Daytime Cheyne-Stokes Respiration in Ambulatory Patients With Severe Congestive Heart Failure Is Associated With Increased Mortality

A Review on Recent Advancements of Biomedical Radar for Clinical Applications

The field of biomedical radar has witnessed significant advancements in recent years, paving the way for innovative and transformative applications in clinical settings. Most medical instruments invented to measure human activities rely on contact electrodes, causing discomfort. Thanks to its non-invasive nature, biomedical radar is particularly valuable for clinical applications. A significant portion of the review discusses improvements in radar hardware, with a focus on miniaturization, increased resolution, and enhanced sensitivity. Then, this paper also delves into the signal processing and machine learning techniques tailored for radar data. This review will explore the recent breakthroughs and applications of biomedical radar technology, shedding light on its transformative potential in shaping the future of clinical diagnostics, patient and elderly care, and healthcare innovation.

Hypoxia sensing in the body: An update on the peripheral and central mechanisms

An adequate supply of O2 is essential for the maintenance of cellular activity. Systemic or local hypoxia can be experienced during decreased O2 availability or associated with diseases, or a combination of both. Exposure to hypoxia triggers adjustments in multiple physiological systems in the body to generate appropriate homeostatic responses. However, with significant reductions in the arterial partial pressure of O2, hypoxia can be life-threatening and cause maladaptive changes or cell damage and death. To mitigate the impact of limited O2 availability on cellular activity, O2 chemoreceptors rapidly detect and respond to reductions in the arterial partial pressure of O2, triggering orchestrated responses of increased ventilation and cardiac output, blood flow redistribution and metabolic adjustments. In mammals, the peripheral chemoreceptors of the carotid body are considered to be the main hypoxic sensors and the primary source of excitatory feedback driving respiratory, cardiovascular and autonomic responses. However, current evidence indicates that the CNS contains specialized brainstem and spinal cord regions that can also sense hypoxia and stimulate brain networks independently of the carotid body inputs. In this manuscript, we review the discoveries about the functioning of the O2 chemoreceptors and their contribution to the monitoring of O2 levels in the blood and brain parenchyma and mounting cardiorespiratory responses to maintain O2 homeostasis. We also discuss the implications of the chemoreflex-related mechanisms in paediatric and adult pathologies.

P2X3 receptor antagonism attenuates the progression of heart failure

Despite advances in the treatment of heart failure, prognosis is poor, mortality high and there remains no cure. Heart failure is associated with reduced cardiac pump function, autonomic dysregulation, systemic inflammation and sleep-disordered breathing; these morbidities are exacerbated by peripheral chemoreceptor dysfunction. We reveal that in heart failure the carotid body generates spontaneous, episodic burst discharges coincident with the onset of disordered breathing in male rats. Purinergic (P2X3) receptors were upregulated two-fold in peripheral chemosensory afferents in heart failure, and when antagonized abolished these episodic discharges, normalized both peripheral chemoreceptor sensitivity and the breathing pattern, reinstated autonomic balance, improved cardiac function, and reduced both inflammation and biomarkers of cardiac failure. Aberrant ATP transmission in the carotid body triggers episodic discharges that via P2X3 receptors play a crucial role in the progression of heart failure and as such offer a distinct therapeutic angle to reverse multiple components of its pathogenesis.

Prevalence and clinical characteristics of sleep-disordered breathing in patients with heart failure of different left ventricular ejection fractions

PURPOSES

The prevalence of sleep-disordered breathing (SDB) is high in patients with heart failure (HF), while the prevalence of SDB in HF with different left ventricular ejection fractions (LVEF) has rarely been reported. We aimed to explore the prevalence and clinical characteristics of SDB in patients with HF having different LVEF.

METHODS

Patients with stable HF were consecutively enrolled. All patients underwent portable overnight cardiorespiratory polygraphy and echocardiography. According to their LVEF, the patients were divided into the HFrEF (HF with reduced EF, EF < 40%), HFmrEF (HF with mid-range EF, 40 ≤ EF < 50), and HFpEF groups (HF with preserved EF, EF ≥ 50%). The prevalence and clinical data of SDB among the 3 groups were then compared.

RESULTS

A total of 252 patients, including 134 men, were enrolled in the study. The prevalence of SDB in patients with HF was 70%. Obstructive sleep apnea (OSA) was diagnosed in 48% and central sleep apnea (CSA) in 22%. The prevalence of SDB in the HFrEE, HFmrEF, and HFpEF groups was 86%, 86%, and 62%, respectively (P = 0.001). The prevalence of OSA among the 3 groups was 42%, 47%, and 49%, respectively (P = 0.708), while the prevalence of CSA among the 3 groups was 44%, 40%, and 13% (P < 0.001). Logistic regression analysis revealed that age and BMI were independent risk factors for OSA in patients with HF, while LVEF and smoking were independent risk factors for CSA in patients with HF. Correlational analyses revealed that LVEF was negatively correlated with apnea-hypopnea index (AHI) (r = -0.309, P < 0.001) and central apnea index (CAI) ( r = -0.558, P < 0.001), while there was no significant correlation with obstructive apnea index (OAI). The ROC curve revealed that LVEF could predict the occurrence of CSA and SDB, with AUC = 0.683 (95%CI 0.600-0.767, P < 0.001) and AUC = 0.630 (95%CI 0.559-0.702, P = 0.001), but not of OSA.

CONCLUSIONS

SDB was highly common in HF, and the prevalence of SDB was different in HF with different LVEF, mainly due to the difference in cardiac functions. The prevalence and severity of SDB in HFrEF and HFmrEF were significantly higher than those in HFpEF, which was mainly related to the increase in CSA. When HFmrEF was similar to HFrEF in cardiac functions, the prevalence, type, and severity of SDB were similar between the two groups. Changes in LVEF had a significant impact on CAI, but not on OAI. LVEF can predict the occurrence of CSA and SDB to a certain extent.

Pharmacological treatment for central sleep apnoea in adults

BACKGROUND

The term central sleep apnoea (CSA) encompasses diverse clinical situations where a dysfunctional drive to breathe leads to recurrent respiratory events, namely apnoea (complete absence of ventilation) and hypopnoea sleep (insufficient ventilation) during sleep. Studies have demonstrated that CSA responds to some extent to pharmacological agents with distinct mechanisms, such as sleep stabilisation and respiratory stimulation. Some therapies for CSA are associated with improved quality of life, although the evidence on this association is uncertain. Moreover, treatment of CSA with non-invasive positive pressure ventilation is not always effective or safe and may result in a residual apnoea-hypopnoea index.

OBJECTIVES

To evaluate the benefits and harms of pharmacological treatment compared with active or inactive controls for central sleep apnoea in adults.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 30 August 2022.

