Modulation of neurocardiac function by oesophageal stimulation in humans

The Autonomic Coumel Triangle: A New Way to Define the Fascinating Relationship between Atrial Fibrillation and the Autonomic Nervous System

Arrhythmogenic substrate, modulating factors, and triggering factors (the so-called Coumel's triangle concept) play a primary role in atrial fibrillation (AF) pathophysiology. Several years have elapsed since Coumel and co-workers advanced the concept of the relevance of autonomic nervous system (ANS) influences on atrial cells' electrophysiological characteristics. The ANS is not only associated with cardiac rhythm regulation but also exerts an important role in the triggering and maintenance of atrial fibrillation. This review aims to describe in detail the autonomic mechanisms involved in the pathophysiology of atrial fibrillation (AF), starting from the hypothesis of an "Autonomic Coumel Triangle" that stems from the condition of the fundamental role played by the ANS in all phases of the pathophysiology of AF. In this article, we provide updated information on the biomolecular mechanisms of the ANS role in Coumel's triangle, with the molecular pathways of cardiac autonomic neurotransmission, both adrenergic and cholinergic, and the interplay between the ANS and cardiomyocytes' action potential. The heterogeneity of the clinical spectrum of the ANS and AF, with the ANS playing a relevant role in situations that may promote the initiation and maintenance of AF, is highlighted. We also report on drug, biological, and gene therapy as well as interventional therapy. On the basis of the evidence reviewed, we propose that one should speak of an "Autonomic Coumel's Triangle" instead of simply "Coumel's Triangle".

An investigation into the effect of nasogastric intubation on markers of autonomic nervous function

BACKGROUND

Nasogastric (NG) intubation for esophageal manometry can be traumatic and may be associated with a temporary reduction/absence in esophageal peristalsis. This study explored the prevalence and effect on esophageal motor function. We also hypothesized that baseline anxiety as well as markers of autonomic nerve function were correlated to attenuated esophageal peristalsis.

METHODS

Twenty-seven patients with esophageal symptoms referred for esophageal manometry investigation (mean age 56.8 ± 16.7 years, range 23-85 years) reported baseline anxiety score (Likert scale) preintubation. Patients had continuous heart rate and blood pressure measured prior to intubation and until 10 min after catheter withdrawal. Quality of motility was assessed for each 5 ml water swallow using standard Chicago Classification metrics.

KEY RESULTS

Nasogastric-intubation elicited a significant increase in heart rate (p < 0.001), systolic (p < 0.001) and diastolic (p < 0.001) blood pressure, which was in part anticipatory. The median time taken for patients' first hypotensive peristalsis (Distal Contractile Integral; DCI ≥100 mmHg s cm) was 130 s (Interquartile range; 47-242 s) and for their first normal peristalsis (DCI ≥450 mm Hg s cm) was 150 s (IQR 61-320 s), with improvement and consistent stabilization in DCI there onward. This corresponded closely to the time for initial recovery of heart rate and systolic and diastolic blood pressure postintubation.

CONCLUSIONS AND INFERENCES

Nasogastric intubation resulted in heightened sympathetic responses and/or dampened parasympathetic responses, and an associated temporary reduction or absence in esophageal peristalsis.

Gastroesophageal Reflux and Its Association With Atrial Fibrillation: A Traditional Review

Atrial fibrillation (AF) is a common arrhythmia, and gastroesophageal reflux disease (GERD) is a common gastroenterology disease; both are highly encountered daily in clinical practice. Since both share common predisposing factors, we can conclude that there is a link between them. To date, the precise mechanism of reflux disease as a possible cause of atrial fibrillation remains uncertain. However, some possibilities can be postulated, such as the inflammation process, and sympathovagal imbalance represents the main factors for how GERD can initiate AF. Vigorous aerobic exercise in healthy people can bring about acidic esophageal reflux, which is a common risk factor for AF. Various inflammatory markers such as C-reaction protein (CRP) and interleukins have been a central role in initiating AF. A large hiatal hernia (HH) can cause direct compression on the left atrium that is possibly predisposing to atrial arrhythmogenesis. It has been sporadically reported that using a proton pump inhibitor to treat GERD in patients with coexisting AF has a noticeable effect on decreasing symptoms of AF and recurrence with less cost and side effects.

Heart Rate Variability and Gastric Electrical Response to a Cold Pressor Task in Youth with Functional Dyspepsia

BACKGROUND/AIMS

While stress has been implicated in functional dyspepsia (FD), the mechanisms by which stress results in symptoms are not well defined. The aim of the current study was to assess gastric myoelectric and autonomic changes in response to a physical stressor in youth with FD.

METHODS

In a group of healthy controls and pediatric FD subjects, we recorded ECG and EGG signals 30 min before and 60 min after, a cold pressor task (CPT). Gastric EGG and heart rate variability (HRV) parameters were calculated in pre- and post-CPT stages and in short intervals.

RESULTS

The pre-CPT percent tachygastria was higher in FD subjects as compared to controls. However, CPT did not induce any EGG changes in either controls or FD subjects and the two groups did not differ from each other post-CPT. The CPT resulted in an increase in HRV and standard deviation of NN intervals in controls; there was no change in any HRV parameter in FD subjects.

CONCLUSIONS

Acute physical stress does not appear to induce gastric electrical abnormalities in youth with FD. Youth with FD appear to lack the normal flexible autonomic response to a physical stressor.

Gastroesophageal reflux disease and atrial fibrillation: Insight from autonomic cardiogastric neural interaction

BACKGROUND

The relationship between gastroesophageal reflux disease (GERD) and atrial fibrillation (AF) has been previously reported. However, the detailed mechanism remains unknown. In this study, we investigated the effects of acid reflux on the intrinsic cardiac autonomic nervous system, atrial/ventricular electrophysiology, and AF inducibility.

METHODS

Eighteen rabbits were randomized into three groups: acid reflux (group 1, n = 6), control (group 2, n = 6), and acid reflux with periesophageal vagal blockade (group 3, n = 6). Atrial and ventricular effective refractory periods (ERPs) and AF inducibility were checked at baseline and then hourly until 5 hours after the experiment.

RESULTS

Three hours after the experiment, atrial ERP prolongation was noted in groups 2 and 3 (P < .05), whereas shortening of the atrial ERPs was observed in group 1, compared with the baseline. However, no changes were observed in ventricular ERPs in the three groups. The AF inducibility was higher in group 1 than in groups 2 and 3. Pathological examination showed clear esophageal mucosal breaks in groups 1 and 3.

