Cheyne-Stokes respiration during sleep in congestive heart failure

Open-source software for respiratory rate estimation using single-lead electrocardiograms

Respiratory rate (RR) is a critical vital sign used to assess pulmonary function. Currently, RR estimating instrumentation is specialized and bulky, therefore unsuitable for remote health monitoring. Previously, RR was estimated using proprietary software that extract surface electrocardiogram (ECG) waveform features obtained at several thoracic locations. However, developing a non-proprietary method that uses minimal ECG leads, generally available from mobile cardiac monitors is highly desirable. Here, we introduce an open-source and well-documented Python-based algorithm that estimates RR requiring only single-stream ECG signals. The algorithm was first developed using ECGs from awake, spontaneously breathing adult human subjects. The algorithm-estimated RRs exhibited close linear correlation to the subjects' true RR values demonstrating an R2 of 0.9092 and root mean square error of 2.2 bpm. The algorithm robustness was then tested using ECGs generated by the ischemic hearts of anesthetized, mechanically ventilated sheep. Although the ECG waveforms during ischemia exhibited severe morphologic changes, the algorithm-determined RRs exhibited high fidelity with a resolution of 1 bpm, an absolute error of 0.07 ± 0.07 bpm, and a relative error of 0.67 ± 0.64%. This optimized Python-based RR estimation technique will likely be widely adapted for remote lung function assessment in patients with cardiopulmonary disease.

Ambulatory monitoring promises equitable personalized healthcare delivery in underrepresented patients

The pandemic has brought to everybody's attention the apparent need of remote monitoring, highlighting hitherto unseen challenges in healthcare. Today, mobile monitoring and real-time data collection, processing and decision-making, can drastically improve the cardiorespiratory-haemodynamic health diagnosis and care, not only in the rural communities, but urban ones with limited healthcare access as well. Disparities in socioeconomic status and geographic variances resulting in regional inequity in access to healthcare delivery, and significant differences in mortality rates between rural and urban communities have been a growing concern. Evolution of wireless devices and smartphones has initiated a new era in medicine. Mobile health technologies have a promising role in equitable delivery of personalized medicine and are becoming essential components in the delivery of healthcare to patients with limited access to in-hospital services. Yet, the utility of portable health monitoring devices has been suboptimal due to the lack of user-friendly and computationally efficient physiological data collection and analysis platforms. We present a comprehensive review of the current cardiac, pulmonary, and haemodynamic telemonitoring technologies. We also propose a novel low-cost smartphone-based system capable of providing complete cardiorespiratory assessment using a single platform for arrhythmia prediction along with detection of underlying ischaemia and sleep apnoea; we believe this system holds significant potential in aiding the diagnosis and treatment of cardiorespiratory diseases, particularly in underserved populations.

Design Implementation and Evaluation of a Mobile Continuous Blood Oxygen Saturation Monitoring System

Objective: In this study, we built a mobile continuous Blood Oxygen Saturation (SpO2) monitor, and for the first time, explored key design principles towards daily applications. Methods: We firstly built a customized wearable computer that can sense two-channel photoplethysmogram (PPG) signals, and transmit the signals wirelessly to smartphone. Afterwards, we explored many SpO2 model building principles, focusing on linear/nonlinear models, different PPG parameter calculation methods, and different finger types. Moreover, we further compared PPG sensor placement principles by comparing different hand configurations and different finger configurations. Finally, a dataset collected from eleven human subjects was used to evaluate the mobile health monitor and explore all of the above design principles. Results: The experimental results show that the root mean square error of the SpO2 estimation is only 1.8, indicating the effectiveness of the system. Conclusion: These results indicate the effectiveness of the customized mobile SpO2 monitor and the selected design principles. Significance: This research is expected to facilitate the continuous SpO2 monitoring of patients with clinical indications.

A Noncontact Breathing Disorder Recognition System Using 2.4-GHz Digital-IF Doppler Radar

In this paper, a noncontact breathing disorder recognition system has been proposed for identifying irregular breathing patterns. The proposed system consists of a Doppler radar-based sensor module and a machine-learning-based breathing disorder recognition module. A custom-designed 2.4-GHz continuous wave digital-IF Doppler radar is utilized as the radar sensor module to accurately capture the time-domain breathing waveform. Then, a recognition module is designed with selected features and optimized classifiers. Four sets of experiments have been carried out to evaluate the proposed system comprehensively. For the laboratorial experiments, the proposed system achieves 94.7% classification accuracy using the linear support vector machine classifier with seven selected features. Results of clinical experiments demonstrate the feasibility of long-term breathing disorder recognition with good accuracy and robustness, and illustrate the potential of the proposed solution for the auxiliary diagnosis of diseases.

A Novel Point-of-Care Smartphone Based System for Monitoring the Cardiac and Respiratory Systems

Cardio-respiratory monitoring is one of the most demanding areas in the rapidly growing, mobile-device, based health care delivery. We developed a 12-lead smartphone-based electrocardiogram (ECG) acquisition and monitoring system (called “cvrPhone”), and an application to assess underlying ischemia, and estimate the respiration rate (RR) and tidal volume (TV) from analysis of electrocardiographic (ECG) signals only. During in-vivo swine studies (n = 6), 12-lead ECG signals were recorded at baseline and following coronary artery occlusion. Ischemic indices calculated from each lead showed statistically significant (p < 0.05) increase within 2 min of occlusion compared to baseline. Following myocardial infarction, spontaneous ventricular tachycardia episodes (n = 3) were preceded by significant (p < 0.05) increase of the ischemic index ~1–4 min prior to the onset of the tachy-arrhythmias. In order to assess the respiratory status during apnea, the mechanical ventilator was paused for up to 2 min during normal breathing. We observed that the RR and TV estimation algorithms detected apnea within 7.9 ± 1.1 sec and 5.5 ± 2.2 sec, respectively, while the estimated RR and TV values were 0 breaths/min and less than 100 ml, respectively. In conclusion, the cvrPhone can be used to detect myocardial ischemia and periods of respiratory apnea using a readily available mobile platform.

