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July2007 Vol.44 Issue:      2 Table of Contents
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Neurophysiological Assessment of Skeletal Muscles in Patients with Chronic Obstructive Pulmonary Disease

Maysa Sharaf El-Din1, Ann Abdel Kader2, Mohamad Abd El-Hakim1, Mona M.Nada2, AyatAllah Farouk2

Departments of Chest1, Clinical Neurophysiology2, Cairo university


Chronic obstructive pulmonary disease (COPD) is a chronic debilitating disease with disabling symptoms. It has recently become apparent that skeletal muscle dysfunction is common in patients with COPD, and may play a role in reducing exercise tolerance. The peripheral muscles seem to be more affected than the respiratory muscles, especially those of the lower limb in comparison to those of the upper limb. In this thesis the relation between skeletal muscles dysfunction and the severity of COPD was studied. The form of dysfunction emphasized in this study was the muscle strength; being measured as amplitude and envelope or as torque. Thirty COPD patients and ten control subjects were included in this study. All were submitted to the following a- thorough history taking. b-Clinical examination. c- Chest X-ray. d- Arterial blood gases, e- Resting spirometry, f- Isokinetic dynamometry, g- Quantitative Interference pattern  electromyography. Results were tabulated and statistically analyzed. There was statistically significant difference between the COPD patients and the control group regarding the strength of the muscle  represented in this study by: quadriceps muscle in isokinetic dynamometry and Vastus medialis, in particular, in EMG. There was also a significant correlation between smoking index represented by pack years and the weakness of the muscle. Ex. smokers were found to be more affected. The COPD patients, whether they showed manifestations of hyperinflation or chronic bronchitis, had significant correlation with muscle weakness by surface EMG. However, the correlation was not significant regarding the isokinetic dynamometry, measuring the torque of the muscle, although it was evident that the isokinetic dynamometry was much lowered in COPD in relation to the control group. So, COPD patients diagnosed by clinical assessment, radiology and resting spirometry, showed significant impairment of the strength of their quadriceps muscle; especially, the vastus medialis muscle. The weakness of peripheral muscles was attributed to severity of COPD, and smoking habits.

(Egypt J. Neurol. Psychiat. Neurosurg., 2007, 44(2): 675-682)




COPD is a debilitating disease. Skeletal muscle dysfunction is common in patients with COPD .The systemic aspects of COPD affecting the lower limb muscle include oxidative stress and altered circulating levels of inflammatory mediators and acute-phase proteins1.

Lower limb muscles undergo structural changes which result in an impairment in their function and in the global exercise capacity of the individual. Deconditioning due to a reduction in daily activities secondary to ventilatory impairment is probably the driving factor for these changes.1

During muscle activity, the initially recruited motor units are the small motor units (type I motor units), they generate small MUAPs and are fatigue resistant .As the force of contraction increases, larger motor units are recruited (type II motor units), they produce larger MUAPs, they fire at higher rate and are susceptible to fatigue2, Quantitative IP analysis provides information about characteristics of  motor units including those recruited by strong force and not easily studied by conventional EMG. Interference pattern is generated by an orderly recruitment of motor units during increased force of contraction as the orderly recruitment of motor units is based upon their size and termed "size principle"3.

Also Quantitative IP analysis can be performed over relatively short epochs  of activity e.g. poor cooperative patients or easily fatigued. QIP studied the amplitude of motor units quantitatively for specific muscles.4

Isokinetic dynamometry is a device designed to measure the torque (maximum strength the muscle can reach). Measuring  the torque of the quadriceps femoris muscle  studies the extensors of a joint as a whole not a selected muscle as the QIP analysis can assess5.




This study was performed on 30 Male COPD patients, all being chronic heavy smokers. Also 10 healthy controls from the same sex and age group were included in the study. Each patient was submitted to the following:

1.             Full history taking

2.             Full clinical examination

3.      Radiological examination plain chest x-ray (PA posteroanterior and lateral views).

4.             Arterial blood gases:

5.      Resting spirometry: This was performed by the Vmax 229 pulmonary function sensor medics.


Patients were seated and asked to tightly close his lips around the mouth piece (sterilized before use) .A nose clip was used to make sure that the patient did not breath through his nose .

