Quantifying oscillatory ventilation during exercise in patients with heart failure

The effects of sinusoidal linear drifts on the estimation of cardiorespiratory dynamic parameters during sinusoidal workload forcing: a simulation study

This study aimed at investigating whether: 1) different sinusoidal linear drifts would affect the estimation of the dynamic parameters amplitude (A) and phase lag (φ) of minute ventilation (V˙_E), oxygen uptake, carbon dioxide production and heart rate (HR) sinusoidal responses when the frequency analysis technique (F) is performed; 2) the Marquardt-Levenberg non-linear fitting technique (ML) would provide more precise estimations of A and φ of drifted sinusoidal responses compared to F. For each cardiorespiratory variable, fifteen responses to sinusoidal forcing of different sinusoidal periods were simulated by using a first-order dynamic linear model. A wide range of linear drifts were subsequently applied. A and φ were computed for all drifted and non-drifted responses by using both F (A_F and φ_F) and ML (A_ML and φ_ML). For non-drifted responses, no differences between A_F vs A_ML and φ_F vs φ_ML were found. Whereas A_F and φ_F were affected by the sinusoidal linear drifts, A_ML and φ_ML were not. Significant interaction effects (technique x drift) were found for A (P <  0.001; ƞ_P² > 0.247) and φ (P <  0.001; ƞ_P² > 0.851). Higher goodness of fit values were observed when using ML for drifted V˙_E and HR responses only. The present findings suggest ML as a recommended technique to use when sinusoidal linear drifts occur during sinusoidal exercise, and provide new insights on how to analyse drifted cardiorespiratory sinusoidal responses.

Lifestyle interventions reduce exercise ventilatory variability in healthy individuals: a randomized intervention study

Aim: Variation of exercise ventilation confers poor prognosis in heart failure. Sedentary men have higher exercise ventilatory variability than athletes. However, the impact of lifestyle intervention on exercise ventilatory variability in sedentary people is unknown and this is the aim of this study. Materials & methods: Prospective controlled single-blinded interventional study that randomly assigned healthy sedentary individuals to diet and exercise (intervention group, n = 12) or no intervention (control group, n = 12) for 12 weeks. Exercise ventilatory variability was accessed before and after intervention. Results: Despite similar values at baseline, there was a 15% reduction in respiratory rate variability (root mean square of the successive differences/n) in intervention group. Conclusion: Diet and exercise training reduced exercise ventilatory variability.

Low-frequency ventilatory oscillations in hypoxia are a major contributor to the low-frequency component of heart rate variability

PURPOSE

Heart rate variability (HRV) may be influenced by several factors, such as environment (hypoxia, hyperoxia, hypercapnia) or physiological demand (exercise). In this retrospective study, we tested the hypothesis that inter-beat (RR) intervals in healthy subjects exercising under various environmental stresses exhibit oscillations at the same frequency than ventilatory oscillations.

METHODS

Spectra from RR intervals and ventilation ([Formula: see text]E) were collected from 37 healthy young male subjects who participated in 5 previous studies focused on ventilatory oscillations (or periodic breathing) during exercise in hypoxia, hyperoxia and hypercapnia. Bland and Altman test and multivariate regressions were then performed to compare respective frequencies and changes in peak powers of the two signals.

RESULTS

Fast Fourier analysis of RR and [Formula: see text]E signals showed that RR was oscillating at the same frequency than periodic breathing, i.e., ~ 0.09 Hz (11 s). During exercise, in these various conditions, the difference between minimum and maximum HRV peak power was positively correlated to the same change in ventilation peak power (P < 0.05). Low-frequency (LF) peak power was correlated to tidal volume (P < 0.01) and breathing frequency (P < 0.001).

CONCLUSIONS

This study suggests that low-frequency ventilatory oscillations in hypoxia are a major contributor to the LF band power of heart rate variability. CLINICAL TRIAL REG. NO.: NCT02201875.

Exercise Oscillatory Ventilation: Interreviewer Agreement and a Novel Determination

INTRODUCTION

Determination of exercise oscillatory ventilation (EOV) is subjective, and the interreviewer agreement has not been reported. The purposes of this study were, among patients with heart failure (HF), as follows: 1) to determine the interreviewer agreement for EOV and 2) to describe a novel, objective, and quantifiable measure of EOV.

METHODS

This was a secondary analysis of the HEART Camp: Promoting Adherence to Exercise in Patients with Heart Failure study. EOV was determined through a blinded review by six individuals on the basis of their interpretation of the EOV literature. Interreviewer agreement was assessed using Fleiss kappa (κ). Final determination of EOV was based on agreement by four of the six reviewers. A new measure (ventilation dispersion index; VDI) was calculated for each test, and its ability to predict EOV was assessed with the receiver operator characteristics curve.

