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PubMedDate not supplied

Pathophysiology of respiratory muscles in course of undernutrition.

Derangements of respiratory muscle function play a key role in the pathogenesis of respiratory failure, as they are able to determine respiratory pump failure and ventilatory insufficiency. Undernutrition negatively influences respiratory muscle function both directly through loss of contractile elements, and indirectly, through worsening or induction of muscle composition derangements. The present review focuses on the importance of undernutrition as a pathogenetic factor of altered respiratory muscle function: respiratory muscle structure and function derangements in both animal models of undernutrition and in undernourished subjects without lung disease are described. The pathophysiology of respiratory muscles in undernourished patients with lung disease is also discussed, along with the complex relationships between undernutrition and some other "metabolic" factors of ventilatory insufficiency.

Animals↗
PubMed2003

Structure and function of the respiratory muscles in patients with COPD: impairment or adaptation?

Respiratory muscles are essential to alveolar ventilation. These muscles work against increased mechanical loads due to airflow limitation and geometrical changes of the thorax derived from pulmonary hyperinflation. Respiratory muscle fibres show several degrees of impairment in cellular and subcellular structures which, in many cases, are proportional to the severity of the disease and accompanying conditions (ageing, deconditioning, starvation, comorbidity). This structural impairment translates, from the functional point of view, to a loss of strength (capacity to generate tension) and an increased susceptibility to failure in the face of a particular load (early onset of fatigue). On the other hand, there is accumulating evidence that the diaphragm and other respiratory muscles are also able to express adaptive changes in response to the chronic mechanical load imposed by the disease. In most cases, impairment and adaptation of the respiratory muscles reaches a balance that permits enough ventilation for patients' survival. However, this balance can be altered for additional increments of the mechanical or metabolic load on the muscles (e.g. abdominal or thoracic surgeries, pneumonia, pulmonary embolism, etc.). Moreover, loss of balance is not always associated with extreme situations. Many patients develop ventilatory failure and require hospital admission even if the cause of the exacerbation is less dramatic (bronchial infections, pain of any nature, electrolyte disturbances, etc.). Although the physiopathology of chronic obstructive pulmonary disease exacerbations is multifactorial, the above-mentioned fragility suggests the existence of a "fragile balance" between respiratory muscle overload and respiratory muscle adaptations. Assessment of respiratory muscle function through specific tests evaluating the strength and endurance could offer valuable information about this particular susceptibility to muscle imbalance. Identification of patients possessing a fragile respiratory muscle balance could have important implications for the application of specific strategies such as respiratory muscle training, nutrition, or anabolic treatment.

Adaptation, Physiological↗
PubMed2006

Six-month nocturnal nasal positive pressure ventilation improves respiratory muscle capacity and exercise endurance in patients with chronic hypercapnic respiratory failure.

BACKGROUND/PURPOSE: This study was designed to investigate the effects of 6 months of nocturnal nasal positive pressure ventilation (NNPPV) on respiratory muscle function and exercise capacity in patients with chronic respiratory failure. METHODS: A prospective, randomized, controlled design was used. Twenty-nine patients with chronic respiratory failure were enrolled and allocated to either the NNPPV (n = 14) or control group (n = 15). Patients in the NNPPV group received bi-level positive pressure ventilation via nasal mask for 6 consecutive months. Arterial blood gas, respiratory muscle assessment and 6-minute walk test (6MWT) were performed before and after the 6-month NNPPV intervention. Respiratory muscle function was assessed using the variables of maximal inspiratory pressure (Pimax), maximal expiratory pressure (Pemax), and maximum voluntary ventilation (MVV). RESULTS: Subjects in the NNPPV group showed a significant improvement in blood gas exchange and increased 6-minute walk distance (6MWD) compared to baseline and the control group. The 6MWD was significantly increased from 257.1 +/- 114.1 to 345.2 +/- 109.9 m (34.3%) in the NNPPV group. NNPPV also significantly improved MVV and Pimax relative to baseline. MVV was significantly increased from 19.2 +/- 6.5 to 22.3 +/- 7.1 L/min (16.1%) in the NNPPV group (p < 0.05). Furthermore, there was a significant correlation between the magnitude of MVV improvement and 6MWD change. CONCLUSION: The 6-month NNPPV treatment significantly decreased the partial pressure of carbon dioxide and improved daytime respiratory muscle function, thus contributing to exercise-capacity increase in patients with chronic respiratory failure.

