Microvascular control of capillary pressure during increases in local arterial and venous pressure

Davis, Michael J.

doi:10.1152/ajpheart.1988.254.4.h772

Cited by 38 publications

(54 citation statements)

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“…The dark cycle (4:00 PM through 10:00 AM) coincided with feeding times for the animals. Bats were then trained to remain sleeping, unanesthetized, inside a plastic box with one wing extended outside of the box (10,38). Since male bats were resistant to training, only female bats were studied.…”

Section: Methodsmentioning

confidence: 99%

“…With a few notable exceptions, experimental procedures were similar to those employed by Davis et al (9,10,12 The bat laboratory room was kept at a constant 24°C at all times. For all experiments, the bats were placed under the intravital microscope, and the thermoregulator of the heat plate was set at 25.0°C.…”

Section: Methodsmentioning

confidence: 99%

“…Of these factors, sensory neural stimulation, shear stress, and metabolic factors could cause vessels to dilate with local heat (7,8,18). A myogenic response would cause a constriction with increased pressure accompanying heating (7,10), and the direct effect of heat on vascular smooth muscle has been noted to cause a constriction in some vascular beds (23). A conducted stimulus would cause a constriction or dilation based on the predominant reaction of the vessel adjacent to the studied vessel (14).…”

Section: The Second Phase Of the Biphasic Flow Response Is Shear-medimentioning

confidence: 99%

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Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Widmer

Laurinec²,

Young³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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-Investigators report that local heat causes an increase in skin blood flow consisting of two phases. The first is solely sensory neural, and the second is nitric oxide mediated. We hypothesize that mechanisms behind these two phases are causally linked by shear stress. Because microvascular blood flow, endothelial shear stress, and vessel diameters cannot be measured in humans, bat wing arterioles (26.6 Ϯ 0.3, 42.0 Ϯ 0.4, and 58.7 Ϯ 2.2 m) were visualized noninvasively on a transparent heat plate via intravital microscopy. Increasing plate temperature from 25 to 37°C increased flow in all three arterial sizes (137.1 Ϯ 0.3, 251.9 Ϯ 0.5, and 184.3 Ϯ 0.6%) in a biphasic manner. With heat, diameter increased in large arterioles (n ϭ 6) by 8.7 Ϯ 0.03% within 6 min, medium arterioles (n ϭ 8) by 19.7 Ϯ 0.5% within 4 min, and small arterioles (n ϭ 8) by 31.6 Ϯ 2.2% in the first minute. Lidocaine (0.2 ml, 2% wt/vol) and N G -nitro-L-arginine methyl ester (0.2 ml, 1% wt/vol) were applied topically to arterioles (ϳ40 m) to block sensory nerves, modulate shear stress, and block nitric oxide generation. Local heat caused only a 10.4 Ϯ 5.5% increase in diameter with neural blockade (n ϭ 8) and only a 7.5 Ϯ 4.1% increase in diameter when flow was reduced (n ϭ 8), both significantly lower than control (P Ͻ 0.001). Diameter and flow increases were significantly reduced with N G -nitro-L-arginine methyl ester application (P Ͻ 0.05). Our novel thermoregulatory animal model illustrates 1) regulation of shear stress, 2) a nonneural component of the first phase, and 3) a shear-mediated second phase. The time course of dilation suggests that early dilation of small arterioles increases flow and enhances second-phase dilation of the large arterioles. nitric oxide; in vivo; shear stress HUMAN SKIN RESPONDS TO LOCAL temperature increases with a biphasic increase in skin blood flow (SkBF). Within the first few minutes after the local application of heat, SkBF reaches a peak and then begins to decline. Three to five minutes after heating, SkBF reaches a nadir and then increases once again (8,16,26). The second slower and more sustained response typically rises above the initial peak value. Typically, SkBF is measured noninvasively in human subjects using laser Doppler flowmetry (LDF), which ensures that the complex interaction of thermoregulatory mechanisms controlling vascular responses remains intact. The resulting behavior is ubiquitous and consistent (8,39). Investigators universally separate the response to local heat into two distinct phases (16,26).Investigators believe that these two phases are controlled by two mechanisms (26). When a local anesthetic is used to block sensory input, the first phase of the biphasic flow response is abolished, suggesting sensory neural-mediated microvascular dilation. The second phase is diminished with the addition of nitric oxide (NO) synthase (NOS) inhibitors (8,16,26), suggesting NO-dependent microvascular dilation. A direct link between the mechanisms of the neural-and NO-mediated increases in...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: The Second Phase Of the Biphasic Flow Response Is Shear-medimentioning

confidence: 99%

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Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Widmer

Laurinec²,

Young³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Pressure measurements were accepted only if the following criteria were satisfied: 1) the micropipette could be manipulated inside the vessel lumen without affecting the pressure tracing; 2) the pressure tracing was insensitive to small changes in the gain of the servo-null system; and 3) the pressure tracing returned to zero when the pipette was removed from the vessel but remained immersed into the superfusate (6).…”

