Repeatability and protocol comparability of presyncopal symptom limited lower body negative pressure exposures.

Data on repeatability and comparability of different presyncopal symptom-limited lower body negative pressure (PSL-LBNP) exposure protocols, while scarce, are critical to the interpretation of studies using PSL-LBNP methods. To investigate if PSL-LBNP tolerance, heart rate, and blood pressure were repeatable, 11 subjects were exposed to 4 PSL-LBNP tests; each test occurring at the same time of day, separated by at least 72 h, and using the same protocol. No significant differences were found in either the heart rate or blood pressure responses to the PSL-LBNP or the tolerance indices (cumulative stress index; maximum negative pressure tolerated; and duration of negative pressure exposure). To study the comparability of different PSL-LBNP protocols, nine subjects were exposed randomly to five PSL-LBNP tests using protocols that varied in stage duration but not pressure profile. The protocols had 1-, 3-, 5-, 7-, or 9-min stage durations. These PSL-LBNP exposures were conducted at the same time of day and separated by at least 72 h. While no differences were noted in either the response pattern or magnitude of heart rate or blood pressure to the differing protocols, the cumulative stress index and the duration of negative pressure exposure varied proportionally with the length of the stage durations. With the exception of the 1-min protocol, the maximum negative pressure tolerated did not vary regardless of the protocol used.(ABSTRACT TRUNCATED AT 250 WORDS)