CONCLUSIONS

In this study, we found that the antimuscarinic blockade prevents GERD induced changes to atrial electrophysiology and susceptibility to AF-making it highly likely that autonomic activity is important in mediating this effect.

Association of atrial fibrillation and gastroesophageal reflux disease: Natural and therapeutic linkage of the two common diseases

Atrial fibrillation (AF) is a common arrhythmia and gastroesophageal reflux disease (GERD) is popular in Japan. The two common diseases share several predisposing factors such as lifestyle and senescence, and inflammation and oxidative stress play an important role in their development and progression. Incidental cases of AF treated successfully by proton pump inhibitor (PPI) applied for coexisting GERD have been sporadically reported. An increasing evidence indicates that GERD induces the initiation and the perpetuation of AF. This is caused by the autonomic nerve influence, mechanical compression, and propagation of local inflammation due to proximity of left atrium (LA) and lower esophagus. Meanwhile, AF also develops GERD by mechanical and inflammatory actions of LA characterized by remodeling and inflammation. The robust association of AF with GERD is not limited to their natural interaction, i.e., pharmacological or nonpharmacological treatment of AF is reported to aggravate GERD. Many cardiac drugs (anticoagulants, calcium antagonists, and nitrates) induce esophageal mucosal damage and lower esophageal sphincter relaxation promoting acid reflux. These drugs are frequently prescribed in patients with AF for stroke prevention, rate control, and for coexisting coronary heart disease. Catheter ablation also yields both GERD and esophageal thermal injury, which is a precursor lesion of atrioesophageal fistula. The notion that AF and GERD are mutually interdependent is widely and empirically recognized. However, mechanistic link of the two common diseases and objective evaluation of PPI as an adjunctive AF treatment warrant future large-scale prospective trials.

Ineffective esophageal motility and the vagus: current challenges and future prospects

Ineffective esophageal motility (IEM) is characterized by low to very low amplitude propulsive contractions in the distal esophagus, hence primarily affecting the smooth muscle part of the esophagus. IEM is often found in patients with dysphagia or heartburn and is commonly associated with gastroesophageal reflux disease. IEM is assumed to be associated with ineffective bolus transport; however, this can be verified using impedance measurements or evaluation of a barium coated marshmallow swallow. Furthermore, water swallows may not assess accurately the motor capabilities of the esophagus, since contraction amplitude is strongly determined by the size and consistency of the bolus. The “peristaltic reserve” of the esophagus can be evaluated by multiple rapid swallows that, after a period of diglutative inhibition, normally give a powerful peristaltic contraction suggestive of the integrity of neural orchestration and smooth muscle action. The amplitude of contraction is determined by a balance between intrinsic excitatory cholinergic, inhibitory nitrergic, as well as postinhibition rebound excitatory output to the musculature. This is strongly influenced by vagal efferent motor neurons and this in turn is influenced by vagal afferent neurons that send bolus information to the solitary nucleus where programmed activation of the vagal motor neurons to the smooth muscle esophagus is initiated. Solitary nucleus activity is influenced by sensory activity from a large number of organs and various areas of the brain, including the hypothalamus and the cerebral cortex. This allows interaction between swallowing activities and respiratory and cardiac activities and allows the influence of acute and chronic emotional states on swallowing behavior. Interstitial cells of Cajal are part of the sensory units of vagal afferents, the intramuscular arrays, and they provide pacemaker activity to the musculature that can generate peristalsis in the absence of innervation. This indicates that a low-amplitude esophageal contraction, observed as IEM, can be caused by a multitude of factors, and therefore many pathways can be potentially explored to restore normal esophageal peristalsis.

Atrial fibrillation and gastroesophageal reflux disease: the cardiogastric interaction

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with significant morbidity and mortality. Multiple conditions like hypertension, heart failure, diabetes, sleep apnoea, and obesity play a role for the initiation and perpetuation of AF. Recently, a potential association between gastroesophageal reflux disease (GERD) and AF development has been proposed due to the close anatomic vicinity of the oesophagus and the left atrium. As an understanding of the association between acid reflux disease and AF may be important in the global multimodal treatment strategy to further improve outcomes in a subset of patients with AF, we discuss potential atrial arrhythmogenic mechanisms in patients with GERD, such as gastric and subsequent systemic inflammation, impaired autonomic stimulation, mechanical irritation due to anatomical proximity of the left atrium and the oesophagus, as well as common comorbidities like obesity and sleep-disordered breathing. Data on GERD and oesophageal lesions after AF-ablation procedures will be reviewed. Treatment of GERD to avoid AF or to reduce AF burden might represent a future treatment perspective but needs to be scrutinized in prospective trials.

Is Atrial Fibrillation a Risk Factor for Gastroesophageal Reflux Disease Occurrence?

Recent studies have reported an association between gastroesophageal reflux disease (GERD) and atrial fibrillation (AF). The objective of the present study was to evaluate whether AF is one of the risk factors for GERD occurrence.In this hospital-based, retrospective, case-control study, the patients were classified into 2 groups. The patients diagnosed with new AF were assigned to the AF group (n = 1612); those diagnosed without AF and GERD were assigned to the control group (n = 1612). The subjects in the control group were selected from outpatients of total healthcare center without a history of AF or GERD, and matched for age and gender. We evaluated the incidence of GERD and risk factors for GERD occurrence between the 2 groups.The number of patients experiencing occurrence of GERD during the follow-up period was significantly higher in the AF group than those in the control group, respectively (129 patients vs 98 subjects, P = 0.037). The incidence of GERD was significantly higher in the AF group than in the control group by Kaplan-Meier analysis with log-rank test (P = 0.008). The AF group's adjusted hazard ratio of GERD occurrence against that of the control group was 1.37 (95% confidence interval [CI]: 1.16-1.57; P = 0.009) according to Cox's proportional hazard model.The presence of AF appears to increase the incidence of GERD and may be considered a risk factor for the development of GERD. Further, large prospective and cohort studies will be required to better establish the correlation of GERD with AF.

Postprandial cardiac vagal tone and transient lower esophageal sphincter relaxation (TLESR)

BACKGROUND

Transient lower esophageal sphincter relaxation (TLESR) is a vagally mediated reflex that occurs most frequently after a meal. Cardiac vagal tone (CVT) decreases after a meal, and correlates with changes in gastric electrical activity. Furthermore, decreased CVT has been reported in patients with gastro-esophageal reflux disease. We therefore aimed to characterize the association between postprandial changes in CVT and the occurrence of TLESR and reflux.

