Negative pressure increases microvascular perfusion during severe hemorrhagic shock

Abstract

Hemorrhagic shock (HS) is a severe life-threatening condition characterized by loss of blood volume and a lack of oxygen (O₂) delivery to tissues. The objective of this study was to examine the impact of manipulating Starling forces in the microcirculation during HS to increase microvascular perfusion without restoring blood volume or increasing O₂ carrying capacity. To decrease interstitial tissue pressure, we developed a non-contact system to locally apply negative pressure and manipulate the pressure balance in capillaries, while allowing for visualization of the microcirculation. Golden Syrian hamsters were instrumented with dorsal window chambers and subjected to a controlled hemorrhaged of 50% of the animal's blood volume without any fluid resuscitation. A negative pressure chamber was attached to the dorsal window chamber and a constant negative pressure was applied. Hemodynamic parameters (including microvascular diameter, blood flow, and functional capillary density [FCD]) were measured before and during the four hours following the hemorrhage, with and without applied negative pressure. Blood flow significantly increased in arterioles during negative pressure. The increase in flow through arterioles also improved microvascular perfusion as reflected by increased FCD. These results indicate that negative pressure increases flow in the microcirculation when fluid resuscitation is not available, thus restoring blood flow, oxygen delivery, and preventing the accumulation of metabolic waste. Applying negative pressure might allow for control of microvascular blood flow and oxygen delivery to specific tissue areas.

Keywords: Intravital microscopy; Reabsorption; Starling forces; Tissue perfusion.

Figure 1.

Schematics of a) Isometric view of the negative pressure chamber with dimensions in millimeters and b) Sectional view of the negative pressure chamber attached to the dorsal skin flap window chamber for intravital microscopy. Note that the rest of the hamster is restrained in an acrylic tube on the left (not depicted). 1) slit for the bolt to secure the negative pressure chamber to the window chamber; 2) female connector for the pneumatic line; 3) rim of the negative pressure chamber where silicone grease was applied; 4) bolt from the window chamber preparation; 5) titanium plates for the window chamber; 6) glass cover to allow for intravital microscopy; 7) dorsal skin flap of the hamster.

Figure 2.

Overview of the experimental procedure. Note that the different colors correspond to the applied negative pressure. BL = baseline, BV = blood volume.

Figure 3.

Normalized microcirculation flow of arterioles and venules during shock and the first cycle of negative pressure: a) arteriole diameter, b) arteriole velocity, c) arteriole flowrate, d) venule diameter, e) venule diameter, f) venule flowrate. Baseline values are: a) CTRL (75 μm) and NP (86 μm), b) CTRL (5.4 mm/s) and NP (4.4 mm/s), c) CTRL (25 nL/s) and NP (28 nL/s), d) CTRL (90 μm) and NP (85 μm), e) CTRL (1.3 mm/s) and NP (1.3 mm/s), f) CTRL (9 nL/s) and NP (10 nL/s). The pressure applied to the skin fold for each measurement is shown in the bottom row of the figure. *P<0.05 between groups, at the same timepoint.

Figure 4.

Normalized functional capillary density during shock and the first negative pressure cycle. Baseline values are: CTRL (299) and NP (236). The pressure applied to the skin fold for each measurement is shown in the bottom row of each graph. *P<0.05 between groups, at the same timepoint.

Figure 5.

Systemic cardiovascular parameters: a) MAP, b) HR. The pressure applied to the skin fold for each measurement is shown in the bottom row of each graph. †P < 0.05 vs BL.

Figure 6.

Effects of applying a second cycle of negative pressure for a) arteriole velocity, b) arteriole flow rate, c) FCD. Baseline values are: a) CTRL (5.4 mm/s) and NP (4.4 mm/s), b) CTRL (25 nL/s) and NP (28 nL/s), c) CTRL (299) and NP (236). The pressure applied to the skin fold for each measurement is shown in the bottom row of each graph. *P<0.05 between groups, at the same timepoint.