Respiratory function in amyotrophic lateral sclerosis

Exploring inspiratory occlusion metrics to assess respiratory drive in patients under acute intermittent hypoxia

Patients living with Amyotrophic Lateral Sclerosis (ALS) experience respiratory weakness and, eventually, failure due to inspiratory motor neuron degeneration. Routine pulmonary function tests (e.g., maximum inspiratory pressure (MIP)) are used to assess disease progression and ventilatory compromise. However, these tests are poor discriminators between respiratory drive and voluntary respiratory function at rest. To better understand ALS disease progression, we can look into compensatory strategies and how patients consciously react to the occlusion and the effort produced to meet the ventilatory challenge of the occlusion. This ventilatory challenge, especially beyond the P_0.1 (200 ms and 300 ms), provides information regarding the patient's ability to recruit additional respiratory muscles as a compensatory strategy. Utilizing a standard P_0.1 protocol to assess respiratory drive, we extend the occlusion time analysis to 200 ms and 300 ms (Detected Occlusion Response (DOR)) in order to capture compensatory respiratory mechanics. Furthermore, we followed an Acute Intermittent Hypoxia (AIH) protocol known to increase phrenic nerve discharge to evaluate the compensatory strategies. Inspiratory pressure, the rate of change in pressure, and pressure generation normalized to MIP were measured at 100 ms, 200 ms, and 300 ms after an occlusion. Airway occlusions were performed three times during the experiment (i.e., baseline, 30 and 60 minutes post-AIH). Results indicated that while AIH did not elicit change in the P_0.1 or MIP, the DOR increased for ALS patients. These results support the expected therapeutic role of AIH and indicate the potential of the DOR as a metric to detect compensatory changes.

How Are Adenosine and Adenosine A2A Receptors Involved in the Pathophysiology of Amyotrophic Lateral Sclerosis?

Adenosine is extensively distributed in the central and peripheral nervous systems, where it plays a key role as a neuromodulator. It has long been implicated in the pathogenesis of progressive neurogenerative disorders such as Parkinson’s disease, and there is now growing interest in its role in amyotrophic lateral sclerosis (ALS). The motor neurons affected in ALS are responsive to adenosine receptor function, and there is accumulating evidence for beneficial effects of adenosine A_2A receptor antagonism. In this article, we focus on recent evidence from ALS clinical pathology and animal models that support dynamism of the adenosinergic system (including changes in adenosine levels and receptor changes) in ALS. We review the possible mechanisms of chronic neurodegeneration via the adenosinergic system, potential biomarkers and the acute symptomatic pharmacology, including respiratory motor neuron control, of A_2A receptor antagonism to explore the potential of the A_2A receptor as target for ALS therapy.

Diaphragmatic dysfunction at the first visit to a chest diseases outpatient clinic in 500 patients with amyotrophic lateral sclerosis

INTRODUCTION

In this study, we aimed to evaluate diaphragmatic dysfunction (DD) by using a practical approach in patients with amyotrophic lateral sclerosis (ALS) at the first visit to a chest diseases outpatient clinic.

METHODS

Patients with ALS seen in our outpatient clinic for the past 5 y and followed up for at least 1 y, were retrospectively evaluated. Having at least one of the following three criteria was accepted as DD: (a) paradoxical abdominal movement (PAM), (b) sitting-supine forced vital capacity (FVC) difference ≥ 20%, (c) sitting-supine arterial oxygen saturation measured by pulse oximetry (SpO₂ ) difference ≥ 4%. Respiratory symptoms, arterial blood gas analysis, sleep studies, noninvasive mechanical ventilation use, and mortality were recorded.

RESULTS

Five-hundred patients with ALS were included (female/male: 220/280, age: 58.9 ± 11.3 y). Of the patients, 22.8% had daytime hypercapnia. DD was observed in 55% of the patients (PAM in 112, sitting-supine FVC difference ≥ 20% in 50, and sitting-supine SpO₂ difference ≥ 4% in 113 patients). Of the patients with DD, 31.6% (n = 87) had no respiratory symptoms, 46.4% had FVC > 70% and 33.5% had FVC <50%. Nocturnal hypoxemia (sleep time spent with SpO₂  < 90% ≥30%) was present in 59.7%, and all patients with nocturnal hypoxemia had DD. Obstructive sleep apnea (8 severe, 14 moderate, 39 mild) was detected in 55% of the patients with polysomnography (n = 61) or polygraphy (n = 50). During follow-up, 52.2% of the patients died. Mean survival time was shorter in patients with DD (P < .001).

CONCLUSION

Paradoxical abdomimal movement (PAM), sitting-supine SpO₂ difference ≥ 4% and sitting-supine FVC difference ≥ 20% are indicators of DD, which should be routinely evaluated at every outpatient visit.

