Respiratory Variation Research Articles

Subclavian Vein Collapsibility as a Predictor of Fluid Responsiveness in Spontaneously Breathing Hypotensive Patients

Background and Objective: Volume replacement remains the cornerstone of resuscitation in critically ill patients. This study explored the ability of the subclavian vein collapsibility index to predict fluid responsiveness. Methods: In this prospective observational study conducted in the Department of Medicine, All India Institute of Medical Sciences (AIIMS), New Delhi, sonographic evaluation of inferior vena cava and the right subclavian vein was carried out at three time points for hypotensive patients admitted to the emergency department. The study population was divided into two groups: responders and non-responders, based on a ≥ 15 % increase in stroke volume following fluid bolus. Results: Among 45 recruited patients, 33 patients were responders. The area under the ROC curve for SCV CI at baseline to predict fluid responsiveness was 0.745 (95% confidence interval: 0.549 – 0.941; p = 0.014). An SCV-CI of 46 % predicted fluid responsiveness in a hypotensive patient in terms of change in stroke volume by 15% following fluid bolus with a sensitivity of 87.88 % (95 % confidence interval: 71.80% to 96.60%) and specificity of 66.67 % (95 % confidence interval: 34.89% to 90.08%). Spearman’s correlation coefficient between IVC CI and SCV CI was 0.59 (p < 0.001, n = 135). Conclusion: The results of the study demonstrated that right subclavian vein respiratory variation has the ability to predict fluid responsiveness in a spontaneously breathing patient in circulatory shock and correlates with the inferior vena cava collapsibility index. The subclavian vein can be an alternative to the inferior vena cava in predicting fluid responsiveness in spontaneously breathing patients.

The use of end-expiratory occlusion test vs. inferior vena cava respiratory variation for the prediction of volume responsiveness in mechanically ventilated patients with sepsis: A comparative study

ABSTRACT Sepsis being a chief prominent fatal condition in critically ill patients. In septic-shocked patients, the first-line therapeutic intervention is fluid resuscitation in an attempt to improve their cardiac output (COP). However, fluids must be given only if the chance of improving COP exists. So, assessing fluid responsiveness is crucial. To our knowledge, yet no studies comparing the end-expiratory occlusion (EEO) test and the variation of the inferior vena cava (IVC) diameter with respiration (ΔIVC) in hypovolemic cases. So, our aim is to use both tests as indices for responsiveness to fluid in septic mechanically ventilated (MV) patients. The Patients and Method: Thirty-four MV septic patients were enrolled and baseline COP assessment was performed followed by an EEO test applied to each patient, after which, COP was measured to detect the probable responders (defined as an increased COP by ≥ 15%) and non-responders. Then, ΔIVC was assessed for the same patients to predict the probable responders (with ΔIVC >12%) and non-responders. Finally, fluid therapy was initiated as per the guidelines of surviving sepsis campaign (2021) followed by COP re-assessment to determine actual fluid responders\ on-responders. Results: 67% of the cases was responding to fluid. Receiver operating characteristic showed areas under curve for EEO and ΔIVC in predicting responsiveness to fluid were 0.597 and 0.925, respectively. EEO (32.4%) was predictive with 47.8% sensitivity and 100% specificity. The ΔIVC (64.7%) was predictive with 91.3% sensitivity and 100% specificity. Conclusion: IVC-respiratory variation showed better values in prediction of response to fluid in MV patients with sepsis than EEO test.

Exploring Biomarkers of Mental Flexibility in Healthy Aging: A Computational Psychometric Study.

Mental flexibility (MF) has long been defined as cognitive flexibility. Specifically, it has been mainly studied within the executive functions domain. However, there has recently been increased attention towards its affective and physiological aspects. As a result, MF has been described as an ecological and cross-subject skill consisting of responding variably and flexibly to environmental cognitive-affective demands. Cross-sectional studies have mainly focused on samples composed of healthy individual and of patients with chronic conditions such as Mild Cognitive Impairment and Parkinson's, emphasizing their behavioral rigidity. Our study is the first to consider a sample of healthy older subjects and to outline physiological and psychological markers typical of mental flexibility, to identify functional biomarkers associated with successful aging. Our results reveal that biomarkers (respiratory and heart rate variability assessments) distinguished between individuals high vs. low in mental flexibility more reliably than traditional neuropsychological tests. This unveiled the multifaceted nature of mental flexibility composed of both cognitive and affective aspects, which emerged only if non-linear multi-variate analytic approaches, such as Supervised Machine Learning, were used.

