Neck Suction Research Articles

Experimental carotid baroreceptor stimulation reduces blood flow velocities in the anterior and middle cerebral arteries of healthy individuals

This study investigated effects of experimental baroreceptor stimulation on bilateral blood flow velocities in the anterior and middle cerebral arteries (ACA and MCA) using functional transcranial Doppler sonography. Carotid baroreceptors were stimulated by neck suction in 33 healthy participants. Therefore, negative pressure (− 50 mmHg) was applied; neck pressure (+ 10 mmHg) was used as a control condition. Heart rate (HR) and blood pressure (BP) were also continuously recorded. Neck suction led to reductions in bilateral ACA and MCA blood flow velocities, which accompanied the expected HR and BP decreases; HR and BP decreases correlated positively with the ACA flow velocity decline. The observations suggest reduction of blood flow in the perfusion territories of the ACA and MCA during baroreceptor stimulation. Baroreceptor-related HR and BP decreases may contribute to the cerebral blood flow decline. The findings underline the interaction between peripheral and cerebral hemodynamic regulation in autoregulatory control of cerebral perfusion.

Abstract 052: Central Gain For Sympathetic Outflow Is Increased In Postural Tachycardia Syndrome

White noise perturbations using neck suction (NS) can be applied to identify open loop transfer function in a closed loop baroreflex system. It allows an estimation of central arc transfer function (H1) which represents how afferent baroreceptor information is translated into sympathetic outflow and peripheral arc transfer function (H2) which describes how muscle sympathetic nerve activity (MSNA) affects blood pressure (BP). We hypothesize that patients with postural tachycardia syndrome (POTS) have elevated central gain compared to healthy controls (CONT). We recorded raw MSNA and continuous finger BP during randomized NS (0 to -50 mmHg, 0.03-0.3 Hz) and controlled breathing at 0.25 Hz for 6 minutes in 10 female POTS and 9 female CONT. Both groups were matched for age (28.4±2.1 vs. 31.9±3.0 p=0.80) and BMI (23.0±0.7 vs 24.5±1.0, p=0.25). We derived the continuous spike rate using wavelet-based denoising. We estimated median central gain in H1 and peripheral gain in H2 for low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.4 Hz) frequency ranges (Figure). We found that POTS have significantly higher central gain in LF range (2.44±0.38 vs 1.53±0.24 spikes/s/mmHg, p=0.028, MN±SE) but not in HF range (9.02±3.02 vs. 5.06±0.52 spikes/s/mmHg, p=0.604). Median peripheral gains were comparable in LF (0.68±0.15 vs 0.58±0.09 mmHg/spikes/s, p>0.99) and HF ranges (0.18±0.02 vs 0.21±0.03 mmHg/spikes/s, p=0.497). Our results indicate that POTS have higher recruitment of neural sympathetic spike activity during BP oscillations in the LF range. This could explain why higher sympathetic activation/modulation and greater BP fluctuations in the LF range are found during upright in POTS.

Carotid Baroreflex Responsiveness in Patients with Heart Failure with a Preserved Ejection Fraction

The carotid baroreflex (CBR) plays an important role in blood pressure regulation by modulating heart rate (HR) and vasomotor tone. In humans, CBR function can be investigated non‐invasively using the variable pressure neck collar, which alters carotid sinus transmural pressure through application of positive and negative pressure within the neck chamber. Using this technique, derangements in CBR function have been identified in a variety of patient populations, but whether patients with heart failure with a preserved ejection fraction (HFpEF) suffer from disease‐related changes in CBR responsiveness has yet to be determined. We evaluated beat‐to‐beat changes in HR and mean arterial pressure (MAP) in response to 5‐sec pulses of neck pressure (NP, +40 Torr) and neck suction (NS, ‐80 Torr) to simulate carotid hypotension and hypertension, respectively in 5 patients with HFpEF (69±3 yrs and BMI: 38±4) and 4 healthy, older controls (68±2 yrs and BMI: 26±3). Resting HR was lower in patients with HFpEF compared to control subjects (77±7 vs. 68±6 bpm, respectively; p<0.005), while MAP was similar between groups (88±2 vs. 88±5mmHg, HFpEF vs controls). Following NP, a disease‐related decrement in CBR responsiveness was evident, with diminished changes in HR (2±1 vs 9±1 bpm, HFpEF vs controls, p=0.041) and MAP (4±2 vs 8±1 mmHg, p=0.095) in the HFpEF group. Similarly, changes in both HR (‐6±1 vs ‐8±1 bpm, HFpEF vs controls, p=0.21) and MAP (‐5±1 vs ‐8±1 mmHg, HFpEF vs controls, p=0.16) in response to carotid hypertension provoked by NS were reduced in patient with HFpEF. Though preliminary in nature, these initial findings appear to indicate a decline in carotid baroreflex‐mediated cardiac and vasomotor control in patients with HFpEF that is likely to contribute significantly to autonomic nervous system dysregulation in this patient group.

