The anal reflex elicited by cough and sniff: validation of a neglected clinical sign

Faecal incontinence in adults

Faecal incontinence, which is defined by the unintentional loss of solid or liquid stool, has a worldwide prevalence of ≤7% in community-dwelling adults and can markedly impair quality of life. Nonetheless, many patients might not volunteer the symptom owing to embarrassment. Bowel disturbances, particularly diarrhoea, anal sphincter trauma (obstetrical injury or previous surgery), rectal urgency and burden of chronic illness are the main risk factors for faecal incontinence; others include neurological disorders, inflammatory bowel disease and pelvic floor anatomical disturbances. Faecal incontinence is classified by its type (urge, passive or combined), aetiology (anorectal disturbance, bowel symptoms or both) and severity, which is derived from the frequency, volume, consistency and nature (urge or passive) of stool leakage. Guided by the clinical features, diagnostic tests and therapies are implemented stepwise. When simple measures (for example, bowel modifiers such as fibre supplements, laxatives and anti-diarrhoeal agents) fail, anorectal manometry and other tests (endoanal imaging, defecography, rectal compliance and sensation, and anal neurophysiological tests) are performed as necessary. Non-surgical options (diet and lifestyle modification, behavioural measures, including biofeedback therapy, pharmacotherapy for constipation or diarrhoea, and anal or vaginal barrier devices) are often effective, especially in patients with mild faecal incontinence. Thereafter, perianal bulking agents, sacral neuromodulation and other surgeries may be considered when necessary.

Territorial and Extraterritorial Trigeminocardiac Reflex: A Review for the Neurosurgeon and a Type IV Reflex Vignette

The trigeminocardiac reflex (TCR) is a complex and, sometimes, fatal event triggered by overstimulation of the trigeminal nerve (TN) and its territorial and spinal cord branches. We reviewed and compiled for the neurosurgeon key aspects of the TCR that include a novel and straightforward classification, as well as morphophysiology, pathophysiology, neuromonitoring and neuromodulation features. Further, we present intraoperative data from a patient who developed extraterritorial, or type IV, TCR while undergoing a cervical surgery. TCR complexity, severity and unwanted outcomes indicate that this event should not be underestimated or overlooked in the surgical room. Timely TCR recognition in surgical settings is valuable for applying effective intraoperative management to prevent catastrophic outcomes.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

Pelvic floor muscle activation in stress urinary incontinent women: Impact of a distraction task

AIMS

Our purpose was to explore the involvement of cognition in voluntary and involuntary pelvic floor muscle (PFM) contraction in stress urinary incontinent women.

METHODS

PFM contraction monitored by surface electromyography (EMG) was measured without a mental distraction task (DT), and with a DT called "paced auditory serial additional test" (PASAT). Forty stress incontinent women performed voluntary contractions of the external anal sphincter (EAS), and reflex EAS contractions induced by means of coughing were studied using the external intercostal muscle (EIC) EMG pattern.

RESULTS

A DT altered PFM pre-activation when coughing: the reaction time between EIC muscle contraction and EAS contraction (called RT3) was respectively -54.94 ms (IQR -87.12; 3.12) without the PASAT and -3.99 ms (IQR: -47.92; 18.69) with a DT (P = 0.02, Wilcoxon's test). Concerning voluntary contraction, women activated their PFM sooner without than with a DT.

CONCLUSION

The PASAT altered voluntary and reflex contractions of the PFM in stress urinary incontinent women. Our study suggests that cognition plays a role in urinary pathophysiology. Future studies should investigate rehabilitation programs that consider the role of cognition in stress urinary incontinent women.

