Cardiovascular and cerebrovascular responses to urodynamics testing after spinal cord injury: The influence of autonomic injury.

Autonomic dysfunction is a prominent concern following spinal cord injury (SCI). In particular, autonomic dysreflexia (AD; paroxysmal hypertension and concurrent bradycardia in response to sensory stimuli below the level of injury) is common in autonomically-complete injuries at or above T6. AD is currently defined as a >20 mmHg increase in systolic arterial pressure (SAP) from baseline, without heart rate (HR) criteria. Urodynamics testing (UDS) is performed routinely after SCI to monitor urological sequelae, often provoking AD. We, therefore, aimed to assess the cardiovascular and cerebrovascular responses to UDS and their association with autonomic injury in individuals with chronic (>1 year) SCI. Following blood draw (plasma norepinephrine [NE]), continuous SAP, HR, and middle cerebral artery blood flow velocity (MCAv) were recorded at baseline (10-minute supine), during standard clinical UDS, and recovery (10-minute supine) (n = 22, age 41.1 ± 2 years, 15 male). Low frequency variability in systolic arterial pressure (LF SAP; a marker of sympathetic modulation of blood pressure) and cerebral resistance were determined. High-level injury (≥T6) with blunted/absent LF SAP (<1.0 mmHg2) and/or low plasma NE (<0.56 nmol•L-1) indicated autonomically-complete injury. Known electrocardiographic markers of atrial (p-wave duration variability) and ventricular arrhythmia (T-peak-T-end variability) were evaluated at baseline and during UDS. Nine participants were determined as autonomically-complete, yet 20 participants had increased SAP >20 mmHg during UDS. Qualitative autonomic assessment did not discriminate autonomic injury. Maximum SAP was higher in autonomically-complete injuries (207.1 ± 2.3 mmHg) than autonomically-incomplete injuries (165.9 ± 5.3 mmHg) during UDS (p < 0.001). HR during UDS was reduced compared to baseline (p = 0.056) and recovery (p = 0.048) only in autonomically-complete lesions. MCAv was not different between groups or phases (all p > 0.05). Cerebrovascular resistance index was increased during UDS in autonomically-complete injuries compared to baseline (p < 0.001) and recovery (p < 0.001) reflecting intact cerebral autoregulation. Risk for both atrial and ventricular arrhythmia increased during UDS compared to baseline (p < 0.05), particularly in autonomically-complete injuries (p < 0.05). UDS is recommended yearly in chronic SCI but is associated with profound AD and an increased risk of arrhythmia, highlighting the need for continued monitoring during UDS. Our data also highlight the need for HR criteria in the definition of AD and the need for quantitative consideration of autonomic function after SCI.

Dynamic wheelchair seating positions impact cardiovascular function after spinal cord injury.

BACKGROUND: Innovative wheelchairs allow individuals to change position easily for comfort and social situations. While these wheelchairs are beneficial in multiple ways, the effects of position changes on blood pressure might exacerbate hypotension and cerebral hypoperfusion, particularly in those with spinal cord injury (SCI) who can have injury to autonomic nerves that regulate cardiovascular control. Conversely, cardiovascular benefits may be obtained with lowered seating. Here we investigate the effect of moderate changes in wheelchair position on orthostatic cardiovascular and cerebrovascular reflex control. METHODS: Nineteen individuals with SCI and ten neurologically-intact controls were tested in supine and seated positions (neutral, lowered, and elevated) in the Elevation™ wheelchair. Participants with SCI were stratified into two groups by the severity of injury to cardiovascular autonomic pathways. Beat-to-beat blood pressure, heart rate and middle cerebral artery blood flow velocity (MCAv) were recorded non-invasively. RESULTS: Supine blood pressure and MCAv were reduced in individuals with lesions to autonomic pathways, and declined further with standard seating compared to those with preserved autonomic control. Movement to the elevated position triggered pronounced blood pressure and MCAv falls in those with autonomic lesions, with minimum values significantly reduced compared to the seated and lowered positions. The cumulative duration spent below supine blood pressure was greatest in this group. Lowered seating bolstered blood pressure in those with lesions to autonomic pathways. CONCLUSIONS: Integrity of the autonomic nervous system is an important variable that affects cardiovascular responses to orthostatic stress and should be considered when individuals with SCI or autonomic dysfunction are selecting wheelchairs. SPONSORSHIP: This work was supported in part by the Heart and Stroke Foundation of British Columbia and the Yukon (V.E.C).