Thrombectomy of Inferior Vena Cava Fat Embolism after Trauma

A 19-year-old man involved in a head-on motor vehicle collision presented with multiple injuries, including a displaced right femur fracture. Two days after presentation, a computed tomography scan was obtained to evaluate new-onset hematuria, and it showed an extensive hypoattenuating filling defect in the inferior vena cava (IVC) (Fig 1), concerning for free-floating fat embolus. The interventional radiology department was consulted for embolectomy due to the risk of pulmonary embolism, contraindication for anticoagulation in the setting of trauma, and decreased likelihood of fat thrombus responding to anticoagulation. Cavogram showed an extensive right iliocaval filling defect (Fig 2a). A suprarenal IVC filter was placed prior to embolectomy to prevent central migration. Following mechanical embolectomy using an Amplatz Goose Neck Snare (Medtronic, Minneapolis, Minnesota) and suction via guiding catheters, a repeat cavogram demonstrated partially embolized fat thrombus trapped at the IVC filter apex (Fig 2b), which was removed with the snare. Histopathology of the fat emboli (Fig 2c) showed “thrombus with entrapped fat.”

Neck Chamber Technique Revisited: Low-Noise Device Delivering Negative and Positive Pressure and Enabling Concomitant Carotid Artery Imaging With Ultrasonography.

Background and Objectives: Recently, novel noiseless device for the assessment of baroreceptor function with the neck suction (NS) has been presented. In this study, we present another in-house approach to the variable-pressure neck chamber method. Our device offers further critical improvements. First, it enables delivery of negative (NS) as well as positive pressure (neck pressurizing, NP) in a noiseless manner. Second, we used small, 3D-printed cups positioned over the carotid sinuses instead of cumbersome neck collar to improve subject comfort and to test feasibility of tracking the pressure-induced changes in carotid artery with ultrasonography.Methods: Five healthy, non-smoking, normal-weight subjects aged 29 ± 3 years (mean ± SD) volunteered for the study. Heart rate (HR, bpm) and mean arterial pressure (MAP, mmHg) responses to short, 7-s long episodes of NS and NP were recorded. Each trial consisted of 12 episodes of variable-pressure: six episodes of NS (suction ranging between -10 and -80 mmHg) and six episodes of NP (pressure ranging between + 10 and + 80 mmHg). Carotid artery sonography was performed during the NS and NP in four subjects, on another occasion.Results: The variable-pressure episodes resulted consistently in the expected pattern of hemodynamic alterations: HR and MAP increases or decreases following the NP and NS, respectively, as evidenced by the coefficient of determination (R2) of ≥0.78 for the carotid-HR response curve (for all five participants) and the carotid-MAP response curve (for four out of five participants; the curve cannot be calculated for one subject). We found a linear, dose-dependent relation between the applied pressure and the systolic-diastolic difference in carotid artery diameter.Conclusion: The novel device enables noiseless stimulation and unloading of the carotid baroreceptors with the negative and positive pressure, respectively, applied on the subject’s neck via small, asymmetric and one-side flattened, 3D-printed cups. The unique design of the cups enables concomitant visualizing of the carotid artery during the NS or NP administration, and thereby direct monitoring of the intensity of mechanical stimulus targeting the carotid baroreceptors.

Auxiliary Tests of Autonomic Functions.

The autonomic nervous system is a complex neural network that controls several organ systems. Its assessment includes a detailed history of autonomic functions, clinical examination, and autonomic tests. Most widely used is a battery of tests that assess cardiovascular reflex autonomic and sudomotor tests, which include deep breathing (assesses parasympathetic function), Valsalva maneuver, tilt test (both assess parasympathetic and adrenergic functions), and sudomotor testing for the evaluation of postganglionic sudomotor fibers. These basic tests represent a foundation of autonomic testing. Nevertheless, the autonomic nervous system also controls organ systems not directly assessed by basic tests. This review describes a number of auxiliary autonomic tests that can be used in addition to basic autonomic tests or can be used independently to explore particular autonomic functions or to answer a specific clinical question. The auxiliary tests described in this review evaluate cardiovascular, thermoregulatory, gastrointestinal, genitourinary, eye, and exocrine functions. These tests are cold pressor test, sustained handgrip maneuver, reverse tilt test, venoarteriolar reflex, laser Doppler flare imaging, microneurography, neck suction, lower body negative pressure, venous occlusion plethysmography, pharmacologic assessment of postganglionic sympathetic outflow, plasma norepinephrine, sympathetic skin response, video cinefluoroscopic swallowing test, esophageal manometry test, small bowel manometry test, wireless motility capsule test, urodynamic studies, penile plethysmography, intracavernosal papaverine injection, infrared video pupillography, corneal confocal microscopy, pupillary response to dilute pilocarpine and hydroxyamphetamine, Schirmer test, tear osmolarity test, and salivary secretion test. The protocol of each test is described in detail. This review can be used as a quick reference for the auxiliary autonomic tests.

