What is normal heart rate and oxygen level

Summary

A pulse oximeter is an instrument that estimates and displays the arterial saturation of oxygen. Originally used in the operating rooms of hospitals, pulse oximeters migrated to intensive care units and then to patient clinics.

Pulse oximetry has been a standard of care since 1986; it allows anesthesiologists to ensure that oxygen is being adequately transported to the tissues during mechanical ventilation. This increase in patient safety is based on the relationship between arterial saturation of oxygen and partial pressure of arterial oxygen, which is known as the oxyhemoglobin dissociation curve.

Originally based on the Beer-Lambert law, pulse oximetry estimation of arterial saturation of oxygen became accurate in the range of 90%–100% when Takuo Aoyagi realized that only pulsatile changes in light transmission were necessary for estimating hemoglobin concentrations. Scott Wilber replaced the Beer-Lambert law with a calibration curve, which enabled accurate estimates throughout the range of SaO2. Joe Kiani and Mohammed Diab applied adaptive noise cancellation to pulse oximetry, for accurate estimation in the presence of reduced signal-to-noise ratio.

Key pulse oximetry features include SpO2 accuracy, accuracy under conditions of motion, accuracy under conditions of low perfusion, signal inadequacy indication, and protection from excessive temperatures.

A respiration waveform can be isolated from lowpass filtering of the ECG waveform. It results from lung impedance artifact, due to breathing, that occurs while the ECG is acquired with surface electrodes.

Estimation of Oxygen Saturation

Pulse oximeters estimate SpO2 from empirically calibrated curves, derived by correlating the measured ratio of absorbencies at red (660 nm) and infrared (940 nm) wavelengths to arterial oxygen saturation (SaO2) measured from in vitro oximeters such as the Cooximeters. The calibration procedure involves desaturating healthy volunteers by asking them to breathe hypoxic gas mixtures (range: 100%–80%) and collecting optical measurements of blood samples at different steady-state oxygenation levels (Aoyagi, 2003). At each oxygenation level, the measured SaO2 value is correlated to the “R” value measured by the pulse oximeter. The same procedure is repeated in a large group of volunteers and a mean calibration curve is then obtained. This curve is programmed into the digital microprocessor within the pulse oximeter and during subsequent use, it is used to estimate the arterial oxygen saturation (SpO2). The percentage saturation of oxygen measured by a pulse oximeter in healthy individuals ranges between 95% and 100%.

5.2.8.2 Nail polish

Pulse oximeters are well known to provide inaccurate readings when the light absorption profile of red and/or infrared light is corrupted. Nail polish and artificial fingernails have been reported to affect the pulse oximeter readings measured at the fingertips. In particular, dark colors (e.g., black or blue) can cause false readings and cause inaccuracies (Çiçek et al., 2011; Coté et al., 1988; Yönt et al., 2014). As this is a well-known limitation of pulse oximetry, removing nail polish or change the measurement site can eliminate the problem. Contrarily to the popular understanding that nail polish causes false SpO2 readings, some studies have determined a limited or insignificant impact on SpO2 readings (Balaraman et al., 2020; Rodden et al., 2007; Yamamoto et al., 2008). However, the reported differences in the literature may be due to methodological differences and more standardized studies are required to assess the existence of such interference across different pulse oximeters manufacturers, nail polish colors, and larger populations.

Instrumentation

Pulse oximeters are small, often battery-operated devices, and are required to be light and compact. The two main hardware components of a probe are a light source and a detector. The light source must emit pulsed, high-intensity light of the selected wavelengths; light-emitting diodes (LEDs) are usually the light source of choice because they are small and cheap and can emit light at the required wavelengths. Standard solid-state photodetectors such as photodiodes are sufficient to detect the light that has traveled through the tissue as they are small, their sensitivity is sufficient, and their response is sufficiently linear. Pulse oximeters can be built to operate either on the transmission or on the reflection of light. In transmission pulse oximetry, the detector is placed opposite the light source with the investigated tissue in between (see Fig. 4A). They are the most commonly used probes as they can be very simple, clip-on devices for use on the finger or earlobe. In reflection pulse oximetry, the detector is placed next to the light source, and the measurement relies on the backscatter of the light (see Fig. 4B). They are usually placed on the forehead. Pulse oximetry can be also performed on the nose, cheeks, tongue, or neonatal foot.

System Description and Diagram

A modern pulse oximeter uses Aoyagi’s approximation of the ratio (Eq. (11.21)) and Wilber’s calibration curve. It may incorporate adaptive noise canceling for minimizing the effects of patient motion and low perfusion.

