Chemo- and ergoreflexes in health, disease and ageing

Autonomic and respiratory consequences of altered chemoreflex function: clinical and therapeutic implications in cardiovascular diseases

The importance of chemoreflex function for cardiovascular health is increasingly recognized in clinical practice. The physiological function of the chemoreflex is to constantly adjust ventilation and circulatory control to match respiratory gases to metabolism. This is achieved in a highly integrated fashion with the baroreflex and the ergoreflex. The functionality of chemoreceptors is altered in cardiovascular diseases, causing unstable ventilation and apnoeas and promoting sympathovagal imbalance, and it is associated with arrhythmias and fatal cardiorespiratory events. In the last few years, opportunities to desensitize hyperactive chemoreceptors have emerged as potential options for treatment of hypertension and heart failure. This review summarizes up to date evidence of chemoreflex physiology/pathophysiology, highlighting the clinical significance of chemoreflex dysfunction, and lists the latest proof of concept studies based on modulation of the chemoreflex as a novel target in cardiovascular diseases.

A Methodological Perspective on the Function and Assessment of Peripheral Chemoreceptors in Heart Failure: A Review of Data from Clinical Trials

Augmented peripheral chemoreceptor sensitivity (PChS) is a common feature of many sympathetically mediated diseases, among others, and it is an important mechanism of the pathophysiology of heart failure (HF). It is related not only to the greater severity of symptoms, especially to dyspnea and lower exercise tolerance but also to a greater prevalence of complications and poor prognosis. The causes, mechanisms, and impact of the enhanced activity of peripheral chemoreceptors (PChR) in the HF population are subject to intense research. Several methodologies have been established and utilized to assess the PChR function. Each of them presents certain advantages and limitations. Furthermore, numerous factors could influence and modulate the response from PChR in studied subjects. Nevertheless, even with the impressive number of studies conducted in this field, there are still some gaps in knowledge that require further research. We performed a review of all clinical trials in HF human patients, in which the function of PChR was evaluated. This review provides an extensive synthesis of studies evaluating PChR function in the HF human population, including methods used, factors potentially influencing the results, and predictors of increased PChS.

Effects of respiratory muscle training on parasympathetic activity in diabetes mellitus

This study verified the effects of respiratory muscle training (RMT) on hemodynamics, heart rate (HR) variability, and muscle morphology in rats with streptozotocin-induced diabetes mellitus (DM). Thirty-six male Wistar rats were randomized into 4 groups and 34 completed the study: i) sham-sedentary (Sham-ST; n=9); ii) sham-RMT (Sham-RMT; n=9); iii) DM-sedentary (DM-ST; n=8); and iv) DM-RMT (DM-RMT; n=8). Hemodynamics were assessed by central cannulation, and R-R intervals were measured by electrocardiogram. In addition, the effects of RMT on the cross-sectional area of the diaphragm, anterior tibial, and soleus muscles were analyzed. The induction of DM by streptozotocin resulted in weight loss, hyperglycemia, reduced blood pressure, and attenuated left ventricular contraction and relaxation (P<0.05). We also observed a decrease in root mean square of successive differences between adjacent RR intervals (RMSSD) index and in the cross-sectional area of the muscles assessed, specifically the diaphragm, soleus, and anterior tibial muscles in diabetic rats (P<0.05). Interestingly, RMT led to an increase in RMSSD in rats with DM (P<0.05). The induction of DM produced profound deleterious changes in the diaphragmatic and peripheral muscles, as well as impairments in cardiovascular hemodynamics and autonomic control. Nevertheless, RMT may beneficially attenuate autonomic changes and improve parasympathetic modulation.

The alpha-melanocyte stimulating hormone is related to heart rate during exercise recovery

