F. Dennis McCool

Dysfunction of the Diaphragm

Dysfunction of one or both hemidiaphragms is an underdiagnosed cause of dyspnea. Weakness or paralysis may be seen during mechanical ventilation, after surgery or trauma, with metabolic or inflammatory disorders, and with myopathy, neuropathy, or diseases causing lung hyperinflation.

Diaphragm ultrasound as a predictor of successful extubation from mechanical ventilation

Introduction The purpose of this study was to evaluate if ultrasound derived measures of diaphragm thickening, rather than diaphragm motion, can be used to predict extubation success or failure. Methods Sixty-three mechanically ventilated patients were prospectively recruited. Diaphragm thickness (tdi) was measured in the zone of apposition of the diaphragm to the rib cage using a 7–10 MHz ultrasound transducer. The percent change in tdi between end-expiration and end-inspiration (Δtdi%) was calculated during either spontaneous breathing (SB) or pressure support (PS) weaning trials. A successful extubation was defined as SB for >48 h following endotracheal tube removal. Results Of the 63 subjects studied, 27 patients were weaned with SB and 36 were weaned with PS. The combined sensitivity and specificity of Δtdi%≥30% for extubation success was 88% and 71%, respectively. The positive predictive value and negative predictive value were 91% and 63%, respectively. The area under the receiver operating characteristic curve was 0.79 for Δtdi%. Conclusions Ultrasound measures of diaphragm thickening in the zone of apposition may be useful to predict extubation success or failure during SB or PS trials.

Monitoring Recovery From Diaphragm Paralysis With Ultrasound

BACKGROUND Diaphragmatic paralysis is an uncommon, yet underdiagnosed cause of dyspnea. Data regarding the time course and potential for recovery has come from a few small case series. The methods that have been traditionally employed to diagnose diaphragmatic weakness or paralysis are either invasive or limited in sensitivity and specificity. A new technique utilizing two-dimensional, B-mode ultrasound (US) measurements of diaphragm muscle thickening during inspiration (Deltatdi%) has been validated in the diagnosis of diaphragm paralysis (DP). The purpose of this study was to assess whether serial US evaluation might be utilized to monitor the potential recovery of diaphragm function. METHODS Twenty-one consecutive patients with clinically suspected DP were referred to the pulmonary physiology laboratory. Sixteen patients were found to have DP by US (unilateral, 10 patients; bilateral, 6 patients). Subjects were followed up for up to 60 months. On initial and subsequent visits, Deltatdi% was measured by US. Additional measurements included upright and supine vital capacity (VC), maximal inspiratory pressure (Pimax), and maximal expiratory pressure. RESULTS Eleven of 16 patients functionally recovered from DP. The mean (+/- SD) recovery time was 14.9 +/- 6.1 months. No diaphragm thickening was noted in those patients who did not recover. Positive correlations were found between improvement in Deltatdi% and interval changes in VC, Pimax, and end-expiratory measurements of diaphragm thickness. CONCLUSIONS US may be used to assess for potential functional recovery from diaphragm weakness or DP. As in previous series, recovery occurs in a substantial number of individuals, but recovery time may be prolonged.

Respiratory Muscle Strength in the Physically Active Elderly

Advancing age is associated with a decline in the strength of the skeletal muscles, including those of respiration. Respiratory muscles can be strengthened with nonrespiratory activities. We therefore hypothesized that regular exercise in the elderly would attenuate this age-related decline in respiratory muscle strength. Twenty-four healthy subjects older than 65 years were recruited (11 males and 13 females). A comprehensive physical activity survey was administered, and subjects were categorized as active (n = 12) or inactive (n = 12). Each subject underwent testing of maximum inspiratory and expiratory pressures (PImax and PEmax). Diaphragmatic thickness (tdi) was measured via two-dimensional B-mode ultrasound. There were no significant differences between the active and inactive groups with respect to age (75 vs. 73 years) or body weight (69.1vs. 69.9 kg). There were more women (9) than men (3) in the inactive group. Diaphragm thickness was greater in the active group (0.31 ± 0.06 cm vs. 0.25 ± 0.04 cm; p = 0.011). PEmax and PImax were also greater in the active group (130 ± 44 cm H2O vs. 80 ± 24 cm H2O; p = 0.002; and 99 ± 32 cm H2O vs. 75 ± 14 cm H2O; p = 0.03). There was a positive association between PImax and tdi (r = 0.43, p = 0.03). Regular exercise was positively associated with diaphragm muscle thickness in this cohort. As PEmax was higher in the active group, we postulate that recruitment of the diaphragm and abdominal muscles during nonrespiratory activities may be the source of this training effect.

