The goal of this study was to establish whether changes in microvascular perfusion play an important role in the development of hypertension. To achieve this goal, we measured the photoplethysmographic waveforms recorded from the fingertips of patients with untreated hypertension. The photoplethysmographic waveforms were obtained from 60 healthy, normotensive male controls (NTs) and 30 untreated hypertensive male patients (HTs). The NTs were divided into two groups: a younger NT group (age 20 to 40 years, 30 individuals) and an older NT group (age 40 to 60 years, 30 individuals). The PPG waveform displayed a steep rise and a notch on the falling slope in the younger NT group. And for younger subjects, there were two positive waves (P1 and P2) and one negative wave (V).In the older NT group, a more gradual rise and fall was observed. For the HT group, no pronounced dicrotic notch was observed. A program was used to calculate the P2/P1 and P2/V ratios. The P2/P1 and P2/V ratios can indicate the perfusion to the fingertips during cardiac diastole. There were no significant differences in P2/P1 between the older NT group and HTs (0.37±0.07 versus 0.33±0.05, p>0.05).The P2/V ratios were significantly different between the older NT group and HTs (0.93±0.11 versus 0.59±0.08, p<0.05). These results indicate that there is a decrease in perfusion to the fingertips in hypertensive subjects during cardiac diastole.

To understand the hemodynamics of the microcirculation, we compared the resistance of vessels that either had an enlarged cross-sectional area in the midsection (denoted vessel 1) or had a uniform diameter (denoted vessel 2). The length of the two vessels and the pressure difference between the ends were equal. The two vessels were filled with water, and the volume of water flowing through the two vessels per second was measured. The volume of water flowing through vessel 1 was 4.05 ml/sec, and the volume of water flowing through vessel 2 was 4.37 ml/sec. Vessel 1 had a higher resistance, and water drained more slowly than from vessel 2. These results demonstrate that vessels with a greater crosssectional area in the midsection have a lower flow than vessels with a constant cross-section, even though resistance in the midsection is lower when the cross-sectional area is greater.

Background: Microvascular perfusion, a kind of regional perfusion, plays important roles in delivering oxygen and nutrients, and regulating blood pressure and responses to inflammation. Aim: The aim of this research is to analyze the characteristics of microvascular perfusion by conducting pipe flow in a circular elastic tube. Methods: A model was established with circular elastic tube to mimic microvascular perfusion. The velocity of pressure waves was calculated according to the time that the liquid took to spilt over. What's more, the characteristics and significance of microvascular flow and arteriovenous anastomoses (AVAs) were analyzed. Results: It took the liquid about 0.1 second to spill over from the model, and the velocity of pressure waves is greater than 100 m/s in the elastic pipe. A mechanical switch structure and the corresponding mechanism were proposed for microvascular perfusion in AVAs. Conclusion: Microvascular perfusion maintains a considerable constancy of hemodynamics in different tissues, when ventricular contraction changes perfusion pressure to meet metabolic demands appropriately. This theory will help us to gain a new perspective in microvascular flow.

Background: Multiple studies have been published using a pulse oximeter's photoplethysmographic (PPG) capability to detect tissue perfusion. However, the origin of the PPG signal is still debatable.Aim: A comparative study was performed of PPG waveforms in hypertensive patients before and after treatment with antihypertensive medication. The aim of this study was to observe the changes of PPG waveforms before and after lowering blood pressure in hypertensive patients and then to detect the relationship between blood pressure and PPG waveforms. Methods:The PPG waveforms of 60 patients with hypertension were collected. After administration of the antihypertensive medication nitroglycerin, PPG waveforms were collected again. The changes of the T3 (time3): This phase occurred between Marker 3 and Marker 4 (this phase occurs mid-diastolic) angle, before and after the antihypertensive medication treatment, were compared. The statistical analyses of two related groups were performed using the Paired t-test. Results:The blood perfusion waveforms of hypertensive patients before and after antihypertensive medication administration were differently indicated with the tilt angle T3. The slope angle of the T3 phase waveform increased significantly when the blood pressure dropped to normal (−41.9 ± 16.2° vs. −25.6 ± 21.9°, p < .0001), and the tilt angle of some patients was similar to that of adults with normal blood pressure. Conclusion:In patients with hypertension, the tilt angle of the PPG waveform in the T3 phase increased significantly after administration of the antihypertensive medication nitroglycerin. It is worth to conduct deeper research about the relationship between hypertension and the blood perfusion of microcirculation in the diastolic period.