Inair is a company that invented a portable lung diffusion apparatus, a diffusion spirometer, that was licensed to Spirometrics, a medical equipment company. My father and I received two SBIR contracts to develop the device. This was a great project, but we accumulated some battle scars along the way. We are currently looking for another licensee. We have also invented a device to simulate a human performing the DLCO test to enable calibration of DLCO instruments. The feasibility of the calibrator was demonstrated on another SBIR contract.
Below is a description of the diffusion spirometer and the calibrator. A local paper also did a story on the company.
The DLCO test can detect early stages of interstitial lung disease in the presence of normal spirometry and chest X-rays. DLCO testing has not been available as a screen for occupational diseases like asbestosis and silicosis because DLCO test equipment is large, expensive and generally confined to hospitals. The DLCO instrument developed by Inair improves pulmonary health care by permitting low-cost DLCO screening to be performed outside the hospital.
Why Do DLCO Tests?
Whereas spirometry measures the mechanical properties of the lungs, the lung diffusing capacity test (DLCO) measures the ability of the lungs to perform gas exchange. The single-breath DLCO test requires the patient to inhale DLCO gas nominally consisting of 10% helium, 3000 ppm carbon monoxide and the balance air. The inhaled volume is held in the lungs for 10 seconds during which time the carbon monoxide diffuses through the lung to the pulmonary blood. The helium does not diffuse, but is diluted by the residual volume of the lung. During exhalation, a portion of the breath is collected in a sample collection system. The difference between the inspired and expired gas concentrations is measured and factored with inspired gas volume and other parameters to calculate the lung's diffusing capacity.
Instruments that measure DLCO such as the Inair diffusion spirometer can be of great benefit to the physician in diagnosing lung disorders not detectable by spirometry or chest X-ray. For clinical screening of patients with interstitial lung disease, the DLCO demonstrates a significantly impaired gas exchange in many patients who have no significant defect in mechanics of breathing (spirometry). Many of these patients have a normal chest x-ray so that reduced DLCO is the only objective evidence of lung disease.(3,4,5,6,7,8)
The ability of the lungs to pass oxygen can be affected by a number of medical conditions. Diffusing capacity is reduced when alveolar walls are destroyed and pulmonary capillaries are obliterated by emphysema, or when the alveolar-capillary membrane is thickened by edema, consolidation or fibrosis. Interstitial lung disease is also caused by the inhalation of inorganic dusts found in many occupations. Asbestosis, coal worker's pneumoconiosis and silicosis are the most common examples of such occupational lung diseases. Annual spirometry is now required by law for all workers exposed to these and over 20 other organic dusts. Measurement of diffusing capacity is not required by law because of the problems associated with available DLCO instruments, even though it has been shown to be more sensitive than spirometric measurements for the detection of interstitial lung diseases.
The primary care physician has never done DLCO measurements in his office for the same reasons that it is not used routinely for occupational screening. However, this test would be useful in this setting if the test could be made simpler with a smaller and less complex instrument.(9,15)
Most DLCO equipment operates in a similar fashion with minor variations depending on the manufacturer. The procedure and equipment performance for the measurement of DLCO are specified by the American Thoracic Society (ATS) (10).
The DLCO test gas is first fed from a gas cylinder into a reservoir where its helium and CO concentrations are measured. This is accomplished by diverting some of the gas flow through discrete helium and CO analyzers or through a gas chromatograph. The gas is then inhaled from the reservoir through a mouthpiece into the lungs. Inspired and expired volumes are typically measured with a spirometer or pneumotach. After the breath hold period, the patient exhales through a valve/gas-bag apparatus which allows a portion of the expirate to be collected in a sample bag after the prescribed washout volume has passed. The collected gas is pumped through scrubbers which remove water vapor and carbon dioxide (CO2) from the gas sample. This is done to prevent their interference with the helium analyzer or gas chromatograph. The gas sample is then pumped to the He and CO gas analyzers or gas chromatograph for measurement of the expired gas concentrations. A computer usually controls the operation and calculates the DLCO result from the gas sensor and volume data.
This basic system is made complicated by the need to provide gas flow between the gas reservoir, sample collection bag, CO2 and water vapor scrubbers, and the gas analyzers. In addition, systems using gas chromatographs require two cylinders of gas to operate, one for DLCO gas and one for carrier gas. Many systems also use pneumatically operated valves which require yet another tank of compressed gas. Clearly, this system does not lend itself to design of a portable, easy-to-use pulmonary function lab.
