Pulmonary artery pulsatility is the main cause of cardiogenic oscillations

Quantitative validation of the suprasternal pressure signal to assess respiratory effort during sleep

Objective.Intra-esophageal pressure (Pes) measurement is the recommended gold standard to quantify respiratory effort during sleep, but used to limited extent in clinical practice due to multiple practical drawbacks. Respiratory inductance plethysmography belts (RIP) in conjunction with oronasal airflow are the accepted substitute in polysomnographic systems (PSG) thanks to a better usability, although they are partial views on tidal volume and flow rather than true respiratory effort and are often used without calibration. In their place, the pressure variations measured non-invasively at the suprasternal notch (SSP) may provide a better measure of effort. However, this type of sensor has been validated only for respiratory events in the context of obstructive sleep apnea syndrome (OSA). We aim to provide an extensive verification of the suprasternal pressure signal against RIP belts and Pes, covering both normal breathing and respiratory events.Approach.We simultaneously acquired suprasternal (207) and esophageal pressure (20) signals along with RIP belts during a clinical PSG of 207 participants. In each signal, we detected breaths with a custom algorithm, and evaluated the SSP in terms of detection quality, breathing rate estimation, and similarity of breathing patterns against RIP and Pes. Additionally, we examined how the SSP signal may diverge from RIP and Pes in presence of respiratory events scored by a sleep technician.Main results.The SSP signal proved to be a reliable substitute for both esophageal pressure (Pes) and respiratory inductance plethysmography (RIP) in terms of breath detection, with sensitivity and positive predictive value exceeding 75%, and low error in breathing rate estimation. The SSP was also consistent with Pes (correlation of 0.72, similarity 80.8%) in patterns of increasing pressure amplitude that are common in OSA.Significance.This work provides a quantitative analysis of suprasternal pressure sensors for respiratory effort measurements.

Extraction of cardiac-related signals from a suprasternal pressure sensor during sleep

Objective.The accurate detection of respiratory effort during polysomnography is a critical element in the diagnosis of sleep-disordered breathing conditions such as sleep apnea. Unfortunately, the sensors currently used to estimate respiratory effort are either indirect and ignore upper airway dynamics or are too obtrusive for patients. One promising alternative is the suprasternal notch pressure (SSP) sensor: a small element placed on the skin in the notch above the sternum within an airtight capsule that detects pressure swings in the trachea. Besides providing information on respiratory effort, the sensor is sensitive to small cardiac oscillations caused by pressure perturbations in the carotid arteries or the trachea. While current clinical research considers these as redundant noise, they may contain physiologically relevant information.Approach.We propose a method to separate the signal generated by cardiac activity from the one caused by breathing activity. Using only information available from the SSP sensor, we estimate the heart rate and track its variations, then use a set of tuned filters to process the original signal in the frequency domain and reconstruct the cardiac signal. We also include an overview of the technical and physiological factors that may affect the quality of heart rate estimation. The output of our method is then used as a reference to remove the cardiac signal from the original SSP pressure signal, to also optimize the assessment of respiratory activity. We provide a qualitative comparison against methods based on filters with fixed frequency cutoffs.Main results.In comparison with electrocardiography (ECG)-derived heart rate, we achieve an agreement error of 0.06 ± 5.09 bpm, with minimal bias drift across the measurement range, and only 6.36% of the estimates larger than 10 bpm.Significance.Together with qualitative improvements in the characterization of respiratory effort, this opens the development of novel portable clinical devices for the detection and assessment of sleep disordered breathing.

Delayed tracheal extubation after cardiac surgery due to cardiogenic ventilator auto-triggering: a case report

Background

Ventilator auto-triggering is associated with poor outcomes. Herein, we present a case of delayed tracheal extubation after cardiac surgery due to cardiogenic auto-triggering.

Case presentation

A 73-year-old male with chronic constrictive pericarditis underwent radical pericardiectomy. After confirming hemodynamic stability, we conducted spontaneous breathing trial (SBT) with a flow-trigger sensitivity of 1 L/min. As his respiratory rate (RR) increased to more than 60 breaths/min and tidal volume decreased to less than 100 mL, this SBT was considered a failure. Next morning, SBT was reperformed and the result was unchanged. However, we noticed that his heart rate and RR were the same and suspected auto-triggering caused by cardiogenic oscillations. We changed ventilator mode from flow triggering to pressure triggering of −2 cmH₂O and he was uneventfully extubated.

