Central sleep apnoea and heart failure (Part I)

Characterizing respiratory parameters, settings and adherence in real-world patients using adaptive servo ventilation therapy: big data analysis

STUDY OBJECTIVES

There is minimal guidance around how to optimize inspiratory positive airway pressure (IPAP) levels during use of adaptive servo ventilation (ASV) in clinical practice. This real-world data analysis investigated the effects of IPAP and minimum pressure support (PSmin) settings on respiratory parameters and adherence in ASV-treated patients.

METHODS

A US-based telemonitoring database was queried for patients starting ASV between 1 August 2014 and 30 November 2019. Patients meeting the following criteria were included: US-based patients aged ≥18 years; AirCurve 10 device (ResMed); and ≥1 session with usage of ≥1 hour in the first 90 days. Key outcomes were mask leak and residual apnea-hypopnea index (AHI) at different IPAP settings, adherence and therapy termination rates, and respiratory parameters at different PSmin settings.

RESULTS

63,996 patients were included. Higher IPAP was associated with increased residual AHI and mask leak but did not impact device usage per session (average >6 h/day at all IPAP settings; 6.7 h/day at 95^th percentile IPAP 25 cmH₂O). There were no clinically relevant differences in respiratory rate, minute ventilation, leak and residual AHI across all possible PSmin settings. Patients with a higher 95^th percentile IPAP or with PSmin of 3 cmH₂O were most likely to remain on ASV therapy at 1 year.

CONCLUSIONS

Our findings showed robust levels of longer-term adherence to ASV therapy in a large group of real-world patients. There were no clinically important differences in respiratory parameters across a range of pressure and pressure settings. Future work should focus on the different phenotypes of patients using ASV therapy.

State-dependent control of breathing by the retrotrapezoid nucleus

KEY POINTS

This study explores the state dependence of the hypercapnic ventilatory reflex (HCVR). We simulated an instantaneous increase or decrease of central chemoreceptor activity by activating or inhibiting the retrotrapezoid nucleus (RTN) by optogenetics in conscious rats. During quiet wake or non-REM sleep, hypercapnia increased both breathing frequency (fR ) and tidal volume (VT ) whereas, in REM sleep, hypercapnia increased VT exclusively. Optogenetic inhibition of RTN reduced VT in all sleep-wake states, but reduced fR only during quiet wake and non-REM sleep. RTN stimulation always increased VT but raised fR only in quiet wake and non-REM sleep. Phasic RTN stimulation produced active expiration and reduced early expiratory airflow (i.e. increased upper airway resistance) only during wake. We conclude that the HCVR is highly state-dependent. The HCVR is reduced during REM sleep because fR is no longer under chemoreceptor control and thus could explain why central sleep apnoea is less frequent in REM sleep.

ABSTRACT

Breathing has different characteristics during quiet wake, non-REM or REM sleep, including variable dependence on PCO2. We investigated whether the retrotrapezoid nucleus (RTN), a proton-sensitive structure that mediates a large portion of the hypercapnic ventilatory reflex, regulates breathing differently during sleep vs. wake. Electroencephalogram, neck electromyogram, blood pressure, respiratory frequency (fR ) and tidal volume (VT ) were recorded in 28 conscious adult male Sprague-Dawley rats. Optogenetic stimulation of RTN with channelrhodopsin-2, or inhibition with archaerhodopsin, simulated an instantaneous increase or decrease of central chemoreceptor activity. Both opsins were delivered with PRSX8-promoter-containing lentiviral vectors. RTN and catecholaminergic neurons were transduced. During quiet wake or non-REM sleep, hypercapnia (3 or 6% FI,CO2 ) increased both fR and VT whereas, in REM sleep, hypercapnia increased VT exclusively. RTN inhibition always reduced VT but reduced fR only during quiet wake and non-REM sleep. RTN stimulation always increased VT but raised fR only in quiet wake and non-REM sleep. Blood pressure was unaffected by either stimulation or inhibition. Except in REM sleep, phasic RTN stimulation entrained and shortened the breathing cycle by selectively shortening the post-inspiratory phase. Phasic stimulation also produced active expiration and reduced early expiratory airflow but only during wake. VT is always regulated by RTN and CO2 but fR is regulated by CO2 and RTN only when the brainstem pattern generator is in autorhythmic mode (anaesthesia, non-REM sleep, quiet wake). The reduced contribution of RTN to breathing during REM sleep could explain why certain central apnoeas are less frequent during this sleep stage.

