Differential effects of mild central hypovolemia with furosemide administration vs. lower body suction on dynamic cerebral autoregulation

Effect of drug interventions on cerebral hemodynamics in ischemic stroke patients

The ischemic penumbra is sensitive to alterations in cerebral perfusion. A myriad of drugs are used in acute ischemic stroke (AIS) management, yet their impact on cerebral hemodynamics is poorly understood. As part of the Cerebral Autoregulation Network led INFOMATAS project (Identifying New Targets for Management and Therapy in Acute Stroke), this paper reviews some of the most common drugs a patient with AIS will come across and their potential influence on cerebral hemodynamics with a particular focus being on cerebral autoregulation (CA). We first discuss how compounds that promote clot lysis and prevent clot formation could potentially impact cerebral hemodynamics, before focusing on how the different classes of antihypertensive drugs can influence cerebral hemodynamics. We discuss the different properties of each drug and their potential impact on cerebral perfusion and CA. With emerging interest in CA status of AIS patients, either during or soon after treatment when timely reperfusion and salvageable tissue is at its most critical, the properties of these pharmacological agents may be relevant for modelling cerebral perfusion accuracy and for setting individualised treatment strategies.

Attenuated spontaneous postural sway enhances diastolic blood pressure during quiet standing

PURPOSE

Spontaneous postural sway during quiet standing has been considered a simple output error of postural control. However, as postural sway and inherent body orientation evoke compensatory activity of the plantar flexors, they might contribute to blood circulation under gravitational stress via the muscle pump. Hence, the present study employed an external support device to attenuate the plantar flexor activity in supported standing (SS), to experimentally identify its physiological impact on blood circulation.

METHODS

Eight healthy young subjects performed two 5-min quiet standing trials (i.e., normal standing (NS) and SS), and the beat-to-beat interval (RRI) and blood pressure (BP) were compared between trials. We confirmed that postural sway and corresponding plantar flexor activity, quantified by the anteroposterior displacement of the foot center of pressure and lower back position with respect to the wall, and by the amplitude of electromyography and mechanomyography, respectively, were attenuated in SS, while mean body orientation angle and relative position of the BP sensor were comparable to NS.

RESULTS

The 5-min averages of diastolic BP and mean arterial pressure during SS were significantly higher than during NS, while RRI and systolic BP did not change. These could be interpreted as an increase in peripheral vascular resistance; meanwhile, in NS, this effect was replaced by the muscle pump of the plantar flexors.

CONCLUSION

The muscle contractions related to spontaneous postural sway and body orientation produce substantial physiological impact on blood circulation during quiet standing.

Incomplete recovery of cerebral blood flow dynamics in sufficiently treated high blood pressure

Objective:

Whether cerebrovascular regulation is different in patients with controlled high blood pressure (HBP) with and without small vessel disease (SVD).

Methods:

Sixty-seven healthy controls (mean age ± SD, 45 ± 16 years; 30 women, 37 men) and 40 patients (mean age, 64 ± 13 years; 14 women, 26 men) with HBP and different stages of SVD, underwent simultaneous recordings of the spontaneous fluctuations of BP, blood flow velocity (CBFV) in both middle cerebral arteries (MCA), and of end-tidal CO₂ (ETCO₂). Coherence and transfer function gain and phase between BP and CBFV were assessed in the frequency ranges of VLF (0.02–0.07 Hz), low frequency (0.07–0.15), and high frequency (>0.15). BP SD indicated BP variability (BPV).

Results:

In controls (BP, 86 ± 13 mmHg; ETCO₂, 39 ± 4 mmHg; BPV, 15 ± 6 mmHg), gain, phase and coherence were not age-dependent in simple or a multiple regression models. BPV correlated significantly in both MCAs with gain in low frequency and high frequency, and with phase in VLF and high frequency. In patients (BP, 91 ± 16 mmHg, ETCO₂, 39 ± 4 mmHg, BPV 18 ± 5 mmHg), only gain showed some differences between different SVD groups. Comparing all patients with 25 controls of similar age and sex, patients exhibited significantly (P < 0.05–P < 0.005): increased coherence and gain in VLF, decreased phase in VLF and low frequency, correlations between BPV with phase in low frequency (left) and with gain in VLF (left) and in high frequency (left and right).

Conclusion:

Phase seems an age independent autoregulatory index. In controlled HBP, CBF regulation is degraded at longlasting CBF changes; BPV effects lose their physiological bilateral distribution.

