How Many Maneuvers Are Required to Measure Maximal Inspiratory Pressure Accurately?

doi:10.1378/chest.111.3.802

Chest

Volume 111, Issue 3, March 1997, Pages 802-807

https://doi.org/10.1378/chest.111.3.802 Get rights and content

Objective

To determine whether performing more maximal inspiratory pressure (MIP) maneuvers per test provides a more accurate assessment of the true maximal inspiratory strength.

Design

Review of MIP data from 367 tests. Each subject was encouraged to perform 20 MIP maneuvers per test, unless the patient reached the highest measurable pressure three times, or because of poor cooperation, fatigue, or respiratory distress. From the same raw data, MIP was calculated in two ways: (1) the “short MIP” was defined as the average of the first three highest values with ≤5% variability; the results from further maneuvers were ignored; and (2) the “long MIP” is defined as the average of the three highest values with ≤5% variability from all recorded maneuvers.

Setting

Pulmonary Physiology Laboratory, Childrens Hospital Los Angeles.

Participants

One hundred seventy-eight pediatric and adult subjects (age, 14 ± 3 [SD] years; 53% male) with suspected inspiratory muscle weakness.

Measurements and results

The long MIP (91 ± 39 cm H₂O) was significantly greater than the short MIP (82 ± 39 cm H₂O) (p<0.000005). In 177 of 367 tests, the short MIP underestimated the peak performance.

Conclusions

From the same raw data, the long MIP was significantly greater than the short MIP. In 48% of the tests, the short MIP method underestimated the peak performance determined by the long MIP method. We speculate that the difference between the long MIP and the short MIP can be attributed to a learning effect.

Section snippets

Subjects

We analyzed raw data from 367 MIP tests performed by 178 patients (age, 14 ± 3 [SD] years; range, 4 to 25 years; 159 children and 19 adults; 53% male; weight, 45 ± 15 kg; total lung capacity, 80 ± 26% predicted, and residual volume, 154 ± 85% predicted) between 1988 to 1995. Adult subjects (age, 20 ± 2 years) performed 26 tests.

At Childrens Hospital Los Angeles, MIP evaluations are performed routinely in patients with neuromuscular diseases and musculoskeletal abnormalities. Patients had

RESULTS

Our study showed that from the same raw data, the long MIP was significantly greater than the short MIP (mean difference, 9 ± 13 cm H₂O). This relationship is seen among children and adults (Fig 2), and female subjects (long MIP, 94 ± 40 cm H₂O; short MIP, 84 ± 40 cm H₂O; p<0.000005) and male subjects (long MIP, 87 ± 38 cm H₂O; short MIP, 79 ± 38 cm H₂O; p<0.000005). In fact, in 177 of 367 tests (48%), the long MIP was larger than the corresponding short MIP. The distribution of MIP results is

DISCUSSION

Our study demonstrates that MIP values calculated by the long MIP method were significantly greater than values determined by the short MIP method in children and adults, and in both male and female subjects. In almost half of the tests, the short MIP underestimated the long MIP. Therefore, performing the MIP maneuver more times resulted in higher MIP values.

The short MIP method assumes that peak performance is observed once results have been reproduced three times. Our observation that the

CONCLUSION

In conclusion, our study demonstrates that from the same raw data, the long MIP was significantly greater than the short MIP. Therefore, attempting 20 maneuvers per test, as in the long MIP method, provides a more accurate assessment of the true inspiratory muscle strength. We speculate that the difference between the long MIP and the short MIP is due to a learning effect. In patients who performed the MIP maneuver four times, with each evaluation separated by a week, there was no difference in

ACKNOWLEDGMENTS

The authors thank Margaret Wen for her invaluable assistance with data entry. We also thank Michael Stabile, MS, RPFT, and the staff at the Childrens Hospital Los Angeles Pulmonary Physiology Laboratory for their technical assistance.

