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White AJ, Boulet LM, Shafer BM, Vermeulen TD, Atwater TL, Stembridge M, Ainslie PN, Wilson RJA, Day TA, Foster GE. The coronary vascular response to the metaboreflex at low-altitude and during acute and prolonged high-altitude in males. J Appl Physiol (1985) 2022; 132:1327-1337. [PMID: 35482323 DOI: 10.1152/japplphysiol.00018.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Myocardial oxygen delivery is primarily regulated through changes in vascular tone to match increased metabolic demands. In males, activation of the muscle metaboreflex during acute isocapnic hypoxia results in a paradoxical coronary vasoconstriction. Whether coronary blood velocity is reduced by metaboreflex activation following travel and/or adaptation to high-altitude is unknown. This study determined if the response of the coronary vasculature to muscle metaboreflex activation at low-altitude differs from acute (1/2 days) and prolonged (8/9 days) high-altitude. Healthy males (n=16) were recruited and performed isometric handgrip exercise (30 % max) followed by post-exercise circulatory occlusion (PECO) to isolate the muscle metaboreflex at low-altitude and following acute and prolonged high-altitude (3,800 m). Mean left anterior descending coronary artery blood velocity (LADvmean, transthoracic Doppler echocardiography), heart rate, mean arterial pressure (MAP), ventilation, and respired gases were assessed during baseline and PECO at all time-points. Coronary vascular conductance index (CVCi) was calculated as LADVmean/MAP. The change in LADvmean (acute altitude: -1.7 ± 3.9 cm/s, low-altitude: 2.6 ± 3.4 cm/s, P = 0.01) and CVCi (acute altitude: -0.05 ± 0.04 cm/s/mmHg, low-altitude: -0.01 ± 0.03 cm/s/mmHg, P = 0.005) induced by PECO differed significantly between acute high-altitude and low-altitude. The change in LADVmean and CVCi induced by PECO following prolonged high-altitude was not different from low-altitude. Our results suggest that coronary vasoconstriction with metaboreflex activation in males is greatest following acute ascent to high-altitude and restored to low-altitude levels following 8-9 days of acclimatization.
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Affiliation(s)
- Austin J White
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Taylor L Atwater
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Glen Edward Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
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2
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Boulet LM, Atwater TL, Brown CV, Shafer BM, Vermeulen TD, Cotton PC, Day TA, Foster GE. Sex differences in the coronary vascular response to combined chemoreflex and metaboreflex stimulation in healthy humans. Exp Physiol 2021; 107:16-28. [PMID: 34788486 DOI: 10.1113/ep090034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 11/08/2021] [Indexed: 12/18/2022]
Abstract
NEW FINDINGS What is the central question of this study? Coronary blood flow in healthy humans is controlled by both local metabolic signalling and adrenergic activity: does the integration of these signals during acute hypoxia and adrenergic activation differ between sexes? What are the main findings and its importance? Both males and females exhibit an increase in coronary blood velocity in response to acute hypoxia, a response that is constrained by adrenergic stimulation in males but not females. These findings suggest that coronary blood flow control differs between males and females. ABSTRACT Coronary hyperaemia is mediated through multiple signalling pathways, including local metabolic messengers and adrenergic stimulation. This study aimed to determine whether the coronary vascular response to adrenergic stressors is different between sexes in normoxia and hypoxia. Young, healthy participants (n = 32; 16F) underwent three randomized trials of isometric handgrip exercise followed by post-exercise circulatory occlusion (PECO) to activate the muscle metaboreflex. End-tidal P O 2 was controlled at (1) normoxic levels throughout the trial, (2) 50 mmHg for the duration of the trial (hypoxia trial), or (3) 50 mmHg only during PECO (mixed trial). Mean left anterior descending coronary artery velocity (LADVmean ; transthoracic Doppler echocardiography), heart rate and blood pressure were assessed at baseline and during PECO. In normoxia, there was no change in LADVmean or cardiac workload induced by PECO in males and females. Acute hypoxia increased baseline LADVmean to a greater extent in males compared with females (P < 0.05), despite a similar increase in cardiac workload. The change in LADVmean induced by PECO was similar between sexes in normoxia (P = 0.31), greater in males during the mixed trial (male: 12.8 (7.7) cm/s vs. female: 8.1 (6.3) cm/s; P = 0.02) and reduced in males but not females in acute hypoxia (male: -4.8 (4.5) cm/s vs. female: 0.8 (6.2) cm/s; P = 0.006). In summary, sex differences in the coronary vasodilatory response to hypoxia were observed, and metaboreflex activation during hypoxia caused a paradoxical reduction in coronary blood velocity in males but not females.
