The long-term reproducibility of clinical tests of autonomic cardiovascular function in normal man.

Tests for the integrity of autonomic cardiovascular reflexes have been widely used in the clinic and in space physiology for decades. However, whereas some information on the short-term reproducibility of such tests are available, little is known about their long-term reproducibility. The work in this study was, therefore, directed towards assessing intra- and inter-subject variations in responses (heart rate, mean arterial blood pressure, forearm blood flow and forearm vascular conductance) to cortical arousal, cold face stimulation and lower body negative pressure (at 10, 30 and 50 mmHg) in eleven healthy male subjects (aged between 22 and 45 years). Subjects were studied repeatedly (each month) over a 6-month period. It was found that forearm vascular conductance responses to cold face stimulation were the most reproducible (mean coefficient of variation 10.9%), and with diminishing reproducibility curve responses to lower body negative pressure at 50 mmHg (mean coefficient of variation 12.4%), lower body negative pressure at 30 mmHg (mean coefficient of variation 18.9%), lower body negative pressure at 10 mmHg (mean coefficient of variation 28.0%), and responses to cortical arousal (mean coefficient of variation 39.6%). Generally, subjects who showed the largest responses to cold face stimulation also showed the largest responses to the other tests, and vice versa. It is concluded that there is intra-individual variability in the responsiveness and reproducibility of cardiovascular tests and that the cardiovascular responses to cold face stimulation and lower body negative pressure at 50 mmHg are the most reproducible.