ORTHOSTATIC HYPOTENSION
Timothy C. Hain, MD. Please read our disclaimer Return to Index. Search this site Page last modified: August 7, 2004
Orthostasis means upright posture, and hypotension means low blood pressure. Thus, orthostatic hypotension consists of symptoms of dizziness, faintness or lightheadedness which appear only on standing, and which are caused by low blood pressure. Only rarely is spinning vertigo caused by orthostasis.
Symptoms that often accompany orthostatic hypotension include chest pain, trouble holding the urine, impotence, and dry skin from loss of sweating.
What Causes Orthostatic Hypotension ?
Blood pressure is maintained by a combination of several things. The heart is the central pump, and a weak or irregular heart can cause orthostasis. Conditions such as arrhythmia, heart failure, deconditioning, and pregnancy are examples where the heart may not be up to the task of providing an adequate blood pressure.
The heart pumps blood, and if there is too little blood volume (anemia, dehydration, dialysis), the pressure drops. The blood vessels in the body also can squeeze (constrict) to raise blood pressure, and if this action is paralyzed, blood pressure may fall. Numerous medications affect blood vessels including most of the medications used for blood pressure, and many of the medications used in psychiatry and for anginal heart pain. Heat, such as a hot shower or from a fever can also dilate blood vessels and cause orthostasis. The nervous system senses and responds to regulate blood pressure. If something is wrong in this control system, blood pressure may fluctuate.
Blood pressure is usually lowered (in persons with orthostasis) by upright posture, food, infection, hyperventilation, hot weather, and lifting of heavy objects. General anesthesia may be unusually dangerous due to blood pressure fluctuations (Bevan et al, 1979).
Vestibular disorders may interact with blood pressure and heart rate control. The vestibular system is one source of information about uprightness (the otoliths), there are some effects of vestibular stimulation on the heart (Radtke, 1992), and there are some patients who have a combination of autonomic and vestibular symptoms.
Neurological disorders can also be caused by orthostasis. This usually takes the form of a TIA precipitated by a blood pressure drop (Brozman et al, 2002).
Diagnosis of Orthostatic Hypotension
Syndromes with orthostatic dizziness or lightheadedness, not associated with low blood pressure include:
Positional orthostatic tachycardia (POT) syndrome. Here, the pulse races on standing.
Low CSF pressure syndrome
Primary orthostatic tremor
Positional vertigo (i.e. BPPV)
Syndromes with orthostatic hypotension that may be diagnosed include:
Cardiogenic (heart related) orthostatic hypotension. In this instance the heart doesn't respond to demands for greater pumping and blood pressure drops.
Low blood volume (e.g. anemia, dehydration, dialysis)
Medication related (usually too high doses of blood pressure medications or medications for depression)
Neurogenic orthostatic hypotension
Sensory neuropathies (diabetes, alcohol, syphilis, Holmes-Adie syndrome, carotid sinus obliteration by endarterectomy, Riley-Day syndrome)
Central types:
MSA - multiple system atrophy or Shy-Drager, Parkinsons, dementia with Lewy bodies. Orthostatic hypotension is nearly universial in MSA, present in about 50% of patients with DLB, and about 5% of patients with Parkinson's. (Thaisetthawatkul et al, 2004). However, since Parkinsonism is by far the most common disorder, there may be as many patients with orthostatic HPN and Parkinson's disease as any of the former.Patients with MSA have intact sympathetic noradrenergic innervation.
Medullary strokes or injuries (rare)
Wernickes syndrome(rare, related to thiamine deficiency)
Output types:
Peripheral neuropathy, especially diabetes and amyloidosis
Spinal cord lesions
PAF - pure autonomic failure or idiopathic orthostatic hypotension. These patients have loss of cardiac sympathetic neurons, and in particular have loss of sympathetic noradrenergic innervation.
Parkinson's disease (post-ganglionic sympathetic denervation). These patients also have loss of cardiac sympathetic neurons.
