1
|
Iyer SH, Hinman JE, Warren T, Matthews SA, Simeone TA, Simeone KA. Altered ventilatory responses to hypercapnia-hypoxia challenges in a preclinical SUDEP model involve orexin neurons. Neurobiol Dis 2024; 199:106592. [PMID: 38971479 DOI: 10.1016/j.nbd.2024.106592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 06/25/2024] [Accepted: 07/02/2024] [Indexed: 07/08/2024] Open
Abstract
Failure to recover from repeated hypercapnia and hypoxemia (HH) challenges caused by severe GCS and postictal apneas may contribute to sudden unexpected death in epilepsy (SUDEP). Our previous studies found orexinergic dysfunction contributes to respiratory abnormalities in a preclinical model of SUDEP, Kcna1-/- mice. Here, we developed two gas challenges consisting of repeated HH exposures and used whole body plethysmography to determine whether Kcna1-/- mice have detrimental ventilatory responses. Kcna1-/- mice exhibited an elevated ventilatory response to a mild repeated hypercapnia-hypoxia (HH) challenge compared to WT. Moreover, 71% of Kcna1-/- mice failed to survive a severe repeated HH challenge, whereas all WT mice recovered. We next determined whether orexin was involved in these differences. Pretreating Kcna1-/- mice with a dual orexin receptor antagonist rescued the ventilatory response during the mild challenge and all subjects survived the severe challenge. In ex vivo extracellular recordings in the lateral hypothalamus of coronal brain slices, we found reducing pH either inhibits or stimulates putative orexin neurons similar to other chemosensitive neurons; however, a significantly greater percentage of putative orexin neurons from Kcna1-/-mice were stimulated and the magnitude of stimulation was increased resulting in augmentation of the calculated chemosensitivity index relative to WT. Collectively, our data suggest that increased chemosensitive activity of orexin neurons may be pathologic in the Kcna1-/- mouse model of SUDEP, and contribute to elevated ventilatory responses. Our preclinical data suggest that those at high risk for SUDEP may be more sensitive to HH challenges, whether induced by seizures or other means; and the depth and length of the HH exposure could dictate the probability of survival.
Collapse
Affiliation(s)
- Shruthi H Iyer
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA
| | - Jillian E Hinman
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA
| | - Ted Warren
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA
| | - Stephanie A Matthews
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA
| | - Timothy A Simeone
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA
| | - Kristina A Simeone
- Department of Pharmacology and Neuroscience, Creighton University School of Medicine, Omaha, NE 68178, USA.
| |
Collapse
|
2
|
Shafer BM, West CR, Foster GE. Advancements in the neurocirculatory reflex response to hypoxia. Am J Physiol Regul Integr Comp Physiol 2024; 327:R1-R13. [PMID: 38738293 DOI: 10.1152/ajpregu.00237.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 04/16/2024] [Accepted: 04/29/2024] [Indexed: 05/14/2024]
Abstract
Hypoxia is a pivotal factor in the pathophysiology of various clinical conditions, including obstructive sleep apnea, which has a strong association with cardiovascular diseases like hypertension, posing significant health risks. Although the precise mechanisms linking hypoxemia-associated clinical conditions with hypertension remains incompletely understood, compelling evidence suggests that hypoxia induces plasticity of the neurocirculatory control system. Despite variations in experimental designs and the severity, frequency, and duration of hypoxia exposure, evidence from animal and human models consistently demonstrates the robust effects of hypoxemia in triggering reflex-mediated sympathetic activation. Both acute and chronic hypoxia alters neurocirculatory regulation and, in some circumstances, leads to sympathetic outflow and elevated blood pressures that persist beyond the hypoxic stimulus. Dysregulation of autonomic control could lead to adverse cardiovascular outcomes and increase the risk of developing hypertension.
