Stephen F. Figoni

Physiologic responses of paraplegics and quadriplegics to passive and active leg cycle ergometry.

The purposes of this study were three-fold: (a) to determine acute physiologic responses of spinal cord injured (SCI) subjects to peak levels of leg cycle ergometry utilizing functional neuromuscular stimulation (FNS) of paralyzed leg muscles, (b) to determine the relative contributions of passive and active components of FNS cycling to the peak physiologic responses, and (c) to compare these physiologic responses between persons who have quadriplegia and those who have paraplegia. Thirty SCI subjects (17 quadriplegics and 13 paraplegics) performed a discontinuous graded FNS exercise test from rest to fatigue on an ERGYS 1 ergometer. Steady-state physiologic responses were determined by open-circuit spirometry, impedance cardiography with ECG, and auscultation. In the combined statistics of both groups, it was noted that peak FNS cycling significantly increased (from rest levels) mean oxygen uptake by 255%, arteriovenous O2 difference VO2 and VE, Q and a-vO2 and VCO by 69%, and stroke volume by 45%, while total peripheral vascular resistance decreased by 43%. Mean peak power output for paraplegics (15 W) was significantly higher than for quadriplegics (9 W), eliciting higher peak levels of pulmonary ventilation and sympathetically mediated hemodynamic responses such as cardiac output, heart rate, and systolic and diastolic arterial blood pressure. Passive cycling without FNS produced no statistically significant increases in physiologic responses above the resting level in either group.

Metabolic and hemodynamic responses to concurrent voluntary arm crank and electrical stimulation leg cycle exercise in quadriplegics

This study determined the metabolic and hemodynamic responses in eight spinal cord injured (SCI) quadriplegics (C5-C8/T1) performing subpeak arm crank exercise (ACE) alone, subpeak functional electrical stimulation leg cycle exercise (FES-LCE) alone, and subpeak FES-LCE concurrent with subpeak ACE (hybrid exercise). Subjects completed 10 minutes of each exercise mode during which steady-state oxygen uptake (VO2), pulmonary ventilation (VE), heart rate (HR), cardiac output (CO), stroke volume (SV), mean arterial pressure (MAP), arteriovenous oxygen difference (a-v O2 diff), and total peripheral resistance (TPR) were determined. Although mean VO2 for both ACE alone and FES-LCE alone was matched at 0.66 l/mi, individualized power outputs ranged from 0-30 W (mean = 19.4 +/- 1.3) and 0-12.2 W (mean = 2.3 +/- 0.6), respectively. Hybrid exercise elicited significantly higher VO2 (by 54 percent), VE (by 39-53 percent), HR (by 19-33 percent), and CO (by 33-47 percent), and significantly lower TPR (by 21-34 percent) than ACE or FES-LCE performed alone (P less than or equal to 0.05). Stroke volume was similar between hybrid exercise and FES-LCE alone, and these two exercise modes evoked a significantly higher SV (by 41-56 percent) than during ACE alone. These data clearly demonstrate that hybrid exercise creates a higher aerobic metabolic demand and cardiac-volume load in SCI quadriplegics than either subpeak levels of ACE or FES-LCE performed separately. Therefore, hybrid exercise may provide more advantageous central cardiovascular training effects in quadriplegics than either ACE or FES-LCE alone.

Acute hemodynamic responses of spinal cord injured individuals to functional neuromuscular stimulation-induced knee extension exercise

The purpose of this study was to determine and compare acute hemodynamic responses of spinal cord injured (SCI) quadriplegics (quads), and paraplegics (paras) during a graded-intensity knee extension (KE) exercise test utilizing functional neuromuscular stimulation (FNS) of paralyzed quadriceps muscles. Seven quads and seven paras (N = 14) performed a series of 4-minute stages of bilateral alternating FNS-KE exercise (approximately zero to 70 degree range of motion at the knee and 6 KE/min/leg) at ankle loads of 0, 5, 10, and 15 kg/leg. Physiologic responses were determined with open-circuit spirometry, impedance cardiography, and auscultation. Comparing rest with peak FNS-KE for both groups combined, FNS-KE exercise elicited significant (p less than 0.05) increases in oxygen uptake (130 percent), pulmonary ventilation (120 percent), respiratory exchange ratio (37 percent), arteriovenous oxygen difference (57 percent), cardiac output (32 percent), stroke volume (41 percent), mean arterial pressure (18 percent), and rate-pressure product (23 percent). Heart rate increased significantly by 11 percent from the 5- to the 15-kg/leg stages. Physiologic responses of quads and paras were very similar, except for lower (p less than 0.05) arterial pressures, rate-pressure product, and peripheral vascular resistance in quads. This graded FNS-KE exercise up to the 15-kg/leg load induced relatively small but appropriate increases in aerobic metabolism and cardiopulmonary responses that appear to be safe and easily tolerated by quads and paras. Arterial pressure needs to be monitored carefully in quads to prevent excessive hypertension or hypotension. Although FNS-KE exercise has been shown to elicit peripheral adaptations to improve muscle strength and endurance, it is probably not an effective central cardiovascular training tool for all but the least fit SCI individuals. This information is important for understanding the effects of FNS use during more complex activities such as cycling and ambulation.