Alpha-melanocyte-stimulating hormone (alpha-MSH) is a part of the hormonal stress system with proven cardiovascular effects. Heart rate recovery (HRR) following exercise is strongly correlated to overall fitness and future adverse cardiovascular events. The current study examined the predictive value of alpha-MSH for HRR following exercise testing.Cardiopulmonary exercise testing (CPET) on a treadmill was used to measure HR and oxygen consumption (V̇O2) in 16 elite male wrestlers (W), 21 water polo player (WP) and 20 sedentary subjects (C) matched for age. Plasma levels of alpha-MSH were measured by radioimmunoassay technique in four phases of CPET: 1) 10 min pre-CPET at rest; 2) at the initation of CPET; 3) at peak CPET; and 4) at the third minute of recovery. The WP group had significantly higher HRR compared to than W and C groups, who did not have significantly different values. Significant difference in alpha-MSH measurements and patterns during CPET between groups was not observed (p > 0.05). When combining all three groups, we observed a significant correlation between V̇O2 recovery and alpha-MSH recovery/peak (r = -0.3, p = 0.022). HRR and ΔHRR/peak significantly correlated with alpha-MSH at all four measurment points (r = -0.4; p < 0.01 for all). On multiple regression analysis, which included anthropometric and hormonal measures, the best independent predictor of HRR and ΔHRR/peak was alpha-MSH during recovery (B = -1.0, -0.5; SE = 0.3, 0.1; CI = -1.5 to -0.4, -0.7 to -0.2; p = 0.001 respectively). In conclusion, alpha-MSH measured during exercise recovery holds predictive value for HRR and ΔHRR/peak, suggesting a contributing role to integrative regulation of overall cardiopulmonary performance.

CONDENSED ABSTRACT

Present study examined the predictive value of alpha-melanocyte stimulating hormone (alpha-MSH) for heart rate recovery (HRR) in elite male wrestlers, water polo players and sedentary subjects matched for age. Alpha-MSH measured during exercise recovery holds predictive value for HRR and ΔHRR/peak, suggesting a contributing role to integrative regulation of overall cardiopulmonary performance.

Autonomic innervation of the carotid body as a determinant of its sensitivity: implications for cardiovascular physiology and pathology

The motivation for this review comes from the emerging complexity of the autonomic innervation of the carotid body (CB) and its putative role in regulating chemoreceptor sensitivity. With the carotid bodies as a potential therapeutic target for numerous cardiorespiratory and metabolic diseases, an understanding of the neural control of its circulation is most relevant. Since nerve fibres track blood vessels and receive autonomic innervation, we initiate our review by describing the origins of arterial feed to the CB and its unique vascular architecture and blood flow. Arterial feed(s) vary amongst species and, unequivocally, the arterial blood supply is relatively high to this organ. The vasculature appears to form separate circuits inside the CB with one having arterial venous anastomoses. Both sympathetic and parasympathetic nerves are present with postganglionic neurons located within the CB or close to it in the form of paraganglia. Their role in arterial vascular resistance control is described as is how CB blood flow relates to carotid sinus afferent activity. We discuss non-vascular targets of autonomic nerves, their possible role in controlling glomus cell activity, and how certain transmitters may relate to function. We propose that the autonomic nerves sub-serving the CB provide a rapid mechanism to tune the gain of peripheral chemoreflex sensitivity based on alterations in blood flow and oxygen delivery, and might provide future therapeutic targets. However, there remain a number of unknowns regarding these mechanisms that require further research that is discussed.

Passive bilateral leg cycling with concomitant regional circulatory occlusion for testing mechanoreflex-metaboreflex interactions in humans

Purpose

The exercise pressor reflex (EPR) plays a fundamental role in physiological reactions to exercise in humans and in the pathophysiology of cardiovascular disorders. There is no “gold standard” method for EPR assessment; therefore, we propose a new protocol for testing interactions between the muscle mechanoreflex and metaboreflex (major components of EPR).

Methods

Thirty-four healthy subjects (mean age [± standard deviation] 24 ± 4 years, 22 men) were enrolled in the study. During the study, the hemodynamic and ventilatory parameters of these subjects were continuously monitored using our proposed assessment method. This assessment method consists of an initial 5-min rest period (baseline) followed by 5 min of passive cycling (PC) on an automated cycle ergometer (mechanoreceptor stimulation), after which tourniquet cuffs located bilaterally on the upper thighs are inflated for 3 min to evoke venous and arterial regional circulatory occlusion (CO) during PC (metaboreceptor stimulation). Deflation of the tourniquet cuffs is followed by a second 5 min of PC and finally by a 5-min recovery time. The control test comprises a 5-min rest period, followed by 3 min of CO only and a final 5-min recovery.

Results

Mean arterial pressure (MAP) and minute ventilation (MV) increased significantly during PC (MAP: from 90 ± 9.3 to 95 ± 9.7 mmHg; MV: from 11.5 ± 2.5 to 13.5 ± 2.9 L/min; both p < 0.05) and again when CO was applied (MAP: from 95 ± 9.7 to 101 ± 11.0 mmHg; MV: from 13.5 ± 2.9 to 14.8 ± 3.8 L/min; both p < 0.05). In the control test there was a slight increase in MAP during CO (from 92 ± 10.5 to 94 ± 10.0 mmHg; p < 0.05) and no changes in the ventilatory parameters.

