Assessment of respiratory function in patients with neck pain
Respiratory function can be best described by assessment of rib cage mobility, respiratory muscle strength, neck posture, and pulmonary function test results [5].
Chest mechanics
Chest mechanics refers to the kinematics involving respiratory muscles and their coordinated action to produce chest wall displacement [25].
Perri and Halford examined the respiratory function with the help of a self-developed “total faulty breathing scale” in neck pain patients. This scale assesses breathing patterns both during relaxed and deep breathing. The scoring is based on three main criteria during inhalation. The absence of outward lateral rib motion is graded as mild affection, lifting of the clavicles is graded as moderate affection, and paradoxical breathing is graded as severe affection in both relaxed and deep breathing. The scoring is done on an ordinal scale of 1, 2, and 3 for mild, moderate, and severe affection respectively. The findings of the above study demonstrated a higher incidence of faulty breathing mechanics in patients with neck pain [13].
Wirth et al. studied rib cage mechanics in patients with chronic neck pain by assessing the thoracic spine mobility using a hand-held, non-invasive electromechanical device called The Spinal Mouse (Idiag, Fehraltorf, Switzerland) which was used to determine the sagittal range of motion (ROM) of the thoracic spine. This test was conducted in the all-fours position to promote a greater range of motion. The device was rolled down the spine starting with the 7th cervical vertebra (C7) and ending at the 3rd lumbar vertebra (L3). The measurements were performed in the neutral, maximally flexed, and maximally extended trunk positions. Mobility between neutral and flexed position (thoracic flexion) and neutral and extended position (thoracic extension) was calculated [7].
Wirth in the same study assessed chest mobility at the level of the xiphoid process using the measure tape method. The measuring tape was drawn tight around the patient’s chest. The patient was asked to perform maximal inspiration and maximal expiration, and the difference in the circumference of the chest was noted. The measurement was taken twice and the average of the two readings was noted.
The findings revealed a decrease in chest expansion in patients with chronic neck pain [7].
Özge Solakoğlu et al., in their study, measured mobility of the chest using a tape measure and correlated its findings with respiratory parameters in patients having chronic neck pain. The findings suggested that chest expansion was correlated to respiratory parameters that included forced vital capacity (FVC)%, peak expiratory flow (PEF)%, maximum voluntary ventilation (MVV), MVV%, and maximal inspiratory mouth pressure (Pimax) and maximal expiratory mouth pressure (Pemax). However, this study did not show any relation of chest expansion with forward head posture (FHP) [22].
Ji Hong Cheon et al. investigated the correlation between thoracic mobility and respiratory muscle strength in chronic neck pain patients. Thoracic kyphotic curvature, thoracic sagittal ROM, maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP) were assessed. Thoracic kyphotic curvature and thoracic sagittal ROM between MEP and MIP (thoracic sagittal ROMMEP-MIP) were measured using flexicurve. Thoracic kyphotic curvature was measured by placing the flexicurve at the C7 spinous process through the 12th thoracic vertebra (T12) spinous process. The angle was measured by calculating the distance with the help of a formula. The participants had a mean angle of 29.30° ± 3.72°. For calculating the thoracic sagittal ROMMEP-MIP, the thoracic kyphotic curvature at MEP was subtracted by the thoracic kyphotic curvature at MIP. It was observed that thoracic mobility during forced respiration was reduced in patients having chronic neck pain, and it correlated well with respiratory muscle strength. The findings suggested that impairment of respiratory strength in chronic neck pain patients may be attributed to changes in the biomechanics of the cervicothoracic spine and rib cage [21].
Pulmonary function
Pulmonary function test is a non-invasive tool used for the assessment of lung function which provides an objective information regarding the diagnosis of lung diseases [26].
Pulmonary function test is performed using an electronic spirometer (Spirolab II; SDI Diagnostics Inc., Easton, MA, USA, and Spirobank II USB MIR, Rome, Italy) with reference to the guidelines of The American Thoracic Society of Standardization of Spirometry and European Respiratory Society (ATS/ERS) [9, 10, 15, 17, 20] or with the help of a Master Scope PC spirometer (Jaeger, Hoechberg, Germany) [7].
The parameters of pulmonary function test that were commonly assessed in the studies relating to neck pain patients were forced FVC, vital capacity (VC), PEF, forced expiratory volume in 1 s (FEV1), FEV1/FVC, forced expiratory flow (FEF25-75%; FEF25%, FEF50%, FEF75%), and MVV [7, 9, 10, 15, 17, 20].