The diffusion spirometer utilizes a proprietary apparatus, called the Tomlinson Diffusion Module (TDM), which integrates a helium sensor, electrochemical CO sensor, and gas collection system into a single unit. The gas sensors operate in the presence of CO2 and water vapor so that both helium and CO can be measured within the TDM, eliminating the need to transport the expired gas sample to separate gas analyzers. This apparatus represents a substantial reduction in the number and size of required pieces of equipment to perform the standard DLCO test and significantly advances the technology beyond the 1973 development of the automated valve sequencer 2.
During a DLCO test, compressed DLCO gas passes from the gas cylinder through an in-line pneumotach to fill the rigid gas collection chamber. This chamber is instrumented with a proprietary ultrasonic helium analyzer and electrochemical CO sensor which measure the He and CO concentration of the chamber gas. After the gas concentrations are measured, the gas is inhaled under control of a demand valve according to the ATS method. After breath hold, the exhaled gas is pushed through the TDM, and a gas sample is trapped in the chamber through appropriate valve sequencing. The expired gas sample is then analyzed in the TDM for He and CO concentrations without moving the sample to separate analyzers.
By eliminating the need to transport the expired gas sample from gas bag to scrubbers to gas analyzers, the size and complexity of the DLCO instrument is reduced while still meeting the ATS requirements for sample collection size, washout volume, and circuit resistance. The rigid sample chamber with detachable gas analyzers is also easier to clean than conventional DLCO instruments, which will reduce the possibility of patient cross-contamination.
Feature |
Benefit |
| integrated sample chamber/gas analyzers | fewer parts, elimination of scrubbers and pumps, lower cost, less maintenance, reduced potential for system leaks. |
| portable, fast set-up time | greater use to a wider patient base, improved diagnoses |
| single gas cylinder | lower cost, contributes to portability |
| short training period | improved return on investment |
| easy to clean | reduced potential for cross-contamination |
Lack of a DLCO calibration standard has reduced the reliability DLCO testing for the diagnosis of lung disease. A calibration system will help DLCO manufacturers and users provide accurate and consistent DLCO tests.
Under an SBIR program, InAir developed a portable DLCO instrument and discovered the problem of finding a DLCO calibration standard to test the new instrument. After investigation, it was discovered that no calibration system existed for DLCO instruments, and in fact, DLCO test variation between pulmonary labs was a significant problem. A recent study by Wanger and Irvin (1) document statistically significant variations between DLCO measurements taken at 13 Denver area laboratories, with variations from 29.4 to 54.2 mL-torr/min in one patient. Although some of the variation can be attributed to technique differences between laboratories, a calibration standard to check instrument accuracy between labs would clearly be beneficial. Without such a standard, the diagnostic benefit of the DLCO test is reduced.
Recently, there have been attempts by other researchers to design a DLCO calibrator. In general, these systems use gas chambers and gas syringe systems to dilute DLCO gas drawn from the DLCO instrument and generate helium (He) and carbon monoxide (CO) gas fractions. To allow the He and CO gas fraction to be independently varied, the operator must add a precise amount of helium to the calibrator. These systems are prone to errors for a number of reasons.
First, they fail to provide adequate mixing of the air, DLCO gas and added helium in the system before being forced back into the DLCO instrument to be calibrated. Without proper mixing, the gas fractions will not be consistent, and the calibration will be inaccurate.
Second, the addition of helium to the system is prone to error. Besides requiring the supply of certified helium containers of various volumes, it is very difficult to design a container to provide both the leak-proof addition of helium and long term storage of helium. One option is to use a gas bag to squeeze the helium into the calibrator. However, because of its small molecular size, helium rapidly diffuses through most non-metallic materials that would be suitable for a gas bag. A metal canister would provide better long term storage for the helium, but it is difficult to know when all the helium has gone from the canister to the calibrator. Also, the valve in the canister would always allow a small amount of helium to leak, either during storage or during addition of the helium, causing additional calibrator inaccuracy.
InAir has developed an innovative solution to the problem of DLCO calibration. InAir's approach is to use a CO catalytic reactor to generate precise CO and helium fractions from the DLCO gas input. This allows the CO and helium gas fractions to be independently varied using only DLCO gas from the DLCO instrument and air. By catalyzing the CO to CO2, the calibrator provides a function similar to CO diffusion in the lungs. In addition, the system is designed to properly mix the gases in the calibrator so that precise, repeatable calibration are obtained. As a result, pulmonary technicians will have a reliable DLCO calibrator to detect problems with their DLCO apparatus and provide a final calibration standard for all DLCO tests. Patient diagnostics will be vastly improved.
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