Negative effects of acute sleep deprivation on left ventricular functions and cardiac repolarization in healthy young adults

BACKGROUND

Sleep deprivation (SD) is associated with an increased incidence of adverse cardiovascular events, we aimed to determine the impact of acute SD on structural and functional alterations of the left ventricle (LV) and on electrocardiogram (ECG) markers including T wave peak-to-end interval (TpTe), QT interval, and TpTe/QT ratio in healthy subjects after a night of SD.

METHODS

The study population consisted of 40 healthy young adults (19 males, 21 females; mean age: 28.2 ± 3.86 years). Echocardiographic images and ECGs were obtained from the participants after a night of regular sleep (RS) and SD. The average sleep time of the subjects was 6.67 ± 1.76 hours during RS and 1.25 ± 0.74 hours during a night of SD.

RESULTS

The myocardial performance index, isovolumic relaxation time, and deceleration time values were significantly higher after SD. In addition, the corrected TpTe interval, corrected QT interval (QTc) max, and TpTe/QT ratio were significantly increased after a night of SD when compared with a night of RS (78.5 ± 6.8 ms vs 70.7 ± 7.6 ms, P < 0.001; 407.5 ± 18.6 ms vs 395.07 ± 21.3 ms, P = 0.001; and 0.189 ± 0.014 ms vs 0. 0.179 ± 0.016 ms, P < 0.001, respectively). However, subjects had similar QTp interval values (defined as beginning of the QRS complex to peak of the T wave) after a night of SD as a night of RS (294.6 ± 19.0 vs 291.9 ± 18.5, P = 233).

CONCLUSION

Our crossover study revealed the presence of subclinical LV diastolic functional changes and increased QT intervals, TpTe intervals, and TpTe/QT ratios in healthy young adults after one night SD. Therefore, the increased QT interval occurred secondary to the increased TpTe interval in this population.

Influence of untreated sleep-disordered breathing on the long-term prognosis of patients with cardiovascular disease

Sleep-disordered breathing (SDB) and cardiovascular disease (CVD) are closely related; however, the effect of SDB on the long-term prognosis of patients with CVD is unknown. Our aim in this study was to assess the association between SDB and fatal cardiovascular events in patients with CVD. We performed a long-term follow-up study of 135 patients with CVD. The average observation period was 610 +/- 268 days. The patients were classified into 2 groups based on their apnea index: patients with apnea index >or=5/h (Group H) were diagnosed with SDB (n = 43), and those with apnea index <5/h (Group L) were diagnosed without SDB (n = 92). In Group H, obstructive sleep apnea (OSA) was diagnosed if obstructive apnea index was >or=5/h, and central sleep apnea was diagnosed if central apnea index was >or=5/h. Group H had a significantly lower survival rate than Group L (p <0.005), particularly those with OSA in Group H (p <0.0005). In a Cox proportional hazards model with presence of OSA, age, brain natriuretic peptide, left ventricular ejection fraction, and cardiovascular risk factors, the odds ratio of fatal cardiovascular events was 2.45 (95% confidence interval 1.26 to 5.08) for OSA (p <0.01), which was associated with an increased risk of mortality. In conclusion, our results suggest that SDB is associated with a poorer long-term prognosis and that the presence of OSA is a strong predictor of fatal cardiovascular events in patients with CVD.

Acetazolamide protects against posthypoxic unstable breathing in the C57BL/6J mouse

Acetazolamide (Acz), a carbonic anhydrase inhibitor, is used to manage periodic breathing associated with altitude and with heart failure. We examined whether Acz would alter posthypoxic ventilatory behavior in the C57BL/6J (B6) mouse model of recurrent central apnea. Experiments were performed with unanesthetized, awake adult male B6 mice (n = 9), ventilatory behavior was measured using flow-through whole body plethysmography. Mice were given an intraperitoneal injection of either vehicle or Acz (40 mg/kg), and 1 h later they were exposed to 1 min of 8% O(2)-balance N(2) (poikilocapnic hypoxia) or 12% O(2)-3% CO(2)-balance N(2) (isocapnic hypoxia) followed by rapid reoxygenation (100% O(2)). Hypercapnic response (8% CO(2)-balance O(2)) was examined in six mice. With Acz, ventilation, including respiratory frequency, tidal volume, and minute ventilation, in room air was significantly higher and hyperoxic hypercapnic ventilatory responsiveness was generally lower compared with vehicle. Poikilocapnic and isocapnic hypoxic ventilatory responsiveness were similar among treatments. One minute after reoxygenation, animals given Acz exhibited posthypoxic frequency decline, a lower coefficient of variability for frequency, and no tendency toward periodic breathing, compared with vehicle treatment. We conclude that Acz improves unstable breathing in the B6 model, without altering hypoxic response or producing short-term potentiation, but with some blunting of hypercapnic responsiveness.