Patient was first asked to breath through his mouth normally. After a few breaths the patient was to inhale maximally and then exhale forcefully and for as long as he can .

Patient then was asked to  take his breath. The best of the three readings was taken.

The test was repeated for three times and the best reading was taken.

Measurements were taken for forced vital capacity (FVC) & forced expiratory volume (FEV).

6.      Isokinetic dynamometry: This was performed using the modified JAMAR hand grip isokinetic dynamometer. The instrument was modified by Sawan5.


Each patient was seated at a high chair such that the knees are flexed and the feet are not reaching the ground. Lower end of the leg just above the level of the malleoli, with a dressing intervening between them, the patient was then asked to extend his knee maximally, while the operator was holding the device firmly against the patient’s leg. The average of three attempts was taken for each lower limb. The torque was measured in kilograms. The test was performed on ten healthy controls of same age group and sex.


7.      Quantitative interference pattern electromyographic study (QIP):

This was done using the Key point device in the clinical neurophysiology department at the Cairo university hospital. QIP studies the amplitude of motor units quantitatively for selected muscles ,it   measures the amplitude and envelope of actively contracting vastus medialis muscle. Amplitude implies the maximum strength the contracting muscle can reach and envelope is the collective parameter for measuring the contraction of the muscle. The patient was seated on chair  with knees flexed and instructed to extend his knee with maximum force.

Two surface electrodes about 2 centimeters in diameter were applied to the surface of quadriceps femoris muscle; the distal one at 2 centimeters above the medial aspect of knee joint, and the proximal one at about 5 centimeters from the medial aspect of the knee joint. The electrodes were fixed by a plaster band after applying conducting gel to the surface in contact with the patient.           

A cable representing earth was applied to the non contracting limb of the patient.

The patient was asked to forcefully and maximally extending his knee, and after recording the readings of contraction he was asked to relax.

This was repeated for several times and only the mean and standard deviation of amplitude and envelope were taken for statistical analysis.

The procedure was done for both lower limbs. Values were measured in microvolts.

As there were no normal values regarding this procedure ten controls were tested in the same way.




The patients were classified according to the GOLD classification6.

Stage  0: (at risk) chronic cough and sputum production. Lung function is normal as measured by spirometry.

Stage (1): (Mild) Mild airflow limitation *FEV1/FVC < 70% but not always, chronic cough and sputum production. At this stage, the individual may not be aware.

Stage (2): (Moderate) Worsening airflow limitation.

Stage (3): (Severe) severe airflow limitation (FEV1/FVC < 70; FEV1 < 30% predicted).


Distribution of the patients group according to the classification declared by  GOLD 2001 (Table 1).  

There were high statistical significant reduction of the muscle activity measured by QIP EMG (amplitude ,envelope) study and the isokinetic dynamometry in the COPD group as compared to the control one (Table 2, Figs. 1,2,3).

There was a high statistical significant positive correlation between  the forced vital capacity (FVC) & forced expiratory volume (FEV) and the QIP EMG parameters  (amplitude ,envelope) study, however the correlation between the FVC, FEV and the  isokinetic dynamometry was non significant (Figs. 4,5).

It was found that the weakness of the muscles in relation to COPD was more evident with the exsmoker than the smoker (Table 3). There is a significant correlation  between the smoking index (No. of packs -each containing 20 cigarettes- smoked per day for how many years) and the peripheral muscle weakness .this relation was found between all parameters of skeletal muscle strength and  the number of cigarettes smoked per day (Table 4).

Table 1. Distribution of the patients group according to the classification declared by GOLD 2001.



Stage 0

Stage I

Stage II

A              B

Stage III

50-60 years



6               3


60-70 years



 2               14




Table 2. Comparison between the control group and the  COPD patients as regards the muscle strength measurements; (QIP EMG and isokinetic dynamometry).



Control group

Control group

COPD group

COPD group

P value





Amp.  Rt uv

Amp  Lt. uv

Env.   Rt.uv

Env.   Lt uv

ISO  Rt. kg

ISO   Lt kg
































Table 3. Muscle strength and smoking in the COPD patients.




