The role of lung volume recruitment therapy in neuromuscular disease: a narrative review

Respiratory muscle weakness results in substantial discomfort, disability, and ultimately death in many neuromuscular diseases. Respiratory system impairment manifests as shallow breathing, poor cough and associated difficulty clearing mucus, respiratory tract infections, hypoventilation, sleep-disordered breathing, and chronic ventilatory failure. Ventilatory support (i.e., non-invasive ventilation) is an established and key treatment for the latter. As survival outcomes improve for people living with many neuromuscular diseases, there is a shift towards more proactive and preventative chronic disease multidisciplinary care models that aim to manage symptoms, improve morbidity, and reduce mortality. Clinical care guidelines typically recommend therapies to improve cough effectiveness and mobilise mucus, with the aim of averting acute respiratory compromise or respiratory tract infections. Moreover, preventing recurrent infective episodes may prevent secondary parenchymal pathology and further lung function decline. Regular use of techniques that augment lung volume has similarly been recommended (volume recruitment). It has been speculated that enhancing lung inflation in people with respiratory muscle weakness when well may improve respiratory system "flexibility", mitigate restrictive chest wall disease, and slow lung volume decline. Unfortunately, clinical care guidelines are based largely on clinical rationale and consensus opinion rather than level A evidence. This narrative review outlines the physiological changes that occur in people with neuromuscular disease and how these changes impact on breathing, cough, and respiratory tract infections. The biological rationale for lung volume recruitment is provided, and the clinical trials that examine the immediate, short-term, and longer-term outcomes of lung volume recruitment in paediatric and adult neuromuscular diseases are presented and the results synthesised.

Lung Inflation With Hydrogen During the Cold Ischemia Phase Alleviates Lung Ischemia-Reperfusion Injury by Inhibiting Pyroptosis in Rats

Background: Lung inflation with hydrogen is an effective method to protect donor lungs from lung ischemia-reperfusion injury (IRI). This study aimed to examine the effect of lung inflation with 3% hydrogen during the cold ischemia phase on pyroptosis in lung grafts of rats.

Methods: Adult male Wistar rats were randomly divided into the sham group, the control group, the oxygen (O₂) group, and the hydrogen (H₂) group. The sham group underwent thoracotomy but no lung transplantation. In the control group, the donor lungs were deflated for 2 h. In the O₂ and H₂ groups, the donor lungs were inflated with 40% O₂ + 60% N₂ and 3% H₂ + 40% O₂ + 57% N₂, respectively, at 10 ml/kg, and the gas was replaced every 20 min during the cold ischemia phase for 2 h. Two hours after orthotopic lung transplantation, the recipients were euthanized.

Results: Compared with the control group, the O₂ and H₂ groups improved oxygenation indices, decreases the inflammatory response and oxidative stress, reduced lung injury, and improved pressure-volume (P-V) curves. H₂ had a better protective effect than O₂. Furthermore, the levels of the pyroptosis-related proteins selective nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), cysteinyl aspartate specific proteinase (caspase)-1 p20, and the N-terminal of gasdermin D (GSDMD-N) were decreased in the H₂ group.

Conclusion: Lung inflation with 3% hydrogen during the cold ischemia phase inhibited the inflammatory response, oxidative stress, and pyroptosis and improved the function of the graft. Inhibiting reactive oxygen species (ROS) production may be the main mechanism of the antipyroptotic effect of hydrogen.

Sustained Lung Inflation in Pre-term Infants at Birth: A Randomized Controlled Trial

BACKGROUND

Invasive mechanical ventilation (IMV) of pre-term infants may be associated with high rate of mortality and iatrogenic complications in low- and middle-income countries. Sustained lung inflation (SLI) may help to reduce their need for IMV.

METHODS

This randomized controlled trial included 160 infants with gestational age (GA) ≥27 and ≤32 weeks who were randomly assigned to receive either SLI; using a pressure of 20 cmH2O for 15 s followed by nasal continuous positive airway pressure (CPAP) of 5 cmH2O or nasal CPAP alone, through an appropriate mask and a T-piece resuscitator. Primary outcome was the need for IMV in the first 72 h of life.