Collapse
Affiliation(s)
- Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Christopher R West
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| |
Collapse
|
3
|
Thrall SF, D'Souza AW, Abrahamson-Durant B, Vianna LC, Limberg JK, Macefield VG, Foster GE. A comparison of wavelet-based action potential detection from the NeuroAmp and the Iowa Bioengineering Nerve Traffic Analysis system. J Neurophysiol 2024; 131:1168-1174. [PMID: 38629146 DOI: 10.1152/jn.00448.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 03/25/2024] [Accepted: 04/12/2024] [Indexed: 06/01/2024] Open
Abstract
Microneurographic recordings of muscle sympathetic nerve activity (MSNA) reflect postganglionic sympathetic axonal activity directed toward the skeletal muscle vasculature. Recordings are typically evaluated for spontaneous bursts of MSNA; however, the filtering and integration of raw neurograms to obtain multiunit bursts conceals the underlying c-fiber discharge behavior. The continuous wavelet transform with matched mother wavelet has permitted the assessment of action potential discharge patterns, but this approach uses a mother wavelet optimized for an amplifier that is no longer commercially available (University of Iowa Bioengineering Nerve Traffic Analysis System; Iowa NTA). The aim of this project was to determine the morphology and action potential detection performance of mother wavelets created from the commercially available NeuroAmp (ADinstruments), from distinct laboratories, compared with a mother wavelet generated from the Iowa NTA. Four optimized mother wavelets were generated in a two-phase iterative process from independent datasets, collected by separate laboratories (one Iowa NTA, three NeuroAmp). Action potential extraction performance of each mother wavelet was compared for each of the NeuroAmp-based datasets. The total number of detected action potentials was not significantly different across wavelets. However, the predictive value of action potential detection was reduced when the Iowa NTA wavelet was used to detect action potentials in NeuroAmp data, but not different across NeuroAmp wavelets. To standardize approaches, we recommend a NeuroAmp-optimized mother wavelet be used for the evaluation of sympathetic action potential discharge behavior when microneurographic data are collected with this system.NEW & NOTEWORTHY The morphology of custom mother wavelets produced across laboratories using the NeuroAmp was highly similar, but distinct from the University of Iowa Bioengineering Nerve Traffic Analysis System. Although the number of action potentials detected was similar between collection systems and mother wavelets, the predictive value differed. Our data suggest action potential analysis using the continuous wavelet transform requires a mother wavelet optimized for the collection system.
Collapse
Affiliation(s)
- Scott F Thrall
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Andrew W D'Souza
- Division of Pulmonary Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Brendan Abrahamson-Durant
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Lauro C Vianna
- NeuroV̇ASQ̇ - Integrative Physiology Laboratory, Faculty of Physical Education, University of Brasília, Brasília, Brazil
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
| | - Vaughan G Macefield
- Department of Neuroscience, Monash University, Melbourne, Victoria, Australia
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| |
Collapse
|
4
|
Young DA, Jones PAT, Matenchuk BA, Sivak A, Davenport MH, Steinback CD. The effect of hyperoxia on muscle sympathetic nerve activity: a systematic review and meta-analysis. Clin Auton Res 2024; 34:233-252. [PMID: 38709357 DOI: 10.1007/s10286-024-01033-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Accepted: 04/09/2024] [Indexed: 05/07/2024]
Abstract
PURPOSE We conducted a meta-analysis to determine the effect of hyperoxia on muscle sympathetic nerve activity in healthy individuals and those with cardio-metabolic diseases. METHODS A comprehensive search of electronic databases was performed until August 2022. All study designs (except reviews) were included: population (humans; apparently healthy or with at least one chronic disease); exposures (muscle sympathetic nerve activity during hyperoxia or hyperbaria); comparators (hyperoxia or hyperbaria vs. normoxia); and outcomes (muscle sympathetic nerve activity, heart rate, blood pressure, minute ventilation). Forty-nine studies were ultimately included in the meta-analysis. RESULTS In healthy individuals, hyperoxia had no effect on sympathetic burst frequency (mean difference [MD] - 1.07 bursts/min; 95% confidence interval [CI] - 2.17, 0.04bursts/min; P = 0.06), burst incidence (MD 0.27 bursts/100 heartbeats [hb]; 95% CI - 2.10, 2.64 bursts/100 hb; P = 0.82), burst amplitude (P = 0.85), or total activity (P = 0.31). In those with chronic diseases, hyperoxia decreased burst frequency (MD - 5.57 bursts/min; 95% CI - 7.48, - 3.67 bursts/min; P < 0.001) and burst incidence (MD - 4.44 bursts/100 hb; 95% CI - 7.94, - 0.94 bursts/100 hb; P = 0.01), but had no effect on burst amplitude (P = 0.36) or total activity (P = 0.90). Our meta-regression analyses identified an inverse relationship between normoxic burst frequency and change in burst frequency with hyperoxia. In both groups, hyperoxia decreased heart rate but had no effect on any measure of blood pressure. CONCLUSION Hyperoxia does not change sympathetic activity in healthy humans. Conversely, in those with chronic diseases, hyperoxia decreases sympathetic activity. Regardless of disease status, resting sympathetic burst frequency predicts the degree of change in burst frequency, with larger decreases for those with higher resting activity.
