08 Oct 2002
A US company developing a laser-based system for asthma diagnosis has received a cash boost to support clinical trials.
The device, called the Breathmeter, works by monitoring spectroscopically the concentration of nitric oxide (NO) in exhaled breath. High levels of the molecule are an indication of an undiagnosed asthmatic patient, or of a known asthmatic whose treatment is not working sufficiently. A recent study concluded that up to 40% of asthma patients in the US received inadequate medication for their condition.
Clinical trials of the Breathmeter are underway at The Lung Center in Oklahoma. The optical system uses tunable diode-laser spectroscopy (TDLAS) in the mid-infrared to detect NO.
The setup is based around a IV-VI double-heterostructure laser made from an alloy of lead, strontium and selenium, with an active region similar in composition to lead selenide. The tunable device emits at around 5.2 µm. It measures levels of carbon dioxide simultaneously, which acts as an internal calibration standard for exhaled NO and corrects for any variations in the flow of gas exhaled.
Patrick McCann, an Oklahoma University researcher who founded Ekips, told Optics.org that the PbSrSe laser is the only laser device currently sensitive enough for asthma diagnosis. "Quantum cascade lasers (QCLs) have been operated at room temperature and used to measure NO, but they have not been able to measure the low concentrations [of around 1 part per billion] that are needed for breath measurements," he said.
"Cryogenic cooling and continuous-wave operation of QCLs improves sensitivity to the necessary range, but then the integration times become too long for real-time analysis."
McCann believes that this demonstration of IV-VI lasers for practical healthcare will serve as a new benchmark for laser performance. He adds that key areas where IV-VI lasers are superior to QCLs are wide tunability and low waste heat generation.
Mark Camp is a lead investigator in the clinical trials, which are taking place at The Lung Center in Oklahoma. He says that the Ekips system looks promising: "Early results show that it provides consistent exhaled NO measurements related to airway inflammation - even when NO measurements vary widely due to environmental conditions."
The clinical trials are expected to be completed in mid-2003. Breath tests for other gases that absorb in the mid-infrared could potentially be used to diagnose conditions as diverse as lung cancer and schizophrenia.
Michael Hatcher is technology editor of Opto and Laser Europe magazine.