Dopamine beta-hydroxylase deficiency (hereditary, very rare -- has very high serum dopamine, often ptosis (droopy eyes) and hyperextensible joints. Prolactin may be high)
Unknown type
Orthostatic intolerance in chronic fatigue syndrome (this mainly seems to be a syndrome of adolescents)
Orthostatic intolerance associated with basilar migraine
The diagnosis of orthostasis is made by finding that the systolic/diastolic blood pressure drops at least 25/10 mm mercury on going from lying to standing. The pulse should be checked also. The lack of a pulse response increase when the blood pressure drops implies a neurological cause. An excessive pulse response is termed "POTS" or positional orthostatic tachycardia syndrome. POTS can be associated with considerable disability (Benrud-Larson et al, 2002). Note that pulse can increase due to anxiety and deconditioning as well as autonomic disorders and considerable caution must be used in making this diagnosis.
Once an orthostatic syndrome is determined, additional tests are used to determine why the blood pressure isn't properly regulated.
Laboratory TESTS for orthostatic hyptension
TEST RATIONALE
CBC (blood count) Check for anemia
EKG, other heart tests Check for weakness or irregularity of the heart
CT or MRI scan of head Exclude other nervous system disorders such as multiple system atrophy (MSA)
Autonomic testing (a battery of tests often including tests of blood pressure control and sweating). Tilt table testing, Valsalva testing, and QSART are often included. Localize lesion in nervous system
Plasma norepinephrine (NE) (supine and standing)
Serum dopamine.
Low levels indicate post-ganglionic level lesion (vasoconstrictors like midodrine will not work in this case). Patients with orthostatic hypotension associated with Parkinsonism have low plasma levels of NE while supine, and thus should not respond to Mitodrine. Patients with MSA have normal levels. See Goldstein (2003). Patients with dopamine beta-hydroxylase deficiency have very high dopamine levels.
Glucose tolerance test Diabetes
RPR or FTA Syphilis
Urine porphyrins Porphyria
Serum electrolytes Dehydration
Serum creatinine and BUN Kidney failure
Gastric and small bowel motility studies Detect diabetic gastroparesis and related conditions.
Rectal biopsy If amyloid is suspected
Not every test is needed in every situation. More tests may be recommended based on the results of the previous tests. Tilt table tests are not needed in orthostatic hypotension, but may be indicated in persons with fainting (syncope).
CASE EXAMPLE:
A 57 year old man presented complaining of lightheadness on standing and a pressure sensation in the back of his neck (on standing). Other medical problems included a low thyroid. Blood pressure was 90/65 standing vs 130/80 supine (on medication). This documents a significant orthostatic hypotension. A sweat test showed about 50% anhidrosis. Norepinephrine level was about 30 units lower supine than upright. He was diagnosed as having neurogenic orthostatic hypotension. Present treatment includes Proamatine (mitodrine) 10 mg TID, salt supplements, and erythropoetin.
TREATMENT
Note that neither drug nor non-drug treatment can do as good a job as a well working body. All of the strategies outlined in the next section are intended to alleviate symptoms, but they are unlikely to cure orthostatic hypotension.
Non-Drug Treatment for Orthostatic Hypotension
Generally it is best to start with non-pharmacological treatment, and proceed to drug treatment only when this fails. Note that measures such as voloume expansion with increased salt and fluid, moderate exercise and tilt training are relatively safe but their effectiveness has not been demonstrated by controlled trials (Kapoor, 2003). Nevertheless, we think it is reasonable to give these things a try.
Use an automatic blood pressure cuff (about $30 at Walgreens or Radio Shack). Check blood pressure daily, preferably standing and lying flat, and record it. Also check blood pressure when you have symptoms.
If possible, eliminate medications that lower blood pressure (usually blood-pressure or heart medications). Check with your doctor first, however, to be sure that this is safe.
Take in extra amounts of salt - about 10 gm/day total. If you start to have trouble breathing or get excessive swelling at the ankles, you may have to use less than 10 gm.
Wear Jobst stockings (tight custom made leotard like garment -- worn by both men and women).
Sleep with head of bed elevated about 15-20 degrees (4-6 inches). This maneuver increases blood volume and, after a few days, is helpful. It is also helpful in that it may reduce supine hypertension( sometimes blood pressure is too high lying flat, and too low standing up). Try to be up during the day, not lying in bed. Reconditioning may be helpful for persons who have been on bed rest for long periods of time.