A disposable or reusable probe is typically positioned on a patient’s digit. The clinician powers on the unit, which may run on lead acid batteries or be connected to AC power. An LED driver powers on and off two LEDs at a modulation rate, such as 625 Hz. Typical red and infrared wavelengths used are 660 and 940 nm, respectively. During each modulation cycle, the red LED is powered on, both LEDs are powered off, the infrared LED is powered on, and both LEDs are powered off in sequence. LED light is naturally isolated from the patient.

Light transmitted from an LED and through the finger is received by a photodiode (discussed in detail in Chapter 1). The photodiode current is amplified and undergoes data acquisition. Within the processor module, the digitized data are demodulated to isolate the photoplethysmogram waveform at each wavelength. Plethysmography is the measurement of volume. The so-called pleth waveform is misnamed because it is not directly proportional to pulse volume.

The AC and DC components in each waveform are used to calculate the ratio. A lookup table determines the SpO2 value associated with this ratio. Adaptive noise cancellation may also be implemented in the processor module to minimize patient motion and low perfusion effects. The final SpO2 value is transmitted to an LCD for display. Optionally the pleth waveforms may also be displayed (Figure 11.13).

12.2.5.1 iHealth Labs

The Wireless Pulse Oximeter (Fig 12.6A), an FDA-cleared and CE-marked device priced at US$ 69.95, is a lightweight and miniaturized device for the noninvasive determination of blood oxygen saturation (SpO2) and the pulse rate at the fingertip by shining two light beams into the finger capillaries. The device runs on an integrated rechargeable battery (3.7 V Li-ion, 300 mAh) that can be recharged using the provided USB cable. It is beneficial for patients with breathing difficulties (pulmonary dysfunction), COPD (chronic obstructive pulmonary disease), coronary heart diseases, and other vascular conditions. Moreover, the athletes or users can understand the working of their bodies during recreation activities and high-intensity sports or exercises. The device is interfaced and connected to the SP by the Bluetooth and iHealth MyVitals app. The current measurement is displayed on the oximeter’s screen and recorded into the device’s memory while the iHealth MyVitals app shows the trends in measurements and can share the information with other family members, friends, doctors or caregivers. The SpO2 level indicating the amount of oxygen in the blood as a percentage of the maximum carrying amount is between 96% and 99% for a healthy individual but can be affected by many factors including high altitudes. The device measure SpO2 in the range of 70%–99% with the accuracy of ±2%. The normal resting pulse rate in humans is between 60 and 100 beats per minute (bpm), but it is also dependent on the fitness level, body weight, emotional state, medication, body position, and the involvement in physical activities. Therefore, the optimum reading guidelines provided in the product insert must be followed as several factors can affect the reading and lead to inaccuracy in results such as cold hands, fingernail polish, acrylic nails, hand movements, and weak pulse.

PULSE OXIMETER

Figure 18.3 illustrates the principle of the pulse oximeter. A red light emitting diode (660 nm) and an infrared one (940 nm) shine light through a finger and the photocell shown detects the transmitted light. The output of the sensor is processed electronically to give a pulse waveform and the arterial oxygen saturation. Appropriate sensors are also available for use on the ear.

As in the previously described oximeters the diodes are switched on in sequence with a pause with both diodes off. This pause allows the photocell and microprocessor to detect and compensate for any ambient light which may have penetrated round the sensor cover. The diodes are switched on and off at high frequency, several hundred times a second. Consequently this does not prevent the oximeter detecting the cyclical changes in the signal due to arterial blood flow during systole. A microprocessor is programmed to analyse these changes of light absorption during the arterial pulsatile flow and ignore the non-pulsatile component of the signal due to the tissues and venous blood. The pulse oximeter can thus give a satisfactory reading of arterial oxygen saturation.

At present pulse oximeters normally use only two diodes and so do not compensate fully for carboxyhaemoglobin or other abnormal haemoglobins. Moreover models of pulse oximeter are not all equally accurate at low oxygen levels or in cases of peripheral vasoconstriction and some pulse oximeters may be slow in their response to a fall in arterial oxygen saturation particularly if a finger sensor rather than an ear sensor is used. Pigments on the finger nail or skin staining may also affect the results. Despite these limitations the pulse oximeter is already established as one of the most important monitors for routine use in anaesthesia.

A device has been introduced for clinical use which permits monitoring of the cytochrome redox state in order to assess the degree of oxygenation in the brain. It is a noninvasive system which, like the pulse oximeter, uses absorption of light as a measuring technique but operates in the near infrared using a low power semiconductor laser as a light source.