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The aim of this study is to examine whether there is a synergistic relationship between the diaphragm and pelvic floor muscles (PFM) in pregnant women.
Our study was carried out as a cross-sectional study in primigravid pregnants in the second and third trimesters. Superficial electromyography (EMG), 2D/3D ultrasonography (USG), pulmonary function test (PFT), PERFECT, maximum expiratory pressure (MEP) and inspiratory pressure (MIP) measurements were used to evaluate pelvic floor and diaphragm muscle functions during pregnancy. Mann-Whitney U test was used to show the change in the second and third trimesters, and Spearman correlation was used to determine the relationship.
No correlation was found between the EMG data of the PFM and diaphragm, or between the USG data of the PFM and diaphragm in all participants, in the second and third trimesters. In the third trimester of the study, diaphragmatic thickness and levator hiatal area (LHA) decreased and both diaphragm and PFM % MVC EMG parameters increased. In the third trimester, FVC, MIP, MEP decreased, and nonsignificant increase in FEV1, FEV1/FVC and peak ekspiratuar flow(PEF) were detected. A significant correlation was found between pelvic floor levator hiatal area USG and FEV1/FVC in both trimesters (r: 0,577p: 0,004).
There may be a synergistic relationship between the diaphragm and PFM in pregnant women, the relationship may weaken as pregnancy progresses, and there may be no coactivation relationship between the two muscles. In order to prevent the occurrence of pelvic floor dysfunction during pregnancy and to increase the effect of rehabilitation programs, the relationship between the diaphragm and the PFM should be determined and more studies should be conducted.
Impact of high-intensity interval hyperpnea on aerobic energy release and inspiratory muscle fatigue
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Respiratory muscle endurance training reportedly has beneficial effects on whole-body endurance performance. We produced a novel high-intensity interval (HII) protocol and characterized the associated physiological responses and respiratory muscle fatigue. Peak oxygen uptake of respiratory muscle (V̇O2peakRM) was estimated during the respiratory incremental test. The HII session consisted of five 3-minute hyperpnea periods at 100%V̇O2peakRM interspersed with 2-minute periods at 40%V̇O2peakRM (25 min total). The high-intensity continuous (HIC) session involved a single time-to-end bout of hyperpnea at 100%V̇O2peakRM. The moderate-intensity continuous (MIC) session involved 25 min of hyperpnea at 60% of maximal voluntary ventilation. V̇O2RM was recorded continuously, and maximal inspiratory pressure (PImax) was assessed before and after the sessions. HII session: V̇O2RM gradually increased as the sets proceeded, whereas PImax decreased significantly. HIC session: V̇O2RM increased progressively, and the time to end was 6.5 ± 0.5 min. PImax decreased significantly. MIC session: V̇O2RM did not change for 25 min, and PImax remained unchanged. The duration of V̇O2RM at near- and supra-maximal levels in the HII session (10 ± 1 min) was longer than that in the HIC session (4 ± 1 min). The decrease in PImax was larger in the HII session (−12 ± 3 %) than MIC session (−4 ± 3 %). The HII protocol is characterized by a longer time to maximally stimulate the aerobic energy system of respiratory muscle than the HIC protocol and greater inspiratory muscle fatigue than the traditional MIC protocol. These results suggest that the HII protocol could enhance the efficacy of respiratory muscle training programs.
A Phase II randomized controlled trial for lung and diaphragm protective ventilation (Real-time Effort Driven VENTilator management)
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Citation Excerpt :
Direct measures of respiratory muscle strength using maximal inspiratory pressure during airway occlusion (PiMax), either of the airway or esophagus, are regarded as the most appropriate tests in adults [23,24]. When patients are intubated, there is divergence in the literature as to whether maximal voluntary efforts can be guaranteed [2,23,25–28]. Alternatively, some investigators advocate twitch stimulation of the phrenic nerve, measuring change in airway pressure in response to a standardized brief stimulation.