Kapreli et al. were the first to provide evidence of pulmonary function affection in chronic neck pain patients. The pilot findings of this study comparing chronic neck pain patients with healthy controls revealed that patients with chronic neck pain had reduced values of FEV1, FVC, and FEV1/FVC ratio (p > 0.05) and MVV (p < 0.00) [9].
Dimitriadis et al., in his study conducted on a larger sample size, confirmed the trends seen in the previously mentioned study. His study finding reported that chronic neck pain patients presented with significantly decreased VC, expiratory reserve volume, FVC, and MVV. Two patients with neck pain were found to have a mild restriction (percent predicted FVC < lower limit of normal but ≥ 70, no reduction in FEV1/FVC) [10].
The findings of the study done by Moawd et al. provided additional support to the findings of the previous studies. It reported significant reductions in VC, inspiratory capacity (IC), expiratory reserve volume (ERV), FEV1, and FVC in patients with chronic neck pain [17].
The Ibai López-de-Uralde-Villanueva study in patients with chronic nonspecific neck pain and healthy controls showed statistically significant differences for FEV1 and FVC but not the ratio FEV1/FVC between the two groups [20].
However, the study done by Yalcinkaya et al., comparing patients with chronic neck pain and healthy controls separately for males and females, did not show a significant difference in values of FEV1, FVC, FEV1/FVC, PEF, FEF 25–75%, and MVV between the genders [15].
A recent study done by Awadallah M F et al. examined the relationship between respiratory function and chronic neck pain. It was found that chronic neck pain patients had reduced pulmonary parameters that included FVC, FEV1, FEF 25–75%, and PEFR. Fifty-two percent of the participants presented with reduced FEV1/FVC values indicating a restrictive pattern [23].
Özge Solakoğlu in his study assessed pulmonary function in neck pain patients with the help of Vmax™ Encore body plethysmography device and body cabin. The neck pain patients were assessed for forward head posture (FHP) and divided into 2 groups. One group had patients who had FHP and the other group included patients having normal head posture (NHP). A weak negative correlation between FHP and FEV1/FVC%, FEF 25–75%, and FEF75% was found [22].
Respiratory muscle strength
Respiratory muscle function can be assessed directly by measuring the pressure developed throughout the maximum voluntary inspiratory and expiratory effort [22, 27]. Maximal expiratory and inspiratory pressures (Pemax and Pimax respectively) are critical to assess the muscle weakness of respiratory muscles. MIP expressed as Pimax measures inspiratory muscle strength whereas MEP expressed as Pemax measures expiratory muscle strength. MVV also indicates the muscle strength, but it is less sensitive than Pimax and Pemax [22] as the MVV is approximately proportional to VC reduction [7, 8].
Özge Solakoğlu in his study on the effects of forward head posture on expiratory muscle strength in chronic neck pain patients assessed maximal respiratory pressures using a digital mouth pressure meter also known as micro respiratory pressure meter (MicroRPM by CareFusion Inc., Yorba Linda, CA, USA). Patients were requested to wrap their mouth around the flanged mouthpiece tightly. A nose clip was applied to ensure that any air leak was prevented. To measure the Pemax, the patients were initially asked to inhale as much as they could and, then, to exhale at maximal exertion against the resistance of the instrument for no less than 1 s. To measure the Pimax, the patients were asked to exhale as much as they could and, then, to inhale at maximal exertion against the resistance of the instrument for no less than 1 s. The results of this study observed a weak relationship between FHP and expiratory muscle strength, whereas no significant relationship was observed between FHP and inspiratory muscle strength [22].
Similar assessment techniques have been used by Wirth B, Dimitriadis Z, Kapreli E, IbaiLo´pez-de-Uralde-Villanueva, and Moawd et al. in their studies that measured maximal mouth pressures using a digital mouth pressure meter (MicroRPM®) and the accompanying PUMA PC software [7,8,9, 17, 20]. In all these studies, MIP and MEP were both significantly reduced in patients with chronic neck pain [7,8,9, 17, 20].
Reduction in respiratory muscle strength in chronic neck pain patients is attributed to the increased activity level of sternocleidomastoid and anterior scalene. Since the increased activity levels of these muscles put them at risk of early fatigue, it causes impairments in the cervical and thoracic spine and the rib cage. Imbalance of neck stabilizer and mobilizer muscles disrupts the optimal activation of respiratory muscles. Thus, alteration in the rib cage mechanics causes respiratory dysfunction [11].
