Measurement of systolic time intervals during exercise using inductive plethysmography

Abstract

Measurement of systolic time intervals (STI) provides a noninvasive assessment of cardiac function in resting subjects. However, large motion artifacts often limit their application during exercise. To improve such measurements, we employed a new lightweight carotid arterial pulse transducer and minimized the artifacts by computerized signal averaging. The carotid pulse was recorded with an inductive plethysmographic transducer band (CIP) wrapped around the neck. STI derived from these measurements were compared to standard measurements from a funnel-shaped cup attached to the neck and connected to a pressure transducer (CUP) in 12 normal subjects at rest and with graded bicycle ergometry. To compare the techniques, CIP and CUP signals, together with the EKG and phonocardiogram, were connected separately to two microcomputer systems. The systems were triggered from the EKG and averaged the signals over 16 or 32 heart beats. Semi-automatic analysis of the averaged signals provided estimates of left ventricular ejection time (LVET), pre-ejection period (PEP) and electromechanical systole (QS2). Motion artifact levels of the unprocessed signals were similar with both CIP and CUP methods but were greatly reduced by signal averaging. All LVET values using CIP fell within 10% of CUP values. 85% of PEP values using CIP were within 20% of CUP values. Increasing exercise loads produced appropriate decreases in QS2, LVET, PEP and PEP/LVET consistent with increased myocardial contractility. The CIP proved comfortable to wear and did not require critical positioning as did the CUP. Measurement of STI complements exercise pulmonary testing with useful information of cardiac function.

Evaluation of Cardiac Monitoring Using Fiber Optic Plethysmography

“…4 In fact, previous plethysmographic studies of systolic time intervals demonstrate that there is a natural time interval variation between the R wave and the maximum left ventricular volume, as detected by the RIP or the FOP. 7 In other words, ECG gating is effective for cardiac phases close to the QRS complex but to target end systolic phases the time offset must become longer and the estimated moment for beginning the pulse sequence becomes less accurate. Intelligent ECG gating methods involve the use of a knowledge base that predicts a time offset according to the instantaneous heart rate and knowledge of the heart dynamics.…”

The LifeShirt

“…Another optional IP sensor band can be attached around the neck to measure changes in its cross-sectional area. Highpass digital filtering of the neck IP trace suppresses respiratory efforts and neck movements and allows display of the higher rate carotid arterial pulses (Jordan et al, 1984), but only in an upright posture. In the supine or semirecumbent posture, because of vascular loading, the signal depicts the jugular venous pulse.…”

“…The posture signal is used to adjust RC and AB gains when posture changes from horizontal to the upright and vice versa, and it is used to interpret the vascular pulses derived from the neck inductive plethysmograph as to the level of central venous pressure. The carotid arterial pulse, together with the ECG R-wave time, allows computation of systolic time intervals, for example, the preejection period (PEP; the time from the R-wave to initiation of the upstroke of the carotid arterial pulse) (Jordan et al, 1984) as well as pulse wave transit time (a measure negatively correlated with diastolic blood pressure) (Steptoe, Smulyan, & Gribbin, 1976), especially over short periods of time. Episodic reduction of pulse transit time signifying a transient rise of blood pressure is consistent with microarousals from sleep (Pitson & Stradling, 1998).…”