Medicine:Hypotension

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Short description: Abnormally low blood pressure
Hypotension
Depiction of a hypotension (low blood pressure) patient getting her blood pressure checked
Image showing patient having blood pressure checked. Systolic blood pressure less than 90 mmHg is considered hypotension (low blood pressure)
SpecialtyCritical care medicine, cardiology
SymptomsDizziness, clumsiness, giddiness, headaches, lightheadedness, fatigue, nausea, blurred vision, shakiness, breathlessness, increased thirst, irregular heartbeat, chest pain, fever, seizures
ComplicationsFainting, bleeding
Risk factorsOlder patient, Malnourishment
Diagnostic methodPhysical examination, based on symptoms
TreatmentIntravenous fluid

Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure.[1] Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood[2] and is indicated by two numbers, the systolic blood pressure (the top number) and the diastolic blood pressure (the bottom number), which are the maximum and minimum blood pressures within the cardiac cycle, respectively.[3] A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension.[4][5] Different numbers apply to children.[6] However, in practice, blood pressure is considered too low only if noticeable symptoms are present.[7]

Symptoms may include dizziness, lightheadedness, confusion, feeling tired, weakness, headache, blurred vision, nausea, neck or back pain, an irregular heartbeat or feeling that the heart is skipping beats or fluttering, and fainting.[4] Hypotension is the opposite of hypertension, which is high blood pressure.[2] It is best understood as a physiological state rather than a disease.[2] Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.[3] Shock is classified based on the underlying cause, including hypovolemic shock, cardiogenic shock, distributive shock, and obstructive shock.[8]

Hypotension can be caused by strenuous exercise, excessive heat, low blood volume (hypovolemia),[9] hormonal changes,[10] widening of blood vessels,[11] anemia,[12] vitamin B12 deficiency,[7][13] anaphylaxis,[7] heart problems,[14] or endocrine problems.[15] Some medications can also lead to hypotension.[16] There are also syndromes that can cause hypotension in patients including orthostatic hypotension,[17] vasovagal syncope,[18] and other rarer conditions.[19][20]

For many people, excessively low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders.[17]

For some people who exercise and are in top physical condition, low blood pressure could be normal.[21] A single session of exercise can induce hypotension and water-based exercise can induce a hypotensive response.[22]

Treatment depends on what causes low blood pressure.[4] Treatment of hypotension may include the use of intravenous fluids or vasopressors.[23] When using vasopressors, trying to achieve a mean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve an MAP of greater than 65 mmHg in adults.[24]

Signs and symptoms

For many people, low blood pressure goes unnoticed.[4] For some people, low blood pressure may be a sign of an underlying health condition, especially when it drops suddenly or occurs with symptoms.[5] Older adults also have a higher risk of symptoms of low blood pressure, such as falls, fainting, or dizziness when standing or after a meal.[4] If the blood pressure is sufficiently low, fainting (syncope) may occur.[17]

Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:[5]


  • confusion
  • dizziness or lightheadedness
  • feeling tired or weak
  • shortness of breath
  • irregular heartbeat, feeling that the heart is skipping beats, or fluttering
  • chest pain
  • fever
  • headache
  • stiff neck
  • severe back or neck pain
  • cough with sputum
  • prolonged diarrhea or vomiting
  • chills
  • loss of appetite
  • nausea
  • dyspepsia (indigestion)
  • dysuria (painful urination)
  • acute, life-threatening allergic reaction
  • seizures
  • loss of consciousness
  • temporary blurring or loss of vision
  • black tarry stools


Causes

Low blood pressure can be caused by low blood volume,[9] hormonal changes,[10] pregnancy,[25] widening of blood vessels, medicine side effects,[11] severe dehydration,[7] anemia,[12] vitamin B12 deficiency,[7] [13] anaphylaxis,[7] heart problems[14] or endocrine problems.[15]

Reduced blood volume, hypovolemia, is the most common cause of hypotension.[26] This can result from hemorrhage; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia can be induced by excessive use of diuretics.[16] Low blood pressure may also be attributed to heat stroke which can be indicated by absence of perspiration, light headedness and dark colored urine.[27]