Collapse
Affiliation(s)
- Desmond A Young
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Paris A T Jones
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Brittany A Matenchuk
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
- Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport, and Recreation, Women and Children's Health Research Institute, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Allison Sivak
- Geoffrey and Robyn Sperber Health Sciences Library, University of Alberta, Edmonton, AB, Canada
| | - Margie H Davenport
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
- Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport, and Recreation, Women and Children's Health Research Institute, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Craig D Steinback
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada.
| |
Collapse
|
5
|
Young BE, Padilla J, Shoemaker JK, Curry TB, Fadel PJ, Limberg JK. Sympathetic transduction to blood pressure during euglycemic-hyperinsulinemia in young healthy adults: role of burst amplitude. Am J Physiol Regul Integr Comp Physiol 2023; 324:R536-R546. [PMID: 36802950 PMCID: PMC10027119 DOI: 10.1152/ajpregu.00162.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 02/07/2023] [Accepted: 02/14/2023] [Indexed: 02/22/2023]
Abstract
Insulin acts centrally to stimulate sympathetic vasoconstrictor outflow to skeletal muscle and peripherally to promote vasodilation. Given these divergent actions, the "net effect" of insulin on the transduction of muscle sympathetic nerve activity (MSNA) into vasoconstriction and thus, blood pressure (BP) remains unclear. We hypothesized that sympathetic transduction to BP would be attenuated during hyperinsulinemia compared with baseline. In 22 young healthy adults, MSNA (microneurography), and beat-to-beat BP (Finometer or arterial catheter) were continuously recorded, and signal-averaging was performed to quantify the mean arterial pressure (MAP) and total vascular conductance (TVC; Modelflow) responses following spontaneous bursts of MSNA at baseline and during a euglycemic-hyperinsulinemic clamp. Hyperinsulinemia significantly increased MSNA burst frequency and mean burst amplitude (baseline: 46 ± 6 au; insulin: 65 ± 16 au, P < 0.001) but did not alter MAP. The peak MAP (baseline: 3.2 ± 1.5 mmHg; insulin: 3.0 ± 1.9 mmHg, P = 0.67) and nadir TVC (P = 0.45) responses following all MSNA bursts were not different between conditions indicating preserved sympathetic transduction. However, when MSNA bursts were segregated into quartiles based on their amplitudes at baseline and compared with similar amplitude bursts during hyperinsulinemia, the peak MAP and TVC responses were blunted (e.g., largest burst quartile: MAP, baseline: Δ4.4 ± 1.7 mmHg; hyperinsulinemia: Δ3.0 ± 0.8 mmHg, P = 0.02). Notably, ∼15% of bursts during hyperinsulinemia exceeded the size of any burst at baseline, yet the MAP/TVC responses to these larger bursts (MAP, Δ4.9 ± 1.4 mmHg) did not differ from the largest baseline bursts (P = 0.47). These findings indicate that increases in MSNA burst amplitude contribute to the overall maintenance of sympathetic transduction during hyperinsulinemia.