Conclusion

Bilateral leg passive cycling with concomitant circulatory occlusion is a new, simple and effective method for testing interactions between the mechanoreflex and metaboreflex in humans.

Electronic supplementary material

The online version of this article (10.1007/s10286-020-00717-x) contains supplementary material, which is available to authorized users.

Exercise intolerance in comorbid COPD and heart failure: the role of impaired aerobic function

Impaired aerobic function is a potential mechanism of exercise intolerance in patients with combined cardiorespiratory disease. We investigated the pathophysiological and sensory consequences of a low change in oxygen uptake (ΔV'_O2 )/change in work rate (ΔWR) relationship during incremental exercise in patients with coexisting chronic obstructive pulmonary disease (COPD) and systolic heart failure (HF).After clinical stabilisation, 51 COPD-HF patients performed an incremental cardiopulmonary exercise test to symptom limitation. Cardiac output was non-invasively measured (impedance cardiography) in a subset of patients (n=18).27 patients presented with ΔV'_O2 /ΔWR below the lower limit of normal. Despite similar forced expiratory volume in 1 s and ejection fraction, the low ΔV'_O2 /ΔWR group showed higher end-diastolic volume, lower inspiratory capacity and lower transfer factor compared to their counterparts (p<0.05). Peak WR and peak V'_O2 were ∼15% and ∼30% lower, respectively, in the former group: those findings were associated with greater symptom burden in daily life and at a given exercise intensity (leg discomfort and dyspnoea). The low ΔV'_O2 /ΔWR group presented with other evidences of impaired aerobic function (sluggish V'_O2 kinetics, earlier anaerobic threshold) and cardiocirculatory performance (lower oxygen pulse, lower stroke volume and cardiac output) (p<0.05). Despite similar exertional hypoxaemia, they showed worse ventilatory inefficiency and higher operating lung volumes, which led to greater mechanical inspiratory constraints (p<0.05).Impaired aerobic function due to negative cardiopulmonary-muscular interactions is an important determinant of exercise intolerance in patients with COPD-HF. Treatment strategies to improve oxygen delivery to and/or utilisation by the peripheral muscles might prove particularly beneficial to these patients.

Ventilatory response to exercise in cardiopulmonary disease: the role of chemosensitivity and dead space

The lungs and heart are irrevocably linked in their oxygen (O₂) and carbon dioxide (CO₂) transport functions. Functional impairment of the lungs often affects heart function and vice versa The steepness with which ventilation (V'_E) rises with respect to CO₂ production (V'_CO2 ) (i.e. the V'_E/V'_CO2 slope) is a measure of ventilatory efficiency and can be used to identify an abnormal ventilatory response to exercise. The V'_E/V'_CO2 slope is a prognostic marker in several chronic cardiopulmonary diseases independent of other exercise-related variables such as peak O₂ uptake (V'_O2 ). The V'_E/V'_CO2 slope is determined by two factors: 1) the arterial CO₂ partial pressure (P_aCO2 ) during exercise and 2) the fraction of the tidal volume (V_T) that goes to dead space (V_D) (i.e. the physiological dead space ratio (V_D/V_T)). An altered P_aCO2 set-point and chemosensitivity are present in many cardiopulmonary diseases, which influence V'_E/V'_CO2 by affecting P_aCO2 Increased ventilation-perfusion heterogeneity, causing inefficient gas exchange, also contributes to the abnormal V'_E/V'_CO2 observed in cardiopulmonary diseases by increasing V_D/V_T During cardiopulmonary exercise testing, the P_aCO2 during exercise is often not measured and V_D/V_T is only estimated by taking into account the end-tidal CO₂ partial pressure (P_ETCO2 ); however, P_aCO2 is not accurately estimated from P_ETCO2 in patients with cardiopulmonary disease. Measuring arterial gases (P_aO2 and P_aCO2 ) before and during exercise provides information on the real (and not "estimated") V_D/V_T coupled with a true measure of gas exchange efficiency such as the difference between alveolar and arterial O₂ partial pressure and the difference between arterial and end-tidal CO₂ partial pressure during exercise.

