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Taboni A, Fagoni N, Fontolliet T, Vinetti G, Ferretti G. Baroreflex dynamics during the rest to exercise transient in acute normobaric hypoxia in humans. Eur J Appl Physiol 2024; 124:2765-2775. [PMID: 38656378 PMCID: PMC11365845 DOI: 10.1007/s00421-024-05485-4] [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: 01/24/2024] [Accepted: 03/26/2024] [Indexed: 04/26/2024]
Abstract
PURPOSE We hypothesised that during a rest-to-exercise transient in hypoxia (H), compared to normoxia (N), (i) the initial baroreflex sensitivity (BRS) decrease would be slower and (ii) the fast heart rate (HR) and cardiac output (CO) response would have smaller amplitude (A1) due to lower vagal activity in H than N. METHODS Ten participants performed three rest-to-50 W exercise transients on a cycle-ergometer in N (ambient air) and three in H (inspired fraction of O2 = 0.11). R-to-R interval (RRi, by electrocardiography) and blood pressure profile (by photo-plethysmography) were recorded non-invasively. Analysis of the latter provided mean arterial pressure (MAP) and stroke volume (SV). CO = HR·SV. BRS was calculated by modified sequence method. RESULTS Upon exercise onset in N, MAP fell to a minimum (MAPmin) then recovered. BRS decreased immediately from 14.7 ± 3.6 at rest to 7.0 ± 3.0 ms mmHg-1 at 50 W (p < 0.01). The first BRS sequence detected at 50 W was 8.9 ± 4.8 ms mmHg-1 (p < 0.05 vs. rest). In H, MAP showed several oscillations until reaching a new steady state. BRS decreased rapidly from 10.6 ± 2.8 at rest to 2.9 ± 1.5 ms mmHg-1 at 50 W (p < 0.01), as the first BRS sequence at 50 W was 5.8 ± 2.6 ms mmHg-1 (p < 0.01 vs. rest). CO-A1 was 2.96 ± 1.51 and 2.31 ± 0.94 l min-1 in N and H, respectively (p = 0.06). HR-A1 was 7.7 ± 4.6 and 7.1 ± 5.9 min-1 in N and H, respectively (p = 0.81). CONCLUSION The immediate BRS decrease in H, coupled with similar rapid HR and CO responses, is compatible with a withdrawal of residual vagal activity in H associated with increased sympathetic drive.
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Affiliation(s)
- Anna Taboni
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy.
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.
| | - Nazzareno Fagoni
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Timothée Fontolliet
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Guido Ferretti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
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Dobashi K, Ichinose M, Fujii N, Fujimoto T, Nishiyasu T. Effects of Pre-Exercise Voluntary Hyperventilation on Metabolic and Cardiovascular Responses During and After Intense Exercise. RESEARCH QUARTERLY FOR EXERCISE AND SPORT 2023; 94:1141-1152. [PMID: 36170018 DOI: 10.1080/02701367.2022.2121371] [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: 10/28/2021] [Accepted: 08/29/2022] [Indexed: 06/16/2023]
Abstract
Purpose: We investigated the effects of pre-exercise voluntary hyperventilation and the resultant hypocapnia on metabolic and cardiovascular responses during and after high-intensity exercise. Methods: Ten healthy participants performed a 60-s cycling exercise at a workload of 120% peak oxygen uptake in control (spontaneous breathing), hypocapnia and normocapnia trials. Hypocapnia was induced through 20-min pre-exercise voluntary hyperventilation. In the normocapnia trial, voluntary hyperpnea was performed with CO2 inhalation to prevent hypocapnia. Results: Pre-exercise end-tidal CO2 partial pressure was lower in the hypocapnia trial than the control or normocapnia trial, with similar levels in the control and normocapnia trials. Average V ˙ O 2 during the entire exercise was lower in both the hypocapnia and normocapnia trials than in the control trial (1491 ± 252vs.1662 ± 169vs.1806 ± 149 mL min-1), with the hypocapnia trial exhibiting a greater reduction than the normocapnia trial. Minute ventilation during exercise was lower in the hypocapnia trial than the normocapnia trial. In addition, minute ventilation during the first 10s of the exercise was lower in the normocapnia than the control trial. Pre-exercise hypocapnia also reduced heart rates and arterial blood pressures during the exercise relative to the normocapnia trial, a response that lasted through the subsequent early recovery periods, though end-tidal CO2 partial pressure was similar in the two trials. Conclusions: Our results suggest that pre-exercise hyperpnea and the resultant hypocapnia reduce V ˙ O 2 during high-intensity exercise. Moreover, hypocapnia may contribute to voluntary hyperventilation-mediated cardiovascular responses during the exercise, and this response can persist into the subsequent recovery period, despite the return of arterial CO2 pressure to the normocapnic level.
