Stimulated Muscle Force Measurements in Neuromuscular Diseases
Muscle strength assessment is necessary for determining distribution
of weakness, disease progression, and/or treatment efficacy for
patients with neuromuscular diseases or those with long-term critical
illnesses. Manual testing is the standard method used to assess
muscle strength, yet it relies on subjective assessment by the clinician
and is thus inadequate to quantify small changes in muscle strength.
Devices to quantify force objectively (i.e., hand-held dynamometry
and isokinetic devices) have been developed and used clinically,
however they still rely on voluntary effort. Additionally, neurologically
impaired or critically ill patients generally have difficulty with
voluntary force assessment tasks.
Our lab has designed and tested a noninvasive muscle force assessment
device to objectively quantify muscle strength for clinical use
(Figure 1). Specifically, we have investigated the following areas
related to the muscle force assessment system:
- Measure force of ankle dorsiflexors (Figure 1) and thumb
adductors muscle groups (Figure 2) in patients with chronic inflammatory
demyelinating polyneuropathy (CIPD) or another peripheral neuromuscular
disorder. The measurement system offered several advantages: 1)
improved objectivity and reliability compared to other methods,
2) ability to distinguish weakness due to peripheral nerve or muscle
disorders from that caused by central nervous system disorders,
and 3) ability to measure temporal aspects of muscle contraction,
leading to better understanding of the pathophysiology of neuromuscular
- Study of ankle dorsiflexion force during induced paralytic
attacks in hyperkalemic and hypokalemic patients. It was found that
stimulated force measurements can characterize phenotypic muscle
function in these neuromuscular diseases; additionally, it offered
several advantages in characterizing muscle dysfunction in periodic
paralysis: 1) force measurement was independent of patient effort,
2) it showed a definitive abnormal response early during provocative
maneuvers; 3) characteristics of muscle contraction could be measured
that were unobservable during voluntary contraction .
- Adaptation of the muscle force assessment system to measure
arm flexor contractile responses of normal subjects (Figure 3).
This modified system provided a high degree of reproducibility in
generating twitch and/or multiple-pulse stimulations of the arm
flexors elicited by either superficially applied motor-point or
nerve stimulation .
- Configuration of the muscle force assessment system for
quantitative evaluation of neck muscles (sternocleidomastoid) using
normal subjects (Figure 4). The adapted system provided for consistent
stimulated force responses in repeated trials, and could be used
clinically for patients affected by alterations in head/neck stability
(i.e., neck injury, cervical dystonia) .
- Quantification of isometric skeletal muscle forces in critically
ill patients (ankle dorsiflexors), baseline and after one week of
ventilation and immobilization in the ICU (Figure 5). It was determined
that muscle weakness begins during the early stages of critical
illness for patients that are immobilized and ventilated (i.e.,
reduced torques, shorter contraction times, prolonged relaxation
times) and that this system should be further evaluated for use
in a long-term ICU setting .
- Measurement of muscle torque (ankle dorsiflexors) in long-term
mechanically ventilated and immobilized ICU patients. The researchers/clinicians
determined that this muscle force measurement system was feasible
for use in a long-term ICU environment; further, there is clinical
merit for monitoring patient status and they plan to modify the
existing system for optimal application to the ICU environment (i.e.,
Figure 1. Muscle force assessment system (ankle dorsiflexors)
Figure 2. Muscle force assessment system modified for thumb adductors
Figure. 3. Muscle force assessment system adapted
for arm flexor muscle
Figure 4. Muscle force assessment system adapted
to measure the sternocleidomastoid muscle
Figure 5. Muscle force assessment system modified
for use on critically ill patients in the ICU
- Brass TJ, Loushin MK, Day JW, Iaizzo PA: An improved method
for muscle force assessment in neuromuscular disease. Journal
of Medical Engineering and Technology 20: 67-74, 1996.
- Day JW, Sakamoto C, Parry GJ, Lehmann-Horn F, Iaizzo PA: Force
assessment in periodic paralysis after electrical muscle stimulation. Mayo Clinic Proceedings 77: 232-240, 2002.
- Hong J, Iaizzo PA: Force assessment of the stimulated arm flexors:
quantification of contractile propoerties. Journal of Medical
Engineering & Technology 26:28-35, 2002.
- Hong J, Falkenberg JH, Iaizzo PA: Stimulated muscle force assessment
of the sternocleidomastoid muscle in humans. Journal of Medical
Engineering & Technology 29: 82-89, 2005.
- Ginz HF, Iaizzo PA, Girard T, Urwyler A, Pargger H: Decreased
isometric skeletal muscle force in critically ill patients. Swiss
Medical Weekly 135:555-561, 2005.
- Ginz HF, Iaizzo PA, Urwyler A, Pargger H: Use of non-invasive
stimulation muscle force assessment in long-term critically ill
patients: a future standard in the intensive care unit? Acta
Anaesthesiologica Scandinavica (in press) 2007.