Lung Protective Mechanical Ventilation (MV) of critically ill adults and children is lifesaving but it may decrease diaphragm contraction and promote Ventilator Induced Diaphragm Dysfunction (VIDD). An ideal MV strategy would balance lung and diaphragm protection. Building off a Phase I pilot study, we are conducting a Phase II controlled clinical trial that seeks to understand the evolution of VIDD in critically ill children and test whether a novel computer-based approach (Real-time Effort Driven ventilator management (REDvent)) can balance lung and diaphragm protective ventilation to reduce time on MV. REDvent systematically adjusts PEEP, FiO₂, inspiratory pressure, tidal volume and rate, and uses real-time measures from esophageal manometry to target normal levels of patient effort of breathing. This trial targets 276 children with pulmonary parenchymal disease. Patients are randomized to REDvent vs. usual care for the acute phase of MV (intubation to first Spontaneous Breathing Trial (SBT)). Patients in either group who fail their first SBT will be randomized to REDvent vs usual care for weaning phase management (interval from first SBT to passing SBT). The primary clinical outcome is length of weaning, with several mechanistic outcomes. Upon completion, this study will provide important information on the pathogenesis and timing of VIDD during MV in children and whether this computerized protocol targeting lung and diaphragm protection can lead to improvement in intermediate clinical outcomes. This will form the basis for a larger, Phase III multi-center study, powered for key clinical outcomes such as 28-day ventilator free days.
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Citation Excerpt :
Anthropometric characteristics, percentage of body fat (7 skinfold points measurement, Harpenden, UK; Norton et al., 1996) and handgrip (Camry, EH 101, USA) were recorded. Respiratory muscle strength was assessed by measuring the maximal inspiratory pressure (PImax) by a MicroRPM portable device (MicroRPM, Care Fusion, California, USA; Wen et al., 1997) and pulmonary function parameters (FEV1, FVC and PEF) were measured by a portable spirometer (Card Guard Spiro Pro, Israel), in accordance with the ATS/ERS recommendation (Miller et al., 2005). Athletes were allocated into groups [Gender: Female (F) vs. Male (M); finswimming style: BF vs. MF (surface events) and swimming distance: <200 m vs. ≥200 m].
The purpose of our study was to investigate the differences in the finswimmers’ physiological characteristics, as far as gender, the swimming style and the different swimming distance are concerned.
52 finswimmers participated in our study (Age: 17.4 ± 2.1yrs, BMI: 21.8 ± 2.3, body fat: 12.2 ± 4.7%) and were allocated into groups [Gender: Female vs. Male, swimming style: Bifin vs. Surface, and swimming distance: <200 m vs. ≥200 m]. Anthropometric characteristics, handgrip, estimated strength of inspiratory muscles (PI_max) and pulmonary function parameters (FEV₁, FVC and PEF) were measured. The Independent T-test was used for statistical comparisons between groups. Multivariate analyses were performed via binary logistic regression.
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Maximal Inspiratory Pressure: Does the Choice of Reference Values Actually Matter?
2017, Chest
Citation Excerpt :
The ample heterogeneity of normal predicted values for MIP has long been recognized.1-4,25 This might stem from several sources including inter- and intrasubject variability of a highly effort-dependent test,15 differences in methods of measurement and reporting (e-Table 1), and biologic variation in variables that are notoriously difficult to control for, such as athleticism, muscularity, and central vs peripheral fat deposition.2,26-29 This issue has been addressed from theoretical and population-based perspectives,4,14-16 which uniformly showed substantial heterogeneity across age ranges in both sexes.
Single-point measurements of maximal inspiratory pressure (MIP) are frequently used to suggest muscle weakness in clinical practice. Although there is a large variability in “mean” predicted MIP depending on the chosen reference values, it remains unclear whether those discrepancies actually impact on the prevalence of weakness, that is, MIP below the lower limit of normal.
