Study of Heart Rate Variability in Control and Hypertensive Subjects

Autonomic nervous system comprising sympathetic and parasympathetic divisions has important role inregulating the cardiovascular system. Heart rate variability has been shown to give objective assessment ofautonomic function. Peripheral Pulse Analyzer has been used to study heart rate variability in controls andhypertensive subjects for understanding manifestations of hypertension on autonomic activity. Subjects havebeen divided in two age groups; 18-30 years and 31-44 years and variability parameters have been comparedwith respect to gender stratification, age stratification and disease stratification. Statistical analysis hasshown marked reduction in the coefficient of variation for variability parameter expressed as logarithm (to thebase 10) in comparison to raw or average value of the parameter and has yielded higher discriminatorystrength in various stratified groups. Excluding age and gender sensitive parameters, significant differenceis observed in amplitude of low frequency component for lower age group male/female hypertensives andamplitude as well as area of low frequency component for higher age group female hypertensives. Theseobservations are in agreement with similarly targeted previous studies. Higher age group male controls andhypertensives, however, could not be discriminated by variability study probably due to similar changesmanifested by senility and hypertension. Thus amplitude and area of low frequency component in heart ratevariability spectrum is identified as hypertension specific parameter.

Seventy-five Years of Use of Impedance Plethysmography in Physiological Data Acquisition and Medical Diagnostics.

Impedance plethysmography (IPG) came into existence in 1940 as a result of Jan Nyboer’s pioneering work in the noninvasive assessment of central and peripheral blood flow. The technique got an impetus after introduction first-time derivative of the impedance for accurate determination of stroke volume (SV) and various cardiac intervals. Later, this signal was employed by Parulkar et al for estimation of blood flow index (BFI) and differential pulse arrival time (DPAT) in various segments of the extremity, which were adequate to detect the aortic and peripheral arterial blocks and estimate collateral circulation and distal arterial runoff. The technique was widely used for measurement of respiration and body water. All these applications have resulted into use of bioimpedance for body composition analysis and continuous monitoring of cardiac output as US Food and Drug Adminstration (FDA) approved technologies, which are being used worldwide. Physiological variability has added more value to this technique as single data acquisition gives variability in heart rate and SV (or peripheral blood flow). Morphology index thus derived is very useful in screening patients suspected with coronary artery disease (CAD). All these milestones are briefly described in this paper.