Cardiorespiratory &
Vascular Dynamics Lab

University of Waterloo
Waterloo, Ontario, Canada

    The research program in the Cardiorespiratory and Vascular Dynamics Laboratory examines the mechanisms responsible for adapting to the stress of physical activity or changes in posture. We have developed a wide range of noninvasive techniques that allow us to explore control mechanisms in transitions between rest and exercise, or between the supine and upright posture. Our research has application to understanding why the sensation of effort might be greater during the transition to exercise in individuals who are on medication to treat cardiovascular diseases or people with diseases that impair the pumping ability of the heart. Our research that explores the cardiovascular responses to the upright posture has widespread application to the many individuals who experience dizziness or faint when they go quickly to standing after lying in bed or resting in a chair. Falls associated with dizziness in older people are serious problems as the risk of bone fractures is greatly increased. Below you can find more detail about our research program including our experiments that will soon be on the International Space Station as well as experiments taking place in Toulouse, France during 2005 in the ESA web site for WISE 2005 or go to candidate recruitment information for the long-term bed rest study of women. Or to the CSA site.

And the profile of our work at the CSA site.

March 13 2007: UW Campus Day Presentation click here

Slides for the presentation "Training and Overtraining for the Marathon and Cross-Country Skiing" can be obtained here

Click on the items in the table below to jump to a selected topic or simply scroll down.

Principal Investigator

Research Focus

Breath-by-Breath

Space Research

Research Funding

Blood Flow Control

Fire Fighter Research

Publications

HR & BP Control

 

The Lab (Being updated 2007)

The Cardiovascular and Respiratory Dynamics Lab, in the Department of Kinesiology at the University of Waterloo has been the home of many outstanding students who have left Waterloo for prestigious positions around the world. The former Ph.D. students include Dr. Gary Butler (Ph.D. 1992) who completed his MD and is associated with the Airline Pilots' Association study of the effects of radiation on pilot health. Dr. Andrew Blaber (Ph.D 1994) is an Assistant Professor at Simon Fraser University and he will be working with us on the Space Station project. Dr. Kevin Shoemaker (Ph.D. 1996) returned to Canada after an NSERC PDF position at Hershey Medical Center. He is now an Associate Professor at University of Western Ontario and also works on the Space Station project. Dr. Maureen MacDonald (Ph.D. 1998) also received an NSERC PDF and is now on faculty at McMaster University. Dr. Mike Tschakovsky (Ph.D. 1998) worked with Dr. Mike Joyner at the world famous Mayo Clinic under support from an NSERC PDF. He is now an Associate Professor at Queen's University. Each of Kevin, Maureen and Mike also won the Young Investigator Award from the Canadian Society for Exercise Physiology based on work from their Ph.D. thesis experiments. This is a significant achievement as they competed against the best graduate students from across Canada. More recently, Stephane Perrey (PhD 2000 from Université Franche-Comté) is an assistant professor in the Faculté des Sciences du Sport, Montpellier, France. Debbie O'Leary (PhD 2001) completed a PDF at UWO and is now a faculty member at Brock University. The most recent PhD graduate is Michael Edwards who has taken a position of scientist with a pharmaceutical company in Texas.
    Recent M.Sc. graudates include Dave Quinlan, Darran Fischer, Kourtney Dupak, and Louis Mattar. Ken Dyson has moved up from MSc to PhD student. There are also many senior undergraduate students in the lab.
     Recent post-docs have included Dr. Mikko Tulppo from University of Oulu, Finland and Dr. Zbigniew Topor who is now back in Calgary and Pascaline Kerbeci from France. The lab technicians include Dave Northey and Myra Gonzales, and Research Associate Danielle Greaves.

Research Focus

    The focus of our research is on the ability of the cardiovascular and respiratory systems to adapt to changing environments. We attempt to integrate the responses of the different components of these systems. One application of this approach examines the body's response at the onset of exercise. This includes the oxygen uptake response measured breath-by-breath, as well as beat-by-beat changes in cardiac output and blood flow distribution patterns in terms of how they impact on the adaptive processes of the energy supply mechanisms (oxidative metabolism versus phosphocreatine depletion versus anaerobic glycolysis). Another application looks at the mechanisms involved in heart rate and blood pressure regulation. Here, various techniques including sequence analysis, cross spectral analysis, autoregressive modelling, and nonlinear methodologies including fractal analysis and chaos mathematics have been applied. With regard to the fractal analysis, the methodology "coarse graining spectral analysis" (CGSA) was developed in our lab by Dr. Yoshi Yamamoto (now at the University of Tokyo). This has provided us with a window through which we can explore the variations that exist in time series data to provide an assessment of overall cardiovascular system complexity.

Space Physiology Takes Off - Maybe This Time!