Eat frequent small meals (because eating lowers blood pressure). Avoid sudden standing after eating.
Avoid straining at stool (because this may lower the blood pressure)
Avoid hot showers or excessive heat. Use air conditioners.
Get up gradually in the morning. Take 5 minutes to get up and use support. Perform isometric exercises before moving about.
DRUG TREATMENT for Orthostatic Hypotension
Certain medications may be helpful, usually as a combination. Most useful drugs are Florinef (fludrocortisone), erythropoetin and Midodrine.
Two strong cups of coffee in the morning
Fludrocortisone (Florinef) forces more salt into the bloodstream, 0.1 mg daily starting dose. Blood pressure raises gradually over several days with maximum effect at 1-2 weeks. Alter doses at weekly or biweekly intervals. Hypokalemia (low potassium) occurs in 50%, and hypomagnesemia in 5%. These may need to be corrected with supplements. Florinef should not be used in persons with CHF (congestive heart failure). Florinef does not work in the orthostatic intolerance syndrome of chronic fatigue syndrome (Rowe et al, 2001). Headache is a common side effect.
Effexor (an antidepressant which raises blood pressure as a side effect).
Inderal and other beta-blockers (small doses are used for positional-orthostatic-tachycardia syndrome (POTS), start inderal at 10 mg/d, increase to 30-60 mg/d over 2-3 weeks. Other useful agents are Nadolol (10 mg qd), Pindolol (2.5-5 mg 2-3 times/day) and atenolol (25). Several controlled trials did not show these agents to be effective in preventing syncope (Kapoor, 2003)
Motrin or Indocin (blocks blood-pressure lowering effects of prostaglandins).
Midodrine. An alpha-1 agonist. Causes increased blood pressure, vasoconstriction, pupil dilation, and "hair standing on end". Other common side effects are paresthesia of the scalp or itching. Usual doses are 2.5 mg at breakfast and lunch or three times daily. Doses are increased quickly until a response occurs or a dose of 30 mg/day is attained (Wright et al, 1998). Midodrine does not cross the blood-brain barrier and it is thus not associated with CNS effects. In theory, Mitodrine might work for the orthostatic hypotension of MSA (or Shy-Drager), but not that of Parkinsonism. Most patients on Midodrine also take Florinef (see above). Mitodrine has been shown to be helpful in controlled trials (Kapoor, 2003).
Erythropoietin. This agent is used if there is also anemia and other measures have failed. Doses of 25 to 75 U/kg TIW are used, by injection.
Methylphenidate 5-10 mg orally 3 times/day given with meals. An amphetamine -- side effects may include agitation, tremor, insomnia, supine hypertension.
Ephedrine 12.5-25 mg orally three times/day. Side effects may include tachycardia, tremor and supine hypertension.
Fluoxetine 10-20 mg daily. Side effects may include nausea and anorexia. Paroxetine (Paxil) has also been shown to reduce syncope at 2 years.
Phenobarbital may improve POTS.
Desmopressin. This analog of vasopressin is used as a nasal spray. Low blood sodium is a possible side effect.
OTHER TREATMENTS:
Atrial pacing can be considered when the heart rate is very low. However pacing has been reported not helpful in treatment of recurrent vasovagal syncop (Connolly et al, 2003)
3,4 Dl-threo-dihydroxyphenylserine (DOPS), an artificial amino-acid, may be helpful in certain situations (Freeman, 1996) including dopamine beta-hydroxylase deficiency and post-prandial hypotension from various etiologies.
REFERENCES:
Benarroch EE, Schmeichel AM, Parisi JE. Involvement of the ventrolateral medulla in parkinsonism with autonomic failure. Neurology 2000:54:963-968
Benrud-Larson L and others. Quality of life in patients with postural tachycardia syndrome. Mayo Clin Proc 2002:77:531-37
Bevan, D. R. (1979). "Shy-Drager syndrome. A review and a description of the anaesthetic management." Anaesthesia 34(9): 866-73.
