Measurement of Inspiratory Muscle Performance with Incremental Threshold Loading^1,2

Abstract

We found that breathing strategies affect measurement of sustainable inspiratory pressure (SIP). After allowing time for learning, the maximum sustainable inspiratory pressure (SIPmax) was 46% greater than SIP. We therefore developed a test of ventilatory muscle performance that used progressive 2-minute increments in threshold inspiratory resistance. Subjects started with a low load and continued to breathe until they could no longer inspire. With increasing load there was a fall in minute ventilation and time of inspiration, and an increase in oxygen consumption and PETCO2-Power was greatest when loads were 55 to 75% of maximum static inspiratory pressure (MIP). The inspiratory mouth pressure corresponding to the greatest load achieved (PmPeak) was the same in trained and naive subjects. PmPeak/MIP was reproducible and was not influenced by fixing subjects' breathing frequency. We concluded that tests of ventilatory muscle performance should allow subjects to develop breathing strategies to handle high inspiratory loads. Two-minute incremental loading is a simple assessment of ventilatory muscle performance and the test may have clinical application where reproducibility is necessary, AM REV RESPIR DIS 1987; 135:919-923

Inspiratory muscle training in chronic airflow limitation: comparison of two different training loads with a threshold device

“…PImax was determined at functional residual capacity (FRC) in a quasistatic way, as proposed by BLACK and HYATT [15] [16], using a modification of the device described by NICKERSON and KEENS [17]. The patient breathed during 2 min against the intrinsic load of the device and, subsequently, external weights were added every 2 min.…”

“…The patient breathed during 2 min against the intrinsic load of the device and, subsequently, external weights were added every 2 min. [16]. Maximal inspiratory pressure which could be sustained for 2 min (SIP) was measured as an index of inspiratory muscle endurance [16].…”

“…[16]. Maximal inspiratory pressure which could be sustained for 2 min (SIP) was measured as an index of inspiratory muscle endurance [16]. In order to evaluate the effect of training on the development of fatigue, we calculated the pressure time index (PTX) during loaded breathing, according to BELLEMARE and GRASSINO [18]: PTX is the product of peak mouth pressure as a fraction of PImax, multiplied by TI/Ttot for each incremental load.…”

Respiratory muscle strength and endurance in individuals with tetraplegia

“…2,14,22 One minute incremental threshold loading test Following a 20 min recovery-break, the endurance capacity or fatiguability of the inspiratory muscles was assessed using the 1 min incremental threshold loading test. 17 A modi®ed breathing valve was used, in which weights could be added to the inspiratory valve to change the threshold pressure without disrupting the system or the breathing pattern. The pressure needed to lift the inspiratory valve was measured with a pressure transducer (Statham USA Gould P23ID), connected to a pressure monitor (Statham USA Gould SP1405) and results were recorded on a chart-recorder (Kipp & Zonen BD41, Delft, The Netherlands).…”

“…11,14,15,18 The ventilatory incremental threshold loading test has shown to be suitable to measure endurance capacity of the inspiratory muscles. 7,17 These methods, however, have never been applied to qualify or quantify respiratory muscle function in individuals with tetraplegia.…”