About TIRE
The Test of Respiratory Endurance (TIRE) is an innovative method for the functional assessment and training of respiratory muscles. It enables objective evaluation of the endurance and performance of both inspiratory and expiratory muscle groups.
A brief history of TIRE
In 1996, K. Chatham presented a new respiratory endurance test called TIRE in his article "Fixed-load respiratory muscle training: A pilot study." In 2015, the first review article by authors L. P. Cahalin and R. Arena, "New methods of inspiratory muscle training using the incremental respiratory endurance test (TIRE)", was published. In 2016, L. P. Cahalin et al. presented the first predictive equations for normative values of inspiratory muscle endurance for the US population in the abstract "Normative Values for the Incremental Respiratory Endurance Test (TIRE)" in the American Journal of Respiratory and Critical Care Medicine. Then, in 2018, an article by M. F. Formiga et al. was published: "Reliability and validity of the incremental inspiratory muscle endurance test in COPD," dealing with the relationship between the results of this test and lung function in patients with chronic obstructive pulmonary disease. L. P. Cahalin then collaborated with other institutions to establish these normative values for other regions of the world, as these standards can sometimes vary significantly between populations and races.
Measuring respiratory endurance using TIRE
When measuring an individual using TIRE, the subject is instructed to sit comfortably and put on a nose clip. In this position, they exhale as much as possible, place the mouthpiece of the measuring device in their mouth, clench their lips tightly around the mouthpiece, inhale as much as possible, and then maintain this inhalation tension for as long as possible. The measurement therefore starts at RV (residual lung volume) and ends at TLC (total lung capacity).
Expiratory parameters are measured analogously. In the same position, the subject is asked to inhale as much as possible outside the device, then place the mouthpiece in their mouth, exhale as much as possible into the device, and exhale for as long as possible. While exhaling, the subject holds the corners of their mouth with their hands to prevent air from escaping. The measurement of expiratory parameters begins at TLC and ends at RV.
A 60-second pause is required between measurements to allow the respiratory muscles to recover. The subject is always instructed that in the event of undesirable symptoms during breath measurement, such as shortness of breath or dizziness, the test is terminated. Usually, 3 to 5 measurements are taken for each phase of breathing, during which a so-called plateau should occur (the values do not differ by more than 10% and do not improve further). From the valid experiments, the best result for inhalation and the best for exhalation are then selected to determine the diagnosis or set up further training using TIRE.
Measured parameters
By converting the measured pressures and times recorded during one inhalation or exhalation using a suitable device, the following parameters can be obtained:
- SMIP (Sustained Maximal Inspiratory Pressure) – maximum sustainable inspiratory pressure measured in PTU (Pressure Time Unit) units. It corresponds to the integral of measured pressures over time and is represented by the area under the measured curve and labeled "POWER" (Figure 3). Higher values are associated with greater inspiratory muscle power per breath;
- ID (Inspiratory Duration) – the duration of inspiratory flow in seconds during maximum inspiratory effort through a 2 mm opening with isokinetic resistance. This could be a substitute parameter for inspiratory endurance;
- MIP (Maximal Inspiratory Pressure) - maximum inspiratory pressure obtained from RV (residual volume) at 1-2 seconds of inhalation measured in cmH2O, with higher values associated with greater inspiratory muscle strength;
- SMEP (Sustained Maximal Expiratory Pressure) - maximum sustainable expiratory pressure measured in PTU (Pressure Time Unit) units. It corresponds to the integral of measured pressures over time and is represented by the area above the measured curve (inverse graph to the inspiration graph). Higher values are associated with greater expiratory muscle performance per exhalation;
- ED (Expiratory Duration) - duration of expiratory flow in seconds during maximum expiratory effort through a 2 mm opening with isokinetic resistance. This could be a substitute parameter for expiratory endurance;
- MEP (Maximal Expiratory Pressure) - maximum expiratory pressure obtained from TLC (total lung capacity) at 1-2 seconds of inspiration measured in cmH2O, with higher values associated with greater expiratory muscle strength.