RESULTS

Among 243 patients with HF (age, 60 ± 12 yr; 45% women), the interreviewer agreement for EOV was fair (κ = 0.303) with 10-s discrete data averages and significantly better, but only moderate (κ = 0.429) with 30-s rolling data averages. Prevalence rates of positive and indeterminate EOVs were 18% and 30% with the 10-s discrete averages and 14% and 13% with the 30-s rolling averages, respectively. VDI was strongly associated with EOV, with areas under the receiver operator characteristics curve of 0.852 to 0.890.

CONCLUSIONS

Interreviewer agreement for EOV in patients with HF is fair to moderate, which can negatively affect risk stratification. VDI has strong predictive validity with EOV; as such, it might be a useful measure of prognosis in patients with HF.

Analysis of Exercise-Induced Periodic Breathing Using an Autoregressive Model and the Hilbert-Huang Transform

Evaluation of exercise-induced periodic breathing (PB) in cardiopulmonary exercise testing (CPET) is one of important diagnostic evidences to judge the prognosis of chronic heart failure cases. In this study, we propose a method for the quantitative analysis of measured ventilation signals from an exercise test. We used an autoregressive (AR) model to filter the breath-by-breath measurements of ventilation from exercise tests. Then, the signals before reaching the most ventilation were decomposed into intrinsic mode functions (IMF) by using the Hilbert-Huang transform (HHT). An IMF represents a simple oscillatory pattern which catches a part of original ventilation signal in different frequency band. For each component of IMF, we computed the number of peaks as the feature of its oscillatory pattern denoted by Δ_i. In our experiment, 61 chronic heart failure patients with or without PB pattern were studied. The computed peaks of the third and fourth IMF components, Δ₃ and Δ₄, were statistically significant for the two groups (both p values < 0.02). In summary, our study shows a close link between the HHT analysis and level of intrinsic energy for pulmonary ventilation. The third and fourth IMF components are highly potential to indicate the prognosis of chronic heart failure.

Periodic Breathing during Incremental Exercise

Periodic breathing during incremental cardiopulmonary exercise testing is a regularly recurring waxing and waning of tidal volume due to oscillations in central respiratory drive. Periodic breathing is a sign of respiratory control system instability, which may occur at rest or during exercise. The possible mechanisms responsible for exertional periodic breathing might be related to any instability of the ventilatory regulation caused by: (1) increased circulatory delay (i.e., circulation time from the lung to the brain and chemoreceptors due to reduced cardiac index leading to delay in information transfer), (2) increase in controller gain (i.e., increased central and peripheral chemoreceptor sensitivity to arterial partial pressure of oxygen and of carbon dioxide), or (3) reduction in system damping (i.e., baroreflex impairment). Periodic breathing during exercise is observed in several cardiovascular disease populations, but it is a particularly frequent phenomenon in heart failure due to systolic dysfunction. The detection of exertional periodic breathing is linked to outcome and heralds worse prognosis in heart failure, independently of the criteria adopted for its definition. In small heart failure cohorts, exertional periodic breathing has been abolished with several dedicated interventions, but results have not yet been confirmed. Accordingly, further studies are needed to define the role of visceral feedbacks in determining periodic breathing during exercise as well as to look for specific tools for preventing/treating its occurrence in heart failure.

Minute-Ventilation Variability during Cardiopulmonary Exercise Test is Higher in Sedentary Men Than in Athletes

BACKGROUND

The occurrence of minute-ventilation oscillations during exercise, named periodic breathing, exhibits important prognostic information in heart failure. Considering that exercise training could influence the fluctuation of ventilatory components during exercise, we hypothesized that ventilatory variability during exercise would be greater in sedentary men than athletes.

OBJECTIVE

To compare time-domain variability of ventilatory components of sedentary healthy men and athletes during a progressive maximal exercise test, evaluating their relationship to other variables usually obtained during a cardiopulmonary exercise test.

METHODS

Analysis of time-domain variability (SD/n and RMSSD/n) of minute-ventilation (Ve), respiratory rate (RR) and tidal volume (Vt) during a maximal cardiopulmonary exercise test of 9 athletes and 9 sedentary men was performed. Data was compared by two-tailed Student T test and Pearson´s correlations test.

RESULTS

Sedentary men exhibited greater Vt (SD/n: 1.6 ± 0.3 vs. 0.9 ± 0.3 mL/breaths; p < 0.001) and Ve (SD/n: 97.5 ± 23.1 vs. 71.6 ± 4.8 mL/min x breaths; p = 0.038) variabilities than athletes. VE/VCO2 correlated to Vt variability (RMSSD/n) in both groups.

CONCLUSIONS

Time-domain variability of Vt and Ve during exercise is greater in sedentary than athletes, with a positive relationship between VE/VCO2 pointing to a possible influence of ventilation-perfusion ratio on ventilatory variability during exercise in healthy volunteers.

