People with Rett syndrome have deficient central autonomic control, which may interfere with walking. We have limited knowledge regarding the effects of exertion during physical activity in Rett syndrome. The aim was to investigate the autonomic responses during walking on a treadmill in Rett syndrome. Twenty-six females, 12 with Rett syndrome and 14 healthy females were included. All individuals started on the treadmill by standing still, followed by walking slowly with progressive speed until reaching maximum individual speed, which they kept for 6 min. Heart rate (HR), systolic (SBP), diastolic (DBP), mean arterial blood pressures (MAP), cardiac vagal tone (CVT), cardiac sensitivity to baroreflex (CSB), transcutaneous partial pressures of oxygen (pO2), carbon dioxide (pCO2), and breathing movements were recorded simultaneously and continuously. Autonomic responses were assessed by MAP, CSB and CVT during walking at 3 and 6 min. The changes in CSB and CVT in people with Rett syndrome compared to controls indicated more arousal, but only when the treadmill was started; as they continued walking, the arousal dropped to control level. People with Rett syndrome exhibited little changes in pCO2 whereas the controls showed increased values during walking. This suggests poor aerobic respiration in people with Rett syndrome during walking. Five people with Rett syndrome had Valsalva type of breathing at rest, three of those had normal breathing while walking on the treadmill while the remaining two started but soon stopped the Valsalva breathing during the walk. Our results show that individuals with Rett syndrome can walk for up to 6 min at their own maximum sustainable speed on a treadmill. Energy production may be low during walking in Rett syndrome, which could cause early tiredness. A treadmill can be used in people with Rett syndrome, but must be introduced slowly and should be individually tailored. We propose that walking promotes regular breathing in Rett syndrome.
Objective: Profound BP variability (BPV) is a major cause of cardiovascular morbidity and poor quality of life as there are no optimal pharmacological strategies to help patients. We hypothesised that in a patient with baroreflex dysfunction and preserved efferent baroreflex pathway, carotid sinus stimulation may help control BP, BPV and heart rate variability (HRV). Design and method: A 52 year old man was referred with profound HR and BPV. Home SBPs were in a range of 60–250 mmHg and DBPs were 40–130 mmHg and heart rate (HR) of 60–200 bpm (confirmed with ABPM, see Figure) despite multiple medications including felodipine 30 mg daily, terazosin 16 mg daily, doxazosin 8 mg daily, bisoprolol 20 mg daily and butrans patch 17.5 mcg/hr. After extensive multi-disciplinary investigations the diagnosis was progressive central and peripheral dysautonomia consequent upon immune-mediated neuropathy secondary to undifferentiated connective tissue disease with Sjogren's syndrome. It was not possible to improve BP control with use of clonidine patches and he had frequent severe epistaxes due to hypertensive surges and blackouts due to hypotension and was therefore retired from work on medical grounds. Results: Autonomic function tests confirmed widespread dysautonomia with preserved but attenuated vasodepressor response to carotid sinus massage. Baroreflex activation therapy (BAT) was undertaken after numerous in-patient attempts to control BPV pharmacologically had failed. The Barostim Neo® device was implanted with a right carotid sinus electrode in March 2015 and subsequently device settings were reprogrammed on several occasions to optimise BP control. The patient's BP profile improved considerably following BAT but significant hypotensive episodes continued and thus all antihypertensives were stopped with substantial improvement in HR and BP and halving of BPV and concomitant reduction in epistaxes and syncopal episodes.Conclusions: Severe BPV is uncommon and challenging to manage when caused by baroreflex failure. Some antihypertensive drugs can increase BPV and elevate sympathetic tone which could further impair BP control in patients with this diagnosis. Use of BAT in this setting may be of benefit as long as the carotid sinus nerve and vasodepressor component of the baroreflex still function.
To study cardiovascular control in the period leading to vasovagal syncope we monitored beat-to-beat blood pressure, heart rate (HR) and forearm blood flow in 14 patients with posturally related syncope, from supine through to tilt-induced pre-syncope. Signals of arterial blood pressure (BP) from a Finapres photoplethysmograph and an electrocardiograph (ECG) were fed into a NeuroScope system for continuous analysis. Non-invasive indices of cardiac vagal tone (CVT) and cardiac sensitivity to baroreflex (CSB) were derived on a beat-to-beat basis from these data. Brachial vascular resistance (VR) was assessed intermittently from brachial blood flow velocity (Doppler ultrasound) divided by mean arterial pressure (MAP). Patients underwent a progressive orthostatic stress test, which continued to pre-syncope and consisted of 20 min head-up tilt (HUT) at 60 deg, 10 min combined HUT and lower body suction (LBNP) at -20 mmHg followed by LBNP at -40 mmHg. Pre-syncope was defined as a fall in BP to below 80 mmHg systolic accompanied by symptoms. Baseline supine values were: MAP (means +/- S.E.M.) 84.9 +/- 3.2 mmHg; HR, 63.9 +/- 3.2 beats min-1; CVT, 10.8 +/- 2.6 (arbitrary units) and CSB, 8.2 +/- 1.6 ms mmHg-1. HUT alone provoked pre-syncope in 30 % of the patients whilst the remaining 70 % required LBNP. The cardiovascular responses leading to pre-syncope can be described in four phases. Phase 1, full compensation: where VR increased by 70.9 +/- 0.9 %, MAP was 89.2 +/- 3.8 mmHg and HR was 74.8 +/- 3.2 beats min-1 but CVT decreased to 3.5 +/- 0.5 units and CSB to 2.7 +/- 0.4 ms mmHg-1. Phase 2, tachycardia: a progressive increase in heart rate peaking at 104.2 +/- 5.1 beats min-1. Phase 3, instability: characterised by oscillations in BP and also often in HR; CVT and CSB also decreased to their lowest levels. Phase 4, pre-syncope: characterised by sudden decreases in arterial blood pressure and heart rate associated with intensification of the symptoms of pre-syncope. This study has given a clearer picture of the cardiovascular events leading up to pre-syncope. However, the mechanisms behind what causes a fully compensated system suddenly to become unstable remain unknown.
The effect of 24-hour sleep deprivation on cardiac vagal tone during the first 90 minutes of sleep was studied in 16 subjects using a new real-time index of cardiac parasympathetic activity. The level of cardiac vagal tone in subjects who were sleep deprived was more than doubled that in non-sleep-deprived subjects during sleep stage 0 immediately prior to the onset of sleep stage 1. The mean cardiac vagal tone fell significantly (p<0.01), from a high level of 19.2 arbitrary units of a linear vagal scale (LVS) to 10 units on reaching slow-wave sleep stage 4 in sleep-deprived epileptic subjects. There was a similar fall in cardiac vagal tone from 18.7 units to 12 units in the LVS in sleep-deprived normal subjects, but this was not statistically significant. There was no change in the mean vagal tone of non-sleep-deprived normal subjects. We propose that the cardiac vagal tone can be used as an objective index of sleep propensity.
In dogs with spontaneous heart disease, an electronically generated measurement of cardiac vagal tone, the cardiac index of parasympathetic activity, was a sensitive, simple and inexpensive measure of the severity of heart failure. Dogs with cardiac disease and an index score less than 3 were at 15.8 (95 per cent confidence interval 2.9 to 87.2) times the risk of dying within a year than those with a score of 3 and over. The measurement of the index provided an objective and reliable beat-by-beat measurement of cardiac vagal tone, which was prognostically useful in dogs with heart disease.
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