Impaired Baroreflex Function during Orthostatic Challenge in Patients after Spinal Cord Injury

Test-retest reliability of the Valsalva maneuver in spinal cord injury

Objective: To determine the test-retest reliability of quantitative and qualitative baroreflex sensitivity (BRS) parameters derived from the Valsalva maneuver (VM) in individuals with traumatic cervical SCI.Design: Test-retest reliability.Setting: Tertiary rehabilitation center.Participants: Fourteen participants with cervical SCI (ranging from C3-C8 neurological level).Outcome Measurements: Beat-to-beat systolic blood pressure (SBP) traces (finger photoplethysmography) were obtained during a 15-second forced expiration at two time points (7.6 ± 2.9 days between sessions) to assess VM reliability. Test-retest reliability of BRS metrics from derived from the VM (Valsalva ratio; VR, pressure recovery time; PRT, vagal baroreflex sensitivity; BRSv, adrenergic baroreflex sensitivity; BRSa₁, and total recovery; TR) were assessed by intra-class correlation coefficient (ICC, with 95% confidence interval; CI) and by qualitative reproducibility (V, N, or M pattern).Results: ICCs for quantitative parameters were (CI): VR = 0.894 (0.703-0.965), TR = 0.927 (0.789-0.976), BRSa₁ = 0.561 (0.149-0.911), PRT = 0.728 (0.343-0.904), BRSv = 0.243 (-0.309-0.673). Qualitatively, 12 subjects (85.7%) demonstrated reproducible VM patterns at both time points (3 "M" pattern, 8 "V" pattern and one "N" pattern).Conclusion: VR (a measure of cardiovagal function) and TR (a measure of sympathetic adrenergic function) are reliable quantitative parameters that can be derived from SBP response to VM in participants with SCI. Qualitative waveform analysis was reproducible in 12/14 participants. This provides the foundational evidence required to pursue further validity testing to establish a role for VM in the assessment of autonomic functions in SCI.

Analytic and Integrative Framework for Understanding Human Sympathetic Arterial Baroreflex Function: Equilibrium Diagram of Arterial Pressure and Plasma Norepinephrine Level

Background

The sympathetic arterial baroreflex is a closed-loop feedback system for stabilizing arterial pressure (AP). Identification of unique functions of the closed system in humans is a challenge. Here we propose an analytic and integrative framework for identifying a static operating point and open-loop gain to characterize sympathetic arterial baroreflex in humans.

Methods and Results

An equilibrium diagram with two crossing functions of mechanoneural (MN) and neuromechanical (NM) arcs was analyzed during graded tilt maneuvers in seven healthy subjects. AP and plasma norepinephrine level (PNE), as a surrogate for sympathetic nerve activity, and were recorded after vagal modulation of heart function was blocked by atropine. The MN-arc curve was described as a locus of operating points during –7, 0, 15, and 60° head-up tilting (HUT) on a PNE-AP plane. The NM-arc curve was drawn as a line between operating points before and after ganglionic blockade (trimethaphan, 0.1 mg⋅ml^–1⋅kg^–1) during 0° or 15° HUT. Gain values were estimated from the slopes of these functional curves. Finally, an open-loop gain, which is a most important index for performance of arterial baroreflex, was given by a product of the gain values of MN (G_MN) and NM arcs (G_NM). Gain values of MN was 8.92 ± 3.07 pg⋅ml⁻¹⋅mmHg⁻¹; and G_NM at 0° and 15° HUT were 0.61 ± 0.08 and 0.36 ± 0.05 mmHg⋅ml⋅pg^–1, respectively. A postural change from supine to 15° HUT significantly reduced the open-loop gain from 5.62 ± 0.98 to 3.75 ± 0.62. The effects of HUT on the NM arc and open-loop gain seemed to be similar to those of blood loss observed in our previous animal studies.

Conclusion

An equilibrium-diagram analysis contributes to a quantitative and integrative understanding of function of human sympathetic arterial baroreflex.