METHODS

Ten healthy volunteers underwent simultaneous autonomic nervous system, gastric myoelectric activity, lower esophageal-sphincter pressure, and reflux monitoring for 30 min in the fasting state, followed by a standard meal, and a further 4 h postprandially. Results are in mean ± SEM.

KEY RESULTS

The number of TLESRs (P < 0.0001) and reflux episodes (P < 0.0001) increased after the meal, while CVT decreased (P < 0.01). Cardiac sensitivity to baroreceptor reflex (CSB) showed similar time course changes to CVT (P = 0.06). During the first postprandial hour there was a strong correlation between the number of TLESRs and reflux episodes with CVT (R(2)  = 0.51 and R(2)  = 0.50, respectively; P < 0.05). There was also an increase in the dominant power and power ratio on electrogastrography (P < 0.05) after the meal.

CONCLUSIONS & INFERENCES

In healthy volunteers, the increase in the number of TLESRs and reflux episodes after a meal occurred mostly at a time of reduced CVT. Further studies should explore whether modulation of CVT can modify frequency of TLESRs and also this relationship should be further explored in patients with reflux disease.

Enterogastroesophageal reflux detected on 99m-technetium sestamibi cardiac imaging as a cause of chest pain

Myocardial perfusion imaging (MPI) with technetium-99m sestamibi (Tc-99m MIBI) is considered a diagnostic technique that is widely used for the investigation of suspected coronary artery disease. Incidental inspection of an extracardiac activity is indirect, but important marker, which can identify a potentially treatable non-coronary cause for chest pain that may mimic cardiac symptoms. Here, we present an illustrative case in which significant enterogastroesophageal reflux of Tc-99m MIBI occurred during the cardiac imaging following prompt hepatobiliary clearance. Because, there was normal myocardial perfusion on MPI, presence of gastroesophageal reflux (GER) on GER scintigraphy and detection of mild inflammation with pathologically confirmed hyperplastic polyp by endoscopy, in view of the above findings we concluded that the probable cause of chest pain was reflux.

Further assessment of atrial fibrillation as a risk factor for gastroesophageal reflux disease: a multicenter questionnaire survey

OBJECTIVE

Although both atrial fibrillation (AF) and gastroesophageal reflux disease (GERD) are common diseases, the relationship between these two conditions remains controversial, depending on the study design and type of AF. Therefore, we focused on the relationship between nonvalvular AF and GERD.

METHODS

A total of 479 consecutive subjects (255 men and 224 women, mean age: 60.4 ± 12.8 years), including outpatients at several hospitals (n=201) and participants of an annual health screening program (n=278), were enrolled. Subjects with valvular AF, malignancy or dementia were excluded. The frequency scale for symptoms of GERD (F-scale) was applied after obtaining each patient's informed consent for screening symptomatic GERD with a total cutoff score of 8 points. The score on the questionnaire was correlated with the baseline characteristics extracted from the patients' medical records.

RESULTS

The total F-scale scores were significantly higher in the older patients (≥ 60 years) than in the younger patients (<60 years) (p=0.017) and increased in the following order: permanent AF > paroxysmal AF > sinus rhythm (p=0.003). The incidence of GERD increased in the same order among the patients with the various heart rhythm classifications (p<0.001). Coronary heart disease, hypertension, diabetes and dyslipidemia were not correlated with the F-scale scores or incidence of GERD. The stepwise discriminant analyses demonstrated that nonvalvular AF alone was significantly associated with symptomatic GERD (Wilks' lambda=0.983, p=0.004).

CONCLUSION

This multicenter study demonstrated that nonvalvular AF is significantly correlated with symptomatic GERD. This small sample survey warrants a future study of a large-scale cohort.

Atrial fibrillation and acid reflux disease

To date, the precise mechanism of atrial fibrillation (AF) as a possible cause of reflux disease remains uncertain, although some possibilities can be postulated. Inflammation and vagal stimulation may have a key role linking these 2 common diseases. There is some evidence in the form of case reports and limited observational studies reporting that reflux disease, and more specifically esophagitis, can cause paroxysmal AF, and various mechanisms have been proposed. Some studies have demonstrated that acid suppressive therapy by proton pump inhibitors (PPIs) may help ameliorate symptoms associated with AF and also facilitate conversion to normal sinus rhythm in a subset of patients. Further prospective studies are needed to determine if a true causal mechanism exists between the two and assess whether the mechanism is dependent on a specific subtype of AF. In addition, the response of AF-related symptoms to PPI therapy and the potential for PPI therapy to reduce the development of AF merits further investigation.

Probiotic Lactobacillus reuteri alleviates the response to gastric distension in rats

Probiotic lactic acid bacteria have been reported to alleviate symptoms in patients with irritable bowel syndrome. However, they have not been tested for use in functional gastric disease. We therefore investigated if strains previously shown to protect from response to colorectal distension (CRD) in rats also modulate response to gastric distension (GD). Healthy, male Sprague-Dawley rats were treated with viable, heat-killed, gamma-irradiated Lactobacillus reuteri or viable Lactobacillus plantarum wild type (WT), L. plantarum Dlt¯mutant, conditioned medium or medium control (9 d), and subjected to GD under anesthesia using an i.g. Teflon catheter. Effects were measured by heart rate (HR) changes during noxious distension (60 mm Hg) compared to baseline HR values. We also investigated the localization of viable, green fluorescent protein-transfected bacteria in the stomach mucosa. Viable L. reuteri decreased the bradycardia induced by noxious GD compared to placebo controls (P < 0.001). Heat-killed or gamma-irradiated L. reuteri and conditioned medium did not have a protective effect in GD. Viable L. plantarum WT and Dlt¯mutant, previously shown to be effective antinociceptive agents in CRD, showed no protective effect in GD. All viable bacteria were associated with the pars glandularis of the rat stomach. Thus, we conclude that the antinociceptive mechanisms of action of probiotic bacteria differ between the stomach and the colon. Symptom alleviation cannot be attributed to the localization of the bacteria in the stomach. Information derived from effects of CRD cannot be extrapolated to effects in the stomach, which are likely to be strain and organ specific.

Accuracy of heartbeat perception is reflected in the amplitude of the heartbeat-evoked brain potential

Neurotransmission from the heart to the brain results in a heartbeat-evoked potential (HEP). In this study, the influence of the ability to detect one's heartbeats based on the HEP was examined. According to their results in a heartbeat perception task, subjects were classified as good (n=18) or poor (n=26) heartbeat perceivers. EEG, EOG, and ECG were recorded while participants attended to their heartbeats. The R-wave of the ECG served as a trigger for EEG averaging. In the latency range of 250-350 ms after the ECG R-wave, the HEP amplitude at the right central location was significantly higher in good heartbeat perceivers. A significantly positive correlation was observed between the heartbeat perception score and the mean HEP amplitude. Our results confirm that the accuracy of heartbeat perception is reflected in the amplitude of the HEP. Thus, the HEP may be a suitable research tool for the study of brain processes related to visceral perception.

