Special types of skeletal muscles are respiratory muscles, which work continuously and rhythmically to provide ventilation suitable for body requirements. The main inspiratory muscle is the diaphragm, which is composed of a peripheral muscular part and a noncontractile central fibrous part. This is an important structure, which separates the thoracic and abdominal cavities. The muscular part comprises similar proportions of slow, fatigue-resistant type 1 fibers and fast type 2 fibers.1 Functionally, the diaphragm can be divided into a rib part, which elevates lower ribs, and a lumbar part, which does not take part in this action.2
In the respiratory system of older people, mobility and ventilation of the lungs could be limited due to the chest stiffness. In addition, maximal voluntary ventilation and vital capacity could also be reduced in comparison with younger people.3 In general, skeletal muscle strength decreases with age due to sarcopenia, which is related to gradual loss of muscle mass due to atrophy of α-motoneurons and as a consequence atrophy of motor units. The specificity of respiratory muscles causes that age-related changes are different in comparison with other skeletal muscles. Inspiratory muscles are also characterized by smaller diameter of fibers than other skeletal muscles. In the diaphragm, the cross-section of fibers does not change with age due to continuous work of this muscle for constant breathing. There is no clear answer to the question whether the diaphragm muscle strength and tension decline with age. The influence of age on diaphragm contractility is underestimated as well.2 The observed decrease in maximum velocity of diaphragm contraction and the decrease in maximum tetanus contraction imply a decrease in the contraction force.4 With age, the diaphragm becomes fatigued faster and returns to normal efficiency slower; this can be observed due to reduction in Ca2+ concentration, reused by the sarcoplasmic reticulum, and increased collagen content, thus increasing diaphragm muscle stiffness.2
It was hypothesized that relaxation techniques can have an influence on decreasing stiffness, normalizing tension, and improving breathing process. Postisometric relaxation (PIR) refers to the effect of the muscle tension reduction after a short period in which isometric contraction has been performed.5 No studies have investigated the effect of diaphragm PIR in older adults. Therefore, the objective of the present study was to evaluate chest circumferences, oxygen saturation, maximal voluntary ventilation, and slow vital capacity after diaphragm training related to PIR. Moreover, diaphragm tension was examined by palpation and heart rate was analyzed to determine whether PIR is a suitable method for older people to improve the tension of the main inspiratory muscle without increasing pulse.
MATERIAL AND METHODS
The study group comprised 23 people (19 women and 4 men) with a mean age of 65 (5) years. The mean height in the examined group was 165 (9) cm and the mean weight was 85 (15) kg. The mean body mass index (BMI) value was 31.2 (15) kg/m2. Most people (39%) were moderately obese (first class of obesity). Overweight was present in 35% of people. Obesity of the second class was observed for 13% and of the third class for 4% of the examined group. Only 9% of people had a normal value of BMI.
All participants were examined twice, before and after the exercises related to PIR of the diaphragm. Examination such as spirometry, chest circumference test according to Buckup,6 pulse oximetry, and palpation of the diaphragm in a sitting position according to Greenman7 were performed. Spirometry analyses, specifically slow vital capacity (SVC) and maximal voluntary ventilation (MVV) analysis, were conducted with a CPFS/D spirometer (MedGraphics). Both parameters were expressed as a percentage value. Chest circumference during inspiration and expiration was evaluated with a measuring metric tape. Chest mobility was defined by the difference between circumference results during inspiration and expiration, and expressed in centimeters. Oxygen saturation and pulse rate were examined with a PC-66B Handheld Pulse Oximeter (Creative Industry Co, Germany).
Participants were asked to perform exercises twice a day, for 2 weeks. Each patient was instructed how to perform PIR in a correct way, meaning, in a sitting position on a chair, was asked to inhale the air for about 20 seconds through clenched nose and mouth. That maneuver caused isometric contraction of the diaphragm. After that, the patient was asked to relax and deeply exhale the air and return to a normal breathing pattern. Isometric contraction and subsequent relaxation were repeated 3 times.
According to Lewit,8 during PIR exercises, isometric contraction lasts for 5 to 10 seconds and at the end stretching is passively done by the therapist. In the present study, due to the region in which PIR was adopted, some modifications were applied. PIR of the diaphragm was performed as a form of autotherapy; therefore, the therapist instructed the patient on how to perform it properly. Isometric contraction was longer because there was no manual resistance provoked by the therapist and too short contractions could not cause the result of relaxation. Moreover, stretching was not passively performed by the therapist, but it was done by the patient during deep exhalation.
The study was approved by the Ethics Committee of the Medical University of Lodz, Poland. Approval number obtained for human investigation was RNN/281/17/KE (September 5, 2017). All participants gave their informed consent prior to inclusion in the study.
Statistical analysis was performed with the Statistica v.12. Elements of summary statistics were used. The Shapiro-Wilk test of normality was applied. In case of normal distribution, the parametric dependent sample t test was chosen. For other parameters, the nonparametric Wilcoxon signed rank test was applied. The accepted level of significance was α= .05.