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Affiliation(s)
- Kohei Dobashi
- University of Tsukuba
- Japan Society for the Promotion of Science
- Hokkaido University of Education
| | | | | | - Tomomi Fujimoto
- University of Tsukuba
- Niigata University of Health and Welfare
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Combined Effects of Hypocapnic Hyperventilation and Hypoxia on Exercise Performance and Metabolic Responses During the Wingate Anaerobic Test. Int J Sports Physiol Perform 2023; 18:69-76. [PMID: 36521190 DOI: 10.1123/ijspp.2022-0121] [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: 03/25/2022] [Revised: 08/25/2022] [Accepted: 09/13/2022] [Indexed: 12/23/2022]
Abstract
Hypoxia during supramaximal exercise reduces aerobic metabolism with a compensatory increase in anaerobic metabolism without affecting exercise performance. A similar response is elicited by preexercise voluntary hypocapnic hyperventilation, but it remains unclear whether hypocapnic hyperventilation and hypoxia additively reduce aerobic metabolism and increase anaerobic metabolism during supramaximal exercise. To address that issue, 12 healthy subjects (8 males and 4 females) performed the 30-second Wingate anaerobic test (WAnT) after (1) spontaneous breathing in normoxia (control, ∼21% fraction of inspired O2 [FiO2]), (2) voluntary hypocapnic hyperventilation in normoxia (hypocapnia, ∼21% FiO2), (3) spontaneous breathing in hypoxia (hypoxia, ∼11% FiO2), or (4) voluntary hypocapnic hyperventilation in hypoxia (combined, ∼11% FiO2). Mean power output during the 30-second WAnT was similar among the control (561 [133] W), hypocapnia (563 [140] W), hypoxia (558 [131] W), and combined (560 [133] W) trials (P = .778). Oxygen uptake during the 30-second WAnT was lower in the hypocapnia (1523 [318] mL/min), hypoxia (1567 [300] mL/min), and combined (1203 [318] mL/min) trials than in the control (1935 [250] mL/min) trial, and the uptake in the combined trial was lower than in the hypocapnia or hypoxia trial (all P < .001). Oxygen deficit, an index of anaerobic metabolism, was higher in the hypocapnia (38.4 [7.3] mL/kg), hypoxia (37.8 [6.8] mL/kg), and combined (40.7 [6.9] mL/kg) trials than in the control (35.0 [6.8] mL/kg) trial, and the debt was greater in the combined trial than in the hypocapnia or hypoxia trial (all P < .003). Our results suggest that voluntary hypocapnic hyperventilation and hypoxia additively reduce aerobic metabolism and increase anaerobic metabolism without affecting exercise performance during the 30-second WAnT.
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Taboni A, Fagoni N, Fontolliet T, Vinetti G, Ferretti G. Dynamics of cardiovascular and baroreflex readjustments during a light-to-moderate exercise transient in humans. Eur J Appl Physiol 2022; 122:2343-2354. [PMID: 35861802 PMCID: PMC9561001 DOI: 10.1007/s00421-022-05011-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 07/07/2022] [Indexed: 12/02/2022]
Abstract
Purpose We hypothesised that, during a light-to-moderate exercise transient, compared to an equivalent rest-to-exercise transient, (1) a further baroreflex sensitivity (BRS) decrease would be slower, (2) no rapid heart rate (HR) response would occur, and (3) the rapid cardiac output (CO) response would have a smaller amplitude (A1). Hence, we analysed the dynamics of arterial baroreflexes and the HR and CO kinetics during rest-to-50 W (0–50 W) and 50-to-100 W (50–100 W) exercise transients. Methods 10 subjects performed three 0–50 W and three 50–100 W on a cycle ergometer. We recorded arterial blood pressure profiles (photo-plethysmography) and R-to-R interval (RRi, electrocardiography). The former were analysed to obtain beat-by-beat mean arterial pressure (MAP) and stroke volume (SV). CO was calculated as SV times HR. BRS was measured by modified sequence method. Results During 0–50 W, MAP transiently fell (− 9.0 ± 5.7 mmHg, p < 0.01) and BRS passed from 15.0 ± 3.7 at rest to 7.3 ± 2.4 ms mmHg−1 at 50 W (p < 0.01) promptly (first BRS sequence: 8.1 ± 4.6 ms mmHg−1, p < 0.01 vs. rest). During 50–100 W, MAP did not fall and BRS passed from 7.2 ± 2.6 at 50 W to 3.3 ± 1.3 ms mmHg−1 at 100 W (p < 0.01) slowly (first BRS sequence: 5.3 ± 3.1 ms mmHg−1, p = 0.07 vs. 50 W). A1 for HR was 9.2 ± 6.0 and 6.0 ± 4.5 min−1 in 0–50 W and 50–100 W, respectively (p = 0.19). The corresponding A1 for CO were 2.80 ± 1.54 and 0.91 ± 0.55 l∙min−1 (p < 0.01). Conclusion During 50–100 W, with respect to 0–50 W, BRS decreased more slowly, in absence of a prompt pressure decrease. BRS decrease and rapid HR response in 50–100 W were unexpected and ascribed to possible persistence of some vagal tone at 50 W. Supplementary Information The online version contains supplementary material available at 10.1007/s00421-022-05011-4.
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Affiliation(s)
- Anna Taboni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Nazzareno Fagoni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.,AAT Brescia, Department of Anaesthesiology, Intensive Care and Emergency Medicine, Spedali Civili University Hospital, Brescia, Italy
| | - Timothée Fontolliet
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy. .,Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.
| | - Guido Ferretti
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy
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Ferretti G, Fagoni N, Taboni A, Vinetti G, di Prampero PE. A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise. Eur J Appl Physiol 2022; 122:1317-1365. [PMID: 35217911 PMCID: PMC9132876 DOI: 10.1007/s00421-022-04901-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 01/25/2022] [Indexed: 12/26/2022]
Abstract
After a short historical account, and a discussion of Hill and Meyerhof's theory of the energetics of muscular exercise, we analyse steady-state rest and exercise as the condition wherein coupling of respiration to metabolism is most perfect. The quantitative relationships show that the homeostatic equilibrium, centred around arterial pH of 7.4 and arterial carbon dioxide partial pressure of 40 mmHg, is attained when the ratio of alveolar ventilation to carbon dioxide flow ([Formula: see text]) is - 21.6. Several combinations, exploited during exercise, of pertinent respiratory variables are compatible with this equilibrium, allowing adjustment of oxygen flow to oxygen demand without its alteration. During exercise transients, the balance is broken, but the coupling of respiration to metabolism is preserved when, as during moderate exercise, the respiratory system responds faster than the metabolic pathways. At higher exercise intensities, early blood lactate accumulation suggests that the coupling of respiration to metabolism is transiently broken, to be re-established when, at steady state, blood lactate stabilizes at higher levels than resting. In the severe exercise domain, coupling cannot be re-established, so that anaerobic lactic metabolism also contributes to sustain energy demand, lactate concentration goes up and arterial pH falls continuously. The [Formula: see text] decreases below - 21.6, because of ensuing hyperventilation, while lactate keeps being accumulated, so that exercise is rapidly interrupted. The most extreme rupture of the homeostatic equilibrium occurs during breath-holding, because oxygen flow from ambient air to mitochondria is interrupted. No coupling at all is possible between respiration and metabolism in this case.