Role of Vena Cava Inferior Ultrasound in Volume Assesment

Regulation of body fluid volume is a key concern for physicians in intensive care units. In intensive care, it is most important to determine the intracellular fluid status because it directly affects the volume status of the patient. Ultrasonography appears to be a useful tool for the assessment of body fluid status. The gold standard for measuring central venous pressure (CVP) is a central venous catheter. Vena cava inferior ultrasound (US-VCI) has been proposed as the non-invasive technique of choice for CVP assessment due to its wide availability, low costs, and ease of use. While a depleted IVC is often observed in hypovolemic patients, typically the IVC is dilated in a hypervolemic condition with a less pronounced or null respiratory collapse in the appropriate clinical context. respiratory variability in VCI diameteris known as the caval index (collapsibility index=VCImaxVCImin /VCImax) and is considered to reflect the intravascular volume state. According to the current updated American and European guidelines, an IVC diameter ≤2.1 cm and collapsibility >50% during inspiration suggest a RAP between 0–5 mm Hg while a diameter >2.1 cm with <50% inspiratory collapse indicates a high RAP of 10–20 mmHg. Primarily because of complicated pathophysiological mechanisms, ultrasound measurement of VCI should not be used as the only parameter in the assessment of volemic status.

Predictors of fluid responsiveness in the operating room: a narrative review.

Prediction of fluid responsiveness has been considered an essential tool for modern fluid management. However, most studies in this field have focused on patients in intensive care unit despite numerous research throughout several decades. Therefore, the present narrative review aims to show the representative method's feasibility, advantages, and limitations in predicting fluid responsiveness, focusing on the operating room environments. Firstly, we described the predictors of fluid responsiveness based on heart-lung interaction, including pulse pressure and stroke volume variations, the measurement of respiratory variations of inferior vena cava diameter, and the end-expiratory occlusion test and addressed their limitations. Subsequently, the passive leg raising test and mini-fluid challenge tests were also mentioned, which assess fluid responsiveness by mimicking a classic fluid challenge. In the last part of this review, we pointed out the pitfalls of fluid management based on fluid responsiveness prediction, which emphasized the importance of individualized decision-making. Understanding the available representative methods to predict fluid responsiveness and their associated benefits and drawbacks through this review will aid anesthesiologists in choosing the most reliable methods for optimal fluid administration in each patient during anesthesia in the operating room.

Interictal respiratory variability predicts severity of hypoxemia after generalized convulsive seizures.

Severe respiratory dysfunction induced by generalized convulsive seizures (GCS) is now thought to be a common mechanism for sudden unexpected death in epilepsy (SUDEP). In a mouse model of seizure-induced death, increased interictal respiratory variability was reported in mice that later died of respiratory arrest after GCS. We studied respiratory variability in epilepsy patients as a predictive tool for severity of postictal hypoxemia, a potential biomarker for SUDEP risk. We then explored the relationship between respiratory variability and central CO2 drive, measured by the hypercapnic ventilatory response (HCVR). We reviewed clinical, video-electroencephalography, and respiratory (belts, airflow, pulse oximeter, and HCVR) data of epilepsy patients. Mean, SD, and coefficient of variation (CV) of interbreath interval (IBI) were calculated. Primary outcomes were: (1) nadir of capillary oxygen saturation (SpO2 ) and (2) duration of oxygen desaturation. Poincaré plots of IBI were created. Covariates were evaluated in univariate models, then, based on Akaike information criteria (AIC), multivariate regression models were created. Of 66 GCS recorded in 131 subjects, 30 had interpretable respiratory data. In the multivariate model with the lowest AIC value, duration of epilepsy was a significant predictor of duration of oxygen desaturation. Duration of tonic phase and CV of IBI during the third postictal minute correlated with SpO2 nadir, whereas CV of IBI during non-rapid eye movement sleep had a negative correlation. Poincaré plots showed that long-term variability was significantly greater in subjects with ≥200 s of postictal oxygen desaturation after GCS compared to those with <200 s desaturation. Finally, HCVR slope showed a negative correlation with measures of respiratory variability. These results indicate that interictal respiratory variability predicts severity of postictal oxygen desaturation, suggesting its utility as a potential biomarker. They also suggest that interictal respiratory control may be abnormal in some patients with epilepsy.