Conclusion

We experienced a case of delayed tracheal extubation after cardiac surgery due to cardiogenic auto-triggering. Auto-triggering can be reduced by changing ventilator trigger mode.

A mathematical model for the first derivative wave analysis of the volumetric capnogram from the perspective of erythrocyte motion profiles

Current trends in monitoring system are leading to the adoption of volumetric capnogram (Vcap). The first derivative wave analysis (FDWA) of Vcap represented the cardiogenic oscillations (CarO) as a propagated wave and the slope of phase III (S_III) as a constant. Until today the genesis of CarO and S_III is however under debate. In this study, we defined motion profiles of erythrocytes in the pulmonary parenchyma as pulsated-run and random-walk, on the basis of which we obtained a new mathematical expression describing FDWA of Vcap. The mathematical model of Vcap provided theoretical explanation concerned with motion profiles of erythrocytes about the genesis of CarO and S_III. As the results, the mathematical model predicted the close relationship between S_III and the transfer factor of carbon monoxide, which will be used for estimating validity of this mathematical model. In addition, the velocity of propagated wave in the phase III was suggested as a new physiological variable to estimate elastic properties of pulmonary arterioles, and a new measuring method of V_D was proposed based on the theoretical reason, as well. Clinical investigations of the new V_D to test its efficacy of monitoring are needed.

Non-invasive diagnosis of pulmonary hypertension from lung Doppler signal: a proof of concept study

Transthoracic Parametric Doppler (TPD) is a novel ultrasound technique recently developed for the investigation of pulmonary blood vessels. Lung Doppler Signals (LDS) recorded from TPD provide information regarding the functional mechanical characteristics of pulmonary blood vessels. We aimed to define the specific profile of LDS generated from TPD imaging in patients with pulmonary hypertension (PH), and to evaluate the diagnostic performance of LDS to detect PH using right heart catheterization (RHC) as gold standard reference. Seventy nine PH patients and 79 healthy controls matched for age, gender and BMI were recruited in a prospective case-control multicenter study. LDS recordings were performed by TPD consisting of a pulsed Doppler with a 2 MHz single element transducer. LDS were recorded within 24 h of RHC. Following LDS extraction, classification and performance evaluation were performed offline using a support vector machine (k-fold cross validation method). The best LDS parameters for PH detection were (1) peak velocity of the systolic (S) and diastolic (D) signals, (2) the rise slope of the S and D signals, and (3) time to peak of the S signal. Overall, the sensitivity and specificity of TPD for detection of PH were 82.7 % (95 % CI 81.3-84.1) and 87.4 % (95 % CI 86.3-88.5), respectively, with an area under the receiver operating curve of 0.95 (95 % CI 0.94-0.96). Detection rate of PH increased progressively with the level of mean pulmonary artery pressure. LDS recorded by TPD display a specific profile in PH and appears to be a promising and reliable tool for PH diagnosis. Further studies are required to confirm the clinical usefulness of LDS.

Observation of cardiogenic flow oscillations in healthy subjects with hyperpolarized 3He MRI

Recently, dynamic MRI of hyperpolarized (3)He during inhalation revealed an alternation of the image intensity between left and right lungs with a cardiac origin (Sun Y, Butler JP, Ferrigno M, Albert MS, Loring SH. Respir Physiol Neurobiol 185: 468-471, 2013). This effect is investigated further using dynamic and phase-contrast flow MRI with inhaled (3)He during slow inhalations (flow rate ∼100 ml/s) to elucidate airflow dynamics in the main lobes in six healthy subjects. The ventilation MR signal and gas inflow in the left lower lobe (LLL) of the lungs were found to oscillate clearly at the cardiac frequency in all subjects, whereas the MR signals in the other parts of the lungs had a similar oscillatory behavior but were smaller in magnitude and in anti-phase to the signal in the left lower lung. The airflow in the main bronchi showed periodic oscillations at the frequency of the cardiac cycle. In four of the subjects, backflows were observed for a short period of time of the cardiac cycle, demonstrating a pendelluft effect at the carina bifurcation between the left and right lungs. Additional (1)H structural MR images of the lung volume and synchronized ECG recording revealed that maximum inspiratory flow rates in the LLL of the lungs occurred during systole when the corresponding left lung volume increased, whereas the opposite effect was observed during diastole, with gas flow redirected to the other parts of the lung. In conclusion, cardiogenic flow oscillations have a significant effect on regional gas flow and distribution within the lungs.