Comparison of indirect and direct blood pressure monitoring in normotensive swine

Quantitative analysis of systemic perfusion and cerebral blood flow in the modeling of aging and orthostatic hypotension

Introduction: Orthostatic hypotension (OH) is common among the older population. The mechanism hypothesized by OH as a risk factor for cognitive decline and dementia is repeated transient cerebral blood flow deficiency. However, to our knowledge, quantitative evaluation of cardiac output and cerebral blood flow due to acute blood pressure changes resulting from postural changes is rare. Methods: We report a new fluid-structure interaction model to analyze the quantitative relationship of cerebral blood flow during OH episodes. A device was designed to simulate the aging of blood vessels. Results and Discussion: The results showed that OH was associated with decreased transient cerebral blood flow. With the arterial aging, lesions, the reduction in cerebral blood flow is accelerated. These findings suggest that systolic blood pressure regulation is more strongly associated with cerebral blood flow than diastolic blood pressure, and that more severe OH carries a greater risk of dementia. The model containing multiple risk factors could apply to analyze and predict for individual patients. This study could explain the hypothesis that transient cerebral blood flow deficiency in recurrent OH is associated with cognitive decline and dementia.

Anatomical characterization of the intraosseous arteries of the porcine tibia

Introduction

Tibial fractures have a high rate of post-fracture complications. Blood supply is recognized as a positive factor in tibial fracture healing. However, it's difficult to assess blood supply damage after tibial fracture because of the lack of understanding of the tibial intraosseous arteries. This study aimed to delineate and anatomically characterize porcine tibial intraosseous arteries, as a model for the human system.

Methods

Twenty right calf specimens with popliteal vessels were prepared from ordinary Landrace pigs. Epoxy resin was perfused into the vasculature from the popliteal artery. After 24 h, casts of the intraosseous arteries of the tibia were exposed through acid and alkali corrosion. The distribution and anatomy of the exposed intraosseous arteries were observed and measured under a microscope, and the data were statistically analyzed.

Results

Sixteen complete specimens were obtained. The medullary artery bifurcated into the main ascending and descending branches, which each split into two upward primary branches that further divided into 1-3 secondary branches. Among all specimens, 56 ascending and 42 descending secondary branches, which were all ≥0.3 mm in diameter. Furthermore, the horizontal plane was divided into three zones-safety, buffer, and danger zones-according to the probability of the presence of intraosseous artery.

Discussion

The cast perfusion and corrosion approach was successfully applied for anatomical characterization of the intraosseous arteries of the porcine tibia. These observations provide a theoretical basis for understanding the tibial vasculature in humans and will facilitate the establishment of novel "safe corridor" in the tibia for the protection of the blood supply during surgery.

Method for generating transparent porcine tibia showing the intraosseous artery

Background

The occurrence of nonunion after tibial fracture surgery is mainly related to insufficient blood supply. Therefore, anatomical study of the internal and external tibial artery is very important, but there is no good method for displaying the intraosseous artery clearly and intuitively. This hinders the protection and reconstruction of it by surgeons, as well as the development of new instruments and techniques by researchers.

Objective

To develop a transparent specimen that could clearly display the intraosseous artery of the tibia.

Methods

In 10 isolated pig calves with popliteal vessels, the popliteal artery was exposed and a tube was placed. A casting agent was then injected at constant pressure, and the tissue around the blood vessel was preliminarily removed after solidification. The perivascular tissue and periosteum were further removed via alkali corrosion, and the tibia was fixed with an external fixator to protect the non-corrosive areas at both ends. Alternate acid corrosion and flushing were then applied until the intraosseous artery was completely exposed. The distribution and branches of intraosseous nutrient arteries were observed with the naked eye and via microscopy. Three-dimensional (3D) scanning and 3D printing filling techniques were used to make transparent tibia specimens with preservation of intraosseous arteries.

