Cold pressor stimulus temperature and resting masseter muscle haemodynamics in normal humans

Hemodynamic changes in the temporalis and masseter muscles during acute stress in healthy humans

PURPOSE

Autonomic control of orofacial areas is an integral part of the stress response, controlling functions such as pupil dilatation, salivation, and skin blood flow. However, the specific control of blood flow in head muscles during stress is unknown. This study aims to investigate the hemodynamic response of temporalis and masseter muscles in response to five different stressors.

METHODS

Sixteen healthy individuals were subjected to a randomized series of stressors, including cold pressor test, mental arithmetic test, apnea, isometric handgrip, and post-handgrip muscle ischemia, while in the sitting posture. Finger-pulse photoplethysmography was used to measure arterial blood pressure, heart rate, and cardiac output. Near-infrared spectroscopy was used to measure changes in tissue oxygenation and hemoglobin indices from the temporalis and masseter muscles.

RESULTS

All stressors effectively and significantly increased arterial blood pressure. Tissue oxygenation index significantly increased in both investigated head muscles during mental arithmetic test (temporalis: 4.22 ± 3.52%; masseter: 3.43 ± 3.63%) and isometric handgrip (temporalis: 3.45 ± 3.09%; masseter: 3.26 ± 3.07%), suggesting increased muscle blood flow. Neither the masseter nor the temporalis muscles evidenced a vasoconstrictive response to any of the stressors tested.

CONCLUSION

In the different conditions, temporalis and masseter muscles exhibited similar hemodynamic patterns of response, which do not include the marked vasoconstriction generally observed in limb muscles. The peculiar sympathetic control of head muscles is possibly related to the involvement of these muscles in aggressive/defensive reactions and/or to their unfavorable position with regard to hydrostatic blood levels.

Differential control of blood flow in masseter and biceps brachii muscles during stress

OBJECTIVE

The present study aimed to compare sympathetic hemodynamic effects in masticatory and limb muscles in response to different stressors.

DESIGN

Twelve healthy participants were subjected to a randomized series of stressors, including cold pressor test (CPT), mental arithmetic test, apnea, isometric handgrip (IHG) and post-handgrip muscle ischemia (PHGMI), while in the supine position. Spatially-resolved near-infrared spectroscopy was used to measure relative changes in blood volume and oxygenation (TOI) of the resting masseter and biceps muscles. Cardiac output, heart rate, and arterial blood pressure (ABP) were also monitored.

RESULTS

Except apnea, all tests increased ABP. Different response patterns were observed in the 2 muscles: TOI significantly increased during contralateral IHG (1.24 ± 1.17%) but markedly decreased during CPT (-4.84 ± 4.09%) and PHGMI (-6.65 ± 5.31%) in the biceps muscle, while exhibiting consistent increases in the masseter (1.88 ± 1.85%; 1.60 ± 1.75%; 1.06 ± 3.29%, respectively) (p < 0.05).

CONCLUSIONS

The results allow us to infer differential control of blood flow in head and limb muscles. In general, the masseter appears more prone to dilatation than the biceps, exhibiting opposite changes in response to painful stimuli (CPT and PHGMI). Several mechanisms may mediate this effect, including reduced sympathetic outflow to the extracranial vasculature of the head, generally exposed to lower hydrostatic loads than the rest of the body.

Mental Stress-induced Physiological Changes in the Human Masseter Muscle

The effect of a long mental stress on the hemodynamics of masticatory muscles has not been investigated to date. We hypothesized some hemodynamic and electromyographic changes in jaw-closure muscles related to sympathetic nervous system activity. While healthy adult female volunteers performed a two-hour mental stress task, electromyographic activity of the temporal and masseteric muscles was recorded, and hemodynamic changes of the masseter muscle were measured non-invasively. Autonomic function was assessed by heart rate spectral analysis. Integrated electromyographic activity of the temporalis muscle, but not the masseter muscle, showed an increase that coincided with the increase in sympathetic nervous activity. In the masseter muscle, despite little change in integrated electromyographic activity, notable changes were found in hemodynamic parameters. These results suggest that hemodynamics of jaw muscles is susceptible to mental stress, implying a potential role in the etiology of jaw muscle dysfunction associated with mental stress.

