Relationship between heart rate and oxygen uptake during submaximal arm cranking in paraplegics and quadriplegics

The relationship between perceived exertion and physiologic indicators of stress during graded arm exercise in persons with spinal cord injuries

OBJECTIVE

To examine the relationship between psychologic cues of somatic stress and physiologic responses to exercise in persons with paraplegia and tetraplegia.

DESIGN

Repeated measures with 2 comparison groups.

SETTING

Academic medical center.

PARTICIPANTS

Forty-two subjects between 18 and 69 years of age with motor-complete spinal cord injury (SCI) resulting in paraplegia or tetraplegia (American Spinal Injury Association grades A and B).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Subjects underwent peak graded arm ergometry during which heart rate, oxygen consumption (VO2), minute ventilation (VE), and ratings of perceived exertion (RPE) (Borg Categorical 6-20 Scale) were measured at successive work rate increments from baseline to fatigue.

RESULTS

There were inconsistent associations among the outcomes. For subjects with tetraplegia, RPE related positively to heart rate at the initial work rate, but there were no other significant correlations. For subjects with paraplegia, RPE did not correlate significantly with heart rate, VO2, or VE. VO2 and Ve related positively at the first and last work rates. In general, heart rate, VO2, and Ve increased as the exercise intensity increased, and were more pronounced in subjects with paraplegia. While RPE values increased with increasing work rates for each group, we found no differences between groups.

CONCLUSIONS

Our findings contradict the well-accepted relationships between RPE and both heart rate and VO2 during exercise by people without disabilities, and challenge the use of RPE as a valid psychophysiologic index of perceived exertion in persons with SCI.

Cardiorespiratory responses during passive walking-like exercise in quadriplegics

STUDY DESIGN

Cross-sectional and comparative investigation using quadriplegics (QP) and nondisabled subjects (ND).

OBJECTIVE

To evaluate cardiorespiratory responses during passive walking-like exercise (PWE) in QP.

SETTING

National Rehabilitation Center for Persons with Disabilities in Japan.

METHOD

The subjects were seven male QP with complete lesion (age: 27.0 +/- 5.4, injured level: C6-C7) and six male ND (age: 26.3 +/- 4.5). Cardiorespiratory responses were measured until voluntary fatigue during PWE, the rhythmical activity of paralyzed lower limbs synchronized with arm movements.

RESULTS

There were no significant differences in oxygen consumption (VO(2)), pulmonary ventilation (VE), heart rate (HR) and oxygen pulse (O(2) pulse) between QP and ND during PWE. ND showed increased ventilatory equivalent for oxygen (VE/VO(2) ratio) during exercise, while QP showed a significantly greater respiratory rate (RR) during exercise than ND (P < 0.05).

CONCLUSION

PWE elicited an increase in VO(2) with workload increment in QP similar to ND. However, higher RR suggested the intrinsic dysfunction of RR control during submaximal exercise in QP. From these results, it was thought that respiratory response would be the restriction factor of efficient oxygen transportation during PWE in QP.

Exercise Recommendations for Individuals with Spinal Cord Injury

Persons with spinal cord injury (SCI) exhibit deficits in volitional motor control and sensation that limit not only the performance of daily tasks but also the overall activity level of these persons. This population has been characterised as extremely sedentary with an increased incidence of secondary complications including diabetes mellitus, hypertension and atherogenic lipid profiles. As the daily lifestyle of the average person with SCI is without adequate stress for conditioning purposes, structured exercise activities must be added to the regular schedule if the individual is to reduce the likelihood of secondary complications and/or to enhance their physical capacity. The acute exercise responses and the capacity for exercise conditioning are directly related to the level and completeness of the spinal lesion. Appropriate exercise testing and training of persons with SCI should be based on the individual's exercise capacity as determined by accurate assessment of the spinal lesion. The standard means of classification of SCI is by application of the International Standards for Classification of Spinal Cord Injury, written by the Neurological Standards Committee of the American Spinal Injury Association. Individuals with complete spinal injuries at or above the fourth thoracic level generally exhibit dramatically diminished cardiac acceleration with maximal heart rates less than 130 beats/min. The work capacity of these persons will be limited by reductions in cardiac output and circulation to the exercising musculature. Persons with complete spinal lesions below the T(10) level will generally display injuries to the lower motor neurons within the lower extremities and, therefore, will not retain the capacity for neuromuscular activation by means of electrical stimulation. Persons with paraplegia also exhibit reduced exercise capacity and increased heart rate responses (compared with the non-disabled), which have been associated with circulatory limitations within the paralysed tissues. The recommendations for endurance and strength training in persons with SCI do not vary dramatically from the advice offered to the general population. Systems of functional electrical stimulation activate muscular contractions within the paralysed muscles of some persons with SCI. Coordinated patterns of stimulation allows purposeful exercise movements including recumbent cycling, rowing and upright ambulation. Exercise activity in persons with SCI is not without risks, with increased risks related to systemic dysfunction following the spinal injury. These individuals may exhibit an autonomic dysreflexia, significantly reduced bone density below the spinal lesion, joint contractures and/or thermal dysregulation. Persons with SCI can benefit greatly by participation in exercise activities, but those benefits can be enhanced and the relative risks may be reduced with accurate classification of the spinal injury.