Other medications can produce hypotension by different mechanisms. Chronic use of alpha blockers or beta blockers can lead to hypotension.[16] Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.[16]

Decreased cardiac output despite normal blood volume, due to severe congestive heart failure, large myocardial infarction, heart valve problems, or extremely low heart rate (bradycardia), often produces hypotension and can rapidly progress to cardiogenic shock.[14] Arrhythmias often result in hypotension by this mechanism.[14]

Excessive vasodilation, or insufficient constriction of the blood vessels (mostly arterioles), causes hypotension.[28] This can be due to decreased sympathetic nervous system output or to increased parasympathetic activity occurring as a consequence of injury to the brain or spinal cord.[29] Dysautonomia, an intrinsic abnormality in autonomic system functioning, can also lead to hypotension.[29] Excessive vasodilation can also result from sepsis,[28] acidosis, or medications, such as nitrate preparations, calcium channel blockers, or AT1 receptor antagonists (Angiotensin II acts on AT1 receptors). Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents, produce significant vasodilation.[30]

Lower blood pressure is a side effect of certain herbal medicines,[31] which can also interact with several medications. An example is the theobromine in Theobroma cacao, which lowers blood pressure[32] through its actions as both a vasodilator and a diuretic,[33] and has been used to treat high blood pressure.[34][35]

Syndromes

Orthostatic hypotension

Orthostatic hypotension, also called postural hypotension, is a common form of low blood pressure.[17] It occurs after a change in body position, typically when a person stands up from either a seated or lying position.[36] It is usually transient and represents a delay in the normal compensatory ability of the autonomic nervous system.[37] It is commonly seen in hypovolemia and as a result of various medications.[17] In addition to blood pressure-lowering medications, many psychiatric medications, in particular antidepressants, can have this side effect.[38] Simple blood pressure and heart rate measurements while lying, seated, and standing (with a two-minute delay in between each position change) can confirm the presence of orthostatic hypotension.[39] Taking these measurements is known as orthostatic vitals.[17] Orthostatic hypotension is indicated if there is a drop of 20 mmHg in systolic pressure (and a 10 mmHg drop in diastolic pressure in some facilities) and a 20 beats per minute increase in heart rate.[39]

Vasovagal syncope

Vasovagal syncope is a form of dysautonomia characterized by an inappropriate drop in blood pressure while in the upright position.[18] Vasovagal syncope occurs as a result of increased activity of the vagus nerve, the mainstay of the parasympathetic nervous system.[18] Patients will feel sudden, unprovoked lightheadedness, sweating, changes in vision, and finally a loss of consciousness.[18] Consciousness will often return rapidly once patient is lying down and the blood pressure returns to normal.[40]

Other

Another, but rarer form, is postprandial hypotension, a drastic decline in blood pressure that occurs 30 to 75 minutes after eating substantial meals.[19] When a great deal of blood is diverted to the intestines (a kind of "splanchnic blood pooling") to facilitate digestion and absorption, the body must increase cardiac output and peripheral vasoconstriction to maintain enough blood pressure to perfuse vital organs, such as the brain.[41] Postprandial hypotension is believed to be caused by the autonomic nervous system not compensating appropriately, because of aging or a specific disorder.[41]

Hypotension is a feature of Flammer syndrome, which is characterized by cold hands and feet and predisposes to normal tension glaucoma.[20]

Hypotension can be a symptom of relative energy deficiency in sport, sometimes known as the female athlete triad, although it can also affect men.[42]

Pathophysiology

Blood pressure is continuously regulated by the autonomic nervous system, using an elaborate network of receptors, nerves, and hormones to balance the effects of the sympathetic nervous system, which tends to raise blood pressure, and the parasympathetic nervous system, which lowers it.[2] The vast and rapid compensation abilities of the autonomic nervous system allow normal individuals to maintain an acceptable blood pressure over a wide range of activities and in many disease states.[2] Even small alterations in these networks can lead to hypotension.[9]

