Cold pressor test in spinal cord injury—revisited

The associations between cardiovascular and pain responses to a cold pressor test differ between males and females

Nociceptors contribute to the cardiovascular responses during a cold pressor test (CPT). While these responses are lower in females, data suggest that they perceive the CPT as more painful. Thus, we examined sex differences in associations between pain and cardiovascular responses to a CPT (Aim 1) as well as differences between females using (OC), and not using (NC), an oral contraceptive (Aim 2). 25 males (23 ± 5 years) and 25 females (21 ± 3 years; 11OC and 14NC) were studied. Cardiovascular data and pain levels (0-10 scale) were recorded at baseline then during a two-minute CPT; changes from baseline to peak response were analyzed. Systolic blood pressure (SBP, p = 0.57), mean arterial pressure (MAP, p = 0.22), heart rate (HR, p = 0.58), and pain (p = 0.71) responses did not differ between sexes; diastolic blood pressure (DBP) increased more in males (17 ± 8 vs. 13 ± 6 mmHg, p < 0.05). Pain was associated with HR in males (r = 0.42, p < 0.05) but not females (r = -0.16, p = 0.44); no other associations were observed in either sex (p = 0.48-0.92). SBP (27 ± 12 vs. 15 ± 6 mmHg), DBP (16 ± 6 vs. 9 ± 5 mmHg), MAP (20 ± 7 vs. 14 ± 5 mmHg), and HR (8 ± 5 vs. 2 ± 5 beats/min) were greater in NC than OC (p < 0.05 for all); pain was similar (p = 0.38). In NC, pain was associated with DBP (r = 0.65, p = 0.01) and MAP (r = 0.65, p = 0.01), but not HR (r = -0.43, p = 0.13), and tended to be associated with SBP (r = 0.46, p = 0.09). In OC, pain was inversely associated with SBP (r = -0.62, p < 0.05) but no other outcome (p = 0.40-0.65). We report a sexual dimorphism in the HR-pain association during a CPT and underscore the impact of oral contraceptives.

Short- and long-term effects of transcutaneous spinal cord stimulation on autonomic cardiovascular control and arm-crank exercise capacity in individuals with a spinal cord injury (STIMEX-SCI): study protocol

INTRODUCTION

Individuals with higher neurological levels of spinal cord injury (SCI) at or above the sixth thoracic segment (≥T6), exhibit impaired resting cardiovascular control and responses during upper-body exercise. Over time, impaired cardiovascular control predisposes individuals to lower cardiorespiratory fitness and thus a greater risk for cardiovascular disease and mortality. Non-invasive transcutaneous spinal cord stimulation (TSCS) has been shown to modulate cardiovascular responses at rest in individuals with SCI, yet its effectiveness to enhance exercise performance acutely, or promote superior physiological adaptations to exercise following an intervention, in an adequately powered cohort is unknown. Therefore, this study aims to explore the efficacy of acute TSCS for restoring autonomic function at rest and during arm-crank exercise to exhaustion (AIM 1) and investigate its longer-term impact on cardiorespiratory fitness and its concomitant benefits on cardiometabolic health and health-related quality of life (HRQoL) outcomes following an 8-week exercise intervention (AIM 2).

METHODS AND ANALYSIS

Sixteen individuals aged ≥16 years with a chronic, motor-complete SCI between the fifth cervical and sixth thoracic segments will undergo a baseline TSCS mapping session followed by an autonomic nervous system (ANS) stress test battery, with and without cardiovascular-optimised TSCS (CV-TSCS). Participants will then perform acute, single-session arm-crank exercise (ACE) trials to exhaustion with CV-TSCS or sham TSCS (SHAM-TSCS) in a randomised order. Twelve healthy, age- and sex-matched non-injured control participants will be recruited and will undergo the same ANS tests and exercise trials but without TSCS. Thereafter, the SCI cohort will be randomly assigned to an experimental (CV-TSCS+ACE) or control (SHAM-TSCS+ACE) group. All participants will perform 48 min of ACE twice per week (at workloads corresponding to 73-79% peak oxygen uptake), over a period of 8 weeks, either with (CV-TSCS) or without (SHAM-TSCS) cardiovascular-optimised stimulation. The primary outcomes are time to exhaustion (AIM 1) and cardiorespiratory fitness (AIM 2). Secondary outcomes for AIM 1 include arterial blood pressure, respiratory function, cerebral blood velocity, skeletal muscle tissue oxygenation, along with concentrations of catecholamines, brain-derived neurotrophic factor and immune cell dynamics via venous blood sampling pre, post and 90 min post-exercise. Secondary outcomes for AIM 2 include cardiometabolic health biomarkers, cardiac function, arterial stiffness, 24-hour blood pressure lability, energy expenditure, respiratory function, neural drive to respiratory muscles, seated balance and HRQoL (eg, bowel, bladder and sexual function). Outcome measures will be assessed at baseline, pre-intervention, post-intervention and after a 6-week follow-up period (HRQoL questionnaires only).