Mechanisms of symptomatic improvement after gastric electrical stimulation in gastroparetic patients

The aims were to investigate the effects of gastric electrical stimulation (GES) on autonomic function, gastric distention and tone, and central control mechanisms in gastroparetic patients. Ten gastroparetic patients refractory to standard medical therapy participated in this study and data were collected at baseline, within two weeks before surgery for implantation of GES system, and at follow-up sessions between 6 and 12 weeks after GES therapy was initiated. In each session, electrocardiogram, electrogastrogram (EGG) and gastric barostat measurements were conducted before and after a caloric liquid meal. Positron Emission Tomography (PET) brain scans were performed on a separate day. During GES therapy there was a significant increase in the discomfort threshold for mean pressure from 21 mmHg at baseline to 25 mmHg at follow-up, and for mean volume from 561 mL to 713 mL. A significant increase in the postprandial EGG power (amplitude) was observed between baseline and follow up. The sympathovagal balance was significantly decreased after GES therapy, indicating a significant increase in vagal activity. The cumulative PET data showed an increase in quantitative radioactive counts relative to the standardized data base in both the thalamic and caudate nuclei after chronic GES therapy. We conclude that our data suggest that the symptomatic improvement achieved by GES in gastroparesis is best explained by activation of vagal afferent pathways to influence CNS control mechanisms for nausea and vomiting accompanied by enhanced vagal efferent autonomic function and decreased gastric sensitivity to volume distention which enhances postprandial gastric accommodation.

Cardiovascular effects of gastric intubation and distension in healthy humans

Few data exist on the effect of upper gut stimuli on the cardiovascular system. Aim of our study was to evaluate the cardiovascular effects of gastric intubation and distension. Eleven healthy subjects (eight men, aged 21-30 years) were studied and a non-invasive beat-to-beat cardiovascular monitoring system was used. After 15-min basal recording, a bag catheter was positioned in the proximal stomach and connected to a barostat. Recordings were first performed for 15 min with the bag deflated, then during inflation of air using a 100 mL per 2 min stepwise protocol until epigastric discomfort was reported, and finally for 15 min with the bag inflated at 75% of discomfort volume spared from the preceding period by 10 min with the bag deflated. Presence of the deflated bag catheter significantly increased mean arterial pressure. Stepwise distension progressively increased heart rate and cardiac index, while mean arterial pressure was affected only at discomfort volume. Peripheral resistances and systemic plasma catecholamines were unaffected. During prolonged distension, the effect on heart rate and cardiac index was transient. In conclusion, both gastric intubation and distension alter cardiovascular parameters, but the effect of distension undergoes rapid adaptation. Experimentally induced gastric distension is a valuable stimulus to study viscero-cardiovascular reflexes and their mechanisms using beat-to-beat measurements.

Cardiac arrest following adjustment of a gastric band

Laparoscopic adjustable gastric banding is an established and popular technique for achieving weight loss in the morbidly obese. It is however not without risks of morbidity and even mortality. The authors present a case report of a 46-year-old female who had a cardiac arrest after adjustment of a gastric band. The pathomechanisms to explain this event are explored and a review of the available literature is undertaken.

The effect of sham feeding on neurocardiac regulation in healthy human volunteers

BACKGROUND

Distension and electrical stimuli in the esophagus alter heart rate variability (HRV) consistent with activation of vagal afferent and efferent pathways. Sham feeding stimulates gastric acid secretion by means of vagal efferent pathways. It is not known, however, whether activation of vagal efferent pathways is organ- or stimulus-specific.

OBJECTIVE

To test the hypothesis that sham feeding increases the high frequency (HF) component of HRV, indicating increased neurocardiac vagal activity in association with the known, vagally mediated, increase in gastric acid secretion.

METHODS

Continuous electrocardiography recordings were obtained in 12 healthy, semirecumbent subjects during consecutive 45 min baseline, 20 min sham feeding (standard hamburger meal) and 45 min recovery periods. The R-R intervals and beat-to-beat heart rate signal were determined from digitized electrocardiography recordings; power spectra were computed from the heart rate signal to determine sympathetic (low frequency [LF]) and vagal (HF) components of HRV.

RESULTS

Heart rate increased during sham feeding (median 70.8 beats/min, 95% CI 66.0 to 77.6; P<0.001), compared with baseline (63.6, 95% CI 60.8 to 70.0) and returned to baseline levels within 45 min. Sham feeding increased the LF to HF area ratio (median: 1.55, 95% C.I 1.28 to 1.77; P<0.021, compared with baseline (1.29, 95% CI 1.05 to 1.46); this increase in LF to HF area ratio was associated with a decrease in the HF component of HRV.

CONCLUSIONS

Sham feeding produces a reversible increase in heart rate that is attributable to a decrease in neurocardiac parasympathetic activity despite its known ability to increase vagally mediated gastric acid secretion. These findings suggest that concurrent changes in cardiac and gastric function are modulated independently by vagal efferent fibres and that vagally mediated changes in organ function are stimulus- and organ-specific.

Autonomic nervous system response to a solid meal and water loading in healthy children: its relation to gastric myoelectrical activity

The aim of this study was to investigate the correlation of gastric myoelectrical and autonomic activities in healthy children. Simultaneous recordings of electrogastrography (EGG) and electrocardiogram (ECG) were performed in healthy children before and after a solid meal and water loading respectively. The autonomic activity was assessed by spectral analysis of the heart rate variability (HRV). The solid meal resulted in an increase in EGG-dominant frequency (2.92 cpm vs 3.16 cpm, P < 0.05), dominant power (46.9 dB vs 53.7 dB, P < 0.05) and percentage normal slow waves (81.9%vs 89.0%, P < 0.05), while only dominant power increased following water loading. Power in the low-frequency band of HRV (LF) was significantly increased and power in the high-frequency band of HRV (HF) significantly decreased following the solid meal. Postprandial LF was positively and HF negatively correlated with the postprandial increase in EGG-dominant power. Water loading was not associated with any significant changes in HRV parameters. These results suggest that both vagal and sympathetic pathways are involved in modulation of gastric myoelectrical activity.

