1
|
Dorff A, Bradford C, Hunsaker A, Atkinson J, Rhees J, Leach OK, Gifford JR. Vascular dysfunction and the age-related decline in critical power. Exp Physiol 2024; 109:240-254. [PMID: 37934136 PMCID: PMC10988715 DOI: 10.1113/ep091571] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 10/18/2023] [Indexed: 11/08/2023]
Abstract
Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1 ± 2.5 years) and 10 younger (24.4 ± 4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (PGXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10 W, 20 W, slightly below CP (90% CP) and PGXT . Despite not differing in leg lean mass (P = 0.901) and physical activity (e.g., steps per day, P = 0.735), older subjects had ∼30% lower mass-specific CP (old = 3.20 ± 0.94 W kg-1 vs. young = 4.60 ± 0.87 W kg-1 ; P < 0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20 W, 90% CP and PGXT (P < 0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R2 = 0.52; P < 0.001) and vascular conductance during knee-extension exercise at 20 W (R2 = 0.34; P = 0.014) and 90% CP (R2 = 0.39; P = 0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function.
Collapse
Affiliation(s)
- Abigail Dorff
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
- Program of GerontologyBrigham Young UniversityProvoUtahUSA
| | - Christy Bradford
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
| | - Ashley Hunsaker
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
| | - Jake Atkinson
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
| | - Joshua Rhees
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
| | - Olivia K. Leach
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
- Program of GerontologyBrigham Young UniversityProvoUtahUSA
| | - Jayson R. Gifford
- Department of Exercise SciencesBrigham Young UniversityProvoUtahUSA
- Program of GerontologyBrigham Young UniversityProvoUtahUSA
| |
Collapse
|
2
|
Karimpour P, May JM, Kyriacou PA. Photoplethysmography for the Assessment of Arterial Stiffness. SENSORS (BASEL, SWITZERLAND) 2023; 23:9882. [PMID: 38139728 PMCID: PMC10747425 DOI: 10.3390/s23249882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 12/08/2023] [Accepted: 12/13/2023] [Indexed: 12/24/2023]
Abstract
This review outlines the latest methods and innovations for assessing arterial stiffness, along with their respective advantages and disadvantages. Furthermore, we present compelling evidence indicating a recent growth in research focused on assessing arterial stiffness using photoplethysmography (PPG) and propose PPG as a potential tool for assessing vascular ageing in the future. Blood vessels deteriorate with age, losing elasticity and forming deposits. This raises the likelihood of developing cardiovascular disease (CVD), widely reported as the global leading cause of death. The ageing process induces structural modifications in the vascular system, such as increased arterial stiffness, which can cause various volumetric, mechanical, and haemodynamic alterations. Numerous techniques have been investigated to assess arterial stiffness, some of which are currently used in commercial medical devices and some, such as PPG, of which still remain in the research space.
Collapse
Affiliation(s)
| | | | - Panicos A. Kyriacou
- Research Centre for Biomedical Engineering, City, University of London, London EC1V 0HB, UK; (P.K.); (J.M.M.)
| |
Collapse
|
3
|
Pedrinolla A, Magliozzi R, Colosio AL, Danese E, Gelati M, Rossi S, Pogliaghi S, Calabrese M, Muti E, Cè E, Longo S, Esposito F, Lippi G, Schena F, Venturelli M. Repeated passive mobilization to stimulate vascular function in individuals of advanced age who are chronically bedridden. A randomized controlled trial. J Gerontol A Biol Sci Med Sci 2021; 77:588-596. [PMID: 34036337 DOI: 10.1093/gerona/glab148] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Vascular dysfunction and associated disorders are major side effects of chronic bed rest, yet passive mobilization as a potential treatment has only been theorized so far. This study investigated the effects of passive mobilization treatment on vascular function in older, chronically bedridden people. METHODS The study sample was 45 chronically bedridden people of advanced age (mean age 87 years; 56% female; mean bed rest 4 years) randomly assigned to a treatment (n=23) or a control group (CTRL, n=22). The treatment group received passive mobilization twice daily (30 min, 5 times/week) for 4 weeks. A kinesiologist performed passive mobilization by passive knee flexion/extension at 1 Hz in one leg (treated leg, T-leg vs ctrl-leg). The CTRL group received routine treatment. The primary outcome was changes in peak blood flow (∆Peak) as measured with the single passive leg movement test (sPLM) at the common femoral artery. RESULTS ∆Peak was increased in both legs in the Treatment group (+90.9 ml/min, p<0.001, in T-leg and +25.7 ml/min, p=0.039 in ctrl-leg). No difference in peak blood flow after routine treatment was found in the CTRL group. CONCLUSION Improvement in vascular function after 4 weeks of passive mobilization was recorded in the treatment group. Passive mobilization may be advantageously included in standard clinical practice as an effective strategy to treat vascular dysfunction in persons with severely limited mobility.