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Affiliation(s)
- Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Taylor L Atwater
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Courtney V Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Paul C Cotton
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
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Ewalts M, Dawkins T, Boulet LM, Thijssen D, Stembridge M. The influence of increased venous return on right ventricular dyssynchrony during acute and sustained hypoxaemia. Exp Physiol 2020; 106:925-937. [PMID: 33369788 DOI: 10.1113/ep088657] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 12/19/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Right ventricular dyssynchrony is a marker of function that is elevated in healthy individuals exposed to acute hypoxia, but does it remain elevated during sustained exposure to high altitude hypoxia, and can it be normalised by augmenting venous return? What is the main finding and its importance? For the first time it is demonstrated that (i) increasing venous return in acute hypoxia restores the synchrony of right ventricular contraction and (ii) dyssynchrony is evident after acclimatisation to high altitude, and remains sensitive to changes in venous return. Therefore, the interpretation of right ventricular dyssynchrony requires consideration the prevailing haemodynamic state. ABSTRACT Regional heterogeneity in timing of right ventricular (RV) contraction (RV dyssynchrony; RVD) occurs when pulmonary artery systolic pressure (PASP) is increased during acute hypoxia. Interestingly, RVD is not observed during exercise, a stimulus that increases both PASP and venous return. Therefore, we hypothesised that RVD in healthy humans is sensitive to changes in venous return, and examined whether (i) increasing venous return in acute hypoxia lowers RVD and (ii) if RVD is further exaggerated in sustained hypoxia, given increased PASP is accompanied by decreased ventricular filling at high altitude. RVD, PASP and right ventricular end-diastolic area (RVEDA) were assessed using transthoracic two-dimensional and speckle-tracking echocardiography during acute normobaric hypoxia ( F i O 2 = 0.12) and sustained exposure (5-10 days) to hypobaric hypoxia (3800 m). Venous return was augmented with lower body positive pressure at sea level (LBPP; +10 mmHg) and saline infusion at high altitude. PASP was increased in acute hypoxia (20 ± 6 vs. 28 ± 7, P < 0.001) concomitant to an increase in RVD (18 ± 7 vs. 38 ± 10, P < 0.001); however, the addition of LBPP during hypoxia decreased RVD (38 ± 0 vs. 26 ± 10, P < 0.001). Sustained hypoxia increased PASP (20 ± 4 vs. 26 ± 5, P = 0.008) and decreased RVEDA (24 ± 4 vs. 21 ± 2, P = 0.042), with RVD augmented (14 ± 5 vs. 31 ± 12, P = 0.001). Saline infusion increased RVEDA (21 ± 2 vs. 23 ± 3, P = 0.008) and reduced RVD (31 ± 12 vs. 20 ± 9, P = 0.001). In summary, an increase in PASP secondary to acute and sustained exposure to hypoxia augments RVD, which can be at least partly reduced via increased venous return.