Sleep Disturbances in Patients with Chronic Heart Failure and Their Holistic Consequences—What Different Care Actions can be Implemented?

Background: Sleep disturbances are prevalent among elderly, especially among those with chronic heart failure (CHF) and can affect all dimensions of quality of life (QOL) negatively.

Aim: To describe the most common causes leading to sleep disturbances in patients with CHF, their consequences from a holistic perspective and different care actions that can be implemented.

Methods: MEDLINE and CINAHL databases were searched from 1989 to July 2004.

Findings: Sleep disordered breathing (SDB), and insomnia were the most common causes for sleep disturbances and occurs in 45–82% (SDB) and one-third (insomnia) of all patients with CHF. SDB cause a disturbed sleep structure with frequent awakenings, as well as several adverse effects on the cardiovascular system causing increased morbidity and mortality. Insomnia, caused by anxiety, an unknown life situation in relation to the debut of CHF, or symptoms/deteriorations of CHF can lead to negative effects on all aspects of QOL, as well as daytime sleepiness.

Conclusion: The high prevalence of sleep disturbances and their holistic consequences should be taken into account when nurses asses and plan the care for patients with CHF. Randomized studies with large sample sizes evaluating non-pharmacological nursing interventions that improve sleep are needed.

Mechanisms and clinical consequences of untreated central sleep apnea in heart failure

Central sleep apnea (CSA) is a highly prevalent, though often unrecognized, comorbidity in patients with heart failure (HF). Data from HF population studies suggest that it may present in 30% to 50% of HF patients. CSA is recognized as an important contributor to the progression of HF and to HF-related morbidity and mortality. Over the past 2 decades, an expanding body of research has begun to shed light on the pathophysiologic mechanisms of CSA. Armed with this growing knowledge base, the sleep, respiratory, and cardiovascular research communities have been working to identify ways to treat CSA in HF with the ultimate goal of improving patient quality of life and clinical outcomes. In this paper, we examine the current state of knowledge about the mechanisms of CSA in HF and review emerging therapies for this disorder.

When insomnia is not just insomnia: the deeper correlates of disturbed sleep with reference to DSM-5

Recent scientific evidences have brought a paradigm shift in our approach towards the concepts of insomnia and its management. The differentiation between primary and secondary insomnia was proved more hypothetical than actual and based upon the current evidences insomnia subtypes described in earlier system have been lumped into one-insomnia disorder. Research in this field suggests that insomnia occurring during psychiatric or medical disorders has a bidirectional and interactive relationship with and coexisting medical and psychiatric illnesses. The new approach looks to coexist psychiatric or medical disorders as comorbid conditions and hence specifies two coexisting conditions. Therefore, the management and treatment plans should address both the conditions. A number of sleep disorders may present with insomnia like symptoms and these disorders should be treated efficiently in order to alleviate insomnia symptoms. In such cases, a thorough history from the patient and his/her bed-partner is warranted. Moreover, some patients may need polysomnography or other diagnostic tests like actigraphy to confirm the diagnosis of the underlying sleep disorder. DSM-5 classification system of sleep–wake disorders has several advantages, e.g., it has seen insomnia across different dimensions to make it clinically more useful; it focuses on the assessment of severity and guides the mental health professional when to refer a patient of insomnia to a sleep specialist; lastly, it may encourage the psychiatrists to opt for sleep medicine as a career.

A novel adaptive servoventilation (ASVAuto) for the treatment of central sleep apnea associated with chronic use of opioids

STUDY OBJECTIVES

To compare the efficacy and patient comfort of a new mode of minute ventilation-targeted adaptive servoventilation (ASVAuto) with auto-titrating expiratory positive airway pressure (EPAP) versus bilevel with back-up respiratory rate (bilevel-ST) in patients with central sleep apnea (CSA) associated with chronic use of opioid medications.

METHODS

Prospective, randomized, crossover polysomnography (PSG) study. Eighteen consecutive patients (age ≥ 18 years) who had been receiving opioid therapy (≥ 6 months), and had sleep disordered breathing with CSA (central apnea index [CAI] ≥ 5) diagnosed during an overnight sleep study or positive airway pressure (PAP) titration were enrolled to undergo 2 PSG studies-one with ASVAuto and one with bilevel-ST. Patients completed 2 questionnaires after each PSG; Morning After Patient Satisfaction Questionnaire and PAP Comfort Questionnaire.

RESULTS

Patients had a mean age of 52.9 ± 15.3 years. PSG prior to randomization showed an apnea hypopnea index (AHI) of 50.3 ± 22.2 and CAI of 13.0 ± 18.7. Titration with ASVAuto versus bilevel-ST showed that there were significant differences with respect to AHI and CAI. The AHI and CAI were significantly lower on ASVAuto than bilevel-ST (2.5 ± 3.5 versus 16.3 ± 20.9 [p = 0.0005], and 0.4 ± 0.8 versus 9.4 ± 18.8 [p = 0.0002], respectively). Respiratory parameters were normalized in 83.3% of patients on ASVAuto versus 33.3% on bilevel-ST. Patients felt more awake and alert on ASVAuto than bilevel-ST based on scores from Morning After Patient Satisfaction Questionnaire (p = 0.0337).

CONCLUSIONS

The ASVAuto was significantly more effective than bilevel-ST for the treatment of CSA associated with chronic opioid use.