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Affiliation(s)
- Guido Ferretti
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy.
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Université de Genève, Genève, Switzerland.
| | - Nazzareno Fagoni
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy
| | - Anna Taboni
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Université de Genève, Genève, Switzerland
| | - Giovanni Vinetti
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy
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Love LK, Hodgson MD, Keir DA, Kowalchuk JM. Data analysis technique influences blood flow kinetics parameter estimates for moderate- and heavy-intensity exercise transitions. Exp Physiol 2021; 107:82-93. [PMID: 34731518 DOI: 10.1113/ep089834] [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: 06/16/2021] [Accepted: 10/22/2021] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? During exercise, there are fluctuations in conduit artery blood flow (BF) caused by both cardiac and muscle contraction-relaxation cycles. What is the optimal method to process Doppler ultrasound-measured BF for the purpose of characterizing the dynamic response of BF during step-transitions in exercise? What is the main finding and its importance? Continuous BF data were processed in relation to either cardiac or muscle contraction-relaxation cycles and computed based on 'binned' or 'rolling' averages over one, two or five consecutive cycles. Kinetics characterization revealed no data processing technique-specific differences in steady-state BF, but variability in the rapidity at which BF attained steady-state (i.e., mean response time) was observed. ABSTRACT The overall rate of blood flow (BF) adjustment (i.e., kinetics) from the onset of an exercise transition can be quantified by the mean response time (MRT). However, the BF response profile can be distorted during rhythmic, dynamic exercise consequent to variations caused by the cardiac cycle (HR) and the muscle contraction-relaxation (CR) cycle. We examined the extent to which distortions imposed by HR and CR cycles affected BF kinetics. Eight healthy, young men (27 (4) years; mean (SD)) performed transitions of alternate-leg knee-extension exercise from 3 W to either a moderate- (MOD) or heavy-intensity (HVY) power output. Femoral artery BF was continuously measured by Doppler ultrasound and averaged over one, two or five 'binned' (e.g., HR2b, etc.) or 'rolling' (e.g., CR5r, etc.) HR and CR cycles. Among analysis techniques, there were no differences for steady-state BF values at the 3 W baseline. In MOD, MRT using contraction-relaxation cycle (CR1) was smaller than most other analysis techniques. For both MOD and HVY, the 95% confidence interval for MRT was generally larger when using HR- compared to CR-related methods, and monoexponential fits based on 'rolling' averages (HR2r, HR5r, CR2r, CR5r) had a poorer ability to estimate the true end-exercise BF in HVY than in MOD. When modelling BF kinetics, we conclude that the CR1 method is a good option because of its ability to accurately estimate the 'data-determined' end-exercise BF value from the 'model-derived' response, maintain a relatively high density of data points during the transition and yield a relatively small 95% CI.
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Affiliation(s)
- Lorenzo K Love
- Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada.,School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada.,Department of Kinesiology and Physical Education, Redeemer University, Ancaster, Ontario, Canada
| | - Michael D Hodgson
- Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada.,School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada
| | - Daniel A Keir
- Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada.,School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada.,Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
| | - John M Kowalchuk
- Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada.,School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada.,Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
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Dobashi K, Fujii N, Ichinose M, Fujimoto T, Nishiyasu T. Voluntary hypocapnic hyperventilation lasting 5 min and 20 min similarly reduce aerobic metabolism without affecting power outputs during Wingate anaerobic test. Eur J Sport Sci 2020; 21:1148-1155. [PMID: 32814502 DOI: 10.1080/17461391.2020.1812728] [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: 10/23/2022]
Abstract
AbstractTwenty minutes of voluntary hypocapnic hyperventilation prior to exercise reduces the aerobic metabolic rate with a compensatory increase in the anaerobic metabolic rate without affecting exercise performance during the Wingate anaerobic test (WAnT). Thus, pre-exercise hypocapnic hyperventilation may be a useful means of stressing the anaerobic energy system during training, ultimately improving anaerobic exercise performance. However, it remains unclear whether a shorter (e.g., 5 min) pre-exercise hypocapnic hyperventilation is sufficient to reduce the aerobic metabolic rate during high-intensity exercise. We therefore compared the effects of 5-min and 20-min pre-exercise hypocapnic hyperventilation on aerobic metabolism during the 30-s WAnT. Ten healthy young males and one female performed the WAnT following 20 min of spontaneous breathing (control trial) or 5 or 20 min of voluntary hypocapnic hyperventilation. Both the 5-min and 20-min hyperventilation reduced end-tidal CO2 partial pressure (an index of arterial CO2 partial pressure) to ∼23 mmHg, whereas it remained unchanged during the spontaneous breathing. The peak, mean and minimum power outputs during the WAnT did not differ among the three trials. Oxygen uptake during the WAnT was lower in both the 5-min (1493 ± 257 mL min-1) and 20-min (1397 ± 447 mL min-1) hyperventilation trials than during the control trial (1847 ± 286 mL min-1), and was similar in the two hyperventilation trials. These results suggest that 5 min of pre-exercise hypocapnic hyperventilation reduces aerobic metabolism during the 30-s WAnT to a level similar to that seen with the 20-min hyperventilation. Moreover, exercise performance was unaffected, which implies anaerobic metabolism was enhanced.
