Effects of graded hemorrhage on short‐term variability of blood pressure in conscious rats

Abstract

A controlled graded bleeding was performed in conscious rats with 15 min intervals between two withdrawals, in order to induce a 25% blood loss without hypotension. Heart rate (HR) was unaffected as well. The spectral profiles of systolic blood pressure (SBP) analyzed on 51.2 s segments exhibited increases in the high frequency (HR, respiratory) component. This increase paralleled the blood loss with a rise ranging from 20% for a 1 mL/kg hemorrhage to 90% for a 11 mL/kg removal. These changes were associated with increases in the mid-frequency (MF, Mayer waves) component of SBP variability. These latter rises were between 30 and 40% of the control value. Breathing frequency (BF) and blood gases were unaltered following hemorrhage. A shift of fluid occurred during the 3 h session as reflected by the significant hemodilution. Rats were also bled after pretreatment with prazosin (1 mg/kg) or with an association of prazosin (1 mg/kg) and losartan (10 mg/kg). These treatments increased HR. A marked fall in SBP occurred with the double blockade. Hemorrhage determined a relative bradycardia together with the SBP decrease (reversible shock) after prazosin and losartan treatment. Prazosin determined opposite changes in MF (-33%) and HF (+58%) SBP components. A further decrease in the MF SBP component was observed following the double blockade. Spectral profiles following hemorrhage were unchanged compared to the prehemorrhage blocked levels. Therefore graded nonhypotensive, ie, normotensive hemorrhage in rats, was associated with progressive increases in the respiratory SBP variations, estimated from the SBP spectrum. This sensitive index could reflect the low preload state due to hypovolemia. The hemorrhage-induced MF SBP component increase could reflect an increased sympathetic vasomotor drive, prevented with prazosin, as a reflex adjustment to hypovolemia. Renin activation could also contribute to the genesis of MF waves and its role in maintaining BP following hemorrhage was exemplified with alpha 1-adrenoceptor blockade.

Stroke volume monitored by modeling flow from finger arterial pressure waves mirrors blood volume withdrawn by phlebotomy

“…The changes in stroke volume and pulse pressure observed during the phlebotomy were still present 4-5 min after completion of the blood withdrawal, indicating that long-term regulatory processes were not efficient within this time range to restore the blood volume. The activation of humoral systems and the shift of fluid from an extravascular compartment to the blood also dampen these changes during longer bleedings [1,22]. However, a recent study showed fluid replacement occurs rapidly, within the time range of the present study i. e. 6-7 min [12].…”

Inappropriate Sympathetic Activation at Onset of Septic Shock

“…comparable between the three groups (26). Second, in healthy volunteers, the infusion of catecholamine may alter the low-frequency fluctuations of blood pressure (27) and has no significant effect on the frequency components of HR (27,28).…”

“…In this context, several factors may interfere with HR or blood pressure fluctuations. First, a reduction of venous return to the thorax may alter the respiratory fluctuation in SBP (25,26). Therefore, patients were studied after fluid replacement with pulmonary wedge pressure between 10 and 18 mm Hg as a target goal.…”

Hemodynamic and autonomic response to acute hemorrhage in streptozotocin-induced diabetic rats

“…Even if the total volume of blood loss is the same, different results may be obtained depending on the method of blood withdrawal. In the present study, a controlled graded bleeding was performed with 20-minute intervals between two withdrawals [39]. This method makes it possible to measure the autonomic and hemodynamic response to each volume of blood loss.…”