An optimized method for estimating the tidal volume from intracardiac or body surface electrocardiographic signals: implications for estimating minute ventilation

The ability to accurately monitor tidal volume (TV) from electrocardiographic (ECG) signals holds significant promise for improving diagnosis treatment across a variety of clinical settings. The objective of this study was to develop a novel method for estimating the TV from ECG signals. In 10 mechanically ventilated swine, we collected intracardiac electrograms from catheters in the coronary sinus (CS), left ventricle (LV), and right ventricle (RV), as well as body surface electrograms, while TV was varied between 0 and 750 ml at respiratory rates of 7-14 breaths/min. We devised an algorithm to determine the optimized respirophasic modulation of the amplitude of the ECG-derived respiratory signal. Instantaneous measurement of respiratory modulation showed an absolute error of 72.55, 147.46, 85.68, 116.62, and 50.89 ml for body surface, CS, LV, RV, and RV-CS leads, respectively. Minute TV estimation demonstrated a more accurate estimation with an absolute error of 69.56, 153.39, 79.33, 122.16, and 48.41 ml for body surface, CS, LV, RV, and RV-CS leads, respectively. The RV-CS and body surface leads provided the most accurate estimations that were within 7 and 10% of the true TV, respectively. Finally, the absolute error of the bipolar RV-CS lead was significantly lower than any other lead configuration (P < 0.0001). In conclusion, we have demonstrated that ECG-derived respiratory modulation provides an accurate estimation of the TV using intracardiac or body surface signals, without the need for additional hardware.

An optimized method for the estimation of the respiratory rate from electrocardiographic signals: implications for estimating minute ventilation

It is well-known that respiratory activity influences electrocardiographic (ECG) morphology. In this article we present a new algorithm for the extraction of respiratory rate from either intracardiac or body surface electrograms. The algorithm optimizes selection of ECG leads for respiratory analysis, as validated in a swine model. The algorithm estimates the respiratory rate from any two ECG leads by finding the power spectral peak of the derived ratio of the estimated root-mean-squared amplitude of the QRS complexes on a beat-by-beat basis across a 32-beat window and automatically selects the lead combination with the highest power spectral signal-to-noise ratio. In 12 mechanically ventilated swine, we collected intracardiac electrograms from catheters in the right ventricle, coronary sinus, left ventricle, and epicardial surface, as well as body surface electrograms, while the ventilation rate was varied between 7 and 13 breaths/min at tidal volumes of 500 and 750 ml. We found excellent agreement between the estimated and true respiratory rate for right ventricular (R(2) = 0.97), coronary sinus (R(2) = 0.96), left ventricular (R(2) = 0.96), and epicardial (R(2) = 0.97) intracardiac leads referenced to surface lead ECGII. When applied to intracardiac right ventricular-coronary sinus bipolar leads, the algorithm exhibited an accuracy of 99.1% (R(2) = 0.97). When applied to 12-lead body surface ECGs collected in 4 swine, the algorithm exhibited an accuracy of 100% (R(2) = 0.93). In conclusion, the proposed algorithm provides an accurate estimation of the respiratory rate using either intracardiac or body surface signals without the need for additional hardware.

Sleep deprivation in critical illness: its role in physical and psychological recovery

Critically ill patients frequently experience poor sleep, characterized by frequent disruptions, loss of circadian rhythms, and a paucity of time spent in restorative sleep stages. Factors that are associated with sleep disruption in the intensive care unit (ICU) include patient-ventilator dysynchrony, medications, patient care interactions, and environmental noise and light. As the field of critical care increasingly focuses on patients' physical and psychological outcomes following critical illness, understanding the potential contribution of ICU-related sleep disruption on patient recovery is an important area of investigation. This review article summarizes the literature regarding sleep architecture and measurement in the critically ill, causes of ICU sleep fragmentation, and potential implications of ICU-related sleep disruption on patients' recovery from critical illness. With this background information, strategies to optimize sleep in the ICU are also discussed.

Control of breathing: two types of delays studied in an integrated model of the respiratory system

We use a recently developed mathematical model that integrates a reduced representation of the brainstem respiratory neural controller together with peripheral gas exchange and transport to study numerically the dynamic response of the respiratory system to several physiological stimuli. We compare between the system responses with two major sources of delay: circulatory transport vs. neural feedback dynamics, and we show that the dynamics of the neural feedback processes dictates the dynamic response to hypoxia and hypercapnia. The source of the circulatory delay (blood velocity vs. distance from the lungs to chemoreceptors) was found to be important. Our model predicts that periodic breathing is associated with the ventilatory "afterdischarge" (slow recovery of ventilation) after a brief perturbation of CO(2). We also predict that there could be two possible mechanisms for the appearance of periodic breathing and that circulatory delay is not a necessary condition for this to occur in certain cases.

The occurrence of cheyne-stokes respiration in congestive heart failure: the effect of age

INTRODUCTION

Up to 50% of adults with congestive heart failure (CHF) and left ventricular dysfunction demonstrate Cheyne-Stokes respiration (CSR), although the mechanisms remain controversial. Because CSR has been minimally studied in children, we sought to assess the prevalence of CSR in children with low and high output cardiac failure. We hypothesized that the existence of CSR only in children with low output CHF would support the importance of circulatory delay as a CSR mechanism.

METHODS

Thirty patients participated: 10 children with CHF, 10 matched children with no heart disease, and 10 adults with CHF. All participants underwent an in-laboratory polysomnographic sleep study.

RESULTS

CHF children's average age (±SEM) was 3.6 ± 2.1 years vs. 3.7 ± 2 years in the age-matched control group. The average ejection fraction of three children with low output CHF was 22 ± 6.8%. The remaining seven had normal-high cardiac output. Compared to control children, CHF children were tachypneic and tachycardic during stable sleep (55.1 ± 6.7 vs. 26.9 ± 3 breath/min and 127.6 ± 8.7 vs. 97.6 ± 6.9 beats/min, respectively, p < 0.05 for both). They had shorter total sleep time (195 ± 49 vs. 373 ± 16 min, p < 0.05) with a low sleep efficiency of 65.6 ± 6%. None of the children had a pattern of CSR at any time during the studies while the adults with CHF had 40% prevalence of CSR.

