Abstract 17085: Heart Rate Variability in Recently Acclimatized Lowlanders, in Healthy Highlanders and in Patients with Chronic Mountain Sickness at the Altitude of 4,350 M
Altitude exposure in lowlanders (LL) has been reported to be associated with sympathetic nervous system activation. The autonomic response to chronic high altitude exposure is, however, less known. Chronic mountain sickness (CMS) is characterized by polycythemia, hypoxemia, pulmonary hypertension and eventual heart failure. Methods. Twelve CMS patients aged 51 ± 10 years, 14 healthy highlanders (HL) (41 ± 9 years) and 25 recently acclimatized LL (31 ± 13 years) without symptoms of acute mountain sickness were investigated in Cerro de Pasco, Peru, at 4,350 m, and underwent echocardiography and spectral power analysis of heart rate variability. LL had undergone the same measurements at sea level. Results. In the LL, the ascent to high altitude increased heart rate (HR, from 67±12 to 77±15 bpm), mean arterial pressure (MAP, from 89±9 to 94±10 mmHg) and mean pulmonary artery pressure (MPAP, from 16±2 to 22±4 mmHg) (p<0.05), whereas cardiac index remained unchanged (from 3.3±1 to 3.5 1 L/min/m2). Pulse oximetry oxygen saturation (SaO2) decreased from 97±1 to 86±3 % (p<0.05). The only change observed in spectral power analysis of heart rate variability was a decrease in the high frequency (HF) component (from 5.94±1.1 to 5.48±1.11 ln, p<0.05). As compared to HL, CMS patients had a lower SaO2 (87±7 vs 92±4 %, in CMS and HL, respectively) (p<0.05), HR was 66±8 vs 62 ± 6 bpm (p=NS), MAP was 95±14 vs 88±8 mmHg (p=NS), MPAP was 26 ± 8 vs 21 ± 2 mmHg (p=NS) and cardiac index was 2.7±1 vs 2.5±1 L/min/m2 (p=NS). CMS patients had both lower low frequency (LF) (5.87±0.98 ln) and HF (4.40±0.92 ln) components as compared to LL (p<0.05) and HL (p<0.05).The LF/HF ratio was significantly higher in CMS patients as compared to LL (1.18±0.14, p<0.05). The LF/HF ratio did not correlate neither with indices of right or left ventricular function nor to CMS score. Conclusion. Maladapted high altitude dwellers with chronic mountain sickness present a marked sympatho-vagal imbalance, with increased sympathetic and decreased parasympathetic modulation as compared to acclimatized LL or HL controls. Moreover, indices of autonomic nervous system disturbance do not appear to be related to the severity of pulmonary hypertension, right or left ventricular function.
- © 2012 by American Heart Association, Inc.