Cutaneous microcirculatory function predicts the responsiveness to tadalafil in patients with erectile dysfunction and coronary artery disease

History of the cutaneous microcirculation from antiquity to modern times

 This review spans a wide arc from the first observations of the early anatomists to the present day. William Harvey was the first to describe the heart as the centre of the large and small circulatory system. He thus replaced the previously valid system of Galenos, It was Marcello Malpighi who first described that the capillary system connects the arteries with the veins. In 1688 Antoni van Leeuwenhoek (1632-1686) confirmed these results with a paper on capillary perfusion in the caudal fin of the glass eel. It was then Hermann Boerhave (1668-1738, Leiden) who was the first to carry out microcirculation tests on patients. He studied the microcirculation in the human bulbar conjunctiva. Even today, microcirculation studies in the conjunctiva bulbi of patients are carried out today. Until 1831, it was never quite clear whether the observations reported belonged mainly to the field of microcirculation, which had not yet been defined. This was done in Great Britain by Marshall Hall (1790-1857). Technical Improvements allowed increasingly sophisticated studies of the morphological structure of the terminal vasculature. According to Gustav Ricker (1870-1948, Vienna), the terminal vasculature comprises the functional unit of the smallest arteries, arterioles, capillaries and venules. In 1921 it was still thought that the blood circulation was the sole response to the pumping action of the heart. Even the classic work by Bayliss on the myogenic hypothesis (later referred to as "blood flow autoregulation") initially received little attention. More strikingly, even the findings of August Krogh, for which he received the Nobel Prize in Medicine in 1920 (for his discovery of the mechanisms of capillary motor regulation), were ignored. During an outstanding autoregulation symposium held in 1963 a broad consensus was reached on active and passive mechanisms, which is more or less valid till today. The mechanisms of regulation of capillary blood flow are now largely understood, although not completely resolved. The development of video systems with recording capability and automated off-line recording of capillary erythrocyte velocities allowed the application of morphological and dynamic studies of cutaneous capillaries in humans. These reopened the field of physiological or pathophysiological questions again for many groups worldwide. Since 1955, many publications on "microcirculation (5423)" and "capillary microscopy (2195)" have been listed in pubmed.

Phosphodiesterase type 5 inhibitors improve endothelial function and may benefit cardiovascular conditions

The effects of phosphodiesterase type 5 inhibitors on vasodilation mediated via nitric oxide-cyclic guanosine monophosphate are well described. Less is known about other mechanisms through which phosphodiesterase type 5 inhibitors benefit endothelial function, including normalization of serum biomarkers, increased levels of endothelial progenitor cells, ischemia-reperfusion protection mechanisms, and other actions specific to patients with diabetes. These various mechanisms are reviewed. Their impact on several cardiovascular diseases, including erectile dysfunction, pulmonary hypertension, heart failure, high-altitude pulmonary edema, Raynaud's phenomenon, coronary artery disease, diabetes, and atherosclerosis, is presented.

Prophylactic effect of tadalafil on bladder function in a rat model of chronic bladder ischemia

PURPOSE

We investigated the effect of tadalafil on chronic ischemia related bladder dysfunction.

MATERIALS AND METHODS

Adult male Sprague-Dawley® rats were divided into control, arterial endothelial injury and arterial endothelial injury with tadalafil treatment groups. The arterial injury and arterial injury-tadalafil groups underwent endothelial injury of the iliac arteries and received a 2% cholesterol diet after injury. Arterial injury-tadalafil rats received tadalafil (2 mg/kg per day) orally for 8 weeks after injury. The control group received a regular diet. At 8 weeks urodynamic investigation was performed. Bladder tissue was harvested for pharmacological studies, and histological examination of the iliac arteries and bladders was performed.

RESULTS

Iliac arteries from arterial injury and arterial injury-tadalafil rats showed neointimal formation and luminal occlusion. In the arterial injury group the micturition interval was significantly shorter (mean ± SEM 5.4 ± 0.5 vs 11.1 ± 1.1 minutes), and bladder capacity and voided volume were less than in controls. Contractile responses of bladder strips to KCl, electrical field stimulation and carbachol were significantly less after arterial injury than in controls. The arterial injury group showed a significantly increased percent of collagen compared with controls (mean 37.4% ± 1.8% vs 21.5% ± 1.8%). In the arterial injury-tadalafil group intimal formation and luminal occlusion were not prevented. However, there were significant improvements in all functional and morphological parameters compared with the arterial injury group.