CONCLUSIONS

The complete absence of CSR in our sample of children with CHF compared to the 40% prevalence in the adults with CHF we studied, suggests that CSR may be an age-dependent phenomenon. Thus, we speculate that regardless of the exact mechanism which drives CSR, age is an over-riding factor.

Sleep-Disordered breathing in patients referred for angina evaluation--association with left ventricular dysfunction

BACKGROUND

Clinical observations have linked sleep-disordered breathing to cardiovascular morbidity and mortality, and especially to coronary artery disease.

HYPOTHESIS

The study was undertaken to determine the prevalence of sleep-disordered breathing in consecutive patients referred for angina evaluation, and analyzed the parameters influencing the severity of sleep-disordered breathing.

METHODS

In all, 68 consecutive patients (53 men, 15 women, aged 63.4 +/- 10.0 years) referred for angina evaluation were studied. Coronary angiography, selective left ventriculography, and a polygraphic study with a validated six-channel monitoring device were performed. Full-night polysomnography was used to reevaluate patients with an apnea/hypopnea index > or = 10/h.

RESULTS

Sleep-disordered breathing as defined by an apnea/hypopnea index > or = 10/h was found in 30.9% of patients; its prevalence was not increased in patients with and without coronary artery disease (26.5 vs. 42.1%). Multiple stepwise linear regression analysis revealed that the severity of sleep-disordered breathing was significantly and independently associated with left ventricular ejection fraction (r = -0.38; p = 0.002), but not with age, body mass index, gender, diabetes mellitus, hypertension, hyperuricemia, hypercholesterolemia, smoking habits, or coronary artery disease. In this group of patients, multiple logistic regression analysis could not demonstrate sleep-disordered breathing to be an independent predictor of coronary artery disease.

CONCLUSIONS

Sleep-disordered breathing is common in patients referred for angina evaluation. The degree of sleep-disordered breathing is mainly determined by the extent of left ventricular dysfunction.

Central sleep apnea in a geriatric patient treated with aripiprazole

We report a case of central sleep apnea in a geriatric patient that was associated with treatment with aripiprazole for an episode of major depressive disorder with psychotic features. The patient was a 72-year-old man who was started on aripiprazole and developed central sleep apnea that improved significantly when the medication was stopped. A rechallenge with aripiprazole led to a worsening of the central sleep apnea, which again improved off the aripiprazole. We postulate that the central sleep apnea was due to aripiprazole. There have been numerous case reports in the literature of obstructive sleep apnea associated with atypical antipsychotics. To our knowledge, this is the first published case of central sleep apnea. We caution clinicians to be aware that there is potential risk of atypical antipsychotics like aripiprazole inducing or exacerbating central sleep apnea.

Behavioral recovery from acute hypoxia is reliant on leptin

Individuals affected by hypoxia experience a variety of immune-associated sickness symptoms including malaise, fatigue, lethargy and loss of interest in the physical and social environment. Recently, we demonstrated that the interleukin (IL)-1beta arm of the neuroimmune system was critical to the sickness symptoms caused by hypoxia, and that IL-1 receptor antagonist (IL-1RA), IL-1beta's endogenous inhibitor, was critical to promoting sickness recovery. Here, we report that leptin is key to recovery from hypoxia because it dramatically augmented IL-1RA production in mice. We found that hypoxia increased leptin in white adipose tissue (WAT) which in turn, caused a marked rise in serum IL-1RA. Interestingly, in-vitro, leptin was a more potent inducer of IL-RA, in macrophages, than hypoxia. In leptin receptor defective (db/db) and leptin deficient (ob/ob) mice, sickness recovery from hypoxia was delayed 3-fold. Importantly, in ob/ob mice, leptin administration completely reversed this delayed recovery and induced a marked increase in serum IL-1RA. Finally, leptin administration to normal mice reduced hypoxia recovery time by 1/3 and dramatically increased WAT and serum IL-1RA. Leptin did not alter recovery from hypoxia in IL-1RA knock out mice. These results show that by enhancing IL-1RA production leptin promoted sickness recovery from hypoxia.

Model based analysis of sleep disordered breathing in congestive heart failure

We employed a computational model of the respiratory control system to examine which of several factors, in isolation and in combination, can contribute to or explain the development of Cheyne-Stokes breathing (CSB). Our approach uses a graphical method for stability analysis similar, in concept, to the phase plane. The results from the computer simulations indicate that a postulated three-fold increase in the chemosensitivity of the central chemoreflex (CCR) loop may, by itself, explain development of CSB. By contrast, a similar increase in the chemosensitivity of the peripheral chemoreflex (PCR) loop cannot, by itself, account for CSB. The analysis reveals that the system is more readily destabilized by increasing the gain of only one chemoreflex loop than by a combined increase in gain of both loops. Reduction in the cardiac output or cardiomegaly decreases the size of the stability region. We conclude that development of CSB is the result of a complex interaction between CCR and PCR loops which may, in turn, interact with decreased cardiac output and cardiomegaly.

