Abstract:
Humans metabolise carbohydrates, fats and proteins to generate energy, using food as a fuel and atmospheric oxygen as an oxidiser. The energy consumption of a human body, Ei (Cal), can be calculated from the amount of oxygen consumed by using the Karlberg’s equation: 
, wherein ?C is the concentration change of CO2 or O2; W (l) is the volume of the inhaled or exhaled air; aCH, afat and aprot (Cal/l) are the calorific values of the carbohydrates, fats and proteins per litter of O2 consumed; XCH, Xfat and Xprot are the ratios of carbohydrates, fats and proteins in the dietary intake. Thus, measuring the volume of the inhaled or exhaled air and knowing the ratio of the basic food groups in the dietary intake allows calculating the energy consumption of the human body.
The present method is based on the fact that for each individual there is a unique correlation between the measured volumes of the inhaled or exhaled air during a respiratory cycle, and the characteristic changes to the time, intensity and frequency spectrum of the recorded breath sounds of the same individual.
The device comprises a spirometer that measures the tidal volume of the breathing air, a sensitive microphone that is used to record the breath sounds and a programmable processor that is combined with a controlling interface, a display, and storage of digital data. Alternatively, a smart phone connected to the spirometer and the microphone can be used to store, process and display the data.
The programmable processor utilises two sub-algorithms: (i) a calibration sub-algorithm, which is used to establish a correlation between the measured tidal volume of the breathing air and the recorded breath sounds, in a form of an equation that fits a calibration curve; and (ii) a reverse sub-algorithm, which uses the equation fitting the calibration curve to find the levels of energy consumption that correspond to particular breath sound patterns.
In practical terms this means that the user firstly completes a set of exercises, simultaneously recording data from the spirometer and the sound recorder, which data is needed to create calibration curves at different levels of physical stress of the user. Then, during the routine use of the device, the user employs only a microphone to provide input data to the reverse sub-algorithm and to obtain real-time, accurate and individualised estimate on his/her energy consumption.
The energy consumption data can be used by dieticians, athletes and people looking to loose weight for an estimate of the energy consumption and demands during different levels of physical activities and when the body rests, as well as for monitoring the balance of energy input and output. The energy consumption data can also be transmitted to external observers (e.g. trainers) for a distant observation of the physical conditions of the users.