Diagnosis

For most adults, the optimal blood pressure is at or below 120/80 mmHg.[43] If the systolic blood pressure is <90 mmHg or the diastolic blood pressure is <60 mmHg, it would be classified as hypotension.[5] However, occasional blood pressure readings below 90/60 mmHg are not infrequent in the general population,[44] and, in the absence of some pathological cause, hypotension appears to be a relatively benign condition in most people.[44] The diagnosis of hypotension is usually made by measuring blood pressure, either non-invasively with a sphygmomanometer or invasively with an arterial catheter (mostly in an intensive care setting). Another way to diagnose low blood pressure is by using the mean arterial pressure (MAP) measured using an arterial catheter [45] or by continuous, non-invasive hemodynamic monitoring which measures intra-operative blood pressure beat-by-beat throughout surgery. A MAP <65 mmHg is considered hypotension.[45] Intra-operative hypotension <65 mmHg can lead to an increased risk of acute kidney injury,[46] myocardial injury [46] or post-operative stroke.[47] While an incidental finding of hypotension during a routine blood pressure measurement may not be particularly worrying, a substantial drop in blood pressure following standing, exercise or eating can be associated with symptoms and may have implications for future health.[43] A drop in blood pressure after standing, termed postural or orthostatic hypotension, is defined as a decrease in supine-to-standing BP >20 mm Hg systolic or >10 mm Hg diastolic within 3 minutes of standing.[48][43] Orthostatic hypotension is associated with increased risk of future cardiovascular events and mortality. Orthostatic vitals are frequently measured to assist with the diagnosis of orthostatic hypotension,[39] and may involve the use of a tilt table test to evaluate vasovagal syncope.[40]

Treatment

Treatment depends on what causes low blood pressure.[4] Treatment may not be needed for asymptomatic low blood pressure.[49] Depending on symptoms, treatment may include drinking more fluids to prevent dehydration, taking medicines to raise blood pressure, or adjusting medicines that cause low blood pressure.[4] Adding electrolytes to a diet can relieve symptoms of mild hypotension, and a morning dose of caffeine can also be effective.[50] Chronic hypotension rarely exists as more than a symptom. In mild cases, where the patient is still responsive, laying the person on their back and lifting the legs increases venous return, thus making more blood available to critical organs in the chest and head.[50] The Trendelenburg position, though used historically, is no longer recommended.[51]

Hypotensive shock treatment always follows the first four following steps. Outcomes, in terms of mortality, are directly linked to the speed that hypotension is corrected.[9] Still-debated methods are in parentheses, as are benchmarks for evaluating progress in correcting hypotension. A study on septic shock provided the delineation of these general principles.[52] However, since it focuses on hypotension due to infection, it is not applicable to all forms of severe hypotension.

  1. Volume resuscitation (usually with crystalloid or blood products)[9]
  2. Blood pressure support with a vasopressor (all seem equivalent with respect to risk of death, with norepinephrine possibly better than dopamine).[53] Trying to achieve a mean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve a MAP of greater than 65 mmHg in adults.[24]
  3. Ensure adequate tissue perfusion (maintain SvO2 >70 with use of blood or dobutamine)[9]
  4. Address the underlying problem (i.e., antibiotic for infection, stent or CABG (coronary artery bypass graft surgery) for infarction, steroids for adrenal insufficiency, etc...)[9]

The best way to determine if a person will benefit from fluids is by doing a passive leg raise followed by measuring the output from the heart.[54]

Medication

Main page: Chemistry:Antihypotensive agent

Chronic hypotension sometimes requires the use of medications.[55] Some medications that are commonly used include Fludrocortisone, Erythropoietin, and Sympathomimetics such as Midodrine and Noradrenaline and precursor (L-DOPS).[17]

  • Fludrocortisone is the first-line therapy (in the absence of heart failure) for patients with chronic hypotension or resistant orthostatic hypotension.[17] It works by increasing the intravascular volume.[17]
  • Midodrine is a therapy used for severe orthostatic hypotension, and works by increasing peripheral vascular resistance.[17]
  • Noradrenaline and its precursor L-DOPS are used for primary autonomic dysfunction by increasing vascular tone.[17]
  • Erythropoietin is given to patients with neurogenic orthostatic hypotension and it works through increasing vascular volume and viscosity.[17]

Pediatrics

The definition of hypotension changes in the pediatric population depending on the child's age as seen in the table below.

