Measurement of thoraco-abdominal synchrony using respiratory inductance plethysmography: technical aspects and a proposal to overcome its limitations.

BACKGROUND: Thoraco-abdominal asynchrony (TAA) is usually assessed by respiratory inductance plethysmography. The main parameter used for its assessment is the calculation of the phase angle based on Lissajous plots. However, there are some mathematical limitations to its use. RESEARCH DESIGN AND METHODS: Sequences of five breaths were selected from a) normal subjects, b) COPD patients, both at rest and during exercise, and c) patients with obstructive apnea syndrome. Automated analysis was performed calculating phase angle, loop rotation (clockwise or counterclockwise), global phase delay and loop area. TAA severity was estimated quantitatively and in subgroups. RESULTS: 2290 cycles were analyzed (55% clockwise rotation). Phase angle ranged from -86.90 to + 88.4 degrees, while global phase delay ranged from -179.75 to + 178.54. Despite a good correlation with global phase delay (p < 0.01, ANOVA test), phase angle and loop area were not able to correctly classify breaths with severe deviation and paradoxical movements (p=ns, Bonferroni post hoc test). CONCLUSIONS: Global phase delay covers the whole spectrum of TAA situations in a single value. It may be a relevant parameter for diagnosis and follow-up of clinical conditions leading to TAA. CLINICAL TRIAL REGISTRATION: The trial from which the traces were obtained was registered at ClinicalTrials.gov ;(identifier: NCT04597606).

Recommended Approaches to Minimize Aerosol Dispersion of SARS-CoV-2 During Noninvasive Ventilatory Support Can Cause Ventilator Performance Deterioration: A Benchmark Comparative Study.

BACKGROUND: SARS-CoV-2 aerosolization during noninvasive positive-pressure ventilation may endanger health care professionals. Various circuit setups have been described to reduce virus aerosolization. However, these setups may alter ventilator performance. RESEARCH QUESTION: What are the consequences of the various suggested circuit setups on ventilator efficacy during CPAP and noninvasive ventilation (NIV)? STUDY DESIGN AND METHODS: Eight circuit setups were evaluated on a bench test model that consisted of a three-dimensional printed head and an artificial lung. Setups included a dual-limb circuit with an oronasal mask, a dual-limb circuit with a helmet interface, a single-limb circuit with a passive exhalation valve, three single-limb circuits with custom-made additional leaks, and two single-limb circuits with active exhalation valves. All setups were evaluated during NIV and CPAP. The following variables were recorded: the inspiratory flow preceding triggering of the ventilator, the inspiratory effort required to trigger the ventilator, the triggering delay, the maximal inspiratory pressure delivered by the ventilator, the tidal volume generated to the artificial lung, the total work of breathing, and the pressure-time product needed to trigger the ventilator. RESULTS: With NIV, the type of circuit setup had a significant impact on inspiratory flow preceding triggering of the ventilator (P < .0001), the inspiratory effort required to trigger the ventilator (P < .0001), the triggering delay (P < .0001), the maximal inspiratory pressure (P < .0001), the tidal volume (P = .0008), the work of breathing (P < .0001), and the pressure-time product needed to trigger the ventilator (P < .0001). Similar differences and consequences were seen with CPAP as well as with the addition of bacterial filters. Best performance was achieved with a dual-limb circuit with an oronasal mask. Worst performance was achieved with a dual-limb circuit with a helmet interface. INTERPRETATION: Ventilator performance is significantly impacted by the circuit setup. A dual-limb circuit with oronasal mask should be used preferentially.

Framework for patient-ventilator asynchrony during long-term non-invasive ventilation.

Episodes of patient-ventilator asynchrony (PVA) occur during acute and chronic non-invasive positive pressure ventilation (NIV). In long-term NIV, description and quantification of PVA is not standardised, thus limiting assessment of its clinical impact. The present report provides a framework for a systematic analysis of polygraphic recordings of patients under NIV for the detection and classification of PVA validated by bench testing. The algorithm described uses two different time windows: rate asynchrony and intracycle asynchrony. This approach should facilitate further studies on prevalence and clinical impact of PVA in long-term NIV.

Sleep and respiratory function after withdrawal of noninvasive ventilation in patients with chronic respiratory failure.