Exercise training attenuates the pressor response evoked by peripheral chemoreflex in rats with heart failure

The effects of exercise training (ExT) on the pressor response elicited by potassium cyanide (KCN) in the rat model of ischemia-induced heart failure (HF) are unknown. We evaluated the effects of ExT on chemoreflex sensitivity and its interaction with baroreflex in rats with HF. Wistar rats were divided into four groups: trained HF (Tr-HF), sedentary HF (Sed-HF), trained sham (Tr-Sham), and sedentary sham (Sed-Sham). Trained animals underwent to a treadmill running protocol for 8 weeks (60 m/day, 5 days/week, 16 m/min). After ExT, arterial pressure (AP), baroreflex sensitivity (BRS), peripheral chemoreflex (KCN: 100 μg/kg body mass), and cardiac function were evaluated. The results demonstrate that ExT induces an improvement in BRS and attenuates the pressor response to KCN relative to the Sed-HF group (P < 0.05). The improvement in BRS was associated with a reduction in the pressor response following ExT in HF rats (P < 0.05). Moreover, ExT induced a reduction in left ventricular end-diastolic pressure and pulmonary congestion compared with the Sed-HF group (P < 0.05). The pressor response to KCN in the hypotensive state is decreased in sedentary HF rats. These results suggest that ExT improves cardiac function and BRS and attenuates the pressor response evoked by KCN in HF rats.

Chemoreflex physiology and implications for sleep apnoea: insights from studies in humans

NEW FINDINGS

What is the topic of this review? This review summarizes chemoreflex physiology in health and disease, with specific focus on chemoreflex-mediated pathophysiology in obstructive and central sleep apnoea. What advances does it highlight? Chemoreflex mechanisms are thought to contribute significantly to the pathophysiology and adverse outcomes seen in sleep apnoea. Clinical implications of altered chemoreflex function in sleep apnoea from recent studies in humans, including cardiac arrhythmias, coronary artery disease, systolic/diastolic heart failure and sudden cardiac death are highlighted. Activation of the chemoreflex in response to hypoxaemia results in an increase in sympathetic neural outflow. This process is predominantly mediated by the peripheral chemoreceptors in the carotid bodies and is potentiated by the absence of the sympatho-inhibitory influence of ventilation during apnoea, as is seen in patients with sleep apnoea. In these patients, repetitive nocturnal hypoxaemia and apnoea elicit sympathetic activation, which may persist into wakefulness and is thought to contribute to the development of systemic hypertension and cardiac and vascular dysfunction. Chemoreflex activation could possibly lead to adverse cardiovascular outcomes, such as nocturnal myocardial infarction, systolic and/or diastolic heart failure, cardiac arrhythmias and sudden death in patients with sleep apnoea. This review summarizes chemoreflex physiology in health and disease, with specific focus on chemoreflex-mediated pathophysiology in obstructive and central sleep apnoea. Measurement of the chemoreflex response may serve as a potential avenue for individualized screening for cardiovascular disease. Whether modulation of this response in sleep apnoea may aid in the prevention and treatment of adverse cardiovascular consequences will require further study.

Age-related reflex responses from peripheral and central chemoreceptors in healthy men

Objective

The study aimed: (i) to characterize reflex responses from peripheral and central chemoreceptors in different age groups of healthy men (<50 years old vs ≥50 years old) and, (ii) to assess, within these groups, whether there is any relationship between ventilatory and hemodynamic responses from chemoreceptors and indices of autonomic nervous system (ANS).

Methods

Peripheral chemoreflex sensitivity was assessed by the transient hypoxia method and respiratory, heart rate (HR) and blood pressure responses were calculated. Central chemoreflex sensitivity was assessed by the rebreathing method and respiratory response was calculated. ANS was assessed using heart rate variability indices and baroreflex sensitivity (BRS).

Results

Sixty-seven healthy men were divided into 2 groups: <50 years (n = 38, mean age: 32 ± 10 years) and ≥50 years (n = 29, mean age: 61 ± 8 years). There were no differences in respiratory response from central and peripheral chemoreceptors between the older and younger groups of healthy males. We found a significantly different pattern of hemodynamic responses from peripheral chemoreceptors between the older and the younger groups. The former expressed attenuated HR acceleration and exaggerated blood pressure increase in response to transient hypoxia. Blunted HR response was related to reduced BRS and sympathovagal imbalance characterized by reduced vagal tone. Blood pressure responses seemed to be independent of sympathovagal balance and BRS.