Brozman B and others (2002). Postural vertigo and impaired vasoreflexes caused by a posterior inferior cerebellar artery infarct. Neurology, 59, 9, 1499-1500
Connolly S and others. Pacemaker therapy for prevention of syncope in patients with recurrent severe vasovagal syncope. Jama 2003:289:2224-2229
Freeman R, Young J, Landsberg L, Lipsitz L. The treatment of postprandial hypotension in autonomic failure with 3,4-Dl-threo-dihydroxyphenylserine. Neurology 1996;47:1414-1420
Goldstein DS et al. Orthostatic hypotension from sympathetic denervation in Parkinson's disease. Neurology 2002:58:1247-55
Goldstein DS and others. Plasma levels of catechols and metanephrines in neurogenic orthostatic hypotension. Neurology 2003,60:1327-1332
Radke A, et. al. Evidence for a vestibulo-cardiac reflex in man. The Lancet (356), 736-7
Wright RA and others. A double-blind, dose-response study of midodrine in neurogenic orthostatic hypotension. Neurology 1998, 51:120-124
Stewart JM and others. Orthostatic intolerance in adolescent chronic fatigue syndrome. Pediatrics 1999:103:116-121
LaMaca et al. Cardiovascular response during head-up tilt in chronic fatigue syndrome. Clin Physiol 1999:19:111-120
Poole J and others. Results of isoproterenol tilt table testing in monozygotic twins discordant for chronic fatigue syndrome. Arch Intern Med 2000:160:3461-3468
Rowe and others. Fludrocortisone acetate to treate neurally mediated hypotension in chronic fatigue syndrome. A randomized controlled trial. JAMA 2001, 285:52-59
Sharabi Y and others. Neurotransmitter specificity of sympathetic denervation in Parkinson's disease. Neurology 2003:60:1036-1039
Thaisetthawatkul P and others. Autonomic dysfunction in dementia with Lewy bodies. Neurology 2004:62:1804-1809
Yarrow and others. Force platform recordings in the diagnosis of primary orthostatic tremor. Gait and Posture 2001:13, 27-34
Related Web pages www.dynakids.org
ninds orthostatic hypotension information page (National Institute of Health)
Relevent Books (with links to Amazon.com)
Orthostatic Disorders of the Circulation: Mechanisms, Manifestations, and Treatment by David H.P. Streeten
Circulatory Response to the Upright Posture by James J. Smith (Editor)
Journal of Applied Physiology, Vol 68, Issue 4 1458-1464, Copyright � 1990 by American Physiological Society
--------------------------------------------------------------------------------
ARTICLES
Head-down bed rest impairs vagal baroreflex responses and provokes orthostatic hypotension
V. A. Convertino, D. F. Doerr, D. L. Eckberg, J. M. Fritsch and J. Vernikos-Danellis
National Aeronautics and Space Administration, Space Center, Florida 32899.
We studied vagally mediated carotid baroreceptor-cardiac reflexes in 11 healthy men before, during, and after 30 days of 6 degrees head-down bed rest to test the hypothesis that baroreflex malfunction contributes to orthostatic hypotension in this model of simulated microgravity. Sigmoidal baroreflex response relationships were provoked with ramped neck pressure-suction sequences comprising pressure elevations to 40 mmHg followed by serial R-wave-triggered 15-mmHg reductions to -65 mmHg. Each R-R interval was plotted as a function of systolic pressure minus the neck chamber pressure applied during the interval. Compared with control measurements, base-line R-R intervals and the minimum, maximum, range, and maximum slope of the R-R interval-carotid pressure relationships were reduced (P less than 0.05) from bed rest day 12 through recovery day 5. Baroreflex slopes were reduced more in four subjects who fainted during standing after bed rest than in six subjects who did not faint (-1.8 +/- 0.7 vs. -0.3 +/- 0.3 ms/mmHg, P less than 0.05). There was a significant linear correlation (r = 0.70, P less than 0.05) between changes of baroreflex slopes from before bed rest to bed rest day 25 and changes of systolic blood pressure during standing after bed rest. Although plasma volume declined by approximately 15% (P less than 0.05), there was no significant correlation between reductions of plasma volume and changes of baroreflex responses. There were no significant changes of before and after plasma norepinephrine or epinephrine levels before and after bed rest during supine rest or sitting.(ABSTRACT TRUNCATED AT 250 WORDS)
This article has been cited by other articles:
W. W. Waters, S. H. Platts, B. M. Mitchell, P. A. Whitson, and J. V. Meck
Plasma volume restoration with salt tablets and water after bed rest prevents orthostatic hypotension and changes in supine hemodynamic and endocrine variables
Am J Physiol Heart Circ Physiol, February 1, 2005; 288(2): H839 - H847.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
