The relationship between orthostatic differences in arterial blood pressure and autonomic tone: gender variability

OBJECTIVES
The differences in orthostatic blood pressure result from dynamic changes in the sympathovagal balance. We studied sex-related variations in autonomic tone regulation.

STUDY DESIGN
The study included 237 individuals (114 males, 123 females) who were asymptomatic and had no abnormal laboratory or physical findings. The mean age was 47 years (range 20 to 79 years) for men, and 39 years (range 20 to 71 years) for women. All the participants were subjected to a careful history taking, physical examination, routine biochemical examinations, electrocardiographic recording, 24-hour Holter monitoring, and orthostatic tests.

RESULTS
In heart rate variability analysis, parasympathetic tone parameters, in particular the high frequency (HF) component was significantly high in females, whereas sympathetic tone parameters, in particular the low frequency (LF)/HF ratio was significantly high in males (p<0.001). The normalized LF component in males showed positive correlations with systolic (r=0.308, p=0.001) and diastolic (r=0.301, p=0.002) blood pressures during the rapid stand test; this correlation was not seen in females. Blood pressures obtained in the second minute of the rapid supine test following the stand test were in positive correlation with the LF/HF ratio in both sexes. In males, variations in systolic and diastolic blood pressures during rest, stand, and supine positions were primarily influenced by the LF component and HF component, respectively. In females, variations in systolic blood pressure during the three positions were not correlated with autonomic tone components, but variations in diastolic blood pressure were primarily affected by the LF/HF ratio.

CONCLUSION
Autonomic system works through varying priorities in both sexes and this causes sex-related differences in orthostatic tolerance.