High-intensity, whole-body exercise improves blood pressure control in individuals with spinal cord injury: A prospective randomized controlled trial.

Blood pressure regulation following spinal cord injury (SCI) is often compromised due to impaired vascular sympathetic control, leading to increased reliance on cardiovagal baroreflex sensitivity to maintain pressure. Whole-body exercise improves cardiovagal baroreflex sensitivity in uninjured individuals, though has not been explored in those with SCI. Our objective was to determine changes in cardiovagal baroreflex sensitivity following 6 months of high-intensity, whole-body exercise in individuals with SCI compared to lower-intensity, arms only exercise, or waitlist. This randomized controlled trial recruited individuals with SCI aged 18–40 years old. Sixty-one individuals were randomized, with 38 completing at least one cardiovagal baroreflex sensitivity assessment. Whole-body exercise was performed with hybrid functional electrical stimulation rowing prescribed as two to three times per week, for 30–60 minutes with a target heart rate of >75% of maximum. The arms only exercise group performed upper body rowing exercise with the same prescription as whole-body exercise. Waitlist controls were not enrolled in any explicit training regimen. After 6 months, those in arms only exercise or waitlist crossed over to whole-body exercise. Cardiovagal baroreflex sensitivity was assessed via the neck suction technique at baseline and at three-month intervals thereafter. Intention to treat analysis with a structured equation model demonstrated no significant effect of waitlist control or arms only exercise on cardiovagal baroreflex sensitivity. Whole-body exercise significantly improved cardiovagal baroreflex sensitivity at 6 months for those initially randomized (p = 0.03), as well as those who crossed over from arms only exercise or waitlist control (p = 0.03 for each). However, amount of exercise performed and aerobic gains (VO2max) each poorly correlated with increases in cardiovagal baroreflex sensitivity (R2<0.15). In post-hoc analyses, individuals with paraplegia made significantly greater gains in baroreflex sensitivity compared to those with tetraplegia (p = 0.02), though gains within this group were again poorly correlated to gains in aerobic capacity. Clinicaltrials.gov number NCT02139436.

Noiseless Variable-Pressure Neck Chamber Device to Assess the Carotid Baroreflex Function.

Background: The blood pressure responses to baroreflex perturbations can be assessed only using the variable-pressure neck chamber technique. However, the application of this approach in hospital environments is limited owing to the loud noise emitted during its operation. This study was aimed at developing a noiseless neck suction chamber device (NCD) that could stimulate the baroreceptors located in the carotid sinus in humans.Methods: A non-invasive device was developed to pressurize the carotid arteries externally. A microcontroller with a computer interface and neck chamber (3D-printed) was used. The anatomical neck chamber was fitted on six healthy, young, asymptomatic participants (five men; 32 ± 6 year), who were normotensive, nonsmoking, in sinus rhythm, free of known cardiovascular or metabolic diseases, and not consuming any acute or chronic medications. A suction of −60 mmHg was applied for 5 s, and the corresponding data were recorded. Before each study visit, the participants were instructed to abstain from caffeine, alcohol, and strenuous exercise for 12–24 h.Results: In all the trials, a significant reflex bradycardia (−10 ± 2 bpm) and depressor response (−15 ± 4 mmHg) to neck suction were observed, consistent with the results in the literature. The neck chamber device operated noiselessly [sound pressure level (SPL) of 34.3 dB] compared to a regular vacuum-cleaner-based system (74.6 dB).Conclusion: Using the proposed approach, consistent blood pressure and heart rate responses to carotid baroreflex hypertensive stimuli could be recorded, as in previous studies conducted using neck collar devices. Furthermore, the neck chamber device operated noiselessly and can thus be applied in hospital environments.