Summary statistics for quantitative variables before and after PIR are presented in the Table. Statistically significant differences were observed for SVC in the dependent sample t test, MVV and oxygen saturation in the Wilcoxon signed rank test. All parameters were higher after PIR.
According to the Wilcoxon signed rank test, there was a statistically significant difference in diaphragm tension during palpation (P value = .0015). Tension of the diaphragm improved in 30% of people in the examined group after PIR (Figure).
Aging can lead to impaired relaxation rate of the diaphragm, which means that after contraction, the muscle has difficulties to return actively to its initial conditions of length and load. At the molecular level, regulation of diaphragm relaxation is related to removal of Ca2+ from the myofilaments, active Ca2+ pumping by the sarcoplasmic reticulum, and the decrease in the number of working cross-bridges. These mechanisms mainly depend on sarcomere length, muscle tension, and intrinsic contractile function. Diaphragm should return at the end of each contraction-relaxation cycle to a relatively constant resting position, and this process play an important role in adaptation to changes in respiratory load and breathing frequency.9
Increased tension of the diaphragm seems to be linked with impaired relaxation processes occurring during aging. Other causes are overweight, obesity, chronic stress, and sedentary lifestyle with postural problems of chest closure in internal rotation.10–12 In the present study, only 9% of people had a normal value of BMI. The aging process and increased BMI could be a reason for increased diaphragm tension in the majority of people examined. After exercises related to PIR, diaphragm tension examined by palpation according to Greenman7 improved in 30% of participants. PIR is considered an effective therapeutic maneuver, which refers to subsequent reduction in the agonist muscle tone after isometric contraction. This type of contraction stimulates Golgi tendon organs, stretch receptors located in the tendon of the agonist muscle. From Golgi tendon organs, the afferent nerve impulse enters the dorsal root of spinal cord where the inhibitory motor neuron stops the discharge of the efferent motor neurons impulse. That mechanism prevents further contraction and the muscle tone decreases.13 Instead of improving muscle tone, PIR also increases muscle tolerance to stretch.14 The muscle has increased flexibility due to decreased resting tension because of the α-motor neuron postcontraction inhibition and reduced motor neuron excitability.13
Ellythy5 observed the positive effect of PIR in case of myofascial tightness reduction of lumbopelvic muscles, while Ptaszkowski et al14 found no significant influence of PIR and kinesiotaping on resting bioelectrical activity of the upper trapezius muscle in young adults. In the present study, related to older adults, PIR seems to be an effective technique in case of increased diaphragm tension. However, examinations were done by palpation without any analysis of bioelectrical signals, limiting therefore this study, which requires further investigation. What is more, PIR of the diaphragm seems to be safe for older people because in the present study there was no statistically significant difference in heart rate after the exercises. Pulse examination was performed because some authors mention that isometric exercises can be contraindicated in older adults due to the increase in blood pressure and heart rate.3,15
Moreover, among others, Ellythy,5 Al-Khayer and Gervitt,16 Blanco et al,17 and Lenehan et al18 observed a significant increase in range of motion after PIR exercises. In our study, a statistically significant increase in chest mobility, measured according to Buckup's6 chest circumference test, was also found. This effect can be presumably due to the release of diaphragm tension. Muniz de Souza et al19 observed differences in abdominal kinematics between young and older adults during respiration. Therefore, in further studies, it is worth to compare those 2 groups in relation to chest mobility after PIR.
In the present study, patients were asked to perform spirometry analyses related to SVC and MVV. Both parameters, expressed as a percentage value, significantly improved after diaphragm PIR. Due to this improvement, significantly better oxygen saturation was also observed. MVV is a tiring maneuver, but it can be performed in older patients.20 Because MVV can cause hyperventilation, especially in older adults, it was decided to perform it with SVC instead of fast vital capacity (FVC). Moreover, due to those examinations, it was possible to assess PIR effects both for maximal respiratory effort and for slow breathing pattern. According to Allen et al.,21 the mean FVC and SVC are very similar, with a small coefficient of variation, and SVC is a more convenient examination in case of uncontrollable coughing that could be triggered during the FVC examination.
The only study that mentions PIR related to correction of biomechanics and the functional status of diaphragm was the research by Vezhnin et al.22 These authors observed easier respiration, lower chest stiffness, and a significant increase in functional capacities after the course of manual reflex therapy comprising mobilization, manipulations, and PIR in patients with tuberculosis. Vezhnin et al22 demonstrated similar results to the present study concerning older adults; however, those authors did not distinguish which of those techniques had the best effect. Manual mobilizations with elements of stretching were also approved as effective in case of diaphragm hypertonia in the study of Kochański et al.11 Therefore, further research is required to examine, for example, effects of diaphragm PIR versus manual mobilization or kinesiotaping in aging conditions.
The main limitation of this study was the lack in the literature of similar research about the effect of diaphragm PIR, to compare the results. The present research leads to recommendation of diaphragm PIR in older adults as a method that improves tension, range of motion, and respiratory parameters without increasing the heart rate.
PIR of the diaphragm can improve respiratory parameters, chest mobility, and diaphragm tension without an influence on the heart rate. It can therefore be recommended for older adults.
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