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Tolerance to central hypovolemia: The influence of cerebral blood flow velocity oscillations
Author(s) -
Rickards Caroline A.,
Ryan Kathy L.,
Convertino Victor A.
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.613.7
Subject(s) - presyncope , hypovolemia , medicine , cerebral blood flow , transcranial doppler , anesthesia , cardiology , blood pressure , heart rate
Higher oscillations in cerebral blood flow velocity (CBFV) and blood pressure (BP) induced by breathing with inspiratory resistance are associated with delayed onset of symptoms and increased tolerance to central hypovolemia. We hypothesized that subjects with high tolerance (HT) to central hypovolemia would display higher oscillations in CBFV and BP at presyncope compared with subjects with low tolerance (LT). 107 subjects were exposed to progressive lower body negative pressure (LBNP) until the presence of presyncopal symptoms. Subjects were classified as HT if they completed at least the ‐60 mmHg level of LBNP (76 subjects; LBNP time, 1893 ± 31 sec) and LT if they did not complete this level (31 subjects; LBNP time, 1333 ± 21 sec). CBFV was measured at the middle cerebral artery by transcranial Doppler, and mean arterial pressure (MAP) was measured at the finger by photoplethysmography. Mean CBFV and MAP decreased progressively from baseline until presyncope for both LT and HT subjects (P=0.001), with a minimum CBFV of 55 ± 3 cm/s for LT compared with 49 ± 1 cm/s for HT (P=0.043). However, total oscillations (sum of high and low frequency oscillations) in mean CBFV and MAP increased in HT subjects (CBFV: baseline, 8.3 ± 1.2 vs. presyncope, 12.6 ± 1.1 cm/s 2 , P=0.014; MAP: baseline, 6.4 ± 0.6 vs. presyncope, 19.5 ± 1.6 mmHg 2 , P<0.001), but did not change in LT subjects (CBFV: baseline, 8.5 ± 1.1 vs. presyncope, 9.0 ± 1.0 cm/s 2 , P=1.0; MAP: baseline, 6.3 ± 0.5 vs. presyncope, 9.4 ± 0.9 mmHg 2 , P=0.733). Consistent with our previous findings using inspiratory resistance, high oscillations in CBFV and MAP are associated with HT to central hypovolemia.