Intrinsic factors contributing to elevated intra-abdominal pressure

Abstract

Pelvic floor disorders affect 24% of US women, and elevated intra-abdominal pressure may cause pelvic injury through musculoskeletal strain. Activity restrictions meant to reduce pelvic strain after traumatic events, such as childbirth, have shown little benefit to patients. Reported high variability in abdominal pressure suggests that technique plays a substantial role in pressure generation. Understanding these techniques could inform evidence-based recommendations for protective pelvic care. We hypothesized use of a motion-capture methodology could identify four major contributors to elevated pressure: gravity, acceleration, abdominal muscle contraction, and respiration. Twelve women completed nineteen activities while instrumented for whole body motion capture, abdominal pressure, hip acceleration, and respiration volume. Correlation and partial least squares regression were utilized to determine primary technique factors that increase abdominal pressure. The partial least squares model identified two principal components that explained 59.63% of relative intra-abdominal pressure variability. The first component was primarily loaded by hip acceleration and relative respiration volume, and the second component was primarily loaded by flexion moments of the abdomen and thorax. While reducing abdominal muscle use has been a primary strategy in protective pelvic floor care, the influence of hip acceleration and breathing patterns should be considered with similar importance in future work.

Keywords: Intra-abdominal Pressure; Motion Capture; Pelvic Floor Disorders.

Figure 1.

Four-element model for IAP generation. Green arrows indicate the primary action that leads to increased IAP. Blue cylinders are the abdominal compartment. Blue arrows are the resulting intra-abdominal pressure forces. Red lines are the pelvic, abdominal, and diaphragm muscles that enclose the abdominal cavity.

Figure 2.

Representative Synchronized Data from 30 cm Box Drop. (Above) Images showing the model of the participant at five discrete time points during a single box drop. (Below) Synchronized physiologic and biomechanical joint data with vertical dashed lines indicating discrete time points associated with the images above. (A) Participant is standing stationary on the 30 cm tall box. (B) Participant removes one foot from the box and holds it approximately 30 cm in front of the box, increasing knee and abdomen flexion moments, but no notable increase in IAP. (C) Participant has removed second foot from box and is in free-fall, there is a reduction in hip acceleration and IAP while falling. (D) Participant makes contact with the ground, creating a sharp increase in both hip acceleration and IAP, but no notable increases in abdomen or knee moments. (E) Participant remains standing after completing box drop and all physiologic and biomechanical joint data return to baseline values.

Figure 3.

Relative IAP across all participants and all tasks. Each box denotes the inter-quartile range (Q1 to Q3), the black whiskers extending each box denotes the 1.5*IQ range, and individual points beyond the end of the whiskers denote outliers.

Figure 4.

Partial Least Squares Regression Results. (A) Mean relative IAP heat map plotted against the first two PLSR principal component scores. Principal component scores are calculated as a linear combination of predictor variables weighted by component loadings. (B) Principal component loading bar graph showing the physiologic and biomechanical joint data predictor variable loadings for the first two principal components. The first principal component (blue) is most heavily loaded by the relative respiration and hip acceleration variables. The second principal component (red) is most heavily loaded by the abdomen and thorax flexion moment variables. Elevated IAP generally occurs when the first and second principal components are positive, indicating that elevated respiration volume, hip acceleration, abdomen and thorax flexion moments are likely primary contributors to elevated IAP. (C) Residuals of the PLSR model. The linear trend between the model residuals and actual relative IAP values may be indicative of an additional influencer on IAP generation not accounted for in our model, or may be due to our use of abdomen and thorax moments as a proxy for abdominal muscle contraction.