Symbolic dynamics of heart rate variability in Parkinson's disease patients with orthostatic hypotension

Women have a greater cardiac vagal withdrawal to heat stress compared to men

The heated environment shifts the sympatho-vagal balance toward sympathetic predominance and vagal withdrawal. Women's heart is more reliant on vagal autonomic control, while men's heart is more dependent on sympathetic control. However, sex differences in cardiovascular autonomic responses to heat stress remain unknown. We aimed to investigate the cardiovascular autonomic regulation under heat stress between sexes. Thirty-two young participants (27 ± 4 years old; 16 women) were enrolled in a single visit, resting for 30min at baseline (thermal reference condition TC; ∼24°C) and 30min under a heated environment (HOT; ∼38°C). Blood pressure (BP), skin temperature, electrocardiogram, and respiratory oscillations were continuously recorded. The heart rate variability (HRV) was assessed by spectral analysis (low-frequency [LFnu; sympathetic and vagal] and high-frequency [HFnu; vagal]), and symbolic analysis (0 V% [sympathetic] and 2UV%, and 2LV% [vagal]). The spontaneous baroreflex sensitivity (BRS) was calculated by the gain between BP and R-R within the LF band (αLF). The estimated maximal aerobic capacity and body surface area were employed as covariates in sex comparisons. The effects of HOT were the following: 1) Women have a greater cardiac vagal withdrawal to heat stress compared to men; 2) Sex differences on cardiac autonomic response to heat stress exist after controlling for the effect of estimated physical fitness and body surface area. Therefore, heat stress provokes a higher vagal withdrawal to the heart in women compared to men. It could be attributed to sex per se since significant differences between men and women were not modified after covariate analysis.

Dysautonomia in Parkinson’s Disease: Impact of Glucocerebrosidase Gene Mutations on Cardiovascular Autonomic Control

Evidence from clinical practice suggests that PD patients with the Glucocerebrosidase gene mutations (GBA-PD) are characterized by more severe dysautonomic symptoms than patients with idiopathic PD (iPD). Therefore, an accurate assessment of cardiovascular autonomic control (CAC) is necessary to clarify the role of GBA mutations in the pathophysiology of PD. We evaluated the CAC at rest and during orthostatic challenge of 15 iPD, 15 GBA-PD and 15 healthy controls (CTR). ECG and respiration were recorded in supine position and during active standing. The analysis of Heart Rate Variability (HRV) was performed on ECG recordings using two different approaches, linear spectral analysis and non-linear symbolic analysis. GBA-PD patients presented more frequently an akinetic-rigid phenotype and cognitive dysfunction than iPD patients. Both iPD and GBA-PD group were characterized by a lower spectral HRV than CTR group. At rest, the GBA-PD group was characterized by a lower parasympathetic modulation and a shift of the sympathovagal balance toward a sympathetic predominance compared to the CTR group. Moreover, the GBA-PD patients presented a lower HR increment and a lower or absent reduction of the vagal modulation in response to the active standing than iPD patients. Lastly, the cardiovascular autonomic dysfunction in PD patients was associated with longer disease duration, and with the occurrence of REM sleep behavior disorder and constipation. Our findings suggest a more severe impairment of the CAC in PD patients with GBA mutations. These results and further studies on the role of GBA mutations could allow a stratification based on cardiovascular risk in PD patients and the implementation of specific prevention programs.

Autonomic Function in Patients With Parkinson's Disease: From Rest to Exercise

Parkinson’s disease (PD) is a common neurodegenerative disorder classically characterized by symptoms of motor impairment (e.g., tremor and rigidity), but also presenting with important non-motor impairments. There is evidence for the reduced activity of both the parasympathetic and sympathetic limbs of the autonomic nervous system at rest in PD. Moreover, inappropriate autonomic adjustments accompany exercise, which can lead to inadequate hemodynamic responses, the failure to match the metabolic demands of working skeletal muscle and exercise intolerance. The underlying mechanisms remain unclear, but relevant alterations in several discrete central regions (e.g., dorsal motor nucleus of the vagus nerve, intermediolateral cell column) have been identified. Herein, we critically evaluate the clinically significant and complex associations between the autonomic dysfunction, fatigue and exercise capacity in PD.

