Purpose: The purpose of this study was to assess cardiovascular responses in young males when exposed to three (-10 mmHg, -20 mmHg and -40 mmHg) lower body negative pressures (LBNP).
Methods: The study was limited to 20 healthy, young adult males, ages 18 – 35 years. The protocol involved five, 10 minute phases all at supine rest, 1) LBNP, 0 mmHg; 2) LBNP, -10 mmHg; 3) LBNP, -20 mmHg; 4) LBNP, -40 mmHg; 5) Recovery 0 mmHg. Blood pressure was taken every 3 minutes and EKG was taken every 2 minutes. Cardiac Output, Stroke Volume and heart rate were continuously monitored throughout all stages.
Results: The results indicated a decline in pulse pressure when exposed to LBNP. The more negative pressure applied the more blood pooled in the lower extremities. The baseline mean of pulse pressure for the 20 participants was 60 + 11.3, to -40 mmHg 46.5 + 9.7. The results of the EKG morphology indicate there was a significant drop in the following: R-R interval; 936.89 ms at 0 mmHg to 800.85 ms at 40 mmHg LBNP, P-R interval; 155 ms at 0 mmHg to 143 at 40 mmHg LBNP, QRS interval 92.58 ms at 0 mmHg to 87.10 ms at 40 mmHg LBNP; Q-T interval 398.58 ms at 0 mmHg to 374.08 ms at -40 mmHg LBNP, Q-Tc interval; 409.03 ms at baseline 0 mmHg to 399.40 ms at -40 mmHg. The Q-T dispersion did not show a significant difference. The P-R axis showed significance from -10 to -40 mmHg and -40 mmHg to recovery. The T axis did not show a significant difference.
Conclusions: The data shows that LBNP induces physiological responses that cause changes in pulse pressure and EKG morphology which replicate the circulatory responses similar to hemorrhage.