    Our space research program received a boost when we had a project approved in 1999 for flight on the International Space Station (ISS). Unfortunately, major construction delays have caused all but the very simplest experiments to be cancelled. Our project approved back in January 2002 is working its way through the detailed procedure of getting the flight experiment ready and we hope to continue recruiting astronauts during 2007-08. The research funding from the Canadian Space Agency allowed us to develop the methods for these future space flight experiments. As astronauts are constructing the ISS they will spend several months in the reduced gravity environment of space. This will have major consequences as the cardiovascular system deconditions in space. In normal daily life, the reflex mechanisms regulate blood pressure so that blood flow to the brain can be maintained as we sit, stand or walk in the upright posture. This is normally accomplished by changes in heart rate and constriction of blood vessels. Without the stress of gravity, these reflexes lose their ability to make quick changes so that when astronauts return to Earth, there is an increased risk that they will faint. The following indicate the experiments that have been approved in the most recent competition.
    We have been selected to perform most of the cardiovascular measurements as part of the Long-Term Bed Rest Study of Women taking place in Toulouse, France beginning February 22, 2005. Women will spend 60 days in bed, with one group receiving regular exercise countermeasures using the LBNP-treadmill device of Dr. Alan Hargens from San Diego. Our project "Vascular remodelling and functional consequences of long-term bed rest" will be in collaboration with Drs. Kevin Shoemaker, Jim Rush, Philippe Arbeille and Marc-Antoine Custaud. On the right is a picture of some of the team members standing outside the MEDES clinic in Toulouse. On the front left is Valerie an ultrasound technician from Pr. Arbeille's lab, Danielle (technician from Waterloo and the person most responsible for the day to day success of the study), Pascaline a PhD student from Tours, Kevin Shoemaker, Philippe Arbeille, back row Richard Hughson and Louis a MSc student from Waterloo.

  • 24-hour heart rate variability and physical activity. This project will examine the pattern of beat-by-beat changes in heart rate to determine whether there have been changes in the balance between the parasympathetic and sympathetic neural control of the heart. Measurements will be made on the ground before flight, at regular intervals on ISS and after return.
  • Arterial baroreflex in space. Due to the limited time available for experiments in space, we will restrict our estimates of the arterial baroreflex response to simply examining the heart rate to blood pressure response during 5-minutes rest and 5-minutes of paced breathing at two time points during the flight. These measurements will allow comparisions with similar experiments on the ground before flight and after return.
  • Arterial Baroreflex on Earth. These experiments will examine changes in the vascular and heart rate components of the arterial baroreflex by measuring continuous cardiac output and peripheral vascular resistance during lower body negative pressure (LBNP) tests as soon as possible after return to Earth. We will also monitor changes in cerebral blood flow as arterial blood pressure and arterial carbon dioxide levels change.
  • Changes in central venous compliance. These experiments will explore the role of the central veins in causing poor blood pressure regulation when astronauts return from space. We will monitor central venous pressure and determine the venous volume during application of low levels of LBNP immediately on return from the ISS. After spending a prolonged period of time in space with the central blood volume elevated because gravity has not been pushing the blood toward the lower regions of the body, we expect to see "floppy" veins that will have difficulty maintaining sufficient filling pressure for the heart. The factors assessed by these experiments on return to Earth could point to mechanisms responsible for greater incidence of dizziness and fainting when astronauts return from space, or when people rise quickly from bed in the morning.

    We have been selected to perform most of the cardiovascular measurements as part of the Long-Term Bed Rest Study of Women taking place in Toulouse, France beginning February 22, 2005. Women will spend 60 days in bed, with one group receiving regular exercise countermeasures using the LBNP-treadmill device of Dr. Alan Hargens from San Diego (see below). Our project "Vascular remodelling and functional consequences of long-term bed rest" will be in collaboration with Drs. Kevin Shoemaker, Jim Rush, Philippe Arbeille and Marc-Antoine Custaud.

This picture shows the space research in action. Heather Naylor, Maureen MacDonald, Dave Northey and Mikko Tulppo take measurements with Derek Kimmerly on the tilt table with the LBNP box. We are studying the relationship between central venous pressure and volume and the cardiopulmonary and arterial baroreflexes after 4-hours head down tilt. We hope to conduct an experiment very similar to this on astronauts before they go to the International Space Station and immediately after they return.


 

    Our research in Waterloo has found a place in the French/Russian space programs with examinations of heart rate and blood pressure variability and the arterial baroreflex, and in the NASA/Russian space programs with our breath-by-breath software for exercise testing. We recently went to the MEDES clinical research facility in Toulouse, France to take part in a women's 9-day head-down tilt bed rest study. We are also working with Dr. Alan Hargens' team at UCSD on a 30-day bed rest study in which one member of a twin pair is doing supine treadmill running in a lower body negative pressure chamber as a potential countermeasure to prevent cardiovascular deconditioning while the other twin serves as an inactive control.

Research Funding

    Funding for the research currently comes from the Natural Sciences and Engineering Research Council (NSERC) and the Canadian Space Agency. Support from the Heart and Stroke Foundation of Ontario (HSFO) goes specifically to projects looking at brain blood flow and the effects of age and gender. NSERC funding supports the gas exchange and blood flow dynamics work including major items of equipment (mass spectrometer, Doppler flow and image systems). The laboratory has received a total of $4.5 million in funding since Dr. Hughson came to Waterloo in 1977.

Breath-by-Breath Gas Exchange

    Beginning in 1981, we developed a computer based system to perform breath-by-breath analysis of ventilation and respiratory gas exchange. This original system was based on a data acquisition computer in combination with a number crunching computer. Since 1990, the new software written for the PC computer has been available to other laboratories (about 50 around the world) as part of a package with the Marquette Electronics Inc. respiratory mass spectrometer. Unfortunately, Marquette has been purchased by GE and the mass spectrometer system is no longer produced. We also collaborated on development of a quadrupole mass spectrometer and software that will be in the GASMAP system on the International Space Station.

