Vascular stiffness determined from a nocturnal digital pulse wave signal: association with sleep, sleep-disordered breathing, and hypertension

Overnight stiffness index from finger photoplethysmography in relation to markers of cardiovascular risk and vascular ageing

Wearable technology, such as photoplethysmography (PPG), enables easily accessible individual health data with the potential for improved risk assessment. We hypothesized that the overnight stiffness index (OSI), derived from nocturnal finger PPG, could be used to assess cardiovascular risk and vascular ageing. Subjects with confirmed or suspected hypertension (n = 79, 56 males) underwent simultaneous ambulatory blood pressure monitoring (ABPM) and overnight sleep polygraphy with a continuous PPG registration. Overnight PPG-based pulse propagation time was used to calculate OSI. Associations between OSI and markers of cardiovascular risk, blood pressure, and indices of arterial stiffness, as indicators of vascular ageing, were assessed. Subjects were stratified into low and high OSI (according to median, 10.9 m/s). SCORE2/SCORE2-OP and Framingham risk scores were calculated. The high OSI group had higher SCORE2/SCORE2-OP (9.5 [5.5;12.5] vs 5.0 [4.0;6.5]), and OSI correlated with SCORE2/SCORE2-OP and Framingham risk score (rs = 0.40 and rs = 0.41; both P < 0.01). Indices of arterial stiffness were increased in the high OSI group including ABPM awake and asleep pulse pressures (59 ± 14 vs 50 ± 9 mmHg, P < 0.01, and 54 ± 14 vs 45 ± 7 mmHg, P < 0.001), and ambulatory arterial stiffness index (0.47 ± 0.12 vs 0.37 ± 0.11, P < 0.001), respectively. OSI correlated with 24-h and asleep pulse pressure also after adjusting for confounders. OSI was related to systolic ABPM (awake r = 0.42, asleep r = 0.55; both P < 0.001) and diastolic ABPM (asleep r = 0.36, P < 0.01). OSI, a novel PPG-based measure of nocturnal arterial stiffness, correlates with established cardiovascular risk scores and with blood pressure-derived indices of vascular ageing. This simple method may facilitate cardiovascular risk assessment using readily available medical and wearable consumer devices.

Insights into vascular physiology from sleep photoplethysmography

STUDY OBJECTIVES

Photoplethysmography (PPG) in consumer sleep trackers is now widely available and used to assess heart rate variability (HRV) for sleep staging. However, PPG waveform changes during sleep can also inform about vascular elasticity in healthy persons who constitute a majority of users. To assess its potential value, we traced the evolution of PPG pulse waveform during sleep alongside measurements of HRV and blood pressure (BP).

METHODS

Seventy-eight healthy adults (50% male, median [IQR range] age: 29.5 [23.0, 43.8]) underwent overnight polysomnography (PSG) with fingertip PPG, ambulatory blood pressure monitoring, and electrocardiography (ECG). Selected PPG features that reflect arterial stiffness: systolic to diastolic distance (∆T_norm), normalized rising slope (Rslope) and normalized reflection index (RI) were derived using a custom-built algorithm. Pulse arrival time (PAT) was calculated using ECG and PPG signals. The effect of sleep stage on these measures of arterial elasticity and how this pattern of sleep stage evolution differed with participant age were investigated.

RESULTS

BP, heart rate (HR) and PAT were reduced with deeper non-REM sleep but these changes were unaffected by the age range tested. After adjusting for lowered HR, ∆T_norm, Rslope, and RI showed significant effects of sleep stage, whereby deeper sleep was associated with lower arterial stiffness. Age was significantly correlated with the amount of sleep-related change in ∆T_norm, Rslope, and RI, and remained a significant predictor of RI after adjustment for sex, body mass index, office BP, and sleep efficiency.

CONCLUSIONS

The current findings indicate that the magnitude of sleep-related change in PPG waveform can provide useful information about vascular elasticity and age effects on this in healthy adults.

Nocturnal Blood Pressure Estimation from Sleep Plethysmography Using Machine Learning

BACKGROUND

Elevated nocturnal blood pressure (BP) is a risk factor for cardiovascular disease (CVD) and mortality. Cuffless BP assessment aided by machine learning could be a desirable alternative to traditional cuff-based methods for monitoring BP during sleep. We describe a machine-learning-based algorithm for predicting nocturnal BP using single-channel fingertip plethysmography (PPG) in healthy adults.

METHODS

Sixty-eight healthy adults with no apparent sleep or CVD (53% male), with a median (IQR) age of 29 (23-46 years), underwent overnight polysomnography (PSG) with fingertip PPG and ambulatory blood pressure monitoring (ABPM). Features based on pulse morphology were extracted from the PPG waveforms. Random forest models were used to predict night-time systolic blood pressure (SBP) and diastolic blood pressure (DBP).