Collapse
Affiliation(s)
- Anna Pedrinolla
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Roberta Magliozzi
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Alessandro L Colosio
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Elisa Danese
- Department of Life and Reproduction Sciences, Laboratory of Clinical Biochemistry, University of Verona, Verona, Italy
| | - Matteo Gelati
- Department of Life and Reproduction Sciences, Laboratory of Clinical Biochemistry, University of Verona, Verona, Italy
| | - Stefania Rossi
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Silvia Pogliaghi
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Massimiliano Calabrese
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | | | - Emiliano Cè
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.,IRCSS Galeazzi Orthopaedic Institute, Milano, Italy
| | - Stefano Longo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Fabio Esposito
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.,IRCSS Galeazzi Orthopaedic Institute, Milano, Italy
| | - Giuseppe Lippi
- Department of Life and Reproduction Sciences, Laboratory of Clinical Biochemistry, University of Verona, Verona, Italy
| | - Federico Schena
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy
| | - Massimo Venturelli
- Department of Neuroscience, Biomedicine, and Movement Science, Section of Movement Science, University of Verona, Verona, Italy.,Department of Internal Medicine section of Geriatrics, University of Utah, Salt Lake City, UT, USA
| |
Collapse
|
4
|
Hoopes EK, Berube FR, D'Agata MN, Patterson F, Farquhar WB, Edwards DG, Witman MAH. Sleep duration regularity, but not sleep duration, is associated with microvascular function in college students. Sleep 2021; 44:5903410. [PMID: 32905591 DOI: 10.1093/sleep/zsaa175] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 07/28/2020] [Indexed: 12/16/2022] Open
Abstract
STUDY OBJECTIVES Vascular dysfunction is a hypothesized mechanism linking poor sleep habits to an increased incidence of cardiovascular diseases (CVDs). However, the vascular profile associated with free-living sleep duration and sleep regularity has not been well elucidated, particularly in young adults. Thus, this study aimed to evaluate the associations between mean sleep duration, regularity in sleep duration, and peripheral vascular function in young adult college students. METHODS Fifty-one healthy undergraduate students (20 ± 1 years) completed 14 days of 24-hour wrist actigraphy and subsequent vascular assessments. Macrovascular function was measured using brachial artery flow-mediated dilation (FMD) while microvascular function was measured via passive leg movement (PLM). RESULTS Mean sleep duration was unrelated to FMD and PLM. Conversely, more irregular sleep duration (14-day sleep duration standard deviation [SD]) was unfavorably associated with all three measures of PLM-induced hyperemia (peak leg blood flow [LBF], p = 0.01; change in LBF from baseline to peak, p < 0.01; LBF area under the curve, p < 0.01), and remained significant in regression models which adjusted for sex, body mass index, blood pressure, physical activity, alcohol and caffeine consumption, and sleep duration (all p < 0.05). When using a median split to dichotomize "low" and "high" sleep duration SD groups, those demonstrating high variability in sleep duration exhibited ~45% lower PLM responses compared with those demonstrating low variability. CONCLUSIONS Irregular sleep duration is associated with poorer microvascular function as early as young adulthood. These findings support the growing body of evidence that irregular sleep patterns may be an independent and modifiable risk factor for CVD.