Inspiratory muscle adaptations following pressure or flow training in humans

Abstract Skeletal muscle adapts differently to training with high forces or with high velocities. The effects of these disparate training protocols on the inspiratory muscles were investigated in ten healthy volunteers. Five subjects trained using high force (pressure) loads (pressure trainers) and five trained using high velocity (flow) loads (flow trainers). Pressure training entailed performing 30 maximal static inspiratory efforts against a closed airway. Flow training entailed performing 30 sets of three maximal dynamic inspiratory efforts against a minimal resistance. Training was supervised and carried out 5 days a week for 6 weeks. Inspiratory flow rates and oesophageal pressure-time curves were measured before and after training. Peak inspiratory pressures during maximal static and dynamic efforts and peak flows during the maximal dynamic efforts were calculated. The time-to-peak pressure and rate of rise in peak pressure during maximal static and dynamic manoeuvres were also calculated before and following training. Maximal static pressure increased in the pressure training group and maximal dynamic pressure increased in the flow training group. Both groups increased the rate of pressure production (dP/dt) during their respective maximal efforts. The post-training decrease in time-to-peak pressure was proportionately greater in the flow trainers than in the pressure trainers. The differences in time-to-peak pressure between the two groups were consistent with the different effects of force and velocity training on the time-to-peak tension of skeletal muscle.

The study design and rationale of the randomized controlled trial: translating COPD guidelines into primary care practice

BackgroundChronic obstructive pulmonary disease (COPD) is a progressive, debilitating disease associated with significant clinical burden and is estimated to affect 15 million individuals in the US. Although a large number of individuals are diagnosed with COPD, many individuals still remain undiagnosed due to the slow progression of the disorder and lack of recognition of early symptoms. Not only is there under-diagnosis but there is also evidence of sub-optimal evidence-based treatment of those who have COPD. Despite the development of international COPD guidelines, many primary care physicians who care for the majority of patients with COPD are not translating this evidence into effective clinical practice.Method/DesignThis paper describes the design and rationale for a randomized, cluster design trial (RCT) aimed at translating the COPD evidence-based guidelines into clinical care in primary care practices. During Phase 1, a needs assessment evaluated barriers and facilitators to implementation of COPD guidelines into clinical practice through focus groups of primary care patients and providers. Using formative evaluation and feedback from focus groups, three tools were developed. These include a computerized patient activation tool (an interactive iPad with wireless data transfer to the spirometer); a web-based COPD guideline tool to be used by primary care providers as a decision support tool; and a COPD patient education toolkit to be used by the practice team. During phase II, an RCT will be performed with one year of intervention within 30 primary care practices. The effectiveness of the materials developed in Phase I are being tested in Phase II regarding physician performance of COPD guideline implementation and the improvement in the clinically relevant outcomes (appropriate diagnosis and management of COPD) compared to usual care. We will also examine the use of a patient activation tool - ‘MyLungAge’ - to prompt patients at risk for or who have COPD to request spirometry confirmation and to request support for smoking cessation if a smoker.DiscussionUsing a multi-modal intervention of patient activation and a technology-supported health care provider team, we are testing the effectiveness of this intervention in activating patients and improving physician performance around COPD guideline implementation.Trial registrationClinicalTrials.gov, NCT01237561

Association of obstructive sleep apnea risk factors with nocturnal enuresis in postmenopausal women.

Objective:The prevalence of obstructive sleep apnea (OSA) in women increases significantly after menopause. However, identifying at-risk women is difficult because they tend to underreport symptoms and their complaints may differ from those traditionally associated with OSA. We investigated whether OSA risk factors are associated with the presence of a “nontraditional” complaint, such as nocturnal enuresis, in postmenopausal women. Methods:A cross-sectional study of postmenopausal women aged 50 to 79 years who participated in the Womens Health Initiative Observational Study and clinical trials (1993-2005) at 40 clinical centers in the United States was performed. Multiple variable logistic regression analysis was used to determine the association of OSA risk factors with nocturnal enuresis. Results:A cohort of 2,789 women (1.7%) reported having nocturnal enuresis. Obesity (odds ratio [OR], 2.29; 95% CI, 2.00-2.62), snoring (OR, 2.01; 95% CI, 1.74-2.32), poor sleep quality (OR, 1.70; 95% CI, 1.52-1.91), sleep fragmentation (OR, 2.44; 95% CI, 2.14-2.79), daytime sleepiness (OR, 1.50; 95% CI, 1.33-1.68), and hypertension (OR, 1.13; 95% CI, 1.01-1.26) were associated with nocturnal enuresis. Each additional OSA risk factor in a predefined OSA score significantly increased the odds of having nocturnal enuresis in a dose-response fashion (OR of 1.38, 2.00, 2.80, 3.87, 5.10, and 7.02 for scores of 1-6, respectively) compared with no risk factors. Conclusions:OSA risk factors are associated with nocturnal enuresis in postmenopausal women. Mechanisms relating nocturnal enuresis to OSA may include apnea-associated changes in intrathoracic pressure, leading to increased urine output. Questioning at-risk postmenopausal women presenting with nocturnal enuresis about other OSA risk factors should be considered.