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Affiliation(s)
- Michiel Ewalts
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK.,Department of Physiology, Radboudumc, Nijmegen, The Netherlands
| | - Tony Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Lindsey M Boulet
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
| | - Dick Thijssen
- Department of Physiology, Radboudumc, Nijmegen, The Netherlands
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
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Hovgaard HL, Nielsen RR, Laursen CB, Frederiksen CA, Juhl-Olsen P. When appearances deceive: Echocardiographic changes due to common chest pathology. Echocardiography 2018; 35:1847-1859. [PMID: 30338539 DOI: 10.1111/echo.14163] [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: 07/19/2018] [Revised: 09/07/2018] [Accepted: 09/14/2018] [Indexed: 11/29/2022] Open
Abstract
Most indications for performing echocardiography focus on the evaluation of properties intrinsic to the heart. However, numerous extra-cardiac conditions indirectly convey changes to the echocardiographic appearance through alterations in the governing physiology. Pulmonary embolism increases pulmonary arterial pressure if a sufficient cross-sectional area of the pulmonary vascular bed is occluded. This may result in dilatation of the right ventricle and, in severe cases, concomitant early diastolic septal collapse into the left ventricle. Acute respiratory failure has been shown to yield a similar echocardiographic appearance in experimental conditions due to the resultant pulmonary vasoconstriction. Echocardiography in the presence of pulmonary disease can reveal underlying cardiac pathologies such as pulmonary hypertension that contribute to the clinical severity of respiratory distress. Positive pressure ventilation affects preload, afterload, and compliance of both ventricles. The echocardiographic net result cannot be uniformly anticipated, but provides information on the deciding physiology or pathophysiology. Mediastinal pathology including tumors, herniation of abdominal content, and pleural effusion can often be visualized directly with echocardiography. Mediastinal pathologies adjacent to the heart may compress the myocardium directly, thus facilitating echocardiographic and clinical signs of tamponade in the absence of pericardial effusion. In conclusion, many pathologies of extra-cardiac origin influence the echocardiographic appearance of the heart. These changes do not reflect properties of the myocardium but may well be mistaken for it. Hence, these conditions are essential knowledge to all physicians performing echocardiography across the spectrum from advanced cardiological diagnostics to rapid point-of-care focused cardiac ultrasonography.
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Affiliation(s)
- Henrik Lynge Hovgaard
- Department of Cardiology, Aalborg University Hospital, Aalborg, Denmark.,Department of Anaesthesiology & Intensive Care, Aarhus University Hospital, Aarhus N, Denmark
| | - Roni Ranghøj Nielsen
- Department of Cardiology, Aarhus University Hospital, Aarhus N, Denmark.,Department of Clinical Medicine, Aarhus University, Aarhus N, Denmark
| | - Christian B Laursen
- Department of Respiratory Medicine, Odense University Hospital, Odense, Denmark
| | | | - Peter Juhl-Olsen
- Department of Anaesthesiology & Intensive Care, Aarhus University Hospital, Aarhus N, Denmark.,Department of Clinical Medicine, Aarhus University, Aarhus N, Denmark
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Vermeulen TD, Boulet LM, Stembridge M, Williams AM, Anholm JD, Subedi P, Gasho C, Ainslie PN, Feigl EO, Foster GE. Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans. Am J Physiol Heart Circ Physiol 2018; 315:H132-H140. [PMID: 29600897 DOI: 10.1152/ajpheart.00689.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial Po2 and Pco2 or if coronary vascular responses are the result of concomitant increases in myocardial O2 consumption/demand ([Formula: see text]). We hypothesized that the coronary vascular response to Po2 and Pco2 would be attenuated in healthy men when [Formula: see text] was attenuated with β1-adrenergic receptor blockade. Healthy men (age: 25 ± 1 yr, n = 11) received intravenous esmolol (β1-adrenergic receptor antagonist) or volume-matched saline in a double-blind, randomized crossover study and were exposed to poikilocapnic hypoxia, isocapnic hypoxia, and hypercapnic hypoxia. Measurements made at baseline and after 5 min of steady state at each gas manipulation included left anterior descending coronary blood velocity (LADV; Doppler echocardiography), heart rate, and arterial blood pressure. LADV values at the end of each hypoxic condition were compared between esmolol and placebo. The rate-pressure product (RPP) and left ventricular mechanical energy (MELV) were calculated as indexes of [Formula: see text]. All gas manipulations augmented RPP, MELV, and LADV, but only RPP and MELV were attenuated (4-18%) after β1-adrenergic receptor blockade ( P < 0.05). Despite attenuated RPP and MELV responses, β1-adrenergic receptor blockade did not attenuate the mean LADV vasodilatory response compared with placebo during poikilocapnic hypoxia (29.4 ± 2.2 vs. 27.3 ± 1.6 cm/s) and isocapnic hypoxia (29.5 ± 1.5 vs. 30.3 ± 2.2 cm/s). Hypercapnic hypoxia elicited a feedforward coronary dilation that was blocked by β1-adrenergic receptor blockade. These results indicate a direct influence of arterial Po2 on coronary vascular regulation that is independent of [Formula: see text]. NEW & NOTEWORTHY In humans, arterial hypoxemia led to an increase in epicardial coronary artery blood velocity. β1-Adrenergic receptor blockade did not diminish the hypoxemic coronary response despite reduced myocardial O2 demand. These data indicate hypoxemia can regulate coronary blood flow independent of myocardial O2 consumption. A plateau in the mean left anterior descending coronary artery blood velocity-rate-pressure product relationship suggested β1-adrenergic receptor-mediated, feedforward epicardial coronary artery dilation. In addition, we observed a synergistic effect of Po2 and Pco2 during hypercapnic hypoxia.