Cough-Anal Reflex May Be the Expression of a Pre-Programmed Postural Action

When coughing, an involuntary contraction of the external anal sphincter occurs, in order to prevent unwanted leakages or sagging of the pelvis muscular wall. Literature originally described such cough-anal response as a reflex elicited by cough, therefore identifying a precise cause-effect relationship. However, recent studies report that the anal contraction actually precedes the rise in abdominal pressure during cough expiratory effort, so that the sphincter activity should be pre-programmed. In recent years, an important family of pre-programmed muscle activities has been well documented to precede voluntary movements: these anticipatory actions play a fundamental role in whole body and segmental postural control, hence they are referred to as anticipatory postural adjustments (APAs). On these basis, we searched in literature for similarities between APAs and the cough-anal response, observing that both follow the same predictive homeostatic principle, namely that anticipatory collateral actions are needed to prevent the unwanted mechanical consequences induced by the primary movement. We thus propose that the cough-anal response also belongs to the family of pre-programmed actions, as it may be interpreted as an APA acting on the abdominal-thoracic compartment; in other words, the cough-anal response may actually be an Anticipatory Sphincter Adjustment, the visceral counterpart of APAs.

Activation of the striated urethral sphincter to maintain continence during dynamic tasks in healthy men

AIMS

Function of the striated urethral sphincter (SUS) in men is debated. Current evidence is limited to electromyographic (EMG) recordings made with concentric needle electrodes in supine. Understanding of SUS function requires investigation of SUS EMG activity using new recording techniques in dynamic tasks. The aim of this study was to evaluate timing and amplitude of SUS EMG at rest and during dynamic tasks that challenge continence by increasing intra-abdominal pressure (IAP).

METHODS

Investigative study of five healthy men aged 25-39 years. Measurements included SUS, anal sphincter (AS), and transversus abdominus (TrA) EMG, and IAP (recorded with a nasogastric pressure catheter). Participants performed four tasks that challenged postural control in standing (single and repetitive arm movement, stepping and load catching).

RESULTS

IAP amplitude and SUS activity were linearly correlated during repetitive arm movement (R(2): 0.67-0.88). During stepping SUS EMG onset preceded the IAP increase, but followed it with rapid arm movements. When the trunk was loaded unpredictably onset of SUS generally followed the increase in IAP. The modest sample size meant only younger men were tested. Future studies might investigate healthy older men or those with certain pathologies.

CONCLUSIONS

Data show that SUS activity increases proportionally with IAP. This provided evidence that SUS contributes to continence when IAP is increased, and that postural control of the trunk involves activation of this muscle.

The evolutionary origin of the mammalian diaphragm

The comparatively low compliance of the mammalian lung results in an evolutionary dilemma: the origin and evolution of this bronchoalveolar lung into a high-performance gas-exchange organ results in a high work of breathing that cannot be achieved without the coupled evolution of a muscular diaphragm. However, despite over 400 years of research into respiratory biology, the origin of this exclusively mammalian structure remains elusive. Here we examine the basic structure of the body wall muscles in vertebrates and discuss the mechanics of costal breathing and functional significance of accessory breathing muscles in non-mammalian amniotes. We then critically examine the mammalian diaphragm and compare hypotheses on its ontogenetic and phylogenetic origin. A closer look at the structure and function across various mammalian groups reveals the evolutionary significance of collateral functions of the diaphragm as a visceral organizer and its role in producing high intra-abdominal pressure.

Manometric, sensorimotor, and neurophysiologic evaluation of anorectal function

With advances in diagnostic technology, it is now accepted that in the field of functional bowel disorders, symptom-based assessment is unsatisfactory as the sole means of directing therapy. A robust taxonomy based on underlying pathophysiology has been suggested, highlighting a crucial role for physiologic testing in clinical practice. A wide number of complementary investigations currently exist for the assessment of anorectal structure and function, some of which have a clinical impact in patients with functional disorders of evacuation and continence by markedly improving diagnostic yield and altering management. The techniques, limitations, measurements, and clinical use of manometric, sensorimotor, and neurophysiologic tests of anorectal function are presented.

Postural and respiratory functions of the pelvic floor muscles

AIMS

Due to their contribution to modulation of intra-abdominal pressure (IAP) and stiffness of the sacroiliac joints, the pelvic floor muscles (PFM) have been argued to provide a contribution to control of the lumbar spine and pelvis. Furthermore, as IAP is modulated during respiration this is likely to be accompanied by changes in PFM activity.