Interpretation

Ageing impacts hemodynamic rather than respiratory response from chemoreceptors. Impaired arterial baroreflex and sympathovagal imbalance related to ageing may contribute to decreased heart rate response, but not to increased blood pressure response from peripheral chemoreceptors.

Role of the carotid body in the pathophysiology of heart failure

Important recent advances implicate a role of the carotid body (CB) chemoreflex in sympathetic and breathing dysregulation in several cardio-respiratory diseases, drawing renewed interest in its potential implications for clinical treatment. Evidence from both chronic heart failure (CHF) patients and animal models indicates that the CB chemoreflex is enhanced in CHF, and contributes to the tonic elevation in sympathetic nerve activity (SNA) and periodic breathing associated with the disease. Although this maladaptive change likely derives from altered function at all levels of the reflex arc, a change in afferent function of the CB is likely to be a main driving force. This review will focus on recent advances in our understanding of the pathophysiological mechanisms that alter CB function in CHF and their potential translational impact on treatment of chronic heart failure (CHF).

[Clinical relevance of cardiopulmonary reflexes in anesthesiology]

The baroreflex, chemoreflex, pulmonary reflexes, Bezold-Jarisch and Bainbridge reflexes and their interaction with local mechanisms, are a demonstration of the richness of cardiovascular responses that occur in human beings. As well as these, the anesthesiologist must contend with other variables that interact by attenuating or accentuating cardiopulmonary reflexes such as, anesthetic drugs, surgical manipulation, and patient positioning. In the present article we review these reflexes and their clinical relevance in anesthesiology.

Efficacy of multiparametric telemonitoring on respiratory outcomes in elderly people with COPD: a randomized controlled trial

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a highly prevalent condition associated with a high health care resource consumption and health care expenditures, driven mainly by exacerbations-related hospitalizations. Telemedicine has been proposed as a mean for timely detection of exacerbation, but the available evidence is inadequate to provide conclusive information on its efficacy. The aim of this study is to evaluate the efficacy of a telemonitoring system in reducing COPD-related hospitalizations in an elderly population with COPD.

METHODS

This is a parallel arms, randomized trial including patients aged 65 or older with COPD in GOLD stages II and III enrolled in a Pulmonary Medicine outpatient facility. Patients were randomly assigned to receive a non-invasive system able to telemonitor vital signs (oxygen saturation, heart rate, near-body temperature, overall physical activity) or standard care, and were followed up for 9 months. The outcome measures were the number of exacerbations and exacerbation-related hospitalization.

RESULTS

Fifty patients were included in the telemonitoring group and 49 in the control group. The incidence rate of respiratory events was 28/100 person/years in the telemonitoring group vs. 42/100 person/years in the control group (incidence rate ratio: 0.67, 95% CI: 0.32 - 1.36). The corresponding figures for hospital admissions where 13/100 person/years and 20/100 person/years, respectively (IRR: 0.66, 95% CI: 0.21 - 1.86).

CONCLUSIONS

In our study, COPD patients followed up with the aid of a multiparametric remote monitoring system experienced a lower rate of exacerbations and COPD-related hospitalizations compared to patients followed up using the standard model of care. These results need to be replicated in larger studies before they can be applied to the general COPD population.

TRIAL REGISTRATION NUMBER

NCT01481506 (clinicaltrials.gov).

FUNDING

co-financed by Lazio Region and Intersistemi Inc.

Evaluation of arterial blood gases and arterial blood pressures in brachycephalic dogs

BACKGROUND

Brachycephalic dogs (BD) are prone to congenital upper airway obstruction (brachycephalic syndrome, BS). In humans suffering from sleep apnea, upper airway obstruction is known to cause hypertension. There is no information regarding the influence of BS in dogs on cardiorespiratory physiology.

HYPOTHESIS

BD are prone to lower P(a) O(2), higher P(a) CO (2), and hypertension compared with meso- or dolicocephalic dogs (MDD).

ANIMALS

Eleven BD and 11 MDD.

METHODS

After a questionnaire was completed by the owner, a physical examination was performed. Height and thoracic circumferences were measured. Arterial blood gases, electrolyte concentrations, and packed cell volume (PCV) were measured. Systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressure recordings were performed.