Collapse
Affiliation(s)
- Benjamin E Young
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas, United States
| | - Jaume Padilla
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
| | | | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Paul J Fadel
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas, United States
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| |
Collapse
|
6
|
Shafer BM, Nardone M, Incognito AV, Vermeulen TD, Teixeira AL, Millar PJ, Sheel AW, West C, Ayas N, Foster GE. Acute hypoxia elicits lasting reductions in the sympathetic action potential transduction of arterial blood pressure in males. J Physiol 2023; 601:669-687. [PMID: 36542455 DOI: 10.1113/jp283979] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 12/16/2022] [Indexed: 12/24/2022] Open
Abstract
Post-hypoxia sympathoexcitation does not elicit corresponding changes in vascular tone, suggesting diminished sympathetic signalling. Blunted sympathetic transduction following acute hypoxia, however, has not been confirmed and the effects of hypoxia on the sympathetic transduction of mean arterial pressure (MAP) as a function of action potential (AP) activity is unknown. We hypothesized that MAP changes would be blunted during acute hypoxia but restored in recovery and asynchronous APs would elicit smaller MAP changes than synchronous APs. Seven healthy males (age: 24 (3) years; BMI: 25 (3) kg/m2 ) underwent 20 min isocapnic hypoxia (PET O2 : 47 (2) mmHg) and 30 min recovery. Multi-unit microneurography (muscle sympathetic nerve activity; MSNA) and continuous wavelet transform with matched mother wavelet was used to detect sympathetic APs during baseline, hypoxia, early (first 7 min) and late (last 7 min) recovery. AP groups were classified as synchronous APs, asynchronous APs (occurring outside an MSNA burst) and no AP activity. Sympathetic transduction of MAP was quantified using signal-averaging, with ΔMAP tracked following AP group cardiac cycles. Following synchronous APs, ΔMAP was reduced in hypoxia (+1.8 (0.9) mmHg) and early recovery (+1.5 (0.7) mmHg) compared with baseline (+3.1 (2.2) mmHg). AP group-by-condition interactions show that at rest asynchronous APs attenuate MAP reductions compared with no AP activity (-0.4 (1.1) vs. -2.2 (1.2) mmHg, respectively), with no difference between AP groups in hypoxia, early or late recovery. Sympathetic transduction of MAP is blunted in hypoxia and early recovery. At rest, asynchronous sympathetic APs contribute to neural regulation of MAP by attenuating nadir pressure responses. KEY POINTS: Acute isocapnic hypoxia elicits lasting sympathoexcitation that does not correspond to parallel changes in vascular tone, suggesting blunted sympathetic transduction. Signal-averaging techniques track the magnitude and temporal cardiovascular responses following integrated muscle sympathetic nerve activity (MSNA) burst and non-burst cardiac cycles. However, this does not fully characterize the effects of sympathetic action potential (AP) activity on blood pressure control. We show that hypoxia blunts the sympathetic transduction of mean arterial pressure (MAP) following synchronous APs that form integrated MSNA bursts and that sympathetic transduction of MAP remains attenuated into early recovery. At rest, asynchronous APs attenuate the reduction in MAP compared with cardiac cycles following no AP activity, thus asynchronous sympathetic APs appear to contribute to the neural regulation of blood pressure. The results advance our understanding of sympathetic transduction of arterial pressure during and following exposure to acute isocapnic hypoxia in humans.