Interactions between β-adrenergic vasodilation and cervical sympathetic nerves are mediated by α2-adrenoceptors in the rat masseter muscle

Neural and humoral autonomic mechanisms may be important in the maintenance of blood flow in the masseter muscle (MBF). However, their interactions remain unclear. In this study, we examined interactions between neural and humoral regulation of MBF and investigated the mechanisms mediating these interactions in urethane-anesthetized rats. Stimulation of the adrenal nerve (AN) projecting to the adrenal medulla increased MBF, and this increase was mediated by β-adrenoceptors. Sectioning of the superior cervical sympathetic trunk (CST) significantly inhibited increases in MBF induced by AN stimulation during high activity in the CST, but not during low activity. AN stimulation with clonidine after CST sectioning induced a significant increased in MBF, however phenylephrine had no observable effect. Pretreatment with yohimbine or propranolol significantly inhibited the increase in the MBF. Our results suggest an interaction between β-adrenergic vasodilation evoked by circulating adrenaline and the cervical sympathetic nerves that is mediated by α₂-adrenoceptors in the masseter muscle.

Autonomic responses to lateralized cold pressor and facial cooling tasks

Asymmetry in central nervous system (CNS) control of autonomic nervous system (ANS) activity, a widely debated topic, was investigated via lateralized presentation of two ANS challenges: cold pressor, which elicits primarily sympathetic activation, and facial cooling, a predominantly vagal task. Seventy-three university students (37 female) engaged in these tasks while cardiovascular and electrodermal measures were acquired. Compared to right-side cold pressor, left cold pressor elicited generally larger cardiac, blood pressure, and skin conductance responses, but did not evoke asymmetric changes in heart rate variability. Facial cooling elicited significant increases in vagally mediated heart rate variability, but they were also not lateralized. These findings are consistent with reports of right hemisphere dominance in sympathetic regulation, but indicate that CNS vagal control is relatively symmetric. These results are framed in terms of polyvagal theory and neurovisceral integration two influential models of CNS-ANS integration in the service of adaptive environmental engagement.

Circulating adrenaline released by sympathoadrenal activation elicits acute vasodilatation in the rat masseter muscle

The present study was designed to examine the effects of circulating catecholamines released by sympathoadrenal system on the haemodynamics of the masseter muscle in deeply urethane-anaesthetized, artificially ventilated, cervically vagotomized and sympathectomized rats. Intravenous administration of adrenaline induced a biphasic change of blood flow in the masseter muscle (MBF). The change of blood flow showed an initial marked increase and successive slight decrease in a dose-dependent manner (0.01-1 microg/kg). The administration of noradrenaline had no significant effect on the MBF. The increase in the MBF evoked by exogenously applied adrenaline was markedly reduced by the intravenous administration of propranolol (100 microg/kg), whereas pretreatment with either hexamethonium (10 mg/kg), atropine (100 microg/kg), or phentolamine (1 mg/kg) failed to affect the MBF increase. Electrical stimulation of splanchnic nerve (SPLN) preganglionic neurones projecting to the adrenal medulla elicited frequency-dependent (1-20 Hz) increases in the MBF. The intravenous administration of the beta(2)-adrenergic receptor selective antagonist, ICI 118551 (0.5 mg/kg), almost abolished the MBF increase induced by SPLN stimulation, but pretreatment with the beta(1)-adrenergic receptor selective antagonist, atenolol (1 mg/kg), had no effect on this response. The results of the present study indicate that circulating adrenaline elicits acute vasodilatation through a beta-adrenergic mechanism in the rat masseter muscle. Vascular beta(2)-adrenergic receptors in the masseter muscle may be activated preferentially by adrenaline released from the adrenal medulla, suggesting that the sympathoadrenal system is involved in the marked MBF increase during sympathoexcitation.

