Abstract
In healthy subjects, variation in cardiovascular responses to sympathetic stimulation evoked by submaximal lower body negative pressure (LBNP) is considerable. This study addressed the question whether inter-subject variation in cardiovascular responses coincides with consistent and reproducible responses in an individual subject. In 10 healthy subjects (5 female, median age 22 years), continuous hemodynamic parameters (finger plethysmography; Nexfin, Edwards Lifesciences), and time-domain baroreflex sensitivity (BRS) were quantified during three consecutive 5-min runs of LBNP at −50 mmHg. The protocol was repeated after 1 week to establish intra-subject reproducibility. In response to LBNP, 5 subjects (3 females) showed a prominent increase in heart rate (HR; 54 ± 14%, p = 0.001) with no change in total peripheral resistance (TPR; p = 0.25) whereas the other 5 subjects (2 females) demonstrated a significant rise in TPR (7 ± 3%, p = 0.017) with a moderate increase in HR (21 ± 9%, p = 0.004). These different reflex responses coincided with differences in resting BRS (22 ± 8 vs. 11 ± 3 ms/mmHg, p = 0.049) and resting HR (57 ± 8 vs. 71 ± 12 bpm, p = 0.047) and were highly reproducible over time. In conclusion, we found distinct cardiovascular response patterns to sympathetic stimulation by LBNP in young healthy individuals. These patterns of preferential autonomic blood pressure control appeared related to resting cardiac BRS and HR and were consistent over time.
Highlights
Lower body negative pressure (LBNP) is used in research settings as a model to study the cardiovascular effects of central hypovolemia in humans (Hinojosa-Laborde et al, 2014)
heart rate (HR) (37 ± 21%, p < 0.001) increased with a fall in systolic (SAP; −11 ± 6%, p < 0.001) and mean arterial pressure (MAP; −5 ± 5%, p = 0.02), stroke volume (SV) (−31 ± 9%, p < 0.001) and cardiac output (CO) (−6 ± 7%, p = 0.02)
The present study demonstrated two qualitatively different cardiovascular reflex patterns in response to a similar degree of exposure of LBNP varying from a predominant effect on HR to a consistent increase in total peripheral (vascular) resistance (TPR) with a smaller change in HR
Summary
Lower body negative pressure (LBNP) is used in research settings as a model to study the cardiovascular effects of central hypovolemia in humans (Hinojosa-Laborde et al, 2014). Cardiovascular Response Patterns to Central Hypovolemia to a progressive reduction of central blood volume as elicited by LBNP, both SV and CO decrease modifying arterial pulse pressure and its pulsatility (Michard et al, 2000; Bronzwaer et al, 2015). This results in a baroreceptor mediated reflex increase in heart rate (HR) and total peripheral (vascular) resistance (TPR) (Schadt and Ludbrook, 1991; Ryan et al, 2012). We questioned whether the large variation in response patterns between subjects to submaximal LBNP coincides with consistent and reproducible responses in an individual subject
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