Regulation of Skeletal Muscle Resistance Arteriolar Tone: Temporal Variability in Vascular Responses

Abstract

Introduction: A full understanding of the integration of the mechanisms of vascular tone regulation requires an interrogation of the temporal behavior of arterioles across vasoactive challenges. Building on previous work, the purpose of the present study was to start to interrogate the temporal nature of arteriolar tone regulation with physiological stimuli.

Methods: We determined the response rate of ex vivo proximal and in situ distal resistance arterioles when challenged by one-, two-, and three-parameter combinations of five major physiological stimuli (norepinephrine, intravascular pressure, oxygen, adenosine [metabolism], and intralumenal flow). Predictive machine learning models determined which factors were most influential in controlling the rate of arteriolar responses.

Results: Results indicate that vascular response rate is dependent on the intensity of the stimulus used and can be severely hindered by altered environments, caused by application of secondary or tertiary stimuli. Advanced analytics suggest that adrenergic influences were dominant in predicting proximal arteriolar response rate compared to metabolic influences in distal arterioles.

Conclusion: These data suggest that the vascular response rate to physiologic stimuli can be strongly influenced by the local environment. Translating how these effects impact vascular networks is imperative for understanding how the microcirculation appropriately perfuses tissue across conditions.

Keywords: Integration of arteriolar reactivity; Machine learning; Microcirculation; Peripheral vasculature; Regulation of vascular tone.

Figure 1.

A schematic representation of the imposed challenges used in the (A) ex vivo and (B) in situ vascular preparations for the present study. Please see text for details. Schematic created using BioRender.com.

Figure 2.

A schematic representation of the combination of imposed challenges used in the ex vivo isolated gracilis muscle arteriole preparation for the present study. Please see text for details. Schematic created using BioRender.com.

Figure 3.

A schematic representation of the combination of imposed challenges used in the in situ cremaster muscle resistance arteriole preparation for the present study. Please see text for details. Schematic created using BioRender.com.

Figure 4.

Data (presented as mean ± 95% CI) describing the (A, D) change in diameter, (B-E) time of vascular response, and (C, F) rate of vascular response to increasing concentrations of adenosine in (A-C) ex vivo proximal resistance arterioles from the gracilis muscle and (D-F) in situ distal resistance arterioles within cremaster muscle of rats. n = 8 distinct observations for each data point.

Figure 5.

Data (presented as mean ± 95% CI) describing the (A, D) change in diameter, (B-E) time of vascular response, and (C, F) rate of vascular response to increasing concentrations of norepinephrine in (A-C) ex vivo proximal resistance arterioles from the gracilis muscle and (D-F) in situ distal resistance arterioles within cremaster muscle of rats. n = 8 distinct observations for each data point.

Figure 6.

Data (presented as mean ± 95% CI) describing the (A, D) change in diameter, (B-E) time of vascular response, and (C, F) rate of vascular response to increasing superfusate oxygen content in (A-C) ex vivo proximal resistance arterioles from the gracilis muscle and (D-F) in situ distal resistance arterioles within cremaster muscle of rats. n = 8 distinct observations for each data point.

Figure 7.

Data (presented as mean ± 95% CI) describing the (A, D) change in diameter, (B-E) time of vascular response, and (C, F) rate of vascular response to increasing intravascular pressure in (A-C) ex vivo proximal resistance arterioles from the gracilis muscle and (D-F) in situ distal resistance arterioles within cremaster muscle of rats. n = 8 distinct observations for each data point.

Figure 8.

Data (presented as mean ± 95% CI) describing the (A, D) change in diameter, (B-E) time of vascular response, and (C, F) rate of vascular response to increasing intralumenal flow rates in (A-C) ex vivo proximal resistance arterioles from the gracilis muscle and (D-F) in situ distal resistance arterioles within cremaster muscle of rats. n = 8 distinct observations for each data point.

Figure 9.

A heat map describing the change in slope of the regression line fit to the rate of vascular response with increasing (A) adenosine concentration, (B) norepinephrine concentration, (C) intravascular pressure, (D) superfusate oxygen content, and (E) intralumenal flow rate in ex vivo proximal resistance arterioles from the gracilis muscle of rats. The slope of this line represents the ability of the arteriole to increase its rate of response to a greater amount of stimulus. The first column in each group of responses shows the change in slope with increasing concentrations of a second stimulus. Subsequent columns in each group represent the addition of a third stimulus at varying concentrations and the associated change in slope as you increase the magnitude of stimulus. All slopes are relative to their control conditions when the arteriole was challenged with only one stimulus. Reduced slopes are represented as cooler hues (blue) and increased slopes are signified by warmer tones (red). n = 8 distinct observations for each data point.

Figure 9.

