Simultaneous assessment of muscle and skin blood fluxes with the laser-Doppler technique

Microcirculatory alterations induced by sedation in intensive care patients. Effects of midazolam alone and in association with sufentanil

Introduction

Sedation is widely used in intensive care unit (ICU) patients to limit the risk of pulmonary barotrauma and to decrease oxygen needs. However, adverse effects of cc5128sedation have not been fully evaluated; in particular, effects of benzodiazepine and opiates on microcirculation have not been extensively studied. The aim of this study was to evaluate the microcirculatory effects of a sedation protocol commonly prescribed in the ICU.

Methods

Ten non-septic patients under controlled ventilation requiring sedation for therapeutic purposes were enrolled in a prospective observational study conducted in an ICU of a university hospital. Sedation was conducted in two successive steps: first, each patient received midazolam (0.1 mg/kg per hour after a bolus of 0.05 mg/kg, then adapted to reach a Ramsay score of between 3 and 5). Second, after one hour, sufentanil was added (0.1 μg/kg per hour after a bolus of 0.1 μg/kg). Arterial pressure, heart rate, cardiac output determined by transthoracic impedance, transcutaneous oxygen (tcPO₂) and carbon dioxide (tcPCO₂) pressures, and microcirculatory blood flow determined by laser Doppler flowmetry at rest and during a reactive hyperaemia challenge were measured before sedation (NS period), one hour after midazolam infusion (H period), and one hour after midazolam-sufentanil infusion (HS period).

Results

Arterial pressure decreased in both sedation periods, but heart rate, cardiac output, tcPO₂, and tcPCO₂ remained unchanged. In both sedation periods, microcirculatory changes occurred with an increase in cutaneous blood flow at rest (H period: 207 ± 25 perfusion units [PU] and HS period: 205 ± 25 PU versus NS period: 150 ± 22 PU, p < 0.05), decreased response to ischaemia (variation of blood flow to peak: H period: 97 ± 16 PU and HS period: 73 ± 9 PU versus NS period: 141 ± 14 PU, p < 0.05), and attenuation of vasomotion.

Conclusion

Sedation with midazolam or a combination of midazolam and sufentanil induces a deterioration of vasomotion and microvascular response to ischaemia, raising the question of whether this effect may further alter tissue perfusion when already compromised, as in septic patients.

Non-invasive monitoring of muscle blood perfusion by photoplethysmography: evaluation of a new application

AIM

To evaluate a specially developed photoplethysmographic (PPG) technique, using green and near-infrared light sources, for simultaneous non-invasive monitoring of skin and muscle perfusion.

METHODS

Evaluation was based on assessments of changes in blood perfusion to various provocations, such as post-exercise hyperaemia and hyperaemia following the application of liniment. The deep penetrating feature of PPG was investigated by measurement of optical radiation inside the muscle. Simultaneous measurements using ultrasound Doppler and the new PPG application were performed to elucidate differences between the two methods. Specific problems related to the influence of skin temperature on blood flow were highlightened, as well.

RESULTS

Following static and dynamic contractions an immediate increase in muscle perfusion was shown, without increase in skin perfusion. Liniment application to the skin induced a rapid increase in skin perfusion, but not in muscle. Both similarities and differences in blood flow measured by Ultrasound Doppler and PPG were demonstrated. The radiant power measured inside the muscle, by use of an optical fibre, showed that the near-infrared light penetrates down to the vascular depth inside the muscle.

CONCLUSIONS

The results of this study indicate the potentiality of the method for non-invasive measurement of local muscle perfusion, although some considerations still have to be accounted for, such as influence of temperature on blood perfusion.

Physiological hyperinsulinaemia increases intramuscular microvascular reactive hyperaemia and vasomotion in healthy volunteers

AIMS/HYPOTHESIS

Insulin possesses vasodilatory actions that may be important in regulating its access to insulin-sensitive tissues. Our study aims to directly measure changes in response to insulin in the human skeletal muscle microcirculation. Measurement was by an implanted laser Doppler probe.