Physiology in Medicine: physiological basis of diaphragmatic dysfunction with abdominal hernias–implications for therapy

An incisional hernia is a common complication after abdominal surgery. Complaints of dyspnea in this population may be attributed to cardiopulmonary dysfunction or deconditioning. Large abdominal incisional hernias, however, may cause diaphragm dysfunction and result in dyspnea, which is more pronounced when standing (platypnea). The use of an abdominal binder may alleviate platypnea in this population. We discuss the link between diaphragm dysfunction and the lack of abdominal wall integrity and how abdominal wall support partially restores diaphragm function.

Prospective Association of Physical Activity and Heart Failure Hospitalizations Among Black Adults With Normal Ejection Fraction: The Jackson Heart Study

Background Given high rates of obesity, hypertension, and diabetes mellitus, black persons are at risk to develop heart failure. The association of moderate to vigorous physical activity (MVPA) and heart failure in black adults is underresearched. The purpose of this study was to explore whether greater MVPA was associated with lower risk of heart failure hospitalizations (HFHs) among black adults with normal ejection fractions. Methods and Results We performed a prospective analysis of 4066 black adults who participated in the Jackson Heart Study and who had physical activity measured, had normal ejection fraction on 2‐dimensional echocardiograms, and were followed for 7 years for incident HFH. We used Cox proportional regression analyses adjusted for age, sex, body mass index, smoking status, hypertension, diabetes mellitus, chronic obstructive pulmonary disease, coronary heart disease, atrial fibrillation, and chronic kidney disease and examined effect modification by sex and body mass index. Of the eligible population, 1925 participants, according to the duration of MVPA, had poor health (0 minutes/week), 1332 had intermediate health (1–149 minutes/week), and 809 had ideal health (≥150 minutes/week). There were 168 incident HFHs. MVPA for intermediate and ideal health was associated with decreasing risk of incident HFH (hazard ratio: 0.70 [95% confidence interval, 49–1.00] and 0.35 [95% confidence interval, 0.19–0.64], respectively; P trend=0.003). The full model revealed hazard ratios of 0.74 [95% confidence interval, 0.52–1.07] and 0.41 [95% confidence interval, 0.22–0.74], respectively. There was no effect modification between MVPA and body mass index or sex on incident HFH. Conclusions A dose‐response relationship between increasing levels of MVPA and protection from incident HFH was found in black men and women with normal ejection fractions.

Methacholine-Induced Airway Hyper-Reactivity Phenotypes

Objective. The incorporation of airways conductance/resistance is a rare feature in clinical methacholine challenge test (MCT) protocols, and the majority of pulmonary laboratories rely solely on the spirometric parameters. The importance and interpretation of an MCT demonstrating a significant decline in specific airway conductance specific airway conductance (sGaw), but not forced expiratory volume in one second (FEV1), remains undefined. This study sought to elucidate the clinical and physiologic phenotypes of individuals with a ≥40% sGaw decline but <20% FEV1 change. Methods. All subjects completed the Asthma Quality of Life Questionnaire (AQLQ), followed by standard MCT, with measurements of sGaw and an additional independent measurement of resistance and reactance by impulse oscillation system (IOS) before and after MCT. Results. Of 201 subjects, 47(23.4%) were in Group 1 (FEV1 declined by ≥20%), 45(22.4%) were in Group 2 (non-significant FEV1 drop, sGaw declined ≥40%), and 109(54.2%) were in Group 3 (no significant decline in FEV1/sGaw). There was a nearly identical change in all oscillometric parameters and sGaw for Groups 1 and 2 versus Group 3. There were no differences between Groups 1 and 2 in any AQLQ category, and Groups 1 and 2 were statistically different from Group 3. Conclusions. Our prospective study suggests that patients with a significant sGaw decline alone during MCT are a clinically and physiologically important hyper-reactivity phenotype—whose hyper-reactivity independently was confirmed to be nearly identical to those with an FEV1 decline. By failing to assess airways conductance/resistance, asthma may be inappropriately “ruled out” in ∼20% of the patients referred for MCT. Based on this, standardized incorporation of body plethysmography and/or IOS to MCT protocols should be considered.