Ex. smoker






Amp.   Rt

Amp    Lt.

Env.    Rt.

Env.    Rl.

ISO     Rt.

ISO     Rl































* Significant

Table 4. Smoking index represented in pack years and muscle strength.








Smoking index







* Significant





Fig. (1): QIP EMG in a normal control subject.



Figs. (2,3): Reduced QIP EMG in a COPD patient.


Fig. (4): Correlation between  FVC and the skeletal muscle strength measurement in COPD patients.



Fig. (5): Correlation between  FEV and the skeletal muscle strength measurement in COPD patients.




Being considered as a systemic disease, affecting the skeletal muscles as well as the respiratory system, attempts at relating the skeletal muscle dysfunction to COPD were carried on. For determining the relation between peripheral muscles and COPD, two procedures were used in COPD patients diagnosed by history taking, physical examination and performance of spirometry.

Quantitative interference pattern EMG (QIP)which measured the amplitude and envelope of actively contracting vastus medialis muscle. Amplitude implies the maximum strength the contracting muscle can reach and envelope is the collective parameter for measuring the contraction of the muscle3,7. The quadriceps femoris muscle was chosen as it was found  that lower limb muscles were more affected than upper limb muscles in patients with severe to moderate disease.8

Measurement of the torque of the quadriceps femoris muscle by the isokinetic manometer when contracting without moving (the change is in the tone of the muscle not the length of its fibers).5,6

Comparison with the control group (same age group and sex of healthy non smokers) showed marked discrepancy regarding both measurements.

As for the Quantitative interference pattern EMG There were high statistical significant reduction of the muscle activity measured by quantitative EMG amplitude ,envelope study and the isokinetic dynamometry. This indicates the presence of significant skeletal muscle weakness in COPD patients even when compared to matched control individuals.

For isokinetic dynamometry (kgs) the mean was 17.5 and 16.5 for the right and left lower limbs respectively. For the normal control group 31 and 29 for the right and left lower limbs respectively. These results agree with Engeten et al.9, Friksson et al.10, and Haccoun et al.11.  Gossetink et al.12 used the same procedures, however he involved the upper limb muscles in a similar study. He found that there is reduction in both groups of peripheral skeletal muscles with much more affection of the lower limb muscles.

However QIP EMG was found to be more accurate and more reliable than the isokinetic dynamometry in depicting the correlation between COPD and peripheral muscle weakness.          though this wasn’t exactly what was found by Friksson et al.10, as he stated that isokinetic dynamometry was of good reliability in relation to surface EMG which he found to show variable reliability with the lateralis muscle.

This may be due to the fact that in this study the surface EMG was done specifically to the vastus medialis muscle whereas the dynamometry was done for the whole extensors of the knee; providing support for each other. On the other hand, the vastus lateralis muscle in another study by Gosselink et al.12, was able to yield satisfactory results by the surface QIP EMG.

In the present study it was found that the weakness of the muscles in relation to COPD was more with the exsmoker group .being an exsmoker gives us an implication that these patients stopped smoking because they were compelled to do so after their smoking related symptoms became unbearable, Moreover, Patients of this group were all over 65 years; suggesting that age was also a contributing factor to the weakness of the muscle as well as the progression of the COPD.13

Lastly, a significant correlation was found between the smoking index (No. of packs -each containing 20 cigarettes- smoked per day for how many years) and the peripheral muscle weakness represented in this relation was found between all parameters of skeletal muscle strength and  the number of cigarettes smoked per day.

So, cigarette smoking seems to be of strong relation to the disease of the muscles in COPD whether related only to increasing the severity of COPD14, or being the culprit in enhancing the role of inflammatory mediators and causing oxidative stress systemically.15




1.      Gea J, Orozco-Levi M, Barreiro E, Ferrer A, Broquetas J. (2001):  structural and functional changes in the skeletal muscles of COPD patients: the “compartment” theory. Monaldi Arch Chest dis; 56: 3, 214-224

2.      Nadedkar,S.D.(1997): “Objective EMG”: Quantitation and documentation in the routine needle Electromyographic examination .In :Practical Electromyography .(eds). Johnson, E.W. and Pease, W.S.3rd ed ,Williams and Wilkins;41-63.

