Accuracy and Reliability of the Optoelectronic Plethysmography and the Heart Rate Systems for Measuring Breathing Rates Compared with the Spirometer.

Measuring breathing rates without a mouthpiece is of interest in clinical settings. Electrocardiogram devices and, more recently, optoelectronic plethysmography (OEP) methods can estimate breathing rates with only a few electrodes or motion-capture markers placed on the patient. This study estimated and compared the accuracy and reliability of three non-invasive devices: an OEP system with 12 markers, an electrocardiogram device and the conventional spirometer. Using the three devices simultaneously, we recorded 72 six-minute epochs on supine subjects. Our results show that the OEP system has a very low limit of agreement and a bias lower than 0.4% compared with the spirometer, indicating that these devices can be used interchangeably. We observed comparable results for electrocardiogram devices. The OEP system facilitates breathing rate measurements and offers a more complete chest-lung volume analysis that can be easily associated with heart rate analysis without any synchronisation process, for useful features for clinical applications and intensive care.

Non-Invasive Assessment of Inspiratory Ribcage Muscle Fatigue and Recovery During Two Endurance Tests in Healthy Individuals

Introduction: Fatigue is defined as a loss in the capacity for developing force and/or velocity of a muscle which is reversible by rest. The aim was to evaluate non-invasively the fatigue and recovery of the inspiratory ribcage muscles during two endurance tests in healthy subjects. Methods: 22 subjects were evaluated before, during and after performing a respiratory endurance test with normocapnic hyperpnea (NH) and inspiratory pressure threshold load (IPTL). Simultaneous measurements of muscle activity (electromyography), tissue oxygenation (NIRS), pressure (nasal inspiratory pressure), and volume (optoelectronic plethysmography) were performed. Results: There was a decrease in the maximum relaxation rate (MRR) and increase in the time constant (τ) after the IPTL test (p <0.05) and a decrease in the peak pressure generated in SNIP after both protocols (p <0.05). Additionally, there was a decrease in shortening velocity and mechanical power only after the IPTL test (p <0.05). The inspiratory ribcage muscles showed a linear drop in the median frequency in the IPTL test and an exponential drop in the NH test, which was not significant for the development of fatigue and there was a linear increase in the NIRS variables in both protocols. Conclusion: It was concluded that the inspiratory ribcage muscles undergo changes after performing an endurance test with NH and IPTL. Additionally, the development of fatigue in these muscles and their consequent changes are more evident in the protocol with IPTL.

Assessing the Tidal Volume through Wearables: A Scoping Review

The assessment of respiratory activity based on wearable devices is becoming an area of growing interest due to the wide range of available sensors. Accordingly, this scoping review aims to identify research evidence supporting the use of wearable devices to monitor the tidal volume during both daily activities and clinical settings. A screening of the literature (Pubmed, Scopus, and Web of Science) was carried out in December 2020 to collect studies: i. comparing one or more methodological approaches for the assessment of tidal volume with the outcome of a state-of-the-art measurement device (i.e., spirometry or optoelectronic plethysmography); ii. dealing with technological solutions designed to be exploited in wearable devices. From the initial 1031 documents, only 36 citations met the eligibility criteria. These studies highlighted that the tidal volume can be estimated by using different technologies ranging from IMUs to strain sensors (e.g., resistive, capacitive, inductive, electromagnetic, and optical) or acoustic sensors. Noticeably, the relative volumetric error of these solutions during quasi-static tasks (e.g., resting and sitting) is typically ≥10% but it deteriorates during dynamic motor tasks (e.g., walking). As such, additional efforts are required to improve the performance of these devices and to identify possible applications based on their accuracy and reliability.

Effect of portable non-invasive ventilation on thoracoabdominal volumes in recovery from intermittent exercise in patients with COPD