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Affiliation(s)
- Kohei Dobashi
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan.,Research Fellow of the Japan Society for the Promotion of Science, Tokyo, Japan
| | - Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
| | - Masashi Ichinose
- Human Integrative Physiology Laboratory, School of Business Administration, Meiji University, Tokyo, Japan
| | - Tomomi Fujimoto
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan.,Department of Health and Sports, Niigata University of Health and Welfare, Niigata, Japan.,Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
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Unexplained exertional intolerance associated with impaired systemic oxygen extraction. Eur J Appl Physiol 2019; 119:2375-2389. [PMID: 31493035 DOI: 10.1007/s00421-019-04222-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 08/28/2019] [Indexed: 10/26/2022]
Abstract
PURPOSE The clinical investigation of exertional intolerance generally focuses on cardiopulmonary diseases, while peripheral factors are often overlooked. We hypothesize that a subset of patients exists whose predominant exercise limitation is due to abnormal systemic oxygen extraction (SOE). METHODS We reviewed invasive cardiopulmonary exercise test (iCPET) results of 313 consecutive patients presenting with unexplained exertional intolerance. An exercise limit due to poor SOE was defined as peak exercise (Ca-vO2)/[Hb] ≤ 0.8 and VO2max < 80% predicted in the absence of a cardiac or pulmonary mechanical limit. Those with peak (Ca-vO2)/[Hb] > 0.8, VO2max ≥ 80%, and no cardiac or pulmonary limit were considered otherwise normal. The otherwise normal group was divided into hyperventilators (HV) and normals (NL). Hyperventilation was defined as peak PaCO2 < [1.5 × HCO3 + 6]. RESULTS Prevalence of impaired SOE as the sole cause of exertional intolerance was 12.5% (32/257). At peak exercise, poor SOE and HV had less acidemic arterial blood compared to NL (pHa = 7.39 ± 0.05 vs. 7.38 ± 0.05 vs. 7.32 ± 0.02, p < 0.001), which was explained by relative hypocapnia (PaCO2 = 29.9 ± 5.4 mmHg vs. 31.6 ± 5.4 vs. 37.5 ± 3.4, p < 0.001). For a subset of poor SOE, this relative alkalemia, also seen in mixed venous blood, was associated with a normal PvO2 nadir (28 ± 2 mmHg vs. 26 ± 4, p = 0.627) but increased SvO2 at peak exercise (44.1 ± 5.2% vs. 31.4 ± 7.0, p < 0.001). CONCLUSIONS We identified a cohort of patients whose exercise limitation is due only to systemic oxygen extraction, due to either an intrinsic abnormality of skeletal muscle mitochondrion, limb muscle microcirculatory dysregulation, or hyperventilation and left shift the oxyhemoglobin dissociation curve.
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Keir DA, Duffin J, Millar PJ, Floras JS. Simultaneous assessment of central and peripheral chemoreflex regulation of muscle sympathetic nerve activity and ventilation in healthy young men. J Physiol 2019; 597:3281-3296. [DOI: 10.1113/jp277691] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Accepted: 05/13/2019] [Indexed: 12/20/2022] Open
Affiliation(s)
- Daniel A. Keir
- University Health Network and Mount Sinai Hospital Division of CardiologyDepartment of Medicine, University of Toronto Toronto Ontario Canada
| | - James Duffin
- Departments of Anaesthesia and PhysiologyUniversity of Toronto Toronto Ontario Canada
- Thornhill Research Inc. Toronto Ontario Canada
| | - Philip J. Millar
- University Health Network and Mount Sinai Hospital Division of CardiologyDepartment of Medicine, University of Toronto Toronto Ontario Canada
- Human Health and Nutritional ScienceUniversity of Guelph Guelph Ontario Canada
| | - John S. Floras
- University Health Network and Mount Sinai Hospital Division of CardiologyDepartment of Medicine, University of Toronto Toronto Ontario Canada
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Slow V˙O 2 kinetics in acute hypoxia are not related to a hyperventilation-induced hypocapnia. Respir Physiol Neurobiol 2018; 251:41-49. [PMID: 29477729 DOI: 10.1016/j.resp.2018.02.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 02/01/2018] [Accepted: 02/16/2018] [Indexed: 11/21/2022]
Abstract
We examined whether slower pulmonary O2 uptake (V˙O2p) kinetics in hypoxia is a consequence of: a) hypoxia alone (lowered arterial O2 pressure), b) hyperventilation-induced hypocapnia (lowered arterial CO2 pressure), or c) a combination of both. Eleven participants performed 3-5 repetitions of step-changes in cycle ergometer power output from 20W to 80% lactate threshold in the following conditions: i) normoxia (CON; room air); ii) hypoxia (HX, inspired O2 = 12%; lowered end-tidal O2 pressure [PETO2] and end-tidal CO2 pressure [PETCO2]); iii) hyperventilation (HV; increased PETO2 and lowered PETCO2); and iv) normocapnic hypoxia (NC-HX; lowered PETO2 and PETCO2 matched to CON). Ventilation was increased (relative to CON) and matched between HX, HV, and NC-HX conditions. During each condition VO2p˙ was measured and phase II V˙O2p kinetics were modeled with a mono-exponential function. The V˙O2p time constant was different (p < 0.05) amongst all conditions: CON, 26 ± 11s; HV, 36 ± 14s; HX, 46 ± 14s; and NC-HX, 52 ± 13s. Hypocapnia may prevent further slowing of V˙O2p kinetics in hypoxic exercise.