Multifunctional changes in the athletes’ body during the formation of autonomic regulations’ overstrain under the influence of training load

Purpose: the purpose of this study was to generalize polysystemic changes that occur in the body of highly qualified athletes with signs of autonomic regulation overstrain under the influence of training load and during the recovery period after it. Material &amp; Methods: test subjects were qualified male athletes (N=202) aged 22.6±2.8 years, who were examined by means of spiroarteriocardiorhythmography (SACR) and computerized motion meter (CMM). In accordance with the design the examinations with the aid of SACR and CMM were carried out three times: in the morning, on an empty stomach, in a sitting position on the day of training (G1), immediately after training (during the first 5-7 minutes) (G2) and the next day in the morning after sleep (G3). Results: according to the data of the examination of athletes in the dynamics of recovery after the training load, options of changes in HRV indicators were determined, which indicated the formation of sympathetic and parasympathetic overstrain in athletes. Two groups were created. The first included 10 athletes, the second included 9 athletes. The analysis of changes in indicators, the research methods used, allowed us to establish differences in their dynamics during the formation of sympathetic and parasympathetic overstrain. Differences were noted among 18 indicators. Among them are indicators of HRV – ABI (c.u.), SRAI (c.u.), ARI (c.u.), RMSSD (ms), VLF (ms2), LFHF (ms2/ms2); variability of arterial pressure – LFSBPn (n.u.), HFSBPn (n.u.), LFHFSBP (mmHg2), TPDBP (mmHg2), LFDBP, (mmHg2), ICDBP (mmHg2/mmHg2); hemodynamics – CO (dm3), GPVR, (dyn/s/cm−5), CI (dm3/m2); respiratory variability – TPR (L×min–1)2; of sensorimotor function – SCSleft (s), SMleft (%). Conclusions: the obtained results on the formation of sympathetic and parasympathetic overstrain under the influence of intense physical activity indicate that changes in the autonomic regulation of the heart rate, which determine the type of heart rate regulation, are accompanied by a number of changes in hemodynamics, autonomic regulation of the pumping function of the heart, vascular tone, respiratory regulation, and sensorimotor function. The determined differential dynamics of changes in cardiorespiratory and sensorimotor indicators will allow further algorithmization of the assessment of the functional state of the athletes’ body in order to detect early states of non-functional overstrain and overtraining.

Inferior vena cava ultrasound and other techniques for assessment of intravascular and extravascular volume: an update.

Goals of volume management are to accurately assess intravascular and extravascular volume and predict response to volume administration, vasopressor support or volume removal. Data are reviewed that support the following: (i)Dynamic parameters reliably guide volume administration and may improve clinical outcomes compared with static parameters, but some are invasive or only validated with mechanical ventilation without spontaneous breathing. (ii)Ultrasound visualization of inferior vena cava (IVC) diameter variations with respiration reliably assesses intravascular volume and predicts volume responsiveness. (iii)Although physiology of IVC respiratory variations differs with mechanical ventilation and spontaneous breathing, the IVC collapsibility index (CI) and distensibility index are interconvertible. (iv)Prediction of volume responsiveness by IVC CI is comparable for mechanical ventilation and spontaneous breathing patients. (v)Respiratory variations of subclavian/proximal axillary and internal jugular veins by ultrasound are alternative sites, with comparable reliability. (vi)Data support clinical applicability of IVC CI to predict hypotension with anesthesia, guide ultrafiltration goals, predict dry weight, predict intra-dialytic hypotension and assess acute decompensated heart failure. (vii)IVC ultrasound may complement ultrasound of heart and lungs, and abdominal organs for venous congestion, for assessing and managing volume overload and deresuscitation, renal failure and shock. (viii)IVC ultrasound has limitations including inadequate visualization. Ultrasound data should always be interpreted in clinical context. Additional studies are required to further assess and validate the role of bedside ultrasonography in clinical care.

Characterisation of the acute hypoxic response using breathing variability parameters: A pilot study in humans

PurposeWe aimed to investigate respiratory rate variability (RRV) and tidal volume (Vt) variability during exposure to normobaric hypoxia (i.e., reduction in the fraction of inspired oxygen - FiO2), and the association of the changes in RRV and Vt variability with the changes in pulse oxygen saturation (SpO2). MethodsThirty healthy human participants (15 females) were exposed to: (1) 15-min normoxia, (2) 10-min hypoxia simulating 2200 m, (3) 10-min hypoxia simulating 4000 m, (4) 10-min hypoxia simulating 5000 m, (5) 15-min recovery in normoxia. Linear regression modelling was applied with SpO2 (dependent variable) and the changes in RRV and Vt variability (independent variables), controlling for FiO2, age, sex, changes in heart rate (HR), changes in HR variability (HRV), and changes in minute ventilation (VE). ResultsWhen modelling breathing parameter variability as root-mean-square standard deviation (RMSSD), a significant independent association of the changes in RRV with the changes in SpO2 was found (B = −4.3e-04, 95% CI = −8.3e-04/−2.1e-05, p = 0.04). The changes in Vt variability showed no significant association with the changes in SpO2 (B = −1.6, 95% CI = −5.5/2.4, p = 0.42). When modelling parameters variability as SD, a significant independent association of the changes in RRV with the changes in SpO2 was found (B = −8.2e-04, 95% CI = −1.5e-03/−9.4e-05, p = 0.03). The changes in Vt variability showed no significant association with the changes in SpO2 (B=1.4, 95% CI = −5.8/8.6, p = 0.69). ConclusionHigher RRV is independently associated with lower SpO2 during acute hypoxic exposure, while Vt variability parameters are not. Therefore, RRV may be a potentially interesting parameter to characterize individual responses to acute hypoxia.