A 90-Day Repeated Oral Dose Toxicity Study of Alismatis Rhizoma Aqueous Extract in Rats

Alismatis rhizoma (AR), the dried rhizome of Alisma orientale (Sam.) Juzep, is a well-known, traditional medicine that is used for the various biological activities including as a diuretic, to lower cholesterol and as an anti-inflammatory agent. The present study was carried out to investigate the potential toxicity of the Alismatis rhizoma aqueous extract (ARAE) following 90-day repeated oral administration to Sprague-Dawley rats. ARAE was administered orally to male and female rats for 90 days at 0 (control), 500, 1,000 and 2,000 mg/kg/day (n = 10 for male and female rats for each dose). Additional recovery groups from the control group and high dose group were observed for a 28-day recovery period. Chromatograms of ARAE detected main compounds with four peaks. Treatment-related effects including an increase in the red blood cells, hemoglobin, hematocrit, albumin, total protein, and urine volume were observed in males of the 2,000 mg/kg/day group (p < 0.05). However, the diuretic effect of ARAE was considered, a major cause of hematological and serum biochemical changes. The oral no-observed-adverse-effect level (NOAEL) of the ARAE was > 2,000 mg/kg/day in both genders, and no target organs were identified.

The Effects of Flumazenil After Midazolam Sedation on Cerebral Blood Flow and Dynamic Cerebral Autoregulation in Healthy Young Males

BACKGROUND

It is unknown whether flumazenil antagonizes the decrease in cerebral blood flow or the alteration in dynamic cerebral autoregulation induced by midazolam. We, therefore, investigated the effects on cerebral circulation of flumazenil administered after midazolam, to test our hypothesis that, along with complete reversal of sedation, flumazenil antagonizes the alterations in cerebral circulation induced by midazolam.

METHODS

Sixteen healthy young male subjects received midazolam followed by flumazenil. The modified Observer's Assessment of Alertness/Sedation (OAA/S) scale and bispectral index (BIS) were used to assess levels of sedation/awareness. For evaluation of cerebral circulation, steady-state mean cerebral blood flow velocity (MCBFV) was measured by transcranial Doppler ultrasonography. In addition, dynamic cerebral autoregulation was assessed by spectral and transfer function analysis between mean arterial pressure (MAP) variability and MCBFV variability.

RESULTS

During midazolam sedation, defined by an OAA/S score of 3 (responds only after name is called loudly and/or repeatedly), BIS, steady-state MAP, steady-state CBFV, and transfer function gain decreased significantly compared with baseline. After flumazenil administration, an OAA/S score of 5 (responds readily to name spoken in a normal tone) was confirmed. Then, BIS and MAP returned to the same level as baseline. However, steady-state MCBFV showed a further significant decrease compared with that under midazolam sedation, and the decreased transfer function gain persisted.

CONCLUSIONS

Contrary to our hypothesis, the present results suggest that despite complete antagonism of the sedative effects of midazolam, flumazenil would not reverse the alterations in cerebral circulation induced by midazolam.

Dynamic cerebral autoregulation after bed rest: effects of volume loading and exercise countermeasures

This study assessed effects of head-down-tilt (HDT) bed rest on dynamic cerebral autoregulation (CA) in 21 healthy young adults with volume loading and exercise countermeasures. Of these, seven underwent an 18-day bed rest without exercise countermeasures ( sedentary group). Volume loading with dextran infusion was performed after bed rest to restore reduced plasma volume to levels before bed rest. In the other 14 subjects, supine cycling during bed rest was performed to preserve cardiac work from before bed rest ( exercise group). Volume loading was also performed in a subgroup of these subjects ( Ex+Dex, n = 7). Dynamic CA was estimated by transfer function analysis of changes in arterial pressure and cerebral blood flow (CBF) velocity in the very low (VLF, 0.02–0.07 Hz), low (LF, 0.07–0.20 Hz), and high frequency ranges (HF, 0.20–0.35 Hz). After bed rest, transfer function gain was reduced in the sedentary group (VLF, 0.93 ± 0.23 to 0.61 ± 0.23 cm−1·s−1·mmHg; P = 0.007) and in the exercise group (LF, 1.22 ± 0.43 to 0.94 ± 0.26 cm−1·s−1·mmHg; P = 0.005, HF, 1.32 ± 0.55 to 1.00 ± 0.32 cm−1·s−1·mmHg; P = 0.010). After volume loading, transfer function gain increased in the sedentary group but not in the Ex+Dex group. Taken together, these findings suggest that dynamic CA was preserved or improved after HDT bed rest in both sedentary and exercise subjects. Furthermore, increases of transfer function gain with volume loading suggest that changes in plasma volume may play an important role in CBF regulation.