The evaluation of gastro-oesophageal reflux and oesophagocardiac reflex in patients with angina-like chest pain following cardiologic investigations

The aims of the study were to assess pathogenetic role of gastro-oesophageal reflux and the oesophago-cardiac reflex in subjects with chest pain. To evaluate the prevalence of gastro-oesophageal reflux disease and the oesophago-cardiac reflex in patients with different coronary artery diseases and in coronary spasm.

PATIENTS, METHODS

Fifty-one patients with chest pain were enrolled after detailed cardiologic evaluation including coronary angiography. The prevalence of gastrooesophageal reflux disease was established by symptom analysis, upper gastrointestinal endoscopy, 24-h oesophageal pH monitoring, and oesophageal manometry. The oesophago-cardiac reflex was established by oesophageal acid perfusion test (0.1 N HCl and 0.9% NaCl, 120-120 ml/10 min in a blinded manner) combined with transoesophageal Doppler echocardiographic coronary flow measurement in the left anterior descending artery.

RESULTS

Gastro-oesophageal reflux disease was established in 45% (23/51) of the patients. Oesophageal acid perfusion decreased the coronary flow velocity in 49% (25/51) of the patients indicating the presence of oesophago-cardiac reflex. Oesophago-cardiac reflex was present more frequently in patients with coronary spasm, than in patients with either epicardial coronary artery disease or microvascular coronary disease (p<0.02). Patients with oesophago-cardiac reflex had higher DeMeester scores, increased number of reflux episodes, fraction time below pH 4, and prolonged acid reflux episodes (p<0.05 for each parameter).

CONCLUSIONS

Gastro-oesophageal reflux disease is frequently established in patients with either epicardial or microvascular coronary artery disease or with coronary spasm. The oesophago-cardiac reflex was more frequently observed in patients with coronary spasm. The combination of oesophageal acid perfusion test and transoesophageal Doppler echocardiographic coronary flow measurement seems to be a useful method for the detection of this reflex. Patients with prolonged gastro-oesophageal acid reflux episodes, erosive oesophagitis and coronary spasm may be at higher risk for the development of linked-angina.

Circadian change of cardiac autonomic function in correlation with intra-esophageal pH

BACKGROUND AND AIM

Although autonomic alterations are observed in patients with gastroesophageal reflux disease (GERD), the influence of visceral receptor responses on the dynamics of autonomic function remains unknown. The aim of this study was to investigate the autonomic functional changes in association with intra-esophageal pH under ambulation.

METHODS

Thirty patients referred for 48 h ambulatory pH monitoring underwent simultaneous 24 h cardiac monitoring for heart rate variability (HRV). We used linear mixed-effects models to estimate the relationship between esophageal acid exposure and power spectral analysis of HRV, including low-frequency power (0.04 < LF < 0.15 Hz), high-frequency power (0.15 < or = HF < 0.4 Hz), and LF/HF power ratio.

RESULTS

Over the 24-h period, patients with pathological reflux had lower average LF and HF powers than patients with functional heartburn, but the LF/HF power ratios were similar for the two patient groups. As we stratified the data according to waking and sleeping times, a significantly higher HF power but lower LF/HF power ratio was found during sleeping time regardless of diagnosis. In the regression analysis, esophageal pH was positively associated with change (not basal tone) of both LF and HF powers during waking, but only with change of HF power during sleeping time. The significant associations between pH values and changes in HRV decreased gradually with time. The LF/HF power ratio did not alter significantly with pH.

CONCLUSION

Esophageal acid exposure is generally associated with decreases in autonomic tone. A predominant parasympathetic fluctuation during sleeping and a superimposed sympathetic interaction during waking dictate diurnal characteristics of autonomic regulation.

Oesophageal acid exposure and altered neurocardiac function in patients with GERD and idiopathic cardiac dysrhythmias

BACKGROUND

Oesophageal sensory stimuli alter neurocardiac function through autonomic reflexes.

AIM

To evaluate in patients with idiopathic supraventricular cardiac dysrhythmias and gastro-oesophageal reflux disease (GERD) whether GE reflux alters neurocardiac function and the effect of acid suppression on cardiac symptoms.

METHODS

Thirty-two patients (13 females and 19 males; age: 20-69 years) with dysrhythmias plus GERD, and nine patients (five females and four males; age: 43-58 years) with GERD only, underwent simultaneous 24-h pH-metry and ECG monitoring. Power spectrum analysis of heart rate variability (PSHRV) was obtained with both its low frequency (LF, sympathetic modulation) and high frequency (HF, vagal modulation) components. Hourly mean oesophageal pH and LF/HF ratio were correlated. A 3 months full-dosage PPI therapy (esomeprazole 40 mg/day) was prescribed.

RESULTS

In 18 (56%) of the 32 patients with dysrhythmia and in none with GERD only, a significant (P < 0.05) correlation between oesophageal pH and LF/HF ratio (oesophagus-heart correlation) was observed. A significant reduction of cardiac symptoms after PPI therapy was observed only in these patients (13/16 vs. 4/11, P < 0.01).

CONCLUSIONS

This study has identified a subgroup of dysrhythmic patients in whom the oesophageal acid stimulus elicited cardiac autonomic reflexes. In these patients acid suppression seems to improve GERD and cardiac symptoms.

Vagal afferent stimulation as a cardioprotective strategy? Introducing the concept

The effect of vagal afferent signaling on cardioinhibition has been well known for over 130 years. Both experimental and clinical studies have demonstrated not only the potential adverse effect of unrestrained sympathoexcitation in high risk patients with ischemic heart disease but the potential for cardioprotection by programmed vagal activity. The vasodepressor and negative chronotropic effects of efferent vagal stimulation has been a cause for concern. However it is becoming clear that favorable shifts towards increased cardiac vagal modulation can be achieved by vagal afferent nerve stimulation. This phasic effect appears to operate though central medullary pathways. Thus by engaging vagal afferent fibers in humans there is the possibility that one can exploit the benefits of central cardioinhibition without adversely affecting heart rate, respiration or hemodynamics. This commentary explores the background and rationale for considering vagal afferent stimulation as a plausible cardioprotective strategy.

Optimal electrical stimulation modality for cortical esophageal evoked potentials: transmural or intraesophageal?

Esophageal electrical stimulation using short and a relatively small number of (200 micros, 0.2 Hz, n = 25) electrical pulses generates a characteristic and well defined cortical evoked potential response (EP). There are two methods of stimulation: either through intraesophageal electrodes or with transmural electrodes. The objective of this paper is to compare EP response, sensations and heart rate variability power spectra elicited by both stimulation modalities in healthy volunteers. Our results suggest that transmural stimulation is more accurately perceived and at lower intensities, produces more reproducible peaks of higher amplitude than during intraesophageal stimulation. During either mode of esophageal stimulation, power within the high-frequency component of the heart rate variability power spectrum is enhanced.

