Neural control of renal medullary perfusion

There is strong evidence that the renal medullary circulation plays a key role in long-term blood pressure control. This, and evidence implicating sympathetic overactivity in development of hypertension, provides the need for understanding how sympathetic nerves affect medullary blood flow (MBF). The precise vascular elements that regulate MBF under physiological conditions are unknown, but likely include the outer medullary portions of descending vasa recta and afferent and efferent arterioles of juxtamedullary glomeruli, all of which receive dense sympathetic innervation. Many early studies of the impact of sympathetic drive on MBF were flawed, both because of the methods used for measuring MBF and because single and often intense neural stimuli were tested. Recent studies have established that MBF is less sensitive than cortical blood flow (CBF) to electrical renal nerve stimulation, particularly at low stimulus intensities. Indeed, MBF appears to be refractory to increases in endogenous renal sympathetic nerve activity within the physiological range in all but the most extreme cases. Multiple mechanisms appear to operate in concert to blunt the impact of sympathetic drive on MBF, including counter-regulatory roles of nitric oxide and perhaps even paradoxical angiotensin II-induced vasodilatation. Regional differences in the geometry of glomerular arterioles are also likely to predispose MBF to be less sensitive than CBF to any given vasoconstrictor stimulus. Failure of these mechanisms would promote reductions in MBF in response to physiological activation of the renal nerves, which could, in turn, lead to salt and water retention and hypertension.     

Transdermally administered nitric oxide by application of acidified nitrite increases blood flow in rat epigastric island skin flaps

Surgical flaps are commonly used in the reconstruction of tissue defects after tumour surgery and trauma. Flap failure continues to be a clinical problem and the underlying causes are not fully understood. In the present study a system that generates nitric oxide (NO) in a non-enzymatic fashion was created through the acidification with vitamin C of a cream containing increasing concentrations (0.125%, 0.25%, 0.5%, 1.25% and 2.5%) of nitrite (NO(2)(-)). The cream was applied for 30 min to a modified epigastric island skin flap in the rat. Blood flow in the supplying artery was measured by transit-time ultrasound flowmetry throughout the experiment and superficial skin blood flow was measured by laser Doppler perfusion imaging before and after treatment. Mean arterial blood pressure was also monitored. NO and the gas nitrogen dioxide (NO(2)), which is formed when NO reacts with atmospheric oxygen, were measured above the cream using chemiluminescence. In flaps treated with the NO generating cream, a concentration-dependent increase in blood flow in the supplying artery and flap skin of up to 130% was observed. Cream base alone or cream base acidified with vitamin C had no effect on blood flow. Also, concentration-dependent formation of both NO and NO(2) was seen. NO increases both supplying artery blood flow and superficial cutaneous blood flow in an epigastric island skin flap model in the rat indicating that NO is of importance in flap physiology and possibly also for flap survival.     

Assessment of haematuria: automated urine flowmetry vs microscopy.

BACKGROUND: Microscopy of the urine sediment may be a useful method in the distinction between a glomerular and a non-glomerular source of urinary bleeding. However, microscopic techniques are time consuming and hampered by inter-observer variations. In the present study we have therefore compared bright-field microscopy with automated urine flowmetry (Sysmex UF-100), examining their ability to differentiate between glomerular and non-glomerular haematuria. METHODS: Fresh urine samples were obtained from 112 patients with a well-defined, single cause of a positive dipstick test. Their urine specimens were examined within 4 h in a blinded manner. Of them, 79 specimens had a positive dipstick for blood and thus could be evaluated for haematuria. RESULTS: The Sysmex UF-100 had a sensitivity and specificity of 0.83 and 0.94 respectively in detecting non-glomerular bleeding. The positive and negative predictive values were 0.95 and 0.78 respectively. The corresponding values of microscopy were 0.79 and 0.90 respectively, and 0.93 and 0.74 respectively. CONCLUSIONS: Automated flowmetry can be used in the distinction between glomerular and non-glomerular haematuria.     

Multiple parameter assessment of skin irritancy

In a previously developed guinea pig model for the study of skin irritancy, the irritant skin reactions caused by repeated open applications of low concentrations of sodium lauryl sulphate (SLS) have been studied macroscopically and microscopically. 2 new assessment methods, evaporimetry, which reflects the water barrier function of stratum corneum, and laser Doppler flowmetry to measure the cutaneous blood flow, have been added and compared with the existing methods of assessment in the model. In the present study of the irritant reaction caused by 1% SLS in 9 test animals, the 5 assessment parameters all showed values which, compared to control untested skin, increased progressively over the 3 days of application. In the assessment of skin irritancy, both evaporimetry and laser Doppler flowmetry have been shown to be useful non-invasive tools which can be quickly and reproducibly performed.     