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Wales Research Ethics Committee 7 (23/WA/0284; 03/11/2024). The recruitment process began in February 2024, with the first enrolment in July 2024. Recruitment is expected to be completed by January 2026. The results will be presented at international SCI and sport-medicine conferences and will be submitted for publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ISRCTN17856698.

Increased respiratory modulation of cardiovascular control reflects improved blood pressure regulation in pregnancy

Hypertensive pregnancy disorders put the maternal-fetal dyad at risk and are one of the leading causes of morbidity and mortality during pregnancy. Multiple efforts have been made to understand the physiological mechanisms behind changes in blood pressure. Still, to date, no study has focused on analyzing the dynamics of the interactions between the systems involved in blood pressure control. In this work, we aim to address this question by evaluating the phase coherence between different signals using wavelet phase coherence. Electrocardiogram, continuous blood pressure, electrocardiogram-derived respiration, and muscle sympathetic nerve activity signals were obtained from ten normotensive pregnant women, ten normotensive non-pregnant women, and ten pregnant women with preeclampsia during rest and cold pressor test. At rest, normotensive pregnant women showed higher phase coherence in the high-frequency band (0.15-0.4 Hz) between muscle sympathetic nerve activity and the RR interval, blood pressure, and respiration compared to non-pregnant normotensive women. Although normotensive pregnant women showed no phase coherence differences with respect to hypertensive pregnant women at rest, higher phase coherence between the same pairs of variables was found during the cold pressor test. These results suggest that, in addition to the increased sympathetic tone of normotensive pregnant women widely described in the existing literature, there is an increase in cardiac parasympathetic modulation and respiratory-driven modulation of muscle sympathetic nerve activity and blood pressure that could compensate sympathetic increase and make blood pressure control more efficient to maintain it in normal ranges. Moreover, blunted modulation could prevent its buffer effect and produce an increase in blood pressure levels, as observed in the hypertensive women in this study. This initial exploration of cardiorespiratory coupling in pregnancy opens the opportunity to follow up on more in-depth analyses and determine causal influences.

Lipid metabolism after mild cold stress in persons with a cervical spinal cord injury

STUDY DESIGN

Experimental study.

OBJECTIVES

To compare lipid metabolism in individuals with a cervical spinal cord injury (SCI_C) and able-bodied (AB) persons in response to mild cold stress.

SETTINGS

Laboratory of Wakayama Medical University, Japan.

METHODS

Nine males with SCI_C and 11 AB wore a water-perfusion suit in a supine position. Following 30-min rest thermoneutrality, the whole body was cooled by perfusing 25 °C water through the suit for 15-20 min (CS). Blood samples were collected before, immediately, and 60 (post-CS60) and 120 min after CS (post-CS120). Concentrations of serum free fatty acid ([FFA]_s), total ketone bodies ([tKB]_s), insulin ([Ins]_s) and plasma adrenaline ([Ad]_p), noradrenaline ([NA]_p) and glucose ([Glc]_p) were assessed.

RESULTS

[Ad]_p in SCI_C were lower than AB throughout the study (p = 0.0002) and remained largely unchanged in both groups. [NA]_p increased after cold stress in AB only (p < 0.0001; GxT p = 0.006). [FFA]_s increased by 62% immediately after cold stress in SCI_C (p = 0.0028), without a difference between groups (p = 0.65). [tKB]_s increased by 69% at post-CS60 and 132% at post-CS120 from the start in SCI_C with no differences between groups (p = 0.54). [Glc]_p and [Ins]_s were reduced in SCIc only (GxT p = 0.003 and p = 0.001, respectively).

CONCLUSION

These data indicate that mild cold stress acutely elevates lipid and ketone body metabolism in persons with SCIc, despite the presence of sympathetic dysfunction.

