Metabolic testing has a wide range of applications, from detecting H.pylori to monitoring asthma patients. It’s even being developed as a way to measure blood glucose levels. Pulmonary Function Testing is a subset of metabolic testing and typically used when a patient is taking a stress test or an athlete is undergoing performance testing. These systems measure CO2 and O2 in the exhaled breath to determine the utilization of oxygen and excretion of carbon dioxide in each respiratory cycle. The results of this testing help gauge the overall efficiency of a patient’s respiratory system and fitness level.
Other uses for Pulmonary Function Testing include Ambulatory systems which are used by athletes during their training to provide a real-time record of their respiratory performance during peak demand. Stationary systems, which look like transparent phone booths, are used in hospitals and healthcare providers’ offices during routine cardiac stress testing and also during metabolic testing to create a profile of a patient’s metabolism, allowing providers to design customized exercise and weight-loss programs.
How Pulmonary Function Testing Equipment Works
A patient may walk or run on a treadmill or ride a stationary bike in the “booth” while breathing through a mouthpiece. Many Pulmonary Function Testing equipment use spirometry and pulse oximetry to measure oxygen utilization and breath volume/lung capacity. Spirometry measures the volume of each inhaled and exhaled breath as well as the speed at which the patient moves the air. This test can be used to diagnose chronic lung diseases such as asthma and Chronic Obstructive Pulmonary Disease (COPD). In pulse oximetry, a sensor is placed across the earlobe or fingertip and sends two wavelengths of light through the body part to a detector. The equipment’s software interprets the difference in absorbance of each wavelength to measure the level of oxygen saturation in a patient’s bloodstream. Metabolic test rigs will also include capnography, which measures carbon dioxide in exhaled breath. By evaluating both CO2 and O2 levels, healthcare providers and athletic trainers can get a better idea of a patient’s individual respiratory performance. Unlike pulse oximetry and spirometry equipment, capnography monitors, also known as capnographs, are very sensitive to the moisture in a patient’s breath.
Capnographs used in Pulmonary Function Testing equipment is especially susceptible because the higher rates of respiration that occur during exercise translate to more exhaled moisture. The exhaled breath travels from the mouthpiece, through a sample line, and to the capnograph. These monitors usually work on the principle that CO2 absorbs infrared radiation. A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of CO2 in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit. The analysis is rapid and accurate. Capnographs display a numerical value as well a waveform, which is a graphical depiction of the CO2 concentration in each exhaled breath. This information provides valuable insights into the CO2 production, pulmonary perfusion, alveolar ventilation, respiratory patterns, and overall respiratory efficiency.
Challenges Associated with Capnography used in Pulmonary Function Testing – Water vapor interferes with the proper operation of analytical equipment in a variety of ways:
- Moisture Interference in Infrared Analysis used for CO2 Monitoring & Measurement – Water vapor appears on the scale in the same region as the CO2 peak, making the results difficult to read and introducing inaccuracies based on the operators’ interpretation of the results. Removal of the water, in vapor phase, preserves the CO2 level while eliminating interference.
- Moisture build‐up in Sample Lines – Condensation from the breath gas sample stream can collect in the sample lines, a problem normally found when the fully saturated sample at body temperature is brought into contact with the lines at standard room temperature.
- Moisture Collection in the Sensor Cell – Condensation in the sample will eventually reach the analyzer, and will cause irreparable harm to the sensor and render the equipment unusable. This is a problem commonly found when the fully saturated breath sample (at 37C body temperature) is brought to the analyzer at a colder room temperature.
How Perma Pure dryers using Nafion® membrane tubing technology help:
- Fast response time – instantaneous and continuous moisture transfer
- Fully bio-compatible for surface contact with patient skin
- Removes up to 90% of moisture in breath samples
- Improves accuracy of IR-based EtCO2 measurements by eliminating moisture interference
- Highly selective – removes water vapor while retaining sample analytes
- Prevents condensation to protect medical monitoring equipment
- Reduces dead volume in sample circuit when compared with a water trap.