Intra-abdominal pressures during voluntary and reflex cough

Abstract

Background: Involuntary coughing such as that evoked from the larynx, the laryngeal cough reflex (LCR), triggers a coordinated contraction of the thoracic, abdominal and pelvic muscles, which increases intra-abdominal pressure (IAP), displaces the diaphragm upwards and generates the expiratory force for cough and airway clearance. Changes in the IAP during voluntary cough (VC) and the LCR can be measured via a pressure catheter in the bladder. This study evaluated the physiological characteristics of IAP generated during VC and the LCR including peak and mean pressures and calculations of the area under the curve (AUC) values during the time of the cough event or epoch.

Methods: Eleven female subjects between the ages of 18 and 75 underwent standard urodynamic assessment with placement of an intravesicular catheter with a fiberoptic strain gauge pressure transducer. The bladder was filled with 200 ml of sterile water and IAP recordings were obtained with VC and the induced reflex cough test (RCT) using nebulized inhaled 20% tartaric acid to induce the LCR. IAP values were used to calculate the area under the curve (AUC) by the numerical integration of intravesicular pressure over time (cm H2O.s).

Results: The mean (+/- SEM) AUC values for VC and the LCR were 349.6 +/- 55.2 and 986.6 +/- 116.8 cm H2O.s (p < 0.01). The mean IAP values were 45.6 +/- 4.65 and 44.5 +/- 9.31 cm H2O (NS = .052), and the peak IAP values were 139.5 +/- 14.2 and 164.9 +/- 15.8 cm H2O (p = 0.07) for VC and LCR, respectively.

Conclusion: The induced LCR is the involuntary rapid and repeated synchronous expiratory muscle activation that causes and sustains an elevated IAP over time, sufficient for airway protection. VC and LCR have different neurophysiological functions. Quantification of the LCR using AUC values and mean or peak IAP values may be useful as a clinical tool for determining neurophysiological airway protection status and provide a quantitative assessment of changes in a patient's functional recovery or decline.

Figure 1

A. An urodynamic (UD) tracing (on a compressed timeline) of a subject demonstrating voluntary cough and an episode of RCT coughs (i.e., LCR) triggered by the RCT. A pressure sensor catheter was inserted into the subject's bladder and rectum, and the bladder was filled to 200 ml using sterile saline. Intravesicular bladder pressure was recorded at 30 samples per second. Subject was asked to voluntarily cough and the RCT was performed. Each cough episode was traced and the coordinates corresponding to a particular bladder pressure measurement (P_ves) and the IAP at that time (T_sec) were recorded for each peak, valley and slope change of the pressure tracing. B. A record was made of the complete cough episode timeline. As a part of this process, maximal IAP for each cough event was determined. Interpolation was used to fill in the remaining P_ves between each annotated point. The average P_ves was then calculated for each second of the timeline, and plotted as a pressure versus time graph of the cough episode.

Figure 2

Area under the Curve Graphs for Subjects 1–5.

Figure 3

Area under the Curve Graphs for Subjects 6–10. Subject 10 had SUI and multiple sclerosis.

Figure 4

Area under the Curve Graphs for Subjects 10 and 11. Subject 10 had SUI and multiple sclerosis and subject 11 had a T₄ complete spinal cord injury. This cohort group represents a sample of AUC values obtained from neurologically impaired subjects.