A heat map describing the change in slope of the regression line fit to the rate of vascular response with increasing (A) adenosine concentration, (B) norepinephrine concentration, (C) intravascular pressure, (D) superfusate oxygen content, and (E) intralumenal flow rate in ex vivo proximal resistance arterioles from the gracilis muscle of rats. The slope of this line represents the ability of the arteriole to increase its rate of response to a greater amount of stimulus. The first column in each group of responses shows the change in slope with increasing concentrations of a second stimulus. Subsequent columns in each group represent the addition of a third stimulus at varying concentrations and the associated change in slope as you increase the magnitude of stimulus. All slopes are relative to their control conditions when the arteriole was challenged with only one stimulus. Reduced slopes are represented as cooler hues (blue) and increased slopes are signified by warmer tones (red). n = 8 distinct observations for each data point.

Figure 9.

A heat map describing the change in slope of the regression line fit to the rate of vascular response with increasing (A) adenosine concentration, (B) norepinephrine concentration, (C) intravascular pressure, (D) superfusate oxygen content, and (E) intralumenal flow rate in ex vivo proximal resistance arterioles from the gracilis muscle of rats. The slope of this line represents the ability of the arteriole to increase its rate of response to a greater amount of stimulus. The first column in each group of responses shows the change in slope with increasing concentrations of a second stimulus. Subsequent columns in each group represent the addition of a third stimulus at varying concentrations and the associated change in slope as you increase the magnitude of stimulus. All slopes are relative to their control conditions when the arteriole was challenged with only one stimulus. Reduced slopes are represented as cooler hues (blue) and increased slopes are signified by warmer tones (red). n = 8 distinct observations for each data point.

Figure 10.

A heat map describing the change in slope of the regression line fit to the rate of vascular response with increasing (A) adenosine concentration, (B) norepinephrine concentration, (C) intravascular pressure, and (D) decreasing superfusate oxygen content in in situ distal resistance arterioles from the cremaster muscle of rats. The slope of this line represents the ability of the arteriole to increase its rate of response to a greater amount of stimulus. The first column in each group of responses shows the change in slope with increasing concentrations of a second stimulus. Subsequent columns in each group represent the addition of a third stimulus at varying concentrations and the associated change in slope as you increase the magnitude of stimulus. All slopes are relative to their control conditions when the arteriole was challenged with only one stimulus. Reduced slopes are represented as cooler hues (blue) and increased slopes are signified by warmer tones (red). n = 8 distinct observations for each data point.

Figure 10.

A heat map describing the change in slope of the regression line fit to the rate of vascular response with increasing (A) adenosine concentration, (B) norepinephrine concentration, (C) intravascular pressure, and (D) decreasing superfusate oxygen content in in situ distal resistance arterioles from the cremaster muscle of rats. The slope of this line represents the ability of the arteriole to increase its rate of response to a greater amount of stimulus. The first column in each group of responses shows the change in slope with increasing concentrations of a second stimulus. Subsequent columns in each group represent the addition of a third stimulus at varying concentrations and the associated change in slope as you increase the magnitude of stimulus. All slopes are relative to their control conditions when the arteriole was challenged with only one stimulus. Reduced slopes are represented as cooler hues (blue) and increased slopes are signified by warmer tones (red). n = 8 distinct observations for each data point.

Figure 11.

Data describing the accuracy of the XGBoost regression model in (A) ex vivo proximal resistance arterioles from the gracilis muscle and (B) in situ distal resistance arterioles from the cremaster muscle of rats. The scatter plot describes the relationship between predicted (y-axis) and experimentally measured (x-axis) rate of vascular response. (A) R² = 0.95, RMSE = 0.06 μm/s, (B) R² = 0.94, RMSE = 0.06 μm/s.

Figure 12.

Data describing the feature importance analysis using three methods performed on the XGBoost regression model for the rate of vascular response of ex vivo proximal resistance arterioles from the gracilis muscle of rats. Feature importance as determined by the (A) gain, (B) permutation, and (C) Shapley Additive Explanations (SHAP) values. (D) A bee swarm plot to demonstrate the local feature importance for each observation as determined by SHAP values methods. On the x-axis is the SHAP value which quantifies the impact of the model in terms of determining the rate of the vascular response. The y-axis denotes the independent variables (features) on the left side, and on the right, the scale from blue to red that each point is colored. Blue represents a low feature value, and red demonstrated a high feature value.

Figure 13.

Data describing the feature importance analysis using three methods performed on the XGBoost regression model for the rate of vascular response of in situ distal resistance arterioles from the cremaster muscle of rats. Feature importance as determined by the (A) gain, (B) permutation, and (C) Shapley Additive Explanations (SHAP) values. (D) A bee swarm plot to demonstrate the local feature importance for each observation as determined by SHAP values methods. On the x-axis is the SHAP value which quantifies the impact of the model in terms of determining the rate of the vascular response. The y-axis denotes the independent variables (features) on the left side, and on the right, the scale from blue to red that each point is colored. Blue represents a low feature value, and red demonstrated a high feature value.