Collapse
Affiliation(s)
- Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Massimo Nardone
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada
| | - Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - André L Teixeira
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada
| | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada
| | - A William Sheel
- School of Kinesiology, University of British Columbia, Vancouver, Canada
| | - Chris West
- Faculty of Medicine, University of British Columbia, Kelowna, Canada.,International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, Canada.,Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, Canada.,Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada
| | - Najib Ayas
- Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| |
Collapse
|
7
|
Shafer BM, Incognito AV, Vermeulen TD, Nardone M, Teixeira AL, Klassen SA, Millar PJ, Foster GE. Action potential amplitude and baroreflex resetting of action potential clusters mediate hypoxia-induced sympathetic long-term facilitation. J Physiol 2022; 600:3127-3147. [PMID: 35661360 DOI: 10.1113/jp282933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Accepted: 05/03/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Acute isocapnic hypoxia resets the arterial baroreflex and permits long-lasting sympathoexcitation called sympathetic long-term facilitation. Our understanding of sympathetic long-term facilitation following hypoxia in humans is based on multiunit muscle sympathetic nerve activity and does not fully characterize the underlying baroreflex control of sympathetic neuronal subpopulations or their discharge/recruitment strategies. We show that sympathetic long-term facilitation is mediated by baroreflex resetting of sympathetic action potential clusters to higher arterial pressure operating points, a reduction in the percentage of action potentials firing asynchronously, and a shift toward larger amplitude action potential activity. The results advance our fundamental understanding of how the sympathetic nervous system mediates sympathetic long-term facilitation following exposure to acute isocapnic hypoxia in humans. ABSTRACT Baroreflex resetting permits sympathetic long-term facilitation (sLTF) following hypoxia; however, baroreflex control of action potential (AP) clusters and AP recruitment patterns facilitating sLTF is unknown. We hypothesized that baroreflex resetting of arterial pressure operating points (OPs) of AP clusters and recruitment of large-amplitude APs would mediate sLTF following hypoxia. Eight men (age: 24 (3) yrs; BMI: 24 (3) kg/m2 ) underwent 20-min isocapnic hypoxia (PET O2 : 47 (2) mmHg) and 30-min recovery. Multi-unit microneurography (muscle sympathetic nerve activity; MSNA) and a continuous wavelet transform with matched mother wavelet was used to detect sympathetic APs during baseline, hypoxia, early (first 5-min), and late recovery (last 5-min). AP amplitude (normalized to largest baseline AP amplitude), percent APs occurring outside a MSNA burst (% asynchronous APs), and proportion of APs firing in small (1-3), medium (4-6), and large (7-10) normalized cluster sizes was calculated. Normalized clusters were used to assess baroreflex OPs and sensitivity. Hypoxia increased total MSNA activity, which remained elevated during recovery (P<0.0001). Baroreflex OPs were shifted rightward for all clusters in recovery, with no effect on slope. Compared to baseline, AP amplitude was elevated by 3 (2) % and 4 (2) % while asynchronous APs were reduced by 9 (5) % and 7 (6) % in early and late recovery, respectively. In early recovery, the proportion of APs firing in large clusters was increased compared to baseline. Hypoxia-induced sLTF is mediated by baroreflex resetting of AP clusters to higher OPs, reduced asynchronous AP firing, and increased contribution from large-amplitude APs. Abstract figure legend Eight healthy men underwent 20-min isocapnic hypoxia and 30-min recovery. The study tested the hypothesis that baroreflex resetting of arterial pressure operating points (OPs) of action potential (AP) clusters and recruitment of large-amplitude APs would mediate sympathetic long-term facilitation (sLTF) following acute hypoxic exposure. Hypoxia increased multi-unit muscle sympathetic nerve activity (MSNA; measured via microneurography), which remained elevated throughout recovery. Sympathetic APs were detected in the filtered MSNA neurogram using a continuous wavelet transform with matched mother wavelet. An effect of condition revealed that compared to baseline, AP amplitude was elevated while asynchronous APs were reduced in early and late recovery, respectively. Our findings show that AP amplitude distributions are shifting towards larger AP amplitudes in all subjects following hypoxia. Our findings indicate that hypoxia-induced sLTF is mediated by baroreflex resetting of AP clusters to higher OPs, reduced asynchronous AP firing, and increased contribution from large-amplitude APs. This article is protected by copyright. All rights reserved.
