Pulse wave amplitude reduction: A surrogate marker of micro-arousals associated with respiratory events occurring under non-invasive ventilation?

Pulse wave amplitude drops during sleep: clinical significance and characteristics in a general population sample

Study Objectives

To explore the clinical significance of pulse wave amplitude (PWA)-drops during sleep as a biomarker for cardiometabolic disorders and describe their main characteristics in a general population sample.

Methods

Cross-sectional study of HypnoLaus cohort, in which 2162 individuals underwent clinical assessment and in-home full polysomnography. PWA-drops were derived from photoplethysmography and processed using a validated automated algorithm. Associations between PWA-drop features (index, mean duration, and mean area under the curve [AUC]) with hypertension, diabetes, and previous cardiovascular (CV) event were analyzed using multivariable-adjusted logistic regression.

Results

Two thousand one hundred forty-nine participants (59 ± 11 years, 51% women, 9.9% diabetes, 41.3% hypertension, 4.4% CV event) were included. Mean ± standard deviation (SD) of PWA-drop index, duration, and AUC during sleep were 51.0 ± 20.3 events/hour, 14.0 ± 2.7 seconds, and 527±115 %seconds, respectively. PWA-drop index was lower in women and decreased with age, while its mean duration and AUC increased in men and elderly. Overall, lower PWA-drop index, longer duration and greater AUC were associated with increased odds of hypertension, diabetes, or CV event after adjustment for confounders. Participants in the lowest quartile of mean duration-normalized PWA-drop index had a significantly higher odds ratio (OR) of hypertension (OR = 1.60 [1.19–2.16]), CV event (OR = 3.26 [1.33–8.03]), and diabetes (OR = 1.71 [1.06–2.76]) compared to those in the highest quartile. Similar results were observed for mean AUC-normalized PWA-drop index regarding hypertension (OR = 1.59 [1.19–2.13]), CV event (OR = 2.45 [1.14–5.26]) and diabetes (OR = 1.76 [1.10–2.83]).

Conclusions

PWA-drop features during sleep seem to be an interesting biomarker independently associated with cardiometabolic outcomes in the general population.

The challenges in scoring hypopneas in children: is pulse wave amplitude drop the answer?

BACKGROUND

Identifying electroencephalogram (EEG) cortical arousals are crucial in scoring hypopneas and respiratory efforts related arousals (RERAs) during a polysomnogram. As children have high arousal threshold, many of the flow limited breaths or hypopneas may not be associated with visual EEG arousals, hence this may lead to potential underestimation of the degree of sleep disordered breathing. Pulse wave amplitude (PWA) is a signal obtained from finger photoplethysmography which correlates directly to finger blood flow. The drop in PWA has been shown to be a sensitive marker for subcortical/autonomic and cortical arousals. Our aim was to use the drop in PWA as a surrogate for arousals to guide scoring of respiratory events in pediatric patients.

METHODS

Ten polysomnograms for patients between the ages of 5-15 years who had obstructive apnea-hypopnea indices between 1 and 5 events/hour were identified. Patients with syndromes were excluded. A drop in PWA signal of at least 30% that lasted for 3 s was needed to identify subcortical/autonomic arousals. Arousals were rescored based on this criteria and subsequently respiratory events were rescored. Paired t-tests were employed to compare PSG indices scored with or without PWA incorporation.

RESULTS

The sample of 10 children included 2 females, and the average age was 9.8 ± 3.1 years. Overall, polysomnography revealed an average total sleep time of 464.1 ± 25 min, sleep efficiency of 92% +/-4.2, sleep latency of 19.6 ± 17.0 min, rapid eye movement (REM) latency 143 ± 66 min, N1 3.9% +/-2.0, N2 50.3% +/-12.0, N3 28.2% +/-9.1, REM 16.7% +/-4.0, and wakefulness after sleep onset (WASO) 18.1 ± 7.5 min. Including arousals from PWA changes, respiratory indices significantly increased including total AHI (2.3 ± 0.7 vs 5.7 ± 2.1, p < 0.001), obstructive AHI (1.45 ± 0.7 vs 4.8 ± 1.8, p < 0.001), and RDI (2.36 ± 0.7 vs 7.6 ± 2.0, p < 0.001). Likewise, total arousal index was significantly higher (8.7 ± 2.3 vs 29.4 ± 6.5, p < 0.001).

CONCLUSIONS

The drop in pulse wave amplitude signal is a useful marker to guide scoring arousals that are not otherwise easily identified in pediatric polysomnography and subsequently helped in scoring respiratory events that otherwise would not be scored. Further studies are needed to delineate if such methodology would affect clinical outcome.

Reliability of autonomic activations as surrogates of cortical arousals in ventilated patients affected by amyotrophic lateral sclerosis

PURPOSE

The study aims to evaluate the performance of autonomic activations as a tool to assess sleep fragmentation and to recognize hypopneas in patients with amyotrophic lateral sclerosis (ALS) under non-invasive mechanical ventilation and secondarily, to evaluate, in patients with the same disease, the relationship between disruption of autonomic nervous system (ANS) activity and the usefulness of the autonomic activations as surrogates of cortical arousals.

METHODS

Sixteen ALS patients underwent simultaneous polysomnography and portable cardiorespiratory monitoring (PM). On the polysomnography, standard rules were used for scoring arousals and respiratory events. On the PM, autonomic arousals were scored as ≥ 15% heart rate (HR) increase with a ≥ 35% pulse wave amplitude (PWA) reduction, HR increase ≥ 20%, or PWA decrease ≥ 40%. Nocturnal HR variability was analyzed in the ALS patients and in 11 control subjects as an index of ANS activity.

