Paul W. Davenport

Cortical and subcortical central neural pathways in respiratory sensations.

Respiratory sensations motivate humans to behaviorally modulate their breathing and are the sensory urge component of the respiratory motivation-to-action neural system. Human and animal studies have provided evidence for the neural substrate for afferents in the respiratory tract and muscles to project to the cerebral cortex. Respiratory afferents continually transduce breathing pattern into a sensory neural code. This neural code is transmitted to a subcortical gating area. Respiratory sensory information is then transmitted by respiratory modality specific convergent and divergent subcortical pathways to the cerebral cortex. There are two primary cortical pathways: (1) the discriminative pathway related to respiratory proprioception and (2) the affective pathway related to the qualitative assessment of breathing. Respiratory sensory information is processed by the discriminatory somatosensory-motor cortex and the affective mesocortex resulting in conscious awareness of breathing that can lead to distressing respiratory sensations. The significance of respiratory sensory information processing is the fundamental interoceptive perception of ventilatory status.

Assessment of aspiration risk in stroke patients with quantification of voluntary cough

Background: Dysphagia and subsequent aspiration are serious complications of acute stroke that may be related to an impaired cough reflex. It was hypothesized that aspirating stroke patients would have impaired objective measures of voluntary cough as compared with both nonstroke control subjects and nonaspirating stroke patients. Methods: Swallowing was evaluated by standard radiologic or endoscopic methods, and stroke patients were grouped by aspiration severity (severe, n = 11; mild, n = 17; no aspiration, n = 15). Airflow patterns and sound pressure level (SPL) of voluntary cough were measured in stroke patients and in a group of normal control subjects (n = 18). Initial stroke severity was determined retrospectively with the Canadian Neurological Scale. Results: All cough measures were altered in stroke patients as a group relative to nonstroke control subjects. Univariate analysis showed that peak flow of the inspiration phase (770.6 ± 80.6 versus 1,120.1 ± 148.4 mL/s), SPL (90.0 ± 3.1 versus 100.2 ± 1.6 dB), peak flow of the expulsive phase (875.1 ± 122.7 versus 1,884.1 ± 221.6 mL/s), expulsive phase rise time (0.34 ± 0.1 versus 0.09 ± 0.01 s), and cough volume acceleration (5.5 ± 1.3 versus 27.8 ± 3.9 mL/s/s) were significantly impaired in severe aspirators as compared with nonaspirators. Aspirating patients had more severe strokes than nonaspirators (mean Canadian Neurological Scale score 7.7 ± 0.7 versus 9.8 ± 0.3). Multivariate logistic regression found only expulsive phase rise time values during cough correlated with aspiration status. Conclusion: Objective analysis of cough may provide a noninvasive way to identify the aspiration risk of stroke patients.

Neurogenesis of cough, other airway defensive behaviors and breathing: A holarchical system?

Cough and breathing are generated by a common muscular system. However, these two behaviors differ significantly in their mechanical features and regulation. The current conceptualization of the neurogenic mechanism for these behaviors holds that the multifunctional respiratory pattern generator undergoes reconfiguration to produce cough. Our previous results indicate the presence of a functional cough gate mechanism that controls the excitability of this airway defensive behavior, but is not involved in the regulation of breathing. We propose that the neurogenesis of cough, breathing, and other nonbreathing behaviors is controlled by a larger network, of which the respiratory pattern generator is part. This network we term a holarchical system. This system is governed by functional control elements known as holons, which confer unique regulatory features to each behavior. The cough gate is an example of such a holon. Neurons that participate in a cough holon may include behavior selective elements. That is, neurons that are either specifically recruited during cough and/or tonically-active neurons with little or no modulation during breathing but with significant alterations in discharge during coughing. We also propose that the holarchical system is responsible for the orderly expression of different airway defensive behaviors such that each motor task is executed in a temporally and mechanically discrete manner. We further propose that a holon controlling one airway defensive behavior can regulate the excitability of, and cooperate with, holons unique to other behaviors. As such, co-expression of multiple rhythmic behaviors such as cough and swallow can occur without compromising airway defense.