Clusters, Gaps, and Randomness: Vasovagal Syncope Recurrence Patterns.

OBJECTIVES: This study elucidated the temporal recurrence patterns of syncope in patients with frequent vasovagal syncope (VVS). BACKGROUND: Understanding the temporal distribution of fainting spells in syncope patients may illuminate biological processes and inform decision making. METHODS: Patients from the POST 2 (Prevention of Syncope Trial 2) were included; all had VVS and fainted ≥4 times in the study year, providing ≥3 interevent intervals (IEIs). Only fainting spells separated by ≥1 day were included. IEI distributions were analyzed using Poisson modeling and cumulative sum distributions. RESULTS: Twenty-four patients (5 males, 19 females; mean 33 years of age) had a total of 286 syncopal events and 262 IEIs, with a median 6 IEI. They resembled excluded subjects in age and sex but fainted more often in their lives (median: 57 vs. 13 fainting spells, respectively; p < 0.0001) and in the previous year (median: 23 vs. 3 fainting spells, respectively; p < 0.0001). Subjects had a median IEI duration of 8 (interquartile range: 4 to 19) days. The IEI distributions were fit well by Poisson models with a median r2 of 0.94 (95% confidence interval: 0.91 to 0.97). The patients' Poisson rate constant frequencies were 7 to 263 fainting spells/year with a median rate of 19 fainting spells/year. The modal syncope frequency was 10 to 15 fainting spells per year. Seven patients had biexponential distributions, and many patients fainted in clusters. CONCLUSIONS: Patients with frequent VVS have fainting spells that occur randomly in time. Clusters of syncope occur, and in this population, there is a central tendency to 10 to 15 fainting spells per year. This provides a quantitative measure of frequency and predictability that may afford individualized treatment goals.

Acute mountain sickness, chemosensitivity, and cardiorespiratory responses in humans exposed to hypobaric and normobaric hypoxia.

We examined the control of breathing, cardiorespiratory effects, and the incidence of acute mountain sickness (AMS) in humans exposed to hypobaric hypoxia (HH) and normobaric hypoxia (NH), and under two control conditions [hypobaric normoxia (HN) and normobaric normoxia (NN)]. Exposures were 6 h in duration, and separated by 2 wk between hypoxic exposures and 1 wk between normoxic exposures. Before and after exposures, subjects (n = 11) underwent hyperoxic and hypoxic Duffin CO2 rebreathing tests and a hypoxic ventilatory response test (HVR). Inside the environmental chamber, minute ventilation (V(E)), tidal volume (V(T)), frequency of breathing (fB), blood oxygenation, heart rate, and blood pressure were measured at 5 and 30 min and hourly until exit. Symptoms of AMS were evaluated using the Lake Louise score (LLS). Both the hyperoxic and hypoxic CO2 thresholds were lower after HH and NH, whereas CO2 sensitivity was increased after HH and NH in the hypoxic test and after NH in the hyperoxic test. Values for HVR were similar across the four exposures. No major differences were observed for Ve or any other cardiorespiratory variables between NH and HH. The LLS was greater in AMS-susceptible than in AMS-resistant subjects; however, LLS was alike between HH and NH. In AMS-susceptible subjects, fB correlated positively and Vt negatively with the LLS. We conclude that 6 h of hypoxic exposure is sufficient to lower the peripheral and central CO2 threshold but does not induce differences in cardiorespiratory variables or AMS incidence between HH and NH.

A pilot study on the prevalence of Acute Mountain Sickness at the Sikh pilgrimage of Hemkund Sahib in the Indian Himalayas.