RESULTS

A total of 7 French and 4 English bulldogs met the inclusion criteria. The control group consisted in 6 Beagles, 2 mixed breed dogs, 1 Staffordshire Bull Terrier, 1 Parson Russell Terrier, and 1 Australian Cattle Dog. Statistically, BD had lower P(a) O(2), higher P(a) CO2, and higher PCV when compared with controls (86.2 ± 15.9 versus 100.2 ± 12.6 mmHg, P = .017; 36.3 ± 4.6 versus 32.7 ± 2.6 mmHg, P = .019; 48.2 ± 3.5 versus 44.2 ± 5.4%, P = .026, respectively). Also, they had significantly higher SAP (177.6 ± 25.0 versus 153.5 ± 21.7 mmHg, P = .013), MAP (123.3 ± 17.1 versus 108.3 ± 12.2 mmHg, P = .014), and DAP (95.3 ± 19.2 versus 83.0 ± 11.5 mmHg, P = .042). BD with a P(a) CO (2) >35 mmHg were significantly older than those with a P(a) CO (2) ≤35 mmHg (58 ± 16 and 30 ± 11 months, P = .004).

CONCLUSION

Results of this study suggest that some BD are prone to lower P(a) O(2), higher P(a) CO (2), and hypertension when compared with MDD. Age may be a contributing factor.

Cardiac resynchronization therapy reduces metaboreflex contribution to the ventilatory response in heart failure population

Background. Metaboreflex overactivation has been proprosed to explain exaggerated hyperventilation in heart failure population. We investigated the metaboreflex activation after cardiac resynchronization therapy (CRT). Methods. 10 heart failure patients (mean left ventricular ejection fraction (LVEF) 27 ± 4%) schedulded for CRT implantation were prospectively studied. At baseline and after 6 month follow up two maximal cardiopulmonary exercise tests with and without regional circulatory occlusion (RCO) during recovery were performed. RCO was achieved by inflation of bilateral upper thigh tourniquets 30 mmHg above peak systolic blood pressure during 3 minutes after peak exercise. Metaboreflex contribution to the ventilatory response was assessed as the difference in ventilatory data at the third minute during recovery between the two tests (Δ). Results. Patients had enhanced VE/VCO(2) slope (40 ± 9) and an evident metaboreflex contribution to the high ventilatory response (ΔVE: 3 ± 4 L/min; P = 0.05, ΔRR: 4.5 ± 4/min; P = 0.003 and ΔVE/VCO(2): 5.5 ± 4; P = 0.007). 6 months after CRT implantation, NYHA class, LVEF, peak VO(2) and VE/VCO(2) were significantly improved (1.4 ± 0.5; P < 0.001, 42 ± 7%; P < 0.001, 16.5 ± 3 mL/kg/min; P = 0.003; 33 ± 10; P = 0.01). Metaboreflex contribution to VE, RR, and VE/VCO(2) was reduced compared with baseline (P = 0.08, P = 0.01 and P = 0.4 resp.). Conclusion. 6 months after CRT metaboreflex contribution to the ventilatory response is reduced.

Neurohumoral stimulation

The temporal relationship between the development of heart failure and activation of the neurohumoral systems involved in chronic heart failure (CHF) has not been precisely defined. When a compensatory mechanism switches to a deleterious contributing factor in the progression of the disease is unclear. This article addresses these issues through evaluating the contribution of various cardiovascular reflexes and cellular mechanisms to the sympathoexcitation in CHF. It also sheds light on some of the important central mechanisms that contribute to the increase in sympathetic nerve activity in CHF.

Influence of locomotor muscle metaboreceptor stimulation on the ventilatory response to exercise in heart failure

BACKGROUND

Whether locomotor muscle afferent neural activity contributes to exercise hyperpnea and symptoms of dyspnea in heart failure (HF) is controversial. We examined the influence of metaboreceptor stimulation on ventilation with and without maintaining end-exercise end-tidal CO(2) levels.

METHODS AND RESULTS

Eleven patients with HF aged 51+/-5 years (ejection fraction, 32+/-3%; New York Heart Association class, 1.6+/-0.2) and 11 age- and gender-matched healthy control participants aged 43+/-3 years were studied. Participants underwent 3 steady-state cycling sessions at 60% of peak oxygen consumption for 4 minutes. The first exercise session was a baseline control trial. Bilateral thigh tourniquets were inflated to suprasystolic pressure at end exercise for 2 minutes during 2 of the trials (regional circulatory occlusion) with the addition of inspired CO(2) to maintain end-exercise partial pressure of end-tidal CO(2) during 1 trial (regional circulatory occlusion+CO(2)). Minute ventilation was measured continuously throughout each trial. At 2 minutes postexercise during the baseline control trial in patients with HF, minute ventilation was 54% of end exercise, whereas the control group averaged 41% (P=0.11). During regional circulatory occlusion in patients with HF, minute ventilation was 60% of end exercise; however, the control group averaged 35% (P<0.001). During regional circulatory occlusion+CO(2), the minute ventilation of patients with HF averaged 67% of end exercise, whereas the control group averaged 44% (P<0.001).