Effect of expiratory muscle strength training on elderly cough function

Age-related loss of muscle strength, known as sarcopenia, in the expiratory muscles, along with reductions in lung elastic recoil and chest wall compliance decreases the intrathoacic airway pressure as well as expiratory flow rates and velocity, greatly impacting an elderly persons ability to generate the forces essential for cough. This study examined the effects of a 4-week expiratory muscle strength training (EMST) program on maximum expiratory pressure (MEP) and cough function in 18 healthy but sedentary elderly adults. MEP significantly increased after the EMST program from 77.14+/-20.20 to 110.83+/-26.11cmH(2)O. Parameters measured during reflexive coughs produced by capsaicin challenge, indicated that compression phase duration significantly decreased (from 0.35+/-0.19 to 0.16+/-0.17s), peak expiratory flow rate decreased (from 4.98+/-2.18 to 8.00+/-3.05l/s) and post-peak plateau integral amplitude significantly increased (from 3.49+/-2.46 to 6.83+/-4.16l/ss) with the EMST program. EMST seems to be an effective program to increase the expiratory muscle strength in the sedentary elderly, which contribute to an enhanced cough function.

Projection of phrenic nerve afferents to the cat sensorimotor cortex

The projection of phrenic nerve afferents to the sensorimotor cortex was studied in cats. The results of these experiments demonstrate that stimulation of phrenic nerve afferents elicits cortical evoked potentials (CEPs) in the sensorimotor cortex of cats. Cortical foci for CEPs classified as primary were found in areas 3b, 3a and 4 gamma. These foci were located medial to forelimb and lateral to hindlimb afferent representations in the sensorimotor cortex.

Urge-to-Cough: What Can It Teach Us About Cough?

The Urge-to-Cough is a component of the brain motivation system that mediates cognitive responses to cough stimuli. There are six stages to the cough motivation-to-action system: (1) stimulus, the trigger for the neural event; (2) urge, the physical need to respond to the stimulus; (3) desire, translation of urge into a central neural targeted goal; (4) action, physical response that satisfies the urge-desire; (5) evidence, feedback to the neural system on the action; (6) reward, sensory system that determines if the urge was satisfied. Urge-to-Cough is related to three fundamental types of cough: (1) reflex cough, (2) voluntary cough, and (3) behavioral cough. Urge-to-Cough with reflex cough can be studied by measuring the sensations elicited by a cough stimulus. Neural processes with voluntary cough can be studied using magnitude production cognitive psychometric methods. Results of these studies have shown if the subjects can reliably estimate their Urge-to-Cough, the urge increases with increasing cough stimulus, there is a correlation between the Urge-to-Cough and cough intensity, there is a threshold for eliciting the sensation of the urge that precedes the motor cough behavior, subjects can voluntarily produce coughs of varying magnitudes, the motor cough pattern is directly related to the perceived magnitude of a cough, volitional triggers of a cough are directly related to the reflex cough pattern, and neural triggers of cough initiate a stereotypic motor output. Understanding the Urge-to-Cough motivation-to-action system opens new strategies for research on central neural cough mechanisms.

Subjecting elite athletes to inspiratory breathing load reveals behavioral and neural signatures of optimal performers in extreme environments.

Background It is unclear whether and how elite athletes process physiological or psychological challenges differently than healthy comparison subjects. In general, individuals optimize exercise level as it relates to differences between expected and experienced exertion, which can be conceptualized as a body prediction error. The process of computing a body prediction error involves the insular cortex, which is important for interoception, i.e. the sense of the physiological condition of the body. Thus, optimal performance may be related to efficient minimization of the body prediction error. We examined the hypothesis that elite athletes, compared to control subjects, show attenuated insular cortex activation during an aversive interoceptive challenge. Methodology/Principal Findings Elite adventure racers (n = 10) and healthy volunteers (n = 11) performed a continuous performance task with varying degrees of a non-hypercapnic breathing load while undergoing functional magnetic resonance imaging. The results indicate that (1) non-hypercapnic inspiratory breathing load is an aversive experience associated with a profound activation of a distributed set of brain areas including bilateral insula, dorsolateral prefrontal cortex and anterior cingulated; (2) adventure racers relative to comparison subjects show greater accuracy on the continuous performance task during the aversive interoceptive condition; and (3) adventure racers show an attenuated right insula cortex response during and following the aversive interoceptive condition of non-hypercapnic inspiratory breathing load. Conclusions/Significance These findings support the hypothesis that elite athletes during an aversive interoceptive condition show better performance and an attenuated insular cortex activation during the aversive experience. Interestingly, differential modulation of the right insular cortex has been found previously in elite military personnel and appears to be emerging as an important brain system for optimal performance in extreme environments.