Autonomic responses to heartburn induced by esophageal acid infusion

BACKGROUND AND AIM

Studies have shown that altered visceral perception and lower pain thresholds in patients with symptomatic gastroesophageal reflux disease (GERD) and non-cardiac chest pain. Autonomic changes associated with the perception of heartburn in patients with GERD are poorly understood.

METHODS

A total of 12 GERD patients (six male, six female; mean age 37.2 +/- 2.7 years) and 12 controls (five male, seven female; mean age 32.8 +/- 2.2 years) were studied. The study protocol included a 20-min water infusion (6 mL/min), and 20-min acid infusion (0.1 N HCl, 6 mL/min). Spectral analysis of heart-rate variability (HRV) was used to assess autonomic functioning. The measured HRV indices included the power in the low-frequency (LF) band (0.04-0.15 Hz) reflecting sympathetic tone, and power in the high-frequency (HF) band (0.15-0.5 Hz) reflecting vagal tone, and the LF/HF ratio as an indicator of sympathovagal balance.

RESULTS

The GERD group experienced more heartburn than controls with acid infusion. Between-group comparisons showed no significant changes in LF band power in any period. The HF band power was significantly lower in GERD patients during all infusion periods. The LF/HF ratio was significantly larger in GERD patients.

CONCLUSIONS

The perception of heartburn induced by esophageal acid infusion is associated with a simultaneous increase in sympathetic modulation in patients with GERD. The autonomic responses with esophageal acid infusion are significantly different between healthy subjects and GERD patients.

Oesophageal acid stimulation in humans: does it alter baroreflex function?

The aim of this study was to investigate if oesophagel acid stimulation (Bernstein test) had an influence on heart rate and blood prsure variability and baroreflex gain. We compared the cardiovascular responses in 10 patients with established gastro-esophageal reflux disease (Group 1) and 10 control subjects (Group 2) during esophageal saline and 0.1 mol/l hydrochloric acid instillation. Indices of heart rate and blood pressure variability and baroreflex gain (derived from linear spontaneous sequences and cross spectral analysis) were calculated. In Group 1 the standard deviation of RR intervals (SDRR: 46 ms vs 51 ms, p=0.030) and the root mean square of successive differences (RMSSD: 24 ms vs. 26 ms p=0.027) were significantly lower during acid infusions, than during saline. We found no significant difference in minimum, maximum and mean RR intervals and systolic blood pressures and in the percentage of RR intervals, which differed from adjacent cycles by more than 50 ms (PNN50). The power spectra of RR intervals in the high frequency band tended to be lower during acid infusion (p=0.055). There was no significant difference in blood pressure spectra, neither in low nor in high frequency band. In Group 2 there was no significant difference between any parameters measured during acid and saline. The baroreflex gain was not changed during the studied conditions in any group. Neither increased vagal tone, nor increased vagal variability occurred and the baroreflex gain was not altered during oesophageal acid simulation.

Evolving concepts in functional gastrointestinal disorders: promising directions for novel pharmaceutical treatments

In recent years there has been an increasing appreciation of the complexity of functional gastrointestinal disorders. These represent a spectrum of conditions which may affect any part of the gastrointestinal tract in which there appears to be dysregulation of visceral function and afferent sensation and a strong association with emotional factors and stress. There is a clear psychological dimension, with up to 60% of irritable bowel syndrome (IBS) patients reported to have psychological co-morbidities and altered pain perception is also common in comparison with control populations. The role of the enteric nervous system, the sensory pathways and the brain as well as the influence of the latter on sympathetic and parasympathetic outflow have likewise attracted increasing interest and have led to exciting new methods to study their complex interactions. The concept of low-grade inflammation, such as might occur after infection, acting as a trigger for neuromuscular dysfunction has also led to the broad integrative hypotheses that help to explain the biopsychosocial dimensions seen in functional gastrointestinal disease. The multi-component model places a major emphasis on neurogastroenterology and enteric and neuro-immune interactions where new approaches to pharmacotherapy lie. Drugs may affect motility, visceral sensation and other aspects of gut function such as secretion or absorption. More particularly, however, has been the search for and attempts to influence important mediators of these primary gut functions. Such targets include serotonin and selected 5-HT receptors, which are involved in gut motility, visceral sensation and other aspects of gut function, CCK receptors which are involved in the mediation of pain in the gut and nociception in the CNS, opioid receptors involved in pain in the brain, spinal cord and periphery, muscarinic M3-receptors, substance P and neurokinin A and B receptors which are involved in motor adaptation and pain transmission in association with inflammation, gabba receptors involved in nociception and cannabinoid receptors which are involved in the control of acetyl choline release in the gut. With a better understanding of the structures and pathways involved in visceral perception and hyperalgesia, in the CNS, spinal cord and the gut and new pharmacological tools we will be better able to elucidate the neuropharmacology of visceral perception and its relationship to gut dysfunction. It is likely that there will be multiple therapeutic options based on the spectrum of abnormalities capable of causing the spectrum of symptoms of functional gastrointestinal disorders in any individual patient.

Changes in blood pressure and muscle sympathetic nerve activity during water drinking in humans

To investigate the possible involvement of the sympathetic nervous system in pressor response during water drinking, muscle sympathetic nerve activity (MSNA), blood pressure (BP), and heart rate (HR) were continuously measured in healthy young volunteers throughout the experiments of a 5-min control, 2 min of drinking 500 ml water, and a 28-min recovery. To avoid the effects of water passing through the oropharyngeal and esophageal regions and/or effects of swallowing, an equal amount of water was directly infused to the stomach through a stomach tube for 2 min. Water drinking caused a transient increase in mean arterial pressure (MAP) and HR immediately after drinking (DeltaMAP, 12.6 +/- 2.1 mmHg; DeltaHR, +19.9 +/- 1.7 beats/min at the peak). An abrupt decrease of MSNA was observed directly during water drinking (Deltaburst rate, -6.9 +/- 1.3 bursts/min; Deltatotal activity, -2,606 +/- 491 U/min), and it increased to the baseline level thereafter. Gastric infusion had little or no effect on MAP, HR, and MSNA. The present study demonstrated that a pressor response during water drinking was associated with the attenuation of MSNA and not generated by gastric infusion of water at the same rate as in this drinking manner. In conclusion, the rapid rise in BP might be caused through stimulations from the oropharyngeal region, swallowing-induced factors, and/or a feedforward mechanism by a central descending signal from the higher brain centers.