CONCLUSIONS

Arterial occlusive disease may lead to chronic bladder ischemia and bladder hyperactivity. Chronic treatment with tadalafil protects bladder function and morphology, resulting in decreased bladder hyperactivity. If valid for humans, the data support phosphodiesterase 5 inhibition as treatment for chronic ischemia related bladder dysfunction.

Blood velocity pulse quantification in the human conjunctival pre-capillary arterioles

Axial red blood cell velocity pulse was quantified throughout its period by high speed video microcinematography in the human eye. In 30 conjunctival precapillary arterioles (6 to 12 microm in diameter) from 15 healthy humans, axial velocities ranged from 0.4 (the minimum of all the end diastolic values) to 5.84 mm/s (the maximum of all the peak systolic values). With the velocity pulse properly quantified, two parameters can be estimated: (1) the average velocity of the pulse during a cardiac cycle AVV (average velocity value) and (2) the magnitude of the pulsation using Pourcelot's resistive index RI. These parameters are important for the estimation of other hemodynamic parameters such as the average volume flow and the average shear stress. The results of this study revealed that the AVV in the human precapillary arterioles ranged between 0.52 and 3.26 mm/s with a mean value for all microvessels of 1.66 mm/s+/-0.11(SE). The RI ranged between 35.5% and 81.8% with a mean value of 53.1%+/-2.2. Quantitative information was obtained for the first time on the velocity pulse characteristics just before the human capillary bed.

Validation of near-infrared laser speckle imaging for assessing microvascular (re)perfusion

The present study was conducted to compare laser speckle imaging (LSI) with sidestream dark field (SDF) imaging (i.e., capillary microscopy) so as to validate the use of LSI for assessing microvascular (re)perfusion. For this purpose, LSI and SDF measurements were performed on the human nail fold during gradual occlusion of the upperarm circulation to modify nail fold perfusion under controlled circumstances. Additionally, a vascular occlusion test was performed to test the ability of LSI to detect rapid changes in tissue perfusion during reactive hyperemia and a hyperthermic challenge was performed to measure LSI perfusion at maximum functional capillary density. Normalized LSI measurements (i.e., normalized to baseline is 100%) were shown to correlate positively with normalized SDF measurements (Pearson's r=0.92). This was supported by linear regression analysis (slope of 1.01, R(2)=0.85, p<0.001). During the vascular occlusion test, LSI perfusion decreased from 307+/-90 AU (baseline) to 42+/-8 AU (ischemia). Peak perfusion during reperfusion was 651+/-93 AU (212% of baseline), which had returned to baseline after 2 min. Hyperthermia increased LSI perfusion from 332+/-90 AU to 1067+/-256 AU (321% of baseline). The main finding was that changes in perfusion as measured by LSI correlated well with changes in capillary red blood cell velocities as measured by SDF imaging during controlled reduction of the (micro)vascular perfusion. It was further shown that LSI is capable of measuring tissue perfusion at high temporal and spatial resolution. In conclusion, LSI can be employed to accurately quantitate microvascular reactivity following ischemic and hyperthermic challenges.

Effect of tadalafil on blood flow, pain, and function in chronic cold complex regional pain syndrome: a randomized controlled trial

Background

This double-blind, randomized, controlled trial investigated the effect of the phosphodiesterase-5 inhibitor tadalafil on the microcirculation in patients with cold Complex Regional Pain Syndrome (CRPS) in one lower extremity.

Methods

Twenty-four patients received 20 mg tadalafil or placebo daily for 12 weeks. The patients also participated in a physical therapy program. The primary outcome measure was temperature difference between the CRPS side and the contralateral side, determined by measuring the skin temperature with videothermography. Secondary outcomes were: pain measured on a Visual Analogue Scale, muscle force measured with a MicroFet 2 dynamometer, and level of activity measured with an Activity Monitor (AM) and walking tests.

Results

At the end of the study period, the temperature asymmetry was not significantly reduced in the tadalafil group compared with the placebo group, but there was a significant and clinically relevant reduction of pain in the tadalafil group. Muscle force improved in both treatment groups and the AM revealed small, non-significant improvements in time spent standing, walking, and the number of short walking periods.

Conclusion

Tadalafil may be a promising new treatment for patients that have chronic cold CRPS due to endothelial dysfunction, and deserves further investigation.

Trial Registration

The registration number in the Dutch Trial Register is ISRCTN60226869.