Expiratory Muscle Training Increases Pressure Support in High School Band Students

An experiment to increase expiratory muscle strength for instrumentalists, using a high-intensity, low-repetition expiratory training method, was conducted with 40 healthy high school band players. Subjects trained five days per week for 2 weeks using four sets of six training breaths for a total of 24 training breaths with a spring-loaded pressure relief valve that provided an adjustable threshold. The training valve pressure was set at 75% of the subjects measured maximum expiratory pressure (up to 80 cm H2O). Results demonstrated that high-intensity, low-repetition expiratory exercises significantly increased expiratory pressure generating capacity in these subjects and the degree of the training effect was similar regardless of the instrument the band member played. The training effect occurred within 2 weeks of initiating expiratory muscle training. Thus, this simple method of expiratory-specific strength training is effective and efficient for increasing expiratory pressure support in high school band students and has possibilities of a respiratory support device for many high pressure generating purposes. The potential mechanisms of the training effect are discussed.

Respiratory strength training: concept and intervention outcomes.

Respiratory muscle strength training (RMST) focuses on increasing the force-generating capacity of the inspiratory and expiratory muscles. The choice of respiratory muscles that are targeted using RMST depends on the outcome desired. For example, if an individual has reduced inspiratory muscle strength due to a neurogenic injury and is unable to ventilate the lungs, then inspiratory muscle strength training may be the chosen rehabilitation target. On the other hand, if a professional voice user is complaining of difficulty generating adequate vocal loudness during song production and is suffering from laryngeal dysfunction, then an expiratory muscle strength training paradigm may be the chosen rehabilitation target. Our most recent work with RMST has focused on increasing expiratory muscle force generation for those with Parkinsons disease who have difficulty with breathing, swallowing, and cough production. This difficulty typically worsens as the disease progresses. Highlights of these outcomes are summarized in this article.

The urge-to-cough and cough motor response modulation by the central effects of nicotine.

The urge-to-cough is a respiratory sensation that precedes the cough motor response. Since affective state modulates the perception of respiratory sensations such as dyspnoea, we wanted to test whether nicotine, an anxiolytic, would modulate the urge-to-cough and hence, the cough motor response. We hypothesized that withdrawal from and administration of nicotine in smoking subjects would modulate their anxiety levels, urge-to-cough and cough motor response to capsaicin stimulation. Twenty smoking (SM) adults (8F, 12M; 22+/-3 years; 2.9+/-2.0 pack years) and matched non-smoking (NS) controls (22+/-2 years) were presented with randomized concentrations of capsaicin (0-200 microM) before and after nicotine (SM only) gum and/or placebo (SM and NS) gum. Subjects rated their urge-to-cough using a Borg scale at the end of each capsaicin presentation. Cough number and cough motor pattern were determined from airflow tracings. Subjects completed State-Trait Anxiety Inventory (STAI) questionnaires before and after gum administration. SM subjects that withdrew from cigarette smoking for 12 h exhibited an increase in anxiety scores, a greater number of coughs and higher urge-to-cough ratings compared to NS subjects. Administration of nicotine gum reduced anxiety scores, cough number and urge-to-cough ratings to match the NS subjects. There was no effect of placebo gum on any of the measured parameters in the SM and NS groups. The results from this study suggest that modulation of the central neural state with nicotine withdrawal and administration in young smoking adults is associated with a change in anxiety levels which in turn modulates the perceptual and motor response to irritant cough stimulants.