Signal intensity changes in T2-weighted MR image of the human trapezius muscle upon cold pressor stimulation

OBJECTIVE

The ability to measure hemodynamics of skeletal muscle proper is one of the major goals for muscle pain researchers. The aim of the present study was to evaluate the ability of signal intensity (SI) in T2-weighted trapezius muscle magnetic resonance imaging (MRI) to detect intramuscular hemodynamic changes during cold pressor stimulation (CPS).

MATERIALS AND METHODS

Fifteen healthy volunteers (mean age, 25.9+/-2.1 years) participated in this study. T2-weighted MRI was acquired using a 1.5 tesla MR unit with a body array coil. The slice level was set perpendicular to the muscle long axis at the mid-point of the horizontal portion of the right trapezius muscle. Cold pressor stimulation (4 degrees C) was applied to each subject's right foot and ankle for 2 min. The SI changes were recorded continuously for 7 min before, 2 min during, and 6 min after withdrawal of cold pressor stimulation. Six of these subjects also underwent a mock-CPS trial.

RESULTS

The mean SI level in T2-weighted trapezius muscle MRI significantly increased during CPS (P<0.0001, one way repeated measure ANOVA) and returned to the baseline level after cold pressor withdrawal. No statistically significant signal changes were observed across the mock-CPS trial subjects. These findings are identical to the cold pressor-induced hemodynamic changes documented in the trapezius muscle by near-infrared spectroscopy evaluation.

CONCLUSIONS

SI measurement in T2-weighted trapezius muscle MRI is sufficiently sensitive to detect intramuscular hemodynamic changes during CPS.

Intramuscular hypoperfusion, adrenergic receptors, and chronic muscle pain

Despite a high prevalence of chronic muscle pain disorders such as fibromyalgia and regional myofascial pain, there is still limited knowledge about the factors that initiate and perpetuate these pain states. Although there are also likely to be downstream neuropathic changes in the central nervous system and spinal cord that sustain and exacerbate the pain states known as fibromyalgia, the focus of this critical review is on studies that examined the connection between both fibromyalgia and regional myofascial pain and sympathetic function. Specifically, we looked at studies that described Raynaud-like symptoms, cardiovascular dysfunction and altered intramuscular perfusion in chronic muscle pain. Our analysis showed that although the first 2 phenomena were intermittently present, a prominent and consistent feature for regional myofascial pain and to a lesser degree for fibromyalgia was intramuscular hypoperfusion. Several hypotheses can be offered why this hypoperfusion exists, and additional studies comparing and contrasting these theories are needed. This review focuses on one of these theories, namely, agonist-induced beta-adrenergic receptor desensitization as an explanatory model for hypoperfusion. What cannot be done at this time and is needed in the future is to compare and contrast to what degree the regional muscle pain disorder (myofascial) is similar or different from the more generalized disorder (fibromyalgia).

Reperfusion response changes induced by repeated, sustained contractions in normal human masseter muscle

The purpose was to evaluate the intramuscular reperfusion response characteristics associated with repeated isometric contractions in normal human masseter. Intramuscular blood volume was quantified with a near-infrared spectroscopic device that measured the total haemoglobin (Hb) concentration in the muscle. Electromyographic (EMG) activity from the masseter and total bite forces were also recorded. Sixteen healthy volunteers, eight females and eight males, without masticatory muscle pain participated. They were asked first to clench their teeth for as long as possible at 50% of their maximum voluntary contraction (MVC). This was followed by a 60s rest and then immediately by a standard clenching task (50% MVC for 30s) and a 60s recovery period, immediately after which they were asked to repeat exactly the same procedure, with a final 5 min recovery period after the second 30s contraction. Bite force, EMG and Hb concentration were measured continuously and the duration of the two endurance tasks and the amplitudes of all recorded signals were compared (first trial versus second trial). Specifically, the difference between the lowest Hb (trough) seen during the standardised 30s contractions and the highest (peak) seen just after them was assessed. The trough-to-peak difference in Hb concentration of the second standard contraction task was significantly smaller than that of the first standard task (P<0.05, paired t-test). These data show that with sustained effort the post-contraction vasodilatory reperfusion responses of the human masseter are diminished, suggesting a progressive desensitisation of the vasodilatory system.