Noiseless Variable-Pressure Neck Chamber Device to Assess the Carotid Baroreflex Function

Background: The blood pressure responses to baroreflex perturbations can be assessed only using the variable-pressure neck chamber technique. However, the application of this approach in hospital environments is limited owing to the loud noise emitted during its operation. This study was aimed at developing a noiseless neck suction chamber device (NCD) that could stimulate the baroreceptors located in the carotid sinus in humans.Methods: A non-invasive device was developed to pressurize the carotid arteries externally. A microcontroller with a computer interface and neck chamber (3D-printed) was used. The anatomical neck chamber was fitted on six healthy, young, asymptomatic participants (five men; 32 ± 6 year), who were normotensive, nonsmoking, in sinus rhythm, free of known cardiovascular or metabolic diseases, and not consuming any acute or chronic medications. A suction of −60 mmHg was applied for 5 s, and the corresponding data were recorded. Before each study visit, the participants were instructed to abstain from caffeine, alcohol, and strenuous exercise for 12–24 h.Results: In all the trials, a significant reflex bradycardia (−10 ± 2 bpm) and depressor response (−15 ± 4 mmHg) to neck suction were observed, consistent with the results in the literature. The neck chamber device operated noiselessly [sound pressure level (SPL) of 34.3 dB] compared to a regular vacuum-cleaner-based system (74.6 dB).Conclusion: Using the proposed approach, consistent blood pressure and heart rate responses to carotid baroreflex hypertensive stimuli could be recorded, as in previous studies conducted using neck collar devices. Furthermore, the neck chamber device operated noiselessly and can thus be applied in hospital environments.

Carotid baroreflex control of central and peripheral hemodynamics during recovery after moderate leg cycling exercise.

This study aimed to examine the carotid baroreflex (CBR) control of the central and peripheral hemodynamics after exercise using the neck pressure (NP) and neck suction (NS) technique. Sixteen healthy young male participants (age: 27 ± 1.5 yr) were in a supine position for 30 min preexercise, followed by 60 min of cycling exercise, and then returned to a supine position for an additional 60 min postexercise. Both pre- and postexercise, the CBR-mediated responses of the central and peripheral hemodynamics were evaluated using 5-s periods of NP and NS (-60, -40, or +40 mmHg). As the central hemodynamics measurements, heart rate (HR), mean arterial pressure (MAP), cardiac output, and total vascular conductance were assessed. To determine peripheral circulation, vascular conductance in active and inactive limbs was measured. Eight participants [responder (RE) group] showed substantial postexercise hypotension (PEH) during recovery from exercise (Δ MAP: approximately -5 ± 0.9 mmHg, P < 0.05). The other eight participants did not display a reduction in MAP after exercise (non-RE group). In the non-RE group, the responsiveness of CBR-mediated changes in HR, MAP, and vascular conductance increased, particularly in response to -40 mmHg NS during postexercise compared with preexercise. However, in the RE group, any alterations in responsiveness to NP and NS were unchanged during PEH compared with preexercise. In conclusion, some normotensive individuals do not show PEH because the responsiveness of the CBR in central and peripheral hemodynamics following exercise is augmented, particularly to high blood pressure.NEW & NOTEWORTHY The carotid baroreflex (CBR) control of central and peripheral hemodynamics was investigated after exercise in both the presence and absence of postexercise hypotension (PEH). In individuals with no PEH, the responsiveness of CBR-mediated changes in all hemodynamics was augmented after exercise, particularly to high blood pressure; conversely, the CBR responsiveness remained unchanged in individuals with PEH. These findings provide insight into the mechanism of CBR control after exercise.

Ideal Drainage Output of Post-operative Neck Suction Drain

Ideal Drainage Output of Post-operative Neck Suction Drain

Interoceptive awareness, conditioned emotion and hypnotizability

Information processing, particularly of salient emotional stimuli, is influenced by cardiovascular afferent signals. Carotid baroreceptors signal the state of cardiovascular arousal to the brain, controlling blood pressure and heart rate via the baroreflex. Animal studies suggest a lateralization of this effect: Experimental stimulation of the right carotid sinus has a greater impact on heart rate when compared to left-sided stimulation. We tested, in humans, whether the processing of emotional information from faces was differentially affected by right versus left carotid afferents. To achieve so, we used an automated neck suction device to stimulate the carotid mechanoreceptors in the carotid sinus (parasympathetic pathway) synchronously with functional magnetic resonance imaging (fMRI) acquisition whilst participants were engaged in an emotional rating task of fearful and neutral faces. We showed that both right and left carotid stimulation (CS) influenced brain activity within opercular regions, although a stronger activation was observed within left insula during right stimulation compared to left stimulation. As regards the processing of fearful faces, right, but not left carotid stimulation attenuated the perceived intensity of fear, and (albeit to a lesser extent) enhanced intensity ratings of neutral faces. Mirroring the behavioural effects, there was a significant expression-by-stimulation interaction for right carotid stimulation only, when bilateral amygdala responses were attenuated to fear faces and amplified to neutral faces. Individual differences in basal heart rate variability (HRV) predicted the extent to which right carotid stimulation attenuated amygdala responses during fear processing. Our study provides unique evidence for lateralized viscerosensory effects on brain systems supporting emotional processing.

