RESUMEN
UNLABELLED: In a previous preliminary work we found a longer inspiration than expiration period during sleep, opposite to what normally happens during wakefulness. These results which derived from quite a few measurements, but only from two male subjects, were not categorized to sleep stages. In the present paper we have studied the heart rate/minute, the respiration rate/minute and also the duration of inspiration and expiration (respiration ratio), in six healthy subjects, four men and two women aged 23-42, in all four stages of sleep, the REM stage and in arousals. These parameters were studied in the same subjects twice, once after a resting pre-sleep period (sleep A) and another time after "exercise" before going to sleep (sleep B), in an attempt to trace any changes in the above parameters that could be related to the "resting procedure". "Exercise" before sleep B consisted of a heavy dinner taken after 21:30 h and some physical activity. Results were analyzed by the Wilcoxon non-parametric tests. The differences between sexes were analyzed by the Mann-Whitney, two independent samples, test and have shown the following: a) The heart rate and the respiration rate did not increase significantly in sleep B as compared to sleep A in most of the sleep stages and arousals. b) Respiration ratio did not change significantly between sleep A and sleep B. c) We have confirmed our previous finding that during sleep, the mean values of inspiration are longer than those of expiration and have also shown that the increase in the duration of inspiration as indicated by the respiration ratio, existed in all four stages of sleep, the REM and the arousal periods. d) Significantly higher heart rate and respiration rate and lower respiration ratio were observed in women as compared to men, throughout the study and especially during sleep B as compared to sleep A. This finding, although statistically acceptable, needs confirmation due to the small number of women studied. e) Statistical analysis by the Wilcoxon test of the accumulated means of all sleep A and B stages in heart rate, respiratory rate and respiration ratio were compared with the same findings during arousal periods and showed no significant difference except for stage 1 sleep B (P=0.002). f) The action of inspiration inducing a negative pressure in the thorax and altering the intra-abdominal pressure may be considered an "elastic" action supporting blood flow and contributing to the "resting procedure" during sleep. IN CONCLUSION: (a) The results a) and b) indicate that in the young subjects studied, the "exercise" they had before sleep B was not sufficient to significantly modify the above parameters. (b) The "arousal" period, according to the above findings, may be considered as part of the usual sleeping period. (c) Women as compared to men had higher heart rate and respiration rate and lower respiration ratio, especially in sleep B as compared to sleep A. This result needs confirmation. (d) We found increased duration of inspiration during sleep. As reminded above, inspiration has favorable hemodynamic action in the thorax, delivers oxygen to the heart and body tissues and exercises an elastic action to the abdominal vessels. Having all these in mind, inspiration may be considered as a factor supporting the circulation of blood and the "resting procedure" during sleep.