Chronic mountain sickness (CMS), a maladaptation syndrome to chronic hypoxia, occurs in some Andean high altitude natives. Recently it has been reported that baroreflex cardiac control is impaired in CMS (Keyl et al. 2003). The experiments reported here were undertaken with the aim of determining whether carotid baroreflex control of vascular resistance is also altered in human subjects with CMS.

Nineteen Andean natives (10 with CMS and 9 control) were recruited in Cerro de Pasco, Peru (altitude 4338 m). The local ethics committee approved the study. Carotid baroreflex function was studied on the day following arrival in Lima (150 m). Baroreflex control of vascular resistance in the forearm was assessed from changes in finger blood pressure (photoplethysmography) divided by brachial flow velocity (Doppler ultrasound). A modified neck chamber and graded pressures of -40 to + 60 mmHg were used to change the stimulus to carotid baroreceptors. Individual stimulus-response curves were defined and sigmoid functions were applied. From the first derivative of the sigmoid curves, the maximal slopes (equivalent to peak gain) and the corresponding carotid pressures (equivalent to ‘set point’) were determined.

There were no significant differences between indicators of carotid baroreflex function at 150 m in the two subject groups. The maximal slope of the stimulus-response curve was -2.1 ± 0.6 units for CMS subjects and -2.4 ± 0.7 units for control subjects (mean ± S.E.M.; unpaired t test, P > 0.05). The corresponding carotid pressures were 82 ± 4 mmHg and 77 ± 6 mmHg for CMS and control subjects respectively (P > 0.05).

We conclude that CMS has no effect on carotid baroreflex regulation of vascular resistance in high altitude Andean natives tested at 150 m.