Interaction between graviception and carotid baroreflex function in humans during parabolic flight-induced microgravity.

The aim of the present study was to assess carotid baroreflex (CBR) function during acute changes in otolithic activity in humans. To address this question, we designed a set of experiments to identify the modulatory effects of microgravity on CBR function at a tilt angle of -2°, which was identified to minimize changes in central blood volume during parabolic flight. During parabolic flight at 0 and 1 g, CBR function curves were modeled from the heart rate (HR) and mean arterial pressure (MAP) responses to rapid pulse trains of neck pressure and neck suction ranging from +40 to -80 Torr; CBR control of HR (carotid-HR) and MAP (carotid-MAP) function curves, respectively. The maximal gain of both carotid-HR and carotid-MAP baroreflex function curves were augmented during microgravity compared with 1 g (carotid-HR, -0.53 to -0.80 beats·min-1·mmHg-1, P < 0.05; carotid-MAP, -0.24 to -0.30 mmHg/mmHg, P < 0.05). These findings suggest that parabolic flight-induced acute change of otolithic activity may modify CBR function and identifies that the vestibular system contributes to blood pressure regulation under fluctuations in gravitational forces. NEW & NOTEWORTHY The effect of acute changes in vestibular activity on arterial baroreflex function remains unclear. In the present study, we assessed carotid baroreflex function without changes in central blood volume during parabolic flight, which causes acute changes in otolithic activity. The sensitivity of both carotid heart rate and carotid mean arterial pressure baroreflex function was augmented in microgravity compared with 1 g, suggesting that the vestibular system contributes to blood pressure regulation in humans on Earth.

Identifying the role of group III/IV muscle afferents in the carotid baroreflex control of mean arterial pressure and heart rate during exercise.

We investigated the contribution of group III/IV muscle afferents to carotid baroreflex resetting during electrically evoked (no central command) and voluntary (requiring central command) isometric knee extension exercise. Lumbar intrathecal fentanyl was used to attenuate the central projection of μ-opioid receptor-sensitive group III/IV leg muscle afferent feedback. Spontaneous carotid baroreflex control was assessed by loading and unloading the carotid baroreceptors with a variable pressure neck chamber. Group III/IV muscle afferents did not influence spontaneous carotid baroreflex responsiveness at rest or during exercise. Afferent feedback accounted for at least 50% of the exercise-induced increase in the carotid baroreflex blood pressure and heart rate operating points, adjustments that are critical for an appropriate cardiovascular response to exercise. These findings suggest that group III/IV muscle afferent feedback is, independent of central command, critical for the resetting of the carotid baroreflex blood pressure and heart rate operating points, but not for spontaneous baroreflex responsiveness. This study sought to comprehensively investigate the role of metabolically and mechanically sensitive group III/IV muscle afferents in carotid baroreflex responsiveness and resetting during both electrically evoked (EVO, no central command) and voluntary (VOL, requiring central command) isometric single-leg knee-extension (15% of maximal voluntary contraction; MVC) exercise. Participants (n=8) were studied under control conditions (CTRL) and following lumbar intrathecal fentanyl injection (FENT) to inhibit μ-opioid receptor-sensitive lower limb muscle afferents. Spontaneous carotid baroreflex control of mean arterial pressure (MAP) and heart rate (HR) were assessed following rapid 5s pulses of neck pressure (NP, +40mmHg) or suction (NS, -60mmHg). Resting MAP (87±10mmHg) and HR (70±8bpm) were similar between CTRL and FENT conditions (P>0.4). In terms of spontaneous carotid baroreflex responsiveness, FENT did not alter the change in MAP or HR responses to NP (+13±5mmHg, P=0.85; +9±3bpm; P=0.99) or NS (-13±5mmHg, P=0.99; -24±11bpm; P=0.49) at rest or during either exercise protocol, which were of a remarkably similar magnitude to rest. In contrast, FENT administrationreduced the exercise-induced resetting of the operating point for MAP and HR during both EVO (116±10mmHg to 100±15mmHg and 93±14bpm to 82±10bpm) and VOL (107±13mmHg to 100±17mmHg and 89±10bpm to 72±10bpm) exercise bouts. Together, these findings document that group III/IV muscle afferent feedback is critical for the resetting of the carotid baroreflex MAP and HR operating points, independent of exercise-induced changes in central command, but not for spontaneous carotid baroreflex responsiveness.