Section: Methodsmentioning

confidence: 99%

Effects of extreme hemodilution with hemoglobin-based O₂ carriers on microvascular pressure

Cabrales¹,

Tsai²,

Winslow³

et al. 2005

American Journal of Physiology-Heart and Circulatory Physiology

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-A surface-modified polyethylene glycol-conjugated human hemoglobin (MP4) and ␣␣-cross-linked human hemoglobin (␣␣Hb) were used to restore oxygen carrying capacity in conditions of extreme hemodilution (hematocrit 11%) in the hamster window model preparation. Changes in microvascular function were analyzed in terms of effects on capillary pressure and functional capillary density (FCD). MP4, at 1.0 Ϯ 0.2 g/dl blood concentration, significantly lowered mean arterial pressure (MAP) below baseline (99.6 Ϯ 7.6 mmHg) to 82.4 Ϯ 6.9 mmHg (P Ͻ 0.05) and decreased of FCD to 70 Ϯ 9%. ␣␣Hb caused a greater recovery in MAP to 94.4 Ϯ 6.2 mmHg and lowered FCD to 62 Ϯ 8%. However, differences between ␣␣Hb and MP4 in FCD were not statistically significant. Capillary pressures were in the ranges of 17-21 mmHg for MP4 and 15-19 mmHg for ␣␣Hb, with both significantly lower than baseline (P Ͻ 0.05). Pressure in 80-mdiameter arterioles was significantly increased with ␣␣Hb relative to MP4 (P Ͻ 0.05). These results were compared with previous findings on the relation between capillary pressure and FCD; they supported the concept of a relationship between FCD and capillary pressure. Measurement of changes in arteriolar diameter, microvascular blood flow, and FCD show that there was no statistical difference between using ␣␣Hb and MP4 in extreme hemodilution. Microvascular resistance in arterioles with a diameter range of 70 -80 m showed an increase relative to control with ␣␣Hb, whereas MP4 caused a decrease. shear stress; perfusion; plasma expander; blood pressure; blood substitutes

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“…Davis (1988) found dilatation of the capillaries in the bat wing during increases in the pressure of a box that was placed around the body but excluded the wing of the animal. Baldwin and Gore (1989) showed that all mesenteric microvessels studied were distensible at intravascular pressures ranging from 5 to 80 mm Hg, with decreasing capillary dis tensibility at increasing pressure.…”

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confidence: 99%

Changes in Brain Capillary Diameter during Hypocapnia and Hypercapnia

Duelli

Kuschinsky

1993

J Cereb Blood Flow Metab

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Summary: Since changes in the surface area of capillaries may be relevant to capillary exchange, the distensibility of brain capillaries was investigated. Brain capillary dia meters were measured after perfusion fixation of brain tissue at a constant perfusion pressure during hypo-or hypercapnia. Sections were embedded, stained, and an alyzed by light microscopy. The results showed signifi cant differences in mean capillary diameter between the hypocapnic and the hypercapnic group. In the eight brain structures analyzed, capillary diameters were alwaysThe present concept of capillary perfusion in the brain postulates a heterogeneity of blood flow in different capillaries (Kuschinsky and Paulson, 1992). In such a system of heterogeneous perfusion, variations of blood flow in single capillaries would result from changes in the intravascular pressure of precapillary vessels. Such changes in intravascular pressure might induce, in addition to changes in mi croflow, an altered degree of distension of capillar ies, which would affect the capillary surface area.The distensibility of capillaries has been a matter of discussion for many years. Most studies investi gating this question have been performed on mes enteric capillaries. Baez et al. (1960) observed cap illary blood vessels of the rat mesentery under the microscope during variations in the driving hydrau lic pressure between 20 and 200 mm Hg. Their con clusion that the capillaries act as rigid tubes is ques tionable since the resolution of their technique did not enable them to detect diameter changes in the expected range. Fung et al. (1966) 1025larger in the hypercapnic group. Mean capillary diameter was 4.93 ± 0.29 f.Lm in the hypocapnic group and 5.91 ± 0.10 f.Lm in the hypercapnic group (means ± SD). We conclude that brain capillaries exhibit a moderate degree of distensibility. Variations in the precapillary pressure of microvessels may therefore influence both capillary flow and capillary surface area.

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Microvascular control of capillary pressure during increases in local arterial and venous pressure

Cited by 38 publications

References 0 publications

Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Effects of extreme hemodilution with hemoglobin-based O₂ carriers on microvascular pressure

Changes in Brain Capillary Diameter during Hypocapnia and Hypercapnia

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Microvascular control of capillary pressure during increases in local arterial and venous pressure

Cited by 38 publications

References 0 publications

Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Local heat produces a shear-mediated biphasic response in the thermoregulatory microcirculation of the Pallid bat wing

Effects of extreme hemodilution with hemoglobin-based O2 carriers on microvascular pressure

Changes in Brain Capillary Diameter during Hypocapnia and Hypercapnia

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Effects of extreme hemodilution with hemoglobin-based O₂ carriers on microvascular pressure