Novel automated “score mapping” of diaphragmatic compound motor action potential for the early detection of phrenic nerve injury during cryoablation

The proximity of phrenic nerve to right sided pulmonary veins (PV) make it susceptible to injury during cryoballoon ablation (CBA) for atrial fibrillation (AF). Monitoring of diaphragmatic compound motor action potentials (CMAP) obtained from lead aVF or modified surface ECG leads placed along the diaphragm have been used for early detection of phrenic nerve injury (PNI). 1 Schaerli N. Badertscher P. Spies F. et al. A Simplified Method to Detect Phrenic Nerve Injury During Cryoballoon Ablation of Atrial Fibrillation Using Lead aVF of the Surface ECG. Circ Arrhythm Electrophysiol. 2021 Aug; 14e009986https://doi.org/10.1161/CIRCEP.121.009986 Crossref Scopus (0) Google Scholar Thirty percent drop in CMAP amplitude has been shown in studies as the threshold for prevention of PNI. 2 Miyazaki S. Hachiya H. Taniguchi H. et al. Prospective Evaluation of Bilateral Diaphragmatic Electromyograms During Cryoballoon Ablation of Atrial Fibrillation. JCE. 2015; 26: 622-628 Google Scholar However, CMAP signals may be susceptible to respiratory variations, catheter movement, inadequate baseline amplitude making it difficult to monitor the change in CMAP. 3 Sharma P.S. Padala S.K. Thompson J.J. Gunda S. Koneru J.N. Ellenbogen K.A. Factors Influencing Diaphragmatic Compound Motor Action Potentials During Cryoballoon Ablation for Atrial Fibrillation. JCE. 2016; 7: 1384-1389 Google Scholar Score-map of the CMAP using template matching with 3D electroanatomic mapping system can be used to automate the monitoring of CMAP. The aims of this study were to assess the relationship of change in CMAP amplitude with change in score-map and then use the automated score-map prospectively for early detection of PNI during CBA.

Association between the degree of iliac venous outflow obstruction by intravascular ultrasound and lower limb venous reflux

ObjectiveThe present study aims to evaluate the association between the degree of iliac venous outflow obstruction (IVOO) identified by intravascular ultrasound (IVUS) and venous reflux presentation in the lower limbs on duplex ultrasound (DU). MethodsPatients with bilateral chronic venous insufficiency, CEAP (clinical-etiology-anatomy-pathophysiology) C3 to C6, and a visual analog scale score for pain >5 underwent DU for reflux evaluation of the deep venous system (reflux ≥1 second); superficial system, great saphenous vein, and small saphenous vein (reflux ≥0.5 second); and perforator system (reflux ≥0.35 second). All patients underwent IVUS in the iliac venous territory. The area of the impaired venous segments was categorized as obstruction <50% (category 1), 50% to 79% (category 2), and ≥80% (category 3). The venous clinical severity score and reflux multisegment score (RMS) were assessed. ResultsA total of 51 patients (n = 102 limbs; age, 50.53 ± 14.5 years; 6 men) were included. The predominant clinical severity CEAP class was C3 in 54 of 102 limbs (52.9%). The mean VCSS was 14.3 ± 6.7. A severe RMS (≥3) was registered in 63.4% of the limbs. Of the 102 limbs, 51 (50%) presented with category 1, 27 (26.5%) with category 2, and 24 (23.5%) with category 3. Previous deep vein thrombosis (DVT) was associated with critical obstruction (odds ratio [OR], 3.65; 95% confidence interval [CI], 1.29-10.38; P = .015). The superficial and perforator venous systems had no association with the degree of IVOO. Deep venous reflux (DVR) had a significant association with significant IVOO (obstruction ≥50%; OR, 6.44; 95% CI, 2.19-18.93; P = .001) and critical IVOO (obstruction ≥80%; OR, 4.57; 95% CI, 1.70-12.27; P = .003) and a significant linear association with the IVOO degree and reflux in the femoral veins (P < .001) and popliteal vein (P = .008). Significant lesions were significantly more likely to develop in the left limb (OR, 5.76; 95% CI, 2.46-13.50; P < .001). After multivariate analysis, DVR remained a predictor for significant and critical obstruction (P < .003 and P < .012, respectively). Left limb and previous DVT remained as predictors for IVOO of ≥50% and ≥80% (P < .001 and P = .043, respectively). ConclusionsWe found a significant linear association between the degree of IVOO and reflux in the deep venous system on DU. Limbs with DVR, a severe RMS, loss of respiratory variation on DU, and previous DVT were more likely to be affected by IVOO of ≥50%, especially with left leg involvement.