Fear processing is differentially affected by lateralized stimulation of carotid baroreceptors

Information processing, particularly of salient emotional stimuli, is influenced by cardiovascular afferent signals. Carotid baroreceptors signal the state of cardiovascular arousal to the brain, controlling blood pressure and heart rate via the baroreflex. Animal studies suggest a lateralization of this effect: Experimental stimulation of the right carotid sinus has a greater impact on heart rate when compared to left-sided stimulation. We tested, in humans, whether the processing of emotional information from faces was differentially affected by right versus left carotid afferents. To achieve so, we used an automated neck suction device to stimulate the carotid mechanoreceptors in the carotid sinus (parasympathetic pathway) synchronously with functional magnetic resonance imaging (fMRI) acquisition whilst participants were engaged in an emotional rating task of fearful and neutral faces. We showed that both right and left carotid stimulation (CS) influenced brain activity within opercular regions, although a stronger activation was observed within left insula during right stimulation compared to left stimulation. As regards the processing of fearful faces, right, but not left carotid stimulation attenuated the perceived intensity of fear, and (albeit to a lesser extent) enhanced intensity ratings of neutral faces. Mirroring the behavioural effects, there was a significant expression-by-stimulation interaction for right carotid stimulation only, when bilateral amygdala responses were attenuated to fear faces and amplified to neutral faces. Individual differences in basal heart rate variability (HRV) predicted the extent to which right carotid stimulation attenuated amygdala responses during fear processing. Our study provides unique evidence for lateralized viscerosensory effects on brain systems supporting emotional processing.

Group III/IV muscle afferents contribute to carotid baroreflex resetting during evoked contractions in humans

BackgroundArterial baroreflexes play an important role in the control and regulation of the cardiovascular response to exercise. In fact, carotid baroreflex control of arterial blood pressure needs to be reset during exercise to tolerate the higher blood pressures associated with physical activities. This resetting of carotid baroreflex control to operate at a higher blood pressure during exercise is thought to be mediated by both feedback and feed forward mechanisms.PurposeTo investigate the contribution of group III/IV muscle afferents to the carotid baroreflex control during evoked quadriceps contractions, devoid of feed forward input (i.e. no central command).MethodsEight recreationally active males (29 ± 5 yrs) performed electrically evoked isometric quadriceps contractions for 10 min (femoral nerve stimulation, 40 Hz, 50‐s on, 10‐s off) under control conditions (CTRL) and following lumbar intrathecal fentanyl (FENT) injection to impair feedback from μ‐opioid receptor sensitive lower limb muscle afferents. Carotid baroreflex function was assessed by applying rapid 5‐s pulses of neck pressure (NP, +40 mmHg) or suction (NS, −60 mmHg) via a customized collar. Heart rate (HR) and mean arterial pressure (MAP) were derived from a 12‐lead ECG and a radial arterial catheter, respectively. The carotid baroreflex operating point was determined using the average pre‐stimulus values for HR and MAP.ResultsResting HR (~70 bpm) and MAP (~87 mmHg) were similar between CTRL and FENT conditions (P &gt; 0.4). FENT administration did not alter the cardiac response to NP (+9 ± 3 bpm; P = 0.99) or NS (−24 ± 11 bpm; P = 0.49) at rest. Similarly, FENT did not alter changes in MAP in response to NP (+13 ± 5 mmHg; P = 0.85) or NS (−13 ± 5 mmHg; P = 0.99) at rest. During exercise, FENT attenuated both HR (82 ± 10 bpm vs 93 ± 14 bpm; P &lt; 0.05) and MAP (100 ± 14 mmHg vs 112 ± 14 mmHg; P &lt; 0.05). However, similar to resting responses (P &gt; 0.4), the cardiac response to NP (+11 ± 4 bpm) or NS (−23 ± 9 bpm) was similar during CTRL and FENT exercise (P &gt; 0.5). Furthermore, changes in MAP in response to NP (+12 ± 4 mmHg) or NS (−14 ± 5 mmHg) were similar during CTRL and FENT exercise (P &gt; 0.4).ConclusionInhibition of group III/IV muscle afferents during evoked muscle contractions reduced the operating point for both HR and MAP, suggesting this feedback pathway is important for carotid baroreflex resetting during exercise. However, carotid baroreflex responsiveness at rest and during exercise was preserved despite muscle afferent blockade, indicating that group III/IV muscle afferents do not govern the carotid baroreflex control of HR and MAP.Support or Funding InformationThe authors were supported by National Heart, Lung, and Blood Institute grants (HL‐103786 and HL‐116579) and a Veterans Affairs Spire grant (E1572P).