Pediatric Hypotension[56]
Age Systolic Pressure
Term Neonates <60 mmHg
Infants <70 mmHg
Children 1–10 years <70 + (age in years x 2) mmHg
Children >10 years <90 mmHg

The clinical history provided by the caretaker is the most important part in determining the cause of hypotension in pediatric patients.[57] Symptoms for children with hypotension include increased sleepiness, not using the restroom as much (or at all), having difficulty breathing or breathing rapidly, or syncope.[57] The treatment for hypotension in pediatric patients is similar to the treatment in adults by following the four first steps listed above (see Treatment).[9] Children are more likely to undergo intubation during the treatment of hypotension because their oxygen levels drop more rapidly than adults.[57] The closing of fetal shunts following birth can create instability in the "transitional circulation" of the fetus, and often creates a state of hypotension following birth; while many infants can overcome this hypotension through the closing of shunts, a mean blood pressure (MBP) of lower than 30 mmHg is correlated with severe cerebral injury and can be experienced by premature infants who have poor shunt closure.[58]

Etymology

Hypotension, from Ancient Greek hypo-, meaning "under" or "less" + English tension, meaning "'strain" or "tightness".[59] This refers to the under-constriction of the blood vessels and arteries which leads to low blood pressure.[60]

See also

References

  1. ↑ TheFreeDictionary > hypotension. Citing: The American Heritage Science Dictionary Copyright 2005
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Costanzo, Linda S. (March 15, 2017). Physiology. Preceded by: Costanzo, Linda S. (Sixth ed.). Philadelphia, PA. ISBN 978-0-323-51189-6. OCLC 965761862. 
  3. ↑ 3.0 3.1 "High Blood Pressure Fact Sheet|Data & Statistics|DHDSP|CDC" (in en-us). 2019-01-09. https://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_bloodpressure.htm. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 "What Is Low Blood Pressure?". 22 November 2022. https://www.nhlbi.nih.gov/health/low-blood-pressure. 
  5. ↑ 5.0 5.1 5.2 5.3 Mayo Clinic staff (May 23, 2009). "Low blood pressure (hypotension) — Definition". MayoClinic.com. Mayo Foundation for Medical Education and Research. http://www.mayoclinic.com/health/low-blood-pressure/DS00590. 
  6. ↑ Flynn, Joseph T.; Kaelber, David C.; Baker-Smith, Carissa M.; Blowey, Douglas; Carroll, Aaron E.; Daniels, Stephen R.; Ferranti, Sarah D. de; Dionne, Janis M. et al. (2017-09-01). "Clinical Practice Guideline for Screening and Management of High Blood Pressure in Children and Adolescents" (in en). Pediatrics 140 (3): e20171904. doi:10.1542/peds.2017-1904. ISSN 0031-4005. PMID 28827377. https://pediatrics.aappublications.org/content/140/3/e20171904. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Mayo Clinic staff (May 23, 2009). "Low blood pressure (hypotension) — Causes". MayoClinic.com. Mayo Foundation for Medical Education and Research. http://www.mayoclinic.com/health/low-blood-pressure/DS00590/DSECTION=causes. 