SELECTION CRITERIA

We included parallel and cross-over randomised controlled trials (RCTs) that evaluated any type of pharmacological agent compared with active controls (e.g. other medications) or passive controls (e.g. placebo, no treatment or usual care) in adults with CSA as defined by the International Classification of Sleep Disorders 3rd Edition. We did not exclude studies based on the duration of intervention or follow-up. We excluded studies focusing on CSA due to periodic breathing at high altitudes.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were central apnoea-hypopnoea index (cAHI), cardiovascular mortality and serious adverse events. Our secondary outcomes were quality of sleep, quality of life, daytime sleepiness, AHI, all-cause mortality, time to life-saving cardiovascular intervention, and non-serious adverse events. We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We included four cross-over RCTs and one parallel RCT, involving a total of 68 participants. Mean age ranged from 66 to 71.3 years and most participants were men. Four trials recruited people with CSA associated with heart failure, and one study included people with primary CSA. Types of pharmacological agents were acetazolamide (carbonic anhydrase inhibitor), buspirone (anxiolytic), theophylline (methylxanthine derivative) and triazolam (hypnotic), which were given for between three days and one week. Only the study on buspirone reported a formal evaluation of adverse events. These events were rare and mild. No studies reported serious adverse events, quality of sleep, quality of life, all-cause mortality, or time to life-saving cardiovascular intervention. Carbonic anhydrase inhibitors versus inactive control Results were from two studies of acetazolamide versus placebo (n = 12) and acetazolamide versus no acetazolamide (n = 18) for CSA associated with heart failure. One study reported short-term outcomes and the other reported intermediate-term outcomes. We are uncertain whether carbonic anhydrase inhibitors compared to inactive control reduce cAHI in the short term (mean difference (MD) -26.00 events per hour, 95% CI -43.84 to -8.16; 1 study, 12 participants; very low certainty). Similarly, we are uncertain whether carbonic anhydrase inhibitors compared to inactive control reduce AHI in the short term (MD -23.00 events per hour, 95% CI -37.70 to 8.30; 1 study, 12 participants; very low certainty) or in the intermediate term (MD -6.98 events per hour, 95% CI -10.66 to -3.30; 1 study, 18 participants; very low certainty). The effect of carbonic anhydrase inhibitors on cardiovascular mortality in the intermediate term was also uncertain (odds ratio (OR) 0.21, 95% CI 0.02 to 2.48; 1 study, 18 participants; very low certainty). Anxiolytics versus inactive control Results were based on one study of buspirone versus placebo for CSA associated with heart failure (n = 16). The median difference between groups for cAHI was -5.00 events per hour (IQR -8.00 to -0.50), the median difference for AHI was -6.00 events per hour (IQR -8.80 to -1.80), and the median difference on the Epworth Sleepiness Scale for daytime sleepiness was 0 points (IQR -1.0 to 0.00). Methylxanthine derivatives versus inactive control Results were based on one study of theophylline versus placebo for CSA associated with heart failure (n = 15). We are uncertain whether methylxanthine derivatives compared to inactive control reduce cAHI (MD -20.00 events per hour, 95% CI -32.15 to -7.85; 15 participants; very low certainty) or AHI (MD -19.00 events per hour, 95% CI -30.27 to -7.73; 15 participants; very low certainty). Hypnotics versus inactive control Results were based on one trial of triazolam versus placebo for primary CSA (n = 5). Due to very serious methodological limitations and insufficient reporting of outcome measures, we were unable to draw any conclusions regarding the effects of this intervention.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support the use of pharmacological therapy in the treatment of CSA. Although small studies have reported positive effects of certain agents for CSA associated with heart failure in reducing the number of respiratory events during sleep, we were unable to assess whether this reduction may impact the quality of life of people with CSA, owing to scarce reporting of important clinical outcomes such as sleep quality or subjective impression of daytime sleepiness. Furthermore, the trials mostly had short-term follow-up. There is a need for high-quality trials that evaluate longer-term effects of pharmacological interventions.

Impact of Sacubitril/Valsartan on surfactant binding proteins, central sleep apneas, lung function tests and heart failure biomarkers: Hemodynamic or pleiotropism?

Purpose

Little is known about the mechanism underlying Sacubitril/Valsartan effects in patients with heart failure (HFrEF). Aim of the study is to assess hemodynamic vs. non-hemodynamic Sacubitril/Valsartan effects by analyzing several biological and functional parameters.

Methods

Seventy-nine patients (86% males, age 66 ± 10 years) were enrolled. At baseline and 6 months after reaching the maximum Sacubitril/Valsartan tolerated dose, we assessed biomarkers, transthoracic echocardiography, polysomnography, spirometry, and carbon monoxide diffusing capacity of the lung (DLCO).

Results

Mean follow-up was 8.7 ± 1.4 months with 83% of patients reaching Sacubitril/Valsartan maximum dose (97/103 mg b.i.d). Significant improvements were observed in cardiac performance and biomarkers: left ventricular ejection fraction increased (31 ± 5 vs. 37 ± 9 %; p &lt; 0.001), end-diastolic and end-systolic volumes decreased; NT-proBNP decreased (1,196 [IQR 648–2891] vs. 958 [IQR 424-1,663] pg/ml; p &lt; 0.001) in parallel with interleukin ST-2 (28.4 [IQR 19.4–36.6] vs. 20.4 [IQR 15.1–29.2] ng/ml; p &lt; 0.001) and circulating surfactant binding proteins (proSP-B: 58.43 [IQR 40.42–84.23] vs. 50.36 [IQR 37.16–69.54] AU; p = 0.014 and SP-D: 102.17 [IQR 62.85–175.34] vs. 77.64 [IQR 53.55-144.70] AU; p &lt; 0.001). Forced expiratory volume in 1 second and forced vital capacity improved. DLCO increased in the patients' subgroup (n = 39) with impaired baseline values (from 65.3 ± 10.8 to 70.3 ± 15.9 %predicted; p = 0.013). We also observed a significant reduction in central sleep apneas (CSA).

Conclusion

Sacubitril/Valsartan effects share a double pathway: hemodynamic and systemic. The first is evidenced by NT-proBNP, proSP-B, lung mechanics, and CSA improvement. The latter is confirmed by an amelioration of DLCO, ST-2, SP-D as well as by reverse remodeling echocardiographic parameters.

Cheyne-stokes respiration in children with heart failure

Cheyne-Stokes respiration (CSA-CSR) is a form of central sleep apnea characterized by alternating periods of hyperventilation and central apneas or hypopneas. CSA-CSR develops following a cardiac insult resulting in a compensatory increase in sympathetic activity, which in susceptible patients causes hyperventilation and destabilizes respiratory control. The physiological changes that occur in CSA-CSR include hyperventilation, a reduced blood gas buffering capacity, and circulatory delay. In adults, 25% to 50% of patients with heart failure are reported to have CSA-CSR. The development of CSA-CSR in this group of patients is considered a poor prognostic sign. The prevalence, progression, and treatment outcomes of CSA-CSR in children remain unclear with only 11 children being described in the literature. The lack of data is possibly not due to the paucity of children with severe heart failure and CSA-CSR but because they may be under-recognized, compounded by the absence of routine polysomnographic assessment of children with moderate to severe heart failure. Building on much broader experience in the diagnosis and management of CSA-CSR in adult sleep medicine and our limited experience in a pediatric quaternary center, this paper will discuss the prevalence of CSA-CSR, its' treatment options, outcomes in children, and the potential future direction for research in this understudied area of pediatric sleep medicine.

Temporal variations in the pattern of breathing: techniques, sources, and applications to translational sciences

The breathing process possesses a complex variability caused in part by the respiratory central pattern generator in the brainstem; however, it also arises from chemical and mechanical feedback control loops, network reorganization and network sharing with nonrespiratory motor acts, as well as inputs from cortical and subcortical systems. The notion that respiratory fluctuations contain hidden information has prompted scientists to decipher respiratory signals to better understand the fundamental mechanisms of respiratory pattern generation, interactions with emotion, influences on the cortical neuronal networks associated with cognition, and changes in variability in healthy and disease-carrying individuals. Respiration can be used to express and control emotion. Furthermore, respiration appears to organize brain-wide network oscillations via cross-frequency coupling, optimizing cognitive performance. With the aid of information theory-based techniques and machine learning, the hidden information can be translated into a form usable in clinical practice for diagnosis, emotion recognition, and mental conditioning.