RESULTS

Our model achieved the highest out-of-sample performance with a window length of 7 s across window lengths explored (60 s, 30 s, 15 s, 7 s, and 3 s). The mean absolute error (MAE ± STD) was 5.72 ± 4.51 mmHg for SBP and 4.52 ± 3.60 mmHg for DBP. Similarly, the root mean square error (RMSE ± STD) was 6.47 ± 1.88 mmHg for SBP and 4.62 ± 1.17 mmHg for DBP. The mean correlation coefficient between measured and predicted values was 0.87 for SBP and 0.86 for DBP. Based on Shapley additive explanation (SHAP) values, the most important PPG waveform feature was the stiffness index, a marker that reflects the change in arterial stiffness.

CONCLUSION

Our results highlight the potential of machine learning-based nocturnal BP prediction using single-channel fingertip PPG in healthy adults. The accuracy of the predictions demonstrated that our cuffless method was able to capture the dynamic and complex relationship between PPG waveform characteristics and BP during sleep, which may provide a scalable, convenient, economical, and non-invasive means to continuously monitor blood pressure.

Impact of nasal dilator strips on measures of sleep-disordered breathing in pregnancy

STUDY OBJECTIVES

Women with sleep-disordered breathing (SDB) in pregnancy are at a greater risk of developing serious adverse perinatal outcomes. However, the pathogenesis of SDB in pregnancy is poorly understood. As nasal congestion is common in pregnancy, nasal obstruction may contribute to SDB in this population. This study aims to assess the impact of nasal dilator strips (NDS) on measures of SDB and their potential for use as a placebo condition.

METHODS

Pregnant women ≥ 18 years old, body mass index ≥ 27 kg/m², and habitual snoring were enrolled. Participants completed 2 consecutive level III home sleep apnea tests and used NDS during the second test. Objective measures including respiratory event index and pulse transit time drop index, a measure of increased arterial stiffness, were compared across tests. Subjective assessments of participants' perceived impact of NDS use was also obtained.

RESULTS

54 women, 59% White, 60% in the third trimester were enrolled. Median time between the 2 studies was 1 day (interquartile range [IQR] 4). There was no significant change between the night without NDS use and the night with NDS use in respiratory event index (5.30 [IQR 6.20] vs 4.80 [IQR 6.78], P = .8) or pulse transit time drop index (6.8 [IQR 13.3] vs 6.6 [IQR 15.8], P = .360). Subjective measures of sleep did not differ between the 2 nights.

CONCLUSIONS

Despite the high prevalence of pregnancy-associated rhinitis, NDS do not have a significant impact on measures of SDB. Results from this study support the use of NDS as an appropriate placebo in prenatal clinical trials.

CITATION

Maxwell M, Sanapo L, Monteiro K, et al. Impact of nasal dilator strips on measures of sleep-disordered breathing in pregnancy. J Clin Sleep Med. 2022;18(2):477-483.

Beyond the AHI-pulse wave analysis during sleep for recognition of cardiovascular risk in sleep apnea patients

Recent evidence supports the use of pulse wave analysis during sleep for assessing functional aspects of the cardiovascular system. The current study compared the influence of pulse wave and sleep study-derived parameters on cardiovascular risk assessment. In a multi-centric study design, 358 sleep apnea patients (age 55 ± 13 years, 64% male, body mass index 30 ± 6 kg m^-2 , apnea-hypopnea index 13 [5-26] events per hr) underwent a standard overnight sleep recording. A novel cardiac risk index was computed based on pulse wave signals derived from pulse oximetry, reflecting vascular stiffness, cardiac variability, vascular autonomic tone and nocturnal hypoxia. Cardiovascular risk was determined using the ESC/ESH cardiovascular risk matrix, and categorized to high/low added cardiovascular risk. Comparisons between cardiac risk index and sleep parameters were performed for cardiovascular risk prediction. Apnea-hypopnea index, oxygen desaturation index and cardiac risk index were associated with high cardiovascular risk after adjustment for confounders (p = .002, .001, < .001, respectively). In a nested reference model consisting of age, gender and body mass index, adding cardiac risk index but not apnea-hypopnea index or oxygen desaturation index significantly increased the area under the receiver operating characteristic curve (p = .012, .22 and .16, respectively). In a direct comparison of oxygen desaturation index and cardiac risk index, only the novel risk index had an independent effect on cardiovascular risk prediction (p_CRI  < .001, p_ODI  = .71). These results emphasize the association between nocturnal pulse wave and overall cardiovascular risk determined by an established risk matrix. Thus, pulse wave analysis during sleep provides a powerful approach for cardiovascular risk assessment in addition to conventional sleep study parameters.