Mathematical models of periodic breathing and their usefulness in understanding cardiovascular and respiratory disorders

Periodic breathing is an unusual form of breathing with oscillations in minute ventilations and with repetitive apnoeas or near apnoeas. Reported initially in patients with heart failure or stroke, it was later recognized to occur especially during sleep. The recurrent hypoxia and surges of sympathetic activity that often occur during the apnoeas have serious health consequences. Mathematical models have helped greatly in the understanding of the causes of recurrent apnoeas. It is unlikely that every instance of periodic breathing has the same cause, but many result from instability in the feedback control involved in the chemical regulation of breathing caused by increased controller and plant gains and delays in information transfer. Even when it is not the main cause of the periodic breathing, unstable control modifies the ventilatory pattern and sometimes intensifies the recurrent apnoeas. The characteristics of disturbances to breathing and their interaction with the control system can be critical in determining ventilation responses and the occurrence of periodic breathing. Large abrupt changes in ventilation produced, for example, in the transition from waking to sleep and vice versa, or in the transition from breathing to apnoea, are potent factors causing periodic breathing. Mathematical models show that periodic breathing is a 'systems disorder' produced by the interplay of multiple factors. Multiple factors contribute to the occurrence of periodic breathing in congestive heart failure and cerebrovascular disease, increasing treatment options.

Postoperative day one: a high risk period for respiratory events

BACKGROUND

In 2001, the Joint Commission on Accreditation of Healthcare Organizations released Pain Management Standards that has led to an increased focus on pain control. Since then the Institute for Safe Medication Practices has noted that overaggressive pain management has led to increases in oversedation and fatal respiratory depression. One of our previous studies found that postoperative patients may be reaching dangerously high levels of sedation as a result of pain management. Our hypothesis is that postoperative patients who have a respiratory event caused by analgesic use are more likely to have that event in the first postoperative day.

METHODS

We performed a retrospective case-control analysis identifying 62 postoperative patients who had a respiratory event. A respiratory event was defined as respiratory depression caused by narcotic use in the postoperative period that was reversed by naloxone. Sixty-two postoperative patients with no such event were chosen randomly and frequency matched based on surgical procedure and diagnosis-related group. Risk factors for an event were identified.

RESULTS

Of the cases, 77.4% had a respiratory event in the first 24 hours postoperatively. Significant risk factors for an event were as follows: 65 years of age or older, having chronic obstructive pulmonary disease, having 1 or more comorbidities, and being placed on hydromorphone.

CONCLUSIONS

The first 24 hours after surgery represents a high-risk period for a respiratory event as a result of narcotic use. The realization of this risk can lead to the implementation of standards to increase patient safety in the first postoperative day.

Impact of symptom prevalence and symptom burden on quality of life in patients with heart failure

BACKGROUND

Heart failure is an escalating health problem around the world. Despite significant scientific advances, heart failure patients experience multiple physical and psychological symptoms that can impact the quality of life.

AIMS

To determine the (1) symptom prevalence, severity, distress and symptom burden in patients with heart failure; (2) impact of age and gender on symptom prevalence, severity, distress and symptom burden; and (3) impact of symptom prevalence and symptom burden on health-related quality of life (HRQOL) in patients with heart failure.

METHODS

A convenience sample of 53 heart failure patients participated in this descriptive, cross-sectional design. Symptoms and HRQOL were measured using the Memorial Symptom Assessment Scale-Heart Failure and the Minnesota Living with Heart Failure Questionnaire.

RESULTS

Patients experienced a mean of 15.1+/-8.0 symptoms. Shortness of breath and lack of energy were the most prevalent. Difficulty sleeping was the most burdensome symptom. Lower age, worse functional status, total symptom prevalence and total symptom burden predicted 67% of the variance in HRQOL.

CONCLUSION

Patients with heart failure experience a high level of symptoms and symptom burden. Nurses should target interventions to decrease frequency, severity, distress and overall symptom burden and improve HRQOL.

Simplified models for gas exchange in the human lungs

This paper presents a hierarchy of models with increasing complexity for gas exchange in the human lungs. The models span from a single compartment, inflexible lung to a single compartment, flexible lung with pulmonary gas exchange. It is shown how the models are related to well-known models in the literature. A long-term purpose of this work is to study nonlinear phenomena seen in the cardio-respiratory system (for example, synchronization between ventilation rate and heart rate, and Cheyne-Stokes respiration). The models developed in this paper can be regarded as the controlled system (plant) and provide a mathematical framework to link between "molecular-level", and "systems-level" models. It is shown how changes in molecular level affect the alveolar partial pressure. Two assumptions that have previously been made are re-examined: (1) the hidden assumption that the air flow through the mouth is equal to the rate of volume change in the lungs, and, (2) the assumption that the process of oxygen binding to hemoglobin is near equilibrium. Conditions under which these assumptions are valid are studied. All the parameters in the models, except two, are physiologically realistic. Numerical results are consistent with published experimental observations.

Impact of heart failure on quality of sleep

Chronic heart failure is an important health problem associated with a high mortality and morbidity. Appropriate treatment reduces mortality and leads to improved exercise tolerance but many patients report poor quality of sleep. Sleep studies of patients with heart failure suggest that sleep disordered breathing is experienced in 50% of patients and is a powerful predictor of poor prognosis. Sleep disordered breathing broadly comprises obstructive sleep apnoea, when upper airway instability causes mechanical obstruction to breathing; and central sleep apnoea, characterised by an absence of ventilatory effort. Sleep disordered breathing occurring in patients with heart failure is in most part attributable to central sleep apnoea and reflects uncompensated instability of the ventilatory feedback mechanism.