Intralingual and Intrapleural AAV Gene Therapy Prolongs Survival in a SOD1 ALS Mouse Model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that results in death from respiratory failure. No cure exists for this devastating disease, but therapy that directly targets the respiratory system has the potential to prolong survival and improve quality of life in some cases of ALS. The objective of this study was to enhance breathing and prolong survival by suppressing superoxide dismutase 1 (SOD1) expression in respiratory motor neurons using adeno-associated virus (AAV) expressing an artificial microRNA targeting the SOD1 gene. AAV-miRSOD1 was injected in the tongue and intrapleural space of SOD1G93A mice, and repetitive respiratory and behavioral measurements were performed until the end stage. Robust silencing of SOD1 was observed in the diaphragm and tongue as well as systemically. Silencing of SOD1 prolonged survival by approximately 50 days, and it delayed weight loss and limb weakness in treated animals compared to untreated controls. Histologically, there was preservation of the neuromuscular junctions in the diaphragm as well as the number of axons in the phrenic and hypoglossal nerves. Although SOD1 suppression improved breathing and prolonged survival, it did not ameliorate the restrictive lung phenotype. Suppression of SOD1 expression in motor neurons that underlie respiratory function prolongs survival and enhances breathing until the end stage in SOD1G93A ALS mice.

Mechanisms of Enhanced Phrenic Long-Term Facilitation in SOD1G93A Rats

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease, causing muscle paralysis and death from respiratory failure. Effective means to preserve/restore ventilation are necessary to increase the quality and duration of life in ALS patients. At disease end-stage in a rat ALS model (SOD1^G93A ), acute intermittent hypoxia (AIH) restores phrenic nerve activity to normal levels via enhanced phrenic long-term facilitation (pLTF). Mechanisms enhancing pLTF in end-stage SOD1^G93A rats are not known. Moderate AIH-induced pLTF is normally elicited via cellular mechanisms that require the following: G_q-protein-coupled 5-HT₂ receptor activation, new BDNF synthesis, and MEK/ERK signaling (the Q pathway). In contrast, severe AIH elicits pLTF via a distinct mechanism that requires the following: G_s-protein-coupled adenosine 2A receptor activation, new TrkB synthesis, and PI3K/Akt signaling (the S pathway). In end-stage male SOD1^G93A rats and wild-type littermates, we investigated relative Q versus S pathway contributions to enhanced pLTF via intrathecal (C4) delivery of small interfering RNAs targeting BDNF or TrkB mRNA, and MEK/ERK (U0126) or PI3 kinase/Akt (PI828) inhibitors. In anesthetized, paralyzed and ventilated rats, moderate AIH-induced pLTF was abolished by siBDNF and UO126, but not siTrkB or PI828, demonstrating that enhanced pLTF occurs via the Q pathway. Although phrenic motor neuron numbers were decreased in end-stage SOD1^G93A rats (∼30% survival; p < 0.001), BDNF and phosphorylated ERK expression were increased in spared phrenic motor neurons (p < 0.05), consistent with increased Q-pathway contributions to pLTF. Our results increase understanding of respiratory plasticity and its potential to preserve/restore breathing capacity in ALS.SIGNIFICANCE STATEMENT Since neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), end life via respiratory failure, the ability to harness respiratory motor plasticity to improve breathing capacity could increase the quality and duration of life. In a rat ALS model (SOD1^G93A ) we previously demonstrated that spinal respiratory motor plasticity elicited by acute intermittent hypoxia is enhanced at disease end-stage, suggesting greater potential to preserve/restore breathing capacity. Here we demonstrate that enhanced intermittent hypoxia-induced phrenic motor plasticity results from amplification of normal cellular mechanisms versus addition/substitution of alternative mechanisms. Greater understanding of mechanisms underlying phrenic motor plasticity in ALS may guide development of new therapies to preserve and/or restore breathing in ALS patients.