Central Apneas Are More Detrimental in Female Than in Male Patients With Heart Failure

Background

Central apneas (CA) are a frequent comorbidity in patients with heart failure (HF) and are associated with worse prognosis. The clinical and prognostic relevance of CA in each sex is unknown.

Methods and Results

Consecutive outpatients with HF with either reduced or mildly reduced left ventricular ejection fraction (n=550, age 65±12 years, left ventricular ejection fraction 32%±9%, 21% women) underwent a 24‐hour ambulatory polygraphy to evaluate CA burden and were followed up for the composite end point of cardiac death, appropriate implantable cardioverter‐defibrillator shock, or first HF hospitalization. Compared with men, women were younger, had higher left ventricular ejection fraction, had lower prevalence of ischemic etiology and of atrial fibrillation, and showed lower apnea‐hypopnea index (expressed as median [interquartile range]) at daytime (3 [0–9] versus 10 [3–20] events/hour) and nighttime (10 [3–21] versus 23 [11–36] events/hour) (all P<0.001), despite similar neurohormonal activation and HF therapy. Increased chemoreflex sensitivity to either hypoxia or hypercapnia (evaluated in 356 patients, 65%, by a rebreathing test) was less frequent in women (P<0.001), but chemoreflex sensitivity to hypercapnia was a predictor of apnea‐hypopnea index in both sexes. At adjusted survival analysis, daytime apnea‐hypopnea index ≥15 events/hour (hazard ratio [HR], 2.70; 95% CI, 1.06–7.34; P=0.037), nighttime apnea‐hypopnea index ≥15 events/hour (HR, 2.84; 95% CI, 1.28–6.32; P=0.010), and nighttime CA index ≥10 events/hour (HR, 5.01; 95% CI, 1.88–13.4; P=0.001) were independent predictors of the primary end point in women but not in men (all P>0.05), also after matching women and men for possible confounders.

Conclusions

In chronic HF, CA are associated with a greater risk of adverse events in women than in men.

A Wearable Multimodal Sensing System for Tracking Changes in Pulmonary Fluid Status, Lung Sounds, and Respiratory Markers

Heart failure (HF) exacerbations, characterized by pulmonary congestion and breathlessness, require frequent hospitalizations, often resulting in poor outcomes. Current methods for tracking lung fluid and respiratory distress are unable to produce continuous, holistic measures of cardiopulmonary health. We present a multimodal sensing system that captures bioimpedance spectroscopy (BIS), multi-channel lung sounds from four contact microphones, multi-frequency impedance pneumography (IP), temperature, and kinematics to track changes in cardiopulmonary status. We first validated the system on healthy subjects (n = 10) and then conducted a feasibility study on patients (n = 14) with HF in clinical settings. Three measurements were taken throughout the course of hospitalization, and parameters relevant to lung fluid status—the ratio of the resistances at 5 kHz to those at 150 kHz (K)—and respiratory timings (e.g., respiratory rate) were extracted. We found a statistically significant increase in K (p < 0.05) from admission to discharge and observed respiratory timings in physiologically plausible ranges. The IP-derived respiratory signals and lung sounds were sensitive enough to detect abnormal respiratory patterns (Cheyne–Stokes) and inspiratory crackles from patient recordings, respectively. We demonstrated that the proposed system is suitable for detecting changes in pulmonary fluid status and capturing high-quality respiratory signals and lung sounds in a clinical setting.

Effects of enriched-potassium diet on cardiorespiratory outcomes in experimental non-ischemic chronic heart failure

Background

Chronic heart failure (CHF) is a global health problem. Increased sympathetic outflow, cardiac arrhythmogenesis and irregular breathing patterns have all been associated with poor outcomes in CHF. Several studies showed that activation of the renin-angiotensin system (RAS) play a key role in CHF pathophysiology. Interestingly, potassium (K⁺) supplemented diets showed promising results in normalizing RAS axis and autonomic dysfunction in vascular diseases, lowering cardiovascular risk. Whether subtle increases in dietary K⁺ consumption may exert similar effects in CHF has not been previously tested. Accordingly, we aimed to evaluate the effects of dietary K⁺ supplementation on cardiorespiratory alterations in rats with CHF.

Methods

Adult male Sprague–Dawley rats underwent volume overload to induce non-ischemic CHF. Animals were randomly allocated to normal chow diet (CHF group) or supplemented K⁺ diet (CHF+K⁺ group) for 6 weeks. Cardiac arrhythmogenesis, sympathetic outflow, baroreflex sensitivity, breathing disorders, chemoreflex function, respiratory–cardiovascular coupling and cardiac function were evaluated.

Results

Compared to normal chow diet, K⁺ supplemented diet in CHF significantly reduced arrhythmia incidence (67.8 ± 15.1 vs. 31.0 ± 3.7 events/hour, CHF vs. CHF+K⁺), decreased cardiac sympathetic tone (ΔHR to propranolol: − 97.4 ± 9.4 vs. − 60.8 ± 8.3 bpm, CHF vs. CHF+K⁺), restored baroreflex function and attenuated irregular breathing patterns. Additionally, supplementation of the diet with K⁺ restores normal central respiratory chemoreflex drive and abrogates pathological cardio-respiratory coupling in CHF rats being the outcome an improved cardiac function.

Conclusion

Our findings support that dietary K⁺ supplementation in non-ischemic CHF alleviate cardiorespiratory dysfunction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00365-z.

Breathing irregularities before sleep onset on polysomnography in patients with heart diseases

PURPOSE

Severe cardiac dysfunction can manifest with diurnal breathing irregularity. However, it remains to be clarified whether or not diurnal breathing irregularity is observed in patients with heart diseases, including relatively mild chronic heart failure (CHF), compared to those without heart diseases.

METHODS

In this cross-sectional study, consecutive inpatients who were admitted for evaluation of sleep-disordered breathing were enrolled. We extracted 3.5 min of stable respiratory signals before sleep onset using polysomnography, analyzed the airflow data using fast Fourier transform, and quantified breathing irregularities using Shannon entropy S.

RESULTS

A total of 162 subjects were evaluated. Among these, 39 subjects had heart diseases, including ischemic heart disease (IHD), atrial fibrillation (Af), CHF, and a history of aortic dissection. The values of Shannon entropy S of airflow signals in subjects with heart diseases were significantly higher than in those without heart diseases (p < 0.001). After excluding CHF, the Shannon entropy S was also significantly higher in subjects with heart diseases than in those without heart diseases (p < 0.001). The values of Shannon entropy S were significantly correlated with plasma brain natriuretic peptide levels (r = 0.443, p < 0.001). Although the values were also significantly correlated with body mass index, the presence of heart diseases was independently associated with breathing irregularity in the multiple logistic analysis. Matching analysis revealed consistent differences between subjects with heart diseases and without heart diseases.

CONCLUSION

Breathing irregularity was observed before sleep onset in subjects with heart diseases who underwent polysomnography to diagnose sleep-disordered breathing.

Evaluation of the Apnea-Hypopnea Index Determined by Adaptive Servo-Ventilation Devices in Patients With Heart Failure and Sleep-Disordered Breathing

Introduction: Adaptive servo-ventilation (ASV) devices are designed to suppress central respiratory events, and therefore effective for sleep-disordered breathing (SDB) in patients with heart failure (HF) and provide information about their residual respiratory events. However, whether the apnea-hypopnea index (AHI), determined by the ASV device AutoSet CS (ASC), correlates with the AHI calculated by polysomnography (PSG) in patients with HF and SDB remains to be evaluated.

Methods: Consecutive patients with SDB titrated on ASC were included in the study. We assessed the correlation between AHI determined by manual scoring during PSG (AHI-PSG) and that determined by the ASC device (AHI-ASC) during an overnight session.

