Cerebrovascular function is preserved during mild hyperthermia in cervical spinal cord injury

The Clinical Relevance of Autonomic Dysfunction, Cerebral Hemodynamics, and Sleep Interactions in Individuals Living With SCI

A myriad of physiological impairments is seen in individuals after a spinal cord injury (SCI). These include altered autonomic function, cerebral hemodynamics, and sleep. These physiological systems are interconnected and likely insidiously interact leading to secondary complications. These impairments negatively influence quality of life. A comprehensive review of these systems, and their interplay, may improve clinical treatment and the rehabilitation plan of individuals living with SCI. Thus, these physiological measures should receive more clinical consideration. This special communication introduces the under investigated autonomic dysfunction, cerebral hemodynamics, and sleep disorders in people with SCI to stakeholders involved in SCI rehabilitation. We also discuss the linkage between autonomic dysfunction, cerebral hemodynamics, and sleep disorders and some secondary outcomes are discussed. Recent evidence is synthesized to make clinical recommendations on the assessment and potential management of important autonomic, cerebral hemodynamics, and sleep-related dysfunction in people with SCI. Finally, a few recommendations for clinicians and researchers are provided.

Hot head-out water immersion does not acutely alter dynamic cerebral autoregulation or cerebrovascular reactivity to hypercapnia

Recurring hot head-out water immersion (HOWI) enhances peripheral vascular function and cerebral blood velocity during non-immersion conditions. However, it is unknown if an acute bout of hot HOWI alters cerebrovascular function. Using two experimental studies, we tested the hypotheses that dynamic cerebral autoregulation (dCA) and cerebrovascular reactivity (CVR) are improved during an acute bout of hot (HOT; 39 °C) vs. thermoneutral (TN; 35 °C) HOWI. Eighteen healthy participants (eight females) completed the dCA study, and 14 participants (6 females) completed the CVR study. Both studies consisted of two randomized (TNdCA vs. HOTdCA; TNCVR vs. HOTCVR) 45minute HOWI visits. Middle cerebral artery blood velocity (MCAvmean) was continuously recorded. dCA was assessed using a respiratory impedance device and analyzed via transfer gain and phase in the low-frequency band. CVR was assessed using stepped hypercapnia. Assessments were completed PRE and 30 minutes into HOWI. Values are reported as a change (Δ) from PRE (mean ± SD). There were no differences at PRE for either study. ΔMCAvmean was greater in TNdCA (TNdCA: 4 ± 4 vs. HOTdCA: -3 ± 5 cm/s; P < 0.01) and TNCVR (TNCVR: 5 ± 4 vs. HOTCVR: -1 ± 6 cm/s; P < 0.01) during HOWI. ΔGain was greater in HOTdCA during HOWI (TNdCA: -0.09 ± 0.15 vs. HOTdCA: 0.10 ± 0.17 cm/s/mmHg; P = 0.04). ΔPhase (P > 0.84) and ΔCVR (P > 0.94) were not different between conditions. These data indicate that hot and thermoneutral water immersion do not acutely alter cerebrovascular function in healthy, young adults.

The effect of heat therapy on blood pressure and peripheral vascular function: A systematic review and meta-analysis

NEW FINDINGS

What is the topic of this review? We have conducted a systematic review and meta-analysis on the current evidence for the effect of heat therapy on blood pressure and vascular function. What advances does it highlight? We found that heat therapy reduced mean arterial, systolic and diastolic blood pressure. We also observed that heat therapy improved vascular function, as assessed via brachial artery flow-mediated dilatation. Our results suggest that heat therapy is a promising therapeutic tool that should be optimized further, via mode and dose, for the prevention and treatment of cardiovascular disease risk factors.

ABSTRACT

Lifelong sauna exposure is associated with reduced cardiovascular disease risk. Recent studies have investigated the effect of heat therapy on markers of cardiovascular health. We aimed to conduct a systematic review with meta-analysis to determine the effects of heat therapy on blood pressure and indices of vascular function in healthy and clinical populations. Four databases were searched up to September 2020 for studies investigating heat therapy on outcomes including blood pressure and vascular function. Grading of Recommendations, Assessment, Development and Evaluations (GRADE) was used to assess the certainty of evidence. A total of 4522 titles were screened, and 15 studies were included. Healthy and clinical populations were included. Heat exposure was for 30-90 min, over 10-36 sessions. Compared with control conditions, heat therapy reduced mean arterial pressure [n = 4 studies; mean difference (MD): -5.86 mmHg, 95% confidence interval (CI): -8.63, -3.10; P < 0.0001], systolic blood pressure (n = 10; MD: -3.94 mmHg, 95% CI: -7.22, -0.67; P = 0.02) and diastolic blood pressure (n = 9; MD: -3.88 mmHg, 95% CI: -6.13, -1.63; P = 0.0007) and improved flow-mediated dilatation (n = 5; MD: 1.95%, 95% CI: 0.14, 3.76; P = 0.03). Resting heart rate was unchanged (n = 10; MD: -1.25 beats/min; 95% CI: -3.20, 0.70; P = 0.21). Early evidence also suggests benefits for arterial stiffness and cutaneous microvascular function. The certainty of evidence was moderate for the effect of heat therapy on systolic and diastolic blood pressure and heart rate and low for the effect of heat therapy on mean arterial pressure and flow-mediated dilatation. Heat therapy is an effective therapeutic tool to reduce blood pressure and improve macrovascular function. Future research should aim to optimize heat therapy, including the mode and dose, for the prevention and management of cardiovascular disease.