Measuring Heart Beats (ECG)
The heart rate of an individual has been defined as the number of times a heart beats every minute (Edlin and Golanty, 2016). When a heart beats, it pushes a volume of blood into the circulatory system. At some points in the circulatory system where the blood flows near the skin surface, one can feel blood flowing as a result of heartbeat. It is at these points where heart rate is measured. Usually, the heart rate of a person is measured at the carotid artery in the neck, radial artery located in the wrist just below the thumb, or femoral artery which is located at the inner thigh. Measuring the heart rate involves three steps: detecting the heart beats, receiving the signals, and finally translating the signals graphically.
In Fig.1. A person detecting heart beat at the radial artery where blood flows near the skin surface. The person detects the blood by pressing on the radial artery. When the artery is constricted, the heart beat will try to force blood through constricted artery and it is then possible to feel the heartbeat.
Detecting the heart beats
The heartbeats are detected by placing a pulse detector at a point where it can easily sense the flow of blood in the artery. The pulse detector can be positioned at the carotid artery (neck), radial artery (wrist), or thigh (femoral artery). As the blood flows in the artery, there are pressure changes which occur in pulses. Alternatively, in case of an infrared pulse detector, the device is positioned in such a way that the infrared light is pointed at the artery. The detected pulses are picked and transmitted as electrical signals. Transmission can take place in many ways. It could be through a wire or wireless system. A wireless transmitter module comprise ECG conditioning circuit, oscillators, amplitude modulator, and a resonator. The ECG conditioning circuit processes the input signal from the probe positioned close to the artery while the oscillator generates a constant AM frequency which is then used as a carrier frequency. Finally, the resonator amplify the AM signal to the transmitting antenna (Moon and Rak-Amnouykit, 2015).
Receiving the signals
Graphic Display of Signal
Visual inspection of ECG signals can be achieved by observing the signals in a graphic display unit. The received signals undergo further processing before finally being displayed on a screen. The display unit could be a liquid crystal display (LCD) or a cathode ray tube (CRT). The signals appear as a wave form as shown in Fig.2. The cardiologist can interpret the condition of the patient by studying the graphic display of the heartbeats.
Conclusion
Measuring the heartbeats involve three stages. First stage is the detection of the heartbeats. The second stage is receiving of the heartbeat signals. Finally, the received signals are processed and displayed in LCD or CRT. The graphic signals appear as wave forms. The cardiologist study and interpret the wave forms in order to tell the condition of the patient.
References
Edlin, G. & Golanty, E. (2016). Health and Wellness. Burlington, MA: Jones & Bartlett Learning.
Healthtap. (2016). what could cause a fast heart rate without exercising? Retrieved from: https://www.healthtap.com/user_questions/244435
Intan Technologies. (2016). Biological Signals. Retrieved from: http://intantech.com/signals_RHD2000.html
Moon, D. & Rak-Amnouykit, T. (2015). Transmitting, Receiving, and Interpreting ECG Signals. Retrieved from: http://web.mit.edu/6.101/www/s2015/projects/thipok16_Project_Final_Report.pdf