Collapse
Affiliation(s)
- Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Massimo Nardone
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
| | - André L Teixeira
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
| | | | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| |
Collapse
|
8
|
Greenlund IM, Carter JR. Sympathetic neural responses to sleep disorders and insufficiencies. Am J Physiol Heart Circ Physiol 2022; 322:H337-H349. [PMID: 34995163 PMCID: PMC8836729 DOI: 10.1152/ajpheart.00590.2021] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Short sleep duration and poor sleep quality are associated with cardiovascular risk, and sympathetic nervous system (SNS) dysfunction appears to be a key contributor. The present review will characterize sympathetic function across several sleep disorders and insufficiencies in humans, including sleep deprivation, insomnia, narcolepsy, and obstructive sleep apnea (OSA). We will focus on direct assessments of sympathetic activation, e.g., plasma norepinephrine and muscle sympathetic nerve activity, but include heart rate variability (HRV) when direct assessments are lacking. The review also highlights sex as a key biological variable. Experimental models of total sleep deprivation and sleep restriction are converging to support several epidemiological studies reporting an association between short sleep duration and hypertension, especially in women. A systemic increase of SNS activity via plasma norepinephrine is present with insomnia and has also been confirmed with direct, regionally specific evidence from microneurographic studies. Narcolepsy is characterized by autonomic dysfunction via both HRV and microneurographic studies but with opposing conclusions regarding SNS activation. Robust sympathoexcitation is well documented in OSA and is related to baroreflex and chemoreflex dysfunction. Treatment of OSA with continuous positive airway pressure results in sympathoinhibition. In summary, sleep disorders and insufficiencies are often characterized by sympathoexcitation and/or sympathetic/baroreflex dysfunction, with several studies suggesting women may be at heightened risk.
Collapse
Affiliation(s)
- Ian M. Greenlund
- 1Department of Health and Human Development, Montana State University, Bozeman, Montana,2Department of Psychology, Montana State University, Bozeman, Montana
| | - Jason R. Carter
- 1Department of Health and Human Development, Montana State University, Bozeman, Montana,2Department of Psychology, Montana State University, Bozeman, Montana
| |
Collapse
|
9
|
Klassen SA, Joyner MJ, Baker SE. The impact of ageing and sex on sympathetic neurocirculatory regulation. Semin Cell Dev Biol 2021; 116:72-81. [PMID: 33468420 PMCID: PMC8282778 DOI: 10.1016/j.semcdb.2021.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 12/30/2020] [Accepted: 01/04/2021] [Indexed: 02/07/2023]
Abstract
The sympathetic nervous system represents a critical mechanism for homoeostatic blood pressure regulation in humans. This review focuses on age-related alterations in neurocirculatory regulation in men and women by highlighting human studies that examined the relationship between muscle sympathetic nerve activity (MSNA) acquired by microneurography and circulatory variables (e.g., blood pressure, vascular resistance). We frame this review with epidemiological evidence highlighting sex-specific patterns in age-related blood pressure increases in developed nations. Indeed, young women exhibit lower blood pressure than men, but women demonstrate larger blood pressure increases with age, such that by about age 60 years, blood pressure is greater in women. Sympathetic neurocirculatory mechanisms contribute to sex differences in blood pressure rises with age. Muscle sympathetic nerve activity increases with age in both sexes, but women demonstrate greater age-related increases. The circulatory adjustments imposed by MSNA - referred to as neurovascular transduction or autonomic (sympathetic) support of blood pressure - differ in men and women. For example, whereas young men demonstrate a positive relationship between resting MSNA and vascular resistance, this relationship is absent in young women due to beta-2 adrenergic vasodilation, which offsets alpha-adrenergic vasoconstriction. However, post-menopausal women demonstrate a positive relationship between MSNA and vascular resistance due to a decline in beta-2 adrenergic vasodilatory mechanisms. Emerging data suggest that greater aerobic fitness appears to modulate neurocirculatory regulation, at least in young, healthy men and women. This review also highlights recent advances in microneurographic recordings of sympathetic action potential discharge, which may nuance our understanding of age-related alterations in sympathetic neurocirculatory regulation in humans.
Collapse
Affiliation(s)
- Stephen A Klassen
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Michael J Joyner
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Sarah E Baker
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA.
