Inspiratory muscle relaxation rate assessed from sniff nasal pressure.

Abstract

Background -Slowing of the maximum relaxation rate (MRR) of inspiratory muscles measured from oesophageal pressure (POES) during sniffs has been used as an index of the onset and recovery of respiratory muscle fatigue. The purpose of this study was to measure MRR at the nose (PNASAL MRR), to investigate its relationship with POES MRR, and to establish whether PNASAL MRR slows with respiratory loading. Methods -Five normal subjects were studied. Each performed sniffs before and after two minutes of maximal isocapnic ventilation (MIV). In a separate session the subjects performed submaximal sniffs. POEs and PNASAL were recorded during sniffs and the MRR (% pressure falllO ms) for each sniff was determined. Results -Before MIV mean POES MRR was 8-9 and PNASAL MRR was 9-3. The mean (SD) difference between PNASAL MRR and POES MRR during a maximal sniff was 0-48 (0.34) (n=64) and during submaximal sniffs was 0-28 (0.46) (n = 526). The subjects showed a mean decrease in sniff POES MRR of27'4% (range 22-5-36%) after MIV and a similar reduction in sniff PNASAL MRR of28-5% (range 24.1-41-3%). Both returned to control values within 5-10 minutes.Conclusions -PNASAL MRR reflects POES MRR over a wide range of sniff pressures, PNASAL MRR of maximal sniffs reflects POES MRR in normal subjects at rest and foliowing MIV, so measurement ofPNASAL MRR may be a useful non-invasive method for measuring inspiratory muscle MRR, thereby providing an index of respiratory muscle fatigue.

Maximum Rate of Pressure Development and Maximal Relaxation Rate of Respiratory Muscles in Patients with Cystic Fibrosis

“…26 Furthermore, maximal effort is more likely to recruit abdominal, upper airway, and neck muscles, resulting this way in a faster MRR, which does not necessarily reflect inspiratory muscle function. 30 On the other hand, and given these limitations, MRR has been applied as a measure to assess respiratory muscle fatigue both after a maximal effort 12,25 as well as against an occluded airway. 25,27 Another limitation of the study might be that the investigated CF subjects suffered as a whole relatively mild airway disease, as demonstrated by the aforementioned median pulmonary function indices, thus restricting the possibility to identify parameters associated with poor respiratory muscle function.…”

“…27 Kyroussis et al introduced the concept of measuring MRR noninvasively at the level of the nostrils during unoccluded sniff of increasing intensity reaching maximal effort, as nasal MRR was found to reflect esophageal MRR over a wide range of sniff pressures. 12 Our study examined MRR after a maximal static inspiratory and expiratory effort against an occluded airway. Although MRR-P Emax was significantly increased in CF patients, compared to healthy controls, this index in CF patients was not related to pulmonary function indices or nutritional indices, with the exception of height.…”

“…MRR was calculated as the first derivative of pressure with respect to time over the first half of the relaxation curve 11 and expressed as a percentage of the pressure fall in 10 ms. 12 MRPD was assessed and defined as the positive peak of…”

“…11 Inspiratory muscle MRR can be assessed noninvasively by measuring the MRR at the nose during a sniff nasal inspiratory pressure maneuver. 11,12 The increased work load faced by the respiratory muscles due to airway obstruction, hyperinflation, and suboptimal nutrition places the respiratory muscles in patients with CF in mechanical disadvantage and predisposes CF patients to respiratory muscle fatigue and respiratory failure. 13 Indices that describe respiratory muscle function have been found to be affected in CF.…”

Direct and indirect measurements relevant to the assessment of fatigue of the respiratory muscles - review

“…During various types of intermittent contractions, the rate of decay of the esophageal pressure ( P es ) and of the mean transdiaphragmatic pressure generated per breath ( P di ), reflects the relaxation rate of inspiratory muscles and of the diaphragm, respectively [24,26]. The measurement of inspiratory muscle relaxation rate requires relatively simple pressure measurement system.…”