Obstructive sleep apnea in pregnancy: one sleep study may not be enough in high-risk women

None

Obstructive sleep apnea (OSA) is a common disorder characterized by multiple episodes of airflow limitations and intermittent hypoxia. Pregnancy is a risk factor for developing OSA and OSA is associated with multiple adverse pregnancy outcomes and maternal morbidities, even beyond the gestational period. Despite the high prevalence of OSA and its impact on perinatal outcomes, there are no standard methods and optimal timing to screen for this disorder. Consequently, OSA is currently underdiagnosed in pregnancy. We present a case of severe OSA in pregnancy that developed in the third trimester of pregnancy after a negative study in early pregnancy. Our report emphasizes how lack of standardized screening and diagnostic methods in pregnancy can misdiagnose OSA, even in severe cases, and highlights the need for further research in this area.

Overnight pulse wave analysis to assess autonomic changes during sleep in insomnia patients and healthy sleepers

Insomnia has been associated with increased cardiovascular (CV) risk, which may be linked to sympathetic activation. Non-invasive overnight pulse wave analysis may be a useful tool to detect early signs of autonomic changes during sleep in insomniacs. Fifty-two participants (26 men, 37±13 years, BMI: 24±5 kg/m², 26 insomniacs/ 26 controls) underwent overnight polysomnography with pulse oximetry and pulse wave analysis including pulse rate, vascular stiffness (pulse propagation time, PPT), and a composite cardiac risk index based on autonomic function and overnight hypoxia. We identified two subgroups of insomniacs, with and without objectively disturbed sleep (sleep efficiency SE≤80%, n = 14 vs. SE>80%, n = 12), and observed increased pulse rate and vascular stiffness in insomnia cases when diagnosis was based on both, subjective and objective criteria. Both insomnia groups were associated with higher overnight pulse rate than controls (median/ IQR: low-SE (low sleep efficiency): 67/ 58-70bpm; high-SE: 66/ 63-69bpm; controls: 58/ 52-63bpm; p = 0.01). Vascular stiffness was higher (reduction of PPT) in low-SE insomniacs compared with high-SE insomniacs and controls (169/ 147-232ms; 237/ 215-254ms; 244/ 180-284ms; p = 0.01). The cardiac risk index was increased in low-SE insomniacs (0.2/ 0.0–0.7; 0.0/ 0.0–0.4; 0.0/ 0.0–0.3; p = 0.05). Our results suggest a hyperarousal state in young and otherwise healthy insomniacs during sleep. The increased pulse rate and vascular stiffness in insomniacs with low SE suggest early signs of rigid vessels and potentially, an elevated CV risk. Overnight pulse wave analysis may be feasible for CV risk assessment in insomniacs and may provide a useful tool for phenotyping insomnia in order to provide individualized therapy.

Pulse transit time in pregnancy: a new way to diagnose and classify sleep disordered breathing?

STUDY OBJECTIVES

There are significant discrepancies between the prevalence of snoring and that of objectively defined sleep disordered breathing among pregnant women, suggesting subtle airflow limitations that may not be captured by conventional scoring. This study examined the performance of pulse transit time, an indirect measure of arterial stiffness and sympathetic activation, in pregnancy.

METHODS

Pregnant women with obesity and snoring and a group of controls without symptoms of sleep disordered breathing were recruited in the first trimester. Women underwent a level III in-laboratory sleep monitoring study including an electrocardiogram and pulse oximetry, and pulse transit time was measured. Sleep disordered breathing was defined as an apnea-hypopnea index at least five events per hour of sleep. Statistical analysis was performed using Spearman correlation, Fisher's exact t-test, and univariate analysis.

RESULTS

Of the 222 women, 38 met criteria for sleep disordered breathing. Pulse transit time drops were very prevalent (95% of participants with snoring had > 5 drops per hour). Median apnea-hypopnea index was 0.7 (interquartile range [IQR]: 2.6) events per hour whereas median pulse transit time drop index was 20.70 (IQR: 35.90) events per hour. Pulse transit time index was significantly higher in snorers with apnea-hypopnea index less than five events per hours and participants with apnea-hypopnea index greater than five events per hour compared to controls. Examination of random epochs with pulse transit time drops showed that 95% of pulse transit time drops were associated with airflow limitation.

CONCLUSIONS

Pulse transit time ascertains frequent events of sympathetic activation in at-risk women with and without sleep disordered breathing beyond conventional apneas and hypopneas. Pulse transit time may be an important addition to the identification of clinically significant sleep disordered breathing in pregnant women, and may identify more sleep disordered breathing than apnea-hypopnea index.