Cardiovascular Responses to Commonly Used Tests in and Outside of the Laboratory Settings

Several tests are available for assessing cardiovascular response to various interventions which may be given in the laboratory, or outside of it in the field. The tests are meant to excite or deactivate cardiovascular and other sensory receptors which signal the central mechanisms. They have been found useful in generating data to study cardiovascular effects on subjects exposed to specialized physical training (e.g., athletes), in the evaluation of people engaged in special occupations such as pilots, astronauts, and other military personnel, and in training undergraduate and postgraduate students. If the response does not fit into the physiological norm, it may reflect a temporary aberration, or a more serious defect in the cardiovascular control mechanism because of disease. Interpretation of data generated may vary between various operators/observers. Here, an attempt has been made to bring out responses of the cardiovascular system to the commonly used tests, and their applicability in clinical situations.

Cold Pressor Test Influences the Cardio-Ankle Vascular Index in Healthy Overweight Young Adults

Objective

The cold pressor test (CPT) has been shown a potential sympathoexcitatory stimulus which increases aortic pulse wave velocity and the aortic augmentation index, suggesting that noninvasively, arterial stiffness parameters are altered by the CPT. The cardio-ankle vascular index (CAVI) is widely used for reflecting arterial stiffness, and the ankle-brachial index (ABI) for evaluating peripheral artery disease in obesity. We aimed to assess CAVI and ABI in overweight young adults in the context of sympathetic activation by using the CPT.

Methods

160 participants were divided into 2 groups: 86 normal-weight (body mass index [BMI] 18.50-22.99 kg/m²) and 74 overweight (BMI ≥23 kg/m²). The CPT was performed by immersing a participant's left hand into cold water (3-5°C) for 3 min, and CAVI and ABI assessment.

Results

At baseline, the CAVI in the overweight group was significantly less than that in the normal-weight group (5.79 ± 0.85 vs. 6.10 ± 0.85; p < 0.05). The mean arterial pressure (MAP) for overweight was significantly greater than that for normal-weight subjects (93.89 ± 7.31 vs. 91.10 ± 6.72; p < 0.05). During the CPT, the CAVI increased in both normal-weight and overweight subjects, the CAVI value was greater during the CPT in overweight subjects by 14.36% (6.62 ± 0.95 vs. 5.79 ± 0.85, p < 0.05) and in normal-weight subjects by 8.03% (6.59 ± 1.20 vs. 6.10 ± 0.85, p < 0.05) than those baseline values. The CPT evoked an increase in systolic blood pressure (SBP), diastolic BP (DBP), heart rate (HR,) and pulse pressure (PP) in both groups. After a 4-min CPT period, the CAVI returned values similar to the baseline values in both groups, and the SBP, DBP, MAP, and PP in overweight participants were significantly higher than those in normal-weight participants. However, there was no significant difference in the ABI at baseline, during CPT, and post-CPT in either group.

Conclusions

Our results indicated that the CAVI was influenced by sympathetic activation response to the CPT in both normal-weight and overweight young adults. Specifically, during the CPT, the percentage change of the CAVI in overweight response was greater in normal-weight participants than baseline values in each group. The ABI was not found significantly associated with CPT. These findings suggesting that sympathoexcitatory stimulus by CPT influence CAVI results.

Is Technology for Orthostatic Hypotension Ready for Primetime?

Spinal cord injury (SCI) often results in the devastating loss of motor, sensory, and autonomic function. After SCI, the interruption of descending sympathoexcitatory pathways disrupts supraspinal control of blood pressure (BP). A common clinical consequence of cardiovascular dysfunction after SCI is orthostatic hypotension (OH), a debilitating condition characterized by rapid profound decreases in BP when assuming an upright posture. OH can result in a diverse array of insidious and pernicious health consequences. Acute effects of OH include decreased cardiac filling, cerebral hypoperfusion, and associated presyncopal symptoms such as lightheadedness and dizziness. Over the long term, repetitive exposure to OH is associated with a drastically increased prevalence of heart attack and stroke, which are leading causes of death in those with SCI. Current recommendations for managing BP after SCI primarily include pharmacologic interventions with prolonged time to effect. Because most episodes of OH occur in less than 3 minutes, this delay in action often renders most pharmacologic interventions ineffective. New innovative technologies such as epidural and transcutaneous spinal cord stimulation are being explored to solve this problem. It might be possible to electrically stimulate sympathetic circuitry caudal to the injury and elicit rapid modulation of BP to manage OH. This review describes autonomic control of the cardiovascular system before injury, resulting cardiovascular consequences after SCI such as OH, and the clinical assessment tools for evaluating autonomic dysfunction after SCI. In addition, current approaches for clinically managing OH are outlined, and new promising interventions are described for managing this condition.