Results: Thirty patients with HF and SDB (age, 68.8 ± 15.4 years; two women; left ventricular ejection fraction, 53.8 ± 17.9%) were included. The median AHI in the diagnostic study was 28.4 events/h, including both obstructive and central respiratory events. During the titration, ASC markedly suppressed the respiratory events (AHI-PSG, 3.3 events/h), while the median AHI-ASC was 12.8 events/h. We identified a modest correlation between AHI-PSG and AHI-ASC (r = 0.36, p = 0.048). The Brand-Altman plot indicated that the ASC device overestimated the AHI, and a moderate agreement was observed with PSG.

Conclusions: There was only a modest correlation between AHI-PSG and AHI-ASC. The discrepancy may be explained by either the central respiratory events that occur during wakefulness or the other differences between PSG and ASC in the detected respiratory events. Therefore, clinicians should consider this divergence when assessing residual respiratory events using ASC.

Assessing the Tidal Volume through Wearables: A Scoping Review

The assessment of respiratory activity based on wearable devices is becoming an area of growing interest due to the wide range of available sensors. Accordingly, this scoping review aims to identify research evidence supporting the use of wearable devices to monitor the tidal volume during both daily activities and clinical settings. A screening of the literature (Pubmed, Scopus, and Web of Science) was carried out in December 2020 to collect studies: i. comparing one or more methodological approaches for the assessment of tidal volume with the outcome of a state-of-the-art measurement device (i.e., spirometry or optoelectronic plethysmography); ii. dealing with technological solutions designed to be exploited in wearable devices. From the initial 1031 documents, only 36 citations met the eligibility criteria. These studies highlighted that the tidal volume can be estimated by using different technologies ranging from IMUs to strain sensors (e.g., resistive, capacitive, inductive, electromagnetic, and optical) or acoustic sensors. Noticeably, the relative volumetric error of these solutions during quasi-static tasks (e.g., resting and sitting) is typically ≥10% but it deteriorates during dynamic motor tasks (e.g., walking). As such, additional efforts are required to improve the performance of these devices and to identify possible applications based on their accuracy and reliability.

All You Need Is Sleep: the Effects of Sleep Apnea and Treatment Benefits in the Heart Failure Patient

PURPOSE OF REVIEW

Recognition and treatment of sleep apnea is an important but easily overlooked aspect of care in the heart failure patient. This review summarizes the data behind the recommendations in current practice guidelines and highlights recent developments in treatment options.

RECENT FINDINGS

Neuromodulation using hypoglossal nerve stimulation has been increasingly used for treatment of OSA; however, it has not been studied in the heart failure population. Alternatively, phrenic nerve stimulation for treatment of CSA is effective for heart failure patients, and cardiac resynchronization therapy can be effective in improving CSA in pacing-induced cardiomyopathy. In patients suspected to have sleep apnea, polysomnography is recommended to better understand the prognosis and treatment options. Positive airway pressure is the standard treatment for sleep apnea; however, neurostimulation can be especially effective in those with predominantly central events. Understanding the pathophysiology of sleep apnea can guide further management decisions.

Sacubitril-valsartan treatment is associated with decrease in central apneas in patients with heart failure with reduced ejection fraction

BACKGROUND

To assess the impact of sacubitril-valsartan on apneic burden in patients with heart failure with reduced ejection fraction (HFrEF), 51 stable HFrEF patients planned for switching from an ACE-i/ARB to sacubitril-valsartan were prospectively enrolled.

METHODS AND RESULTS

At baseline and after 6 months of treatment, all patients underwent echocardiography, 24-h cardiorespiratory monitoring, neurohormonal evaluation, and cardiopulmonary exercise testing. At baseline 29% and 65% of patients presented with obstructive and central apneas, respectively. After 6 months, sacubitril-valsartan was associated with a decrease in NT-proBNP, improvement in LV function, functional capacity and ventilatory efficiency. After treatment, the apnea-hypopnea index (AHI) decreased across the 24-h period (p < 0.001), as well as at daytime (p < 0.001) and at nighttime (p = 0.026), proportionally to baseline severity. When subgrouping according to the type of apneas, daytime, nighttime and 24-h AHI decreased in patients with central apneas (all p < 0.01). Conversely, in patients with obstructive apneas, the effect of drug administration was neutral at nighttime, with significant decrease only in daytime events (p = 0.007), mainly driven by reduction in hypopneas.

CONCLUSIONS

Sacubitril-valsartan on top of medical treatment is associated with a reduction in the apneic burden among a real-life cohort of HFrEF patients. The most marked reduction was observed for central apneas.

Benefit of buspirone on chemoreflex and central apnoeas in heart failure: a randomized controlled crossover trial

AIMS

Increased chemosensitivity to carbon dioxide (CO2 ) is an important trigger of central apnoeas (CA) in heart failure (HF), with negative impact on outcome. We hypothesized that buspirone, a 5HT1A receptor agonist that inhibits serotonergic chemoreceptor neuron firing in animals, can decrease CO2 chemosensitivity and CA in HF.

METHODS AND RESULTS

The BREATH study was a randomized, double-blind, placebo-controlled, crossover study (EudraCT-code 2015-005383-42). Outpatients with systolic HF (left ventricular ejection fraction <50%) and moderate-severe CA [nocturnal apnoea-hypopnoea index (AHI) ≥15 events/h] were randomly assigned to either oral buspirone (15 mg thrice daily) or placebo for 1 week, with a crossover design (1 week of wash-out). The primary effectiveness endpoint was a decrease in CO2 chemosensitivity >0.5 L/min/mmHg. The primary safety endpoint was freedom from serious adverse events. Sixteen patients (age 71.3 ± 5.8 years, all males, left ventricular ejection fraction 29.8 ± 7.8%) were enrolled. In the intention-to-treat analysis, more patients treated with buspirone (8/16, 50%) had a CO2 chemosensitivity reduction >0.5 L/min/mmHg from baseline than those treated with placebo (1/16, 6.7%) (difference between groups 43%, 95% confidence interval 14-73%, P = 0.016). Buspirone compared to baseline led to a 41% reduction in CO2 chemosensitivity (P = 0.001) and to a reduction in the AHI, central apnoea index and oxygen desaturation index of 42%, 79%, 77% at nighttime and 50%, 78%, 86% at daytime (all P < 0.01); no difference was observed after placebo administration (all P > 0.05). No patient reported buspirone-related serious adverse events.

CONCLUSIONS

Buspirone reduces CO2 chemosensitivity and improves CA and oxygen saturation across the 24 h in patients with HF.

A Wrist-worn Respiration Monitoring Device using Bio-Impedance

In the US alone, 22 million individuals suffer from obstructive sleep apnea (OSA), with 80% of the cases symptoms undiagnosed. Hence, there is an unmet need to continuously and unobtrusively monitor respiration and detect possible occurrences of apnea. Recent advancements in wearable biomedical technology can enable the capture of the periodicity of the heart pressure pulse from a wrist-worn device. In this paper, we propose a bio-impedance (Bio-Z)-based respiration monitoring system. We establish close contact with the skin using gold e-tattoos with a 35 mm by 5 mm active sensing area. We extracted the respiration from the wrist Bio-Z signal leveraging three different techniques and showed that we can detect the start of each respiration beat with an average root mean square error (RMSE) less than 13% and mean error of 0.3% over five subjects.