Correlation of the near-infrared spectroscopy signals with signal intensity in T(2)-weighted magnetic resonance imaging of the human masseter muscle

The purpose of this study was to compare and contrast blood volume changes transcutaneously measured using near-infrared (NIR) spectroscopy against water signal intensity changes taken from a transverse T(2)-weighted MR image of the masseter muscle in healthy human subjects before, during and after contraction. Eight healthy non-smoking males with no history of chronic muscle pain or vascular headaches participated (mean age: 23.9+/-0.6 years). The MRI data were gathered using a turbo spin echo sequence (TR: 2300 ms; TE: 90 ms; FOV: 188x300 mm; scanning time: 30 s; slice thickness: 10 mm) and the slice level was set at the mid-point between the origin and insertion of the masseter. Intramuscular haemoglobin (Hb) levels and water content of the right masseter muscle were continuously monitored for 2 min before, 30 s during and 15 min after a maximum voluntary clenching (MVC) task. Both the near-infrared and MRI data were baseline-corrected and normalized and mean levels were established and plotted. Plots of the data showed that both near-infrared-based total Hb and T(2)-weighted MRI-based signal-intensity levels clearly decreased during contraction and a clear post-contraction rebound response was evident after the contraction. The near-infrared data were found to be highly correlated with MRI-based signal-intensity data (Pearson's r=0.909, P<0.0001). In conclusion, these data provide powerful evidence that near-infrared data (total Hb), transcutaneously taken from the masseter muscle in humans, will reflect the intramuscular water signal intensity changes seen using a T(2)-weighted MRI imaging method.

Intramuscular haemodynamic responses to different durations of sustained extension in normal human masseter

Ten healthy non-smoking males (mean age 24.3+/-0.8 years) with no history of chronic muscle pain or migraine participated in this study. Intramuscular total haemoglobin (Hb), an indicator of blood volume in the illuminated area, was measured with a non-invasive, near-infrared spectroscopic device. Each participant was told to maintain maximal mouth opening to extend the masseter muscle for 30, 60 or 120 s in random order. Data were continuously recorded from the right masseter 1 min before, at set times during and for 5 min after sustained muscle extension in each trial. Each trial was separated by a 10-min interval. Heart rate (HR) and blood pressure (BP) were also recorded. The mean normalized Hb decreased during muscle extension and rebound hyperaemia was observed after it in each trial (P=0.0001). Hb returned to baseline within 60 s. The magnitude of the decremental change during extension and of the incremental change in the rebound hyperaemia was not significantly different among the three trials (P=0.9071); neither were mean normalized HR and BP. These data suggest that sustained extension of the masseter produces a reduction in total intramuscular Hb during extension and a secondary increase in Hb following a return to the resting muscle's normal length.

Effect of cold pressor stimulation (4 degrees C) on human masseter muscle haemodynamics during and after sustained isometric contraction

The effect of cold pressor (CP) stimulation and sustained isometric contraction on the blood volume of the right masseter muscle was examined in seven healthy males, who performed 1 min of isometric jaw clenching at 50% of their maximum voluntary contraction without, with and again without a 4 degrees C CP stimulation. Total haemoglobin was measured in the masseter before, during and after the contraction task using near-infrared spectroscopy. CP stimulation during the isometric contraction diminished the magnitude of the contraction-induced decrease of blood volume when compared to the trials without CP stimulation. However, in the immediate post-contraction period (while the CP stimulation was still in place), no increase in blood volume above the usual post-contraction hyperaemia was evident. Once the CP stimulation had been removed, there was a clear decrease (faster return to baseline) in the vasodilation occurring in the post-contraction period. This diminished period of vasodilation occurred in spite of the fact that the vascular resistance (blood pressure) and heart rate were still substantially elevated by the CP effect during this same period. These data suggest that the strong CP stimulation produced a biphasic response. First, there was an early-onset strong vasodilation (during CP), which was followed by a period of diminished vasodilation, suggesting that an active, but delayed, vasoconstrictive drive may be induced by the CP stimulus.