Evolving concepts in the pathophysiology of functional gastrointestinal disorder

Functional gastrointestinal disorder (FGID) is common and may affect any part of the digestive tract from the esophagus to the rectum. Functional dyspepsia and the irritable bowel syndrome (IBS) are the most commonly recognized and until recently were considered distinct entities. In recent years, however, new observations and studies of the afferent nervous system have extended our concepts of both IBS and dyspepsia and suggest that these conditions may have common triggers and expression from similar pathophysiological processes.

Update on anorexia and cachexia

Declining physical, emotional, and social function as a result of anorexia and cachexia are considerable contributors to discomfort for cancer patients and their families, and they impair the patient's ability to express optimal physical and psychosocial potential as long as possible. This decline no longer has to be accepted as an indispensable sequel to advanced cancer, just as pain is no longer considered to be unavoidable. A routine screening for anorexia and cachexia and associated symptoms is necessary, as is a careful, comprehensive assessment, because the condition is not always obvious. Decisions about anorexia and cachexia treatment are guided by prioritizing the different, concurrent physical, psychosocial, and existential problems and by considering the natural course of the cancer and the effects of antineoplastic therapies. Reversible causes for anorexia and cachexia need to be identified and treated, if appropriate. Nutritional interventions are often indicated; patients with a predominant starvation component and without inflammation may profit the most. New pharmacologic therapies for primary anorexia and cachexia syndrome are expected to enter clinical practice soon; however, until then, treatment with corticosteroids, progestins, or prokinetics may be indicated for some patients. To understand a multicausal syndrome, multimodal and interdisciplinary therapy is required. Specialist palliative care services can be helpful to provide, hand-in-hand with the disease specialists [172], assessment and management of psychophysical symptoms and sociospiritual needs of patients during the course of the illness and at the end of life [173]. Research efforts aim to better characterize subgroups of patients suffering from secondary causes of anorexia and cachexia and to elucidate the mechanisms involved in the primary anorexia and cachexia syndrome. Increasingly individualized treatments are expected with combination treatments that involve different mechanisms including nutrition.

Afferent vagal modulation. Clinical studies of visceral sensory input

The frequency composition of a continuous time series of R-R intervals may be viewed as the phasic output of a central processing system intimately dependent on sensory input from a variety of afferent sources. While different measures of heart rate variability permit a glimpse into the autonomic efferent limb of this complex system, direct access of afferent fibers in humans has remained elusive. Using a specially designed esophageal catheter/manometer probe, we have been able to gain access to vagal afferent fibers in the distal esophagus. Our studies on the effect of vagal afferent electrostimulation on both cerebral evoked potentials (EvP) and the power spectrum of heart rate variability have yielded the following observations: 1. Stimulation of esophageal vagal afferents dramatically and reproducibly increases the high frequency (HF) vagal power and reduces the low frequency (LF) power of the heart rate autospectrum. 2. This effect is constant across stimulation frequencies from 0.1 to 1.0 Hz and across stimulation intensities from 2.5 to 20 mA. 3. Regardless of the stimulation parameters, there are only minimal changes in heart rate (2-6 bpm) and no change in respiratory frequency. 4. There is a linear correlation between electrical stimulation intensity and the amplitude of cerebral evoked potentials, whereas there is a non-linear relationship with all short-term power spectral indices. 5. While cerebral evoked potentials are only elicited at stimulation intensities above perception threshold, there is already a significant shift to increased vagal efferent modulation well below perception threshold.

CONCLUSION

These studies support the concept that power spectral indices of heart rate variability represent phasic output responses to tonic afferent viscerosensory signals in humans. These studies also demonstrate the feasibility of accessing vagal afferents in humans.

Centrally mediated effects of bromocriptine on cardiac sympathovagal balance

Bromocriptine, a dopamine agonist, is known to lower cardiovascular mortality in L-dopa-treated patients with Parkinson's disease, probably by reducing the cardiac sympathetic activity. We aimed at unmasking the central effects of bromocriptine on the heart by power spectrum analysis. Ten healthy subjects (aged 31+/-2 years) in supine and sitting positions were evaluated after the administration of bromocriptine (2.5 mg) alone and after pharmacological peripheral D(2)-like blockade by domperidone (20 mg). We calculated (autoregressive method) the following: the low-frequency (LF) component (an index of cardiac sympathetic tone), the high-frequency (HF) component (an index of cardiac vagal tone), and the LF/HF ratio (an index of cardiac sympathovagal balance). With subjects in the supine position, bromocriptine alone induced a significant increase in the LF component and the LF/HF ratio, together with a reduction in norepinephrine plasma levels and blood pressure values. These conflicting effects can be explained as the combined result of direct and indirect (reflex-mediated) actions of bromocriptine in vivo. No changes in cardiac autonomic drive were observed with subjects in the sitting position. After domperidone pretreatment, bromocriptine induced a reduction in the LF component and in the LF/HF ratio. The sitting position caused an increase in heart rate and in the LF/HF ratio. We demonstrated both peripheral and central effects of bromocriptine. In particular, pretreatment with a peripheral antagonist (domperidone) allowed us to unmask the central effect of bromocriptine on cardiac sympathetic drive.

Abnormal cerebral processing of oesophageal stimuli in patients with noncardiac chest pain (NCCP)

In noncardiac chest pain (NCCP), altered visceral perception may result from abnormal cerebral processing of sensory input rather than abnormalities of afferent pathways. However, the interactions between symptoms, autonomic function and oesophageal stimuli are poorly studied. Oesophageal stimulation elicits reproducible cortical evoked potentials [CEP] and modulates heart rate variability via vagal pathways, as visible on power spectrum analysis of heart rate variability [PS-HRV]. These methods are increasingly used to study the function of visceral afferent neural pathways in human. The aim of this study was to compare EP and PS-HRV during oesophageal stimuli in NCCP and controls. Twelve healthy volunteers (one female, 11 male; aged 24-51 years; mean 32 +/- 8 years), and eight NCCP patients (three female, five male; age range 26-58, mean 40.5 +/- 10 years) were studied. Electrical oesophageal stimulation (EOS; 200 microseconds, 0.2 Hz, 25 stimuli) was applied to the oesophageal wall 5 cm above the lower oesophageal sphincter (LOS), and perception thresholds (measured in mA) determined. EP responses were recorded using 22 standard electroencephalogram scalp electrodes. Autonomic activity was assessed using PS-HRV, before, during, and after oesophageal stimulation. Measured PS-HRV indices included high frequency (HF; 0. 15-0.5 Hz) and low frequency (LF; 0.06-0.15 Hz) power, respectively, assessing vagal and sympathetic activity, and the LF/HF ratio. EOS perception occurred at lower thresholds in NCCP than in controls (3. 6 +/- 1 vs. 7.8 +/- 2 mA, P < 0.05). EP amplitude was greater (13 +/- 2 vs. 6 +/- 1 microV, P < 0.0001), and latency longer in controls vs. NCCP (191 +/- 7 ms vs. 219 +/- 6 ms, P < 0.001). In NCCP, EOS decreased sympathetic outflow (low frequency peak on PS-HRV) and increased cardiovagal activity (high frequency peak, P < 0.02) to a significantly higher degree in comparison with controls. During EOS, heart rate decreased in NCCP from 68 vs. 62 beats min-1 (P < 0.003) but not in controls. In NCCP patients, EOS was perceived at lower intensities and was associated with a greater cardiovagal reflex response. EP responses associated with EOS were smaller in NCCP than in controls, suggesting that an increased perception of oesophageal stimuli results from an enhanced cerebral processing of visceral sensory input in NCCP, rather than from hyperalgesic responses in visceral afferent pathways.