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Dobashi K, Fujii N, Watanabe K, Tsuji B, Sasaki Y, Fujimoto T, Tanigawa S, Nishiyasu T. Effect of voluntary hypocapnic hyperventilation or moderate hypoxia on metabolic and heart rate responses during high-intensity intermittent exercise. Eur J Appl Physiol 2017; 117:1573-1583. [PMID: 28527012 DOI: 10.1007/s00421-017-3646-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2017] [Accepted: 05/12/2017] [Indexed: 11/28/2022]
Abstract
PURPOSE To investigate the effect of voluntary hypocapnic hyperventilation or moderate hypoxia on metabolic and heart rate responses during high-intensity intermittent exercise. METHODS Ten males performed three 30-s bouts of high-intensity cycling [Ex1 and Ex2: constant-workload at 80% of the power output in the Wingate anaerobic test (WAnT), Ex3: WAnT] interspaced with 4-min recovery periods under normoxic (Control), hypocapnic or hypoxic (2500 m) conditions. Hypocapnia was developed through voluntary hyperventilation for 20 min prior to Ex1 and during each recovery period. RESULTS End-tidal CO2 pressure was lower before each exercise in the hypocapnia than control trials. Oxygen uptake ([Formula: see text]) was lower in the hypocapnia than control trials (822 ± 235 vs. 1645 ± 245 mL min-1; mean ± SD) during Ex1, but not Ex2 or Ex3, without a between-trial difference in the power output during the exercises. Heart rates (HRs) during Ex1 (127 ± 8 vs. 142 ± 10 beats min-1) and subsequent post-exercise recovery periods were lower in the hypocapnia than control trials, without differences during or after Ex2, except at 4 min into the second recovery period. [Formula: see text] did not differ between the control and hypoxia trials throughout. CONCLUSIONS These results suggest that during three 30-s bouts of high-intensity intermittent cycling, (1) hypocapnia reduces the aerobic metabolic rate with a compensatory increase in the anaerobic metabolic rate during the first but not subsequent exercises; (2) HRs during the exercise and post-exercise recovery periods are lowered by hypocapnia, but this effect is diminished with repeated exercise bouts, and (3) moderate hypoxia (2500 m) does not affect the metabolic response during exercise.
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Affiliation(s)
- Kohei Dobashi
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan
| | - Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan
| | - Kazuhito Watanabe
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan.,Japan Society for the Promotion of Science, Tokyo, Japan
| | - Bun Tsuji
- Faculty of Human Culture and Science, Prefectural University of Hiroshima, Hiroshima, Japan
| | - Yosuke Sasaki
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan
| | - Tomomi Fujimoto
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan.,Japan Society for the Promotion of Science, Tokyo, Japan
| | - Satoru Tanigawa
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan.
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Effects of overground locomotor training on the ventilatory response to volitional treadmill walking in individuals with incomplete spinal cord injury: a pilot study. Spinal Cord Ser Cases 2017; 3:17011. [PMID: 28435743 DOI: 10.1038/scsandc.2017.11] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 02/22/2017] [Accepted: 03/02/2017] [Indexed: 11/09/2022] Open
Abstract
INTRODUCTION Although there has been substantial emphasis on the neuromuscular and cardiovascular adaptations following rehabilitation, pulmonary adaptations in individuals with incomplete SCI (iSCI) in response to locomotor training have been less frequently studied. In healthy individuals, effective transition from rest to work is accomplished by a hyperpneic response, which exhibits an exponential curve with three phases. However, the degree to which our current understanding of exercise hyperpnea can be applied to individuals with iSCI is unknown. The purpose of this case series was to characterize exercise hyperpnea during a rest to constant work rate (CWR) transition before and after 12-15 weeks of overground locomotor training (OLT). CASE PRESENTATION Six subjects with cervical motor incomplete spinal cord injury participated in 12-15 weeks of OLT. Subjects were trained in 90-min sessions twice a week. All training activities were weight-bearing and under volitional control without the assistance of body-weight support harnesses, robotic devices or electrical stimulation. Six minutes of CWR treadmill walking was performed at self-selected pace with cardiorespiratory analysis throughout the tests before and after OLT. Averaged group data for tidal volume, breathing frequency or VE showed no difference before and after training. VE variability was decreased by 46.7% after OLT. DISCUSSION CWR VE from rest to work was linear throughout the transition. Following OLT, there was a substantial reduction in VE variability. Future research should investigate the lack of a phasic ventilatory response to exercise, as well as potential mechanisms of ventilatory variability and its implications for functional performance.
