Are cardiac syndrome X, irritable bowel syndrome and reflex sympathetic dystrophy examples of lateral medullary ischaemic syndromes?

Circadian rhythm of airways caliber and its autonomic modulation

The autonomic nervous system (ANS) is one of the effector pathways for circadian variation of many physiological parameters. Autonomic tone and airways caliber have been reported to exhibit circadian variation in separate studies. A simultaneous investigation of heart rate variability (HRV) and airway caliber might ascertain how airway caliber is modulated by autonomic tone. This study was planned to identify the variations in airway caliber and autonomic function tone during a 24-hour span. A total of 56 healthy male subjects with almost similar daily routines were studied. Time domain, frequency domain and nonlinear analysis of R-R interval from 5 min electrocardiogram (ECG) was done seven times during the daytime wake span at 3-hour intervals starting at 05:00 h in the morning until 23:00 h in the night. Simultaneously peak expiratory flow rate (PEFR) was determined using a mini Wright's peak flow meter. Rhythmometric analysis was done for PEFR and HRV parameters. Significant circadian variation in low frequency (LF) and high frequency (HF) variance was identified in this group of healthy subjects. The circadian rhythm of LF variance was characterized by a gradual increase and corresponding reciprocal change in HF variance from morning until night. The LF/HF ratio and SD2/SD1 ratio reflecting sympatho-vagal balance showed low to high values from morning to evening. The acrophase of the PEFR temporal pattern is similar to that of LF power and almost opposite in phase to that of HF power. PEFR is positively correlated with LF power. The circadian rhythm of airway caliber co-varies with cardiac autonomic tone. It appears that the temporal pattern of cardiac autonomic tone precedes in time that of airways caliber, thereby suggesting the latter operates under the modulatory effect of the 24-hour pattern in sympatho-vagal balance.

Irritable bowel syndrome: an integrated explanatory model for clinical practice

BACKGROUND

Although irritable bowel syndrome (IBS) is a symptom-based diagnosis, clinicians' management of and communication about the disorder is often hampered by an unclear conceptual understanding of the nature of the problem. We aimed to elucidate an integrated explanatory model (EM) for IBS from the existing literature for pragmatic use in the clinical setting.

METHODS

Systematic and exploratory literature searches were performed in PubMed to identify publications on IBS and EMs.

KEY RESULTS

The searches did not identify a single, integrated EM for IBS. However, three main hypotheses were elucidated that could provide components with which to develop an IBS EM: (i) altered peripheral regulation of gut function (including sensory and secretory mechanisms); (ii) altered brain-gut signaling (including visceral hypersensitivity); and (iii) psychological distress. Genetic polymorphisms and epigenetic changes may, to some degree, underlie the etiology and pathophysiology of IBS and could increase the susceptibility to developing the disorder. The three model components also fit into one integrated explanation for abdominal symptoms and changes in stool habit. Additionally, IBS may share a common pathophysiological mechanism with other associated functional syndromes.

CONCLUSIONS & INFERENCES

It was possible to elucidate an integrated, three-component EM as a basis for clinicians to conceptualize the nature of IBS, with the potential to contribute to better diagnosis and management, and dialog with sufferers.

Completely reversed flow in the vertebral artery does not always indicate subclavian steal phenomenon

We evaluated the causes, differential diagnosis and clinical significance of completely reversed flow (CRF) in the vertebral artery (VA). Twenty-three patients diagnosed with CRF in the VA by Doppler ultrasound were studied retrospectively. CRF was divided into intermittent CRF and continuous CRF. The peak reversed velocity (PRV) and ratio of time in intermittent CRF to one cardiac cycle (tICRF/CC) were calculated. Causes of CRF were determined on the basis of previous angiography results. The results indicated that subclavian steal phenomenon (SSP) caused all cases of continuous CRF (n = 8). Intermittent CRF was caused by SSP (n = 6) or proximal VA occlusion (n = 9). PRV and tICRF/CC were increased in SSP as compared with VA occlusion (p < 0.05). Using a cutoff of tICRF/CC = 0.30, we achieved excellent accuracy in predicting the cause of intermittent CRF (100%) and posterior circulatory infarction (91%). Thus, analysis of CRF patterns and measurements of VA parameters can be used in differential diagnosis of the causes of CRF and in prediction of posterior circulatory infarction.

Autonomic nervous system dysfunction and their relationship with disease severity in children with atopic asthma

The involvement of autonomic imbalance has been reported in the pathogenesis of allergic diseases. The aim of this study was to investigate the association between the clinical severity of childhood asthma with autonomic nervous system (ANS) dysfunction and to define whether the severity of asthma correlates with ANS activity. In this case-control study, we evaluated the ANS activity by testing heart rate variability (HRV) and sympathetic skin response (SRR) in 77 asthmatic children, age 7-12 yrs, who had no co-morbidity and compared them with 40 gender- and age-matched control subjects. According to the severity of their asthma, study subjects were further divided into three groups: I (mild asthmatics), II (moderate asthmatics), and III (severe asthmatics). Inter-group ANS scale scores differed significantly (p<0.01) between Groups I and III and between Groups II and III. Combined use of HRV and SSR provides a higher degree of sensitivity for assessing disease severity in cases of pediatric asthma.