Exercise oscillatory ventilation: Mechanisms and prognostic significance

Alteration in breathing patterns characterized by cyclic variation of ventilation during rest and during exercise has been recognized in patients with advanced heart failure (HF) for nearly two centuries. Periodic breathing (PB) during exercise is known as exercise oscillatory ventilation (EOV) and is characterized by the periods of hyperpnea and hypopnea without interposed apnea. EOV is a non-invasive parameter detected during submaximal cardiopulmonary exercise testing. Presence of EOV during exercise in HF patients indicates significant impairment in resting and exercise hemodynamic parameters. EOV is also an independent risk factor for poor prognosis in HF patients both with reduced and preserved ejection fraction irrespective of other gas exchange variables. Circulatory delay, increased chemosensitivity, pulmonary congestion and increased ergoreflex signaling have been proposed as the mechanisms underlying the generation of EOV in HF patients. There is no proven treatment of EOV but its reversal has been noted with phosphodiesterase inhibitors, exercise training and acetazolamide in relatively small studies. In this review, we discuss the mechanistic basis of PB during exercise and the clinical implications of recognizing PB patterns in patients with HF.

An overview of the applied definitions and diagnostic methods to assess exercise oscillatory ventilation--a systematic review

The variable "exercise oscillatory ventilation" (EOV), assessed during cardiopulmonary exercise test (CPET), recently became a fundamental prognostic parameter in patients with heart failure. In literature, various definitions are suggested, but an uniformly accepted description to identify EOV still lacks. We performed a systematic review of the literature in order to determine the different definitions and diagnostic techniques to assess EOV. A systematic search strategy was established and executed in seven databases (PubMed, Google Scholar, Cochrane Clinical Trials, Science Direct, Pedro, Web Of Science library and Medline (Ovid)) resulting in 605 citations after de-duplication. Full-text articles (n=124) were assessed for eligibility, resulting in 75 citations. The review accounted 17,440 patients of whom 4,638 subjects presented EOV. Seven studies described EOV in a non-heart failure population accounting 168 EOV subjects. The definitions could be categorized in nine subdivisions of which four (n=43) referred to an original description. The other subdivisions were combinations of the original definitions (n=11), quantifications (n=4), computational (n=3), vaguely described (n=8) or not defined (n=6). Symptom limited maximal exercise tests were conducted to assess EOV, however the modes, protocols, software and data sampling were divers. Heterogeneity in the numerous definitions to identify EOV and the vaguely described assessment methods are hindering the evolution to a standardized uniformly accepted definition and technique to identify this abnormal breathing pattern. Unity in definition and international adopted assessment is warranted to strengthen its validity as a prognostic marker and could promote communication. It may facilitate clinical trials on pathophysiology and origin of EOV.

Exercise oscillatory ventilation in patients with Fontan physiology

BACKGROUND

Exercise oscillatory ventilation (EOV) refers to regular oscillations in minute ventilation (VE) during exercise. Its presence correlates with heart failure severity and worse prognosis in adults with acquired heart failure. We evaluated the prevalence and predictive value of EOV in patients with single ventricle Fontan physiology.

METHODS AND RESULTS

We performed a cross-sectional analysis and prospective survival analysis of patients who had undergone a Fontan procedure and subsequent cardiopulmonary exercise test. Data were reviewed for baseline characteristics and incident mortality, heart transplant, or nonelective cardiovascular hospitalization. EOV was defined as regular oscillations for >60% of exercise duration with amplitude >15% of average VE. Survival analysis was performed using Cox regression. Among 253 subjects, EOV was present in 37.5%. Patients with EOV were younger (18.8±9.0 versus 21.7±10.1 years; P=0.02). EOV was associated with higher New York Heart Association functional class (P=0.02) and VE/VCO2 slope (36.8±6.9 versus 33.7±5.7; P=0.0002), but not with peak VO2 (59.7±14.3 versus 61.0±16.0% predicted; P=0.52) or noninvasive measures of cardiac function. The presence of EOV was associated with slightly lower mean cardiac index but other invasive hemodynamic variables were similar. During a median follow-up of 5.5 years, 22 patients underwent transplant or died (n=19 primary deaths, 3 transplants with 2 subsequent deaths). EOV was associated with increased risk of death or transplant (hazard ratio, 3.9; 95% confidence interval, 1.5-10.0; P=0.002) and also predicted the combined outcome of death, transplant, or nonelective cardiovascular hospitalization after adjusting for New York Heart Association functional class, peak VO2, and other covariates (multivariable hazard ratio, 2.0; 95% confidence interval, 1.2-3.6; P=0.01).

CONCLUSIONS

EOV is common in the Fontan population and strongly predicts lower transplant-free survival.