The effect of autonomic nervous system dysfunction on oxygen consumption during daily living activities in patients with spinal cord injury

STUDY DESIGN

Case-control study.

OBJECTIVES

To investigate the level of autonomic nervous system dysfunction in patients with spinal cord injury and to determine its effect on the basal metabolic rate and oxygen consumption during daily living activities.

SETTING

Turkish Armed Forces Rehabilitation Center, Ankara, Turkey.

METHODS

Thirty-six patients with chronic spinal cord injury (SCI) were allocated into two groups according to the presence of autonomic nervous system dysfunction. Autonomic nervous system dysfunction was investigated with the measurements of blood pressure and heart rate during urodynamic examination and several provocative maneuvers (standing at tilt table, forcing deep respiration and Valsalva). Groups were compared in terms of the basal metabolic rate and oxygen consumption during daily living activities. Measurement of the basal metabolic rate was determined by indirect calorimetry under standardized conditions. Total body fat mass and lean tissue mass were measured in all participants using dual-energy X-ray absorptiometry by standard methods. Telemetric intrapulmonary gas exchange analyzer was used to measure oxygen consumption during daily living activities.

RESULTS

There was no statistically significant difference between the groups in age, time since injury, body mass lean and fat rates, or sensory and motor scores (P>0.05). Basal metabolic rates and oxygen consumption during daily living activities were not different between the groups (P>0.05).

CONCLUSIONS

These results suggest that the presence of autonomic dysfunction does not change oxygen consumption at rest and during daily living activities.

The effect of functional electrical stimulation cycling on late functional improvement in patients with chronic incomplete spinal cord injury

STUDY DESIGN

Prospective single-arm study.

OBJECTIVES

To investigate the effect of functional electrical stimulation (FES) cycling on late functional recovery, spasticity, gait parameters and oxygen consumption during walking in patients with chronic incomplete spinal cord injury (SCI).

SETTING

Turkish Armed Forces Rehabilitation Center, Ankara, Turkey.

METHODS

Ten patients with chronic (duration of more than 2 years) incomplete SCI who could ambulate at least 10 m independently or with the assistance of a cane or walker, but no hip-knee-ankle-foot orthosis. The subjects underwent 1-h FES cycling sessions three times a week for 16 weeks. Outcome measures including the total motor score, the Functional Independence Measure (FIM) score, the Modified Ashworth Scale for knee spasticity, temporal spatial gait parameters and oxygen consumption rate during walking were assessed at baseline, 3 and 6 months after the baseline.

RESULTS

There were statistically significant improvements in total motor scores, the FIM scores and spasticity level at the 6-month follow-up (P<0.01). The changes in gait parameters reached no significant level (P>0.05). Oxygen consumption rate of the patients showed significant reduction at only 6 months compared with baseline (P<0.01).

CONCLUSION

The results suggest that FES cycling may provide some functional improvements in the late period of SCI.

SPONSORSHIP

The study was supported by The Scientific and Technological Research Council of Turkey (TUBITAK).

Computational modeling of chemo-electro-mechanical coupling: a novel implicit monolithic finite element approach

Computational modeling of the human heart allows us to predict how chemical, electrical, and mechanical fields interact throughout a cardiac cycle. Pharmacological treatment of cardiac disease has advanced significantly over the past decades, yet it remains unclear how the local biochemistry of an individual heart cell translates into global cardiac function. Here, we propose a novel, unified strategy to simulate excitable biological systems across three biological scales. To discretize the governing chemical, electrical, and mechanical equations in space, we propose a monolithic finite element scheme. We apply a highly efficient and inherently modular global-local split, in which the deformation and the transmembrane potential are introduced globally as nodal degrees of freedom, whereas the chemical state variables are treated locally as internal variables. To ensure unconditional algorithmic stability, we apply an implicit backward Euler finite difference scheme to discretize the resulting system in time. To increase algorithmic robustness and guarantee optimal quadratic convergence, we suggest an incremental iterative Newton-Raphson scheme. The proposed algorithm allows us to simulate the interaction of chemical, electrical, and mechanical fields during a representative cardiac cycle on a patient-specific geometry, robust and stable, with calculation times on the order of 4 days on a standard desktop computer.

Computational modeling of growth: systemic and pulmonary hypertension in the heart

We introduce a novel constitutive model for growing soft biological tissue and study its performance in two characteristic cases of mechanically induced wall thickening of the heart. We adopt the concept of an incompatible growth configuration introducing the multiplicative decomposition of the deformation gradient into an elastic and a growth part. The key feature of the model is the definition of the evolution equation for the growth tensor which we motivate by pressure-overload-induced sarcomerogenesis. In response to the deposition of sarcomere units on the molecular level, the individual heart muscle cells increase in diameter, and the wall of the heart becomes progressively thicker. We present the underlying constitutive equations and their algorithmic implementation within an implicit nonlinear finite element framework. To demonstrate the features of the proposed approach, we study two classical growth phenomena in the heart: left and right ventricular wall thickening in response to systemic and pulmonary hypertension.