J. Spaak, S. Montmerle, P. Sundblad, and D. Linnarsson
Long-term bed rest-induced reductions in stroke volume during rest and exercise: cardiac dysfunction vs. volume depletion
J Appl Physiol, February 1, 2005; 98(2): 648 - 654.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
J. Powers and D. Bernstein
The mouse as a model of cardiovascular adaptations to microgravity
J Appl Physiol, November 1, 2004; 97(5): 1686 - 1692.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
K.-i. Iwasaki, R. Zhang, M. A. Perhonen, J. H. Zuckerman, and B. D. Levine
Reduced baroreflex control of heart period after bed rest is normalized by acute plasma volume restoration
Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2004; 287(5): R1256 - R1262.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
T. Laitinen, L. Niskanen, G. Geelen, E. Lansimies, and J. Hartikainen
Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects
J Appl Physiol, June 1, 2004; 96(6): 2333 - 2340.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
S. M. Grenon, S. Hurwitz, N. Sheynberg, X. Xiao, C. D. Ramsdell, C. L. Mai, C. Kim, R. J. Cohen, and G. H. Williams
Role of individual predisposition in orthostatic intolerance before and after simulated microgravity
J Appl Physiol, May 1, 2004; 96(5): 1714 - 1722.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
X. Xiao, R. Mukkamala, N. Sheynberg, S. M. Grenon, M. D. Ehrman, T. J. Mullen, C. D. Ramsdell, G. H. Williams, and R. J. Cohen
Effects of simulated microgravity on closed-loop cardiovascular regulation and orthostatic intolerance: analysis by means of system identification
J Appl Physiol, February 1, 2004; 96(2): 489 - 497.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
P-F. Migeotte, G. K. Prisk, and M. Paiva
Microgravity alters respiratory sinus arrhythmia and short-term heart rate variability in humans
Am J Physiol Heart Circ Physiol, June 1, 2003; 284(6): H1995 - 2006.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
P. J. Mueller and E. M. Hasser
Enhanced sympathoinhibitory response to volume expansion in conscious hindlimb-unloaded rats
J Appl Physiol, May 1, 2003; 94(5): 1806 - 1812.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
H. Waki, T. Shimizu, K. Katahira, T. Nagayama, M. Yamasaki, and S.-I. Katsuda
Effects of microgravity elicited by parabolic flight on abdominal aortic pressure and heart rate in rats
J Appl Physiol, December 1, 2002; 93(6): 1893 - 1899.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
J. A. Moffitt, C. M. Heesch, and E. M. Hasser
Increased GABAA inhibition of the RVLM after hindlimb unloading in rats
Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2002; 283(3): R604 - 614.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
M. H. Khan, A. R. Kunselman, U. A. Leuenberger, W. R. Davidson Jr., C. A. Ray, K. S. Gray, C. S. Hogeman, and L. I. Sinoway
Attenuated sympathetic nerve responses after 24 hours of bed rest
Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2210 - 2215.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
D. S. Kimmerly and J. K. Shoemaker
Hypovolemia and neurovascular control during orthostatic stress
Am J Physiol Heart Circ Physiol, February 1, 2002; 282(2): H645 - 655.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
E. M. HASSER and J. A. MOFFITT
Regulation of Sympathetic Nervous System Function after Cardiovascular Deconditioning
Ann. N.Y. Acad. Sci., June 1, 2001; 940(1): 454 - 468.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
D. Nyhan, S. Kim, S. Dunbar, D. Li, A. Shoukas, and D. E. Berkowitz
Impaired pulmonary artery contractile responses in a rat model of microgravity: role of nitric oxide
J Appl Physiol, January 1, 2002; 92(1): 33 - 40.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
S. D. Beske, G. E. Alvarez, T. P. Ballard, and K. P. Davy
Gender difference in cardiovagal baroreflex gain in humans
J Appl Physiol, November 1, 2001; 91(5): 2088 - 2092.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
M. H. Bestle, P. Norsk, and P. Bie
Fluid volume and osmoregulation in humans after a week of head-down bed rest
Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2001; 281(1): R310 - 317.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
J. A. Pawelczyk, J. H. Zuckerman, C. G. Blomqvist, and B. D. Levine
Regulation of muscle sympathetic nerve activity after bed rest deconditioning
Am J Physiol Heart Circ Physiol, May 1, 2001; 280(5): H2230 - 2239.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
M. A. Perhonen, J. H. Zuckerman, and B. D. Levine
Deterioration of Left Ventricular Chamber Performance After Bed Rest : ""Cardiovascular Deconditioning"" or Hypovolemia?