 

This picture shows Andrew Betik (who finished his M.Sc. in May 2001) on the cycle ergometer with Dr. Richard Hughson and Dave Northey on the right. The MGA-1100 breath-by-breath system is shown. This mass spectrometer-based system was originally purchased in 1982 with the assistance of an NSERC equipment grant. Another NSERC grant supported the purchase of the cycle ergometer.


 

 

Blood Flow Control

    This area of research has advanced since our acquisition in 1990 of a Doppler velocity measurement system to include simultaneous, and continuous, measurement of arterial cross sectional area with a Toshiba SSH-140A colour Doppler echo imaging system. With this approach, we have now been able to quantify the time course of the increase in blood flow to exercising forearm and leg muscles. One of the most exciting recent findings is that the muscle pump, advocated by some to be the sole mechanism responsible for the initial increase in blood flow with muscle contraction, actually works in concert with an immediate (within 2 s) vasodilation (this was work from former PhD students, Kevin Shoemaker and Mike Tschakovsky). We have also shown that there is a tight linear relationship over a wide range of metabolic demands between the supply of oxygen (calculated from the time course of increased blood flow times arterial oxygen content) and the muscle utilization of that oxygen. This provides further support for our model of rate limiting steps described above from whole body exercise. Work in progress is attempting to evaluate the blood flow responses in working and non-working vascular beds.

Here, Heather Naylor is measuring the diameter of the femoral artery with our Toshiba SSH-140A imaging system while Andrew Betik works on our custom built "kicking" ergometer. This ergometer is electrically braked and allows for one- or two-leg exercise with either or both of knee extension or flexion. The Doppler system was purchased with the support of a large equipment grant from NSERC. The ergometer was built with the assistance of the Department of Kinesiology.

 

 

This is Mike Tschakovsky measuring blood flow into the forearm with the Multigon system. Mike Chambers is the willing subject while Debbie O'Leary looks on. The hand grip device was built with support from an American College of Sports Medicine grant to Mike Tschakovsky for a proposal based on his Ph.D. thesis research. Mike T has gone on to successfully complete PDF work at the Mayo Clinic with Dr. Mike Joyner and he has taken up a faculty position at Queen's University.


 

Heart Rate and Blood Pressure Control

    In the past 10 years, we have refined and developed a number of tools that have allowed us to explore the beat-by-beat interactions that occur within the cardiovascular system, and to better understand how this interaction is involved in the regulatory process. Beginning with the work of Gary Butler with his MSc thesis and into his PhD thesis, we have done some short-term bed rest studies in Waterloo. In 1990, we had the opportunity to collaborate with Pr. C. Gharib in Lyon, France, and to be involved with the French medical space research group (MEDES) in Toulouse during the MEDES-CNES 28 day head down bedrest. The methodologies that we had developed related to spontaneous baroreflex function and coarse graining spectral analysis allowed us to contribute by exploring the autonomic nervous function during a period of cardiovascular deconditioning. This work provided the opportunity for continued involvement with the French/Russian space programs (e.g. see J. Appl. Physiol. 77: 69-77, 1994).
    Continued work in this area is being carried on by Debbie O'Leary and Dr. Mikko Tulppo. This research focuses on the cardiorespiratory interactions by simultaneous measurements of heart rate, blood pressure, cardiac stroke volume by Doppler methods, respiration, and cerebral blood flow.

Fire Fighter Research

    We have recently become aligned with Dr. Beth Weckman from Mechanical Engineering on her major initiative for a live fire research centre. Dr. Weckman will study the behaviour of fires while we study the responses of the fire fighters. Mike Williams-Bell and several senior undergraduates have been busy testing student volunteers and incumbent firefighters to determine the demands of the Candidate Physical Abilities Test (CPAT) that was developed by a joint initiative of the International Association of Fire Chiefs and the International Association of Fire Fighters. The CPAT test is a bone fide occupational requirement and more information can be found at the UW Fitness website.

    This text is WHITE and is just to fill space. Can remove if I figure out how to palce figures! We have recently become aligned with from Mechanical Engineering on her major initiative for a live fire research centre. Dr. Weckman will study the behaviour of fires while we study the responses of the fire fighters. Mike Williams-Bell and several senior undergraduates have been busy testing student volunteers and incumbent firefighters to determine the demands of the Candidate Physical Abilities Test (CPAT) that was developed by a joint initiative of the International Association of Fire Chiefs and the International Association of Fire Fighters. The CPAT test is a bone fide occupational requirement and more information can be found at the

Journal Publications from the Cardiovascular and Respiratory Dynamics Laboratory from 1991-2001 (sorry but there hasn't been time to update this for a while). Some papers are listed with links to download PDF format copies. Be aware that publishers might place restrictions on access to some papers.

