PHAHD, also named ISMS, is a syndrome, which is the occurrence of symptomatic, severe pulmonary hypertension in infants or young children who were born or brought up at high altitude above 3000 m; symptoms result from an excessive increase in pulmonary artery pressure and right heart failure. These infants often died if continuously exposed to high altitude and autopsy revealed extreme medial hypertrophy of the pulmonary arteries and an increased muscularization of the pulmonary arterioles, as well as right ventricular dilatation and hypertrophy, attributed to secondary to pulmonary vascular disease. The cure for this syndrome is oxygen administration and early evacuation.
Various authors use different terms to denote identical altitude illnesses. Since Wu and Liu in 1955  first used the term "pediatric high altitude heart disease, PHAHD", it is now well accepted for this syndrome in China . After that, in the year 1988, Sui GJ, a Chinese pathologist and his colleagues, in collaboration with an English research group in Lhasa, Tibet, noted that it is an often fatal disease affecting infants and manifesting itself over a period of weeks and months rather than days or years, it came to be designated as "subacute infantile mountain sickness" . Otherwise, because it is known that mild pulmonary hypertension without symptoms is one of the common features of altitude residents, to draw a clear distinction between physiologic and pathologic pulmonary hypertension, a term "symptomatic high altitude pulmonary hypertension" (SHAPH) was first proposed by Jones et al. (1982) , then by Pollard and Niermeyer (2002) . Furthermore, Niermeyer (2003)  suggest the term of SHAPH includes acute exacerbation of pulmonary hypertension and the subacute form. In this regard, Hultgren (1997)  suggested this asymptomatic condition is best defined as "high altitude pulmonary hypertension" whereas in those with symptomatic cases, a more appropriate term would be "accelerated pulmonary hypertension of high altitude". The lack of a common term has always confused scientists. In August 2004, the VI World Congress on Mountain Medicine and High Altitude Physiology was held in Xining, Qinghai, China. An International Working Group reached agreement on the "Consensus Statement by and Ad Hoc Committee of the International Society for Mountain Medicine on Chronic High Altitude Diseases". Of these, PHAHD or ISMS was defined as "A subacute clinical syndrome characterized by severe pulmonary hypertension leading in infant (or adult) lowlanders who migrate to high altitude to congestive failure of the right heart within weeks or months". And the term for the syndrome was proposed as "Cardiac subacute mountain sickness" .
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...