Yachuan Pu

Voluntary cardio-respiratory synchronization

During stereovectorelectrocardiographic (SVEC) measurements, respiration influences the cardiac vector. This cardiac vector is modulated by the change in the heart position due to diaphragm movement, changes in conductivity in thoracic tissues caused by lung inflation, and shifts in the blood volume. For years, the only method to control the respiratory induced variation was for subject or patient to hold his breath, that was until the voluntary cardio-respiratory synchronization (VCRS) technique. The VCRS technique involves instructing a subject to breathe in synchronization with his/her heartbeat by using either a light or sound signal. Triggered by the R wave of the electrocardiogram, the device signals the subject when to inhale and exhale based on a fixed number of heart beats for each phase of the respiratory cycle. With VCRS techniques, respiratory influences of heart rate variability (HRV), which are mostly parasympathetic, can be separated from nonrespiratory effects, in which sympathetic influences may dominate along with very slow changes due to thermo-regulation and other factors. This work shows how VCRS can be used in unique ways to measure HRV and also separate out respiratory influences on other cardiovascular signals.

Nocturnal Cardio-Respiratory Indices - A Novel Screening Tool for Pediatric Obstructive Sleep Disordered Breathing

Obstructive sleep apnea (OSA) is a common breathing disorder among children with a prevalence estimated at 2-4%. Electrocardiography (ECG) based signal processing, especially heart rate analysis, demonstrated its promising future as both an alternative to other expensive portable sleep study methods and additional approach to sleep cardio-respiratory autonomic interactions which the current clinical standard polysomnography (PSG) lacks. A novel strategy was applied on pediatric OSA detection using RR intervals. A sensitivity of 89%, specificity of 96%, positive predictive value of 89%, and negative predictive value of 96% was achieved in case-to-case detection using 37 clinical pediatric full PSG data

Comparison of R-wave detection errors of four wireless heart rate belts in the presence of noise

Four commercial wireless chest belts (Vetta, Nashbar, Polar and new Polar) were assessed for their susceptibility to noises in R-wave detection. A normal ECG signal was generated using a LionHeart simulator (Bio-tek Instruments, Inc.) with a fixed RR interval (750 ms) and R-wave amplitude (1 mV). Different levels of EMG and baseline wanderings (sinusoidal waves) were recorded from a healthy subject and a Quartec Model MFG-1 generator, respectively. They were added to the ECG signal in a BioPac system (BioPac systems Inc., Santa Barbara, CA) to simulate an ECG in physiological noise. The BioPac system applied the contaminated ECG to the belts via a voltage divider. A PC-based Polar Precision Performance system was used to receive the detected R-wave pulses transmitted from the wireless belts and to calculate the RR intervals. Two types of detection errors were observed in the RR intervals: small time shifts, the potentially non-fixable small variance, and missed/false beats, the abnormally large and potentially fixable intervals. Results showed that small time shifts exist in all tests ranging from -10 ms to 10 ms and increase with the level of EMG before missed/false beats occur. Missed/false beats occur only when EMG level is beyond the threshold of 0.4 mV, 1.6 mV, 1.2 mV and 1.2 mV for Vetta, Nashbar, Polar and new Polar, respectively. The potential to detect and fix EMG introduced missed/false beats showed that this type of error could only be improved when the added EMG was below a certain value. Results also showed that no missed/false beats occur when the frequency and amplitude of sinusoidal waves were below 1 Hz and 5 mV.

Detecting pediatric obstructive sleep apnea using ECG

Heart rate variability (HRV), Atrioventricular conduction (PR), and ECG-derived respiration (EDR) were studied retrospectively on nine pediatric polysomnography (PSG) files for obstructive sleep apnea. Signals were extracted from the first half of overnight ECG from PSG files. A five-epoch (150 s) window segmented each signal into OSA contaminated or normal breathing sections without overlap according to the physicians documented diagnosis. Standard HRV parameters such as mean, standard deviation, VLF, LF, HF and LF/HF were analyzed for each HRV segment; mean and standard deviation were studied for each PR segment; frequency and amplitude of respiration peak were studied for each EDR segment. Results showed significant difference (p<0.001) for HF, LF/HF, PR standard deviation and EDR parameters between normal breathing segments and OSA contaminated segments in each OSA patient. Cyclic variation of heart rate (CVHR) was found only in OSA patients.

Voluntary cardio-respiratory synchronization: hardware and software development and evaluation

Voluntary cardio-respiratory synchronization (VCRS) is a technique where an individuals breathing is voluntarily phase locked with his/her heart beat. A signal is generated (tone or light) from the ECG that is used to pace the breath with a fixed number of heart beats for inspiration and expiration. A small portable device was developed that can create a tone to pace the breathing and record the data for repeated measurements for extended periods of time (days or weeks). The device was tested on an individual over a four-week period. Measurements of heart rate variability were made at various times throughout the day for a total of 68 recordings. The data were analyzed to separate out respiratory and non-respiratory induced changes in the heart rate using a unique time domain analysis. The results showed significant variability over the measurement period.