Aged↗
PubMed2006

Assessment of respiratory muscles endurance in diabetic patients.

OBJECTIVE: Respiratory muscle endurance is of interest in pulmonary, critical care and many other areas of medicine. The maximal voluntary ventilation (MVV) test is an objective dynamic method for measuring the working capacity of respiratory muscles. Therefore, we designed the present study to determine the effect imposed by diabetes mellitus on respiratory muscle endurance in Saudi diabetic patients. METHODS: We conducted this study in the Department of Physiology, College of Medicine, King Khalid University Hospital and Diabetic Centre, King Abdul-Aziz University Hospital, Riyadh, Saudi Arabia during the year 2002-2004. In this study, we recruited 39 male diabetic patients and equal number of control subjects and all participants were non-smokers with age range of 23-71 years. The subjects were matched for age, height and weight. We determined the respiratory muscles endurance by a direct MVV test during inspiratory and expiratory phases of respiration by using a MP-100 student Bio Pac system and compared the results using a paired t-test. RESULTS: In inspiratory and expiratory phases of respiration, diabetic patients showed a significant reduction in the mean values of direct MVV test (p<0.001) relative to their matched controls. CONCLUSION: We conclude that in diabetic patients the respiratory muscles endurance is impaired by a decreased in MVV values. This decline in MVV further showed that the diabetic patients have a reduced inhaled and exhaled volumes during consecutive breaths.

Adult↗
PubMed1998

Respiratory muscle endurance in heart failure--the effect of clinical severity.

UNLABELLED: In chronic heart failure there is no single explanation for reduced effort tolerance. Recently, abnormalities of skeletal muscles, which include respiratory muscles, have been described in cases of chronic heart failure. The aim of this study was to investigate the effect of clinical severity of heart failure, measured by means of the Boston score, on respiratory muscle performance (strength and endurance). METHODS: Using the Boston score, we compared 20 patients with chronic heart failure and low ejection fraction to 20 normal people, measuring maximal inspiratory mouth pressures (MIPs), maximal expiratory mouth pressures (MEPs) and endurance. Endurance was measured by repeated maximal static contractions of MIP and MEP as well as maximal voluntary ventilation (MVV). RESULTS: Inspiratory strength (MIP 75 +/- 34 cmH2O) but not expiratory strength (MEP 116.9 +/- 43.7 cmH2O) were reduced in heart failure patients, compared with controls (MIP 96.2 +/- 29.2, MEP 120.4 +/- 31 cmH2O). Endurance of inspiratory muscles was significantly reduced (P < 0.007) but not of expiratory muscles (P > 0.25). Clinical severity did not correlate with reduced endurance. CONCLUSION: Endurance of the inspiratory muscles was reduced in chronic heart failure unrelated to clinical severity.

Adult↗
PubMed1995

[Muscle relaxants in the morphometric study of the respiratory muscles in human beings].

The morphological examination of respiratory muscle can be affected by muscular contraction following biopsy. Most morphometric studies of respiratory muscles, however, have been carried out without taking into account this factor, the effect of which can be reduced by using relaxants when taking samples. Objective. To examine the effect of using a relaxant in the morphometric analysis of muscle fibers. We examined 31 muscle samples from 7 patients. Immediately after removal, each pipe was divided in half. One was placed in an isotonic physiological solution and the other in a solution of curare 0.02%. Later, both samples were processed for morphometric study with ATP-ase, NADTH and PAS tincture. Morphological data recorded for the different types of fibers included measurement of minimum diameter (Dmin), atrophy and hypertrophy indices (AI and HI) and heterogeneity of distribution (SDDmin). The Dmin was smaller in fibers transported in a curare solution than in those transported in physiological solution (67 +/- 2 microns vs. 71 +/- microns, p < 0.05). The same was true of SDDmin (13 +/- 3 vs. 12 +/- 3, p < 0.05), HI (300 +/- 88 vs. 457 +/- 107, p < 0.05). Likewise, we found a similar direct correlation between size of fibers processed with physiological solution and those processed in curare (Dmin, r = 0.731, p < 0.001; HI, r = 0.827, p < 0.001; SDDmin, r = 0.636, p < 0.0001). The use of relaxants in processing muscle samples prevents contraction and should be used systematically in the morphological analysis of muscle fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Biopsy↗
PubMed2005

Changes in respiratory muscle endurance during puberty.

