In the era of medicine, the heart and cardiovascular system has become one of the standard observation targets. Palpation and auscultation in the precordial area is performed as part of the regular physical examination to detect possible cardiovascular and pulmonary problems. However, due to the large number of people suffering from cardiovascular problems, labor-intensive methods such as auscultation might be inefficient in preventive cardiovascular condition screening. Seismocardiography (SCG) could have the potential to be a part of the solution to this problem. SCG is one of many modalities of cardiac-induced vibration measurements, and it has been shown to be of use in detecting coronary artery disease and assessing myocardial contractility. Lately, due to advances in sensor technologies, the SCG measurement is being developed by introducing three-dimensional measurements. Three-dimensional approach is considered to yield more information about the cardiovascular system than any single uniaxial approach. In conclusion, SCG seems to have the potential to offer a complementary view to cardiovascular function and a cost-effective method for screening of cardiovascular diseases. SCG is explored in this chapter.
Top1. Introduction
In living person, the function of the heart and cardiovascular system can easily be monitored by listening and palpating the vibrations transmitted to the chest. This fact has apparently been known during the whole history of the mankind. In the era of medicine, the heart and cardiovascular system has become one of the standard observation targets (Agress et al., 1964). Palpation and auscultation in precordial area is performed as part of the regular physical examination to detect possible cardiovascular and pulmonary problems. However, due to the large number of people suffering from cardiovascular problems (Lawes, Hoorn, & Rodgers, 2008; Young, 2004), labor- and skill-intensive methods such as auscultation might be inefficient in preventive cardiovascular condition screening. To address this problem, in addition to promoting a healthy lifestyle, developing efficient cardiovascular screening techniques could be beneficial.
The cardiovascular system palpation is a well-established technique (Kurtz, 1990), but it has not reached the interpretation and diagnostic level of heart sound examination and analysis. The stethoscope, on the other hand, is a standard auscultation instrument, but 90% of the vibrational energy encountered in the body lies in the infrasonic region (DIMOND, 1964). Thus, to take advantage of the majority of the vibrational energy produced by myocardial activity, infrasonic measurement methods could be used as a part of the solution to the growing need of cardiovascular monitoring. The current state of microelectronics and signal processing technologies provide new opportunities to develop these techniques as noninvasive cardiac diagnostic and monitoring tools (Tavakolian, Ngai, Blaber, & Kaminska, 2011).
Ballistocardiography (BCG) which was first reported by Gordon (Gordon, 1877) is an old yet rare infrasonic measurement method. In BCG, the vibrations of the entire body are registered and it has been shown to reflect the functions of the cardiovascular system (Mandelbaum & Mandelbaum, 1953; Starr & Wood, 1961) . Therefore, BCG could be a solution to the need of cost-effective assessing of the cardiovascular function. In seismocardiography (SCG), on the other hand, the vibrations are measured locally. SCG has also been proposed to be a valuable tool (Tavakolian et al., 2011). This fundamental difference in the measurement loci of BCG and SCG might lead to BCG being more prone to inter-subject differences due to different structure of subjects’ bodies. Thus, in terms of cardiac event detection, SCG could be more accurate because there is less distance between the heart and the sensor. SCG and BCG are, however, two of many modalities of cardiac induced vibration measurements (Giovangrandi, Inan, Wiard, Etemadi, & Kovacs, 2011) and should not be thought of as exclusive but rather complementary methods due to their different nature.