Cold pressor stimulation effect on hemodynamic changes following sustained isometric contraction in human jaw-closure muscles

It is postulated that an altered adrenergic response pattern may be associated with chronic muscle pain states. To evaluate this hypothesis, one must fully understand the effect of an adrenergic activation on masticatory muscle blood flow under various conditions. This study evaluated the effect of a 12 degrees C cold pressor stimulation (a mild adrenergic activator), applied to the hand-forearm area, on intramuscular hemodynamics in the human masseter and temporalis muscles following a sustained isometric contraction. We assessed hemodynamics by measuring intramuscular hemoglobin concentration repeatedly, using a non-invasive near-infrared spectroscopy device. Measurements were taken before, during, and after a 30-second sustained 50% maximum voluntary contraction task. Fourteen healthy subjects, seven males and seven females, with no history of muscle pain in the masticatory system participated in this study. This protocol was repeated three times, but in the second trial, the cold pressor stimulation was applied to the subject during and for 5 min after the sustained contraction task. Repeated-measure analysis of variance performed on these data revealed that the peak hemoglobin concentration levels in the post-contraction recovery period were significantly reduced (between 13 and 14%) with cold pressor stimulation, both in the masseter (p < 0.001) and in the temporalis (p < 0.001) muscles. The results suggest that cold pressor stimulation produced a reduced intramuscular vasodilative response in these muscles during the immediate post-contraction period. One explanation for these results is that altering the local chemical environment of the muscle affects the adrenergic response pattern typically induced by a cold pressor stimulation.

Haemodynamic responses in chronically painful, human trapezius muscle to cold pressor stimulation

The aim was to compare haemodynamic responses in trapezius muscles to cold pressor stimulation in individuals with localized trapezius myalgia and asymptomatic controls. Nine males with chronic localized pain in the trapezius (mean age, 23.2 years) and nine male controls (mean age, 24.6 years) who had no medical history of migraine, hypertension or sustained pain in the trapezius region were investigated. Two experimental (cold pressor and mock) trials were performed in a randomly assigned sequence. In the cold pressor trial the participant's left foot and ankle were immersed in 4 degrees C cold water for 2 min; the mock trial was done without that stimulus. Blood volume was continuously recorded 1 min before, 2 min during, and 5 min after cold pressor stimulation using near-infrared spectroscopy. Each participant's blood-volume data were baseline-corrected and submitted to statistical analysis. Results showed that the individuals with muscle pain exhibited a significantly lower mean blood volume than the controls during cold pressor stimulation (p = 0.0367). Upon withdrawal of that stimulation, the mean blood volume in both groups fell below the baseline. These results suggest that individuals with chronic regional trapezius myalgia have less capacity to vasodilate this muscle during cold pressor stimulation than those without such myalgia. It is not yet known if this difference in the haemodynamic response is a cause or an effect of the myalgia.

Effect of intravenous infusion of a beta-adrenergic blocking agent on the haemodynamic changes in human masseter muscle induced by cold-pressor stimulation