Acute intermittent hypoxia induced phrenic long-term facilitation despite increased SOD1 expression in a rat model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease characterized by motor neuron death. Since most ALS patients succumb to ventilatory failure from loss of respiratory motor neurons, any effective ALS treatment must preserve and/or restore breathing capacity. In rats over-expressing mutated super-oxide dismutase-1 (SOD1(G93A)), the capacity to increase phrenic motor output is decreased at disease end-stage, suggesting imminent ventilatory failure. Acute intermittent hypoxia (AIH) induces phrenic long-term facilitation (pLTF), a form of spinal respiratory motor plasticity with potential to restore phrenic motor output in clinical disorders that compromise breathing. Since pLTF requires NADPH oxidase activity and reactive oxygen species (ROS) formation, it is blocked by NADPH oxidase inhibition and SOD mimetics in normal rats. Thus, we hypothesized that SOD1(G93A) (mutant; MT) rats do not express AIH-induced pLTF due to over-expression of active mutant superoxide dismutase-1. AIH-induced pLTF and hypoglossal (XII) LTF were assessed in young, pre-symptomatic and end-stage anesthetized MT rats and age-matched wild-type littermates. Contrary to predictions, pLTF and XII LTF were observed in MT rats at all ages; at end-stage, pLTF was actually enhanced. SOD1 levels were elevated in young and pre-symptomatic MT rats, yet superoxide accumulation in putative phrenic motor neurons (assessed with dihydroethidium) was unchanged; however, superoxide accumulation significantly decreased at end-stage. Thus, compensatory mechanisms appear to maintain ROS homoeostasis until late in disease progression, preserving AIH-induced respiratory plasticity. Following intrathecal injections of an NADPH oxidase inhibitor (apocynin; 600 μM; 12 μL), pLTF was abolished in pre-symptomatic, but not end-stage MT rats, demonstrating that pLTF is NADPH oxidase dependent in pre-symptomatic, but NADPH oxidase independent in end-stage MT rats. Mechanisms preserving/enhancing the capacity for pLTF in MT rats are not known.

Usefulness of phrenic latency and forced vital capacity in patients with ALS with latent respiratory dysfunction

OBJECTIVES

The pulmonary function test (PFT) is a non-invasive and easily available technique to assess respiratory function in patients with amyotrophic lateral sclerosis (ALS); however, patients with dyspnea sometimes show normal PFT findings. Herein, we investigated whether phrenic nerve conduction study (NCS) and PFT are useful to evaluate respiratory function of patients with ALS with normal value ranges in the PFT.

METHODS

We prospectively enrolled 34 patients with definite or probable ALS, who showed FVC (%) ⩾80 of predicted and 78 healthy subjects. PFT and phrenic NCS were performed with the measurement of forced vital capacity (FVC, %), forced expiratory volumes in 1s (FEV1, %), FEV1/FCV ratio (%), and phrenic compound muscle action potential amplitude, and latency.

RESULTS

Compared to healthy controls, ALS patients showed delayed phrenic nerve latency and the decrease of FVC (%) (p=0.006 and p<0.0001, respectively). ROC curve analysis demonstrated that phrenic latency (AUC=0.7655) and FVC (%) (AUC=0.8239) discriminated ALS patients from healthy subjects.

CONCLUSION

We demonstrated that ALS patients had early respiratory dysfunction, despite normal PFT findings.

SIGNIFICANCE

Phrenic latency and FVC (%) can be helpful to discriminate ALS patients with latent respiratory dysfunction from healthy subjects.

Common mechanisms of compensatory respiratory plasticity in spinal neurological disorders

In many neurological disorders that disrupt spinal function and compromise breathing (e.g. ALS, cervical spinal injury, MS), patients often maintain ventilatory capacity well after the onset of severe CNS pathology. In progressive neurodegenerative diseases, patients ultimately reach a point where compensation is no longer possible, leading to catastrophic ventilatory failure. In this brief review, we consider evidence that common mechanisms of compensatory respiratory plasticity preserve breathing capacity in diverse clinical disorders, despite the onset of severe pathology (e.g. respiratory motor neuron denervation and/or death). We propose that a suite of mechanisms, operating at distinct sites in the respiratory control system, underlies compensatory respiratory plasticity, including: (1) increased (descending) central respiratory drive, (2) motor neuron plasticity, (3) plasticity at the neuromuscular junction or spared respiratory motor neurons, and (4) shifts in the balance from more to less severely compromised respiratory muscles. To establish this framework, we contrast three rodent models of neural dysfunction, each posing unique problems for the generation of adequate inspiratory motor output: (1) respiratory motor neuron death, (2) de- or dysmyelination of cervical spinal pathways, and (3) cervical spinal cord injury, a neuropathology with components of demyelination and motor neuron death. Through this contrast, we hope to understand the multilayered strategies used to "fight" for adequate breathing in the face of mounting pathology.

Intermittent hypoxia and stem cell implants preserve breathing capacity in a rodent model of amyotrophic lateral sclerosis

RATIONALE

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease causing paralysis and death from respiratory failure. Strategies to preserve and/or restore respiratory function are critical for successful treatment. Although breathing capacity is maintained until late in disease progression in rodent models of familial ALS (SOD1(G93A) rats and mice), reduced numbers of phrenic motor neurons and decreased phrenic nerve activity are observed. Decreased phrenic motor output suggests imminent respiratory failure.

OBJECTIVES

To preserve or restore phrenic nerve activity in SOD1(G93A) rats at disease end stage.