Perspectives on Cardiovascular Fitness and SCI

The purpose of these papers is to review and discuss the fundamental concepts and problems underlying cardiovascular fitness and spinal cord injury. Particular attention is paid to several modes of exercise available to individuals with spinal cord injury (SCI)--voluntary arm-crank and wheelchair ergometry, electrical stimulation leg cycle ergometry, and combined voluntary arm-cranking and electrical stimulation leg (hybrid) exercise. The effects of level of injury, active muscle mass, and sympathetic dysfunction upon acute central hemodynamic adjustments during exercise testing and chronic training adaptations are discussed for both quadriplegics and paraplegics. Several topics for future research are suggested.

Efficiency of FNS leg cycle ergometry

The efficiency of electrically induced leg cycle ergometry performed by spinal-cord-injured (SCI) subjects was compared to voluntary leg cycle ergometry performed by able-bodied (AB) subjects at power output (PO) levels of 6-42 W. Twenty SCI (nine quadriplegics and 11 paraplegics) and twenty AB subjects exercised on a leg cycle ergometer. SCI subjects received functional neuromuscular stimulation (FNS) of paralyzed leg musculature, while AB subjects pedaled voluntarily. Subjects performed a discontinuous, progressive intensity exercise test with 6-W (for SCI) or 12-W (for AB) PO increments between stages. Each exercise bout was 5 min in duration and was followed by a 5-min rest period. Steady-rate oxygen uptake (VO/sub 2/) and respiratory exchange ratio (RER) values were determined by open-circuit spirometry during the final minute of each stage. Gross, net, work, and data efficiencies were calculated for each PO. These efficiencies ranged from 2 to 14% for FNS cycling by SCI subjects and from 4 to 34% during voluntary cycling by AB subjects. At most POs, efficiencies for FNS cycling were significantly lower (by approximately one-half) than those for voluntary cycling. Despite the apparent energy-wastefulness or inefficiency of FNS leg cycle ergometry, the relatively high metabolic rates elicited by the exercise may be advantageous to SCI individuals seeking aerobic (cardiopulmonary) training effects.<<ETX>>

Physiologic responses of SCI subjects to electrically induced leg cycle ergometry

The purpose of this study was to determine steady-state physiologic responses of spinal-cord-injured (SCI) subjects to electrically induced leg-cycle ergometry, and to compare these responses to those of able-bodied (AB) individuals performing voluntary leg-cycle ergometry at the same power output (PO) levels. Twelve SCI subjects and 6 AB subjects exercised on a microprocessor-controlled functional neuromuscular stimulation (FNS) cycle ergometer. FNS of paralyzed leg muscles was delivered via skin-surface electrodes over the quadriceps, hamstring, and gluteal muscle groups. Subjects performed several 5-min bouts of progressive intensity cycling (6- or 12-W increments) at 50 r.p.m. Each bout was followed by a 5-min rest period. Oxygen uptake, pulmonary ventilation, and heart rate were significantly higher for the SCI group at each PO level. The data suggest that this FNS exercise may elicit metabolic and cardiopulmonary responses from FNS-trained SCI individuals that are of similar magnitudes to those elicited from AB individuals during jogging exercise. The authors therefore hypothesize that this mode of FNS exercise training may promote higher levels of aerobic fitness in many SCI individuals than can be obtained by conventional arm exercise (e.g. wheelchair propulsion, cranking).<<ETX>>

Preamputation Evaluation of Lower-Limb Skeletal Muscle Perfusion with H2 15O Positron Emission Tomography

Scremin OU, Figoni SF, Norman K, Scremin AME, Kunkel CF, Opava-Rutter D, Schmitter ED, Bert A, Mandelkern M: Preamputation Evaluation of Lower-Limb Skeletal Muscle Perfusion with H215O Positron Emission Tomography. Objective:To establish whether muscle blood flow (MBF) measurements with 15O-water positron emission tomography could reliably identify patients with critical limb ischemia and detect and quantify a distal deficit in skeletal MBF in these cases. Design:15O-water positron emission tomography scans were performed at rest or during unloaded ankle plantar and dorsiflexion exercise of the diseased leg in 17 subjects with leg ischemia or on a randomly selected leg of 18 age-matched healthy control subjects. TcPO2 was evaluated with Novametrix monitors and perfusion of skin topically heated to 44°C and adjacent nonheated areas with a Moor Instruments laser Doppler imaging scanner. Results:The enhancement of MBF induced by exercise was significantly lower in ischemic than in normal legs, and the sensitivity and specificity of this phenomenon were similar to those of laser Doppler imaging or TcPO2 in identifying ischemia subjects. In addition, the exercise MBF deficit was predominant at the distal-leg levels, indicating the ability of the technique to help determine the correct level of amputation. Conclusions:Skeletal MBF of legs with severe ischemia can be detected accurately with 15O-water positron emission tomography and could add valuable information about viability of skeletal muscle in the residual limb when deciding the level of an amputation.