Bedside ultrasound of the internal jugular vein to assess fluid status and right ventricular function: The POCUS-JVD study

BackgroundAccurate estimation of fluid status is important in the management of heart failure patients, however, the current methods for bedside assessment can be unreliable or impractical for daily use. MethodsNon-ventilated patients were enrolled immediately prior to scheduled right heart catheterization (RHC). Using M-mode, IJV maximum (Dmax) and minimum (Dmin) anteroposterior diameters were measured during normal breathing, while supine. Respiratory variation in diameter (RVD) was calculated as [(Dmax - Dmin)/Dmax] in percentage. Collapsibility with sniff maneuver (COS) was assessed. Lastly, inferior vena cava (IVC) was assessed. Pulmonary artery pulsatility index (PAPi) was calculated. Data was obtained by five investigators. ResultsTotal 176 patients were enrolled. Mean BMI was 30.5 kg/m2, LVEF 14–69% (range), 38% with LVEF ≤35%. The POCUS of IJV could be performed in all patients in <5 min.Increasing RAP demonstrated progressive increase in IJV and IVC diameters. For high filling pressure (RAP ≥10 mmHg), an IJV Dmax ≥1.2 cm or IJV-RVD < 30% had specificity >70%. Combining the POCUS of IJV to physical examination improved the combined specificity to 97% for RAP ≥10 mmHg. Conversely, a finding of IJV-COS was 88% specific for normal RAP (<10 mmHg). An IJV-RVD <15% is suggested as a cutoff for RAP ≥15 mmHg. The performance of IJV POCUS was comparable to IVC.For RV function assessment, IJV-RVD < 30% had 76% sensitivity and 73% specificity for PAPi <3, while IJV-COS was 80% specific for PAPi ≥3. ConclusionPOCUS of IJV is an easy to perform, specific and reliable method for volume status estimation in daily practice. An IJV-RVD < 30% is suggested for estimation of RAP ≥10 mmHg and PAPi <3.

1039 The Progression of Sleep-Related Breathing Disorders in a Patient with Joubert syndrome

Abstract Introduction Joubert syndrome (JS) is a rare autosomal recessive disease characterized by malformations of the cerebellar vermis, hypotonia, developmental delay, and respiratory variability. Among the potential health challenges that children with congenital malformations of the central nervous system including JS, may face, sleep concerns are frequent and may include sleep-related breathing disorders (SRBDs). Report of case(s) A 17-month-old female with JS was referred to the pediatric pulmonary clinic due to disrupted and fragmented sleep. She had frequent nocturnal awakenings, snoring, mouth breathing, and witnessed apneas. There was no family history of SRBDs. Physical exam was notable for high-arched palate, diffuse hypotonia, and intermittent periods of tachypnea followed by apneas, even when awake. Her polysomnography (PSG) demonstrated an apnea-hypopnea index (AHI) of 27.1/hour, with the obstructive apnea-hypopnea index (oAHI) of 18/hr with central apnea index (CAI) of 9.1/hr and nadir oxygen saturation (SpO2) of 87%. An attempt was made to initiate supplemental oxygen; however, the patient did not tolerate the cannula. At that time, neither adenoid nor tonsillar hypertrophy were noted and surgical intervention was not indicated. The repeat PSG one year later demonstrated AHI of 9.1/hour, oAHI of 4.7/hr with CAI of 4.4/hr and nadir SpO2 of 84%. At this time, she did demonstrate enlarged adenoids and tonsils and underwent adenotonsillectomy with some clinical improvement in snoring. Her mother noted continued pauses in breathing and post operative PSG demonstrated AHI of 12.8/hour, oAHI of 1.4/hr and CAI of 11.4/hr and nadir SpO2 of 79%. The patient had demonstrated worsening episodic tachypnea and central apneas and the decision was made to attempt initiation of a respiratory assist device to regulate breathing and ventilation. Due to the patient’s age, intensive therapy desensitization is required to allow her to tolerate positive airway pressure therapy. Conclusion Patients with JS are at high risk for complex SRBDs as part of their clinical presentation. It is therefore important to carefully monitor the character of sleep-disordered breathing, offering appropriate treatments where indicated. It is important to note the added challenges of young pediatric patients who often require deliberate desensitization interventions to proceed with successful treatment. Support (if any)

Relating Spinal Injury-Induced Neuropathic Pain and Spontaneous Afferent Activity to Sleep and Respiratory Dysfunction.