Carotid baroreflex function at the onset of cycling in men.

Arterial baroreflex function is important for blood pressure control during exercise, but its contribution to cardiovascular adjustments at the onset of cycling exercise remains unclear. Fifteen healthy male subjects (24 ± 1 yr) performed 45-s trials of low- and moderate-intensity cycling, with carotid baroreceptor stimulation by neck suction at -60 Torr applied 0-5, 10-15, and 30-35 s after the onset of exercise. Cardiovascular responses to neck suction during cycling were compared with those obtained at rest. An attenuated reflex decrease in heart rate following neck suction was detected during moderate-intensity exercise, compared with the response at rest (P < 0.05). Furthermore, compared with the reflex decrease in blood pressure elicited at rest, neck suction elicited an augmented decrease in blood pressure at 0-5 and 10-15 s during low-intensity exercise and in all periods during moderate-intensity exercise (P < 0.05). The reflex depressor response at the onset of cycling was primarily mediated by an increase in the total vascular conductance. These findings evidence altered carotid baroreflex function during the first 35 s of cycling compared with rest, with attenuated bradycardic response, and augmented depressor response to carotid baroreceptor stimulation.

Carotid baroreflex control of heart rate is enhanced, while control of mean arterial pressure is preserved during whole body heat stress in young healthy men.

Whole body heat stress (WBH) results in numerous cardiovascular alterations that ultimately reduce orthostatic tolerance. While impaired carotid baroreflex (CBR) function during WBH has been reported as a potential reason for this decrement, study design considerations may limit interpretation of previous findings. We sought to test the hypothesis that CBR function is unaltered during WBH. CBR function was assessed in 10 healthy male subjects (age: 26 ± 3; height: 185 ± 7 cm; weight: 82 ± 10 kg; BMI: 24 ± 3 kg/m2; means ± SD) using 5-s trials of neck pressure (+45, +30, and +15 Torr) and neck suction (-20, -40, -60, and -80 Torr) during normothermia (NT) and passive WBH (Δ core temp ∼1°C). Analyses of stimulus response curves (four-parameter logistic model) for CBR control of heart rate (CBR-HR) and mean arterial pressure (CBR-MAP), as well as separate two-way ANOVA of the hypotensive and hypertensive stimuli (factor 1: thermal condition, factor 2: chamber pressure), were performed. For CBR-HR, maximal gain was increased during WBH (-0.73 ± 0.11) compared with NT (-0.39 ± 0.04, mean ± SE, P = 0.03). In addition, the CBR-HR responding range was increased during WBH (33 ± 5) compared with NT (19 ± 2 bpm, P = 0.03). Separate analysis of hypertensive stimulation revealed enhanced HR responses during WBH at -40, -60, and -80 Torr (condition × chamber pressure interaction, P = 0.049) compared with NT. For CBR-MAP, both logistic analysis and separate two-way ANOVA revealed no differences during WBH. Therefore, in response to passive WBH, CBR control of heart rate (enhanced) and arterial pressure (no change) is well preserved.

Impaired carotid baroreflex control of arterial blood pressure in multiple sclerosis.

Multiple sclerosis (MS), a progressive neurological disease, can lead to impairments in the autonomic control of cardiovascular function. We tested the hypothesis that individuals with relapsing-remitting MS (n = 10; 7 females, 3 males; 13 ± 4 yr from diagnosis) exhibit impaired carotid baroreflex control of blood pressure and heart rate compared with sex, age, and body weight-matched healthy individuals (CON: n = 10; 7 females, 3 males). At rest, 5-s trials of neck pressure (NP; +40 Torr) and neck suction (NS; -60 Torr) were applied to simulate carotid hypotension and hypertension, respectively, while mean arterial pressure (MAP; finger photoplethysmography), heart rate (HR), cardiac output (CO; Modelflow), and total vascular conductance (TVC) were continuously measured. In response to NP, there was a blunted increase in peak MAP responses (MS: 5 ± 2 mmHg) in individuals with MS compared with healthy controls (CON: 9 ± 3 mmHg; P = 0.005), whereas peak HR responses were not different between groups. At the peak MAP response to NP, individuals with MS demonstrated an attenuated decrease in TVC (MS, -10 ± 4% baseline vs. CON, -15 ± 4% baseline, P = 0.012), whereas changes in CO were similar between groups. Following NS, all cardiovascular responses (i.e., nadir MAP and HR and percent changes in CO and TVC) were not different between MS and CON groups. These data suggest that individuals with MS have impaired carotid baroreflex control of blood pressure via a blunted vascular conductance response resulting in a diminished ability to increase MAP in response to a hypotensive challenge.