Increased parasympathetic tone as the underlying cause of asthma: a hypothesis

Asthma is a chronic inflammatory disease of airways that is characterized by increased responsiveness of the tracheo-bronchial tree to multiple number of stimuli. Immunological theory does not explain all features in asthma, for example hyper-reactivity of the airways. Neurogenic theory also fails to explain the pathogenesis of asthma comprehensively. Higher parasympathetic tone has been reported in asthmatics but has never been suggested as a major underlying cause of asthma. This article attempts to explain the occurrence of hyper-responsiveness, inflammatory/allergic reactions and broncho-constriction in asthma on a common basis of inherent higher parasympathetic tone in asthmatics. The higher background parasympathetic firing leads to increased nitric oxide (NO) production owing to its co-localization with acetylcholine (ACh) in inhibitory non-adrenergic and non-cholinergic (i-NANC) nerves. NO is a neurotransmitter of i-NANC system and it mediates bronchodilation. Increased NO release has been found to be responsible for hyper-responsiveness and increased inflammation in the airways. The authors suggest that an inherently higher background parasympathetic tone in concert with inflammation or a specific genetic background could modify the effects of NO on lung homeostasis in humans leading to increased susceptibility to an asthmatic state.

A Spectrum of Knock-Type Doppler Signals in the Intracranial Vessels

Background and Purpose— Knock-type Doppler signals (KTDS) are detectable by transcranial Doppler, and it has been hypothesized that they are related to an occlusion of a small perforating artery and microvascular ischemia. However, the nature of KTDS has not been prospectively defined. We aimed at describing the spectral and power motion Doppler characteristics of KTDS and ultrasound exposure conditions that lead to their appearance.

Methods— Consecutive patients referred with symptoms of stroke or transient ischemic attacks to our cerebrovascular ultrasound laboratory were screened for the presence of KTDS. The presence of microvascular ischemia was assessed using brain MRI.

Results— Among 327 patients with cerebrovascular symptoms, 46 (14%) had KTDS. KTDS were found more frequently in posterior circulation vessels (55% vertebral artery, 21.5% basilar artery, and 6% posterior cerebral artery). There was no association between ultrasound identification of KTDS and the presence of brain ischemia in the distribution of any vessel (OR, 0.37; 95% CI, 0.09–1.53; P =0.171) on univariate logistic regression analyses. KTDS was not related to the presence of microvascular ischemia on brain MRI (OR, 1.12; 95% CI, 0.55–2.29; P =0.761). We described the range of spectral and power motion Doppler appearances of KTDS and experimentally demonstrated the most likely underlying mechanism being a large vessel wall movement artifact.

Conclusions— Although KTDS can be distinguished from other spectral flow signals, they can be found in normal vessels, they do not seem to be associated with the vessel affected by ischemia, and they should not be overinterpreted.

Influence of sympathetic nervous system on sensorimotor function: whiplash associated disorders (WAD) as a model

There is increasing interest about the possible involvement of the sympathetic nervous system (SNS) in initiation and maintenance of chronic muscle pain syndromes of different aetiology. Epidemiological data show that stresses of different nature, e.g. work-related, psychosocial, etc., typically characterised by SNS activation, may be a co-factor in the development of the pain syndrome and/or negatively affect its time course. In spite of their clear traumatic origin, whiplash associated disorders (WAD) appear to share many common features with other chronic pain syndromes affecting the musculo-skeletal system. These features do not only include symptoms, like type of pain or sensory and motor dysfunctions, but possibly also some of the pathophysiological mechanisms that may concur to establish the chronic pain syndrome. This review focuses on WAD, particular emphasis being devoted to sensorimotor symptoms, and on the actions exerted by the sympathetic system at muscle level. Besides its well-known action on muscle blood flow, the SNS is able to affect the contractility of muscle fibres, to modulate the proprioceptive information arising from the muscle spindle receptors and, under certain conditions, to modulate nociceptive information. Furthermore, the activity of the SNS itself is in turn affected by muscle conditions, such as its current state of activity, fatigue and pain signals originating in the muscle. The possible involvement of the SNS in the development of WAD is discussed in light of the several positive feedback loops in which it is implicated.

Mechanisms underlying development of spatially distributed chronic pain (fibromyalgia)

Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. Similarly, psychophysical testing reveals allodynia and hyperalgesia for cutaneous stimulation at locations beyond regions of clinical pain referral. The combination of widely distributed clinical pain and generalized hypersensitivity is highly disabling, but no satisfactory treatment is regularly prescribed. A thorough understanding of mechanisms will likely be required to develop and document adequate therapies. The generalized hypersensitivity associated with FM has focused considerable interest on central (CNS) mechanisms for the disorder. These include central sensitization, central disinhibition and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. However, the central effects associated with FM can be produced by a peripheral source of pain. Chronic nociceptive input induces central sensitization, magnifying pain, and it activates the HPA and the sympathetic nervous system. Chronic sympathetic activation indirectly sensitizes peripheral nociceptors and sets up a vicious cycle. Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.