Intra- and inter-rater reliability of maximum inspiratory pressure measured using a portable capsule-sensing pressure gauge device in healthy adults.

Muscles in the human body have two functions: to develop force and to shorten. In the respiratory system, force is usually estimated as pressure, and shortening as lung volume change or displacement of chest wall structures. To test respiratory muscle properties, pressures can be measured either during voluntary manoeuvres or during involuntary contractions, notably in response to phrenic nerve stimulation (1). The literature describes many respiratory muscle strength measurement tools, which can be divided into invasive and noninvasive. Although invasive techniques, such as esophageal and gastric balloons for recording esophageal, gastric and transdiaphragmatic pressure, are considered to be more reliable, they require difficult, long and unpleasant procedures. Therefore, noninvasive procedures, such as measurement of mouth or nasal pressure, which are easily performed, are usually preferred and are widely applied and accepted (2). Measurement of maximum inspiratory pressure (MIP) is a simple, quick and noninvasive clinical procedure for determining inspiratory (diaphragm, abdominal, intercostal and accessory) muscle strength both in healthy subjects, and in patients with pulmonary or neuromuscular diseases (3). MIP is the greatest subatmospheric pressure that can be generated during inspiration against an occluded airway. It is a relatively simple and inexpensive measurement to perform (4). It reflects the force-generating ability of the combined inspiratory muscles during a brief-static contraction (5), thus reflecting the strength of the inspiratory muscle. The capsule-sensing pressure gauge (CSPG-V, Gauges Bourdon [I] Pvt Ltd, India [Figure 1]) is a new tool that measures mouth pressure, which is classically established as the standard for assessment of inspiratory muscle strength. This particular CSPG-V was designed, tested and calibrated by an ISO 9001-certified company (General Instruments Consortium Company, India). It is a small, handheld, portable, lightweight, noninvasive, nonbattery-powered, inexpensive device with a mouth pressure manometer attached to a flexible tube with a plastic rigid flanged mouthpiece and a small monitor that displays the test results in cmH2O. This device measures pressure in the range of −500 cmH2O to 0 cmH2O with markings at every 5 cmH2O; accuracy is rated as ±5 cmH2O. Figure 1) Capsule-sensing pressure gauge (Gauges Bourdon [I] Pvt Ltd, India) MIP measurement is not routinely performed during pulmonary function testing. It is indicated when muscle weakness is a suspected contributing cause of abnormal results from routine testing, such as a low vital capacity or reduced forced expiratory volume without signs of obstruction, or an abnormality of the flow volume loop that is recognized to be associated with muscle weakness or if muscle weakness is a possibility in the given clinical scenario. Weakness of the respiratory muscles may be present in patients with dyspnea; respiratory failure; neuromuscular diseases, such as myasthenia gravis, Guillain-Barre syndrome, amyotrophic lateral sclerosis, stroke, polio or quadriplegia; and in multisystem diseases such as polymyositis and sarcoidosis (6). MIP is also used to monitor patients with acute conditions (myasthenia gravis, motor neuron diseases, etc) who are at risk for rapid loss of strength in inspiratory muscles, to follow the progress of patients with chronic diseases (chronic obstructive pulmonary disease [COPD], muscular dystrophy) and also to detect muscle weakness in undiagnosed patients. There is an increased awareness that respiratory muscle weakness can be a compounding factor in other disease processes, such as malnutrition, and steroid therapy (5). Apart from having a role in the diagnosis and prognosis of several neuromuscular and pulmonary disorders, respiratory muscle weakness is also associated with health status, physical fitness and even postsurgical general morbidity/mortality of an individual (4). For example, inspiratory muscle training after assessment using an MIP device has been reported to be useful in COPD when patients presented with significant respiratory muscle weakness, and also showed that tapering of oral corticosteroid successfully restored the respiratory muscle strength and improved dyspnea in patients with corticosteroid-induced myopathy (7). MIP is also helpful in evaluating the success of weaning patients from mechanical ventilators and in predicting the outcome of cardiac transplantation surgery in patients with chronic congestive heart failure (8). Maximum mouth pressure measurements with some portable manometers have been found to be reliable and valid both in healthy volunteers as well as pulmonary and neuromuscular disease patients. However, to our knowledge, there is little awareness of these portable devices because they are scarcely available in a developing country such as India. Also, previous manometer reliability studies used inappropriate or insufficient statistical indexes of reliability (eg, Pearson correlation coefficient), which makes their assumptions problematic (2). The objective of the present study was to develop evidence regarding the intra- and inter-rater reliability of MIP using a CSPG device in healthy adults so that it can be readily used in a typical clinical setting; thereby facilitating enhanced patient care with inspiratory muscle weakness of various causes.