Abstract Spinal cord injury (SCI) can induce dysfunction in a multitude of neural circuits including those that lead to impaired sleep, respiratory dysfunction, and neuropathic pain. We used a lower thoracic rodent contusion SCI model of neuropathic pain that has been shown to associate with increased spontaneous activity in primary afferents and hindlimb mechanosensory stimulus hypersensitivity. Here we paired capture of these variables with chronic capture of three state sleep and respiration to more broadly understand SCI-induced physiological dysfunction and to assess possible interrelations. Noncontact electric field sensors were embedded into home cages to non-invasively capture the temporal evolution of sleep and respiration changes for six weeks after SCI in naturally behaving mice. Hindlimb mechanosensitivity was assessed weekly, and terminal experiments measured primary afferent spontaneous activity in situ from intact lumbar dorsal root ganglia (DRG). We observed that SCI led to increased spontaneous primary afferent activity (both firing rate and the number of spontaneously active DRGs) that correlated with increased respiratory rate variability and measures of sleep fragmentation. This is the first study to measure and link sleep dysfunction and variability in respiratory rate in a SCI model of neuropathic pain, and thereby provide broader insight into the magnitude of overall stress burden initiated by neural circuit dysfunction after SCI.

Live-view 4D GRASP MRI: A framework for robust real-time respiratory motion tracking with a sub-second imaging latency.

To propose a framework called live-view golden-angle radial sparse parallel (GRASP) MRI for low-latency and high-fidelity real-time volumetric MRI. Live-view GRASP MRI has two stages. The first one is called an off-view stage and the second one is called a live-view stage. In the off-view stage, 3D k-space data and 2D navigators are acquired alternatively using a new navi-stack-of-stars sampling scheme. A 4D motion database is then generated that contains time-resolved MR images at a sub-second temporal resolution, and each image is linked to a 2D navigator. In the live-view stage, only 2D navigators are acquired. At each time point, a live-view 2D navigator is matched to all the off-view 2D navigators. A 3D image that is linked to the best-matched off-view 2D navigator is then selected for this time point. This framework places the typical acquisition and reconstruction burden of MRI in the off-view stage, enabling low-latency real-time 3D imaging in the live-view stage. The accuracy of live-view GRASP MRI and the robustness of 2D navigators for characterizing respiratory variations and/or body movements were assessed. Live-view GRASP MRI can efficiently generate real-time volumetric images that match well with the ground-truth references, with an imaging latency below 500 ms. Compared to 1D navigators, 2D navigators enable more reliable characterization of respiratory variations and/or body movements that may occur throughout the two imaging stages. Live-view GRASP MRI represents a novel, accurate, and robust framework for real-time volumetric imaging, which can potentially be applied for motion adaptive radiotherapy on MRI-Linac.

P398 ACUTE PERICARDITIS COMPLICATED BY RAPID DEVELOPMENT OF CONSTRICTION: A CASE REPORT

Abstract A 57–years–old man with no previous cardiovascular history presented with fever, hypotension, dyspnoea at rest and chest pain. The electrocardiogram showed sinus tachycardia, PR–segment depression and diffuse concave–upwards ST–segment elevation. Elevated C–reactive protein and low pro–BNP level were found at lab tests, procalcitonin and troponin were negative. Chest X–ray showed bilateral pleural effusion. Transthoracic echocardiogram (TTE) revealed mild–to–moderate serofibrinous pericardial effusion with initial diastolic collapse of right chambers, suggesting cardiac pre–tamponade. Because of the exiguity of liquid component, pericardiocentesis was not performed, patient was stabilized by fluid–challenge with hypertonic solution. Ibuprofen and colchicine were started. Left thoracentesis was performed removing one liter of fluid overall compatible with transudate. Cytological and microbiological examinations were negative. Despite of initial clinical improvement, the patient showed kidney failure and worsening of lung failure; perianal abscess was detected causing sepsis and requiring surgical drainage and antibiotic therapy with vancomycin and piperacillin/tazobactam. Culture exams were negative. After ibuprofen replacement with indomethacin a repeated TTE showed reduced pericardial effusion, but also respiratory variation in ventricular filling with signs of interventricular dependence. Cardiac magnetic resonance showed thickening and high signal intensity of pericardial layers on T2 weighted imaging and ventricular septal shift on free–breathing cine sequences, suggesting effusive–constrictive pericarditis. Left and right cardiac catheterization demonstrated ventricular “dip and plateau” pattern and ventricular discordance. Considering the lack of clinical improvement on medical therapy, off–bypass pericardiectomy was performed. Incomplete adhesion between the two pericardial layers and thick gelatinous material were found. After surgery patient experienced rapid clinical improvement; cardiac index increased from 1.5 to 3.5 L/min/m2. Effusive–constrictive pericarditis is a rare and dreaded complication of acute pericarditis. Surgery, when appropriated, is crucial for prognosis. In our case initial response to anti–inflammatory therapy with reduced pericardial effusion unmasked constrictive physiology in an effusive–constrictive pericarditis. Clinical management was complicated by sepsis which could have played a role in constriction developing.