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13
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Bringard A, Adami A, Fagoni N, Fontolliet T, Lador F, Moia C, Tam E, Ferretti G. Dynamics of the RR-interval versus blood pressure relationship at exercise onset in humans. Eur J Appl Physiol 2017; 117:619-630. [PMID: 28238048 DOI: 10.1007/s00421-017-3564-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 02/07/2017] [Indexed: 10/20/2022]
Abstract
PURPOSE The dynamics of the postulated phenomenon of exercise baroreflex resetting is poorly understood, but can be investigated using closed-loop procedures. To shed light on some mechanisms and temporal relationships participating in the resetting process, we studied the time course of the relationship between the R-R interval (RRi) and arterial pressure with a closed-loop approach. METHODS On ten young volunteers at rest and during light exercise in supine and upright position, we continuously determined, on single-beat basis, RRi (electrocardiography), and arterial pressure (non-invasive finger pressure cuff). From pulse pressure profiles, we determined cardiac output (CO) by Modelflow, computed mean arterial pressure (MAP), and calculated total peripheral resistance (TPR). RESULTS At exercise start, RRi was lower than in quiet rest. As exercise started, MAP fell to a minimum (MAPm) of 72.8 ± 9.6 mmHg upright and 73.9 ± 6.2 supine, while RRi dropped. The initial RRi versus MAP relationship was linear, with flatter slope than resting baroreflex sensitivity, in both postures. TPR fell and CO increased. After MAPm, RRi and MAP varied in opposite direction toward exercise steady state, with further CO increase. CONCLUSION These results suggest that, initially, the MAP fall was corrected by a RRi reduction along a baroreflex curve, with lower sensitivity than at rest, but eventually in the same pressure range as at rest. After attainment of MAPm, a second phase started, where the postulated baroreflex resetting might have occurred. In conclusion, the change in baroreflex sensitivity and the resetting process are distinct phenomena, under different control systems.
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Affiliation(s)
- Aurélien Bringard
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.,Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland
| | - Alessandra Adami
- Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland.,Division of Respiratory and Critical Care Physiology and Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson St, Torrance, CA, 90502, USA
| | - Nazzareno Fagoni
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Viale Europa 11, 25123, Brescia, Italy
| | - Timothée Fontolliet
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.,Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland
| | - Frédéric Lador
- Service de Pneumologie, Programme Hypertension Pulmonaire, Département des Spécialités de Médecine, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève, Switzerland
| | - Christian Moia
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.,Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland
| | - Enrico Tam
- Dipartimento di Scienze Neurologiche, Biomediche e del Movimento, Università di Verona, Via Felice Casorati 43, 37131, Verona, Italy
| | - Guido Ferretti
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland. .,Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland. .,Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Viale Europa 11, 25123, Brescia, Italy.
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14
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Fujii N, Tsuchiya SI, Tsuji B, Watanabe K, Sasaki Y, Nishiyasu T. Effect of voluntary hypocapnic hyperventilation on the metabolic response during Wingate anaerobic test. Eur J Appl Physiol 2015; 115:1967-74. [PMID: 25944513 DOI: 10.1007/s00421-015-3179-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Accepted: 04/21/2015] [Indexed: 10/23/2022]
Abstract
PURPOSE We evaluated whether hypocapnia achieved through voluntary hyperventilation diminishes the increases in oxygen uptake elicited by short-term (e.g., ~30 s) all-out exercise without affecting exercise performance. METHODS Nine subjects performed 30-s Wingate anaerobic tests (WAnT) in control and hypocapnia trials on separate days in a counterbalanced manner. During the 20-min rest prior to the 30-s WAnT, the subjects in the hypocapnia trial performed voluntary hyperventilation (minute ventilation = 31 L min(-1)), while the subjects in the control trial continued breathing spontaneously (minute ventilation = 14 L min(-1)). RESULTS The hyperventilation in the hypocapnia trial reduced end-tidal CO2 pressure from 34.8 ± 2.5 mmHg at baseline rest to 19.3 ± 1.0 mmHg immediately before the 30-s WAnT. In the control trial, end-tidal CO2 pressure at baseline rest (35.9 ± 2.5 mmHg) did not differ from that measured immediately before the 30-s WAnT (35.9 ± 3.3 mmHg). Oxygen uptake during the 30-s WAnT was lower in the hypocapnia than the control trial (1.55 ± 0.52 vs. 1.95 ± 0.44 L min(-1)), while the postexercise peak blood lactate concentration was higher in the hypocapnia than control trial (10.4 ± 1.9 vs. 9.6 ± 1.9 mmol L(-1)). In contrast, there was no difference in the 5-s peak (842 ± 111 vs. 850 ± 107 W) or mean (626 ± 74 vs. 639 ± 80 W) power achieved during the 30-s WAnT between the control and hypocapnia trials. CONCLUSIONS These results suggest that during short-period all-out exercise (e.g., 30-s WAnT), hypocapnia induced by voluntary hyperventilation reduces the aerobic metabolic rate without affecting exercise performance. This implies a compensatory elevation in the anaerobic metabolic rate.
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Affiliation(s)
- Naoto Fujii
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan
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15
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Balzan FM, da Silva RC, da Silva DP, Sanches PRS, Tavares AMV, Ribeiro JP, Berton DC, Clausell NO. Effects of diaphragmatic contraction on lower limb venous return and central hemodynamic parameters contrasting healthy subjects versus heart failure patients at rest and during exercise. Physiol Rep 2014; 2:2/12/e12216. [PMID: 25501441 PMCID: PMC4332204 DOI: 10.14814/phy2.12216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The main objective was to assess the effects of abdominal breathing (AB) versus subject's own breathing on femoral venous blood flow (Qfv) and their repercussions on central hemodynamics at rest and during exercise contrasting healthy subjects versus heart failure (HF) patients. We measured esophageal and gastric pressure (PGA), Qfv and parameters of central hemodynamics in eight healthy subjects and nine HF patients, under four conditions: subject's own breathing and AB (∆PGA ≥ 6 cmH2O) at rest and during knee extension exercises (15% of 1 repetition maximum) until exhaustion. Qfv and parameters of central hemodynamics [stroke volume (SV), cardiac output (CO)] were measured using Doppler ultrasound and impedance cardiography, respectively. At rest, healthy subjects Qfv, SV, and CO were higher during AB than subject's breathing (0.11 ± 0.02 vs. 0.06 ± 0.00 L·min−1, 58.7 ± 3.4 vs. 50.1 ± 4.1 mL and 4.4 ± 0.2 vs. 3.8 ± 0.1 L·min−1, respectively, P ≤ 0.05). ∆SV correlated with ∆PGA during AB (r = 0.89, P ≤ 0.05). This same pattern of findings induced by AB was observed during exercise (SV: 71.1 ± 4.1 vs. 65.5 ± 4.1 mL and CO: 6.3 ± 0.4 vs. 5.2 ± 0.4 L·min−1; P ≤ 0.05); however, Qfv did not reach statistical significance. The HF group tended to increase their Qfv during AB (0.09 ± 0.01 vs. 0.07 ± 0.03 L·min−1, P = 0.09). On the other hand, unlike the healthy subjects, AB did not improve SV or CO neither at rest nor during exercise (P > 0.05). In healthy subjects, abdominal pump modulated venous return improved SV and CO at rest and during exercise. In HF patients, with elevated right atrial and vena caval system pressures, these findings were not observed. Circulatory function of the diaphragm produces an increase in circulatory output. Moreover, the peripheral muscle contraction produces greater venous blood return due to increased blood expulsion. In this study, we focused on the effects of diaphragm contraction at rest and during knee extension exercise on venous return and central hemodynamics in healthy subjects and heart failure patients. These results help us understand the mechanisms of abdominal pump modulation on venous return in healthy subjects and under conditions of elevated pressure of the right atrium and the vena cava.