Acetazolamide affects breathing differently in ICR and C57 mice

Acetazolamide (ACZ) administration was compared on ventilation in outbred male ICR Swiss Webster (ICR) and inbred C57BL/6J (C57) mice, used in development of transgenic strains. We hypothesized that in both strains ACZ would affect breathing similarly. Mice received intraperitoneally vehicle and the next week ACZ (40 mg/kg), and were exposed to air for 90 min, followed by 5-min exposure to 10% O(2), air for 15 min, and to 5 min of 5% CO(2) in O(2). Ventilation was evaluated using plethysmography. ACZ stimulated ventilation in both stains exposed to air. C57 mice minimally increased frequency and tidal volume, whereas ICR mice markedly increased frequency. Strain differences in the ventilatory pattern in response to hypoxia and hypercapnia occurred. ACZ-treated ICR mice decreased hypoxic responsiveness to 50% of vehicle values, whereas ACZ had no effect in C57 mice. ACZ decreased hypercapnic ventilatory responsiveness in both strains. Differential effects of ACZ breathing in these two strains suggest that genetic factors modulate its effect on breathing.

Congestive heart failure and continuous positive airway pressure therapy: support of a new modality for improving the prognosis and survival of patients with advanced congestive heart failure

Nasal continuous positive airway pressure therapy has recently been studied as a nonpharmacologic adjunct to congestive heart failure therapy. In patients with congestive heart failure, it was reported that continuous positive airway pressure therapy for the condition Cheyne-Stokes respiration with central sleep apnea led to long-term improvements in cardiac function and alleviation of heart failure symptoms. Cheyne-Stokes respiration with central sleep apnea is a frequent breathing disorder well described in patients with congestive heart failure, and is an associated risk factor for increased cardiovascular morbidity and mortality. These apneas cause an increase in sympathetic nervous system activity, which would maintain afterload at a high level or tend to increase it with time, leading to further compromise of ejection fraction. Continuous positive airway pressure appears to benefit the failing heart by increasing intrathoracic pressure, which is believed to cause an increase in cardiac output by decreasing the pressure gradient across the heart wall and allowing the left-ventricular end diastolic volume to decrease, thereby reducing the afterload. This beneficial "resting" of the heart has been documented to increase left-ventricular ejection fraction, increase cardiac index, improve inspiratory muscle strength, lower blood pressure and heart rate, decrease plasma and overnight urinary levels of norepinephrine, lower levels of atrial natriuretic peptide and endothelin-1, and increase heart rate variability. Other benefits include improvement in New York Heart Association functional class status and improvement in dyspnea.

Is obstructive sleep apnoea a rapid eye movement-predominant phenomenon?

Obstructive sleep apnoea (OSA) is thought to be worse during rapid eye movement (REM) sleep. REM rebound in the late postoperative period can follow the REM suppression shown to occur after some types of surgery. This is thought to worsen nocturnal episodic hypoxaemia, leading to greater cardio-respiratory risk. We set out to determine if OSA was a REM-predominant phenomenon. We reviewed the sleep clinic records of 64 consecutive patients with a diagnosis of OSA on full overnight polysomnography and sufficient data to determine the presence of a sleep stage predominance. OSA was diagnosed if the number of apnoeas/hypopnoeas per hour of sleep, the respiratory disturbance index (RDI), was greater than 10. The variables recorded for the purposes of this study were the RDI and the minimum blood oxygen saturation using pulse oximetry (SpO2min) for both REM and non-rapid eye movement (NREM) sleep. All values are presented as mean (SD). The Wilcoxon signed rank test was used for statistical analysis. The means for NREM and REM RDI were, respectively, 36 (26) and 38 (27) per hour (P = 0.96). In 32 of the 64 patients (50%) the RDI in NREM was greater than in REM. Thirty-one (48%) had a larger number during REM. One patient had identical RDIs for both REM and NREM. Sixty-two patients had satisfactory pulse oximetry recordings for both NREM and REM, and the mean SpO2min values were, respectively, 84 (7) and 82 (13)% (P = 0.15). Twenty-nine patients (47%) had a lower SpO2min in REM (seven by more than 10% and two by more than 40%), while 24 (39%) were lower in NREM (two by more than 10%). Nine patients (14%) had identical values in REM and NREM. In contrast to suggestions that OSA is a REM-predominant phenomenon, this study suggests that respiratory disturbance is not greatly affected by sleep stage, in most patients. While a small number clearly desaturate much more during REM, the majority do not. Thus, postoperative REM rebound may worsen OSA in some patients, but in many it may do otherwise. The implications of postoperative sleep disturbance are therefore likely to be more complex than previously suggested.