Dynamic Carotid Baroreflex Function at the Onset of Leg Cycling

Carotid baroreflex (CBR) controls blood pressure (BP) by altering heart rate (HR), cardiac output (CO) and total vascular conductance (TVC) on a beat‐to‐beat basis at rest and during exercise. However, functional changes in CBR are known to occur during exercise. For example, the decrease in HR during CBR stimulation with neck suction (NS) is attenuated in the first 5 s of static handgrip exercise. In contrast, BP decrease by NS in the first 5 s of static handgrip exercise is similar to that obtained in resting conditions, and the decrease in both HR and BP by NS are similar to rest after 40 s of static handgrip exercise, evidencing a dynamic modulation of CBR control of HR at the onset of handgrip and a differential CBR control of HR and BP. Considering that regulatory mechanisms and physiological responses to exercise are affected by muscle mass, type and intensity of muscle contraction, we investigated whether CBR function is dynamically modulated during 45‐s leg cycling. Fifteen male healthy subjects (age: 24 ± 1 years (mean ± SEM); height: 182 ± 2 cm; weight: 74 ± 3 kg) were screened for CBR responsiveness at rest, using an adjustable collar around the anterior portion of the neck for application of 5‐s NS pulses at −60 mmHg. In addition, workloads for steady‐state low‐ (90 heart beats/min; LI) and moderate‐intensity (130 heart beats/min; MI) exercise at 60 rpm were determined by 3‐min cycling bouts. These workloads were used in a second visit, when subjects performed 45‐s LI and MI leg cycling bouts, without (CTRL) or with NS application during 0–5 s (NS 0–5), 10–15 s (NS 10–15) or 30–35 s (NS 30–35) after the onset of cycling. NS was applied at the end of a normal expiration. Each combination of exercise intensity and NS application was repeated for three exercise bouts and data were averaged for individual responses. Resting CBR was also assessed during a breath hold. Beat‐to‐beat HR (ECG) and BP (Finometer) were measured, stroke volume (SV) was obtained by Modelflow, CO and TVC were calculated (CO = HR SV; TVC = CO/BP), and the respiratory movements were monitored (Pneumobelt). Compared to CTRL cycling, reflex bradycardia was obtained at all exercising NS applications (P &lt; 0.05). The reflex response was small at NS 0–5 in both cycling intensities, as compared to resting NS (LI and MI: −7 ± 1 vs. Rest: −9 ± 1 beats/min; P &lt; 0.05). NS 10–15 and NS 30–35 in both cycling intensities resulted in bradycardia similar to resting NS (P &gt; 0.05). Transient BP decrease was observed at all exercising NS applications (P &lt; 0.05), compared to CTRL cycling. The NS‐induced BP decrease at NS 0–5 (LI and MI: −9 ± 1 mmHg) and NS 10–15 (LI and MI: −8 ± 1 mmHg) was significantly greater than at rest (−5 ± 1 mmHg; P &lt; 0.05 vs. NS 0–5 and NS 10–15). NS 30–35 in both cycling intensities resulted in BP decrease similar to resting NS (P &gt; 0.05). The NS‐induced exaggerated BP decrease during cycling was accompanied by a greater increase of TVC at NS 0–5 (LI: +13 ± 4; MI: +15 ± 3 mL/min/mmHg) and at NS 10–15 of MI cycling (+12 ± 2 mL/min/mmHg) than that obtained at rest (+3 ± 2 mL/min/mmHg; P &lt; 0.05), while the decrease in CO during NS was similar to rest (P &gt; 0.05). Cardiovascular responses to NS were similar between exercise intensities (P &gt; 0.05). A differential dynamic CBR control of HR and BP was detected in the transition from rest to cycling, i.e., CBR control of HR was blunted in the first 5 s, while CBR control of BP was exaggerated in the first 15 s cycling.Support or Funding InformationCAPES Foundation, Science without Borders Program, Brazil; Ehrenreich Fond, Denmark.