Influences of neural mechanisms on heart period and arterial pressure variabilities in quadriplegic patients

Abstract

The heart period (R-R) variability power spectrum presents two components, at low (LF; approximately 0.10 Hz) and high (approximately 0.25 Hz) frequencies, whose reciprocal powers appear to furnish an index of sympathovagal interaction modulating heart rate. In addition, the LF component of the systolic arterial pressure variability spectrum furnishes a marker of sympathetic modulation of vasomotor activity. The contribution of spinal and supraspinal neural circuits to the genesis of these rhythmic oscillatory components remains largely unsettled. Therefore we performed spectral analysis of R-R and systolic arterial pressure variabilities in 15 chronic neurologically complete quadriplegic patients (QP) and in 15 control subjects during resting conditions, controlled respiration, and head-up tilt. At rest, in seven QP the LF component was undetectable in both cardiovascular variability spectra; in two QP this component was present only in R-R variability spectrum, whereas the remaining six showed a significantly reduced LF in both signals. In QP, the LF component, when present, underwent paradoxical changes with respect to controls, decreasing during tilt and increasing during controlled respiration. In five QP in whom the recording session was repeated after 6 mo, a significant increase in LF was observed in both variability spectra. These data confirm the finding that a disconnection of sympathetic outflow from supraspinal centers can cause the disappearance of the LF spectral component. However, LF presence in some QP supports the hypothesis of a spinal rhythmicity likely to be modulated by the afferent sympathetic activity.

Clinical correlates of frequency analyses of cardiovascular control after spinal cord injury

“…LF BPV in the thoracic SCI group tended to be reduced compared with controls, although to a lesser extent than in the cervical SCI group. These results are similar to those of others (25,27,44). This probably reflects reduced sympathetic drive to the lower body in individuals with autonomically complete thoracic SCI.…”

“…Decreased LF HRV in cervical SCI subjects at rest probably predominantly reflects reduced cardiac sympathetic control in cervical SCI. The fact that LF oscillations were not abolished after cervical SCI suggests that 1) some of the LF HRV after cervical SCI is mediated by parasympathetic mechanisms (2, 17, 34), 2) sympathetic oscillations may occur in the absence of descending sympathetic control, e.g., due to rhythmic firing patterns of spinal sympathetic neurons (25,34), and 3) the destruction of descending sympathetic pathways was incomplete in some subjects with cervical SCI (10). There is probably some contribution from all these potential mechanisms in the generation of LF HRV after cervical SCI.…”

“…LF BPV could be generated at a spinal level in subjects with SCI (26,44). Indeed, LF HRV and BPV are reported to increase over time following injury, presumably due to emerging spinal rhythmicity of oscillations in sympathetic outflow (25,26) or recovery of descending sympathetic pathways. However, in some subjects, injury to descending autonomic pathways is not complete (8,10), and in this study LF BPV was correlated with other indexes of preservation of sympathetic control after SCI, including SSR, plasma norepinephrine levels, and blood pressure control.…”

Risk factors for atherogenesis and cardiovascular autonomic function in persons with spinal cord injury

“…The presence of the LF RRI component in the group with complete tetraplegia may represent sympathetic-like oscillations or, conceptually, may also represent excitation of supraspinal re¯exes and/or an up-regulation of receptor function. 174 Finally, the signi®cant differences in the LF RRI component at rest and during provocation between the complete and incomplete groups with tetraplegia imply that the measurement of HRV may be useful to distinguish between complete and incomplete injuries, and may assist in the neurological assessment of persons with SCI.…”

Characteristics and Theoretical Foundations of Methods to Analyze Heart Rate Variability

“…Це було пояснено руйнуванням нервових шляхів, що передають ритми від головного мозку до спинного. Однак у деяких пацієнтів з такими порушеннями спостерігались повільні хвилі артеріального тиску та інтервалу R-R [56,72]. Guzzetti S. et al [56] ці явища були інтерпретовані як прояв спинальної ритміки, що впливає на синусову пейсмекерну ак-тивність та судинний фон.…”