CONCLUSIONS

These data suggest that increased afferent neural activity from the large locomotor muscles associated with metabolites generated during exercise contribute to the augmented ventilatory response to exercise in patients with HF.

Carotid barochemoreceptor pathological findings regarding carotid plaque status and aging

BACKGROUND

Carotid barochemoreceptor pathological lesions have been studied in animals, but few human necropsies have been performed. Therefore, data rely on case patients following surgery, radiotherapy and carotid endarterectomy. Almost no data are available regarding whether the effect of aging prevails over pathological conditions, despite the classic description that glomic fibrosis increases with age.

OBJECTIVE

To morphometrically characterize the alterations of the carotid barochemoreceptors and their supplying arteries.

METHODS

Patients (n=23) who had suffered and died from stroke, with and without complicated internal carotid atheromatosis, were divided by age (group 1: older than 80 years; group 2: 65 to 80 years; and group 3: younger than 65 years). Carotid segments were obtained at autopsy. The specimens were stained for light microscopy and immunohistochemistry.

RESULTS

Carotid glomus presented from moderate-to-severe atrophy and fibrosis. A focal decrease in vascularization (CD34-positive) of the glomus (greater than 50%) was observed in areas of atrophy and fibrosis. Damaged nerve endings (S100 protein-positive) were observed at the media of the carotid sinus. Morphometric data showed no differences between groups for glomus area, number of type 1 and 2 cells, and the wall to lumen arteriole ratio. No statistical differences were demonstrated in the pathological findings of the carotid glomus when comparing complicated with noncomplicated plaques or age groups.

CONCLUSION

Severe carotid chemoreceptor damage exists in patients who have died from stroke and suffered from carotid atheromatosis. These findings were independent from aging and plaque type. However, damage was correlated with a marked narrowing of the supplying arterioles as a consequence of hemodynamic and/or metabolic alterations (dyslipidemia, diabetes).

Multimodal signal processing for the analysis of cardiovascular variability

Cardiovascular (CV) variability as a primary vital sign carrying information about CV regulation systems is reviewed by pointing out the role of the main rhythms and the various control and functional systems involved. The high complexity of the addressed phenomena fosters a multimodal approach that relies on data analysis models and deals with the ongoing interactions of many signals at a time. The importance of closed-loop identification and causal analysis is remarked upon and basic properties, application conditions and methods are recalled. The need of further integration of CV signals relevant to peripheral and systemic haemodynamics, respiratory mechanics, neural afferent and efferent pathways is also stressed.

Current concepts of neurohormonal activation in heart failure: mediators and mechanisms

Neurohormonal activation is a commonly cited array of phenomena in the body's physiologic response to heart failure. Although various neurohormones and pharmacologic agents that moderate their pathophysiologic effects have been reviewed in the nursing literature, both the mechanisms of neurohormonal system activation and cellular and organ system effects have been described only in brief. Accordingly, this article reviews mechanisms of neurohormonal activation and describes cellular and cardiovascular effects of the (1) sympathetic nervous system, (2) renin-angiotensin-aldosterone system, (3) kallikrein-kininogen-kinin system, (4) vasopressinergic system, (5) natriuretic peptide systems, and (6) endothelin in the context of heart failure. This article implicitly details the physiologic basis for numerous current and potential future pharmacologic agents used in the management of heart failure. It is intended that this article be used as a reference for advanced clinical nursing practice, research, and education.