  1. Tordi, N., Perrey, S., Harvey, A., and Hughson, R.L. Oxygen uptake kinetics during two bouts of heavy cycling separated by fatiguing sprint exercise in humans. J Appl Physiol 2002 Oct 11 [epub ahead of print] PDF
  2. Edwards, M.R., Shoemaker, J.K., and Hughson, R.L. Dynamic modulation of cerebrovascular resistance as an index of autoregulation under tilt and controlled PETCO2. Am J Physiol Regul Integr Comp Physiol. 283: R653-R662, 2002. PDF
  3. Edwards, M.R., Martin, D.H., and Hughson, R.L. Cerebral hemodynamics and resistance exercise. Med. Sci. Sports Exerc. 34: 1207-1211, 2002. PDF
  4. Sigaudo-Roussel, D., Maillet, A., Custaud, M.A., Frutoso, J., Güell, A., Kaspranski, R., Hughson, R.L., Gharib, C., and Fortrat, J.O. Heart rate variability after prolonged spaceflights. Eur J Appl Physiol. 86: 258-265, 2002.
  5. Lin, DC, Hughson, RL. A phenomenology model of normal sinus rhythm in healthy humans. IEEE Trans. Biomed. Eng. 49: 97-109, 2002.
  6. Hughson, R.L., Edwards, M.R., O'Leary, D.D., and Shoemaker, J.K. Critical analysis of cerebrovascular autoregulation during repeated head up tilt. Stroke 32: 2403-2408, 2001. PDF
  7. Perrey, S., Tschakovsky, M.E., and Hughson, R.L. Ischemic muscle chemoreflex elevates muscle blood flow and oxygen uptake during onset of exercise in nonischemic human forearm. J. Appl. Physiol. 91: 2010-2016, 2001. PDF
  8. Perrey, S., Betik, A., Candau, R., Rouillon, J.D., and Hughson, R.L. Comparison of oxygen uptake kinetics during concentric and eccentric cycle exercise. J. Appl. Physiol. 91: 2135-2142, 2001. PDF
  9. Shoemaker, J.K., O'Leary, D.D., and Hughson, R.L. PETCO2 inversely affects MSNA response to orthostatic stress. Am J Physiol Heart Circ Physiol 281: H1040-H1046, 2001. PDF
  10. Blaber, A.P., Bondar, R.L., Moradshahi, P., Serrador, J.M., and Hughson, R.L. Inspiratory CO2 increases orthostatic tolerance during repeated tilt. Aviat. Space Environ Med 72: 985-991, 2001.
  11. K. H. Doyon, S. Perrey, D. Abe, and R. L. Hughson. Field testing of VO2peak in cross country skiers with portable breath-by-breath system. Can. J. Appl. Physiol. 26: 1-11, 2001.
  12. J. O. Fortrat, D. Sigaudo, R. L. Hughson, A. Maillet, Y. Yamamoto, and C. Gharib. Effect of prolonged head-down bed rest on complex cardiovascular dynamics. Autonomic Neuroscience 86: 192-201, 2001.
  13. Tulppo, M.P., R.L. Hughson, T.H. Mäkikallio, K.E. Juhani Airaksinen, T. Seppänen and H.V. Huikuri. Effects of exercise and passive head-up tilt on fractal and complexity properties of heart rate dyanmics. Am. J. Physiol.: Heart Circ. Physiol. 280: H1081-H1087, 2001. PDF
  14. Green, H.J., B. Roy, S. Grant, R. Hughson, M. Burnett, C. Otto, A. Pipe, D. McKenzie and M. Johnson. Increases in submaximal cycling efficiency mediated by altitude acclimatization. J. Appl. Physiol. 89: 1189-1197, 2000. PDF
  15. MacDonald MJ, Green HJ, Naylor HL, Otto C, and Hughson RL. Reduced oxygen uptake during steady state exercise after 21-day mountain climbing expedition to 6,194 m. Can J Appl Physiol 26: 143-156, 2001.
  16. Shoemaker JK, O'Leary DD, and Hughson RL. PETCO2 inversely affects MSNA response to orthostatic stress. Am J Physiol Heart Circ Physiol 281: 2001. PDF
  17. Tulppo MP, Mäkikallio TH, Seppänen T, Shoemaker JK, Tutungi E, Hughson RL, and Huikuri HV. Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamics. Clin Physiol 21: 2001.
  18. Griffin L, Garland SJ, Ivanova T, and Hughson RL. Blood flow in the triceps brachii muscle in humans during sustained submaximal isometric contractions. Eur J Appl Physiol. 84:432-7, 2001.
  19. van Beekvelt MCP, Shoemaker JK, Tschakovsky ME, Hopman MTE, and Hughson RL. Blood flow and muscle oxygen uptake at the onset and end of moderate and heavy dynamic forearm exercise. Am J Physiol Regul Integr Comp Physiol 280: 2001. PDF
  20. Hughson RL, Tschakovsky ME, and Houston ME. Regulation of oxygen consumption at the onset of exercise (Invited Review). Exercise and Sports Science Reviews 29: 2001.
  21. Lin, D.C. and Hughson, R.L. Using gaussians to model increment distribution of the long-term R-wave interval in healthy humans. Chaos, Solitons and Fractals 12: 1335-1345, 2001.
  22. MacDonald,M.J., Naylor,H.L., Tschakovsky,M.E., and Hughson,R.L. Evidence that peripheral circulatory factors limit the rate of increase in muscle O2 uptake at the onset of heavy exercise. J. Appl. Physiol. 90: 83-89, 2001. PDF