| |
Collapse
|
10
|
Puri S, Panza G, Mateika JH. A comprehensive review of respiratory, autonomic and cardiovascular responses to intermittent hypoxia in humans. Exp Neurol 2021; 341:113709. [PMID: 33781731 PMCID: PMC8527806 DOI: 10.1016/j.expneurol.2021.113709] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/17/2021] [Accepted: 03/24/2021] [Indexed: 01/08/2023]
Abstract
This review explores forms of respiratory and autonomic plasticity, and associated outcome measures, that are initiated by exposure to intermittent hypoxia. The review focuses primarily on studies that have been completed in humans and primarily explores the impact of mild intermittent hypoxia on outcome measures. Studies that have explored two forms of respiratory plasticity, progressive augmentation of the hypoxic ventilatory response and long-term facilitation of ventilation and upper airway muscle activity, are initially reviewed. The role these forms of plasticity might have in sleep disordered breathing are also explored. Thereafter, the role of intermittent hypoxia in the initiation of autonomic plasticity is reviewed and the role this form of plasticity has in cardiovascular and hemodynamic responses during and following intermittent hypoxia is addressed. The role of these responses in individuals with sleep disordered breathing and spinal cord injury are subsequently addressed. Ultimately an integrated picture of the respiratory, autonomic and cardiovascular responses to intermittent hypoxia is presented. The goal of the integrated picture is to address the types of responses that one might expect in humans exposed to one-time and repeated daily exposure to mild intermittent hypoxia. This form of intermittent hypoxia is highlighted because of its potential therapeutic impact in promoting functional improvement and recovery in several physiological systems.
Collapse
Affiliation(s)
- Shipra Puri
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America
| | - Gino Panza
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America
| | - Jason H Mateika
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America; Department of Internal Medicine, Wayne State University School of Medicine, Detroit, MI 48201, United States of America.
| |
Collapse
|
11
|
Klassen SA, Shoemaker JK. Action potential subpopulations within human muscle sympathetic nerve activity: Discharge properties and governing mechanisms. Auton Neurosci 2020; 230:102743. [PMID: 33202287 DOI: 10.1016/j.autneu.2020.102743] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 11/01/2020] [Accepted: 11/02/2020] [Indexed: 12/21/2022]
Abstract
Sympathetic emissions directed towards the skeletal muscle circulation - muscle sympathetic nerve activity (MSNA) - represent a key mechanism for maintaining homeostasis and supporting human survival during physiological stress. Pulse-rhythmic bursts formed by the synchronous discharge of differently-sized sympathetic action potentials (APs) represent the primary characteristic of MSNA. Of the APs firing under baseline conditions (reflecting low-threshold c-fibre activity), a range of subpopulations exists, of which three general categories can be discussed based on their peak-to-peak amplitude in the filtered raw neurogram - small, medium, and large. These subpopulations express nonuniform discharge, recruitment, and synchronization patterns. The subpopulation of medium APs fires synchronously in most bursts, while the subpopulations of small and large APs fire less often. However, 30% of total AP discharge occurs asynchronously between sympathetic bursts, a pattern expressed most often by small APs. In response to physiological stress (e.g., baroreflex unloading), the subpopulation of medium APs exhibits the largest increase in firing probability and a subpopulation of previously-silent larger and faster-conducting APs (reflecting high-threshold c-fibre activity) becomes recruited. Heterogeneous discharge, synchronization, and recruitment thresholds among AP subpopulations stem from differential regulation within the sympathetic organization including the arterial baroreflex and paravertebral ganglia. Indeed, the arterial baroreflex strongly regulates medium APs at baseline and enhances its control over this subpopulation during periods of baroreflex unloading. Conversely, small and large APs express weak baroreflex control. Trimethaphan infusion has revealed that ganglionic processes including nicotinic and non-nicotinic mechanisms may contribute to heterogenous firing behaviours among low-threshold AP subpopulations. This review highlights recent work revealing new insight to the discharge properties expressed by, and mechanisms governing, AP subpopulations within human MSNA.
Collapse
Affiliation(s)
- Stephen A Klassen
- Neurovascular Research Laboratory, School of Kinesiology, University of Western Ontario, London, Ontario, Canada; Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - J Kevin Shoemaker
- Neurovascular Research Laboratory, School of Kinesiology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
| |
Collapse
|
12
|
Ott EP, Jacob DW, Baker SE, Holbein WW, Scruggs ZM, Shoemaker JK, Limberg JK. Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans. Am J Physiol Regul Integr Comp Physiol 2020; 318:R961-R971. [PMID: 32267729 DOI: 10.1152/ajpregu.00004.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence (P < 0.01), AP incidence (P = 0.01), and AP content per burst (P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once (P < 0.01) and more than once (P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH (P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst (P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.
Collapse
Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | | | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| |
Collapse
|