Cardiac Output measurement by Inert Gas Rebreathing (IGR)adminax5
Inert Gas Rebreathing (IGR) method
The IGR method is based on the principle that the flow of blood through the lungs (pulmonary blood flow) is proportional to the wash-out rate of a gas that is soluble in blood and that is absorbed during breathing by the pulmonary alveoli.
If the patient has an intrapulmonary shunt, the percentage shunt flow will be calculated on the basis of the Fick principle for oxygen, stated in % and the pulmonary blood flow to Cardiac Output corrected.
Cardiac Output measurement in Innocor®
Cardiac Output measurement in Innocor uses a redesigned gas analyser that was originally developed for space research to measure the pulmonary gas exchange by means of a mass spectrometer (Amis 2000). For the gas analysis, Innocor uses patented photoacoustic spectrometry (PAS) specially developed for this purpose that conducts particularly precise measurements and offers long-term stability. This makes it very easy to use the IGR method with Innocor in daily routine for the non- invasive measurement of cardiac output at rest and under stress.
Performing the measurement
The patient first breathes ambient air, the Ergo-Spirometry parameters being measured breath-by-breath, displayed and stored. To measure Cardiac Output, a rebreathing valve switches automatically from ambient air to a rebreathing bag. The bag contains a gas mixture comprising 90 % ambient air enriched with 9.4 % oxygen and the inert gases SF6 (0.1%, non-soluble in blood) and nitrous oxide (0.5%, soluble in blood). The two inert gases are continually measured by means of photoacoustic spectroscopy (PAS).
While rebreathing from the bag, the patient’s CO2 level remains constantly low thanks to the supply of oxygen. After four to five breaths from the bag, the rebrea- thing valve switches back to ambient air breathing and breath-by-breath measurement of the Ergo-Spirometry parameters resumes. The times at which Cardiac Output measurement is conducted can be incorporated at any time into the stress test protocol or initiated manually (e.g. for peak measurement).