Eight healthy non-smoking males (mean age: 24.1 +/- 1.1 years) without any history of chronic muscle pain and migraine participated in this study. Haemoglobin (Hb) and oxygen (O2) saturation in the right masseter muscle were continuously recorded with a non-invasive near-infrared spectroscopic device. Heart rate and blood pressure were also recorded. The experiment had three phases: a placebo drug (physiological saline) with cold-pressor trial, a 30-sec maximal voluntary clenching (MVC) trial, and a propranolol with cold-pressor trial. The saline and drug trials each involved continuous recording for 1 min before, 2 min during and 5 min after the cold-pressor stimulation (4 degrees C). Physiological saline (20 ml) or propranolol hydrochloride (20 ml) were infused at the rate of 2 ml/min. This infusion was begun 20 min before the baseline recording and participants did not know which solution (saline or propranolol) was being infused. For the MVC trial, each participant was asked to perform a 30-sec clench of their jaw-closing muscles. There was a rest period of 15 min between each trial. The individual Hb and O2 data were normalized so that the baseline at the beginning of the experiment was equal to zero, and the Hb and O2 data were normalized as a percentage of the individual's own highest absolute Hb and O2 after and during the MVC, respectively. The results showed that the mean baseline Hb 1 min before cold-pressor stimulation was significantly lower in the beta-blocker trial than in the placebo trial (p = 0.035). The mean change in Hb from baseline during cold-pressor stimulation in the beta-blocker trial was also significantly less than in the placebo trial (p = 0.035). The mean Hb rebound change after the cold-pressor stimulation in the beta-blocker trial was significantly higher than in the placebo trial, and no significant heart-rate differences were observed in the period after cold-pressor stimulation. Overall, the mean heart rate before and during that stimulation was significantly lower in the beta-blocker trial than the placebo trial (p < 0.001). There was no significant mean blood-pressure difference between placebo and beta-blocker trials at any time. These results suggest that beta-adrenoceptor blocking decreases the blood volume in the resting masseter, suppresses the incremental blood-volume change during cold-pressor stimulation, and discloses a hidden vasoconstrictive effect after that stimulation.

Effect of intravenous infusion of an alpha-adrenergic blocking agent on the haemodynamic changes in human masseter muscle induced by cold pressor stimulation

This study evaluated the effect of intravenous infusion of a non-selective alpha-adrenergic blocking agent on masseter muscle haemodynamics induced by 4 degrees C cold pressor stimulation (CPS) of the right foot and ankle, which reportedly evokes a rapidly increasing sympathetic nerve activity in human skeletal muscle. Nine healthy non-smoking males (mean age 23.7+/-2.1 year) with no history of chronic muscle pain or migraine participated. The haemoglobin (Hb) concentration in the right masseter was continuously recorded by non-invasive, near-infrared spectroscopy. Heart rate and blood pressure were also recorded. The experiment involved the following sequence: (1) a placebo (physiological saline) with a CPS trial; (2) a 30-sec maximal voluntary clenching (MVC)-only trial; and (3) an alpha-adrenergic blocking agent with a CPS trial. The saline and drug trials each involved continuous recording for 1 min before, 2 min during and 5 min after the CPS. Physiological saline (20 ml) or phentolamine mesylate (20 ml) were infused at the rate of 2 ml/min. This infusion was begun 15 min before baseline recording and participants were not aware which solution (saline or phentolamine) was being infused. For the MVC trial, each participant performed a 30-sec MVC of his jaw-closing muscles followed by a 15-min rest between each trial. The individual Hb data were adjusted so that the baseline at the beginning of the experiment was equal to zero and all data were normalized as a percentage of the individual's highest absolute Hb change seen after the MVC. The mean baseline Hb concentrations 1 min before CPS were significantly higher in the alpha-blocker trial (83.6%) than in the placebo saline trial (P < 0.001). The change in mean Hb concentration from baseline during CPS in the alpha-blocker trial was significantly less than in the placebo trial (P = 0.006). Mean heart rate before CPS was also significantly higher in the alpha-blocker trial (85.2 beats/min) than in the placebo trial (69.6 beats/min) (P < 0.001). There were no significant differences in the mean systolic and diastolic blood pressures between the placebo and alpha-blocker trials in any time period. The results suggest that non-selective alpha-adrenoceptor blockade increases the blood volume in the masseter muscle. This change might be due to a combination of peripheral vasodilation and an increase in cardiac output.