Poster discussion: summary

Intra-abdominal pressures during voluntary and reflex cough

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.

What is cough and what should be measured?

Cough is usually defined as a three-phase event, although for convenience clinicians may prefer to define it as only the expiratory expulsive efforts. Cough may occur as a single event or as a cough 'epoch' (or 'bout' or 'attack') that includes several or many expiratory efforts in a single episode. The distinction between a single cough and a cough epoch is important, both in mechanistic and clinical implications, since the latter may include many 'expiration reflexes' (ERs), for which the functions and neural mechanisms are different from those of the cough reflex. We describe the various ways in which cough can be assessed. For simplicity in clinical work the main methods are patient scores or automated cough counters; these assess only one aspect of the complex changes in cough. For analytical and basic medical studies other facets of cough need to be included: expiratory EMGs, respiratory pressures, airflows and lung volume changes. Cough 'intensity', a much used expression, needs to be defined in terms of the facets of cough which are being measured.