  23. MacDonald, M.J., M.A. Tarnopolsky and R.L. Hughson. Effect of hyperoxia and hypoxia on leg blood flow and pulmonary and leg oxygen uptake at the onset of kicking exercise. Can. J. Physiol. Pharmacol. 78: 67-74, 2000
  24. Tschakovsky, M.E. and R.L. Hughson. Venous emptying mediates a transient vasodilation in the human forearm. Am. J. Physiol.: Heart Circ. Physiol. 279: 1007-1014, 2000. PDF
  25. Lucy,S.D., Hughson,R.L., Kowalchuk,J.M., Paterson,D.H., and Cunningham,D.A. Body position and cardiac dynamic and chronotropic responses to steady-state isocapnic hypoxaemia in humans. Exp. Physiol. 85: 227-237, 2000.
  26. McGill,S.M., Hughson,R.L., and Parks,K. Lumbar erector spinae oxygenation during prolonged contractions: implications for prolonged work. Ergonomics 43: 486-493, 2000.
  27. McGill,S.M., Hughson,R.L., and Parks,K. Changes in lumbar lordosis modify the role of the extensor muscles. Clin. Biomech. 15: 777-780, 2000.
  28. S. Houtman, B. Oeseburg, R. L. Hughson, and M. T. E. Hopman. Tilt induced changes in the sympathetic nervous system activity and cardiovascular stability in spinal cord injured and able-bodied individuals. Clin. Auton. Res. 10: 207-212, 2000.
  29. Hughson R.L., D.D. O'Leary, A.C. Betik and H. Hebestreit. Kinetics of oxygen uptake at the onset of exercise near or above peak oxygen uptake. J. Appl. Physiol. 88: 1812-1819, 2000. PDF
  30. Hughson, R.L. and R.L. Bondar. (Invited Review) Autonomic nervous system function in space. Handbook of Clinical Neurology Vol. 74 (30): 273-305, 1999. O. Appenzeller, ed.
  31. Tschakovsky, M. and R.L. Hughson. Invited Review: Interaction of factors determining oxygen uptake at the onset of exercise. J. Appl. Physiol. 86: 1101-1113, 1999. PDF
  32. Hughson, R.L. (Invited Review) Oxygen uptake kinetics during exercise in humans in relatio nto muscle blood flow. J. Exerc. Sci. 9: 1-12, 1999.
  33. MacDonald, M.J., M.A. Tarnopolsky and R.L. Hughson. Effect of hyperoxia and hypoxia on leg blood flow and pulmonary and leg oxygen uptake at the onset of kicking exercise. Can. J. Physiol. Pharmacol. In press, 1999
  34. Serrador, J.M., H.C. Finlayson and R.L. Hughson. Physical activity is a major contributor to the ultra-low frequency components of heart rate variability. Heart 82: e9, 1999. (http://www.heartjnl.com/cgi/content/full/82/6/e9)
  35. O'Leary, D.D., D.C. Lin, and R.L. Hughson. Determination of baroreflex gain using autoregressive moving average analysis during spontaneous breathing. Clin. Physiol. 19: 369-377, 1999.
  36. Hicks, A., S. McGill, and R.L. Hughson. Tissue oxygenation by near-infrared spectroscopy and muscle blood flow during isometric contractions of the forearm. Can. J. Appl. Physiol. 24: 216-230, 1999.
  37. MacDonald, M.J., M.A. Tarnopolsky, H.J. Green, and R.L. Hughson. Comparison of femoral blood gases and muscle near infrared spectroscopy at the onset of exercise in humans. J.Appl.Physiol. 86: 687-693, 1999. PDF
  38. Naylor, H.L., J.K. Shoemaker, R.W. Brock, and R.L. Hughson. Prostaglandin inhibition causes an increase in reactive hyperaemia after ischaemic exercise in human forearm. Clin. Physiol. 19: 211-220, 1999.
  39. Hughson, R.L. and M.E. Tschakovsky. Cardiovascular dynamics at the onset of exercise. Med. Sci. Sports Exerc. 31: 1005-1010, 1999.
  40. Shoemaker, J.K. and R.L. Hughson. Adaptation of blood flow during the rest to work transition in humans. Med. Sci. Sports Exerc. 31: 1019-1026, 1999
  41. Tschakovsky, M. and R.L. Hughson. Ischemic muscle chemoreflex response elevates blood flow in non-ischemic exercising human forearm muscle. Am. J. Physiol.Heart Circ. Physiol. 277: H635-H642, 1999. PDF
  42. Parlow, J.L., G. Begou, P. Sagnard, J.M. Cottet-Emard, J.C. Levron, G. Annat, F. Bonnet, M. Ghignone, R.L. Hughson, J.P. Viale, L. Quintin. Cardiac baroreflex during the postoperative period in patients with hypertension. Anesthesiology 90: 681-692, 1999.
  43. Brock, R.W., M.E. Tschakovsky, J.K. Shoemaker, J.R. Halliwill, M.J. Joyner, and R.L. Hughson. Effects of acetylcholine and nitric oxide on forearm blood flow at rest and after a single muscle contraction. J.Appl.Physiol. 85: 2249-2254, 1998. PDF
  44. Hebestreit, H., S. Kriemler, R.L. Hughson, and O. Bar-Or. Kinetics of oxygen uptake at the onset of exercise in boys and men. J.Appl.Physiol. 85: 1833-1841, 1998. PDF
  45. Hughson, R.L., M.J. MacDonald, R.C. Ter-Vrugt, and D.R. Northey. Central venous pressure-volume relationship with head-down tilt and LBNP. J.Gravit.Physiol. In Press: 1998.