Effects of Respiratory Muscle Training on Baroreflex Sensitivity, Respiratory Function, and Serum Oxidative Stress in Acute Cervical Spinal Cord Injury

Background: respiratory complications are a leading cause of morbidity and mortality in individuals with spinal cord injury (SCI). We examined the effects of respiratory muscle training (RMT) in patients with acute cervical SCI. Methods: this prospective trial enrolled 44 adults with acute cervical SCI, of which twenty received RMT and twenty-four did not receive RMT. Respiratory function, cardiovascular autonomic function, and reactive oxidative species (ROS) were compared. The experimental group received 40-min high-intensity home-based RMT 7 days per week for 10 weeks. The control group received a sham intervention for a similar period. The primary outcomes were the effects of RMT on pulmonary and cardiovascular autonomic function, and ROS production in individuals with acute cervical SCI. Results: significant differences between the two groups in cardiovascular autonomic function and the heart rate response to deep breathing (p = 0.017) were found at the 6-month follow-up. After RMT, the maximal inspiratory pressure (p = 0.042) and thiobarbituric acid-reactive substances (TBARS) (p = 0.006) improved significantly, while there was no significant difference in the maximal expiratory pressure. Significant differences between the two groups in tidal volume (p = 0.005) and the rapid shallow breathing index (p = 0.031) were found at 6 months. Notably, the SF-36 (both the physical (PCS) and mental (MCS) component summaries) in the RMT group had decreased significantly at the 6-month follow-up, whereas the clinical scores did not differ significantly (p = 0.333) after RMT therapy. Conclusions: High-intensity home-based RMT can improve pulmonary function and endurance and reduce breathing difficulties in patients with respiratory muscle weakness after injury. It is recommended for rehabilitation after spinal cord injury.

Cardiovagal baroreflex gain relates to sensory loss after spinal cord injury

Spinal cord injury (SCI) leads to autonomic nervous system damage, resulting in loss of sympathetic control to the vasculature and the heart proportional to injury level. Given maintained cardiac parasympathetic control, we hypothesized that SCI demonstrates a compensatory, higher baroreflex gain compared to able-bodied that relates to injury level (neurological and/or sensory). We compared baroreflex gain (average and across 10-20, 20-30, and 30-40 mmHg input stimuli) derived from neck chamber technique in SCI (N = 29; neurological level C1-T10, sensory zone of partial preservation C4-S4/5; ≤2 yrs since injury) and able-bodied (N = 14). Average gain tended to be higher in able-bodied compared to SCI (p = 0.06), primarily due to higher gains at 10-20 and 20-30 mmHg (p = 0.03, p = 0.06). In SCI, although gain was not related to neurological level, average gain and gain at 10-20 mmHg was related to sensory zone of partial preservation and resting RR-interval (all p < 0.02). Multiple regression showed that both sensory level and RR-interval were strongly predictive of average baroreflex gain (r² = 0.41, p < 0.01) and gain at 10-20 mmHg (r² = 0.51, p < 0.01); gain decreased with higher sensory zone of partial preservation and lower resting RR-interval. Moreover, gain was significantly lower in those with high sensory level compared to both able-bodied (average gain and gain at 10-20 and 20-30 mmHg p < 0.01) and those with low level injury (all p < 0.05). In SCI, sensory zone of partial preservation is more predictive of gain than neurological level. This might reflect that those with high level sensory injuries may have the lowest likelihood of intact cardiac sympathetic innervation and therefore lesser cardiac vagal responsiveness due to vagal-sympathetic interactions.

Status of nutrition and cardiovascular system in children from the south Moravian region of the Czech Republic: a pilot study

Nutritional status, its assessment and its influence on numerous diseases is currently still being discussed. The aim of this study was to determine the current state of nutrition by various research methods in school children. Also, to verify the accuracy of body mass index (BMI) determination in school environment and to compare the nutritional status in two different types of school. We used a quantitative questionnaire method in 64 children from schools in the South Moravian Region. We have verified the weight and height measurement in the same group by sophisticated instruments. We have determined the basic parameters of the cardiovascular system (non-invasive continuously blood pressure recording; mutual spectral analysis for estimation of baroreflex sensitivity; applanation tonometry and cardiac polygraphy for arterial stiffness evaluation). The indicative questionnaire method encountered a problem with the weight of almost 40 % of the population approached - both obesity (14.3 %) and malnutrition (25.2 %). Cardiovascular parameters were in physiological range for the given age categories. We found increased values in BMI, % of body fat and heart rate in children from countryside type of school, respectively. We concluded that obesity/malnutrition are both common phenomena in the children population in the Czech Republic.