BACKGROUND: Hemkund Sahib is a popular pilgrimage located at 4,330 m in the Garhwal range of the Indian Himalayas. Many travelers to the region have observed pilgrims exhibiting Acute Mountain Sickness (AMS)-like symptoms. However, no systematic study on its prevalence at Hemkund has been conducted. MATERIALS AND METHODS: We surveyed 25 adults. AMS rates were determined using a standard Lake Louise Score (LLS). Responses to questions related to awareness of AMS, the perceived difficulty of the trek, and physiological data including arterial oxygen saturation (SpO2) and pulse rate, amongst others, were collected. RESULTS: Overall prevalence of AMS was 28% (mild AMS 20%, severe AMS 8%). Borg Rating of Perceived Exertion (RPE) was 3.9/10. Water consumption for the 4-5 hour trek to Hemkund was only 0.9 L and 20% of pilgrims consumed no water at all. Nine pilgrims claimed to be aware of AMS although only one had taken prophylactic medication. SpO2 was 82.2 ± 1.2% and pulse rate was 106.5 ± 2.9 bpm (mean ± SEM). There were no differences in non-LLS-related parameters when pilgrims were subdivided by presence or absence of AMS. CONCLUSION: This pilot study has, for the first time, documented the prevalence of AMS amongst pilgrims to Hemkund Sahib in the Indian Himalayas.

The perspectives of educators, regulators and funders of massage therapy on the state of the profession in British Columbia, Canada.

BACKGROUND: Registered Massage Therapists (RMTs) are valuable members of the healthcare team who assist in health promotion, disease prevention, treatment, rehabilitation and palliation. RMT visits have increased across Canada over the past decade with the highest increase in British Columbia (BC). Currently, RMTs are private practitioners of healthcare operating within a largely publicly funded system, positioning them outside of the dominant system of healthcare and making them an important case study in private healthcare. In another paper we examined the perspectives of RMTs themselves. Here, we offer perspectives of regulators, educators and funders of Massage Therapy (MT) on advancement of the profession. METHODS: We interviewed 28 stakeholders of MT in BC - including members of the MT regulatory board, representatives from MT colleges in BC and public and private health insurers. RESULTS: All three groups identified research, particularly on efficacy of MT, as playing a vital role in enhancing the professional credibility of MT. However, participants noted that presently research is not a large feature of the current MT curricula and we analyze why this may be and how it can improve. Finally, conferral of baccalaureate degree status could assist RMTs in gaining recognition with the general public and other healthcare professionals. CONCLUSION: RMTs have potential to ameliorate population health in a cost-effective manner. Their role in British Columbia's healthcare landscape could be expanded if they produce more research and earn degree status.

Cerebrovascular responses to orthostatic stress after spinal cord injury.

Orthostatic hypotension (OH) is a debilitating condition affecting individuals with spinal cord injury (SCI) that may be associated with cerebral hypoperfusion. We studied orthostatic cerebral control in individuals with SCI with different levels and severities of injury to spinal cardiovascular autonomic pathways. We measured beat-to-beat cardiovascular and cerebrovascular responses to passive orthostatic stress in 16 controls and 26 subjects with chronic SCI. Cerebrovascular control was assessed from diastolic cerebral blood flow velocity (CBFV(D)), and indices of static and dynamic cerebral autoregulation. Severity of autonomic injury was inferred from spectral analyses of systolic arterial pressure, and supine plasma noradrenaline concentrations. Symptoms of OH were evaluated using questionnaires. CBFV(D) decreased during orthostasis only in individuals with autonomically complete injuries above T6. Orthostatic CBFV(D) was significantly correlated (p<0.05) with the severity of autonomic injury. Individuals with injuries above T6 had impaired dynamic autoregulation (p<0.05) compared to controls, and this was correlated (p<0.05) with the severity of autonomic injury. Individuals with autonomically complete SCI reported increased severity of symptoms relative to controls (p<0.05). Symptom severity was correlated with the efficacy of dynamic autoregulation. During orthostatic stress, SCI individuals have impaired cerebrovascular control that is related to the level and severity of autonomic injury.