METHODS

We investigated changes in intramuscular and skin microvascular perfusion in 12 healthy individuals during a hyperinsulinaemic and a control clamp. We determined leg blood flow with plethysmography, finger skin functional capillary recruitment with capillaroscopy, endothelium-(in)dependent vasodilation by iontophoresis of acetylcholine and sodium nitroprusside, and leg intramuscular reactive hyperaemia and vasomotion with laser Doppler measurements.

RESULTS

Compared to the control study, hyperinsulinaemia (416+/-82 pmol/l) caused: (i) an increase in leg blood flow (1.0+/-1.0 vs 0.1+/-0.6 ml.min(-1).100 ml, p<0.05); (ii) an increase in finger skin capillary recruitment (14.9+/-10.1 vs -5.6+/-11.0%, p<0.01); (iii) no change in baseline laser Doppler perfusion either in finger skin or leg muscle; (iv) a tendency to increase acetylcholine-mediated vasodilation (475+/-534 vs 114+/-337%, p=0.07) with no change in sodium-nitroprusside-mediated vasodilation ( p=0.2) in finger skin; (v) an increase in intramuscular reactive hyperaemia (423+/-507 vs 0+/-220%, p<0.01); and (vi) a decrease in time needed to reach peak intramuscular perfusion (-3.6+/-3.0 vs 1.1+/-3.1 s, p<0.01). In addition, hyperinsulinaemia induced an increase in intramuscular vasomotion by increasing the contribution of frequencies between 0.01 and 0.04 Hz ( p<0.05 for all), which probably represents increased endothelial and neurogenic activity.

CONCLUSIONS/INTERPRETATION

Physiological hyperinsulinaemia not only stimulates total blood flow and skin microvascular perfusion, but also augments human skeletal muscle microvascular recruitment and vasomotion as detected directly by laser Doppler measurements.

A novel approach for comparative study of periosteum, muscle, subcutis, and skin microcirculation by intravital fluorescence microscopy

Herein, we report a new model, which allows comparative study of the microcirculation of different peripheral tissues, i.e., periosteum, skeletal muscle, subcutis, and skin. Using dextran-insensitive Wistar rats gracilis and semitendinosus muscles of the left hindlimb were prepared in association with their appertaining tibial fragments, subcutis, and skin. Blood supply was guaranteed by the femoral artery via the saphenous vessels. High-resolution intravital epi-illumination microscopy of the two muscles displayed the typical microvascular architecture with the capillaries running in parallel to each other (capillary density (CD) 128.4 +/- 4.5 cm-1). In subcutis and skin, capillaries were found arranged as interconnecting mesh-like networks with a density, which was significantly higher (P < 0.05) in subcutis (191.0 +/- 5.5 cm-1) compared with skin (108.9 +/- 3.3 cm-1). Analysis of periosteal tissue revealed two distinct types of arrangements of microvascular architecture. Adjacent to the major feeding and draining vessels of the periosteum, capillaries were organized in densely meshed shunt-like networks, revealing the highest capillary density (242.7 +/- 13.2 cm-1; P < 0.05) of all tissues studied. Periosteal capillaries distant from the major feeding and draining vessels were arranged in parallel to the longitudinal axis of the tibial bone and presented with a density similar to that of the skeletal muscle (128. 6 +/- 9.4 cm-1). Topical application of acetylcholine for analysis of physiological reactivity of the microvasculature showed dose-dependent arteriolar dilation. Moreover, a 3-min upstream femoral artery occlusion demonstrated an appropriate hyperemic response in all tissues studied, indicating intact myogenic control. A prolonged period of ischemia (120 min) followed by reperfusion (60 min) caused massive (P < 0.05) leukocyte-endothelial cell interaction in postcapillary venules, similarly as reported in other microvascular tissue preparations. We propose that the model presented provides a good approach to all peripheral tissues for both the analysis of the physiology of tissue-confined microvascular control and the development of novel therapeutic strategies to counteract manifestation of nutritional dysfunction and inflammatory response in disease.