No Influence of Ovarian Hormones on Cerebrovascular Responses to the Valsalva Maneuver

Cerebral blood flow is modulated in part by arterial perfusion pressure and autonomic neural activity. Valsalva straining drives increases in cerebral perfusion pressure that may challenge cerebrovascular regulatory mechanisms. These challenges may be even greater during the normal menstrual cycle due to vasoactive influences of ovarian hormones. PURPOSE: To test the hypothesis that cerebral vascular responses to Valsalva straining are enhanced with increased plasma concentrations of estrogen and progesterone. METHODS: Twelve healthy eumenorrheic females (mean age 25 ± 1 yr; height 165 ± 3 cm; weight 66 ± 2 kg; mean ± SE) were studied during the early and late follicular (EF and LF) and early and late luteal (EL and LL) phases of the menstrual cycle. We recorded the ECG, beat-by-beat arterial pressure (Finometer), end-tidal CO2, and cerebral blood velocity (CBV) from the middle cerebral artery (transcranial Doppler ultrasound). Plasma ovarian hormone concentrations were assessed with high performance liquid chromatography. Supine subjects strained to an expiratory pressure of 40 mmHg for 15 seconds, and we recorded magnitudes of changes in arterial pressure and CBV. RESULTS: Compared with EF, estrogen was significantly higher during LF (111 ± 20 pg/ml) and EL (113 ± 27 pg/ml) (both P\u3c0.05). During EL (12 ± 6 pg/ml) and LL (7 ± 2 pg/ml), progesterone was significantly higher when compared with EF(1 ± .3 pg/ml) and LF(1 ± .2 pg/ml) (both P\u3c0.05). The magnitude of arterial pressure overshoot at the release of strain (an indirect indicator of peripheral sympathetic neural activation during straining) was significantly higher during LF (54 ± 9 mmHg) compared to EL and EF (both phases = 35 ± 4 mmHg; P=0.003). Changes in CBV during Valsalva straining and during release from strain were statistically identical across menstrual phases (P\u3e0.05). CONCLUSIONS: Despite indirect evidence that sympathetic neural activity during the Valsalva maneuver is increased when plasma estrogen concentrations are high, responses of the cerebral vasculature to Valsalva straining are unaffected by cycling ovarian hormones

Non-Invasive Techniques to Track Stroke Volume during Simulated Uncontrolled Hemorrhage

Battlefield medics and civilian first-responders have limited tools to assess the magnitude of blood loss in traumatically-injured patients. Accurate measures of stroke volume would provide important quantitative values for blood volume reductions, but battlefield medics and civilian first responders do not have access to standard laboratory methods to measure stroke volume. They may have access to arterial pulse wave detectors (for example, SPO2 monitors), but the usefulness of pulse wave detectors for determining stroke volume during hemorrhage has not been determined. PURPOSE: To compare stroke volumes estimated a with a standard laboratory rebreathing (RB) method to stroke volumes estimated from finger pulse waves using pulse contour (PC) analysis during simulated hemorrhage with lower body negative pressure (LBNP). METHODS: We studied nine healthy volunteers (5 female and 4 male; 24±2 yrs; 170±4 cm; 67±4 kg). ECG, beat-by-beat finger arterial pressure (Finometer), respiratory rate (pneumobelt), and cardiac output (RB and PC methods) were measured every two minutes during progressive LBNP at a decompression rate of 3 mmHg/min to -60 mmHg. Slopes relating changes of stroke volume were compared using linear regression. RESULTS: At baseline, stroke volumes were higher (P=0.003) for RB (116 ± 6.5 ml) than PC (91 ± 4.3 ml). Compared with baseline, stroke volumes were lower (P = 0.001) by minute four of LBNP for RB but not for PC. Slopes relating changes of stroke volumes during LBNP calculated from the RB method (-1.3 ± 0.1 ml/mmHg) were significantly steeper (P = 0.001) than those calculated for the PC method (-0.63 ml/mmHg). CONCLUSIONS: Stroke volumes measured with PC underestimate stroke volumes measured with RB at rest, and are less sensitive in detecting early changes during simulated hemorrhage. Blunted slopes recorded for PC compared with RB suggest that estimates of stroke volume based on pulse contour analysis of arterial pressure waveforms may be inaccurate for tracking reductions of blood volume during hemorrhage

Non-Invasive Techniques to Track Stroke Volume during Simulated Uncontrolled Hemorrhage

Battlefield medics and civilian first-responders have limited tools to assess the magnitude of blood loss in traumatically-injured patients. Accurate measures of stroke volume would provide important quantitative values for blood volume reductions, but battlefield medics and civilian first responders do not have access to standard laboratory methods to measure stroke volume. They may have access to arterial pulse wave detectors (for example, SPO2 monitors), but the usefulness of pulse wave detectors for determining stroke volume during hemorrhage has not been determined. PURPOSE: To compare stroke volumes estimated a with a standard laboratory rebreathing (RB) method to stroke volumes estimated from finger pulse waves using pulse contour (PC) analysis during simulated hemorrhage with lower body negative pressure (LBNP). METHODS: We studied nine healthy volunteers (5 female and 4 male; 24±2 yrs; 170±4 cm; 67±4 kg). ECG, beat-by-beat finger arterial pressure (Finometer), respiratory rate (pneumobelt), and cardiac output (RB and PC methods) were measured every two minutes during progressive LBNP at a decompression rate of 3 mmHg/min to -60 mmHg. Slopes relating changes of stroke volume were compared using linear regression. RESULTS: At baseline, stroke volumes were higher (P=0.003) for RB (116 ± 6.5 ml) than PC (91 ± 4.3 ml). Compared with baseline, stroke volumes were lower (P = 0.001) by minute four of LBNP for RB but not for PC. Slopes relating changes of stroke volumes during LBNP calculated from the RB method (-1.3 ± 0.1 ml/mmHg) were significantly steeper (P = 0.001) than those calculated for the PC method (-0.63 ml/mmHg). CONCLUSIONS: Stroke volumes measured with PC underestimate stroke volumes measured with RB at rest, and are less sensitive in detecting early changes during simulated hemorrhage. Blunted slopes recorded for PC compared with RB suggest that estimates of stroke volume based on pulse contour analysis of arterial pressure waveforms may be inaccurate for tracking reductions of blood volume during hemorrhage