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Affiliation(s)
- Fernanda Machado Balzan
- Exercise Pathophysiology Research Laboratory, Programa de Pós-Graduação em Ciências da Saúde, Cardiologia e Ciências Cardiovasculares, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
| | | | - Danton Pereira da Silva
- Biomedical Engineering Division, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
| | - Paulo Roberto Stefani Sanches
- Biomedical Engineering Division, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
| | | | - Jorge Pinto Ribeiro
- Exercise Pathophysiology Research Laboratory, Programa de Pós-Graduação em Ciências da Saúde, Cardiologia e Ciências Cardiovasculares, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
| | - Danilo Cortozi Berton
- Respiratory Division, Programa de Pós-Graduação em Ciências Pneumológicas, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
| | - Nadine Oliveira Clausell
- Cardiology Division, Programa de Pós-Graduação em Ciências da Saúde, Cardiologia e Ciências Cardiovasculares, Universidade Federal do Rio Grande do Sul (UFRGS), Hospital de Clinicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
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16
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Ives SJ, Fadel PJ, Brothers RM, Sander M, Wray DW. Exploring the vascular smooth muscle receptor landscape in vivo: ultrasound Doppler versus near-infrared spectroscopy assessments. Am J Physiol Heart Circ Physiol 2014; 306:H771-6. [PMID: 24414068 DOI: 10.1152/ajpheart.00782.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ultrasound Doppler and near-infrared spectroscopy (NIRS) are routinely used for noninvasive monitoring of peripheral hemodynamics in both clinical and experimental settings. However, the comparative ability of these methodologies to detect changes in microvascular and whole limb hemodynamics during pharmacological manipulation of vascular smooth muscle receptors located at varied locations within the arterial tree is unknown. Thus, in 10 healthy subjects (25 ± 2 yr), changes in resting leg blood flow (ultrasound Doppler; femoral artery) and muscle oxygenation (oxyhemoglobin + oxymyoglobin; vastus lateralis) were simultaneously evaluated in response to intra-arterial infusions of phenylephrine (PE, 0.025-0.8 μg·kg(-1)·min(-1)), BHT-933 (2.5-40 μg·kg(-1)·min(-1)), and angiotensin II (ANG II, 0.5-8 ng·kg(-1)·min(-1)). All drugs elicited significant dose-dependent reductions in leg blood flow and oxyhemoglobin + oxymyoglobin. Significant relationships were found between ultrasound Doppler and NIRS changes across doses of PE (r(2) = 0.37 ± 0.08), BHT-933 (r(2) = 0.74 ± 0.06), and ANG II (r(2) = 0.68 ± 0.13), with the strongest relationships evident with agonists for receptors located preferentially "downstream" in the leg microcirculation (BHT-933 and ANG II). Analyses of drug potency revealed similar EC50 between ultrasound Doppler and NIRS measurements for PE (0.06 ± 0.02 vs. 0.10 ± 0.01), BHT-933 (5.0 ± 0.9 vs. 4.5 ± 1.3), and ANG II (1.4 ± 0.8 vs. 1.3 ± 0.3). These data provide evidence that both ultrasound Doppler and NIRS track pharmacologically induced changes in peripheral hemodynamics and are equally capable of determining drug potency. However, considerable disparity was observed between agonist infusions targeting different levels of the arterial tree, suggesting that receptor landscape is an important consideration for proper interpretation of hemodynamic monitoring with these methodologies.
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Affiliation(s)
- Stephen J Ives
- Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah
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17
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Abstract
This paper describes the interactions between ventilation and acid-base balance under a variety of conditions including rest, exercise, altitude, pregnancy, and various muscle, respiratory, cardiac, and renal pathologies. We introduce the physicochemical approach to assessing acid-base status and demonstrate how this approach can be used to quantify the origins of acid-base disorders using examples from the literature. The relationships between chemoreceptor and metaboreceptor control of ventilation and acid-base balance summarized here for adults, youth, and in various pathological conditions. There is a dynamic interplay between disturbances in acid-base balance, that is, exercise, that affect ventilation as well as imposed or pathological disturbances of ventilation that affect acid-base balance. Interactions between ventilation and acid-base balance are highlighted for moderate- to high-intensity exercise, altitude, induced acidosis and alkalosis, pregnancy, obesity, and some pathological conditions. In many situations, complete acid-base data are lacking, indicating a need for further research aimed at elucidating mechanistic bases for relationships between alterations in acid-base state and the ventilatory responses.