Hemodynamic responses of quadriplegics to maximal arm-cranking and FNS leg cycling exercise

The purpose of this study was to compare maximal central hemodynamic responses of spinal-cord-injured quadriplegic subjects to voluntary arm-crank exercise (ACE) and to electrically induced leg cycling exercise. Six C6-C7 quadriplegic men performed graded exercises to maximum with both an arm-crank ergometer and a leg-cycle ergometer, utilizing functional neuromuscular stimulation (FNS) of paralyzed leg musculature. Both exercise modes produced a V-dot O/sub 2/ peak of approximately 1 l/min, with peak power outputs for the arm and leg exercises of 38 and 11 W, respectively. Compared with voluntary ACE, FNS cycling elicited a significantly higher mean cardiac output, stroke volume, and mean arterial blood pressure, and significantly lower mean heart rate and rate-pressure product. While maximal FNS cycling is mechanically less efficient than ACE, it appears to produce a more desirable hemodynamic response pattern, i.e. greater venous return and cardiac volume-load with less myocardial stress. Thus, FNS leg cycling may be more effective than ACE for aerobic cardiovascular training of quadriplegics.<<ETX>>

Scanning laser-doppler imaging of leg-and foot-skin perfusion in normal subjects : Analysis of age, gender, site, and laser-type effects

Kunkel CF, Figoni SF, Baumgarten JM, Carvalho CM, Kim HS, Oshiro RL, Zirovich MD, Scremin OU, Scremin AME: Scanning laser-Doppler imaging of leg- and foot-skin perfusion in normal subjects: analysis of age, gender, site, and laser-type effects. Am J Phys Med Rehabil 2007;86:262–271. Objectives:To report normal values of skin perfusion in healthy subjects in three age groups using a laser Doppler imager; to determine differences attributable to gender, age, site, and use of red or near-infrared lasers; and to correlate transcutaneous oxygen with laser flux values Design:Flux and transcutaneous oxygen were measured at ten sites in the lower extremity in 60 subjects from three age groups. Heated and unheated sites were scanned with red and near-infrared lasers. Results:Heat hyperemia was prominent at all sites. Small, statistically significant mean ± SD differences were found between heated and nonheated sites for the red and near-infrared lasers (P = 0.02). All flux ratios were independent of gender but were higher in the oldest group. Plantar sites demonstrated higher flux in unheated areas and lower flux ratios compared with leg sites. Transcutaneous oxygen did not correlate significantly with flux for either laser type. Conclusions:Scanning laser-Doppler imaging flux values provide a reference for identifying patients at risk for tissue ischemia and poor healing potential caused by impaired circulatory reserve in the legs and distal feet. The lack of correlation between flux and transcutaneous oxygen in healthy individuals suggests that they measure different physiologic processes.

Preamputation Evaluation of Limb Perfusion with Laser Doppler Imaging and Transcutaneous Gases

We studied 31 subjects with severe leg ischemia and 29 age-matched nonischemic control subjects to compare preamputation assessments of leg ischemia using laser Doppler imaging (LDI), transcutaneous partial pressure of oxygen (TcPO(2)), and transcutaneous partial pressure of carbon dioxide (TcPCO(2)). TcPO(2) and TcPCO(2) were evaluated with Novametrix Medical Systems, Inc, monitors (Wallingford, Connecticut) and perfusion (flux) of skin topically heated to 44 degrees C, and adjacent nonheated areas were evaluated with a Moor Laser Doppler Imager (Moor Instruments, Ltd; Devon, England). LDI flux of heated areas, its ratio to nonheated areas, and TcPO(2) (not TcPCO(2)) were lower in ischemic subjects than in control subjects. LDI flux ratio performed better than TcPO(2) in identifying ischemia, with fewer false positive and false negative results. Moreover, LDI flux of heated skin detected a proximal to a distal gradient of perfusion in ischemic subjects, while TcPO(2) did not. LDI was superior to TcPO(2) in discriminating correctly between ischemic and nonischemic skin. The results suggest that an LDI ratio below 5 indicates nonviable skin.