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

Abstract

Abstract-Voluntary cardio-respiratory synchronization (VCRS) is a technique where an individual's 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. Keywords -heart rate variability, VCRS, breathing I. INTRODUCTIONIt is well know that respiration is one of the strong contributors to heart rate variability. Under normal respiration, the breathing is not locked in time with the cardiac contraction. Therefore, the respiratory induced cardiac variations are non-stationary, and have a significantly different influence depending on when in the cardiac cycle respiration starts [1]. To improve stationarity, voluntary cardio-respiratory synchronization (VCRS) was developed [2]. The subject breathes in a normal manner but the breathing is synchronized with the heartbeat, using a signal in a predetermined ratio of the number of heartbeats for inspiration and expiration. An example of this is shown in Figure 1 for a 10 beat cycle. For the first four heart beats a tone comes on indicating to the subject to inspire. For the next six heart beats the tone is off indicating to the subject to expire. ECG Respiration Signal (Tone or Light) Inspiration ExpirationHeart beat number 0 1 2 3 4 5 6 7 8 9 10Fig. 1. Example of respiratory signal generated for a 10 heart beat cycle (four beats inspiration -six beats expiration).This technique has been used to study heart rate variability as a function of age [2,3], body position [3] and cardiotoxicity caused by chemotherapy [4]. Also, it has been used to reduce respiratory variations in cardiac impedance signals [5].The purpose of the research was to develop and test a small portable device for the study of heart rate variability and R wave to pulse interval as a function of time over a period of many weeks. II. METHODOLOGYIn order to record data repeatedly over many days a small portable device (11 x 6 x 2 cm) was designed, which is referred to as the SynchroMax. It was developed around a PIC microprocessor with memory (64K) capable of holding 32,000 beats. It can be programmed for various numbers of beats for inspiration and expiration. It was designed to measure the time interval between the R waves of the ECG (RR) and the R wave to a peripheral pulse (RP) detected with a photo-sensor. The RP interval represents the pre-ejection period plus the pulse wave velocity. The s...

Determining the relationship of heart rate and blood pressure using voluntary cardio-respiratory synchronization (VCRS)

“…Voluntary cardio-respiratory synchronized breathing, VCRS, was modulated with a device designed to generated a tone to indicate to the subject when to inspire and expire. The device was developed in our laboratory (Patterson et al 2001).…”