RESPIRATORY VARIABILITY OF VALVULAR PEAK SYSTOLIC VELOCITY AS A NEW INDICATOR OF FLUID RESPONSIVENESS IN PATIENTS WITH SEPTIC SHOCK.

Objective: The aim of this study was to evaluate the reliability and feasibility of pulse Doppler measurements of peak velocity respiratory variability of mitral and tricuspid valve rings during systole as new dynamic indicators of fluid responsiveness in patients with septic shock. Methods: Transthoracic echocardiography (TTE) was performed to measure the respiratory variability of aortic velocity-time integral (∆VTI), respiratory variability of tricuspid annulus systolic peak velocity (∆RVS), respiratory variability of mitral annulus systolic peak velocity (∆LVS), and other related indicators. Fluid responsiveness was defined as a 10% increase in cardiac output after fluid expansion, assessed by TTE. Results: A total of 33 patients with septic shock were enrolled in this study. First, there was no significant difference in the population characteristics between the fluid responsiveness positive group (n = 17) and the fluid responsiveness negative group (n = 16) ( P > 0.05). Second, Pearson correlation test showed that ∆RVS, ∆LVS, and TAPSE with the relative increase in cardiac output after fluid expansion ( R = 0.55, P = 0.001; R = 0.40, P = 0.02; R = 0.36, P = 0.041). Third, multiple logistic regression analysis demonstrated that ∆RVS, ∆LVS, and TAPSE were significantly correlated with fluid responsiveness in patients with septic shock. Fourth, receiver operating characteristic (ROC) curve analysis revealed that ∆VTI, ∆LVS, ∆RVS, and TAPSE had good predictive ability for fluid responsiveness in patients with septic shock. The area under the curve (AUC) of ∆VTI, ∆LVS, ∆RVS, and TAPSE for predicting fluid responsiveness was 0.952, 0.802, 0.822, and 0.713, respectively. The sensitivity (Se) values were 1.00, 0.73, 0.81, and 0.83, whereas the specificity (Sp) values were 0.84, 0.91, 0.76, and 0.67, respectively. The optimal thresholds were 0.128, 0.129, 0.130, and 13.9 mm, respectively. Conclusion: Tissue Doppler ultrasound evaluation of respiratory variability of mitral and tricuspid annular peak systolic velocity could be a feasible and reliable method for the simple assessment of fluid responsiveness in patients with septic shock.

Rapid extraction of respiratory waveforms from photoplethysmography: A deep corr-encoder approach

Much of the information related to breathing is contained within the photoplethysmography (PPG) signal, through changes in venous blood flow, heart rate and stroke volume. We aim to leverage this fact, by employing a novel deep learning framework which is a based on a repurposed convolutional autoencoder. Our corr-encoder model aims to encode all of the relevant respiratory information contained within photoplethysmography waveform, and decode it into a waveform that is similar to a gold standard respiratory reference — the Capnogram. The model is employed on two photoplethysmography data sets, namely Capnobase and BIDMC. We show that the model is capable of producing respiratory waveforms that approach the gold standard, while in turn producing state of the art respiratory rate estimates. We also show that when it comes to capturing more advanced respiratory waveform characteristics such as duty cycle, our model is for the most part unsuccessful. A suggested reason for this, in light of a previous study on in-ear PPG, is that the respiratory variations in finger-PPG are far weaker compared with other recording locations. Importantly, our model can perform these waveform estimates in a fraction of a millisecond, giving it the capacity to produce over 6 hours of respiratory waveforms in a single second. Moreover, we attempt to interpret the behaviour of the kernel weights within the model, showing that in part our model intuitively selects different breathing frequencies. The model proposed in this work could help to improve the usefulness of consumer PPG-based wearables for medical applications, where detailed respiratory information is required.

