). TSI did not vary. Negative correlations were observed between Δ[O₂Hb] and changes in expiratory flow rate (ΔVt/Te) and between ΔTSI and Δ V˙E (r = -0.78 and -0.74; p ≤ 0.01).

CONCLUSION

Despite decreases in Hb concentrations, saturation in oxygen was not reduced with ETL in intercostal muscles, suggesting a satisfactory ventilatory and/or hemodynamic arrangement.

Surface electromyography (sEMG) of extradiaphragm respiratory muscles in healthy subjects: A systematic review

The aim of this systematic review was to examine procedures used and outcome measures reported from surface EMG (sEMG) of extradiaphragm inspiratory muscles in healthy people. Relevant articles were searched using the concepts "electromyography (EMG)", "respiratory muscles (sternocleidomastoid [SM], scalene, intercostal [IC] and parasternal)" and "healthy" in the electronic databases: MEDLINE, PubMed, EMBASE, Cochrane CENTRAL and Database of Systematic Reviews, CINAHL, SPORTDiscus, LILACS, and PEDro. Twenty-five papers were included and quality assessment was performed using an adapted Downs and Black checklist. Twenty-eight percent of included papers were classified as moderate quality and the rest were low quality. The SM was the muscle most often investigated. Description of EMG techniques were often incomplete for features such as the procedure before electrode placement, description of the surface electrodes, the EMG detection mode and amplification. Of note, descriptions of the IC muscle electrode positioning varied widely. Comparison of outcomes among studies was challenging because of the very diverse EMG outcomes reported. There are many controversies regarding methods and technique used to assess sEMG of extradiaphragm inspiratory muscles. Therefore, studies with higher methodological quality utilizing standardized EMG procedures including electrode positioning will enable accurate and reliable comparison among studies of the extradiaphragm inspiratory muscles.