METHODS

SOD1(G93A) rats were injected with human neural progenitor cells (hNPCs) bracketing the phrenic motor nucleus before disease onset, or exposed to acute intermittent hypoxia (AIH) at disease end stage.

MEASUREMENTS AND MAIN RESULTS

The capacity to generate phrenic motor output in anesthetized rats at disease end stage was: (1) transiently restored by a single presentation of AIH; and (2) preserved ipsilateral to hNPC transplants made before disease onset. hNPC transplants improved ipsilateral phrenic motor neuron survival.

CONCLUSIONS

AIH-induced respiratory plasticity and stem cell therapy have complementary translational potential to treat breathing deficits in patients with ALS.

Resentment, hate, and hope in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal and progressive neurodegenerative disease. Despite much research having been conducted about psychological issues involved in living with ALS, anger, and resentment have yet to be investigated. Moreover, the construct of “hope” has received little attention, so far. An online survey was created to investigate hate, resentment, and hope issues in people with ALS, in relation to the willingness to adopt a strict nutrient-dense diet if it were shown to increase longevity. Results indicate that there is a high level of hope in the sample. People who have lived with ALS for more time expressed a higher level of hope to live 10 years or more. Those who are married were more likely to have hope of living 10 years or longer and more likely to have lower levels of hate against ALS. Dietary self-care choices appear to be related to hope issues. Resentment and hate tended to be higher in people who have had ALS for less time, and in women. Despite some methodological limitations, the results suggest that hope, hate, and resentment could be important issues to explore in future studies.

Respiratory function of people with amyotrophic lateral sclerosis and caregiver distress level: a correlational study

Background

Amyotrophic Lateral Sclerosis (ALS) is a rare, fatal neurodegenerative disorder with no curative treatment characterized by degeneration of motor neurons involving a progressive impairment of motor and respiratory functions. Most patients die of ventilator respiratory failure. Caregivers have a great influence on the patient”s quality of life as well as on the quality of care. Home influence of the caregiver on patient care is notable. To date, no study has investigated how psychological issues of caregivers would influence respiratory variables of ALS patients. The study aimed at finding out if there is a relationship between the respiratory function of ALS patients and the level of distress of their caregivers.

Methods

A cross-sectional study was conducted to investigate respiratory issues (PCF and FVC) and the perception of social support of ALS patients. Caregivers filled questionnaires about trait anxiety, depression, and burden of care. Forty ALS patients and their caregivers were recruited.

Results

FVC and PCF were positively related to patient perception of social support and negatively related to caregiver anxiety, depression, and burden.

Discussion

The distress of ALS caregivers is related to patient respiratory issues. The first and more intuitive explanation emphasizes the impact that the patient’s clinical condition has with respect to the caregiver. However, it is possible to hypothesize that if caregivers feel psychologically better, their patient’s quality of life improves and that a condition of greater well-being and relaxation could also increase ventilatory capacity. Furthermore, care management could be carried out more easily by caregivers who pay more attention to the patient's respiratory needs.

Conclusion

Patient perception of social support and caregiver distress are related to respiratory issues in ALS.

The cortico-diaphragmatic pathway involvement in amyotrophic lateral sclerosis: neurophysiological, respiratory and clinical considerations

Cortico-diaphragmatic pathway was investigated by means of transcranial magnetic stimulation (TMS), in 14 patients affected by definite amyotrophic lateral sclerosis (ALS) without clinical signs of respiratory impairment. Spirometry, gas analysis, and measurement of static inspiratory and expiratory pressures were performed in all patients. Forced vital capacity, forced expiratory volume at the first and second peak expiratory flow, sniff effort from FRC level (SNIP), maximal inspiratory and expiratory pressure at mouth (MIP/MEP), maximal transdiaphragmatic pressure (Pdimx) were considered. TMS was performed, recording by surface electrodes from hemidiaphragm, bilaterally. Latency of cortical and spinal motor-evoked potentials (Cx-MEP/Sp-MEP) and central motor conduction time (CMCT) were measured. None of the patients showed altered spirometry and gas levels. Seven patients showed decreased Pdimx and eight of MEP values. Four patients showed a delayed Sp-MEP. In one patient the Cx-MEP was abolished while the mean values of both Cx-MEP and CMCT were significantly increased (19.2+/-4.1 ms, P<0.0001; 10.8+/-4.8 ms, P<0.0001). Cx-MEP and CMCT did not show significant correlations with any of the respiratory measures. The patients with prolonged Sp-MEP, showed longer disease duration, lower Norris score, lower Pdimx and MEP values. In conclusion, cortico-diaphragmatic study is a sensitive measure to reveal subclinical diaphragmatic impairment although not correlated to respiratory measures.