Baroreflex dysfunction in Parkinson's disease: integration of central and peripheral mechanisms

The incidence of Parkinson's disease (PD) is increasing worldwide. Although the PD hallmark is the motor impairments, nonmotor dysfunctions are now becoming more recognized. Recently, studies have suggested that baroreflex dysfunction is one of the underlying mechanisms of cardiovascular dysregulation observed in patients with PD. However, the large body of literature on baroreflex function in PD is unclear. The baroreflex system plays a major role in the autonomic, and ultimately blood pressure and heart rate, adjustments that accompany acute cardiovascular stressors on a daily basis. Therefore, impaired baroreflex function (i.e., decreased sensitivity or gain) can lead to altered neural cardiovascular responses. Since PD affects parasympathetic and sympathetic branches of the autonomic nervous system and both are orchestrated by the baroreflex system, understanding of this crucial mechanism in PD is necessary. In the present review, we summarize the potential altered central and peripheral mechanisms affecting the feedback-controlled loops that comprise the reflex arc in patients with PD. Major factors including arterial stiffness, reduced number of C1 and activation of non-C1 neurons, presence of central α-synuclein aggregation, cardiac sympathetic denervation, attenuated muscle sympathetic nerve activity, and lower norepinephrine release could compromise baroreflex function in PD. Results from patients with PD and from animal models of PD provide the reader with a clearer picture of baroreflex function in this clinical condition. By doing so, our intent is to stimulate future studies to evaluate several unanswered questions in this research area.

Baroreflex function in Parkinson's disease: insights from the modified-Oxford technique

Nonmotor symptoms are common in Parkinson's disease (PD) and they include dysregulation of cardiovascular system, which adversely affects quality of life. Recent studies provide indirect evidence that baroreflex dysfunction may be one of the mechanisms of cardiovascular dysregulation in PD. Herein, we tested the hypothesis that the baroreflex gain, assessed across an extensive range of the reflex arc by eliciting rapid changes in blood pressure (BP) induced by sequential boluses of vasoactive drugs (modified-Oxford technique) would be attenuated in middle-aged patients with PD. Beat-to-beat heart rate (electrocardiography) and BP (finger photoplethysmography) were obtained during 10 min of supine rest preceding the modified-Oxford (bolus of nitroprusside followed by phenylephrine 1 min afterward) in 11 patients with PD (51 ± 6 yr) and 7 age-matched controls (47 ± 6 yr). The resulting systolic BP and R-R interval responses were plotted and fitted with segmental linear regression and symmetric sigmoid model. Spontaneous indices obtained via sequence technique were also used to estimate baroreflex gain. Compared with controls, the estimated gains measured by segmental linear regression (patients: 3.83 ± 2.6 ms/mmHg versus controls: 7.78 ± 1.7 ms/mmHg; P = 0.003) and symmetric sigmoid model (patients: 12.36 ± 6.9 ms/mmHg versus controls: 32.02 ± 19.0 ms/mmHg; P = 0.009) were lower in patients with PD. The operating range of BP was larger in patients with PD compared with controls (13 ± 7 mmHg versus controls: 7 ± 3 mmHg; P = 0.032). Of note, the gain obtained from spontaneous indices was similar between groups. These data indicate that baroreflex gain was reduced by >50% in PD, thereby providing clear and direct evidence that cardiovagal baroreflex dysfunction occurs in PD.NEW & NOTEWORTHY Attenuated baroreflex gain may contribute to adverse cardiovascular outcomes, including orthostatic intolerance symptoms typically observed in patients with Parkinson's disease. We found that the baroreflex gain (assessed by the modified-Oxford technique) is attenuated and accompanied by an increased operating range in patients with Parkinson's disease. These findings highlight that cardiovascular perturbations are required to detect baroreflex impairments and that spontaneous indices do not reveal cardiovagal-baroreflex dysfunction in a middle-aged group of patients with Parkinson's disease.