4 Experimental setup

In this work, the main hardware includes the pulse oximeter, Wi-Fi module, embedded computer, and Arduino microcontroller. The pulse oximeter MAX30100 is used to take input from users. The oxygen saturation (SpO2) percentage of the user is estimated as the output from the pulse oximeter. The IC MAX30100 pulse oximeter sensor board consists of six pins. The sensor board has an inbuilt LED that indicates the connectivity between the sensor and the Wi-Fi communicating unit ESP8266 NodeMCU. The microcontroller unit ESP8266 provides wireless local area network protocol (Wi-Fi) based connectivity. This unit supports full stack TPC/IP Internet protocol along with a microcontroller computing unit. The module further consists of an L106 processing unit with 32-bit RISC architecture running at a frequency rate of 80 MHz. The ESP8266 includes individual memory units including 32kB system RAM, internal cache of 32kB, and user data RAM of 32kB. A flash memory of 16MB is also supported. Additional hardware units include a breadboard and USB type B cable.

The heavy processing tasks like gathering, storage, accessing, and processing data are performed on a personal computer having Intel Core with central processing unit i5-8250 at a speed of 1.60/1.8 GHz. The 64-bit Windows 10 operating system is used for performing various application processes. The system has 8GB of RAM.

This project also includes software, namely the Arduino Integrated Development Environment (IDE), Android Studio IDE, Sublime Text processor, and XAMPP control panel. The Arduino IDE version 1.1.13 is used for hardcoding the microcontroller programming for the Arduino NodeMCU microcontroller unit and its associated processors. The Arduino IDE incorporates a wide range of library functions that are capable of executing complex tasks. It also provides a convenient graphical user interface for programming and debugging. Fig. 9.7 depicts the IoT-based oximeter sensor hardware components hardwired on a breadboard.

The Android Studio IDE is a complete package for Android OS programming. The IDE provides rich library support to emulate different Android mobile phones. Also, it offers enhanced testing tools, applications framework, and extended library support. The IDE is optimized to emulate and execute on a wide range of Android devices. Sublime Text is a code editor that supports lightweight execution. It has additional features such as auto completion of text, highlighting the inbuilt system syntax and keywords, code folding and user friendly coding environment. The XAMPP control panel is an open source software and is used for a cross-platform support system. XAMPP provides interconnection between Apache software, MySQL, and the PhP and Perl environment. It supports implementation of local servers on the local devices. Next, Jupyter Notebook is used for developing Python applications. It is an open source software that supports web application development. The Notebook allows line coding, computing equations, graphical visualization of data, and also exploratory text handling. It provides a rich library of machine learning and deep learning models. It also supports easy integration of external libraries and application programming interface (APIs) within the Python environment. Other software used in this work includes SQL to create/update/delete tables in the database. Python 3 is used to create and train machine learning models. The C programming language is used in Arduino IDE. XML is used for layout and interface in Android app programming. Finally, the MCU-Arduino IDE is used for collecting and displaying the oximeter readings from the sensor. Fig. 9.8 illustrates the activity of the IoT-based oximeter and GPS-assisted Sleep Apnea Android Application.

Abstract

The photoplethysmographic (PPG) waveform, also widely known as the pulse oximeter waveform, is a noninvasive low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. The pulsatile component of PPG waveform (AC) is attributed to cardiac synchronous changes in the blood volume with each heartbeat and is superimposed on a slowly varying baseline (DC) component that is attributed to respiration, sympathetic nervous system activity, and thermoregulation. In current pulse oximetry devices, the PPG signal is optimized (amplified and highly filtered) to accentuate its pulsatile component.

Pulse oximeters have been used in commercially available medical devices for measuring oxygen saturation and heart rate. The utilization of powerful methods of digital signal processing allows for uncovering the true potential of the PPG waveform in order to guide early goal-directed therapeutic interventions (fluid, vasopressors, and inotropes), to assess of vascular compliance and autonomic function, and to estimate of respiratory rate, blood pressure, and cardiac output.

3.11.4 Chemical Resistance

Several medical devices like infusion pumps, dialysis systems, epidural pumps, pulse oximeters, ultrasound machines, and ventilators may require cleaning or disinfecting after use. In addition, reusable devices such as bronchoscopes, ear-nose-and-throat endoscopes, colonoscopes, arthroscopes, and laparoscopic instruments may require cleaning and disinfecting. Devices may come into contact for various durations of time with different types of oils, greases, processing aids, disinfectants, bleaches, alcohols, and other hospital chemicals. Chemical resistance to such chemicals must be considered for the product both during processing and during use over the product’s life.