BACKGROUND: In patients with restrictive thoracic disease, little is known about changes in sleep and breathing if the patient stops using nocturnal noninvasive ventilation (NIV). Better understanding of those changes may affect NIV management and improve our understanding of the relationship of night-to-night variability of respiratory and sleep variables and morning gas exchange. METHODS: With 6 stable patients with restrictive chronic respiratory failure who were being treated with home NIV we conducted a 5-step study: (1) The subject underwent an in-hospital baseline sleep study while on NIV, then next-morning pulmonary function tests. (2) At home, on consecutive nights, the subject underwent the same sleep-study measurements while not using NIV, until the patient had what we defined as respiratory decompensation (oxygen saturation measured via pulse oximetry [S(pO(2))] < 88% or end-tidal CO(2) pressure [P(ETCO(2))] > 50 mm Hg, with or without headaches, fatigue, or worsening dyspnea). Each morning after each home sleep-study night off NIV, we also measured S(pO(2)) and P(ETCO(2)). (3) The patient returned to the hospital for a second overnight assessment, the same as the baseline assessment except without NIV. (4) The patient went home and restarted using NIV with his or her pre-study NIV settings. (5) After the number of nights back on home NIV matched the number of nights the patient had been off NIV, the patient returned to the hospital for a third in-hospital assessment. We measured static lung volumes, maximum inspiratory and expiratory static mouth pressure, breathing pattern, arterial blood gases, S(pO(2)), P(ETCO(2)), and full overnight polysomnography values. RESULTS: Respiratory decompensation occurred 4-15 days after NIV discontinuation (mean 6.8 d). On the first and second in-hospital assessment nights, respectively, the mean nadir nocturnal S(pO(2)) values were 84 +/- 2% and 64 +/- 4%, the total apnea-hypopnea index values were 0 +/- 0 and 9 +/- 2, and the obstructive hypopnea index values were 0 +/- 0 and 7 +/- 1 episodes per total sleep hour. Respiratory events started on the first night off NIV. Spirometry, muscle strength, and sleep architecture did not change significantly. With resumption of NIV, baseline conditions were recovered. CONCLUSIONS: NIV discontinuation in patients with restrictive chronic respiratory failure previously stabilized on NIV promptly leads to nocturnal respiratory failure and within days to diurnal respiratory failure. Stopping NIV for more than a day or two is not recommended.

Inspiratory pressure-volume curves obtained using automated low constant flow inflation and automated occlusion methods in ARDS patients with a new device.

OBJECTIVE: To compare the inspiratory volume pressure (VP) curves of the respiratory system (rs) produced by static occlusion (OCC) and dynamic low constant flow inflation (LCFI) methods using a new device in acute respiratory distress syndrome (ARDS) patients. SETTING: A multidisciplinary 24-bed ICU in a tertiary university hospital. PATIENTS: Eleven intubated and mechanically ventilated patients with ARDS. MEASUREMENTS AND RESULTS: OCC and LCFI methods were performed using the same ventilator, which had been specifically implemented for this purpose. LCFI of 5, 10, and 15 l/min and OCC were applied in a random order at zero end-expiratory positive pressure. Airway pressure was measured both proximal (P(ao)) and distal (P(tr)) to the endotracheal tube. Lower inflection point (LIP) and maximal slope (C(max,rs)) were estimated using unbiased iterative linear regressions. LIP(rs) was obtained in all patients under LCFI and in nine patients under OCC. With LCFI of 5, 10, 15 l/min and OCC the average LIP(rs) values were 12.2 +/- 3.9, 12.9 +/- 4, 14.3 +/- 3.4, and 11.9 cm H(2)O for P(ao) and 11.9 +/- 3.9, 11.5 +/- 3.3, 12.5 +/- 3.4 and 11.8 +/- 4.4 for P(tr), respectively. Only the mean values of LIP(rs) for P(ao) with LCFI at 15 l/min were significantly different from those obtained for OCC. The C(max,rs) values found with the two methods were similar. CONCLUSIONS: An LCFI less than or equal to 10 l/min seems to be a quick, safe, and reliable method to determine LIP(rs) and C(max,rs) at the bedside.