Central Sleep Apnea in Patients with Heart Failure-How to Screen, How to Treat

PURPOSE OF REVIEW

Central sleep apnea occurs in up to 50% of heart failure patients and worsens outcomes. Established therapies are limited by minimal supporting evidence, poor patient adherence, and potentially adverse cardiovascular effects. However, transvenous phrenic nerve stimulation, by contracting the diaphragm, restores normal breathing throughout sleep and has been shown to be safe and effective. This review discusses the mechanisms, screening, diagnosis, and therapeutic approaches to CSA in patients with HF.

RECENT FINDINGS

In a prospective, multicenter randomized Pivotal Trial (NCT01816776) of transvenous phrenic nerve stimulation with the remedē System, significantly more treated patients had a ≥ 50% reduction in apnea-hypopnea index compared with controls, with a 41 percentage point difference between group difference at 6 months (p < 0.0001). All hierarchically tested sleep, quality of life, and daytime sleepiness endpoints were significantly improved in treated patients. Freedom from serious related adverse events at 12 months was 91%. Benefits are sustained to 36 months. Transvenous phrenic nerve stimulation improves quality of life in patients with heart failure and central sleep apnea. Controlled trials evaluating the impact of this therapy on mortality/heart failure hospitalizations and "real world" experience are needed to confirm safety and effectiveness.

A signal demodulation-based method for the early detection of Cheyne-Stokes respiration

Cheyne-Stokes respiration (CSR) is a sleep-disordered breathing characterized by recurrent central apneas alternating with hyperventilation exhibiting a crescendo-decrescendo pattern of tidal volume. This respiration is reported in patients with heart failure, stroke or damage in respiratory centers. It increases mortality for patients with severe heart failure as it has adverse impacts on the cardiac function. Early stage of CSR, also called periodic breathing, is often undiagnosed as it only provokes hypopneas instead of apneas, which are much more difficult to detect. This paper demonstrates the proof of concept of a new method devoted to the early detection of CSR. The proposed approach relies on a signal demodulation technique applied to ventilation signals measured on 15 patients with chronic heart failure whose respiration goes from normal to severe CSR. Based on a modulation index and its instantaneous frequency, oscillation zones are detected and classified into three categories: CSR, periodic breathing and no abnormal pattern. The modulation index is used as an efficient indicator to quantify the degree of certainty of the pathology for each patient. Results show high correlation with experts’ annotations with sensitivity and specificity values of 87.1% and 89.8% respectively. A final decision leads to a classification which is confirmed by the experts’ conclusions.

Effect of Treatment of Central Sleep Apnea/Cheyne-Stokes Respiration on Left Ventricular Ejection Fraction in Heart Failure: A Network Meta-Analysis

STUDY OBJECTIVES

Patients who have experienced heart failure with central sleep apnea/Cheyne-Stokes respiration (CSA/CSR) have an impaired prognosis. Continuous positive airway pressure (CPAP) and adaptive servoventilation (ASV) as well as nocturnal oxygen (O₂) are proposed treatment modalities of CSA/CSR. The goal of the study is to assess whether and how different treatments of CSA/CSR affect cardiac function.

METHODS

Databases were searched up to December 2017 for randomized controlled trials (RCTs) comparing the effect of any combination of CPAP, ASV, O₂ or an inactive control on left ventricular ejection fraction (LVEF) in patients with heart failure and CSA/CSR. A systematic review and network meta-analysis using multivariate random-effects meta-regression were performed.

RESULTS

Twenty-four RCTs (1,289 patients) were included in the systematic review and data of 16 RCTs (951 patients; apnea-hypopnea-index 38 ± 3/h, LVEF 29 ± 3%) could be pooled in a network meta-analysis. Compared to an inactive control, both CPAP and ASV significantly improved LVEF by 4.4% (95% confidence interval 0.3-8.5%, P = 0.036) and 3.8% (95% confidence interval 0.6-7.0%, P = 0.025), respectively, whereas O₂ had no effect on LVEF (P = 0.35). There was no difference in treatment effects on LVEF between CPAP and ASV (P = 0.76). The treatment effect of positive pressure ventilation was larger when baseline LVEF was lower in systolic heart failure.

CONCLUSIONS

CPAP and ASV are effective in improving LVEF in patients with heart failure and CSA/CSR to a clinically relevant amount, whereas nocturnal O₂ is not. There is no difference between CPAP and ASV in the comparative beneficial effect on cardiac function.

Central sleep apnoea and periodic breathing in heart failure: prognostic significance and treatment options

Central sleep apnoea (CSA) including periodic breathing is prevalent in more than one-third of patients with heart failure and is highly and independently associated with poor outcomes. Optimal treatment is still debated and well-conducted studies regarding efficacy and impact on outcomes of available treatment options are limited, particularly in cardiac failure with preserved ejection fraction. While continuous positive airway pressure and oxygen reduce breathing disturbances by 50%, adaptive servoventilation (ASV) normalises breathing disturbances by to controlling the underlying mechanism of CSA. Results are contradictory regarding impact of ASV on hard outcomes. Cohorts and registry studies show survival improvement under ASV, while secondary analyses of the large SERVE-HF randomised trial showed an excess mortality in cardiac failure with reduced ejection fraction. The current priority is to understand which phenotypes of cardiac failure patients may benefit from treatment guiding individualised and personalised management.

Central and Obstructive Apneas in Heart Failure With Reduced, Mid-Range and Preserved Ejection Fraction

Background: Although central apneas (CA) and obstructive apneas (OA) are highly prevalent in heart failure (HF), a comparison of apnea prevalence, predictors and clinical correlates in the whole HF spectrum, including HF with reduced ejection fraction (HFrEF), mid-range EF (HFmrEF) and preserved EF (HFpEF) has never been carried out so far.

Materials and methods: 700 HF patients were prospectively enrolled and then divided according to left ventricular EF (408 HFrEF, 117 HFmrEF, 175 HFpEF). All patients underwent a thorough evaluation including: 2D echocardiography; 24-h Holter-ECG monitoring; cardiopulmonary exercise testing; neuro-hormonal assessment and 24-h cardiorespiratory monitoring.

Results: In the whole population, prevalence of normal breathing (NB), CA and OA at daytime was 40, 51, and 9%, respectively, while at nighttime 15, 55, and 30%, respectively. When stratified according to left ventricular EF, CA prevalence decreased (daytime: 57 vs. 43 vs. 42%, p = 0.001; nighttime: 66 vs. 48 vs. 34%, p < 0.0001) from HFrEF to HFmrEF and HFpEF, while OA prevalence increased (daytime: 5 vs. 8 vs. 18%, p < 0.0001; nighttime 20 vs. 29 vs. 53%, p < 0.0001).

In HFrEF, male gender and body mass index (BMI) were independent predictors of both CA and OA at nighttime, while age, New York Heart Association functional class and diastolic dysfunction of daytime CA. In HFmrEF and HFpEF male gender and systolic pulmonary artery pressure were independent predictors of CA at daytime, while hypertension predicted nighttime OA in HFpEF patients; no predictor of nighttime CA was identified. When compared to patients with NB, those with CA had higher neuro-hormonal activation in all HF subgroups. Moreover, in the HFrEF subgroup, patients with CA were older, more comorbid and with greater hemodynamic impairment while, in the HFmrEF and HFpEF subgroups, they had higher left atrial volumes and more severe diastolic dysfunction, respectively. When compared to patients with NB, those with OA were older and more comorbid independently from background EF.

Conclusions: Across the whole spectrum of HF, CA prevalence increases and OA decreases as left ventricular systolic dysfunction progresses. Different predictors and specific clinical characteristics might help to identify patients at risk of developing CA or OA in different HF phenotypes.