  8. ↑ Haseer Koya, Hayas; Paul, Manju (2021), "Shock", StatPearls (Treasure Island (FL): StatPearls Publishing), PMID 30285387, http://www.ncbi.nlm.nih.gov/books/NBK531492/, retrieved 2021-11-29 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 Kalkwarf, Kyle J.; Cotton, Bryan A. (December 2017). "Resuscitation for Hypovolemic Shock". The Surgical Clinics of North America 97 (6): 1307–1321. doi:10.1016/j.suc.2017.07.011. ISSN 1558-3171. PMID 29132511. 
  10. ↑ 10.0 10.1 Bett, Glenna C. L. (1 May 2016). "Hormones and sex differences: changes in cardiac electrophysiology with pregnancy". Clinical Science 130 (10): 747–759. doi:10.1042/CS20150710. ISSN 1470-8736. PMID 27128800. 
  11. ↑ 11.0 11.1 Oparil, Suzanne; Acelajado, Maria Czarina; Bakris, George L.; Berlowitz, Dan R.; Cífková, Renata; Dominiczak, Anna F.; Grassi, Guido; Jordan, Jens et al. (22 March 2018). "Hypertension". Nature Reviews. Disease Primers 4: 18014. doi:10.1038/nrdp.2018.14. ISSN 2056-676X. PMID 29565029. 
  12. ↑ 12.0 12.1 Vieth, Julie T.; Lane, David R. (December 2017). "Anemia". Hematology/Oncology Clinics of North America 31 (6): 1045–1060. doi:10.1016/j.hoc.2017.08.008. ISSN 1558-1977. PMID 29078923. 
  13. ↑ 13.0 13.1 "How a Vitamin B Deficiency Affects Blood Pressure" (in en). https://www.livestrong.com/article/489318-connection-between-low-blood-pressure-and-vitamin-b-deficiency/. 
  14. ↑ 14.0 14.1 14.2 14.3 Tewelde, Semhar Z.; Liu, Stanley S.; Winters, Michael E. (February 2018). "Cardiogenic Shock". Cardiology Clinics 36 (1): 53–61. doi:10.1016/j.ccl.2017.08.009. ISSN 1558-2264. PMID 29173681. 
  15. ↑ 15.0 15.1 Bornstein, Stefan R.; Allolio, Bruno; Arlt, Wiebke; Barthel, Andreas; Don-Wauchope, Andrew; Hammer, Gary D.; Husebye, Eystein S.; Merke, Deborah P. et al. (February 2016). "Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline". The Journal of Clinical Endocrinology and Metabolism 101 (2): 364–389. doi:10.1210/jc.2015-1710. ISSN 1945-7197. PMID 26760044. 
  16. ↑ 16.0 16.1 16.2 16.3 Laurent, Stéphane (October 2017). "Antihypertensive drugs". Pharmacological Research 124: 116–125. doi:10.1016/j.phrs.2017.07.026. ISSN 1096-1186. PMID 28780421. 
  17. ↑ 17.00 17.01 17.02 17.03 17.04 17.05 17.06 17.07 17.08 17.09 17.10 17.11 Joseph, Adrien; Wanono, Ruben; Flamant, Martin; Vidal-Petiot, Emmanuelle (April 2017). "Orthostatic hypotension: A review". Nephrologie & Therapeutique 13 (Suppl 1): S55–S67. doi:10.1016/j.nephro.2017.01.003. ISSN 1872-9177. PMID 28577744. 
  18. ↑ 18.0 18.1 18.2 18.3 Jardine, David L.; Wieling, Wouter; Brignole, Michele; Lenders, Jacques W. M.; Sutton, Richard; Stewart, Julian (June 2018). "The pathophysiology of the vasovagal response". Heart Rhythm 15 (6): 921–929. doi:10.1016/j.hrthm.2017.12.013. ISSN 1556-3871. PMID 29246828. 
  19. ↑ 19.0 19.1 Merck Manual Home Edition. "Postprandial Hypotension." Last accessed October 26, 2011.
  20. ↑ 20.0 20.1 Konieczka Katarzyna et al. (2014). "Flammer syndrome". EPMA Journal 5 (1): 11. doi:10.1186/1878-5085-5-11. PMID 25075228. 
  21. ↑ "Low blood pressure (hypotension)". BUPA.co.uk. https://web.archive.org/web/20140223194728/http://www.bupa.co.uk/individuals/health-information/directory/l/low-blood-pressure. 