The effect of locomotor training combined with functional electrical stimulation in chronic spinal cord injured subjects: walking and reflex studies

With the new developments in traumatology medicine, the majority of spinal cord injuries sustained are clinically incomplete and the proportion is likely to continue to rise. Thus, it is necessary to continue to develop new treatment and rehabilitation strategies and understand the factors that can enhance recovery of walking following spinal cord injury (SCI). One new development is the use of functional electrical stimulation (FES) device to assist locomotion. The objective of this review is to present findings from some recent studies on the effect of long-term locomotor training with FES in subjects with SCI. Promising results are shown in all outcome measures of walking, such as functional mobility, speed, spatio-temporal parameters, and the physiological cost of walking. Furthermore, the change in the walking behavior could be associated with plasticity in the CNS organization, as seen by the modification of the stretch reflex and changes in the corticospinal projection to muscles of the lower leg. In conclusion, recovery of walking is an increasing possibility for a large number of people with SCI. New modalities of treatment have become available for this population but most still need to be evaluated for their efficacy. This review has focused on FES assisted walking as a therapeutic modality in subjects with chronic SCI, but it is envisaged that the care and recovery of SCI in the early phase of recovery could also be improved.

Catecholamines, heart rate, and oxygen uptake during exercise in persons with spinal cord injury

The purpose of this study was to investigate the influence of different injury levels in persons with spinal cord injury (SCI) on epinephrine (Epi) and norepinephrine (NE) at rest and during graded wheelchair exercise and the related changes in heart rate and O2 uptake (VO2). Twenty tetraplegics (Tetra), 10 high-lesion paraplegics (HLPara), 20 paraplegics with SCI below T5 (MLPara), and 18 able-bodied, nonhandicapped persons (AB) were examined. Because of the higher level of interruption of the sympathetic pathways, Tetra persons showed lower Epi and NE at rest and only slight increases during exercise compared with all other groups; the Tetra subjects' impaired cardiac sympathetic innervation caused restricted cardioacceleration and strongly reduced maximal VO2. When compared with AB persons, HLPara had comparable NE but lower Epi levels as a result of partial innervation of the noradrenergic system and denervation of the adrenal medulla. MLPara subjects showed an augmented basal and exercise-induced upper spinal thoracic sympathetic activity compared with AB subjects. The increase in heart rate in relation to VO2 was higher in HLPara because of a smaller stroke volume as a result of venous blood pooling. The different exercise response in persons with SCI is a result of the interruption of pathways in the spinal cord to the peripheral sympathetic nervous system in addition to the motor paralysis.

Effect of arm cranking exercise on skin blood flow of lower limb in people with injuries to the spinal cord

The purpose of this study was to examine whether arm cranking exercise induces changes in skin blood flow in the paralyzed lower limbs of people with injuries to the spinal cord (PISC). Ten PISC with lesions located between Th5 and L5 and six control subjects performed arm cranking exercise for 6 min at three intensities, 10, 30 and 50 W, at a room temperature of 25 degrees C. Oxygen uptake (Vo2) and heart rate (HR) were measured for the last 2 min of each exercise period. The skin blood flow at the anterior thigh (BFsk,t) was continuously monitored using laser Doppler flowmetry for the whole 6-min period and for the first 10 min of recovery following exercise. During exercise, the PISC showed lower Vo2 and greater HR than the control subjects. No increase in BFsk,t was found in six of the PISC with lesions at or above Th12, irrespective of the exercise intensity. On the other hand, in PISC with lesions at L1 or below, BFsk,t increased significantly (P < 0.05) with an increase in Vo2 and HR, although the BFsk,t at a given Vo2 and HR was lower than that in the control subjects. These results would suggest that arm exercise can promote the blood circulation in the skin of the lower limbs if the injury level is below L1.