Collapse
Affiliation(s)
- Elissa K Hoopes
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| | - Felicia R Berube
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| | - Michele N D'Agata
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| | - Freda Patterson
- Department of Behavioral Health and Nutrition, College of Health Sciences, University of Delaware, Newark, DE
| | - William B Farquhar
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| | - David G Edwards
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| | - Melissa A H Witman
- Department of Kinesiology and Applied Physiology, College of Health Sciences, University of Delaware, Newark, DE
| |
Collapse
|
5
|
Trinity JD, Kwon OS, Broxterman RM, Gifford JR, Kithas AC, Hydren JR, Jarrett CL, Shields KL, Bisconti AV, Park SH, Craig JC, Nelson AD, Morgan DE, Jessop JE, Bledsoe AD, Richardson RS. The role of the endothelium in the hyperemic response to passive leg movement: looking beyond nitric oxide. Am J Physiol Heart Circ Physiol 2020; 320:H668-H678. [PMID: 33306447 DOI: 10.1152/ajpheart.00784.2020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Passive leg movement (PLM) evokes a robust and predominantly nitric oxide (NO)-mediated increase in blood flow that declines with age and disease. Consequently, PLM is becoming increasingly accepted as a sensitive assessment of endothelium-mediated vascular function. However, a substantial PLM-induced hyperemic response is still evoked despite nitric oxide synthase (NOS) inhibition. Therefore, in nine young healthy men (25 ± 4 yr), this investigation aimed to determine whether the combination of two potent endothelium-dependent vasodilators, specifically prostaglandin (PG) and endothelium-derived hyperpolarizing factor (EDHF), account for the remaining hyperemic response to the two variants of PLM, PLM (60 movements) and single PLM (sPLM, 1 movement), when NOS is inhibited. The leg blood flow (LBF, Doppler ultrasound) response to PLM and sPLM following the intra-arterial infusion of NG-monomethyl-l-arginine (l-NMMA), to inhibit NOS, was compared to the combined inhibition of NOS, cyclooxygenase (COX), and cytochrome P-450 (CYP450) by l-NMMA, ketorolac tromethamine (KET), and fluconazole (FLUC), respectively. NOS inhibition attenuated the overall LBF [area under the curve (LBFAUC)] response to both PLM (control: 456 ± 194, l-NMMA: 168 ± 127 mL, P < 0.01) and sPLM (control: 185 ± 171, l-NMMA: 62 ± 31 mL, P = 0.03). The combined inhibition of NOS, COX, and CYP450 (i.e., l-NMMA+KET+FLUC) did not further attenuate the hyperemic responses to PLM (LBFAUC: 271 ± 97 mL, P > 0.05) or sPLM (LBFAUC: 72 ± 45 mL, P > 0.05). Therefore, PG and EDHF do not collectively contribute to the non-NOS-derived NO-mediated, endothelium-dependent hyperemic response to either PLM or sPLM in healthy young men. These findings add to the mounting evidence and understanding of the vasodilatory pathways assessed by the PLM and sPLM vascular function tests.NEW & NOTEWORTHY Passive leg movement (PLM) evokes a highly nitric oxide (NO)-mediated hyperemic response and may provide a novel evaluation of vascular function. The contributions of endothelium-dependent vasodilatory pathways, beyond NO and including prostaglandins and endothelium-derived hyperpolarizing factor, to the PLM-induced hyperemic response to PLM have not been evaluated. With intra-arterial drug infusion, the combined inhibition of nitric oxide synthase (NOS), cyclooxygenase, and cytochrome P-450 (CYP450) pathways did not further diminish the hyperemic response to PLM compared with NOS inhibition alone.