The evaluation of respiratory muscle endurance provides clinically useful information on muscle function, especially in children with respiratory and neuromuscular diseases. However, endurance may be lower in young children than in older children because of the major physical changes of puberty. We thus compared respiratory muscle endurance in 15 healthy pre- and peripubertal children (S1-S2/P1 group) and 14 healthy children near the end of the pubertal process (S4P4 group). All performed a respiratory muscle endurance test threshold load fixed at 50% of the individual maximal inspiratory pressure; (Pi(max)), using a standardized method with a controlled breathing pattern. No significant difference was found between groups for Pi(max). The mean endurance time limit for the S1-S2/P1 group was 138 +/- 20 sec. The S4P4 group was able to breathe with the threshold valve for more than 20 min (1,200 sec) without task failure, except for one girl (385 sec). This study shows that inspiratory muscle endurance is significantly lower in children in early puberty compared to children at the end of the pubertal process. If the underlying mechanisms are not well-known, the present study revealed that if we use the same inspiratory load in prepubertal children as in adults during clinical testing, we are likely to underestimate the susceptibility to task failure of their respiratory muscles. To define a fatigue threshold for the respiratory muscles, as a function of age, thus appears clinically important in further studies, particularly for the management of children with respiratory diseases.

Adolescent↗
PubMed1992

Respiratory muscle strength in hypothyroidism.

To investigate respiratory muscle strength in patients with hypothyroidism, global respiratory muscle strength was assessed by measuring mouth pressure during PImax and PEmax efforts. Maximum pressures, VC, FEV1, FVC, T3, T4, and TSH were measured in 43 hypothyroid patients. Measurements were made before and three months after replacement therapy with thyroxine. The results showed that the mean value of PImax and PEmax increased after treatment. Significant change was found in the mean value of VC, FEV1, and FVC after treatment but not in the FEV1/FVC ratio. A highly statistically significant linear relationship was found between PImax and TSH and between PEmax and TSH as well as between PImax and T3 and PEmax and T3. We conclude that hypothyroidism affects respiratory muscle strength and that this weakness is linearly related to thyroid hormone levels. Respiratory muscle weakness is present in both inspiratory and expiratory muscles and is reversible with treatment.

Adult↗
PubMed1987

Ineffective breathing pattern related to respiratory muscle fatigue.

In brief, preliminary research suggests that respiratory muscle fatigue contributes to the clinical manifestations of CAL and is associated with changes in breathing patterns. The specific mechanisms for changes in breathing patterns have not been clearly elucidated. Moreover, the mechanisms of respiratory muscle fatigue remain unclear, and clinical methods for diagnosing respiratory muscle fatigue are inconclusive. Until we improve our understanding of respiratory muscle fatigue, interventions are mostly directed toward preventing respiratory muscle fatigue by improving respiratory muscle function. One way to achieve this goal is by inspiratory muscle training. However, further research is needed to elucidate the physiologic mechanisms, clinical implications, and therapeutic interventions for respiratory muscle fatigue so that we can improve the associated ineffective breathing patterns.

Breathing Exercises↗
PubMed1988

Respiratory muscle function in myasthenia gravis.

Global respiratory muscle function and diaphragmatic strength were assessed and compared with quadriceps femoris muscle strength in 17 patients with generalized mild-to-moderate myasthenia gravis and breathlessness. Initial measurements, made 10 h after the last dose of oral anticholinesterase therapy, demonstrated reduced maximal static expiratory (52.4 +/- 26.8% predicted) and inspiratory (54.0 +/- 23.5% predicted) mouth pressures in 16 patients, and reduced quadriceps femoris muscle strength in all cases. Vital capacity (VC) (70.9 +/- 19.0% predicted) was abnormal in 12 patients. Transdiaphragmatic pressure recorded during maximal sniffs (sniff Pdl) was reduced in eight patients, whereas pressure recorded during bilateral phrenic nerve stimulation at 1 Hz (twitch Pdi) was reduced in only three. There was no relationship between the grade of myasthenia or the severity of dyspnea and any of the measurements of respiratory muscle strength. After the administration of edrophonium hydrochloride (Tensilon), there was a significant increase in maximal static expiratory and inspiratory mouth pressures in quadriceps muscle strength and in sniff Pdi. The small increase in VC was not significant, and twitch Pdi increased in only one patient. Phrenic nerve conduction time was normal before and after Tensilon. Two patients with severe long-standing myasthenia showed no improvement in any measurement after Tensilon. We conclude that expiratory and inspiratory muscle weakness was not uncommon in patients with myasthenia gravis. Respiratory muscle strength improved after Tensilon. Vital capacity was a less sensitive measure of respiratory muscle strength than were respiratory mouth pressures and sniff Pdi. Diaphragmatic involvement was not detected by twitch Pdi unless the weakness was severe.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Efficiency of the respiratory muscles in healthy individuals.