METHODS

In order to evaluate the postural and respiratory function of the PFM, recordings of anal and vaginal electromyographic activity (EMG) were made with surface electrodes during single and repetitive arm movements that challenge the stability of the spine. EMG recordings were also made during respiratory tasks: quiet breathing and breathing with increased dead-space to induce hypercapnoea.

RESULTS

EMG activity of the PFM was increased in advance of deltoid muscle activity as a component of the pre-programmed anticipatory postural activity. This activity was independent of the direction of arm movement. During repetitive movements, PFM EMG was tonic with phasic bursts at the frequency of arm movement. This activity was related to the peak acceleration of the arm, and therefore the amplitude of the reactive forces imposed on the spine. Respiratory activity was observed for the anal and vaginal EMG and was primarily expiratory. When subjects moved the arm repetitively while breathing, PFM EMG was primarily modulated in association with arm movement with little respiratory modulation.

CONCLUSIONS

This study provides evidence that the PFM contribute to both postural and respiratory functions.

Differences in motor activation of voluntary and reflex cough in humans

OBJECTIVES

To study motor activation patterns of voluntary and reflex cough adjusted for cough flow rates.

METHODS

Surface electromyography (EMG) and cough flow rate were measured in 10 healthy volunteers. Voluntary cough was assessed for 20 efforts in each quintile of increasing cough flow rate. Reflex cough was assessed for 25 efforts produced by nebulised l-tartaric acid. EMG was recorded over the expiratory (rectus abdominis, obliques, lower intercostals) and accessory (trapezius, pectoralis major, deltoid, latissimus dorsi) muscles. EMG activity, burst duration and onset were compared for each quintile of voluntary cough, and between voluntary and reflex cough matched for cough flow rate.

RESULTS

EMG activity and burst duration of expiratory and accessory muscles during voluntary cough increased in proportion to cough flow. Expiratory muscles had longer EMG burst duration (difference 68 ms (95% CI 34 to 102), p<0.01) and earlier onset of EMG activity (difference 44 ms (95% CI 20 to 68), p<0.0001) compared with accessory muscles. EMG activity in all muscles was increased (mean 110.2% v 56.1%, p<0.001) and burst duration (mean 206 ms v 280 ms, p = 0.013) decreased in reflex cough compared with voluntary cough of equal flow rate. There were no differences in EMG onset (difference 8 ms (95% CI 25 to -9) or burst duration (difference 27 ms (95% CI 58 to -4) between expiratory and accessory muscles.

CONCLUSIONS

Functional organisation of motor activity differs between voluntary and reflex cough. Voluntary cough is characterised by sequential activation whereas reflex cough is associated with early and simultaneous activation of expiratory and accessory muscles.

External anal sphincter contraction during cough: Not a simple spinal reflex

AIMS

To assess whether the anal contraction during voluntary coughing is a simple spinal reflex-mediated activity or not. To address this question we studied the external intercostal (EIC) muscle activity and external anal sphincter (EAS) response to cough.

MATERIALS AND METHODS

Electromyographic recordings were made from pre-gelled disposable surface electrodes. EAS electromyographic recordings were made from the EAS of the pelvic floor in 15 continent women all suffering from urgency and/or frequency without urge or stress urinary incontinence, and referred for urodynamic investigation. Electromyographic signal was immediately integrated (EMGi). The abdominal pressure was recorded with bladder and rectal pressure. EAS EMGi was recorded during successive voluntary cough. In three women, we have also recorded EIC EMGi activity since it is synchronous with diaphragmatic EMG activity during cough initiation.

RESULTS

In all subjects, EAS EMGi activity precedes the onset of the abdominal pressure increase. The mean latency of EAS EMGi was 615 msec (+/-278). In the three subjects whose EMGi activity was recorded both on EAS and EIC, the onset of EAS EMGi activity occurred before the EIC EMGi activity (latency ranging from 40 to 780 msec) and before the increase in the abdominal pressure.

CONCLUSIONS

The present study suggests that during coughing, EAS EMG activity increases before external intercostal muscle EMGi activity. The contraction of the EAS preceding the activation of muscles involved in coughing indicates that this response is not a result of a simple spinal reflex, but more likely the result of a more intricate reflex involving complex integrative centers.