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Affiliation(s)
- Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Alexandra M Williams
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | | | | | - Chris Gasho
- Loma Linda University , Loma Linda, California
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Eric O Feigl
- Department of Physiology and Biophysics, University of Washington , Seattle, Washington
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
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van Mil ACCM, Tymko MM, Kerstens TP, Stembridge M, Green DJ, Ainslie PN, Thijssen DHJ. Similarity between carotid and coronary artery responses to sympathetic stimulation and the role of α 1-receptors in humans. J Appl Physiol (1985) 2018; 125:409-418. [PMID: 29565771 DOI: 10.1152/japplphysiol.00386.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Carotid artery (CCA) dilation occurs in healthy subjects during cold pressor test (CPT), while the magnitude of dilation relates to cardiovascular risk. To further explore this phenomenon and mechanism, we examined carotid artery responses to different sympathetic tests, with and without α1-receptor blockade and assessed similarity to these responses between carotid and coronary arteries. In randomized order, 10 healthy participants (25 ± 3 yr) underwent sympathetic stimulation using the CPT (3-min left-hand immersion in ice-slush) and lower-body negative pressure (LBNP). Before and during sympathetic tests, CCA diameter and velocity (Doppler ultrasound) and left anterior descending (LAD) coronary artery velocity (echocardiography) were recorded across 3 min. Measures were repeated 90 min following selective α1-receptor blockade via oral prazosin (0.05 mg/kg body wt). CPT significantly increased CCA diameter, LAD maximal velocity, and velocity-time integral area-under-the-curve (all P < 0.05). In contrast, LBNP resulted in a decrease in CCA diameter, LAD maximal velocity, and velocity time integral (VTI; all P < 0.05). Following α1-receptor blockade, CCA and LAD velocity responses to CPT were diminished. In contrast, during LBNP (-30 mmHg), α1-receptor blockade did not alter CCA or LAD responses. Finally, changes in CCA diameter and LAD VTI responses to sympathetic stimulation were positively correlated ( r = 0.66, P < 0.01). We found distinct carotid artery responses to different tests of sympathetic stimulation, where α1 receptors partly contribute to CPT-induced responses. Finally, we found agreement between carotid and coronary artery responses. These data indicate similarity between carotid and coronary responses to sympathetic tests and the role of α1 receptors that is dependent on the nature of the sympathetic challenge. NEW & NOTEWORTHY We showed distinct carotid artery responses to cold pressor test (CPT; i.e., dilation) and lower-body negative pressure (LBNP; i.e., constriction). Blockade of α1-receptors significantly attenuated dilator responses in carotid and coronary arteries during CPT, while no changes were found during LBNP. Our findings indicate strong similarity between carotid and coronary artery responses to distinct sympathetic stimuli, and for the role of α-receptors.
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Affiliation(s)
- Anke C C M van Mil
- Department of Physiology, Radboudumc, Nijmegen , The Netherlands.,Research Institute for Sport and Exercise Sciences, Liverpool John Moores University , Liverpool , United Kingdom
| | - Michael M Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna , Canada
| | - Thijs P Kerstens
- Department of Physiology, Radboudumc, Nijmegen , The Netherlands
| | - Mike Stembridge
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna , Canada.,Cardiff School of Sport, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Daniel J Green
- School of Sports Science, Exercise and Health, the University of Western Australia , Nedlands , Australia
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna , Canada
| | - Dick H J Thijssen
- Department of Physiology, Radboudumc, Nijmegen , The Netherlands.,Research Institute for Sport and Exercise Sciences, Liverpool John Moores University , Liverpool , United Kingdom
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