  22. ↑ Rodriguez, D; Silva, V; Prestes, J; Rica, RL; Serra, AJ; Bocalini, DS; Pontes FL, Jr; Silva, Valter (2011). "Hypotensive response after water-walking and land-walking exercise sessions in healthy trained and untrained women.". International Journal of General Medicine 4: 549–554. doi:10.2147/IJGM.S23094. PMID 21887107. 
  23. ↑ Hunter, Benton R.; Martindale, Jennifer; Abdel-Hafez, Osama; Pang, Peter S. (September 2017). "Approach to Acute Heart Failure in the Emergency Department". Progress in Cardiovascular Diseases 60 (2): 178–186. doi:10.1016/j.pcad.2017.08.008. ISSN 1873-1740. PMID 28865801. 
  24. ↑ 24.0 24.1 Hylands, M; Moller, MH; Asfar, P; Toma, A; Frenette, AJ; Beaudoin, N; Belley-Côté, É; D'Aragon, F et al. (July 2017). "A systematic review of vasopressor blood pressure targets in critically ill adults with hypotension.". Canadian Journal of Anaesthesia 64 (7): 703–715. doi:10.1007/s12630-017-0877-1. PMID 28497426. 
  25. ↑ Health, Narayana (2020-04-28). "Low Blood Pressure: Can it affect your pregnancy?" (in en-US). https://www.narayanahealth.org/blog/low-blood-pressure-can-it-affect-your-pregnancy/. 
  26. ↑ Perner, Anders; Cecconi, Maurizio; Cronhjort, Maria; Darmon, Michael; Jakob, Stephan M.; Pettilä, Ville; van der Horst, Iwan C. C. (June 2018). "Expert statement for the management of hypovolemia in sepsis". Intensive Care Medicine 44 (6): 791–798. doi:10.1007/s00134-018-5177-x. ISSN 1432-1238. PMID 29696295. https://research.rug.nl/en/publications/expert-statement-for-the-management-of-hypovolemia-in-sepsis(1956f1c3-61de-4ac7-b662-5d6f8c77e6ef).html. 
  27. ↑ Al Mahri, Saeed; Bouchama, Abderrezak (2018). Heatstroke. Handbook of Clinical Neurology. 157. pp. 531–545. doi:10.1016/B978-0-444-64074-1.00032-X. ISBN 9780444640741. 
  28. ↑ 28.0 28.1 Singer, Mervyn; Deutschman, Clifford S.; Seymour, Christopher Warren; Shankar-Hari, Manu; Annane, Djillali; Bauer, Michael; Bellomo, Rinaldo; Bernard, Gordon R. et al. (2016-02-23). "The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)". JAMA 315 (8): 801–810. doi:10.1001/jama.2016.0287. ISSN 0098-7484. PMID 26903338. 
  29. ↑ 29.0 29.1 Dave, Sagar; Cho, Julia J. (2019), "Neurogenic Shock", StatPearls (StatPearls Publishing), PMID 29083597, http://www.ncbi.nlm.nih.gov/books/NBK459361/, retrieved 2020-01-21 
  30. ↑ Ripollés Melchor, J.; Espinosa, Á; Martínez Hurtado, E.; Casans Francés, R.; Navarro Pérez, R.; Abad Gurumeta, A.; Calvo Vecino, J. M. (September 2015). "Colloids versus crystalloids in the prevention of hypotension induced by spinal anesthesia in elective cesarean section. A systematic review and meta-analysis". Minerva Anestesiologica 81 (9): 1019–1030. ISSN 1827-1596. PMID 25501602. 
  31. ↑ Tabassum, Nahida; Feroz Ahmad (2011). "Role of natural herbs in the treatment of hypertension". Pharmacognosy Reviews 5 (9): 30–40. doi:10.4103/0973-7847.79097. PMID 22096316. 
  32. ↑ "Differential contributions of theobromine and caffeine on mood, psychomotor performance and blood pressure". Physiol. Behav. 104 (5): 816–822. 2011. doi:10.1016/j.physbeh.2011.07.027. PMID 21839757. "Theobromine ... lowered blood pressure relative to placebo". 