A cardiovascular-respiratory control system model including state delay with application to congestive heart failure in humans

This paper considers a model of the human cardiovascular-respiratory control system with one and two transport delays in the state equations describing the respiratory system. The effectiveness of the control of the ventilation rate is influenced by such transport delays because blood gases must be transported a physical distance from the lungs to the sensory sites where these gases are measured. The short term cardiovascular control system does not involve such transport delays although delays do arise in other contexts such as the baroreflex loop (see [46]) for example. This baroreflex delay is not considered here. The interaction between heart rate, blood pressure, cardiac output, and blood vessel resistance is quite complex and given the limited knowledge available of this interaction, we will model the cardiovascular control mechanism via an optimal control derived from control theory. This control will be stabilizing and is a reasonable approach based on mathematical considerations as well as being further motivated by the observation that many physiologists cite optimization as a potential influence in the evolution of biological systems (see, e.g., Kenner [29] or Swan [62]). In this paper we adapt a model, previously considered (Timischl [63] and Timischl et al. [64]), to include the effects of one and two transport delays. We will first implement an optimal control for the combined cardiovascular-respiratory model with one state space delay. We will then consider the effects of a second delay in the state space by modeling the respiratory control via an empirical formula with delay while the the complex relationships in the cardiovascular control will still be modeled by optimal control. This second transport delay associated with the sensory system of the respiratory control plays an important role in respiratory stability. As an application of this model we will consider congestive heart failure where this transport delay is larger than normal and the transition from the quiet awake state to stage 4 (NREM) sleep. The model can be used to study the interaction between cardiovascular and respiratory function in various situations as well as to consider the influence of optimal function in physiological control system performance.

Sleep disruption in critically ill patients--pharmacological considerations

Sleep disturbances are common in critically ill patients and contribute to morbidity. Environmental factors, patient care activities and acute illness are all potential causes of disrupted sleep. Additionally, it is important to consider drug therapy as a contributing factor to this adverse experience, which patients perceive as particularly stressful. Sedative and analgesic combinations used to facilitate mechanical ventilation are among the most sleep disruptive drugs. Cardiovascular, gastric protection, anti-asthma, anti-infective, antidepressant and anticonvulsant drugs have also been reported to cause a variety of sleep disorders. Withdrawal reactions to prescribed and occasionally recreational drugs should also be considered as possible triggers for sleep disruption. Tricyclic antidepressants and benzodiazepines are commonly prescribed in the treatment of sleep disorders, but have problems with decreasing slow wave and rapid eye movement sleep phases. Newer non-benzodiazepine hypnotics offer little practical advantage. Melatonin and atypical antipsychotics require further investigation before their routine use can be recommended.

Sleep-related breathing disorders in patients who are critically ill

This descriptive study describes the frequency and severity of sleep-related breathing disorders in men who are hemodynamically stable who have an acute cardiovascular illness and are hospitalized in a critical care unit. Sixty-four males, aged 55-79 years, with an acute cardiovascular illness, stable hemodynamics, and no ongoing chest pain or history of sleep apnea were studied for 1 night in the critical care unit using polysomnography. Forty-seven percent of the sample had an apnea-hypopnea index > or = 5, with events of both obstructive and central etiologies, including Cheyne-Stokes respiration. Oxygen desaturation to < or = 90% occurred in 61% of the sample. There were no episodes of chest pain, ventricular tachycardia, or heart block associated with apneic or hypopneic events; however, dysrhythmias, including sinus bradycardia, supraventricular tachycardia, and premature ventricular beats, were associated with apneic and hypopneic events.

Sleep and heart failure

Sleep problems and symptoms of sleep disturbance are very prevalent in patients with heart failure (HF). Numerous contributing factors include sleep-related breathing disorders, increasing age, medications, anxiety and depression, and comorbidities. Thus, the cardiovascular nurse has an important role in the recognition and management of sleep-related problems in persons with HF. This article provides an overview of sleep disturbances in patients with HF, suggests evidence-based strategies for managing the sleep problems, and identifies pertinent areas for future nursing inquiry.

Central sleep apnoea syndrome in patients with chronic heart disease: a critical review of the current literature

The prevalence, prognosis, clinical presentation, pathophysiology, diagnosis, and treatment of the central sleep apnoea syndrome (CSAS) are reviewed and its relationship with congestive heart failure (CHF) is discussed. Adequately powered trials are needed with survival and health status as end points to establish whether correction of sleep related breathing abnormalities improves the outcome in patients with CHF.

Apnea and bradypnea in patients receiving epidural bupivacaine-morphine for postoperative pain relief as assessed by a new monitoring method

STUDY OBJECTIVE

To evaluate postoperative breathing patterns with a new monitoring device in patients given bupivacaine-morphine epidural analgesia.

DESIGN

Open explorative study.

SETTING

Inpatient anesthesia in a university hospital setting.

PATIENTS

15 ASA physical status I and II patients aged 28 to 87 years and scheduled for major abdominal surgery.

INTERVENTIONS

All patients underwent abdominal surgery with epidural anesthesia combined with general anesthesia. Postoperatively, they continued with epidural analgesia consisting of bupivacaine and morphine. On the first postoperative night, the breathing pattern was studied with a new noninvasive monitoring device measuring respiratory frequency and apnea. Arterial blood gas analysis was performed in case of apnea or low respiratory frequency.

MEASUREMENTS AND MAIN RESULTS

A total of 84 alarm events were registered in 11 patients. Twenty-one percent (18/84) of the alarms were associated with arterial carbon dioxide tension (PaCO2) levels greater than 48.8 mmHg. Three of the four patients with PaCO2 levels greater than 48.8 mmHg were older than 80 years of age.

CONCLUSION

The tested noninvasive monitoring device may detect abnormal respiratory breathing patterns in patients at risk for respiratory depression during epidural analgesia with bupivacaine-morphine.

Dynamic ventilatory response to CO(2) in congestive heart failure patients with and without central sleep apnea

Nonobstructive (i.e., central) sleep apnea is a major cause of sleep-disordered breathing in patients with stable congestive heart failure (CHF). Although central sleep apnea (CSA) is prevalent in this population, occurring in 40-50% of patients, its pathogenesis is poorly understood. Dynamic loop gain and delay of the chemoreflex response to CO(2) was measured during wakefulness in CHF patients with and without CSA by use of a pseudorandom binary CO(2) stimulus method. Use of a hyperoxic background minimized responses derived from peripheral chemoreceptors. The closed-loop and open-loop gain, estimated from the impulse response, was three times greater in patients with nocturnal CSA (n = 9) than in non-CSA patients (n = 9). Loop dynamics, estimated by the 95% response duration time, did not differ between the two groups of patients. We speculate that an increase in dynamic gain of the central chemoreflex response to CO(2) contributes to the genesis of CSA in patients with CHF.