Posture
Forward head posture (FHP) commonly seen in patients with neck pain is caused by a reduced strength of deep flexors and extensors which in turn cause muscle imbalance and segmental instability [6]. It is also associated with changes in the thoracic spine and reduction of thoracic mobility. These morphological changes are believed to cause impairment in respiratory function [28].
Wirth B, Dimitriadis Z, and Kapreli E assessed the forward head posture with the help of a digital picture taken in the lateral view for each subject. Cranio-vertebral angle being the angle between the line extending from the tragus of the ear to the C7 spinous process and the horizontal line through C7 was calculated with the 3D drawing program (Auto-CAD 2000; Autodesk Inc., San Raphael, CA, USA) [7,8,9,10].
A pilot study conducted by Kapreli et al. in chronic neck pain patients and healthy controls suggested that forward head posture was associated with the lung function parameters in the patients with neck pain [8]. However, similar studies performed by Dimitriadis, Wirth et al., and IbaiLo´pez-de-Uralde-Villanueva did not find any significant differences in head posture when compared in patients with chronic neck pain and healthy controls [7, 8, 20].
Özge Solakoğlu et al. investigated the relationship between FHP and respiratory dysfunctions in chronic neck pain patients. For the assessment of FHP, two measurements were obtained through radiographs using the Picture Archiving and Communication System (PACS, General Electric Healthcare, NY, USA) software. In the first one, the anterior head translation distance which is the perpendicular distance between the vertical line from the posterior inferior corner of C7 and the vertical line from the posterior superior edge of the vertebral body of C2 was measured and was recorded in millimeters. Patients with an anterior head translation distance of > 15 mm were assigned as the FHP group, and those with a displacement of ≤ 15 mm were assigned as the normal head posture group. In the second method, C7 vertebrae position (C7°) was measured through the angle between the line parallel to the disc plane of the C7 disc and a line constructed parallel to the base of the X-ray film. The C7° is closely related to the static alignment of the cervical spine and was thought to be proportional to FHP [24]. This study demonstrated a weak relationship between FHP mm and Pemax% for small effect size and a weak relationship between C7° and Pemax% for medium effect size [22].
Management of respiratory dysfunction in chronic neck pain
There is a paucity of literature concerning the management of respiratory dysfunction in chronic neck pain.
Yeampattanaporn O et al. evaluated the immediate effects of breathing re-education in 36 chronic neck pain patients. Subjects in the study were re-educated with three breathing patterns for 30 min. Pain, cervical range of motion, chest expansion and upper trapezius, anterior scalene, and sternocleidomastoid muscle activity were recorded before and after the intervention. The pain intensity and the muscle activity were significantly decreased, whereas the cervical range of motion and chest expansion at the lower rib cage were significantly increased after the intervention. The study suggests incorporation of breathing re-education has a potential to change breathing patterns and cause an increase in chest expansion and improvement in the cervical range of motion [16].
B. Wirth et al., in his study, demonstrated the effects of 4-week respiratory muscle endurance training (RMET) on chronic neck pain. RMET was performed with a SpiroTiger, a hand-held device that allows for hyperpnoea ensuring normocapnia by partial CO2 rebreathing from a bag. The participants performed five sessions of RMET per week. This study concluded that RMET significantly increased MVV, Pimax, and Pemax. During RMET, neck disability significantly decreased, while neck flexor endurance and chest wall expansion increased. Reduction in hyperventilation and hypocapnia were attributed to the effects of respiratory muscle endurance training [18].
Laurie McLaughlin et al. studied the short-term effects of breathing retraining on pain intensity, functional status, and end-tidal CO2 (ETCO2) in patients with neck and back pain. A muscle strategy problem was identified, and a manual therapy or motor control approach was implemented. Awareness training and biofeedback with capnography and manual therapy to restore mobility were used to retrain breathing. Significant improvement in pain, function, and ETCO2 after the intervention was noted. The study suggests assessing breathing dysfunction using capnography can be incorporated into a manual therapy approach which may in turn improve patient outcome [14].
In a pilot study conducted by Vikram Mohan et al., effects of respiratory exercises on chronic neck pain patients were assessed. Ten participants were divided into control and experimental groups. The control group received routine physiotherapy sessions which included electrotherapeutic modalities for pain, stretching of neck muscles, and range of motion exercises. The experimental group received routine physiotherapy sessions and a respiratory exercise program which included diaphragmatic breathing exercise, volume-oriented device incentive spirometer, and pursed lip breathing exercise. The exercises were carried out with supervision two times per week for a period of 8 weeks. The study concluded that respiratory exercise program significantly improved the endurance of respiratory muscles and reduced pain in patients having chronic neck pain [19].