  46. MacDonald, M.J., J.K. Shoemaker, M.E. Tschakovsky, and R.L. Hughson. Alveolar oxygen uptake and femoral artery blood flow dynamics in upright and supine leg exercise in humans. J.Appl.Physiol. 85: 1622-1628, 1998.
  47. Pavy-Le Traon, A., D. Sigaudo, P. Vasseur, A. Maillet, J.O. Fortrat, R.L. Hughson, G. Gauquelin-Koch, and C. Gharib. Cardiovascular responses to orthostatic tests after a 42-day head-down bed-rest. Eur.J.Appl.Physiol.Occup.Physiol. 77: 50-59, 1998.
  48. Serrador, J.M., R.L. Bondar, and R.L. Hughson. Ventilatory response to passive head up tilt. Adv.Exp.Med.Biol. 450: 133-139, 1998.
  49. Shoemaker, J.K., M.E. Tschakovsky, and R.L. Hughson. Vasodilation contributes to the rapid hyperemia with rhythmic contractions in humans. Can.J.Physiol.Pharmacol. 76: 418-427, 1998.
  50. Sigaudo, D., J.O. Fortrat, A.M. Allevard, A. Maillet, J.M. Cottet-Emard, A. Vouillarmet, R.L. Hughson, G. Gauquelin-Koch, and C. Gharib. Changes in the sympathetic nervous system induced by 42 days of head-down bed rest. Am.J.Physiol.Heart Circ.Physiol. 274: H1875-H1884, 1998. PDF
  51. Shoemaker, J.K, M.E. Tschakovsky and R.L. Hughson. Vasodilation contributes to the rapid hyperaemia with rhythmic contractions in humans. Can. J. Physiol. Pharmacol. In press, 1998.
  52. Sigaudo, D. J.-O. Fortrat, A.-M. Allevard, A. Maillet, J.-M. Cottet-Emard, A. Vouillarmet, R.L. Hughson, G. Gauquelin-Koch and C. Gharib. Changes in the sympathetic nervous system induced by 42-days of head-down bed-rest. Am. J. Physiol.: Heart Circ. Physiol. In press, 1998.
  53. Shoemaker, J.K., M.J. MacDonald and R.L. Hughson. Time course of brachial artery diameter responses to rhythmic handgrip exercise in humans. Cardiovasc. Res. 35: 125-131, 1997.
  54. Fortrat, J.O., Y. Yamamoto and R.L. Hughson. Respiratory influences on nonlinear dynamics of heart rate variability. Biol. Cybern. 77: 1-10, 1997.
  55. MacDonald, M., P.K. Pedersen and R.L. Hughson. Acceleration of oxygen uptake kinetics in heavy submaximal exercise by hyperoxia and prior high intensity exercise. J. Appl. Physiol. 83: 1318-1325, 1997.
  56. Shoemaker, J.K., J.R. Halliwill, R.L. Hughson and M.J. Joyner. Contributions of acetylcholine and nitric oxide to forearm blood flow at exercise onset and recovery. Am. J. Physiol.: Heart Circ. Physiol. 273: H000-H000, 1997. PDF
  57. Pavy-Le Traon, A., D. Siguado, P. Vasseur, A. Maillet, J.O. Fortrat, R.L Hughson, G. Gauquelin-Koch and C. Gharib. Cardiovascular responses to orthostatic tests after a 42-day head-down bed-rest. Eur. J. Appl. Physiol. In press, 1997.
  58. Gratadour,P., P. Sagnard, H. Counioux, B. Bagou, G. Annat, R.L. Hughson, J.-P. Viale and L. Quintin. Sympathovagal effects of spinal anaesthesia assessed by the spontaneous cardiac baroreflex. Anaesthesiology 87: 1359-1367, 1997.
  59. Pavy-Le Traon,A., D. Siguaudo, P. Vasseur, J.O. Fortat, A. Güell, R.L. Hughson and C. Gharib. Orthostatic tests after a 4-day confinement or simulated weightlessness. Clin. Physiol. 17: 41-55, 1997.
  60. Shoemaker, J.K., S.M. Phillips, H.J. Green and R.L. Hughson. Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training. Cardiovasc. Res. 31: 278-286, 1996.
  61. Blaber, A.P., and R.L. Hughson. Cardiorespiratory interactions during fixed pace resistive breathing. J. Appl. Physiol. 80:1618-1626, 1996.
  62. Sigaudo, D., J.O. Fortrat, A. Maillet, A. Allevard, A. Pavy-Le Traon, R.L. Hughson, A. Güell, C. Gharib and G. Gauquelin. Comparison of a 4-day confinement and head-down tilt on endocrine response and cardiovascular variability in humans. Eur. J. Appl. Physiol. 73: 28-37, 1996.
  63. Hughson, R.L., J.K. Shoemaker, M.E. Tschakovsky and J.M. Kowalchuk. Dependence of muscle O2 on blood flow dynamics at the onset of forearm exercise. J. Appl. Physiol. 81: 1619-1626, 1996.
  64. Shoemaker, J.K., H.L. Naylor, Z.I. Pozeg and R.L. Hughson. Failure of postraglandins to modulate the time course of blood flow during dynamic forearm exercise in humans. J. Appl. Physiol. 81: 1516-1521, 1996.
  65. Shoemaker, J.K., Z.I. Pozeg and R.L. Hughson. Forearm blood flow by Doppler ultrasound during rest and exercise: tests of day-to-day repeatability. Med. Sci. Sports Exerc. In press 81: 1144-1149, 1996.
  66. Tschakovsky, M.E., J.K. Shoemaker and R.L. Hughson. Vasodilation and muscle pump contribution to immediate exercise hyperemia. Am. J. Physiol.: Heart Circ. Physiol. 271: H1697-H1701, 1996.