Carotid artery corrected flow time and respiratory variation of blood flow peak velocity for prediction of hypotension after induction of general anesthesia in adult patients undergoing emergency laparotomy for peritonitis: A prospective, observational study.

Doppler waveform analysis of carotid artery has been found to predict fluid responsiveness in patients undergoing elective surgeries. We evaluated the role of carotid artery corrected flow time (FTc) and respiratory variation of blood flow peak velocity (ðVpeak) in predicting post induction hypotension in patients undergoing emergency laparotomy for peritonitis. Adult patients (n = 60) with perforation peritonitis undergoing emergency laparotomy under general anesthesia (GA) were recruited in this prospective, observational study. Carotid ultrasonography was performed pre-induction, to determine FTc and ðVpeak. Post-induction hemodynamic parameters were recorded for 5 minutes. Spearman's rank correlation coefficient was used to determine the relationship between hypotension and carotid artery measurements. Post-induction hypotension occurred in 48.3% of patients. The carotid artery FTc was significantly lower (P = 0.008) in patients who developed post-induction hypotension, but ðVpeak was statistically similar (P = 0.62) in both groups. Spearman's rank correlation coefficient revealed a statistically significant correlation between FTc and systolic blood pressure (SBP) change at one-minute post induction (r2 = -0.29, P = 0.03); however statistical significance were not achieved at 2 minutes and 3 minutes (P = 0.05 at both time points). Carotid artery FTc had an area under the receiver operating characteristic (AUROC) curve (95% CI) of 0.70 (0.57-0.84) to predict post-induction hypotension and best cutoff value of 344.8 ms with a sensitivity and specificity of 61% and 79%, respectively. Carotid artery ðVpeak had an AUROC curve (95% CI) of 0.54 (0.39-0.69) to predict post-induction hypotension and best cutoff value of 7.9% with a sensitivity and specificity of 62% and 55%, respectively. Carotid artery FTc and ðVpeak are not reasonable predictors of hypotension in patients undergoing emergency laparotomy for perforation peritonitis.

AB-453068-1 NOVEL ‘SCORE-MAPPING’ OF DIAPHRAGMATIC COMPOUND MOTOR ACTION POTENTIAL FOR EARLY DETECTION OF PHRENIC NERVE INJURY DURING CRYOABLATION

The proximity of the phrenic nerve to right-sided pulmonary veins makes it susceptible to injury during cryoballoon ablation (CBA) for atrial fibrillation (AF). Although there are no specific preprocedural predictors for phrenic nerve injury (PNI), monitoring of diaphragmatic compound motor action potentials (CMAP) has been used for the early detection of PNI. A 30% drop in CMAP amplitude has been shown in animal and clinical studies as the threshold for the prevention of PNI The aims of this study were to assess the relationship of change in CMAP amplitude with change in score map and then use the automated score map prospectively for early detection of PNI during CBA In the first half of the study, we paced the phrenic nerve at 10,8,6,4,2 milliamperes or till loss of capture in 20 pts. The relationship between the change in amplitude of CMAP with a corresponding change in the score map was studied by linear regression. 30% drop in CMAP amplitude was associated with a score map of 89%(R2 0.77). In the second half of the study, we used a score map threshold of 90% and studied 84 pts. Ablation was stopped if the score map of CMAP dipped below 90% consistently for >4 beats to take respiratory variation into account A total of 174 cryo applications were done for the right-sided veins in 84 pts. A consistent score-map >98% was obtained in all pts before the beginning of the CBA. Ablation had to be stopped in 13 pts due to a drop in the score map or CMAP amplitude or decreased diaphragm contraction. 5 pts had transient PNI. Change in score map was noticeable before change in CMAP amplitude or decrease in diaphragm contraction. In 8 pts drop in the score map was attributed to catheter movement which was noted by the change in catheter position on the 3D mapping system. Score-map of CMAP returned to >98% with catheter adjustment or within 5 minutes of ablation termination along with improvement of CMAP amplitude in all cases. No pts were noted to have persistent PNI at the end of the procedure Beat-to-beat changes in CMAP amplitude can be noted with respiratory variation or catheter movement making it difficult to monitor the change in amplitude. By using an automated score rather than continuously measuring CMAP amplitude, score mapping can make monitoring changes in CMAP amplitude easier. This descriptive study demonstrates that a 90 % score-map threshold correlates with a 30% drop in CMAP amplitude and can be safely and reliably used for the early detection of PNI