Fast and Accurate Exhaled Breath Ammonia Measurement

Summary

Ammonia is an important physiologic metabolite relevant to various disease and wellness states. It is also a difficult molecule to measure in breath, which demands particular precautions be taken to obtain accurate results. Not all factors influencing ammonia are known, but progress can be difficult without accounting for these factors.

Abstract

This exhaled breath ammonia method uses a fast and highly sensitive spectroscopic method known as quartz enhanced photoacoustic spectroscopy (QEPAS) that uses a quantum cascade based laser. The monitor is coupled to a sampler that measures mouth pressure and carbon dioxide. The system is temperature controlled and specifically designed to address the reactivity of this compound. The sampler provides immediate feedback to the subject and the technician on the quality of the breath effort. Together with the quick response time of the monitor, this system is capable of accurately measuring exhaled breath ammonia representative of deep lung systemic levels.

Because the system is easy to use and produces real time results, it has enabled experiments to identify factors that influence measurements. For example, mouth rinse and oral pH reproducibly and significantly affect results and therefore must be controlled. Temperature and mode of breathing are other examples. As our understanding of these factors evolves, error is reduced, and clinical studies become more meaningful. This system is very reliable and individual measurements are inexpensive.

The sampler is relatively inexpensive and quite portable, but the monitor is neither. This limits options for some clinical studies and provides rational for future innovations.

Introduction

Ammonia is a ubiquitous byproduct of protein metabolism¹. Ammonia measurement can therefore help clinicians assess various disease and wellness states². However, ammonia is difficult to measure accurately, via blood or breath, because it is very reactive. Though commonly used, blood assays have numerous drawbacks, including basic concerns about accuracy³. But the major problem with blood assays is the reality that they only ever collected episodically. This is important because ammonia physiology, much like blood glucose and many other metabolic processes, are fluid and ever changing⁴. In contrast, breath assays are fully no....

Protocol

1. Preparation of Instruments

1. Turn on the external power supply to the ammonia optical sensor platform, laser diode controller, a custom built control electronics unit (CEU), the breath sampler, air pump, and laptop.
2. Check that both the exhaust and cooling fans of the ammonia sensor are operating. NOTE: One is located in the rear of the sensor, the second is found within the sensor, which is easily accessible.
3. Ensure the acoustic detection module and needle valve temperature are at 38.0 °C by checking the digital display located on the side of the ammonia sensor box. Wait approximately 35 min from the time the sensor is provided po....

Results

Subjects can be expected to produce a wide range of baseline breath ammonia levels. Healthy individuals may begin the day with a breath ammonia measurement of 100-1,000 ppb. Rinsing the mouth out with any fluid immediately changes the amount of detectable breath ammonia. Neutral and acidic fluids typically cut the amount of observable ammonia by more than half. These levels then return to baseline as the effects of the rinse wears off. The effects of water seem to dissipate within 15 min, while an acid can keep detectabl.......

Discussion

The benefits of a non-invasive procedure capable of detecting trace metabolites in real time are obvious. However, the field of breath research has struggled to fulfill this potential. Breath measurement is a dynamic process vulnerable to many confounding factors. Our approach has important strengths: specifically, the sensitivity and speed of the Rice QEPAS based ammonia monitor coupled to the breath sampler have enabled us to evaluate and identify breath collection factors germane to accurate measurement. This approach.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Rice Ammonia Monitor System	N/A	N/A	Not available for commercial purchase
Loccioni Breath Sampler	Loccioni Humancare	N/A	Single breath version
Disposable Mouth Piece	WestPrime Healthcare	G011-200	Manufacturer is AlcoQuant
Laptop	Lenovo	N/A	Old model no longer sold by manufacturer
Acid Rinse	N/A	N/A	Household acidic drink (coffee, soft drink, citrus juices, etc)
Base Rinse	N/A	N/A	Water mixed with a nonexact amount of sodium bicarbonate (Arm & Hammer Baking Soda)
Neutral Rinse	N/A	N/A	Water