RESULTS

Synchronized epoch by epoch analysis of the polysomnography and PM recordings showed that only 31.0 (22.5-58.7)% cortical and 36.1 (20.5-47.2)% autonomic arousals were associated with one another. Among hypopneas scored at polysomnography, 71.7% were associated with a cortical arousal but not with a desaturation. On average, HR variability in ALS showed signs of depressed ANS activity that was particularly evident in the patients where the cortical arousals exceeded the autonomic ones.

CONCLUSIONS

In ventilated ALS patients, autonomic activations may hardly have a role as surrogates of cortical arousals for assessment of sleep fragmentation and for respiratory scoring. Depression of ANS activity may be related to their poor performance.

Contribution of systemic vascular effects to fMRI activity in white matter

To investigate a potential contribution of systemic physiology to recently reported BOLD fMRI signals in white matter, we compared photo-plethysmography (PPG) and whole-brain fMRI signals recorded simultaneously during long resting-state scans from an overnight sleep study. We found that intermittent drops in the amplitude of the PPG signal exhibited strong and widespread correlations with the fMRI signal, both in white matter (WM) and in gray matter (GM). The WM signal pattern resembled that seen in previous resting-state fMRI studies and closely tracked the location of medullary veins. Its temporal cross-correlation with the PPG amplitude was bipolar, with an early negative value. In GM, the correlation was consistently positive. Consistent with previous studies comparing physiological signals with fMRI, these findings point to a systemic vascular contribution to WM fMRI signals. The PPG drops are interpreted as systemic vasoconstrictive events, possibly related to intermittent increases in sympathetic tone related to fluctuations in arousal state. The counter-intuitive polarity of the WM signal is explained by long blood transit times in the medullary vasculature of WM, which cause blood oxygenation loss and a substantial timing mismatch between blood volume and blood oxygenation effects. A similar mechanism may explain previous findings of negative WM signals around large draining veins during both task- and resting-state fMRI.

Arousal responses to respiratory events during sleep: the role of pulse wave amplitude

The study aims at assessing the changes in electroencephalography (as measured by the A-phases of cyclic alternating pattern) and autonomic activity (based on pulse wave amplitude) at the recovery of airway patency in patients with obstructive sleep apnea syndrome. Analysis of polysomnographic recordings from 20 male individuals with obstructive sleep apnea syndrome was carried out in total sleep time, non-rapid eye movement and rapid eye movement sleep. Scoring quantified the combined occurrence (time range of 4 s before and 4 s after respiratory recovery) or separate occurrence of A-phases (cortical activation), and pulse wave amplitude drops (below 30%) to apneas, hypopneas or flow limitation events. A dual response (A-phase associated with a pulse wave amplitude drop) was the most frequent response (71.8% in total sleep time) for all types of respiratory events, with a progressive reduction from apneas to hypopneas and flow limitation events. The highly significant correlation in total sleep time (r = 0.9351; P < 0.0001) between respiratory events combined with A-phases and respiratory events combined with pulse wave amplitude drops was confirmed both in non-rapid eye movement (r = 0.9622; P < 0.0001) and rapid eye movement sleep (r = 0.7162; P < 0.0006). In conclusion, a dual cortical and autonomic activation is the most common manifestation at the recovery of airway patency. The significant correlation between A-phases and relevant pulse wave amplitude drops suggests a possible role of pulse wave amplitude as a marker of cerebral response to respiratory events.

Scoring criteria for portable monitor recordings: a comparison of four hypopnoea definitions in a population-based cohort

RATIONALE

Limited-channel portable monitors (PMs) are increasingly used as an alternative to polysomnography (PSG) for the diagnosis of obstructive sleep apnoea (OSA). However, recommendations for the scoring of PM recordings are still lacking. Pulse-wave amplitude (PWA) drops, considered as surrogates for EEG arousals, may increase the detection sensitivity for respiratory events in PM recordings.

OBJECTIVES

To investigate the performance of four different hypopnoea scoring criteria, using 3% or 4% oxygen desaturation levels, including or not PWA drops as surrogates for EEG arousals, and to determine the impact of measured versus reported sleep time on OSA diagnosis.

METHODS

Subjects drawn from a population-based cohort underwent a complete home PSG. The PSG recordings were scored using the 2012 American Academy of Sleep Medicine criteria to determine the apnoea-hypopnoea index (AHI). Recordings were then rescored using only parameters available on type 3 PM devices according to different hypopnoea criteria and patients-reported sleep duration to determine the 'portable monitor AHIs' (PM-AHIs).

MAIN RESULTS

312 subjects were included. Overall, PM-AHIs showed a good concordance with the PSG-based AHI although it tended to slightly underestimate it. The PM-AHI using 3% desaturation without PWA drops showed the best diagnostic accuracy for AHI thresholds of ≥ 5/h and ≥ 15/h (correctly classifying 94.55% and 93.27% of subjects, respectively, vs 80.13% and 87.50% with PWA drops). There was a significant but modest correlation between PWA drops and EEG arousals (r=0.20, p=0.0004).

CONCLUSION

Interpretation of PM recordings using hypopnoea criteria which include 3% desaturation without PWA drops as EEG arousal surrogate showed the best diagnosis accuracy compared with full PSG.