Nasal high flow reduces minute ventilation during sleep through a decrease of carbon dioxide rebreathing

Nasal high flow (NHF) is an emerging therapy for respiratory support, but knowledge of the mechanisms and applications is limited. It was previously observed that NHF reduces the tidal volume but does not affect the respiratory rate during sleep. The authors hypothesized that the decrease in tidal volume during NHF is due to a reduction in carbon dioxide (CO2) rebreathing from dead space. In nine healthy males, ventilation was measured during sleep using calibrated respiratory inductance plethysmography (RIP). Carbogen gas mixture was entrained into 30 l/min of NHF to obtain three levels of inspired CO2: 0.04% (room air), 1%, and 3%. NHF with room air reduced tidal volume by 81 ml, SD 25 ( P < 0.0001) from a baseline of 415 ml, SD 114, but did not change respiratory rate; tissue CO2 and O2 remained stable, indicating that gas exchange had been maintained. CO2 entrainment increased tidal volume close to baseline with 1% CO2 and greater than baseline with 3% CO2 by 155 ml, SD 79 ( P = 0.0004), without affecting the respiratory rate. It was calculated that 30 l/min of NHF reduced the rebreathing of CO2 from anatomical dead space by 45%, which is equivalent to the 20% reduction in tidal volume that was observed. The study proves that the reduction in tidal volume in response to NHF during sleep is due to the reduced rebreathing of CO2. Entrainment of CO2 into the NHF can be used to control ventilation during sleep.

NEW & NOTEWORTHY The findings in healthy volunteers during sleep show that nasal high flow (NHF) with a rate of 30 l/min reduces the rebreathing of CO2 from anatomical dead space by 45%, resulting in a reduced minute ventilation, while gas exchange is maintained. Entrainment of CO2 into the NHF can be used to control ventilation during sleep.

Alterations of the respiratory system in heart failure

The review discusses mechanisms for the development of the pathology of the respiratory system in patients with CHF, such as various types of periodic respiration, pulmonary hypertension due to the pathology of the left chambers of the heart, and remodeling of the respiratory musculature. The role of chemo- and baroreceptors of the carotid zone, as well as the hyperactivation of the respiratory muscle metaboreflex in the development of the pathology of the respiratory system, and the mediated exacerbation of CHF are discussed.

Multicenter, Prospective Study on Respiratory Stability During Recovery From Deterioration of Chronic Heart Failure

BACKGROUND

The respiratory instability frequently observed in advanced heart failure (HF) is likely to mirror the clinical status of worsening HF. The present multicenter study was conducted to examine whether the noble respiratory stability index (RSI), a quantitative measure of respiratory instability, reflects the recovery process from HF decompensation. Methods and Results: Thirty-six of 44 patients hospitalized for worsening HF completed all-night measurements of RSI both at deterioration and recovery phases. Based on the signs, symptoms, and laboratory data during hospitalization, the Central Adjudication Committee identified 22 convalescent patients and 14 patients with less extent of recovery in a blinded manner without any information on RSI or other respiratory variables. The all-night RSI in the convalescent patients was increased from 27.8±18.4 to 34.6±15.8 (P<0.05). There was no significant improvement of RSI, however, in the remaining patients with little clinical improvement. Of the clinical and laboratory variables, on stepwise linear regression modeling, body weight, peripheral edema, and lung congestion were closely related to the RSI of recovered patients and accounted for 56% of the changes in RSI (coefficient of determination, R²=0.56).

CONCLUSIONS

All-night RSI, a quantitative measure of respiratory instability, could faithfully reflect congestive signs and clinical status of HF during the recovery process from acute decompensation.

ECG derived Cheyne-Stokes respiration and periodic breathing are associated with cardiorespiratory arrest in intensive care unit patients

BACKGROUND

Cheyne-Stokes respiration and periodic breathing (CSRPB) have not been studied sufficiently in the intensive care unit setting (ICU).

OBJECTIVES

To determine whether CSRPB is associated with adverse outcomes in ICU patients.

METHODS

The ICU group was divided into quartiles by CSRPB (86 patients in quartile 1 had the least CSRPB and 85 patients in quartile 4 had the most CSRPB). Adverse outcomes (emergent intubation, cardiorespiratory arrest, inpatient mortality and the composite of all) were compared between patients with most CSRPB (quartile 4) and those with least CSRPB (quartile 1).

RESULTS

ICU patients in quartile 4 had a higher proportion of cardiorespiratory arrests (5% versus 0%, (p=.042), and more adverse events over all (19% versus 8%, p=.041) as compared to patients in quartile 1.

CONCLUSIONS

CSRPB can be measured in the ICU and it's severity is associated with adverse outcomes in critically ill patients.

Long-term effects of device-guided slow breathing in stable heart failure patients with reduced ejection fraction

Background

Slow breathing (SLOWB) alleviates symptoms of chronic heart failure (HF) but its long-term effects are unknown. We examined the acute and long-term impact of device-guided breathing on hemodynamics and prognostic parameters in HF patients with reduced ejection fraction (HFrEF).

Methods and results

Twenty-one patients with HFrEF (23.9 ± 5.8%, SD ± mean) on optimal medical therapy underwent blood pressure (BP), heart rate (HR), HR variability, 6-min walk test (6MWT), cardiopulmonary exercise testing (CPET), and echocardiography measurements before and 3 months after SLOWB home training (30 min daily). After 3 months, all patients were assigned to continue SLOWB (Group 1) or no-SLOWB (Group 2). All tests were repeated after 6 months. Acute SLOWB (18 ± 5 vs 8 ± 2 breaths/min, P < 0.001) had no influence on BP and HR but improved saturation (97 ± 2 vs 98 ± 2%, P = 0.01). Long-term SLOWB reduced office systolic BP (P < 0.001) but not central or ambulatory systolic BP. SLOWB reduced SDNN/RMSSD ratio (P < 0.05) after 3 months. One-way repeated measures of ANOVA revealed a significant increase in 6MWT and peak RER (respiratory exchange ratio) from baseline to 6-month follow-up in group 1 (P < 0.05) but not group 2 (P = 0.85 for 6MWT, P = 0.69 for RER). No significant changes in echocardiography were noted at follow-up. No HF worsening, rehospitalisation or death occurred in group 1 out to 6-month follow-up. Two hospitalizations for HF decompensation and two deaths ensued in group 2 between 3- and 6-month follow-up.

Conclusions

SLOWB training improves cardiorespiratory capacity and appears to slow the progression of HFrEF. Further long-term outcome studies are required to confirm the benefits of paced breathing in HFrEF.

Prognostic Significance of Central Apneas Throughout a 24-Hour Period in Patients With Heart Failure

BACKGROUND

Large trials using noninvasive mechanical ventilation to treat central apnea (CA) occurring at night ("sleep apnea") in patients with systolic heart failure (HF) have failed to improve prognosis. The prevalence and prognostic value of CA during daytime and over an entire 24-h period are not well described.

OBJECTIVES

This study evaluated the occurrence and prognostic significance of nighttime, daytime, and 24-h CA episodes in a large cohort of patients with systolic HF.

METHODS

Consecutive patients receiving guideline-recommended treatment for HF (n = 525; left ventricular ejection fraction [LVEF] of 33 ± 9%; 66 ± 12 years of age; 77% males) underwent prospective evaluation, including 24-h respiratory recording, and were followed-up using cardiac mortality as an endpoint.

