Reduced hypoxic sympathetic response in mild Parkinson's disease: Further evidence of early autonomic dysfunction

Acute and cumulative effects of hypoxia exposure in people with Parkinson's disease: A scoping review and evidence map

Hypoxia exposure may promote neuroprotection for people with Parkinson's disease (PwPD). However, to implement hypoxia in practical settings and direct future research, it is necessary to organize the current knowledge about hypoxia responses/effects in PwPD. Thus, the present scoping review elucidates the evidence about hypoxia exposure applied to PwPD. Following the PRISMA Extension for Scoping Reviews, papers were searched in PubMed/NCBI, Web of Science, and Scopus (descriptors: Parkinson and hypoxia, mountain, or altitude). We included original articles published in English until August 12, 2023. Eight studies enrolled participants with early to moderate stages of disease. Acute responses demonstrated that PwPD exposed to normobaric hypoxia presented lower hypoxia ventilatory responses (HVR), perceptions of dyspnea, and sympathetic activations. Cumulative exposure to hypobaric hypoxia (living high; 7 days; altitude not reported) induced positive effects on motor symptoms (hypokinesia) and perceptions of PwPD (quality of life and living with illness). Normobaric hypoxia (isocapnic rebreathe, 14 days, three times/day of 5-7 min at 8-10 % of O2) improved HVR. The included studies reported no harmful effects. Although these results demonstrate the effectiveness and safety of hypoxia exposure applied to PwPD, we also discuss the methodological limitations of the selected experimental design (no randomized controlled trials), the characterization of the hypoxia doses, and the range of symptoms investigated. Thus, despite the safety of both normobaric hypoxia and hypobaric hypoxia for early to moderate levels of disease, the current literature is still incipient, limiting the use of hypoxia exposure in practical settings.

Respiratory Abnormalities in Parkinson's Disease: What Do We Know from Studies in Humans and Animal Models?

Parkinson’s disease (PD) is the second most common progressive neurodegenerative disease characterized by movement disorders due to the progressive loss of dopaminergic neurons in the ventrolateral region of the substantia nigra pars compacta (SNpc). Apart from the cardinal motor symptoms such as rigidity and bradykinesia, non-motor symptoms including those associated with respiratory dysfunction are of increasing interest. Not only can they impair the patients’ quality of life but they also can cause aspiration pneumonia, which is the leading cause of death among PD patients. This narrative review attempts to summarize the existing literature on respiratory impairments reported in human studies, as well as what is newly known from studies in animal models of the disease. Discussed are not only respiratory muscle dysfunction, apnea, and dyspnea, but also altered central respiratory control, responses to hypercapnia and hypoxia, and how they are affected by the pharmacological treatment of PD.

Dyspnea Is a Specific Symptom in Parkinson's Disease

BACKGROUND

Dyspnea is a multidimensional sensation that is reported in Parkinson's disease (PD). The multidimensional dyspnea profile (MDP) questionnaire can help to distinguish the perceptive dimension and the emotion response.

OBJECTIVE

The aim was to assess the clinical features associated with dyspnea using the MDP questionnaire in order to determine which aspects of the symptom was linked with anxiety, depression or motor severity of the disease.

METHODS

Non-demented patients were asked whether they experienced shortness of breath in the last month. In case of positive answer, dyspnea was assessed by the MDP. MDS-UPDRS, global cognitive performance, non-motor symptoms and quality of life were assessed.

RESULTS

60/163 patients were dyspneic since 4.6±2.4 years. The most frequent best sensory quality (SQ) described were: hyperpnoea (35%), physical breathing effort (25%) and air hunger (20%). Hyperpnoea and air hunger had the highest SQ intensity. Anxiety had the highest intensity in the emotional domain.

CONCLUSION

Dyspnea is a frequent symptom in PD, with specific presentations and two main aspects: one related with anxiety and another with ventilation control impairment.

Ventilatory Dysfunction in Parkinson's Disease

In contrast to some other neurodegenerative diseases, little is known about ventilatory dysfunction in Parkinson’s disease (PD). To assess the spectrum of ventilation disorders in PD, we searched for and reviewed studies of dyspnea, lung volumes, respiratory muscle function, sleep breathing disorders and the response to hypoxemia in PD. Among the studies, we identified some limitations: (i) small study populations (mainly composed of patients with advanced PD), (ii) the absence of long-term follow-up and (iii) the absence of functional evaluations under “off-drug” conditions. Although there are many reports of abnormal spirometry data in PD (mainly related to impairment of the inspiratory muscles), little is known about hypoventilation in PD. We conclude that ventilatory dysfunction in PD has been poorly studied and little is known about its frequency and clinical relevance. Hence, there is a need to characterize the different phenotypes of ventilation disorders in PD, study their relationships with disease progression and assess their prognostic value.

Breathing in Parkinsonism in the Rat

Parkinsonism is underlain by dopamine (DA) deficiency in the mid-brain, a neurotransmitter innately involved with respiratory regulation. However, the state of respiration in parkinsonism is an unsettled issue. In this study we seek to determine ventilation and its responses to hypoxia in a reserpine--alpha-methyl-tyrosine model of parkinsonism in the rat. We also attempted to differentiate between the role of discrete brain and carotid body DA stores in the modulation of the hypoxic ventilatory response (HVR). To this end we used domperidone, a peripheral D2 receptor antagonist, and levodopa, a central D2 receptor agonist. The HVRs to acute 12% and 8% hypoxia were studied in a whole body plethysmograph in the same rats before and after the induction of parkinsonic symptoms in conscious rats. We found that resting ventilation and the HVR were distinctly reduced in parkinsonism. The reduction was particularly evident in the peak hypoxic hyperpneic augmentation. Domperidone, which enhanced ventilation in the control healthy condition, failed to reverse the reduced parkinsonic HVR. In contrast, levodopa, which did not appreciably affected ventilation in the healthy condition, caused the parkinsonic HVR to return to and above the baseline healthy level. The findings demonstrate the predominance of a lack of the central DA stimulatory element and minimize the role of carotid body DA in the ventilatory impediment of parkinsonism. In conclusion, the study provides the pathophysiological savvy concerning the respiratory insufficiency of parkinsonism, a sequela which carries a risk of chronically impaired blood oxygenation, which may drive the disease worsening.