RESULTS

There was no difference in the primary outcome between SLI group; 55% (44 out of 80) and the control group; 65% (52 out of 80) [odds ratio (OR): 0.623, 95% confidence interval (CI): 0.33-1.18; p = 0.145]. However, SLI significantly reduced the primary outcome in the sicker infants; who had clinical eligibility criteria (CEC; OR: 0.224, 95% CI: 0.076-0.663; p = 0.005) and in the smaller babies; whose GA was <30 weeks (OR: 0.183, 95% CI: 0.053-0.635; p = 0.005).

CONCLUSION

SLI was not harmful. Although, it did not lead to reduction in the need for IMV in the first 72 h of life in pre-term infants with GA ≥27 and ≤32 weeks, SLI reduced this outcome in the subgroup of infants with CEC and those with GA <30 weeks. Future trials are needed to investigate the effect of SLI on these two subgroups.

TRIAL REGISTRATION

Clinical trials.gov, NCT03518762. https://www.clinicaltrials.gov/ct2/show/NCT03518762?term=NCT03518762&rank=1.

Comparison of breathing patterns, pressure, volume, and flow characteristics of three breathing techniques to encourage lung inflation in healthy older people

Background: It is important to encourage lung inflation to prevent postsurgical pulmonary complications and we compared three breathing techniques that place different emphasis on inspiratory flow and breath-holding. Methods: Fourteen healthy older people (69 ± 3.6 yrs) used diaphragmatic breathing (DB), Triflo II (TF), and a water pressure threshold device (BreatheMAX; BM) in a randomized and balanced crossover design. Outcome measures were inspiratory flow and pressure, inspiratory time (Ti), tidal volume (Vt), and breathing frequency. Results: Inspiratory flow with TF was significantly faster than DB and BM (p < 0.001: 0.96 ± 0.1; 0.43 ± 0.20 and 0.28 ± 0.1 L.s^-1, respectively) and pressures greater (p < 0.001: -1.3 ± 0.6, -5.5 ± 1.2 and -2.8 ± 3.6 cm H₂O). However, Ti was shorter (TF, 1.16 ± 0.21s; DB, 3.31 ± 0.97 s, p < 0.001; BM, 5.53 ± 1.92 s, p < 0.001), resulting in smaller Vt (TF, 1.12 ± 0.29 L; DB, 1.28 ± 0.29L, p = 0.003; BM, 1.37 ± 0.43L, p = 0.016). Breathing frequency was faster with TF compared to DB and BM (p < 0.001). Conclusions: Substantial lung inflation could be achieved with any of the above-mentioned methods, although Vt was smaller with TF and the high inspiratory flow with this method may not inflate the lower lung. The high pressures and rapid breathing with TF could increase the sense of effort. Trials are needed to determine the clinical value of the different breathing exercises.

Real-time imaging of inflation-induced ATP release in the ex vivo rat lung

Extracellular ATP and other nucleotides are important autocrine/paracrine mediators that regulate diverse processes critical for lung function, including mucociliary clearance, surfactant secretion, and local blood flow. Cellular ATP release is mechanosensitive; however, the impact of physical stimuli on ATP release during breathing has never been tested in intact lungs in real time and remains elusive. In this pilot study, we investigated inflation-induced ATP release in rat lungs ex vivo by real-time luciferin-luciferase (LL) bioluminescence imaging coupled with simultaneous infrared tissue imaging to identify ATP-releasing sites. With LL solution introduced into air spaces, brief inflation of such edematous lung (1 s, ∼20 cmH₂O) induced transient (<30 s) ATP release in a limited number of air-inflated alveolar sacs during their recruitment/opening. Released ATP reached concentrations of ∼10^-6 M, relevant for autocrine/paracrine signaling, but it remained spatially restricted to single alveolar sacs or their clusters. ATP release was stimulus dependent: prolonged (100 s) inflation evoked long-lasting ATP release that terminated upon alveoli deflation/derecruitment while cyclic inflation/suction produced cyclic ATP release. With LL introduced into blood vessels, inflation induced transient ATP release in many small patchlike areas the size of alveolar sacs. Findings suggest that inflation induces ATP release in both alveoli and the surrounding blood capillary network; the functional units of ATP release presumably consist of alveolar sacs or their clusters. Our study demonstrates the feasibility of real-time ATP release imaging in ex vivo lungs and provides the first direct evidence of inflation-induced ATP release in lung air spaces and in pulmonary blood capillaries, highlighting the importance of purinergic signaling in lung function.