  33. ↑ William Marias Malisoff (1943). Dictionary of Bio-Chemistry and Related Subjects. Philosophical Library. pp. 311, 530, 573. 
  34. ↑ Theobromine Chemistry – Theobromine in Chocolate. Chemistry.about.com (May 12, 2013). Retrieved on 2013-05-30.
  35. ↑ Kelly, Caleb J (2005). "Effects of theobromine should be considered in future studies". American Journal of Clinical Nutrition 82 (2): 486–487; author reply 487–488. doi:10.1093/ajcn.82.2.486. PMID 16087999. 
  36. ↑ Freeman, Roy; Abuzinadah, Ahmad R.; Gibbons, Christopher; Jones, Pearl; Miglis, Mitchell G.; Sinn, Dong In (11 September 2018). "Orthostatic Hypotension: JACC State-of-the-Art Review". Journal of the American College of Cardiology 72 (11): 1294–1309. doi:10.1016/j.jacc.2018.05.079. ISSN 1558-3597. PMID 30190008. 
  37. ↑ Mar, Philip L.; Raj, Satish R. (January 2018). "Orthostatic hypotension for the cardiologist". Current Opinion in Cardiology 33 (1): 66–72. doi:10.1097/HCO.0000000000000467. ISSN 1531-7080. PMID 28984649. 
  38. ↑ Carvalho, André F.; Sharma, Manu S.; Brunoni, André R.; Vieta, Eduard; Fava, Giovanni A. (2016). "The Safety, Tolerability and Risks Associated with the Use of Newer Generation Antidepressant Drugs: A Critical Review of the Literature". Psychotherapy and Psychosomatics 85 (5): 270–288. doi:10.1159/000447034. ISSN 1423-0348. PMID 27508501. 
  39. ↑ 39.0 39.1 39.2 Low, Phillip A. (October 2015). "Neurogenic orthostatic hypotension: pathophysiology and diagnosis". The American Journal of Managed Care 21 (13 Suppl): s248–257. ISSN 1936-2692. PMID 26790109. 
  40. ↑ 40.0 40.1 Kenny, R. A.; McNicholas, T. (December 2016). "The management of vasovagal syncope". QJM: Monthly Journal of the Association of Physicians 109 (12): 767–773. doi:10.1093/qjmed/hcw089. ISSN 1460-2393. PMID 27340222. 
  41. ↑ 41.0 41.1 Pavelić, Antun; Krbot Skorić, Magdalena; Crnošija, Luka; Habek, Mario (August 2017). "Postprandial hypotension in neurological disorders: systematic review and meta-analysis". Clinical Autonomic Research 27 (4): 263–271. doi:10.1007/s10286-017-0440-8. ISSN 1619-1560. PMID 28647892. 
  42. ↑ Mountjoy, Margo (2014). "The IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport (RED-S)". British Journal of Sports Medicine 48 (7): 491–497. doi:10.1136/bjsports-2014-093502. PMID 24620037. https://bjsm.bmj.com/content/48/7/491.info. 
  43. ↑ 43.0 43.1 43.2 "Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure". Hypertension 42 (6): 1206–1252. December 2003. doi:10.1161/01.HYP.0000107251.49515.c2. PMID 14656957. 
  44. ↑ 44.0 44.1 Owens, Pe; Lyons, Sp; O’Brien, Et (2000-04-01). "Arterial hypotension: prevalence of low blood pressure in the general population using ambulatory blood pressure monitoring" (in en). Journal of Human Hypertension 14 (4): 243–247. doi:10.1038/sj.jhh.1000973. ISSN 0950-9240. PMID 10805049. https://www.nature.com/articles/1000973. 
  45. ↑ 45.0 45.1 Mookherjee, S. Lai, C., Rennke, St. The UCSF Hospitalist Handbook. 
  46. ↑ 46.0 46.1 Walsh, M., Devereaux, P. et al. Relationship between Intraoperative Mean Arterial Pressure and Clinical Outcomes a er Noncardiac Surgery. Anaesthesiology. 2013;119:507-515.