A total of 1,729 subjects (50.1% men, aged 20 to 94 years) who underwent MIP measurements in a clinical laboratory comprised the study group. MIP was predicted according to the most frequently cited regression equations as of August 2015. Pretest probability of weakness was defined by a cluster of clinical and physiologic variables.
Prevalence of weakness ranged from 33.4 to 66.9%. Set 2 equations agreed well in indicating weakness (κ [95% CI] ranging from 0.81 [0.79-0.83] to 0.83 [0.81-0.85]; P < .01). There was closer agreement between higher pretest probability of weakness and low MIP according to set 2 equations compared with set 1 equations. Thus, a significant fraction of subjects with abnormal MIP according to set 1 equations but preserved MIP according to set 2 equations had higher pretest probability of weakness (P < .05).
The choice of MIP reference values strongly impacts on the prevalence of weakness. Some specific equations relate better to clinical and physiologic indicators of weakness, suggesting that they might be particularly useful to screen subjects for advanced respiratory neuromuscular assessment.
Respiratory Muscle Strength in Chronic Stroke Survivors and Its Relation with the 6-Minute Walk Test
2016, Archives of Physical Medicine and Rehabilitation
Citation Excerpt :
However, we aimed for 6 acceptable maneuvers (without leaks and with a plateau on the curves), 3 of them reproducible with a maximum of 5% of variation. We followed this procedure26 to achieve more accuracy and to minimize the learning effect because this can influence the results of MEP and MIP.33,34 Most of the reviewed articles8,16,17,31 have not considered smokers or ex-smokers within the exclusion criteria.
To compare respiratory muscle strength in stroke survivors (SS) with that in a control group (CG) of healthy people matched by age and sex, as well as to investigate any relation between respiratory muscle strength and the distance walked during the 6-minute walk test (6MWT).
Cross-sectional study.
This study comprised patients from a private neurological rehabilitation center and a public association for patients with acquired brain injury.
Chronic SS with a diagnosis of hemiplegia/hemiparesis who were able to walk (n=30) and healthy individuals matched by sex and age (n=30) (N=60).
Not applicable.
Respiratory muscle strength was assessed using maximal expiratory pressure (MEP) and maximal inspiratory pressure (MIP) with a pressure transducer and a diver nozzle. The distance walked during the 6MWT was also registered for both groups. The motricity index and the Scale Impact of Stroke version 16.0 were also measured in SS.
The Student t test revealed significantly lower values of MIP and MEP in SS than in the CG (MEP, 95.93±43.12cmH₂O in SS vs 158.43±41.6cmH₂O in the CG; MIP, 58.7±24.67cmH₂O in SS vs 105.7±23.14cmH₂O in the CG; P<.001). Moreover, these findings were clinically relevant because both MIP and MEP in SS were <60% of the predicted values. A positive correlation between the 6MWT and MIP was found using the Pearson coefficient (r=.43; P<.018).
Respiratory muscle weakness should be considered in a holistic approach to stroke rehabilitation.

View all citing articles on Scopus

: Reprint requests: Dr. Marlyn Woo, Division of Pediatric Pulmonology-mailstop 83, Childrens Hospital Los Angeles, 4650 Sunset Blvd, Los Angeles, CA 90027

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Chest

Pulmonary Physiologic Test of the MonthHow Many Maneuvers Are Required to Measure Maximal Inspiratory Pressure Accurately?

Objective

Design

Setting

Participants

Measurements and results

Conclusions

Section snippets

Subjects

RESULTS

DISCUSSION

CONCLUSION

ACKNOWLEDGMENTS

Chest

Chest

Clin Chest Med

Chest

Chest

Chest

Chest

Chest

Chest

The ventilatory capacity in healthy patients: an analysis of causal factors with special reverence to respiratory forces

Scand J Clin Lab Invest

Maximal respiratory pressures: normal values and relationship to age and sex

Am Rev Respir Dis

Respiratory muscle strength in the elderly

Am J Respir Crit Care Med

Pulmonary Physiologic Test of the Month
How Many Maneuvers Are Required to Measure Maximal Inspiratory Pressure Accurately?