Background: We previously showed that use of portable non-invasive ventilation (pNIV) during recovery periods within intermittent exercise improved breathlessness and exercise tolerance in COPD patients compared to pursed-lip breathing (PLB). However, in a minority of patients recovery from dynamic hyperinflation (DH) was better with PLB, based on inspiratory capacity. We further explored this using Optoelectronic Plethysmography to assess total and compartmental thoracoabdominal volumes. Methods: Fourteen COPD patients (mean±SD) (FEV1: 55±22% predicted) underwent, in a balanced order sequence, two intermittent exercise protocols on the cycle ergometer consisting of five repeated 2-min exercise bouts at 80% peak capacity, separated by 2-min recovery periods, with application of pNIV or PLB in the first minute of recovery.Results: Our findings identified 7 patients showing clinically meaningful recovery in DH with pNIV (DH responders) while 7 showed similar or better recovery in DH with PLB. When pNIV was applied, DH responders compared to DH non-responders exhibited greater tidal volume (by 0.8±0.3 L, p=0.015), inspiratory flow rate (by 0.6±0.5 L/sec, p=0.049), prolonged expiratory time (by 0.6±0.5 sec, p=0.006) and duty cycle (by 0.7±0.6 sec, p=0.007). DH responders showed a clinically meaningful reduction in end-expiratory thoracoabdominal DH (by 265±633 ml) predominantly driven by reduction in the abdominal compartment (by 210±494 ml); this effectively offset end-inspiratory rib-cage DH. Compared to DH non-responders, DH responders had significantly greater BMI by 8.4±3.2, p=0.022 and tended towards less severe resting hyperinflation by 0.3±0.3 L.Conclusion: COPD patients who mitigate end-expiratory rib-cage DH by expiratory abdominal muscle recruitment benefit from pNIV application.

Partitioning the work of breathing during running and cycling using optoelectronic plethysmography

Work of breathing (Wb) derived from a single lung volume and pleural pressure is limited and does not fully characterize the mechanical work done by the respiratory musculature. It has long been known abdominal activation increases with increasing exercise intensity, yet the mechanical work done by these muscles is not reflected in Wb. Using Optoelectronic plethysmography (OEP) we sought to show first, the volumes obtained from OEP (VCW) were comparable to volumes obtained from flow integration (Vt) during cycling and running, and second, to show partitioned volume from OEP could be utilized to quantify the mechanical work done by the ribcage (WBRC) and abdomen (WBAB) during exercise. We fit 11 subjects (6 males/ 5 females) with reflective markers and balloon catheters. Subjects completed an incremental ramp cycling test to exhaustion and a series of submaximal running trials. We found good agreement between VCW vs Vt during cycling (p>0.05) and running (p>0.05). From rest to maximal-exercise, WBAB increased by 84% (range: 30 - 99%;WBAB: 1 ± 1 J/min to 61 ± 52 J/min). The relative contribution of the abdomen increased from 17 ± 9% at rest to 26 ± 16% during maximal-exercise. Our study highlights and provides a quantitative measure of the role of the abdominal muscles during exercise. Incorporating the work done by the abdomen allows for a greater understanding of the mechanical tasks required by the respiratory muscles and could provide further insight into how the respiratory system functions during disease and injury.

Adaptation of lung, chest wall, and respiratory muscles during pregnancy: preparing for birth

A plethora of physiological and biochemical changes occur during normal pregnancy. The changes in the respiratory system have not been as well elucidated, in part because radioimaging is usually avoided during pregnancy. We aimed to use several noninvasive methods to characterize the adaptation of the respiratory system during the full course of pregnancy in preparation for childbirth. Eighteen otherwise healthy women (32.3 ± 2.8 yr) were recruited during early pregnancy. Spirometry, optoelectronic plethysmography, and ultrasonography were used to study changes in chest wall geometry, breathing pattern, lung and thoraco-abdominal volume variations, and diaphragmatic thickness in the first, second, and third trimesters. A group of nonpregnant women were used as control subjects. During the course of pregnancy, we observed a reorganization of rib cage geometry, in shape but not in volume. Despite the growing uterus, there was no lung restriction (forced vital capacity: 101 ± 15% predicted), but we did observe reduced rib cage expansion. Breathing frequency and diaphragmatic contribution to tidal volume and inspiratory capacity increased. Diaphragm thickness was maintained (1st trimester: 2.7 ± 0.8 mm, 3rd trimester: 2.5 ± 0.9 mm; P = 0.187), possibly indicating a conditioning effect to compensate for the effects of the growing uterus. We conclude that pregnancy preserved lung volumes, abdominal muscles, and the diaphragm at the expense of rib cage muscles. NEW & NOTEWORTHY Noninvasive analysis of the kinematics of the chest wall and the diaphragm during resting conditions in pregnant women revealed significant changes in the pattern of thoracoabdominal breathing across the trimesters. That is, concomitant with the progressive changes of chest wall shape, the diaphragm increased its contribution to both spontaneous and maximal breathing, maintaining its thickness despite its lengthening due to the growing uterus. These results suggest that during pregnancy the diaphragm is conditioned to optimize its active role provided during parturition.