Analysis of Gas Metabolism in the Human Body Under Stress
Vyaire Medical develops devices for the diagnosis, treatment, and monitoring of respiratory diseases. Alongside our other products, we can provide a spiroergometric system for lung function diagnostics, such as the VyntusTM CPX. Integrated into the VyntusTM CPX is the pyroelectric detector LMM-242 from InfraTec.
In order for the human body to achieve peak performance, it has to be provided with the required energy for the work to be done. This energy is primarily produced by the breakdown of carbohydrates, fats and proteins in the presence of oxygen (aerobic metabolism). In addition to food intake, it is necessary that the body also, depending on the load, provides enough oxygen for this metabolism process of the muscles. As with any other burning process, carbon dioxide (CO
We have several bodily functions that interlock and interact like a gearbox. If a human body’s organs or organ systems are impaired in any way, they will be unable to cope with the increasing load placed upon them. In such a case, the characteristic patterns of measurement parameters obtained during ergo spirometry can provide important information about which organs contribute to the impairment.
Ergo spirometry is the analysis of the performance of the human body during physical exercise by measuring or calculating gas metabolism and a variety of other parameters. Ergo spirometry is a valuable differential diagnosis in cardiology, pneumology or sports medicine. Furthermore, it has become the routine standard procedure for preoperative risk assessment in areas such as occupational medicine, rehabilitation or anesthesiology.
For an ergo spirometry measurement, the patient is loaded on a bicycle ergometer or treadmill for about 8 to 12 minutes, with increasing intensity. At the same time, the patient is connected to the measuring system, with which minute ventilation, breathing frequency, oxygen uptake, carbon dioxide production as well as other parameters are continuously recorded.
Measurement Range 0 – 2,000 Watts
For a socket with energy consumption measurement, a measuring range of 0 – 2,000 Watt is not very high. However, this is a major challenge for measuring human metabolic rate. With such high physical exertion, the heart rate can exceed 200 beats per minute and the respiratory rate can exceed 70 breaths per minute. This means that the average inhalation and exhalation time is less than 500 milliseconds, during which gas flow and composition change and must be measured by the device accordingly fast.
A real-time analysis of the inhaled and exhaled gas per breath is only possible with methods optimized for speed. For the precise measurement of the inhaled volume of oxygen and the exhaled carbon dioxide, in addition to a suitable fast flow sensor, correspondingly fast gas sensors with a rise time of 75 milliseconds are also required.
There are not many areas of application for fast, and at the same time highly accurate and cost-efficient gas sensors. There are usually only those available on the market that meet only two of these three criteria. Therefore, Vyaire Medical develops and produces gas sensors according to the needs of its customers.
The interaction of pneumatics, infrared source, detector, signal processing, and application software must be optimized for the non-dispersive infrared sensor for carbon dioxide in such a way that all requirements are met. This is made possible using the two-channel pyroelectric detector LMM-242 from InfraTec. In addition to the measuring channel for carbon dioxide, this detector has a reference channel that is used to compensate for fluctuations in the infrared source, among other things. The integrated operational amplifier of the LMM-242 allows the use of slim analog signal processing and increases robustness against electromagnetic interference.
In addition to gas analysis, sample conditioning also plays an important role: the fluctuating temperatures between inhalation and exhalation and the high proportion of water vapor of up to 6 % in the exhaled air require technical conditioning measures to avoid or compensate for cross-sensitivities to the sensors and contamination effects. Various signal filters and correction algorithms, together with sensors for measuring the ambient conditions, ensure highly accurate measured values.
About Vyaire
The company Vyaire Medical takes on the challenges that its customers have in the field of pulmonary function diagnostics and ergo spirometry. The VyntusTM CPX is the result of over 60 years of experience in the development of spiroergometric systems. The powerful VyntusTM CPX is a precise, reliable system that captures the subject's metabolic response. The system can be used flexibly – from children to adults, and from sick patients to competitive athletes.
Modern technology has contributed to the fact that the additional physical effort for ergometry is only minimal, while the evaluation and diagnostic possibilities have greatly increased. In addition to the individual measured values such as oxygen uptake, the graphical preparation of dynamic changes is particularly noteworthy.
Use of Pyroelectric Detectors in Practice
One advantage of pyroelectric detectors is the versatility of their applications. Detecting and analyzing gases and gas mixtures, investigating the material composition of organic and inorganic compounds, monitoring flames – all this is of great importance in a wide range of industries. Selected examples will help you to get to know some of the possible applications and, at best, to gain valuable ideas for solving your own measurement and testing tasks.
