Acclimatization and associated changes in phonocardiographic recordings during a high-altitude climb.

were then registered on a laptop computer in base camp and on a PDA in the high altitude camps. These signals, together with the pulsioximetry values and other data of clinical importance, were sent via satellite to the medical team using a Web interface and a data compression algorithm developed for this purpose.7 Statistical analysis of the data was carried out using the Pearson correlation coefficient between the average S2/S1 ratio for each register and SaO2 values and other parameters, over a total of 14 ratios for each subject. Following a prior baseline examination carried out on each subject at an altitude of 50 m above sea level, phonocardiographic data and recordings were taken at different altitudes up to 7100 m. Upon analysing the relationship between the S2/S1 ratio values and the SaO2 values for each mountaineer, correlation indexes were obtained of –0.79 and –0.91, where the negative value indicates that these parameters develop in different directions. Studying the data in detail we can see that, due to the normal altitude acclimatisation process, the progress of both parameters on successive days at the same altitude differs; whilst the SaO2 increases (Figure 1A) as a consequence of acclimatisation and it stabilises at 88% and 89%—figures clearly lower than the baseline values—the S2/S1 ratio decreases in both subjects (Figure 1B) until it reaches values similar to the baseline ones. This indicates that certain mechanisms for altitude acclimatisation do not depend solely on SaO2. If, for the correlation analysis of SaO2 parameters and S2/S1 ratios, only the first of the recordings obtained at each different altitude are taken, which to some extent corrects the effect of altitude adaptation, the correlation indexes increase very significantly until they reach -0.92 and -0.96 Acclimatization and Associated Changes in Phonocardiographic Recordings During a High-Altitude Climb