Effects of effortful swallowing on cardiac autonomic control in individuals with neurogenic dysphagia: a prospective observational analytical study

Considering that neurogenic oropharyngeal dysphagia is a prevalent condition with or without cardiac disease we should contemplate issues surrounding cardiovascular difficulties during rehabilitation. This study aims to evaluate the effects of effortful swallowing maneuver (ESM) on heart rate variability (HRV) in subjects with neurogenic oropharyngeal dysphagia. We studied 22 individuals [8 Stroke and 14 Parkinson Disease (PD) subjects aged between 41 and 75 years old] with neurogenic oropharyngeal dysphagia regardless of gender. HRV was assessed under two circumstances: spontaneous swallowing versus ESM. Surface electromyography of the suprahyoid muscles was undertaken to measure the swallowing muscle excitation, which then confirmed higher muscle activity during ESM. We attained no changes in HRV between the two swallowing events [HR: spontaneous swallowing 78.68 ± 13.91 bpm vs. ESM 102.57 ± 107.81 bpm, p = 0.201; RMSSD (root-mean square of differences between adjacent normal RR intervals in a time interval): spontaneous swallowing 16.99 ± 15.65 ms vs. ESM 44.74 ± 138.85 ms, p = 0.312; HF (high frequency): spontaneous swallowing 119.35 ± 273 ms² vs. ESM 99.83 ± 194.58 ms², p = 0.301; SD1 (standard deviation of the instantaneous variability of the beat-to-beat heart rate): spontaneous swallowing 12.02 ± 1.07 ms vs. ESM 31.66 ± 98.25 ms, p = 0.301]. The effortful swallowing maneuver did not cause clinically significant changes in autonomic control of HR in this group of subjects with oropharyngeal dysphagia.

Altered cardiorespiratory regulation during exercise in patients with Parkinson's disease: A challenging non-motor feature

The incidence of Parkinson’s disease is increasing worldwide. The motor dysfunctions are the hallmark of the disease, but patients also experience non-motor impairments, and over 40% of the patients experience coexistent abnormalities, such as orthostatic hypotension. Exercise training has been suggested as a coping resource to alleviate Parkinson’s disease symptoms and delay disease progression. However, the body of knowledge is showing that the cardiovascular response to exercise in patients with Parkinson’s disease is altered. Adequate cardiovascular and hemodynamic adjustments to exercise are necessary to meet the metabolic demands of working skeletal muscle properly. Therefore, since Parkinson’s disease affects parasympathetic and sympathetic branches of the autonomic nervous system and the latter are crucial in ensuring these adjustments are adequately made, the understanding of these responses during exercise in this population is necessary. Several neural control mechanisms are responsible for the autonomic changes in the cardiovascular and hemodynamic systems seen during exercise. In this sense, the purpose of the present work is to review the current knowledge regarding the cardiovascular responses to dynamic and isometric/resistance exercise as well as the mechanisms by which the body maintains appropriate perfusion pressure to all organs during exercise in patients with Parkinson’s disease. Results from patients with Parkinson’s disease and animal models of Parkinson’s disease provide the reader with a well-rounded knowledge base. Through this, we will highlight what is known and not known about how the neural control of circulation is responding during exercise and the adaptations that occur when individuals exercise regularly.

Circulatory responses at the onset of handgrip exercise in patients with Parkinson's disease

NEW FINDINGS

What is the central question of this study? The initial circulatory response to isometric exercise in young healthy subjects is thought to be cholinergically mediated. Do patients with Parkinson's disease, a specific population known to present cholinergic dysfunction, present impairment in these initial circulatory responses? What is the main finding and its importance? The initial reduction in total peripheral resistance was absent in patients with Parkinson's disease and in older subjects, which augmented the pressor response at the onset of isometric handgrip exercise. Given that cholinergic mechanisms play an important role in the circulatory responses at the onset of isometric exercise in humans, our data suggest that cholinergic mechanisms might be compromised with ageing.

ABSTRACT

Physical exercise has been used as coping strategy for Parkinson's disease (PD). Thus, a better understanding of circulatory responses to exercise in this population is warranted. During the onset of isometric handgrip (IHG) exercise there is an increase in blood pressure (BP) and a reduction in the total peripheral resistance (TPR) in young subjects. This immediate reduction of TPR is thought to be mediated by a cholinergic mechanism. Given that PD also affects cholinergic neurons, we hypothesized that patients with PD would present blunted circulatory responses at the onset of IHG exercise. Mean BP, stroke volume, heart rate, cardiac output and TPR were measured during performance of 20 s of IHG at 40% maximal voluntary contraction in 12 patients with PD (66 ± 2 years old, 171 ± 7 cm, 74 ± 7 kg), 11 older subjects (65 ± 9 years old, 171 ± 7 cm, 74 ± 10 kg) and 10 young subjects (21 ± 1 years old, 178 ± 6 cm, 79 ± 9 kg). Isometric handgrip elicited an augmented BP increase in patients with PD and older subjects at 10 and 20 s compared with young subjects. However, the BP augmentation was lower at 20 s in patients with PD. The IHG-induced reduction in TPR was attenuated in patients with PD and older subjects compared with young subjects. Our results show that the circulatory responses at the onset of IHG are impaired in patients with PD and older subjects. Overall, these findings suggest that the cholinergic mechanism might be compromised with ageing.