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Affiliation(s)
- Michael I Lindinger
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
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18
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Chin LMK, Heigenhauser GJF, Paterson DH, Kowalchuk JM. Effect of voluntary hyperventilation with supplemental CO2on pulmonary O2uptake and leg blood flow kinetics during moderate-intensity exercise. Exp Physiol 2013; 98:1668-82. [DOI: 10.1113/expphysiol.2013.074021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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19
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Koga S, Poole DC, Fukuoka Y, Ferreira LF, Kondo N, Ohmae E, Barstow TJ. Methodological validation of the dynamic heterogeneity of muscle deoxygenation within the quadriceps during cycle exercise. Am J Physiol Regul Integr Comp Physiol 2011; 301:R534-41. [DOI: 10.1152/ajpregu.00101.2011] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The conventional continuous wave near-infrared spectroscopy (CW-NIRS) has enabled identification of regional differences in muscle deoxygenation following onset of exercise. However, assumptions of constant optical factors (e.g., path length) used to convert the relative changes in CW-NIRS signal intensity to values of relative concentration, bring the validity of such measurements into question. Furthermore, to justify comparisons among sites and subjects, it is essential to correct the amplitude of deoxygenated hemoglobin plus myoglobin [deoxy(Hb+Mb)] for the adipose tissue thickness (ATT). We used two time-resolved NIRS systems to measure the distribution of the optical factors directly, thereby enabling the determination of the absolute concentrations of deoxy(Hb+Mb) simultaneously at the distal and proximal sites within the vastus lateralis (VL) and the rectus femoris muscles. Eight subjects performed cycle exercise transitions from unloaded to heavy work rates (>gas exchange threshold). Following exercise onset, the ATT-corrected amplitudes (Ap), time delay (TDp), and time constant (τp) of the primary component kinetics in muscle deoxy(Hb + Mb) were spatially heterogeneous (intersite coefficient of variation range for the subjects: 10–50 for Ap, 16–58 for TDp, 14–108% for τp). The absolute and relative amplitudes of the deoxy(Hb+Mb) responses were highly dependent on ATT, both within subjects and between measurement sites. The present results suggest that regional heterogeneity in the magnitude and temporal profile of muscle deoxygenation is a consequence of differential matching of O2 delivery and O2 utilization, not an artifact caused by changes in optical properties of the tissue during exercise or variability in the overlying adipose tissue.
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Affiliation(s)
- Shunsaku Koga
- Applied Physiology Laboratory, Kobe Design University, Kobe
| | - David C. Poole
- Department of Anatomy and Physiology, and Kinesiology, Kansas State University, Manhattan, Kansas
| | | | | | | | | | - Thomas J. Barstow
- Department of Anatomy and Physiology, and Kinesiology, Kansas State University, Manhattan, Kansas
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20
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Patil AV, Safaie J, Moghaddam HA, Wallois F, Grebe R. Experimental investigation of NIRS spatial sensitivity. BIOMEDICAL OPTICS EXPRESS 2011; 2:1478-93. [PMID: 21698012 PMCID: PMC3114217 DOI: 10.1364/boe.2.001478] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Revised: 04/28/2011] [Accepted: 04/28/2011] [Indexed: 05/09/2023]
Abstract
Near infrared spectroscopy (NIRS) is regarded as a potential medical diagnostic technique for investigation of hemodynamic changes. However, uncertainties pertaining to the origin of NIRS signals have hampered its clinical interpretation. The uncertainities in NIRS measurements especially in case of living tissues are due to lack of rigorous combined theoretical-experimental studies resulting in clear understanding of the origin of NIRS signals. For their reliable interpretation it is important to understand the relationship between spatial changes in optical properties and corresponding changes in the NIRS signal. We investigated spatial sensitivity of near infrared optical measurements using an experimental approach. It uses a liquid optical phantom as tissue equivalent, which is explored under robot-control by a small, approximately point like perturbation of desired optical properties, and a NIRS instrument for trans-illumination/reflection measurements. The experimentally obtained sensitivity has been analyzed and compared with numerical simulations. In preliminary experiments we investigated the influence of various optical properties of the medium and of source/detector distances on the spatial sensitivity distribution. The acquired sensitivity maps can be used to define characteristic parameters. As an example, we used a 25% threshold to define a penetration depth measure which provides values in good accordance with published ones. To the best of our knowledge this is the first experimental study of NIRS spatial sensitivity. The presented method will allow in depth experimental investigation of the influence of various conditions pertaining to medium such as optical properties of tissue (scattering and absorption) and of the source/detector configuration.
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Affiliation(s)
- Amol V. Patil
- GRAMFC EA 4293, Fac. Medicine, University of Picardie Jules Verne, Amiens,
France
- Indian Institute of Technology, Bombay,
India
| | - Javad Safaie
- GRAMFC EA 4293, Fac. Medicine, University of Picardie Jules Verne, Amiens,
France
| | - Hamid Abrishami Moghaddam
- GRAMFC EA 4293, Fac. Medicine, University of Picardie Jules Verne, Amiens,
France
- Electrical Engineering Department, K. N. Toosi University of Technology, Teheran,
Iran
| | - Fabrice Wallois
- GRAMFC EA 4293, Fac. Medicine, University of Picardie Jules Verne, Amiens,
France
- GRAMFC EA 4293, EFSN Pediatrique, North Hospital, Amiens,
France
| | - Reinhard Grebe
- GRAMFC EA 4293, Fac. Medicine, University of Picardie Jules Verne, Amiens,
France
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