Pulmonary haemodynamic response to exercise in highlanders versus lowlanders

Abstract

The aim of the study was to investigate the pulmonary haemodynamic response to exercise in Central Asian high- and lowlanders. This was a cross-sectional study in Central Asian highlanders (living >2500 m) compared with lowlanders (living <800 m), assessing cardiac function, including tricuspid regurgitation pressure gradient (TRPG), cardiac index and tricuspid annular plane systolic excursion (TAPSE) by echocardiography combined with heart rate and oxygen saturation measured by pulse oximetry (S _pO2 ) during submaximal stepwise cycle exercise (10 W increase per 3 min) at their altitude of residence (at 760 m or 3250 m, respectively). 52 highlanders (26 females; aged 47.9±10.7 years; body mass index (BMI) 26.7±4.6 kg·m^-2; heart rate 75±11 beats·min^-1; S _pO2 91±5%;) and 22 lowlanders (eight females; age 42.3±8.0 years; BMI 26.9±4.1 kg·m^-2; heart rate 68±7 beats·min^-1; S _pO2 96±1%) were studied. Highlanders had a lower resting S _pO2 compared to lowlanders but change during exercise was similar between groups (highlanders versus lowlanders -1.4±2.9% versus -0.4±1.1%, respectively, p=0.133). Highlanders had a significantly elevated TRPG and exercise-induced increase was significantly higher (13.6±10.5 mmHg versus 6.1±4.8 mmHg, difference 7.5 (2.8 to 12.2) mmHg; p=0.002), whereas cardiac index increase was slightly lower in highlanders (2.02±0.89 L·min^-1 versus 1.78±0.61 L·min^-1, difference 0.24 (-0.13 to 0.61) L·min^-1; p=0.206) resulting in a significantly steeper pressure-flow ratio (ΔTRPG/Δcardiac index) in highlanders 9.4±11.4 WU and lowlanders 3.0±2.4 WU (difference 6.4 (1.4 to 11.3) WU; p=0.012). Right ventricular-arterial coupling (TAPSE/TRPG) was significantly lower in highlanders but no significant difference in change with exercise in between groups was detected (-0.01 (-0.20 to 0.18); p=0.901). In highlanders, chronic exposure to hypoxia leads to higher pulmonary artery pressure and a steeper pressure-flow relation during exercise.

FIGURE 1

Patient flow. GOLD: Global Initiative for Chronic Obstructive Lung Disease.

FIGURE 2

Pressure–flow relationship displayed as tricuspid regurgitation pressure gradient (TRPG) in relation to the cardiac index from baseline to end-exercise, reflecting the pressure/flow relationship for (a) highlanders and lowlanders and (b) all groups: lowlanders, no high-altitude pulmonary hypertension (HAPH; resting mean pulmonary artery pressure mPAP<20 mmHg), borderline HAPH (resting mPAP 20–30 mmHg) and HAPH (resting mPAP>30 mmHg).

FIGURE 3

Vital signs of the lowlanders and highlanders during exercise (baseline, 3 min, 6 min, 9 min and individual end exercise). TAPSE: tricuspid annular plane systolic excursion; TRPG: tricuspid regurgitation pressure gradient.