The respiratory responses to the combined activation of the muscle metaboreflex and the ventilatory chemoreflex

The excessive hyperventilation seen during exercise in chronic heart failure (CHF) contributes to the limited exercise capacity in this condition. The hyperactivation of reflexes originating, independently, from muscle (ergoreflex) and from chemoreceptors (chemoreflex) has been suggested to play an important part in the mediation of the CHF ventilatory abnormalities. In this study we aimed to assess the ventilatory responses to the combined activation of the muscle ergoreflex and the ventilatory chemoreflex, achieved by post-exercise circulatory occlusion (PECO) and euoxic hypercapnia (end-tidal PCO(2) = 7 mmHg above normal), respectively.Three healthy women and three healthy men (29.33 +/- 1.28 yrs; mean +/- SD) undertook four trials, in random order, separated from each other by 30 min of rest: 2 min of isometric handgrip exercise followed by 2 min of PECO with hypercapnia, 2 min of isometric handgrip exercise followed by 2 min of PECO while breathing room air, 4 min of rest with hypercapnia and 4 min of rest while breathing room air.Ventilation (V(E)) was significantly elevated by the ventilatory chemoreflex and it was further elevated by 5.13+/-0.83 L/min (P<0.05) when the muscle ergoreflex was superimposed upon it. The response to the combination of these stimuli was significantly greater than the sum of the responses to the two stimuli when given independently (P<0.05).The results indicate that the interaction between the two reflexes has an additional stimulatory effect on ventilation and consequently could be involved in the limited exercise capacity in CHF.

Reduced peripheral skeletal muscle mass and abnormal reflex physiology in chronic heart failure

BACKGROUND

The muscle hypothesis implicates abnormalities in peripheral muscle as a source for the stimulus to the symptoms and reflex abnormalities seen in chronic heart failure (CHF). We investigated the relationship between skeletal muscle mass (with dual-energy x-ray absorptiometry) and activation of the ergoreflex (a peripheral reflex originating in skeletal muscle sensitive to products of muscle work) in CHF patients and whether this rapport is affected by the progression of the syndrome.

METHODS AND RESULTS

We assessed 107 consecutive CHF patients (mean age, 61.9+/-10.9 years; 95% male; 25 cachectics) and 24 age-matched normal subjects (mean age, 59.0+/-11.1 years; 91% male). Compared with normal subjects, patients had a higher ergoreflex (in ventilation, 6.2+/-.6.1 versus 0.6+/-0.6 L/min; P<0.0001) and a reduction in muscle mass (51.9+/-10.0 versus 60.3+/-8.8 kg; P<0.001). The ergoreflex was particularly overactive in cachectics (P<0.05), accompanied by marked muscle mass depletion (P<0.0005). In CHF, ergoreceptor hyperresponsiveness in both the arm and leg correlated with reduced muscle mass, abnormal indexes of exercise tolerance (peak V(O2), V(E)/V(CO2) slope), ejection fraction, and NYHA functional class (P<0.0001). In the cachectic population, the ventilatory response from ergoreflex to arm exercise was strongly inversely correlated with arm (r=-0.65), leg (r=-0.64), and total (r=-0.61) lean tissues (P<0.001 for all). Multivariate analysis showed that these relationships were independent of NYHA class, peak V(O2), and V(E)/V(CO2) slope.

CONCLUSIONS

Depleted peripheral muscle mass is associated with ergoreflex overactivity and exercise limitation in CHF, particularly in cachectic patients. The systemic activation of the muscle reflex system in CHF may reflect progression and deterioration of the clinical syndrome.

Prognostic impact of autonomic information flow in multiple organ dysfunction syndrome patients

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is the sequential failure of several organ systems after a trigger event, like cardiogenic shock or decompensated heart failure. Mortality is high, up to 70%. Autonomic dysfunction (AD) may substantially contribute to the development of MODS. In cardiology, it has recently been shown that nonlinear parameters could predict mortality. Our study aimed at 1. characterising the complex characteristics of AD of critically ill MODS patients by the nonlinear parameters of autonomic information flow (AIF), 2. comparing AIF with autonomic function of healthy controls, and 3. characterising the accuracy of this parameter in predicting mortality in MODS.

METHODS

We enrolled 43 score-defined MODS patients who were consecutively admitted to a twelve-bed medical intensive care unit in a university centre into this prospective outcome study. Additionally, we assigned 50 healthy controls to the study. AIF was assessed as a complexity function of AD using 24-h ECG. Measures of AIF were introduced according to the standard HRV concept. The patients were followed up for 28-day mortality.

RESULTS

MODS causes a disorganisation of short term AIF in favour of an enhanced (rigid) long term AIF. Concerning prognosis increased short term AIF was associated with survival. Short term AIF discriminated between MODS survivors and non-survivors at the level of APACHE II score.

CONCLUSIONS

This is the first study providing evidence that complex AD of MODS patients is specifically assessed by AIF time scales and that AIF has significant prognostic impact.