Inflation with carbon monoxide in rat donor lung during cold ischemia phase ameliorates graft injury

Carbon monoxide (CO) attenuates lung ischemia reperfusion injury (IRI) via inhalation, and as an additive dissolved in flush/preservation solution. This study observed the effects of lung inflation with CO on lung graft function in the setting of cold ischemia. Donor lungs were inflated with 40% oxygen + 60% nitrogen (control group) or with 500 ppm CO + 40% oxygen + nitrogen (CO group) during the cold ischemia phase and were kept at 4℃ for 180 min. Recipients were sacrificed by exsanguinations at 180 min after reperfusion. Rats in the sham group had no transplantation and were performed as the recipients. Compared with the sham group, the oxygenation determined by blood gas analysis and the pressure-volume curves of the lung grafts decreased significantly, while the wet weight/dry weight (W/D) ratio, inflammatory reaction, oxidative stress, and cell apoptosis increased markedly (P < 0.05). However, compared to the control group, CO treatment improved the oxygenation (381 ± 58 vs. 308 ± 78 mm Hg) and the pressure-volume curves (15.8 ± 2.4 vs. 11.6 ± 1.7 mL/kg) (P < 0.05). The W/D ratio (4.6 ± 0.6) and the serum levels of interleukin-8 (279 ± 46 pg/mL) and tumor necrosis factor-α (377 ± 59 pg/mL) in the CO group decreased significantly compared to the control group (5.8 ± 0.8, 456 ± 63 pg/mL, and 520 ± 91 pg/mL) (P < 0.05). In addition, CO inflation also significantly decreased malondialdehyde activity and apoptotic cells in grafts, and increased the superoxide dismutase content. Briefly, CO inflation in donor lungs in the setting of cold ischemia attenuated lung IRI and improved the graft function compared with oxygen.

Impaired response to deep inspiration in obesity

Deep inspirations modulate airway caliber and airway closure and their effects are impaired in asthma. The association between asthma and obesity raises the question whether the deep inspiration (DI) effect is also impaired in the latter condition. We assessed the DI effects in obese and nonobese nonasthmatics. Thirty-six subjects (17 obese, 19 nonobese) underwent routine methacholine (Mch) challenge and 30 of them also had a modified bronchoprovocation in the absence of DIs. Lung function was monitored with spirometry and forced oscillation (FO) [resistance (R) at 5 Hz (R5), at 20 Hz (R20), R5-R20 and the integrated area of low-frequency reactance (AX)]. The response to Mch, assessed with area under the dose-response curves (AUC), was consistently greater in the routine challenge in the obese (mean ± SE, obese vs. nonobese AUC: R5: 15.7 ± 2.3 vs. 2.4 ± 2.0, P < 0.0005; R20: 5.6 ± 1.4 vs. 1.4 ± 1.2, P = 0.027; R5-R20: 10.2 ± 1.6 vs. 0.9 ± 0.1.4, P < 0.0005; AX: 115.6 ± 22.0 vs. 1.5 ± 18.9, P < 0.0005), but differences between groups in the modified challenge were smaller, indicating reduced DI effects in obesity. Given that DI has bronchodilatory and bronchoprotective effects, we further assessed these components separately. In the obese subjects, DI prior to Mch enhanced Mch-induced bronchoconstriction, but DI after Mch resulted in bronchodilation that was of similar magnitude as in the nonobese. We conclude that obesity is characterized by increased Mch responsiveness, predominantly of the small airways, due to a DI effect that renders the airways more sensitive to the stimulus.