Collapse
Affiliation(s)
- Joel D Trinity
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Medical Center, Salt Lake City, Utah.,Department of Internal Medicine, University of Utah, Salt Lake City, Utah.,Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah
| | - Oh Sung Kwon
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah.,Department of Kinesiology, University of Connecticut, Storrs, Connecticut
| | - Ryan M Broxterman
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Medical Center, Salt Lake City, Utah.,Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Jayson R Gifford
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Medical Center, Salt Lake City, Utah.,Department of Exercise Science, Brigham Young University, Provo, Utah
| | - Andrew C Kithas
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Jay R Hydren
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah
| | - Catherine L Jarrett
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Medical Center, Salt Lake City, Utah
| | - Katherine L Shields
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah
| | - Angela V Bisconti
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Soung Hun Park
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah
| | - Jesse C Craig
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Ashley D Nelson
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - David E Morgan
- Department of Anesthesiology, University of Utah, Salt Lake City, Utah
| | - Jacob E Jessop
- Department of Anesthesiology, University of Utah, Salt Lake City, Utah
| | - Amber D Bledsoe
- Department of Anesthesiology, University of Utah, Salt Lake City, Utah
| | - Russell S Richardson
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Medical Center, Salt Lake City, Utah.,Department of Internal Medicine, University of Utah, Salt Lake City, Utah.,Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, Utah
| |
Collapse
|
6
|
Kithas AC, Broxterman RM, Trinity JD, Gifford JR, Kwon OS, Hydren JR, Nelson AD, Jessop JE, Bledsoe AD, Morgan DE, Richardson RS. Nitric oxide synthase inhibition with N(G)-monomethyl-l-arginine: Determining the window of effect in the human vasculature. Nitric Oxide 2020; 104-105:51-60. [PMID: 32979497 DOI: 10.1016/j.niox.2020.09.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 09/07/2020] [Accepted: 09/21/2020] [Indexed: 11/17/2022]
Abstract
Nitric oxide synthase (NOS) inhibition with N(G)-monomethyl-l-arginine (L-NMMA) is often used to assess the role of NO in human cardiovascular function. However, the window of effect for L-NMMA on human vascular function is unknown, which is critical for designing and interpreting human-based studies. This study utilized the passive leg movement (PLM) assessment of vascular function, which is predominantly NO-mediated, in 7 young male subjects under control conditions, immediately following intra-arterial L-NMMA infusion (0.24 mg⋅dl-1⋅min-1), and at 45-60 and 90-105 min post L-NMMA infusion. The leg blood flow (LBF) and leg vascular conductance (LVC) responses to PLM, measured with Doppler ultrasound and expressed as the change from baseline to peak (ΔLBFpeak and ΔLVCpeak) and area under the curve (LBFAUC and LVCACU), were assessed. PLM-induced robust control ΔLBFpeak (1135 ± 324 ml⋅min-1) and ΔLVCpeak (10.7 ± 3.6 ml⋅min-1⋅mmHg-1) responses that were significantly attenuated (704 ± 196 ml⋅min-1 and 6.7 ± 2 ml⋅min-1⋅mmHg-1) immediately following L-NMMA infusion. Likewise, control condition PLM ΔLBFAUC (455 ± 202 ml) and ΔLVCAUC (4.0 ± 1.4 ml⋅mmHg-1) were significantly attenuated (141 ± 130 ml and 1.3 ± 1.2 ml⋅mmHg-1) immediately following L-NMMA infusion. However, by 45-60 min post L-NMMA infusion all PLM variables were not significantly different from control, and this was still the case at 90-105 min post L-NMMA infusion. These findings reveal that the potent reduction in NO bioavailability afforded by NOS inhibition with L-NMMA has a window of effect of less than 45-60 min in the human vasculature. These data are particularly important for the commonly employed approach of pharmacologically inhibiting NOS with L-NMMA in the human vasculature.
