Hypertension Journal

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Effect of Altitude on Blood Pressure
  JOHTN
PHYSIOLOGY OF BLOOD PRESSURE REGULATION
Effect of Altitude on Blood Pressure
1Narsingh Verma, 2Arvind K Pal
1Professor, 2Senior Resident
1,2Department of Physiology, King George's Medical UniversityLucknow, Uttar Pradesh, India
Corresponding Author: Narsingh Verma, Professor, Departmentof Physiology, King George's Medical University, Lucknow, UttarPradesh, India
e-mail: narsinghverma@gmail.com
 
ABSTRACT
The effect of higher altitude over the blood pressure (BP) is notexactly known, and it appears to vary both between and withinindividuals. The effects of lower temperature, light, increasedphysical stress, and duration of living at higher altitude alsoplay a significant role. Most of the studies showed that higheraltitude correlated with rising BP. This change in BP is due tomany factors, the important one being the effect of hypoxiacausing activation of sympathetic nervous system. Activationof sympathetic nervous system causes an increase in cardiacoutput, heart rate, and peripheral vasoconstriction, which leadto increase in BP. The incidence of BP in high latitudes is controversial;some research shows greater rates while others showlesser rates of hypertension in these individuals. It may be dueto the effects of multiple other confounding factors like genetic,ecological, and lifestyle variables. Hence, increasing popularityof high-altitude travel needs further research to evaluate thisproblem. Furthermore, the implications of altitude-inducedhypertension for cardiovascular risk and end-organ damagerequire more clarification.
Keywords: Altitude, Hypertension, Hypoxia.
How to cite this article: Verma N, Pal AK. Effect of Altitudeon Blood Pressure. Hypertens J 2017;3(4):171-172.
Source of support: Nil
Conflict of interest: None
 
 

INTRODUCTION

Studies evaluating the effects of high altitude on arterialBP are not enough. There is a contradiction aboutthe effect of higher altitude on arterial BP. The results ofvarious research generally support the positive relationshipbetween arterial BP and higher altitude.1-5 Individualpredisposition is very important, as the effect of higheraltitude appears to vary both between and within individuals.6 Even there are differences in susceptibilityamong races.2 Duration of living at higher altitude alsoplays a significant role. Persons who have acclimatizedover weeks show less effect of higher altitude on BP.Studies have shown that altitude-induced BP elevationscan persist for months.1 The effects of lower temperature, light, and increased physical stress also play an importantrole in survival in more difficult environments.

Most of the studies showed that higher altitude correlatedwith rising BP.2,5 Susceptible individuals undergoingshort-term ascents above 2,500 m showed an acute effecton BP. This change in BP is due to many factors, the importantone being the effect of hypoxia causing activation ofsympathetic nervous system. Activation of sympatheticnervous system causes increase in cardiac output, heartrate, and peripheral vasoconstriction. These facts havemany implications for patients suffering from diseaseconditions that can lead to hypoxia. Hence, appropriatemeasures should be taken in these patients whenever theyare going to higher altitudes. Some studies demonstrate anincrease in BPs,7-9 and others describe a decrease in BP10 innonhypertensive individuals acutely exposed to hypoxia,while some other studies report no change in BP.11,12Similarly, in the hypertensive patient, various studiesreport elevations in BP upon acute exposure to higheraltitudes,13-16 yet others report no significant change.9,11,17
 
A recent study demonstrated that among residentsof Tibet, there is a significant correlation between thehigher altitude and incidence of raised BP. It was foundthat prevalence of hypertension increased by 2% forevery 100 m increase in altitude.18 In another study,Italian researchers found that during ascend at higheraltitude BP steadily increases. They also found thatmedicines are not very effective for treatment of high BPonce a certain height is reached. Forty-seven individualstraveled to the base camp of Mount Everest at an altitudeof approximately 5400 m. All participants checked BPround-the-clock during their ascent. The volunteerswere also randomized to take either a placebo or 80 mgof telmisartan. Telmisartan is an angiotensin receptorblocker. Angiotensin receptor blocker blocks angiotensinII, which causes constriction of blood vessels.The study also showed that at an altitude of 5400 m anincrease in BP by 14/10 mm Hg is caused.19 This studyalso showed that although telmisartan significantlyreduced BP up to 3400 m but no effect was seen at 5400m.19 The findings impact on people who ascend at highaltitude and also in those living at sea level.

Some people may also be prone to consistent elevationsin BP while living at high altitudes. On the contrary,in the higher land, the prevalence of hypertension is moremixed.4,5 Some research show greater rates while othersshow lesser rates of hypertension in these individuals. It may be due to the effects of multiple other confoundingfactors like genetic, ecological, and lifestyle variables.The literature to support the occurrence of hypertensionat altitude is variable. At higher altitude, the prevalenceof severe hypertension is not exactly known. The exactincidence and severity of the hypertensive response tohigh altitude are still not precisely evaluated.20-22 Furthermore,the implications of altitude-induced hypertensionfor cardiovascular risk and end-organ damage requiremore clarification. Health care workers should be aware ofthese relationships. Hypertension guidelines23,24 shouldbe addressing the importance of the higher altitude onBP during hypertension treatment. To ascend to a higheraltitude, BP monitoring is necessary for each individual.

Hypertension Journal, October-December, Vol 3, 2017 171

Narsingh Verma, Arvind K Pal

Hence, increasing popularity of high altitude traveland high prevalence of hypertension need furtherresearch to evaluate this problem. Research shouldfocus on identifying various factors for increase in BP athigh altitude and also see whether hypoxia at sea levelcan predict the altitude hypertensive response in anindividual. Persistence of altitude-induced high BP onreturn to sea level should also be evaluated. It shouldimply for future hypertensive risk at sea level. Finally,clinical trials needed to determine the most appropriatetreatment for BP elevations in this type of situation. Theeffects of altitude, acclimatization, exposure durations,and patient susceptibilities require more investigation.

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