The effect of cigarette smoking on gingival blood flow in humans

This paper presents the acute effects of cigarette smoking on blood flow to the gingiva in 12 young smokers. Relative gingival blood flow (GBF) was measured by a laser Doppler fiberoptic probe placed 1 mm into the buccal sulcus of tooth no. 26. The probe continuously measured the flux of blood cells (velocity X number of cells) in the gingival crest. Relative skin blood flow (SBF) to the forearm and heart rate were also monitored continously; blood pressure (BP) was assessed at 5-min intervals. After resting for 5 min, subjects sham smoked an unlighted cigarette for 5 min, then smoked the cigarette, and finally rested for 25 min afterwards. Mean changes from resting for all variables were compared to sham smoking for each 5 min block. Mean GBF rose significantly above sham smoking values during smoking, and remained elevated during the first 5 min after smoking (p less than 0.05). Mean SBF decreased slightly during and after smoking, but the changes were not significantly depressed compared to sham smoking (p greater than 0.05). During smoking, BP and heart rate increased significantly over sham smoking (p less than 0.05). GBF increased almost linearily when the probe was placed into the gingival sulcus; this phenomenon did not occur when the probe was placed externally to the gingival crest. The theory that smoking impairs gingival blood flow may not be true in humans.     

Viscero‐somatic reflexes in referred pain areas evoked by capsaicin stimulation of the human gut

The interaction between visceral pain and the sympathetic nervous system is only sparsely investigated in quantitative human studies. Referred visceral pain can be evoked experimentally by application of substances such as capsaicin (the pungent substance of chilli pepper) to the gut. The aim of the present study was to induce referred visceral pain from the small and large intestine in 32 volunteers via the stomal opening in patients with ileo‐ or colostomy and quantify the viscero‐somatic reflex responses in these referred pain areas by thermography and laser doppler flowmetry. Capsaicin evoked pain and referred pain areas in all subjects. In the referred pain area, the temperature increased by approximately 0.6°C (P<0.001) and the blood flow by approximately 35AU (P<0.001). Saline was used in a control experiment, and no temperature and blood flow changes were found. The present quantitative human study of viscero‐somatic reflexes showed dramatic sympathetic responses in the referred pain areas after experimentally induced gut pain.     

Disturbances in renal cortical perfusion with reference to the microsphere technique

The microsphere technique for studying renal blood flow is based on injection of a small volume containing radioactively labelled microspheres into the left atrium, left ventricle or possibly the root of the aorta. In the present methodological study, superficial renal cortical blood flow and tissue oxygenation were measured in anaesthetized pigs by laser Doppler flowmetry and by oxygen surface electrode technique. Rapid and profound transient decreases in superficial renal cortical blood flow and tissue oxygenation were found after injection of small volumes of plasma and saline into the left atrium. This response was present also when solutions without microspheres were injected. The reaction was not abolished by careful adjustment of the injectate temperature. When the rapid onset of flow reduction is related to the estimated time of delivery of the bolus with microspheres, the validity of regional blood flow measurements using the microsphere technique within the superficial renal cortex must be seriously questioned.     

Flowmetry‐based portal inflow manipulation for a small‐for‐size liver graft in a recipient with spontaneous splenorenal shunt

Chan SC, Lo CM, Chik BH, Chow LC, Fan ST. Flowmetry‐based portal inflow manipulation for a small‐for‐size liver graft in a recipient with spontaneous splenorenal shunt.
Clin Transplant 2010: 24: 410–414. © 2009 John Wiley & Sons A/S. Abstract: We report a case of living donor liver transplantation using a small‐for‐size graft (SFSG) with graft to estimated standard liver volume of only 28% in a recipient with spontaneous splenorenal shunt and demonstrate the value of intraoperative ultrasonic flowmetry. Despite an SFSG, the graft was underperfused. This was recognized by flowmetry and was rectified by ligation of the splenorenal shunt.     

Review of methodological developments in laser Doppler flowmetry

Laser Doppler flowmetry is a non-invasive method of measuring microcirculatory blood flow in tissue. In this review the technique is discussed in detail. The theoretical and experimental developments to improve the technique are reviewed. The limitations of the method are elaborated upon, and the research done so far to overcome these limitations is critically assessed.