The evaluation and management of hypoxemia in the chronic critically ill patient

Hypoxemia is a prevalent problem in the chronically critically ill patient. This article reviews the pathophysiologic mechanisms of hypoxemia in this patient population, discusses how oxygenation is evaluated, and reviews methods for delivery of oxygen. Other topics directly related to oxygen use, such as oxygen toxicity, heliox use, and portable oxygen devices, are included.

Periodic breathing in heart failure patients: testing the hypothesis of instability of the chemoreflex loop

In this study, we applied time- and frequency-domain signal processing techniques to the analysis of respiratory and arterial O(2) saturation (Sa(O(2))) oscillations during nonapneic periodic breathing (PB) in 37 supine awake chronic heart failure patients. O(2) was administered to eight of them at 3 l/min. Instantaneous tidal volume and instantaneous minute ventilation (IMV) signals were obtained from the lung volume signal. The main objectives were to verify 1) whether the timing relationship between IMV and Sa(O(2)) was consistent with modeling predictions derived from the instability hypothesis of PB and 2) whether O(2) administration, by decreasing loop gain and increasing O(2) stores, would have increased system stability reducing or abolishing the ventilatory oscillation. PB was centered around 0.021 Hz, whereas respiratory rate was centered around 0.33 Hz and was almost stable between hyperventilation and hypopnea. The average phase shift between IMV and Sa(O(2)) at the PB frequency was 205 degrees (95% confidence interval 198-212 degrees). In 12 of 37 patients in whom we measured the pure circulatory delay, the predicted lung-to-ear delay was 28.8 +/- 5.2 s and the corresponding observed delay was 30.9 +/- 8.8 s (P = 0.13). In seven of eight patients, O(2) administration abolished PB (in the eighth patient, Sa(O(2)) did not increase). These results show a remarkable consistency between theoretical expectations derived from the instability hypothesis and experimental observations and clearly indicate that a condition of loss of stability in the chemical feedback control of ventilation might play a determinant role in the genesis of PB in awake chronic heart failure patients.

Sleep disordered breathing in the elderly

Sleep disordered breathing (SDB), i.e., obstructive, central or mixed sleep apneas, has been recognized as a common occurrence in the elderly. Aging is per se associated with a decrease in the quality of sleep; SDB may further disrupt the sleep architecture in older subjects. The prevalence of obstructive sleep apnea (OSA) increases with aging; available studies report prevalence rates of 11-62%. Furthermore, OSA has been associated with increased mortality in older adults. Central apneas and periodic breathing occur with increased frequency either in subjects with neurological disorders such as infarction, tumor, sequelae of infection, diffuse encephalopathies, or in chronic heart failure. Patients with cerebrovascular disease (stroke, or transient ischemic attacks) have a markedly high prevalence of SDB, mainly OSA. In these patients, SDB is associated with a poorer functional prognosis at 3 and 12 months after the acute event, and a higher mortality. The clinical impact of SDB on cognitive function appears to be modest in patients without dementia, although there is a moderate increase in daytime sleepiness. In Alzheimer's disease (AD) however, SDB occurs more frequently than in non-demented older subjects, and its severity is correlated with the degree of cognitive impairment. The hypothesis of a causal relationship between AD and SDB remains a subject of controversy. The possibility of SDB should be considered in the elderly in the differential diagnosis of "reversible dementias", increased daytime sleepiness, or unexplained right-sided heart failure.

Quantitative general theory for periodic breathing in chronic heart failure and its clinical implications

BACKGROUND

In patients with chronic heart failure (CHF), periodic breathing (PB) predicts poor prognosis. Clinical studies have identified numerous risk factors for PB (which also includes Cheyne-Stokes respiration). Computer simulations have shown that oscillations can arise from delayed negative feedback. However, no simple general theory quantitatively explains PB and its mechanisms of treatment using widely-understood clinical concepts. Therefore, we introduce a new approach to the quantitative analysis of the dynamic physiology governing cardiorespiratory stability in CHF.

METHODS AND RESULTS

An algebraic formula was derived (presented as a simple 2D plot), enabling prediction from easily acquired clinical data to determine whether respiration will be unstable. Clinical validation was performed in 20 patients with CHF (10 with PB and 10 without) and 10 healthy normal subjects. Measurements, including chemoreflex sensitivity (S) and delay (delta), alveolar volume (V(L)), and end-tidal CO(2) fraction (C), were applied to the stability formula. The breathing pattern was correctly predicted in 28 of the 30 subjects. The principal combined parameter (CS)x(delta/V(L)) was higher in patients with PB (14.2+/-3.0) than in those without PB (3.1+/-0.5; P:=0.0005) or in normal controls (2.4+/-0.5; P:=0.0003). This was because of differences in both chemoreflex sensitivity (1749+/-235 versus 620+/-103 and 526+/-104 L/min per atm CO(2); P:=0.0001 and P:<0.0001, respectively) and chemoreflex delay (0.53+/-0.06 vs 0.40+/-0.06 and 0.30+/-0.04 min; P:=NS and P:=0.02).

CONCLUSION

This analytical approach identifies the physiological abnormalities that are important in the genesis of PB and explicitly defines the region of predicted instability. The clinical data identify chemoreflex gain and delay time (rather than hyperventilation or hypocapnia) as causes of PB.