Circulation, April 10, 2001; 103(14): 1851 - 1857.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
V. A. Convertino
Mechanisms of blood pressure regulation that differ in men repeatedly exposed to high-G acceleration
Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2001; 280(4): R947 - 958.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
W. B. Farquhar, J. A. Taylor, S. E. Darling, K. P. Chase, and R. Freeman
Abnormal Baroreflex Responses in Patients With Idiopathic Orthostatic Intolerance
Circulation, December 19, 2000; 102(25): 3086 - 3091.
[Abstract] [Full Text] [PDF]
--------------------------------------------------------------------------------
K.-I. Iwasaki, R. Zhang, J. H. Zuckerman, J. A. Pawelczyk, and B. D. Levine
Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure
Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2000; 279(6): R2189 - 2199.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
A. Kamiya, S. Iwase, H. Kitazawa, T. Mano, O. L. Vinogradova, and I. B. Kharchenko
Baroreflex control of muscle sympathetic nerve activity after 120 days of 6{degrees} head-down bed rest
Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2000; 278(2): R445 - 452.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
P. Arbeille, S. Herault, G. Fomina, J. Roumy, I. Alferova, and C. Gharib
Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest
J Appl Physiol, December 1, 1999; 87(6): 2168 - 2176.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
J. A. Moffitt, J. C. Schadt, and E. M. Hasser
Altered central nervous system processing of baroreceptor input following hindlimb unloading in rats
Am J Physiol Heart Circ Physiol, December 1, 1999; 277(6): H2272 - 2279.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
J. K. Shoemaker, C. S. Hogeman, and L. I. Sinoway
Contributions of MSNA and stroke volume to orthostatic intolerance following bed rest
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R1084 - 1090.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
D. E. Watenpaugh; and V. A. Convertino
Gender and Heart Rate Regulation
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R1246 - 1246.
[Full Text]
--------------------------------------------------------------------------------
R. Zhang, J. H. Zuckerman, J. A. Pawelczyk, and B. D. Levine
Effects of head-down-tilt bed rest on cerebral hemodynamics during orthostatic stress
J Appl Physiol, December 1, 1997; 83(6): 2139 - 2145.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
V. A. Convertino
Gender differences in autonomic functions associated with blood pressure regulation
Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1998; 275(6): R1909 - 1920.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
B. D. Levine, J. H. Zuckerman, and J. A. Pawelczyk
Cardiac Atrophy After Bed-Rest Deconditioning : A Nonneural Mechanism for Orthostatic Intolerance
Circulation, July 15, 1997; 96(2): 517 - 525.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
J. A. Moffitt, C. M. Foley, J. C. Schadt, M. H. Laughlin, and E. M. Hasser
Attenuated baroreflex control of sympathetic nerve activity after cardiovascular deconditioning in rats
Am J Physiol Regulatory Integrative Comp Physiol, May 1, 1998; 274(5): R1397 - 1405.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
S. Sagawa, R. Torii, K. Nagaya, F. Wada, Y. Endo, and K. Shiraki
Carotid baroreflex control of heart rate during acute exposure to simulated altitudes of 3,800 m and 4,300 m
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1997; 273(4): R1219 - 1223.
[Abstract] [Full Text]
--------------------------------------------------------------------------------
D. Sigaudo, 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, June 1, 1998; 274(6): H1875 - 1884.
[Abstract] [Full Text]
[This message has been edited by sizzled (edited 17 January 2005).]