Respiratory modulations in the photoplethysmogram (DPOP) as a measure of respiratory effort

Respiratory activity extracted from wrist-worn reflective photoplethysmography in a sleep-disordered population

OBJECTIVE

Respiratory activity is an essential parameter to monitor healthy and disordered sleep, and unobtrusive measurement methods have important clinical applications in diagnostics of sleep-related breathing disorders. We propose a respiratory activity surrogate extracted from wrist-worn reflective photoplethysmography validated on a heterogeneous dataset of 389 sleep recordings.

APPROACH

The surrogate was extracted by interpolating the amplitude of the PPG pulses after evaluation of pulse morphological quality. Subsequent multistep post-processing was applied to remove parts of the surrogate with low quality and high motion levels. In addition to standard respiration rate performance, we evaluated the similarity between surrogate respiratory activity and reference inductance plethysmography of the thorax, using Spearman's correlations and spectral coherence, and assessed the influence of PPG signal quality, motion levels, sleep stages and obstructive sleep apnea.

MAIN RESULTS

Prior to post-processing, the surrogate already had a strong similarity with the reference (correlation = 0.54, coherence = 0.81), and reached respiration rate estimation performance in line with the literature (estimation error = 0.76± 2.11 breaths/min). Detrimental effects of low PPG quality, high motion levels and sleep-dependent physiological phenomena were significantly mitigated by the proposed post-processing steps (correlation = 0.62, coherence = 0.88, estimation error = 0.53± 1.85 breaths/min).

SIGNIFICANCE

Wrist-worn PPG can be used to extract respiratory activity, thus allowing respiration monitoring in real-world sleep medicine applications using (consumer) wearable devices.

Tracking tidal volume noninvasively in volunteers using a tightly controlled temperature-based device: A proof of concept paper

INTRODUCTION

There is a paucity of noninvasive respiratory monitors for patients outside of critical care settings. The Linshom respiratory monitoring device is a novel temperature-based respiratory monitor that measures the respiratory rate as accurately as capnography.

OBJECTIVES

Determine whether the amplitude of the Linshom temperature profile was an accurate, surrogate and qualitative metric of the tidal volume (V_T ) that tracks V_T in healthy volunteers.

METHODS

Forty volunteers breathed room air spontaneously through a tight-fitting continuous positive airway pressure mask with a Linshom device mounted in the mask. V_T was measured contemporaneously using a standalone Maquet Servo-i ICU ventilator. The amplitudes of the Linshom temperature profiles were paired with the contemporaneous V_T measurements using least squares linear regression analysis and the coefficient of variation (R² ) was determined.

RESULTS

Forty volunteers completed the study. The data from 30 of the volunteers were analysed and are presented; data from 10 volunteers were not included due to protocol violations and/or technical issues unrelated to Linshom. The fluctuations in the amplitude of the Linshom temperature profiles mapped closely with the measured V_T using least squares linear regression analyses yielding a mean R² (95% CI) value of 0.87 (0.84-0.90).

CONCLUSION

These results support the notion that the Linshom temperature profile is an accurate and reliable surrogate that tracks changes in V_T in healthy volunteers. Further studies are warranted in patients in clinical settings to establish the effectiveness of this monitor.

The value of dynamic preload variables during spontaneous ventilation

PURPOSE OF REVIEW

To discuss the physiological significance and clinical value of dynamic preload variables in spontaneously breathing patients.

RECENT FINDINGS

Dynamic preload variables reflect the response of the cardiac output to a modification of preload and can therefore be used to assess fluid responsiveness. Continuous dynamic parameters that are calculated from the variations in the arterial and plethysmographic waveforms following a mechanical breath have been shown to predict fluid responsiveness much better than static preload parameters. These parameters are displayed on many patient monitors though their use is limited to mechanically ventilated patients. However, spontaneous breathing may also induce significant hemodynamic changes because of the repetitive negative swings in the pleural pressure. By better understanding the physiological basis of these changes, the same 'dynamic parameters' can be used to gain unique physiological insights during spontaneous breathing. These include the ability to identify and/or monitor respiratory rate, respiratory effort (e.g., patient-ventilator asynchrony), fluid responsiveness (to some degree), pulsus paradoxus (e.g. asthma, cardiac tamponade), and, importantly, upper airway obstruction.

SUMMARY

Although originally intended to be used only during mechanical ventilation, 'dynamic parameters' may offer valuable clinical information in spontaneously breathing patients.

Journal of Clinical Monitoring and Computing 2016 end of year summary: respiration

This paper reviews 16 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2016, within the field of respiration. Papers were published covering peri- and post-operative monitoring of respiratory rate, perioperative monitoring of CO₂, modeling of oxygen gas exchange, and techniques for respiratory monitoring.

Respiratory effort from the photoplethysmogram

The potential for a simple, non-invasive measure of respiratory effort based on the pulse oximeter signal - the photoplethysmogram or 'pleth' - was investigated in a pilot study. Several parameters were developed based on a variety of manifestations of respiratory effort in the signal, including modulation changes in amplitude, baseline, frequency and pulse transit times, as well as distinct baseline signal shifts. Thirteen candidate parameters were investigated using data from healthy volunteers. Each volunteer underwent a series of controlled respiratory effort maneuvers at various set flow resistances and respiratory rates. Six oximeter probes were tested at various body sites. In all, over three thousand pleth-based effort-airway pressure (EP) curves were generated across the various airway constrictions, respiratory efforts, respiratory rates, subjects, probe sites, and the candidate parameters considered. Regression analysis was performed to determine the existence of positive monotonic relationships between the respiratory effort parameters and resulting airway pressures. Six of the candidate parameters investigated exhibited a distinct positive relationship (p<0.001 across all probes tested) with increasing upper airway pressure repeatable across the range of respiratory rates and flow constrictions studied. These were: the three fundamental modulations in amplitude (AM-Effort), baseline (BM-Effort) and respiratory sinus arrhythmia (RSA-Effort); two pulse transit time modulations - one using a pulse oximeter probe and an ECG (P2E-Effort) and the other using two pulse oximeter probes placed at different peripheral body sites (P2-Effort); and baseline shifts in heart rate, (BL-HR-Effort). In conclusion, a clear monotonic relationship was found between several pleth-based parameters and imposed respiratory loadings at the mouth across a range of respiratory rates and flow constrictions. The results suggest that the pleth may provide a measure of changing upper airway dynamics indicative of the effort to breathe.