Medex 2015: The key role of cardiac mechanics to maintain biventricular function at high altitude

Abstract

New Findings What is the central question of this study?This study is the first to investigate the effects of high‐altitude trekking on biventricular mechanics, including measurements of left ventricular subendocardial and subepicardial function. What is the main finding and its importance?We provide new evidence that an increased contractility and untwisting efficiency, a key element of diastolic function, probably plays a key role in preservation of cardiac function during high‐altitude trekking. Persistent increased loading conditions during several weeks at high altitude might have a key role in the appearance of left or right ventricular dysfunction. Abstract Cardiac responses to acute hypoxic exposure have been thoroughly investigated. We analysed the effects of high‐altitude trekking (i.e. prolonged hypoxic exposure) on biventricular function, including the evaluation of subendocardial and subepicardial function in the left ventricle (LV). Resting evaluations of LV and right ventricular (RV) function and mechanics were assessed by speckle tracking echocardiography on 20 subjects at sea level and at high altitude (5085 m, after a 10 day ascent). Pulmonary artery systolic pressure was increased at high altitude (sea level, 13.1 ± 5.9 mmHg; high altitude, 26.6 ± 10.8 mmHg; P < 0.001). Left ventricular volumes were decreased, whereas RV volumes were increased at high altitude. Alterations in pulmonary artery systolic pressure and cardiac volumes were correlated with hypoxaemia. We observed neither RV nor LV systolic dysfunction, including analysis of LV subendocardial and subepicardial function. Left ventricular systolic strain rates were enhanced at high altitude. Transmitral and transtricuspid diastolic filling ratios were decreased at high altitude. Diastolic apical rotational rate, untwisting rate and untwisting rate/peak twist ratio (i.e. untwisting efficiency) were enhanced at high altitude. We observed no echocardiographic signs of LV and RV pathological dysfunction at rest at high altitude. In contrast, our data highlighted major changes in the LV mechanics, with an increased LV contractility and a higher untwisting efficiency at high altitude. Biventricular interaction, alterations in loading conditions and an increase in plasma catecholamine concentration might partly explain these modifications. Thus, we demonstrated that LV mechanics (i.e. increased strain rates and untwisting efficiency) have a key role in preservation of cardiac function during high‐altitude trekking.

No heartbreak at high altitude; preserved cardiac function in chronic hypoxia

“…This difference in twist response might be explained by the shorter exposure in the study by Maufrais et al. (). Despite the absence of a change in twist, the authors did observe an increase in circumferential strain and strain rate that was driven by increased deformation in the subendocardial layer.…”

“…Of further note is the increase in right ventricular volume observed by Maufrais et al. (), presumably attributable to the increase in right ventricular afterload via hypoxic pulmonary vasoconstriction. Lowering pulmonary artery pressure at altitude has previously been shown to increase left ventricular filling (Stembridge et al., ), and direct ventricular interaction through pericardial constraint might play a significant role in the reduction of left ventricular filling observed in the present study and others.…”

“…In this issue of Experimental Physiology , Maufrais et al. () use modern speckle‐tracking technology to investigate region‐specific cardiac performance in chronic hypoxia.…”

“…Maufrais et al. () therefore set out to characterize regional and global myocardial function comprehensively, using region‐specific speckle‐tracking imaging before and after a 10 day ascent to Manaslu Basecamp at 5085 m.…”

“…The authors also cited an increase in the twist-to-shortening ratio as evidence of impaired contractile function in the subendocardial layer. Maufrais et al (2019) therefore set out to characterize regional and global myocardial function comprehensively, using region-specific speckle-tracking imaging before and after a If subendocardial dysfunction does not occur, then the question remains, why is left ventricular twist elevated at high altitude? To address this question, the authors also highlight the increase in strain rate as a key finding from their work and interpret this change as an increase in contractility attributable to the relatively load-independent nature of strain rate.…”