  47. ↑ Bijker J., Persoon S., Peelen L., et al. Intraoperative Hypotension and Perioperative Ischemic Stroke a er General Surgery. Anesthesiology. 2012;116(3):658-664.
  48. ↑ Williams, Bryan et al. (2018). "2018 ESC/ESH Guidelines for the management of arterial hypertension". European Heart Journal 39 (33): 3021–3104. doi:10.1093/eurheartj/ehy339. PMID 30165516. https://academic.oup.com/eurheartj/article/39/33/3021/5079119. Retrieved 2022-08-18. 
  49. ↑ Sharma, Sandeep; Hashmi, Muhammad F.; Bhattacharya, Priyanka T. (2019), "Hypotension", StatPearls (StatPearls Publishing), PMID 29763136, http://www.ncbi.nlm.nih.gov/books/NBK499961/, retrieved 2020-01-23 
  50. ↑ 50.0 50.1 Chisholm, Peter; Anpalahan, Mahesan (April 2017). "Orthostatic hypotension: pathophysiology, assessment, treatment and the paradox of supine hypertension". Internal Medicine Journal 47 (4): 370–379. doi:10.1111/imj.13171. ISSN 1445-5994. PMID 27389479. 
  51. ↑ Kettaneh, Nicolas (October 30, 2008). "BestBets: Use of the Trendelenburg Position to Improve Hemodynamics During Hypovolemic Shock". Grand Rapids Medical Education & Research/Michigan State University. http://www.bestbets.org/bets/bet.php?id=1710. 
  52. ↑ Rivers, E; Nguyen, B; Havstad, S; Ressler, J; Muzzin, A; Knoblich, B; Peterson, E; Tomlanovich, M et al. (8 November 2001). "Early goal-directed therapy in the treatment of severe sepsis and septic shock.". The New England Journal of Medicine 345 (19): 1368–1377. doi:10.1056/nejmoa010307. PMID 11794169. 
  53. ↑ Gamper, G; Havel, C; Arrich, J; Losert, H; Pace, NL; Müllner, M; Herkner, H (15 February 2016). "Vasopressors for hypotensive shock.". Cochrane Database of Systematic Reviews 2 (2): CD003709. doi:10.1002/14651858.CD003709.pub4. PMID 26878401. 
  54. ↑ Bentzer, P; Griesdale, DE; Boyd, J; MacLean, K; Sirounis, D; Ayas, NT (27 September 2016). "Will This Hemodynamically Unstable Patient Respond to a Bolus of Intravenous Fluids?". JAMA 316 (12): 1298–1309. doi:10.1001/jama.2016.12310. PMID 27673307. 
  55. ↑ Arnold, Amy C.; Raj, Satish R. (December 2017). "Orthostatic Hypotension: A Practical Approach to Investigation and Management". The Canadian Journal of Cardiology 33 (12): 1725–1728. doi:10.1016/j.cjca.2017.05.007. ISSN 1916-7075. PMID 28807522. 
  56. ↑ "Hypotension (PICU chart)" (in en). 2013-06-05. https://uichildrens.org/health-library/hypotension-picu-chart. 
  57. ↑ 57.0 57.1 57.2 Mendelson, Jenny (May 2018). "Emergency Department Management of Pediatric Shock". Emergency Medicine Clinics of North America 36 (2): 427–440. doi:10.1016/j.emc.2017.12.010. ISSN 1558-0539. PMID 29622332. 
  58. ↑ Kluckow, Martin (2018). "The Pathophysiology of Low Systemic Blood Flow in the Preterm Infant". Frontiers in Pediatrics 6: 29. doi:10.3389/fped.2018.00029. ISSN 2296-2360. PMID 29503814. 
  59. ↑ "Online Etymology Dictionary" (in en). http://etymonline.com/index.php. 
  60. ↑ Speden, R.N.; Ryan, Ann T. (1982). "Constriction of Ear Arteries from Normotensive and Renal Hypertensive Rabbits against Different Transmural Pressures". Journal of Vascular Research 19 (5): 247–262. doi:10.1159/000158391. ISSN 1423-0135. PMID 7115984. http://dx.doi.org/10.1159/000158391. 

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