PULMONARY FUNCTION TESTING IN SPINAL CORD INJURY:
EFFECTS OF ABDOMINAL MUSCLE STIMULATION
C Maloney1 WE
Langbein1,2 F Kandare3 U Stani…4 B Nemchausky5 RJ Jaeger1,4
1Research Service, Edward
Hines, Jr VA Hospital, USA; 2Dept
Medicine, Loyola Univ Medical Center, Maywood, USA; 3Univ
Clinic of Respiratory Diseases & Allergy, Golnik, Slovenia; 4Institute
>>Jońef Stefan<<, Ljubljana, Slovenia; 5Spinal
Cord Injury Service, Edward Hines, Jr VA
Hospital, USA
ABSTRACT
The
purpose of this study was to assess the effects of applying transcutaneous
electrical stimulation to upper motor neuron paralyzed abdominal muscles during
pulmonary function testing (PFT) in four male spinal cord injured (SCI)
patients with anatomical level of injury between C3 to T7. Patients performed
PFTs with and without electrical stimulation delivered to abdominal
muscles. The predicted values were
computed for comparable nonsmoking neurologically intact individuals based on
height and age. The patients with the
lowest predicted expiratory volumes and flows demonstrated the greatest
improvement when electrical stimulation was delivered during forced
expiration. The results indicate that
electrical stimulation of the expiratory muscles during forced expiration can
significantly improve expiratory volumes and flows in some patients with
SCI.
KEYWORDS: Pulmonary Function Testing, Spinal Cord
Injuries, Electrical Stimulation.
INTRODUCTION
Expiratory muscle weakness or paralysis in patients with spinal
cord injuries (SCI) results in decreased peak expiratory flow rates (PEFR),
forced expiratory volume in one second (FEV1) and forced vital
capacity (FVC).1,2 Moreover,
expiratory muscle weakness or paralysis is responsible for decreased cough
efficiency, and contributes to the excess respiratory morbidity in these
patients.3 The purpose of the
present study was to assess the effect of transcutaneous
electrical stimulation of upper motor neuron paralyzed abdominal muscles in
patients with SCI on expiratory flows and volumes. The hypothesis to be tested was that FVC, FEV1,
and PEFR could be increased over purely volitional levels by applying
electrical stimulation to abdominal muscles during the performance of a
standard PFT.
METHODS
Patients: Four male patients (ages 29, 29, 40, 58) were
recruited from the inpatient and outpatient populations of the Hines Veterans
Affairs Hospital SCI Service. The
selection criteria included volitional (unassisted) FVC < 90% of
predicted, anatomical level of injury between C4 and T7, upper motor neuron
paralysis of the abdominal muscles, visible abdominal muscle contraction upon
application of electrical stimulation, tolerance of the electrical stimulation,
and no current pulmonary complaint. The study was approved by the Hospital’s
Human Studies Subcommittee and written informed consent was obtained from each
patient.
Evaluation of Pulmonary Function: Lung volumes were
measured by timed spirometry. The
spirometer software provided predicted values for each patient, based on
neurologically intact non-smoking individuals with no known pulmonary
complaints (sex, age, and height).
Electrical Stimulation: Electrical stimulation was delivered via
eight surface electrodes. Two pairs of
electrodes were placed on the lower abdomen, near the midline, and just above
the iliac crest. Two other pairs of
electrodes were placed on the upper abdomen near the midline, just below the
ribs. Spacing between the edges of
electrodes was approximately 3 cm. Two
standard commercial neuromuscular stimulators delivered a pulse train of 8 s
duration. The pulse amplitude was
manually set by the investigator, based on visual inspection of the contraction
obtained (up to a maximum of approximately 100 mA) and was constant throughout the
pulse train. Pulse repetition rate and
width were fixed at 50 pulses/s and 250 ms, respectively.
Protocol: Patients were studied while seated in their
personal wheelchair. Six PFTs were obtained from each patient, alternating methods
(volitional only and volitional with electrical stimulation). The trial under each condition with the
maximum FVC was retained for analysis.
In addition, the two best measurements of FVC under each condition had
to be within 5% of each other to be accepted for analysis.
RESULTS
All
patients tolerated the procedure well.
No local or systemic adverse effects of electrical stimulation were
recorded. Three of the four patients
demonstrated a significant enhancement in expiratory flows and volumes (i.e.,
10% or greater improvement as compared to volitional PFT), as shown in Table
I.
Figure 1 below shows a spirometric
tracing from patient # 272 (C 4-5 lesion) for unassisted PFT (solid line) PFT
with electrical stimulation (dotted line).
Panel A (lower right): volume-time relationship; Panel B (upper left):
flow-volume relationship. As compared to
the unassisted maneuver, the electrically assisted maneuver produced a 650 ml
increase in FEV1 (Panel A)
and a 1.60 L/s rise in PEFR (Panel B).
FIGURE 1: Spirometric Tracing
DISCUSSION
The results of the present study suggest that electrical
stimulation of the abdominal muscles can improve expiratory flows and volumes
in some patients with SCI. The larger the disparity between achieved and
predicted values for the expiratory flows and volumes during the volitional
effort, the greater the gain in the measured PFT value when electrical
stimulation was applied.
The feasibility of using abdominal muscle stimulation to improve
cough in patients with SCI has been demonstrated in a number of studies.4,5,6,7 Researchers employing surface electrodes in
patients have reported that maximum expiratory pressure can be increased over
volitional when either manually assisted cough or electrically assisted cough
are used.4 Investigators
measuring PEFR during cough have reported similar improvements over volitional
for manually assisted or electrically assisted cough.5 The use of electromagnetic stimulation has
also been studied with human subjects, showing increases in cough peak flow
rate.6,7
In all of the human studies which involved the expiratory muscles
previously discussed,4,5,6,7 none have attempted to assess the state
of the upper motor neuron paralyzed muscles with respect to atrophy. It is likely that these muscles in most
patients had undergone varying degrees of disuse atrophy. Thus, it is reasonable to assume that the
immediate increases over volitional obtained with electrical stimulation in the
present study are “worst case” values.
These values might be improved as
the abdominal muscles are more frequently activated by electrical stimulation,
since chronic electrical stimulation of upper motor neuron paralyzed skeletal
muscle has been shown to increase the strength of stimulated contractions, as
well as improve fatigue resistance.
Chronic stimulation in phrenic pacing has also been shown to strengthen
the diaphragm, and improve fatigue resistance.8
In
conclusion, the present study has indicated that electrical stimulation of
abdominal muscles in patients with SCI can be used to improve performance
during standard clinical PFT. The challenge of the future is to exploit the
untapped potential of abdominal muscles in improving pulmonary function for
patients with SCI on a daily basis. This
could potentially lead to a reduction of pulmonary complications and an
increased quality of life for patients with SCI.
ACKNOWLEDGEMENTS
The authors thank the individual veterans who participated in this
study. This study was supported by the Department of Veterans Affairs, Merit
Review Grant Number B2027-RA. We are
especially indebted to F. Laghi, MD, for advice and
assistance with pulmonary function testing, and for substantial medical and
editorial assistance with this paper.
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ADDRESS: Christine
Maloney, Research Service (151), Edward Hines, Jr VA
Hospital,
Fifth Avenue and Roosevelt Road, Hines, IL 60141, USA.
tel +1 708.202.8387 ext. 23526 fax +1 708.202.8387 ext. 23609.
