Intensive Care Unit and Critical Care Unit


Intensive Care Unit and Critical Care Unit or Coronary Care Unit are specific care units utilized as a part of doctor's prescription in different nations that gives intensive care medicines. Excellent ICUs are equipped with medicinal devices, for example, mechanical ventilators, bedside monitors, digital cardiotachometers, pacemakers, defibrillators, dialysis instruments and so on. The biological data related with the patient from the bedside monitors can be dissected by the concerned doctor or nurse to give better care. The quality of care of an ICU relies upon the patient to nurse ratio. For a decent ICU a proportion of 2 patients to a nurse is suggested. Likewise the different parameters from various ICU units can be sent to a central monitoring console for detailed analysis and care (figure shown).

 Bedside monitors and CMC

CCU (Critical or coronary) care unit is a unique care unit managing with the care of patients with diseases associated with heart(such as heart attack).The principle highlight of CCU is the accessibility of telemetry or the consistent monitoring of ECG in order to check the proper functionality of heart.


Cardio tachometers

The cardio tachometers are used to count the heart rate of patients. For a normal human the heart rate is 72 pulses minute. By using digital cardio tachometers which directly display the heart rate, we can examine the health of patients. The cardio tachometers can be of analog or digital type.


The block diagram representation of an analog cardio tachometer is shown below (figure).The analog cardio tachometers are not commonly used now a day. They provide a DC voltage proportional to the patients' heart rate. This DC voltage can be displayed on analog or digital voltmeter.

 The different blocks are explained below. 


The ECG of patient under test is measured by using a proper electrode and applied to a differentiator. The function of differentiator is to avoid double counting. The basic principle -of cardio tachometer is to measure the number of R-waves in the ECG. Since for each heart pulse the R-wave have the highest amplitude level, it can, provide the heart rate. But in some patients T-wave or P-wave may be predominant. It may produce double counting false. But by using differentiator we can avoid this error. This is because even if the T-wave or P-wave is large, the fast changing R-wave will always produce a large output voltage than P-wave or T-wave due to the effect of differentiator. This block is also called R-wave discriminator.

2.Level Detector 

Since each R-wave can produce a specific voltage, the output of R-wave discriminator is applied to a level detector .The level detector produce an output voltage change only when the predetermined input voltage level is exceeded.(That means it will produce an output voltage change for each R-wave).The differentiator and level detector stages are collectively called as QRS-discriminators.

3.Mono stable multivibrator 

The o/p of level detector is corresponding to no. of R-waves. The output from level detector is applied to the mono stable multi vibrator. So an output pulse is generated for each R-wave. These pulses have constant duration. But the pulse repetition rate will vary with respect to the heart rate.


Integrator averages the pulses applied to its input from the mono stable output. In a mono stable multi vibrator one o/p pulse is generated for each R-wave and the pulses have constant width. So the DC o/p voltage of integrator will be proportional to the number of R-waves per unit time.

5.Digital /analog voltmeter

Even though we are using analog technique the o/p from the integrator is applied to a digital voltmeter. For more indication the o/p from integrator can also be applied a tone indicator which produces specific tone corresponding to each heart rate and a lamp indicator in which the LED glows corresponding to the heart rate.


Here ECG is taken from patient using suitable electrode and passed through differentiator, level detector and mono stable circuits as in the case of analog cardio tachometers. The difference between analog and digital tachometer is that the o/p from the mono stable is applied to a 4- in -1 generator. The 4- in -1 generator generates 4 o/p pulses corresponding to one pulse from the mono stable multivibrator. The o p, from the 4-in -1 generator is applied to one of the AND gate inputs and the other input is the o/p from a 15 s time base. So the AND gate will be on for -15 seconds. Since AND gate will be ON for 15s, the gate will pass the pulses to a digital counter connected to its 6-1p. So the counter counts the pulses from 4-in -1 generator within 15 s. Suppose 17 pulses are generated from the mono stable within 15s.These 17 pulses will be converted in to 68 pulses by the 4- in- 1 generator.(17*4).So the counter will show the count rate as 68 pulses .After 15 seconds, the counter o/p will be displayed and updated by the 15 s time base. Sometimes the gating error of the AND gate can create certain errors in a digital cardiotachometer. Digital tachometers which can count from 27 to 199 beats per minute are available. They have less power consumption. Also accuracy can be enhanced by using a programmed read-only memory. The block diagram of Digital Cardiotachometer is shown below.


Since the heart rate is an important physiological parameter, it has to be monitored continuously. If the heart rate crosses the limit in either direction, it has to be highlighted. In cardio tachometers, alarm circuits are provided on bedside monitors to warn the staff on an emergency condition. Here the mechanical arrangement of alarm is designed in such a way that it will turn ON when heart rate is too low or too high. A metal vane connected to the, meter pointer trigger the alarm circuit when pointer moves on either side exceeding a limit. When the pointer exceeds the limit, the metal vane will blind the photocell assembly .So the resistance will increase and it causes triggering of alarm circuit. Same condition occurs when the pointer exceeds limit in opposite direction. Here also the metal vane will blind the photocell assembly to trigger alarm (figure shown below).

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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