Nocturnal respiratory rate as a predictor of mortality in patients with acute coronary syndrome

Validating a Consumer Smartwatch for Nocturnal Respiratory Rate Measurements in Sleep Monitoring

Wrist-based respiratory rate (RR) measurement during sleep faces accuracy limitations. This study aimed to assess the accuracy of the RR estimation function during sleep based on the severity of obstructive sleep apnea (OSA) using the Samsung Galaxy Watch (GW) series. These watches are equipped with accelerometers and photoplethysmography sensors for RR estimation. A total of 195 participants visiting our sleep clinic underwent overnight polysomnography while wearing the GW, and the RR estimated by the GW was compared with the reference RR obtained from the nasal thermocouple. For all participants, the root mean squared error (RMSE) of the average overnight RR and continuous RR measurements were 1.13 bpm and 1.62 bpm, respectively, showing a small bias of 0.39 bpm and 0.37 bpm, respectively. The Bland-Altman plots indicated good agreement in the RR measurements for the normal, mild, and moderate OSA groups. In participants with normal-to-moderate OSA, both average overnight RR and continuous RR measurements achieved accuracy rates exceeding 90%. However, for patients with severe OSA, these accuracy rates decreased to 79.45% and 75.8%, respectively. The study demonstrates the GW's ability to accurately estimate RR during sleep, even though accuracy may be compromised in patients with severe OSA.

Successful continuous positive airway pressure treatment reduces skin sympathetic nerve activity in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with cardiovascular diseases and increased sympathetic tone. We previously demonstrated that patients with OSA have increased skin sympathetic nerve activity (SKNA).

OBJECTIVE

The purpose of this study was to test the hypothesis that continuous positive airway pressure (CPAP) treatment reduces SKNA.

METHODS

The electrocardiogram, SKNA, and polysomnographic recording were recorded simultaneously in 9 patients with OSA. After baseline recording, CPAP titration was performed and the pressure was adjusted gradually for the optimal treatment, defined by reducing the apnea-hypopnea index (AHI) to ≤5/h. Otherwise the treatment was considered suboptimal (AHI > 5/h). Fast Fourier transform analyses were performed to investigate the frequency spectrum of SKNA.

RESULTS

There were very low frequency (VLF), low frequency (LF), and high frequency (HF) oscillations in SKNA. The HF oscillation matched the frequency of respiration. OSA episodes were more frequently associated with the VLF and LF than with the HF oscillations of SKNA. Compared with baseline, CPAP significantly decreased the arousal index and AHI and increased the minimal and mean oxyhemoglobin levels. Optimal treatment significantly increased the dominant frequency and reduced the heart rate, average SKNA (aSKNA), SKNA burst duration, and total burst area. The dominant frequency negatively correlated with aSKNA.

CONCLUSION

VLF, LF, and HF oscillations are observed in human SKNA recordings. Among them, VLF and LF oscillations are associated with OSA while HF oscillations are associated with normal breathing. CPAP therapy reduces aSKNA and shifts the frequency of SKNA oscillation from VLF or LF to HF.

Nocturnal respiratory rate predicts ICD benefit: A prospective, controlled, multicentre cohort study

BACKGROUND

Implantable cardioverter defibrillators (ICDs) prevent sudden cardiac death. ICD implantation decisions are currently based on reduced left ventricular ejection fraction (LVEF≤35%). However, in some patients, the non-arrhythmic death risk predominates thus diminishing ICD-therapy benefits. Based on previous observations, we tested the hypothesis that compared to the others, patients with nocturnal respiratory rate (NRR) ≥18 breaths per minute (brpm) benefit less from prophylactic ICD implantations.

METHODS

This prospective cohort study was a pre-defined sub-study of EU-CERT-ICD trial conducted at 44 centers in 15 EU countries between May 12, 2014, and September 6, 2018. Patients with ischaemic or non-ischaemic cardiomyopathy were included if meeting primary prophylactic ICD implantation criteria. The primary endpoint was all-cause mortality. NRR was assessed blindly from pre-implantation 24-hour Holters. Multivariable models and propensity stratification evaluated the interaction between NRR and the ICD mortality effect. This study is registered with ClinicalTrials.gov (NCT0206419).

FINDINGS

Of the 2,247 EU-CERT-ICD patients, this sub-study included 1,971 with complete records. In 1,363 patients (61.7 (12) years; 244 women) an ICD was implanted; 608 patients (63.2 (12) years; 108 women) were treated conservatively. During a median 2.5-year follow-up, 202 (14.8%) and 95 (15.6%) patients died in the ICD and control groups, respectively. NRR statistically significantly interacted with the ICD mortality effect (p = 0.0070). While the 1,316 patients with NRR<18 brpm showed a marked ICD benefit on mortality (adjusted HR 0.529 (95% CI 0.376-0.746); p = 0.0003), no treatment effect was demonstrated in 655 patients with NRR≥18 brpm (adjusted HR 0.981 (95% CI 0.669-1.438); p = 0.9202).

INTERPRETATION

In the EU-CERT-ICD trial, patients with NRR≥18 brpm showed limited benefit from primary prophylactic ICD implantation. Those with NRR<18 brpm benefitted substantially.

FUNDING

European Community's 7th Framework Programme FP7/2007-2013 (602299).