3.      Preston, D.C.; and shapiro, B.E. (1997): Fundamentals of electro myography. In: Electromyography and Neuromuscular disorders; Clinical and electrophysiologic correlations.1st ed  Butterworth- Heinemann;143-207.

4.      Shields,R.W. (2000): Quantitative Electromyo-graphy and Special electromyographic techniques. In Comprehensive clinical neurophysiology.(eds): Levin, K.H.and Luders H.O.,1st ed ,W.B.Saunders company;140-162.

5.      SWan S. (2002): The modified JAMAR isokinetic dynamometer. By. Personal contact

6.      Global Initiative for Chronic Obstructive Lung Disease. (2001): Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Pulmonary Disease: NHLBI/ WHO Workshop Report. Bethesda, MI): National Heart, Lung, and Blood Institute; National Institutes of Health; April.

7.      Shields, R.W. (2000): Quantitative Electromyo-graphy and Special electromyographic techniques. In Comprehensive clinical neurophysiology.(eds): Levin, K.H. and Luders H.O., 1st ed., W.B. Saunders Company; 140-162.

8.      Gosselink R, Troosters T, Decramer M. (1996): Peripheral muscle weakness contributes to exercise limitation in COPD. Am J Respir Cdt Care Med; 153:976-980

9.      Engelen MPKJ, Scholes AMWJ, Does, JD and Eouters EFM. (2000): Skeletal muscle weakness is associated with wasting of extremity fat-free mass but not with airflow obstruction in patients with chronic obstructive pulmonary disease. Am. J. Cl Nut; Vol. 71: No 3

10.    Friksson M, Karlesson S. Gerdle B, Larsson B. (2000): Intra-rater reliability of peak torque and EMG in knee extensors during endurance testing in an isokinetic dynamometer. Student Journal of health sciences; Vol. 3: No.2.

11.    Haccoun C, Smountas AA, Gibbons W, Bourbeau J, Lands LC. (2002): Isokinetoic muscle function in COPD. Chest; vol. 121: No. 4.

12.    Gosselink R Troosters T, Decramer M. (2000): Distribution of muscle weakness in patients with chronic obstructive r pulmonary disease. J Cardiopulm Rehab; 20:353-360

13.    Broods SV and Faulkner JA. (1995): Effects of aging on the structure and function of skeletal muscle. In: C Roussos (ed.) The thorax. Marcel Dekker, New York: p295-312.

14.    Shapiro SD. (1994): Elastolytic metalloproteinases produced by human monouclear phagocytes. Postential roles in destructive lung disease. Am. Respir crit care. Med; 150: S159-4.

15.    Di Francia, M., D. Barbier, J.L. Mege, and J. Orehek (1994): Tumor necrosis factor-alpha levels and weight loss in chronic obstructive pulmonary disease. Am. J. Respir Crit Care Med; 150: 1453-1455.



الملخـص العربى


دراسة الخلل الوظيفي للعضلات الهيكلية في مرضي السدة الرئوية المزمنة


مرض السدة الرئوية المزمنة يعد مؤخرا مرضا عاما يصيب الجهاز التنفسي الي جانب تأثيرات عامة من بينها الخلل الوظيفي للعضلات الهيكلية وخاصة عضلات الأطراف السفلية. أجريت هذه الدراسة علي ثلاثين من المرضي بالسدة الرئوية المزمنة وعشرة من الأصحاء، واشتملت الدراسة علي ما يلي:

1-      دراسة تاريخ المرض.                                     2-      الفحص الإكلينيكي.

3-      أشعة عادية علي الصدر.                        4-      اختبار وظائف الرئة.

5-      قياس عينات الدم بالشرايين.                     6-      قياس العزم بواسطة مقياس حركي متساوي النشاط.

7-      رسم العضلات السطحي  لقياس العزم والظرف.


وقد وجد أن مرضي السدة الرئوية المزمنة أظهروا خللا واضحا بقوة العضلة الرباعية وقد اعزي هذا الضعف الى شدة مرض السدة الرئوية وعادات التدخين.

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