  67. Gregoire, J., S. Tuck, Y. Yamamoto and R.L. Hughson. Heart rate variability at rest and exercise: Influence of age, gender, and physical training. Can. J. Appl. Physiol. 21: 455-470, 1996.
  68. Blaber, A. P., Y. Yamamoto, and R. L. Hughson. Change in phase relationship between systolic BP and RR-interval during lower body negative pressure. Am. J. Physiol. Heart Circ. Physiol. 268: H1688-H1693, 1995.
  69. Blaber, A. P., Y. Yamamoto, and R. L. Hughson. Methodology of spontaneous baroreflex relationship assessed by surrogate data analysis. Am. J. Physiol. Heart Circ. Physiol. 268: H1682-H16871995.
  70. Hughson, R. L., A. Maillet, G. Dureau, Y. Yamamoto, and C. Gharib. Harmonic and fractal blood pressure variability in heart transplant patients. Hypertension 25: 643-650, 1995.
  71. Hughson, R. L., A. Maillet, G. Gauquelin, P. Arbeille, Y. Yamamoto, and C. Gharib. Investigation of hormonal effects during 10 hour head down tilt on heart rate and blood pressure variability. J. Appl. Physiol. 78: 583-596, 1995.
  72. Hughson, R. L. Coupling of ventilation and gas exchange during transitions in work rate by humans. Resp. Physiol. 101: 87-98, 1995.
  73. Hughson, R. L. and J. M. Kowalchuk. Kinetics of oxygen uptake for submaximal exercise in hyperoxia, normoxia, and hypoxia. Can. J. Appl. Physiol. 20: 198-210, 1995.
  74. Hughson, R. L. Coupling of ventilation and gas exchange during transitions in work rate by humans. Respir. Physiol. 101: 87-98, 1995.
  75. Hughson, R. L., H. J. Green, and M. T. Sharratt. Gas exchange, blood lactate, and plasma catecholamines during incremental exercise in hypoxia and normoxia. J. Appl. Physiol. 79: 1134-1141, 1995.
  76. Parlow, J., J.-P. Viale, G. Annat, R. Hughson, and L. Quintin. Spontaneous cardiac baroreflex in humans: Comparison with drug-induced responses. Hypertension 25: 1058-1068, 1995.
  77. Phillips, S. M., H. J. Green, M. J. MacDonald, and R. L. Hughson. Progressive effect of endurance training on VO2 kinetics at the onset of submaximal exercise. J. Appl. Physiol. 79: 1914-1920, 1995.
  78. Tschakovsky, M. E., J. K. Shoemaker, and R. L. Hughson. Beat-by-beat forearm blood flow with Doppler ultrasound and strain-gauge plethysmography. J. Appl. Physiol. 79: 713-719, 1995.
  79. Yamamoto, Y., J. O. Fortrat, and R. L. Hughson. On the fractal nature of heart rate variability in humans: effects of respiratory sinus arrhythmia. Am. J. Physiol. Heart Circ. Physiol. 269: H480-H486, 1995.
  80. Yamamoto, Y., Y. Nakamura, H. Sato, M. Yamamoto, K. Kato, and R. L. Hughson. On the fractal nature of heart rate variability in humans: Effects of vagal blockade. Am. J. Physiol. Regul. Integr. Comp. Physiol. 269: R830-R837, 1995.
  81. Butler, G. C., Y. Yamamoto, and R. L. Hughson. Heart rate variability to monitor autonomic nervous system activity during orthostatic stress. J. Clin. Pharmacol. 34: 558-562, 1994.
  82. Butler, G. C., Y. Yamamoto, and R. L. Hughson. Fractal nature of short-term systolic BP and HR variability during lower body negative pressure. Am. J. Physiol. Regul. Integr. Comp. Physiol. 267: R26-R33, 1994.
  83. Hughson, R. L., Y. Yamamoto, R. E. McCullough, J. R. Sutton, and J. T. Reeves. Sympathetic and parasympathetic indicators of heart rate control at altitude studied by spectral analysis. J. Appl. Physiol. 77: 2537-2542, 1994.
  84. Hughson, R. L., Y. Yamamoto, A. Maillet, J. O. Fortrat, A. Pavy-Le Traon, G. C. Butler, A. Güell, and C. Gharib. Altered autonomic regulation of cardiac function during head-up tilt after 28-day head-down bed-rest with counter-measures. Clin. Physiol. 14: 291-304, 1994.
  85. Hughson, R. L., A. Maillet, C. Gharib, J. O. Fortrat, Y. Yamamoto, A. Pavy-Le Traon, D. Riviere, and A. Güell. Reduced spontaneous baroreflex response slope during lower body negative pressure after 28 day head down bedrest. J. Appl. Physiol. 77: 69-77, 1994.
  86. Hughson, R. L., Y. Yamamoto, A. P. Blaber, A. Maillet, J. O. Fortrat, A. Pavy-Le Traon, A. Guell, and C. Gharib. Effect of 28-day head-down bed rest with countermeasures on heart rate variability during LBNP. Aviat. Space Environ. Med. 65: 293-300, 1994.
  87. Iellamo, F., R. L. Hughson, F. Castrucci, J. M. Legramante, G. Raimondi, and G. Tallarida. Evaluation of spontaneous baroreflex modulation of sinus node during isometric exercise in healthy humans. Am. J. Physiol. Heart Circ. Physiol. 267: H994-H1001, 1994.