Cardiorespiratory interactions during periodic breathing in awake chronic heart failure patients

We applied spectral techniques to the analysis of cardiorespiratory signals [instantaneous lung volume (ILV), instantaneous tidal volume (ITV), arterial O(2) saturation (Sa(O(2))) at the ear, heart rate (HR), systolic (SAP), and diastolic (DAP) arterial pressure] during nonapneic periodic breathing (PB) in 29 awake chronic heart failure (CHF) patients and estimated the timing relationships between respiratory and slow cardiovascular (<0.04 Hz) oscillations. Our aim was 1) to elucidate major mechanisms involved in cardiorespiratory interactions during PB and 2) to test the hypothesis of a central vasomotor origin of PB. All cardiovascular signals were characterized by a dominant (>/=84% of total power) oscillation at the frequency of PB (mean +/- SE: 0.022 +/- 0.0008 Hz), highly coherent (>/=0.89), and delayed with respect to ITV (ITV-HR, 2.4 +/- 0.72 s; ITV-SAP, 6.7 +/- 0.65 s; ITV-DAP, 3.2 +/- 0.61 s; P < 0.01). Sa(O(2)) was highly coherent with (coherence function = 0.96 +/- 0. 009) and almost opposite in phase to ITV. These findings demonstrate the existence of a generalized cardiorespiratory rhythm led by the ventilatory oscillation and suggest that 1) the cyclic increase in inspiratory drive and cardiopulmonary reflexes and 2) mechanical effects of PB-induced changes in intrathoracic pressure are the more likely sources of the HR and blood pressure oscillations, respectively. The timing relationship between ITV and blood pressure signals excludes the possibility that PB represents the effect of a central vasomotor rhythm.

High prevalence and persistence of sleep apnoea in patients referred for acute left ventricular failure and medically treated over 2 months

AIMS

Cardiac failure patients were studied systematically using polysomnography 1 month after recovering from acute pulmonary oedema, and again after 2 months of optimal medical treatment for cardiac failure.

METHODS AND RESULTS

This prospective study of consecutive patients was conducted in a cardiac care unit of a university hospital. V o(2)measurements and left ventricular ejection fraction were recorded. Thirty-four patients, initially recruited with pulmonary oedema, improved after 1 month of medical treatment to NYHA II or III. They were aged less than 75 years and had a left ventricular ejection fraction less than 45% at the time of inclusion. Age was 62 (9) years, body mass index= 27 (5) kg x m(-2)and an ejection fraction= 30 (10)%. Eighteen of the 34 patients (53%) had coronary artery disease. Twenty-eight of the 34 had sleep apnoea syndrome with an apnoea+hypopnoea index >15 x h(-1)of sleep. Thus, the prevalence of sleep apnoea in this population was 82%. Twenty-one of 28 (75%) patients had central sleep apnoea and seven of 28 (25%) had obstructive sleep apnoea. Patients with central sleep apnoea had a lower Pa co(2)than those with obstructive sleep apnoea (33 (5) vs 37 (5) mmHg, P<0.005). Significant correlations were found between apnoea+hypopnoea index and peak exercise oxygen consumption (r= -0.73, P<0.01), and apnoea+hypopnoea index and Pa co(2)(r= -0.42, P = 0.03). When only central sleep apnoea patients were considered, a correlation between apnoea+hypopnoea index and left ventricular ejection fraction was also demonstrated (r= -0.46, P<0.04). After 2 months of optimal medical treatment only two patients (both with central sleep apnoea) showed improvement (apnoea+hypopnoea index <15 x h(-1)).

CONCLUSIONS

We have demonstrated a high prevalence of sleep apnoea, which persisted after 2 months of medical treatment, in patients referred for acute left ventricular failure. Central sleep apnoea can be considered a marker of the severity of congestive heart failure.

Respiratory aspects of neurological disease

Neurological disease may result in respiratory dysfunction; however the manifestations of respiratory dysfunction in such patients may be atypical because of wider effects of their underlying condition. In the present review we have considered separately acute neuromuscular respiratory disease (as well as aspects of respiratory muscle function relevant to intensive care), chronic neuromuscular respiratory disease, sleep related disorders, respiratory consequences of specific neurological diseases, and neurological features of respiratory disease. Approaches to specific clinical problems are discussed; in many instances this can be expedited by close cooperation with a respiratory physician. We suggest that management of respiratory dysfunction in neurological disease depends critically on three factors: firstly, knowledge of when respiratory dysfunction is likely to occur; secondly, maintaining a high index of clinical suspicion (specifically apparently vague symptoms should not be uncritically attributed to the underlying neurological condition); and, thirdly, the pursuing of appropriate investigations.

Efficacy of nasal continuous positive airway pressure therapy in chronic heart failure: importance of underlying cardiac rhythm

BACKGROUND

Some previous reports have indicated beneficial cardiac effects of nasal continuous positive airway pressure (NCPAP) in patients with severe congestive heart failure (CHF), but others have reported deleterious cardiac effects, particularly among patients in atrial fibrillation (AF). The aim of this study was to determine if differences in cardiac rhythm influence the acute cardiac response to NCPAP.

METHODS

Eleven consecutive patients with CHF were recruited, six in atrial fibrillation (AF) and five with sinus rhythm (SR). Cardiac index was measured during awake NCPAP application by the thermodilution technique during cardiac catheterisation. NCPAP was applied in a randomised sequence at pressures of 0, 5, and 10 cm H2O with three 30 minute applications separated by 20 minute recovery periods without NCPAP.

RESULTS

Significant differences were found between the AF and SR groups for cardiac index responses to NCPAP (p = 0.004, ANOVA) with a fall in cardiac index in the AF group (p = 0.02) and a trend towards an increase in the SR group (p = 0.10). Similar differences were seen between the groups in stroke volume index responses but not in heart rate responses. Changes in systemic vascular resistance were also significantly different between the two groups (p < 0.005, ANOVA), rising in the AF group but falling in the SR group.

CONCLUSIONS

These data indicate an important effect of underlying cardiac rhythm on the awake haemodynamic effects of NCPAP in patients with CHF.