Noninvasive screening of osteoporosis using bio-impedance and quantitative ultrasound

Bone mineral loss is a serious health issue all over the globe resulting in osteoporosis, without showing any pre-indication of its occurrence. Dual Energy X-ray Absorptiometry test is a widely accepted method for its diagnosis which gives areal information about the bone mineral. Other methods like Quantitative Computed Tomography (QCT) and Peripheral QCT give volumetric information. Application of these methods for mass screening is not recommended due to the use of ionizing radiations. Few non-ionizing methods, namely Bioelectric Impedance Analysis and Quantitative Ultrasound, have evolved in the past few decades. Bioelectric Impedance Analysis, a non-invasive and low-cost tool, has been immensely recognized for its promising use in estimating body composition and body fluids. Similarly, Quantitative Ultrasound is another non-invasive technique for determining bone density at fixed locations, making noninvasive assessment much faster, easier to use, and portable. A multi-parametric approach combining these two modalities has yielded higher efficiency for the detection of bone mineral loss. These developments are briefly reviewed in this paper.

Pulse arrival time: Measurement and clinical applications

Pulse arrival time is the time elapsed between the R-wave of electrocardiogram and systolic peak in peripheral pulse obtained by any of the plethysmographic methods. Similarly, differential pulse arrival time, also known as pulse transit time, is the time elapsed between systolic peaks of proximal and distal peripheral pulse recordings in an extremity. Distance between the proximal and distal site in the extremity (in meters) divided by differential pulse arrival time (in seconds) gives arterial pulse wave velocity in the limb segment. Differential pulse arrival time has been used to discriminate between an aortic or arterial block from generalized atherosclerosis in aortic and arterial occlusive diseases for nearly four decades. All along there have been efforts to monitor beat-to-beat blood pressure with the help of these time intervals and other pulse parameters. Encouraging correlation has been observed with that obtained by Finapres. Recently pulse arrival time has been explored for the prompt detection of sudden hypertensive episodes during laryngeal microsurgery, for detection of mental stress, monitoring of baroreflex sensitivity, and real-time monitoring of blood pressure. This paper briefly describes the measurement technique of pulse arrival time and an overview of its clinical applications.

New method of electrode placement for determination of cardiac output using impedance cardiography.

In thirty eight young healthy adult subjects, cardiac output was determined non-invasively by using two methods of electrode placement viz. vertical (uses silver braided wires in a band shape) and horizontal (conventional stick-on type surface ECG electrodes), using the technique of Impedance Cardiography. The recordings were taken in supine position on the same day in two separate sets with 30.0 min interval between two sets. In each set of recording, five successive recordings, each at an interval of five minutes were taken. The mean values of cardiac out put by two methods were compared. For the set I, the respective values (Mean +/- SD) of cardiac output by horizontal and vertical methods for the each of the five recordings were 4.87 +/- 0.77 and 5.03 +/- 0.64 for the first, 4.87 +/- 0.71 and 4.91 +/- 0.66 for the second, 4.99 +/- 0.67 and 5.00 +/- 0.70 for the third, 4.78 +/- 0.69 and 4.98 +/- 0.61 for the fourth, 4.84 +/- 0.69 and 4.98 +/- 0.62 for the fifth recording in supine position. The respective P values for these pairs for between the group comparisons were 0.33, 0.50, 0.96, 0.17, and 0.36. In addition, to see the repeatability for each method, within the group comparison was done, the P values were 0.71 and 0.91 for the horizontal and vertical methods, respectively. The mean value of cardiac output did not differ significantly between two methods for recordings of set II in supine position. The cardiac output measurement by placing four spot electrodes horizontally, gave consistent result on repeated measurements and their values showed concordance with the cardiac output values obtained by conventional four band electrodes tied around the chest.