Collapse
Affiliation(s)
- Andrew C Kithas
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Ryan M Broxterman
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA; Geriatric Research, Education, and Clinical Center, Salt Lake City, VAMC, UT, USA
| | - Joel D Trinity
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA; Department of Nutrition and Integrative Physiology, USA; Geriatric Research, Education, and Clinical Center, Salt Lake City, VAMC, UT, USA
| | - Jayson R Gifford
- Department of Exercise Sciences, Brigham Young University, Provo, UT, USA
| | - Oh Sung Kwon
- Department of Kinesiology, University of Connecticut, Storrs, CT, USA
| | - Jay R Hydren
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA; Department of Nutrition and Integrative Physiology, USA; Geriatric Research, Education, and Clinical Center, Salt Lake City, VAMC, UT, USA
| | - Ashley D Nelson
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Jacob E Jessop
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Amber D Bledsoe
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - David E Morgan
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Russell S Richardson
- Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA; Department of Nutrition and Integrative Physiology, USA; Geriatric Research, Education, and Clinical Center, Salt Lake City, VAMC, UT, USA.
| |
Collapse
|
7
|
Poole DC, Pittman RN, Musch TI, Østergaard L. August Krogh's theory of muscle microvascular control and oxygen delivery: a paradigm shift based on new data. J Physiol 2020; 598:4473-4507. [PMID: 32918749 DOI: 10.1113/jp279223] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 07/13/2020] [Indexed: 12/16/2022] Open
Abstract
August Krogh twice won the prestigious international Steegen Prize, for nitrogen metabolism (1906) and overturning the concept of active transport of gases across the pulmonary epithelium (1910). Despite this, at the beginning of 1920, the consummate experimentalist was relatively unknown worldwide and even among his own University of Copenhagen faculty. But, in early 1919, he had submitted three papers to Dr Langley, then editor of The Journal of Physiology in England. These papers coalesced anatomical observations of skeletal muscle capillary numbers with O2 diffusion theory to propose a novel active role for capillaries that explained the prodigious increase in blood-muscle O2 flux from rest to exercise. Despite his own appraisal of the first two papers as "rather dull" to his friend, the eminent Cambridge respiratory physiologist, Joseph Barcroft, Krogh believed that the third one, dealing with O2 supply and capillary regulation, was"interesting". These papers, which won Krogh an unopposed Nobel Prize for Physiology or Medicine in 1920, form the foundation for this review. They single-handedly transformed the role of capillaries from passive conduit and exchange vessels, functioning at the mercy of their upstream arterioles, into independent contractile units that were predominantly closed at rest and opened actively during muscle contractions in a process he termed 'capillary recruitment'. Herein we examine Krogh's findings and some of the experimental difficulties he faced. In particular, the boundary conditions selected for his model (e.g. heavily anaesthetized animals, negligible intramyocyte O2 partial pressure, binary open-closed capillary function) have not withstood the test of time. Subsequently, we update the reader with intervening discoveries that underpin our current understanding of muscle microcirculatory control and place a retrospectroscope on Krogh's discoveries. The perspective is presented that the imprimatur of the Nobel Prize, in this instance, may have led scientists to discount compelling evidence. Much as he and Marie Krogh demonstrated that active transport of gases across the blood-gas barrier was unnecessary in the lung, capillaries in skeletal muscle do not open and close spontaneously or actively, nor is this necessary to account for the increase in blood-muscle O2 flux during exercise. Thus, a contemporary model of capillary function features most muscle capillaries supporting blood flow at rest, and, rather than capillaries actively vasodilating from rest to exercise, increased blood-myocyte O2 flux occurs predominantly via elevating red blood cell and plasma flux in already flowing capillaries. Krogh is lauded for his brilliance as an experimentalist and for raising scientific questions that led to fertile avenues of investigation, including the study of microvascular function.
Collapse
Affiliation(s)
- David C Poole
- Departments of Kinesiology and Anatomy and Physiology, Kansas State University Manhattan, Manhattan, KS, 66506, USA
| | - Roland N Pittman
- Department of Physiology and Biophysics, Virginia Commonwealth University Richmond, Richmond, VA, 23298-0551, USA
| | - Timothy I Musch
- Departments of Kinesiology and Anatomy and Physiology, Kansas State University Manhattan, Manhattan, KS, 66506, USA
| | - Leif Østergaard
- Center of Functionally Integrative Neuroscience, Aarhus University, Denmark
| |
Collapse
|