RESULTS

The 24-h prevalence of predominant CAs (apnea/hypopnea index [AHI] ≥5 events/h, with CA of >50%) was 64.8% (nighttime: 69.1%; daytime: 57.0%), whereas the prevalence of predominant obstructive apneas (OA) was 12.8% (AHI ≥5 events/h with OAs >50%; nighttime: 14.7%; daytime: 5.9%). Episodes of CA were associated with neurohormonal activation, ventricular arrhythmic burden, and systolic/diastolic dysfunction (all p < 0.05). During a median 34-month follow-up (interquartile range [IQR]: 17 to 36 months), 50 cardiac deaths occurred. Nighttime, daytime, and 24-h moderate-to-severe CAs were associated with increased cardiac mortality (AHI of </≥15 events/h; log-rank: 6.6, 8.7, and 5.3, respectively; all p < 0.05; central apnea index [CAI] of </≥10 events/h; log-rank 8.9, 11.2, and 10.9, respectively; all p < 0.001). Age, B-type natriuretic peptide level, renal dysfunction, 24-h AHI, CAI, and time with oxygen saturation of <90% were independent predictors of outcome.

CONCLUSIONS

In systolic HF patients, CAs occurred throughout a 24-h period and were associated with a neurohormonal activation, ventricular arrhythmic burden, and worse prognosis.

How to take arms against central apneas in heart failure

Introduction Despite being a risk mediator in several observational studies, central apneas are currently orphan of treatment in heart failure. After the neutral effects on survival of two randomized controlled trials (RCTs) based on the use of positive airway pressure (the CANPAP and SERVE-HF trials), two alternative hypotheses have been formulated: 1) Periodic breathing/Cheyne-Stokes respiration (PB/CSR) in HF is protective. Indeed, the Naughton's hypothesis assumes that hyperventilation leads to increased cardiac output, lung volume, oxygen storage and reduced muscle sympathetic nerve activity, while central apnea to respiratory muscle rest and hypoxia-induced erythropoiesis. 2) The use of positive airway pressure is just a wrong treatment for PB/CSR. If this is the case, the search for novel potential alternative treatment approaches is mandatory in HF. Areas covered This review will focus on the crucial issue of whether PB/CSR should be treated or not in HF, first by outlining the ideal design of pathophysiological studies to test the Naughton's hypothesis and second by summarizing the treatment strategies so far proposed for PB/CSR in HF and identifying the most promising options to be tested in future RCTs. Expert commentary It is likely that PB/CSR may be compensatory in some cases, but after a certain threshold (to be defined) it becomes maladaptive with negative prognostic meaning in HF. The development of a pathophysiologically based treatment targeting feedback resetting and neurohormonal activation underlying PB/CSR is likely to be the best option to obtain survival benefits in HF.

Sympathetic Activation in Chronic Heart Failure: Potential Benefits of Interventional Therapies

Heart failure (HF) is a major and growing public health problem. This condition is associated with poor prognosis, a high rate of mortality, frequent hospitalization and increasing costs to health care systems. Pharmacological approaches aimed at reducing morbidity and mortality in HF have primarily focused on inhibition of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS), both of which have been associated with disease development, progression and adverse cardiovascular (CV) outcomes. The increasing number of hospitalizations for HF decompensation suggests the failure of available treatment options, indicating the necessity for alternative therapeutic approaches. Alongside pharmacological and cardiac resynchronization therapies in selected patients with arrhythmia, recent advancements in the management of HF have been directed at inhibiting relevant neurogenic pathways underlying disease development and progression. Initial evidence regarding the safety and effectiveness of interventional procedures suggests that HF patients may benefit from novel adjunctive therapies. Here we review the critical role of sympathetic activation in HF and the rationale for therapeutic interventions including device-based and interventional approaches aimed at restoring autonomic neural balance in this condition.

Resonance as the Mechanism of Daytime Periodic Breathing in Patients with Heart Failure

RATIONALE

In patients with chronic heart failure, daytime oscillatory breathing at rest is associated with a high risk of mortality. Experimental evidence, including exaggerated ventilatory responses to CO₂ and prolonged circulation time, implicates the ventilatory control system and suggests feedback instability (loop gain > 1) is responsible. However, daytime oscillatory patterns often appear remarkably irregular versus classic instability (Cheyne-Stokes respiration), suggesting our mechanistic understanding is limited.

OBJECTIVES

We propose that daytime ventilatory oscillations generally result from a chemoreflex resonance, in which spontaneous biological variations in ventilatory drive repeatedly induce temporary and irregular ringing effects. Importantly, the ease with which spontaneous biological variations induce irregular oscillations (resonance "strength") rises profoundly as loop gain rises toward 1. We tested this hypothesis through a comparison of mathematical predictions against actual measurements in patients with heart failure and healthy control subjects.

METHODS

In 25 patients with chronic heart failure and 25 control subjects, we examined spontaneous oscillations in ventilation and separately quantified loop gain using dynamic inspired CO₂ stimulation.

MEASUREMENTS AND MAIN RESULTS

Resonance was detected in 24 of 25 patients with heart failure and 18 of 25 control subjects. With increased loop gain-consequent to increased chemosensitivity and delay-the strength of spontaneous oscillations increased precipitously as predicted (r = 0.88), yielding larger (r = 0.78) and more regular (interpeak interval SD, r = -0.68) oscillations (P < 0.001 for all, both groups combined).

CONCLUSIONS

Our study elucidates the mechanism underlying daytime ventilatory oscillations in heart failure and provides a means to measure and interpret these oscillations to reveal the underlying chemoreflex hypersensitivity and reduced stability that foretells mortality in this population.

ECG-derived Cheyne-Stokes respiration and periodic breathing in healthy and hospitalized populations

BACKGROUND

Cheyne-Stokes respiration (CSR) has been investigated primarily in outpatients with heart failure. In this study we compare CSR and periodic breathing (PB) between healthy and cardiac groups.

METHODS

We compared CSR and PB, measured during 24 hr of continuous 12-lead electrocardiographic (ECG) Holter recording, in a group of 90 hospitalized patients presenting to the emergency department with symptoms suggestive of acute coronary syndrome (ACS) to a group of 100 healthy ambulatory participants. We also examined CSR and PB in the 90 patients presenting with ACS symptoms, divided into a group of 39 (43%) with confirmed ACS, and 51 (57%) with a cardiac diagnosis but non-ACS. SuperECG software was used to derive respiration and then calculate CSR and PB episodes from the ECG Holter data. Regression analyses were used to analyze the data. We hypothesized SuperECG software would differentiate between the groups by detecting less CSR and PB in the healthy group than the group of patients presenting to the emergency department with ACS symptoms.

RESULTS

Hospitalized patients with suspected ACS had 7.3 times more CSR episodes and 1.6 times more PB episodes than healthy ambulatory participants. Patients with confirmed ACS had 6.0 times more CSR episodes and 1.3 times more PB episodes than cardiac non-ACS patients.

CONCLUSION

Continuous 12-lead ECG derived CSR and PB appear to differentiate between healthy participants and hospitalized patients.