Results

A cast specimen of the intraosseous artery of porcine tibia was successfully generated via epoxy resin perfusion combined with acid–alkali etching, and the intraosseous artery was clearly visible. The 3D printing and filling technique successfully produced a transparent tibia specimen with preservation of internal bone arteries, and accurately restored the external shape of the tibia. The foramen of the nutrient artery appeared near the middle upper third of the lateral edge of the tibia. After entering the tibia, the nutrient artery proceeded forward, medial, and downward for a certain distance, twisted and turned near the midpoint of the medullary cavity, and divided into the ascending and descending branches. After going in the opposite direction for a distance, the ascending trunk sent out 2–3 branches, and the descending trunk sent out 2–3 branches.

Conclusion

The cast specimen of pig intraosseous artery generated via the above-described perfusion corrosion method provides methodological guidance for the study of anatomical characteristics of the intraosseous artery, and a theoretical basis for the study of new methods of internal fixation and reconstruction of the blood supply of the lower tibia.

A fluid-structure interaction model accounting arterial vessels as a key part of the blood-flow engine for the analysis of cardiovascular diseases

According to the classical Windkessel model, the heart is the only power source for blood flow, while the arterial system is assumed to be an elastic chamber that acts as a channel and buffer for blood circulation. In this paper we show that in addition to the power provided by the heart for blood circulation, strain energy stored in deformed arterial vessels in vivo can be transformed into mechanical work to propel blood flow. A quantitative relationship between the strain energy increment and functional (systolic, diastolic, mean and pulse blood pressure) and structural (stiffness, diameter and wall thickness) parameters of the aorta is described. In addition, details of blood flow across the aorta remain unclear due to changes in functional and other physiological parameters. Based on the arterial strain energy and fluid-structure interaction theory, the relationship between physiological parameters and blood supply to organs was studied, and a corresponding mathematical model was developed. The findings provided a new understanding about blood-flow circulation, that is, cardiac output allows blood to enter the aorta at an initial rate, and then strain energy stored in the elastic arteries pushes blood toward distal organs and tissues. Organ blood supply is a key factor in cardio-cerebrovascular diseases (CCVD), which are caused by changes in blood supply in combination with multiple physiological parameters. Also, some physiological parameters are affected by changes in blood supply, and vice versa. The model can explain the pathophysiological mechanisms of chronic diseases such as CCVD and hypertension among others, and the results are in good agreement with epidemiological studies of CCVD.

Relationship between retinal capillary vessel density of OCT angiography and intraocular pressure in pig

The purpose of this study was to evaluate density change in the retinal capillary plexus during intra ocular pressure (IOP) elevation in vitrectomized pigs’ eyes using optical coherence tomography angiography (OCTA). Eight eyes of eight micro pigs received vitrectomy and the IOP was controlled from 15 mmHg (baseline) to 105 mmHg in 15 mmHg increments using a vented-gas forced-infusion system, and then decreased back to normal IOP (recovery state). The spectral-domain OCTA device was set to scan an area of 8.8 × 4.4 mm (30° × 15°) above the optic nerve head for each IOP. The relative vessel density (rVAD) compared to baseline was determined for the total retinal blood flow (RBF) which included major retinal artery and venous vessels, radial peripapillary capillaries (RPCs), superficial (SVP), intermediate (IVP), and deep vascular plexus (DVP). The mean rVAD was 0.890 in RBF, 0.826 in RPCs, 0.817 in SVP, 0.819 in IVP, and 0.794 in DVP at 30 mmHg. While the rVAD of RBF and RPCs decreased to 0.504 and 0.541 at 45 mmHg, the SVP, IVP, and DVP decreased to 0.433, 0.359, and 0.345, respectively. When IOP was normalized, the rVAD was recovered in all layers and the VAD of RBF, IVP, and DVP were higher than baseline (P = 0.040, 0.019, and 0.019, respectively). Retinal capillary density deterioration in each layer was found from 30 mmHg using an OCTA system which showed excellent depth-resolved segmentation of retinal capillary layers even at higher IOPs. Reduction in VAD showed full recovery after IOP normalization.