Hemodynamic responses to an exercise stress test in Parkinson's disease patients without orthostatic hypotension

The presence of postganglionic sympathetic denervation is well established in Parkinson's disease (PD). Denervation at cardiac and blood vessel sites may lead to abnormal cardiovascular and hemodynamic responses to exercise. The aim of the present investigation was to examine how heart rate (HR) and hemodynamics are affected by an exercise test in PD patients without orthostatic hypotension. Thirty individuals without orthostatic hypotension, 14 individuals with PD, and 16 age-matched healthy controls performed an exercise test on a cycle ergometer. Heart rate, blood pressure, and other hemodynamic variables were measured in a fasted state during supine rest, active standing, exercise, and supine recovery. Peak HR and percent of age-predicted maximum HR (HR_max) achieved were significantly blunted in PD (p < 0.05, p < 0.01). HR remained significantly elevated in PD during recovery compared with controls (p = 0.03, p < 0.05). Systolic, diastolic, and mean arterial pressures were significantly lower at multiple time-points during active standing in PD compared with controls. Systemic vascular resistance index (SVRI) decreased significantly at the onset of exercise in PD, and remained significantly lower during exercise and the first minute of supine recovery. End diastolic volume index (EDVI) was significantly lower in PD during supine rest and recovery. Our results indicate for the first time that normal hemodynamics are disrupted during orthostatic stress and exercise in PD. Despite significant differences in EDVI at rest and during recovery, and SVRI during exercise, cardiac index was unaffected. Our finding of significantly blunted HR_max and HR recovery in PD patients has substantial implications for exercise prescription and recovery guidelines.

Blunted cardiovascular responses to exercise in Parkinson’s disease patients: role of the muscle metaboreflex

Patients with Parkinson’s disease (PD) exhibit attenuated cardiovascular responses to exercise. The underlying mechanisms that are potentially contributing to these impairments are not fully understood. Therefore, we sought to test the hypothesis that patients with PD exhibit blunted cardiovascular responses to isolated muscle metaboreflex activation following exercise. For this, mean blood pressure, cardiac output, and total peripheral resistance were measured using finger photoplethysmography and the Modelflow method in 11 patients with PD [66 ± 2 yr; Hoehn and Yahr score: 2 ± 1 a.u.; time since diagnosis: 7 ± 1 yr; means ± SD) and 9 age-matched controls (66 ± 3 yr). Measurements were obtained at rest, during isometric handgrip exercise performed at 40% maximal voluntary contraction, and during postexercise ischemia. Also, a cold pressor test was assessed to confirm that blunted cardiovascular responses were specific to exercise and not representative of generalized sympathetic responsiveness. Changes in mean blood pressure were attenuated in patients with PD during handgrip (PD: ∆25 ± 2 mmHg vs. controls: ∆31 ± 3 mmHg; P < 0.05), and these group differences remained during postexercise ischemia (∆17 ± 1 mmHg vs. ∆26 ± 1 mmHg, respectively; P < 0.01). Additionally, changes in total peripheral resistance were attenuated during exercise and postexercise ischemia, indicating blunted reflex vasoconstriction in patients with PD. Responses to cold pressor test did not differ between groups, suggesting no group differences in generalized sympathetic responsiveness. Our results support the concept that attenuated cardiovascular responses to exercise observed in patients with PD are, at least in part, explained by an altered skeletal muscle metaboreflex.

NEW & NOTEWORTHY Patients with Parkinson’s disease (PD) presented blunted cardiovascular responses to exercise. We showed that cardiovascular response evoked by the metabolic component of the exercise pressor reflex is blunted in patients with PD. Furthermore, patients with PD presented similar pressor response during the cold pressor test compared with age-matched controls. Altogether, our results support the hypothesis that attenuated cardiovascular responses to exercise observed in patients with PD are mediate by an altered skeletal muscle metaboreflex.