The electrical and magnetical cerebral responses evoked by electrical stimulation of the esophagus and the location of their cerebral sources

OBJECTIVES

After electrical stimulation of the esophagus cerebral responses are recordable, their cortical source is under discussion. Brain mapping using electroencephalography recordings demonstrated partially controversial results. Sources of evoked responses can be localized more easily using magnetoencephalography than electroencephalography.

METHODS

We examined 22 volunteers by recording electrical somatosensory potentials after electrical stimulation of the esophagus. In 9 of these 22 subjects additional recording of magnetic fields was performed and the sources of the evoked magnetic fields were computed.

RESULTS

The evoked potentials after electrical stimulation of the esophagus had a similar latency as the previously published data. The source localization done by magnetoencephalography suggest that first a region of the postcentral gyrus is activated which is temporo-lateral to the primary somatosensory cortex of the pharynx. This region is suggested to be the primary somatosensory region of the esophagus. This source was followed by a source in the parietal operculum thought being part of the secondary somatosensory cortex. Simultaneously the insular cortex was activated pointing to a parallel neuronal pathway to the central autonomic nervous system.

CONCLUSION

After electrical stimulation of the esophagus somatosensory cortical areas of the temporal postcentral gyrus and the operculum are activated. In parallel activation of the insular cortex as part of the central autonomic network was found.

Pseudoaffective cardioautonomic responses to gastric distension in rats

We examined the heart rate response to gastric distension, the involvement of vagal and sympathetic sensory afferents, adrenergic and cholinergic neural pathways, and the effects of capsaicin on this response in anesthetized rats. Gastric distension volume dependently decreased heart rate by 24.5% (resting rate = 219.87 +/- 14.06 beats/min, mean rate during gastric distension with 15 ml = 165.97 +/- 17.36 beats/min, P < 0.05). The bradycardic response was significantly decreased after removal of the celiac plexus (9.71 +/- 1.77 vs. 38.03 +/- 7.06% in controls, P < 0.05) or after bilateral subdiaphragmatic vagotomy (6.38 +/- 2.65%, P = 0.05). The response to gastric distension was largely prevented by systemic capsaicin (29.92 +/- 4.93% in controls, 2.58 +/- 4.19% after systemic capsaicin, P < 0.05) and decreased by perivagal capsaicin (18.72 +/- 4.75%, P < 0.05). Atropine almost completely prevented the cardiac response to distension, while propranolol and bretylium partially blocked it, implying the response is primarily mediated by cholinergic efferents but also involves adrenergic pathways. We conclude that unmyelinated, capsaicin-sensitive vagal afferents are essential to the pseudoaffective cardioautonomic response to a noxious gastric stimulus.

The Pattern of Sympathovagal Balance Explored in the Frequency Domain

In most physiological conditions, sympathetic and vagal activities modulating heart period undergo a reciprocal regulation, leading to the concept of sympathovagal balance. This pattern can be indirectly quantified by computing the spectral powers of the oscillatory components corresponding to respiratory acts (high frequency) and to vasomotor waves (low frequency) present in heart rate variability.

Stomach distension increases efferent muscle sympathetic nerve activity and blood pressure in healthy humans

Although the enteric nervous system is usually described as a separate and independent entity, animal studies show that gastric distension causes a reflex increase in arterial pressure and a sympathetically mediated increase in heart rate and peripheral vascular resistance. To assess the influence of gastric distension on sympathetic outflow and blood pressure, we recorded muscle sympathetic nerve activity (MSNA) from the peroneal nerve by microneurography in eight healthy volunteers. The stomach was distended by means of a barostat, using a single staircase protocol by which pressure was increased by 2 mmHg every 3 min. Gastric sensory function was assessed at each distension step by using a visual analog scale (VAS) for sensations of fullness, nausea and pain. For comparison, we also performed a cold pressor test. The MSNA increased on barostat-induced gastric distension with an almost concomitant elevation of blood pressure. The increase in both was proportional to the intragastric pressure and both decreased towards initial values after the end of distension. Heart rate increased inconsistently and only at higher distension pressures that were associated with high VAS scores. The opposite was found for the cold pressor test. The results of this study confirm the existence of a functional relationship between gastrointestinal distension and cardiovascular function. Decrease in this gastrovascular response may play a role in postprandial hypotension in the elderly, since the MSNA responses to simulated microgravity decrease with age.

Individual recognition by heart rate variability of two different autonomic profiles related to posture

BACKGROUND

Power spectrum analysis of heart rate variability (HRV) can estimate the state of sympathovagal balance modulating sinus node activity. In view of the large distribution of spectral variables, a recognition of well-defined physiological conditions has never been attempted on an individual basis.

METHODS AND RESULTS

We considered 10 spectral variables extracted from short segments (200 to 500 cardiac cycles) of 350 ECG tracings recorded in normal subjects in both supine and upright positions (700 patterns). The tracings were first ordered consecutively and subsequently assigned alternatively to a training or to a test set (each consisting of 175 cases, providing 350 patterns considered to be independent). A forecasting linear method estimated a normalized activation index (ranging from -1 for supine to +1 for upright) that concentrated the information derived from spectral variables and that identified, in the test set, individual by individual, approximately 84% of corresponding body postures.

CONCLUSIONS

The combined use of spectral methodology and forecasting analysis has revealed an information content embedded, per se, in a short series of RR intervals capable of recognizing, individual by individual, two different autonomic profiles related to posture.