Recognition and treatment of sleep-disordered breathing: an important component of chronic disease management

Sleep-disordered breathing (SDB) is a highly prevalent condition, and is associated with many debilitating chronic diseases. The role of untreated obstructive sleep apnea (OSA) in arterial hypertension has been recognized in international guidelines. Treatment with continuous positive airway pressure (CPAP) is associated with clinically-relevant reductions in blood pressure. In heart failure (HF), SDB is associated with worse prognosis and increased mortality. Major HF guidelines recommend that patients should be treated for sleep apnea to improve their HF status. Severe OSA increases the risk of arrhythmias, including atrial fibrillation, influences risk management in stroke, and is highly prevalent in patients with type 2 diabetes. Effective treatment with CPAP improves the success of antiarrhythmic interventions, improves outcomes in stroke and reduces hyperglycemia in diabetes. Patients with coronary artery disease also have a high prevalence of SDB, which is independently associated with worse outcomes. The role of CPAP for secondary cardiovascular prevention remains to be determined. Data from large, well-conducted clinical trials have shown that noninvasive ventilation, targeted to markedly reduce hypercapnia, significantly improves survival and reduces readmission in stable hypercapnic chronic obstructive pulmonary disease. The association of SDB with chronic diseases contributes to the high healthcare costs incurred by SDB patients. SDB also has an important negative impact on quality of life, which is reversed by CPAP treatment. The high prevalence of SDB, and its association with diseases that cause significant morbidity and mortality, suggest that the diagnosis and management of SDB is an important therapeutic goal. First, adherent CPAP treatment significantly improves the quality of life of all patients with SDB; second, it eliminates the negative impact of untreated SDB on any associated chronic diseases; and third, it significantly reduces the increased costs of all hospital and medical services directly associated with untreated SDB. In short, the recognition and treatment of SDB is vital for the continued health and wellbeing of individual patients with SDB.

Independent prognostic importance of respiratory instability and sympathetic nerve activity in patients with chronic heart failure

BACKGROUND

Respiratory instability in chronic heart failure (CHF) is characterized by irregularly rapid respiration or non-periodic breathing rather than by Cheyne-Stokes respiration. We developed a new quantitative measure of respiratory instability (RSI) and examined its independent prognostic impact upon CHF.

METHODS

In 87 patients with stable CHF, respiratory flow and muscle sympathetic nerve activity (MSNA) were simultaneously recorded. RSI was calculated from the frequency distribution of respiratory spectral components and very low frequency components.

RESULTS

During a mean follow-up of 85±38 months, 24 patients died. Sixteen patients who died of cardiac causes had a lower RSI (16±6 vs. 30±21, p<0.01), a lower specific activity scale (4.3±1.4 Mets vs. 5.7±1.4 Mets, p<0.005), a higher MSNA burst area (16±5% vs. 11±4%, p<0.001), and a higher brain natriuretic peptide (BNP) level (514±559pg/ml vs. 234±311pg/ml, p<0.05) than 71 patients who did not die of cardiac causes. Multivariate analysis revealed that RSI (p=0.015), followed by MSNA burst area (p=0.033), was an independent predictor of subsequent all-cause deaths and that RSI (p=0.026), MSNA burst area (p=0.001), and BNP (p=0.048) were independent predictors of cardiac deaths. Patients at very high risk of fatal outcome could be identified by an RSI<20.

CONCLUSIONS

The daytime respiratory instability quantified by a new measure of RSI has prognostic importance independent of sympathetic nerve activation in patients with clinically stable CHF. An RSI of <20 identifies patients at very high risk for subsequent all-cause and cardiovascular death.

Consequences of Obstructive Sleep Apnea: Cardiovascular Risk of Obstructive Sleep Apnea and Whether Continuous Positive Airway Pressure Reduces that Risk

Obstructive sleep apnea (OSA) is present in up to 25% of otherwise healthy individuals. OSA is associated with intermittent hypoxia, oxidative stress, sympathetic activation, and an inflammatory response. These perturbations mediate the role of OSA as an independent and modifiable risk factor for cardiovascular disease (CVD). OSA can induce CVD or accelerate the progression of CVD into an end-stage disorder, including heart failure and stroke. Current clinical recommendations are based on existing clinical trial data and the clinical experience of our program; current and future clinical trials will help to optimize management of OSA in the setting of CVD.

Precapillary Pulmonary Hypertension and Sleep-Disordered Breathing: Is There a Link?

Among patients with sleep apnea the reported prevalence of precapillary pulmonary hypertension (PH) has varied largely, depending on patient selection, disease definition, and associated conditions, in particular chronic pulmonary disease. However, in the absence of comorbidities, PH seems to be rare in patients with sleep apnea. Conversely, sleep-related breathing disorders have been commonly found in patients with PH and they have been associated with an impaired quality of life. Since sleep-related breathing disorders may affect the pulmonary circulation and vice versa, patients with sleep-related breathing disorders should be evaluated for risk factors, symptoms and clinical signs of PH and right ventricular heart failure and patients with PH should be evaluated for sleep apnea. Therapeutic options for patients with sleep apnea and PH may include supplemental oxygen, drugs and positive pressure ventilation. Both nocturnal oxygen administration and acetazolamide have been shown to improve sleep apnea in patients with PH. In addition, oxygen therapy also improved exercise performance. Further studies are needed to corroborate the efficacy of these and other treatments.

Heart failure and sleep disorders

Awareness of the importance of sleep-related disorders in patients with cardiovascular diseases is growing. In particular, sleep-disordered breathing, short sleep time, and low sleep quality are frequently reported by patients with heart failure (HF). Sleep-disordered breathing, which includes obstructive sleep apnoea (OSA) and central sleep apnoea (CSA), is common in patients with HF and has been suggested to increase the morbidity and mortality in these patients. Both OSA and CSA are associated with increased sympathetic activation, vagal withdrawal, altered haemodynamic loading conditions, and hypoxaemia. Moreover, OSA is strongly associated with arterial hypertension, the most common risk factor for cardiac hypertrophy and failure. Intrathoracic pressure changes are also associated with OSA, contributing to haemodynamic alterations and potentially affecting overexpression of genes involved in ventricular remodelling. HF treatment can decrease the severity of both OSA and CSA. Indeed, furosemide and spironolactone administration, exercise training, cardiac resynchronization therapy, and eventually heart transplantation have shown a positive effect on OSA and CSA in patients with HF. At present, whether CSA should be treated and, if so, which is the optimal therapy is still debated. By contrast, more evidence is available on the beneficial effects of OSA treatment in patients with HF.

Impact of Heart Transplantation on Cheyne-Stokes Respiration in a Child

Sleep disordered breathing is well described in adults with heart failure but not in pediatric population. We describe a 13-year-old Caucasian male with severe heart failure related to dilated cardiomyopathy who demonstrated polysomnographic features of Cheyne-Stokes respiration, which completely resolved following cardiac transplantation. Cheyne-Stokes respiration in children with advanced heart failure and its resolution after heart transplant can be observed similar to adults.

Relationship between central sleep apnea and Cheyne-Stokes Respiration

Central sleep apnea (CSA) in patients with heart failure (HF) occurs frequently and shows a serious influence on prognosis in this population. The key elements in the pathophysiology of CSA are respiratory instability with chronic hyperventilation, changes of arterial carbon dioxide pressure (pCO2) and elongated circulation time. The main manifestation of CSA in patients with HF is Cheyne-Stokes Respiration (CSR). The initial treatment is the optimization of HF therapy. However, many other options of the therapeutic management have been studied, particularly those based on positive airway pressure methods. In patients with heart failure we often can observe the overlap of CSA and CSR; we will discuss the differences between these forms of breathing disorders during sleep. We will also discuss when CSA and CSR occur independently of each other and the importance of CSR occurring during the daytime in context of CSA during the nighttime.

Altered breathing syndrome in heart failure: newer insights and treatment options

In patients with heart failure (HF), altered breathing patterns, including periodic breathing, Cheyne-Stokes breathing, and oscillatory ventilation, are seen in several situations. Since all forms of altered breathing cause similar detrimental effects on clinical outcomes, they may be considered collectively as an "altered breathing syndrome." Altered breathing syndrome should be recognized as a comorbid condition of HF and as a potential therapeutic target. In this review, we discuss mechanisms and therapeutic options of altered breathing while sleeping, while awake at rest, and during exercise.