Abstract
BackgroundWe investigated cardiovascular responses to an orthostatic challenge in trained spinal cord-injured (SCI) individuals compared to able-bodied (AB) individuals.MethodsA total of 23 subjects participated, divided into three groups: seven were trained as spinal cord-injured (Tr-SCI) individuals, seven were able-bodied individuals trained as runners (Tr-AB), and nine were untrained able-bodied individuals (UnTr-AB). We measured the cardiovascular autonomic responses in all three groups during each 5-min head-up tilt (HUT) of 0°, 40°, and 80°. Stroke volume (SV), heart rate (HR), and cardiac output (Qc) as cardiovascular responses were measured by impedance cardiography. Changes in deoxyhemoglobin (∆[HHb]) and total hemoglobin (∆[Hbtot]) concentrations of the right medial gastrocnemius muscle were measured using near-infrared spectroscopy (NIRS).ResultsAs the HUT increased from 0° to 80°, Tr-SCI group showed less change in SV at all HUT levels even if HR increased significantly. Mean arterial pressure (MAP) also did not significantly increase as tilting increased from 0° to 80°. Regarding peripheral vascular responses, the alterations of ∆[Hbtot] from 0° to 80° were less in Tr-SCI group compared to AB individuals.ConclusionThere is a specific mechanism whereby blood pressure is maintained during a HUT in Tr-SCI group with the elicitation of peripheral vasoconstriction and the atrophy of the vascular vessels in paraplegic lower limbs, which would be associated with less change in SV in response to an orthostatic challenge.
Highlights
We investigated cardiovascular responses to an orthostatic challenge in trained spinal cord-injured (SCI) individuals compared to able-bodied (AB) individuals
Increased heart rate (HR) and inversely decreased stroke volume (SV) were proportionally observed in association with increased head-up tilt (HUT) from 0° to 80° in both AB groups, whereas the trained as spinal cord-injured (Tr-SCI) group exhibited no change in SV at any degree of tilt
In the supine position (0°), the HR in the Tr-SCI group (73 ± 6 bpm) was significantly greater than that in the Tr-AB group (58 ± 3 bpm, F(2,20) = 3.63, p < 0.01), whereas a significantly lower SV at 0° was found in the Tr-SCI group (78 ± 9 mL) in comparison with the Tr-AB group (104 ± 11 mL, F(2,20) = 4.10, p < 0.05) (Fig. 2)
Summary
We investigated cardiovascular responses to an orthostatic challenge in trained spinal cord-injured (SCI) individuals compared to able-bodied (AB) individuals. The level of SCI lesions, increased peripheral vascular resistance [3], reduced peripheral capillarization [4], and decreased conduit artery diameters have been observed [5,6,7]. These findings indicate that less blood pooling may occur in paraplegic lower limbs. Despite the absence of central sympathetic control of limb vascular adjustment, SCI patients showed remarkable orthostatic tolerance during posture stress and their BP level was maintained during orthostatic challenges by augmented local vasoconstriction, most likely as part of the myogenic response [9]. Theisen et al showed a vasoconstriction response during leg dependency in paraplegia, suggesting that a veno-arteriolar axon reflex (VAR) or myogenic activity was present in spinal
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