  88. Maillet, A., J. O. Fortrat, D. Sigaudo, A. Pavy-Le-Traon, R. L. Hughson, C. Gharib, and G. Gauquelin. Variabilité de l'intervalle R-R et baroréflexe spontané avant et après un séjour en apensateur. Presse Med. 23: 10431994.
  89. Maillet, A., A. Pavy-Le Traon, A. M. Allevard, D. Siguardo, R. L. Hughson, C. Gharib, and G. Gauquelin. Hormone changes induced by 37.5-h head-down tilt (-6°) in humans. Eur. J. Appl. Physiol. 68: 497-503, 1994.
  90. Shoemaker, J. K., L. Hodge, and R. L. Hughson. Cardiorespiratory kinetics and femoral artery blood velocity during dynamic knee extension exercise. J. Appl. Physiol. 77: 2625-2632, 1994.
  91. Yamamoto, Y. and R. L. Hughson. On the fractal nature of heart rate variability in humans: effects of data length and b-adrenergic blockade. Am. J. Physiol. Regul. Integr. Comp. Physiol. 266: R40-R49, 1994.
  92. Butler, G. C., Y. Yamamoto, and R. L. Hughson. Heart rate variability and fractal dimension during orthostatic challenges. J. Appl. Physiol. 75: 2602-2612, 1993.
  93. Hughson, R. L., Y. Yamamoto, G. C. Butler, A. Guell, and C. Gharib. Evaluation of spontaneous baroreflex response during head up tilt after 28 days of head down tilt bed rest. Acta Astronautica 29: 601-605, 1993.
  94. Hughson, R. L., J. E. Cochrane, and G. C. Butler. Faster O2 uptake kinetics at onset of supine exercise with than without lower body negative pressure. J. Appl. Physiol. 75: 1962-1967, 1993.
  95. Hughson, R. L., L. Quintin, G. Annat, Y. Yamamoto, and C. Gharib. Spontaneous baroreflex by sequence and power spectral methods in humans. Clin. Physiol. 13: 663-676, 1993.
  96. Yamamoto, Y., R. L. Hughson, J. R. Sutton, C. S. Houston, A. Cymerman, E. L. Fallen, and M. V. Kamath. Operation Everest II: An indication of deterministic chaos in human heart rate variability at extreme simulated altitude. Biol. Cybern. 69: 205-212, 1993.
  97. Yamamoto, Y. and R. L. Hughson. Extracting fractal components from time series. Physica D 68: 250-264, 1993.
  98. Butler, G. C., Y. Yamamoto, H. C. Xing, D. R. Northey, and R. L. Hughson. Probing heart rate and blood pressure control mechanisms during graded levels of lower body negative pressure (LBNP). Microgravity Q. 2: 133-140, 1992.
  99. Cochrane, J. E. and R. L. Hughson. Computer simulation of O2 transport and utilization mechanisms at the onset of exercise. J. Appl. Physiol. 73: 2382-2388, 1992.
  100. Yamamoto, Y., R. L. Hughson, and Y. Nakamura. Autonomic nervous system responses to exercise in relation to ventilatory threshold. Chest 101 Suppl. 206S-210S, 1992.
  101. Butler, G. C., H. C. Xing, D. R. Northey, and R. L. Hughson. Reduced orthostatic tolerance following 4 h head-down tilt. Eur. J. Appl. Physiol. 62: 26-30, 1991.
  102. Hughson, R. L., D. R. Northey, H. C. Xing, B. H. Dietrich, and J. E. Cochrane. Alignment of ventilation and gas fraction for breath-by-breath respiratory gas exchange calculations in exercise. Comput. Biomed. Res. 24: 118-128, 1991.
  103. Hughson, R. L. and J. M. Kowalchuk. b-blockade and oxygen delivery to muscle during exercise. Can. J. Physiol. Pharmacol. 69: 285-289, 1991.
  104. Hughson, R. L., L. A. Cuervo, A. E. Patla, D. A. Winter, H. C. Xing, B. H. Dietrich, and G. D. Swanson. Time domain analysis of oxygen uptake during pseudorandom binary sequence exercise tests. J. Appl. Physiol. 71: 1991.
  105. Hughson, R. L., H. C. Xing, C. Borkhoff, and G. C. Butler. Kinetics of ventilation and gas exchange during supine and upright cycle exercise. Eur. J. Appl. Physiol. 63: 300-307, 1991.
  106. Xing, H. C., J. E. Cochrane, Y. Yamamoto, and R. L. Hughson. Frequency domain analysis of ventilation and gas exchange kinetics in hypoxic exercise. J. Appl. Physiol. 71: 2394-2401, 1991.
  107. Yamamoto, Y., R. L. Hughson, and J. C. Peterson. Autonomic control of heart rate during exercise studied by heart rate variability spectral analysis. J. Appl. Physiol. 71: 1136-1142, 1991.
  108. Yamamoto, Y., M. Miyashita, R. L. Hughson, S. Tamura, M. Shinohara, and Y. Mutoh. The ventilatory threshold gives maximal lactate steady state. Eur. J. Appl. Physiol. 63: 55-59, 1991.
  109. Yamamoto, Y. and R. L. Hughson. Coarse graining spectral analysis: a new method for studying heart rate variability. J. Appl. Physiol. 71: 1143-1150, 1991.

Send comments and mail to Dave Northey

Cardiorespiratory & Vascular Dynamics Laboratory
Dept. of Kinesiology
University of Waterloo
Waterloo, ON N2L 3G1
CANADA
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Last updated by Richard Hughson on 10/25/2002