We evaluated respiratory muscle performance by determining the energy cost of breathing against incremental threshold loads and calculating the efficiency of the respiratory apparatus for handling the added work. In five subjects, the energy cost of breathing against the loads, and thus the calculated efficiency of the respiratory muscles, was reproducible on repeated measurements. In all subjects, the calculated efficiency varied while breathing with low loads but was relatively constant at loads that resulted in a mouth pressure of 20 to 60% of the subjects' maximal static inspiratory pressure (PImax). The mean efficiency calculated between 20 to 60% of PImax in 30 normal subjects (15 males and 15 females) ranged between 1.54 and 7.98%. It was significantly greater in males (5.41 +/- 0.43%) (mean +/- SEM) than in females (2.41 +/- 0.17%). There was no relationship between efficiency and body size, but the efficiency correlated with inspiratory muscle strength (PImax). We suggest that measurement of the efficiency of the respiratory muscles over a spectrum of incremental threshold loads is a simple, noninvasive, and reproducible method of assessing respiratory muscle performance and may have clinical application.

Adolescent↗
PubMed2000

Effects of respiratory muscle work on exercise performance.

The normal respiratory muscle effort at maximal exercise requires a significant fraction of cardiac output and causes leg blood flow to fall. We questioned whether the high levels of respiratory muscle work experienced in heavy exercise would affect performance. Seven male cyclists [maximal O(2) consumption (VO(2)) 63 +/- 5 ml. kg(-1). min(-1)] each completed 11 randomized trials on a cycle ergometer at a workload requiring 90% maximal VO(2). Respiratory muscle work was either decreased (unloading), increased (loading), or unchanged (control). Time to exhaustion was increased with unloading in 76% of the trials by an average of 1.3 +/- 0.4 min or 14 +/- 5% and decreased with loading in 83% of the trials by an average of 1.0 +/- 0.6 min or 15 +/- 3% compared with control (P < 0.05). Respiratory muscle unloading during exercise reduced VO(2), caused hyperventilation, and reduced the rate of change in perceptions of respiratory and limb discomfort throughout the duration of exercise. These findings demonstrate that the work of breathing normally incurred during sustained, heavy-intensity exercise (90% VO(2)) has a significant influence on exercise performance. We speculate that this effect of the normal respiratory muscle load on performance in trained male cyclists is due to the associated reduction in leg blood flow, which enhances both the onset of leg fatigue and the intensity with which both leg and respiratory muscle efforts are perceived.

Adult↗
PubMed1989

Effects of the menstrual cycle on respiratory muscle function.

To investigate the effect of the menstrual cycle on respiratory muscle function, respiratory muscle and pulmonary functions were measured and compared in the midfollicular phase and in the midluteal phase of the menstrual cycle in 30 healthy adult women. Respiratory muscle strength was indicated by maximal static inspiratory and expiratory pressures. Inspiratory muscle endurance was determined by the product of pressure load and the sustained time, i.e., pressure-time index, while the subject breathed against an inspiratory pressure load on a modified Nickerson-Keens device. The results showed that the inspiratory muscle endurance was greater in the midluteal phase than in the follicular phase (815 +/- 43 versus 649 +/- 62 cmH2O.min, respectively), whereas the respiratory muscle strength and pulmonary function were unchanged. We conclude that inspiratory muscle endurance is affected by the menstrual cycle, i.e., higher in the midluteal phase and lower in the midfollicular phase.

Adult↗