Papers by Michael McKenna
Journal of applied physiology (Bethesda, Md. : 1985), 1998
Six men were studied during four 30-s "all-out" exercise bouts on an air-braked cycle e... more Six men were studied during four 30-s "all-out" exercise bouts on an air-braked cycle ergometer. The first three exercise bouts were separated by 4 min of passive recovery; after the third bout, subjects rested for 4 min, exercised for 30 min at 30-35% peak O2 consumption, and rested for a further 60 min before completing the fourth exercise bout. Peak power and total work were reduced (P < 0. 05) during bout 3 [765 +/- 60 (SE) W; 15.8 +/- 1.0 kJ] compared with bout 1 (1,168 +/- 55 W, 23.8 +/- 1.2 kJ), but no difference in exercise performance was observed between bouts 1 and 4 (1,094 +/- 64 W, 23.2 +/- 1.4 kJ). Before bout 3, muscle ATP, creatine phosphate (CP), glycogen, pH, and sarcoplasmic reticulum (SR) Ca2+ uptake were reduced, while muscle lactate and inosine 5'-monophosphate were increased. Muscle ATP and glycogen before bout 4 remained lower than values before bout 1 (P < 0.05), but there were no differences in muscle inosine 5'-monophosphate, lactat...
Reactive oxygen species (ROS) have been linked with both depressed Na + ,K + -pump activity and s... more Reactive oxygen species (ROS) have been linked with both depressed Na + ,K + -pump activity and skeletal muscle fatigue. This study investigated N -acetylcysteine (NAC) effects on muscle Na + ,K + -pump activity and potassium (K + ) regulation during prolonged, submaximal endurance exercise. Eight well-trained subjects participated in a double-blind, randomised, crossover design, receiving either NAC or saline (CON) intravenous infusion at 125 mg kg −1 h −1 for 15 min, then 25 mg kg −1 h −1 for 20 min prior to and throughout exercise. Subjects cycled for 45 min at 71%V O 2 peak , then continued at 92%V O 2 peak until fatigue. Vastus lateralis muscle biopsies were taken before exercise, at 45 min and fatigue and analysed for maximal in vitro Na + ,K + -pump activity (K + -stimulated 3-O-methyfluorescein phosphatase; 3-O-MFPase). Arterialized venous blood was sampled throughout exercise and analysed for plasma K + and other electrolytes. Time to fatigue at 92%V O 2 peak was reproducible in preliminary trials (C.V. 5.6 ± 0.6%) and was prolonged with NAC by 23.8 ± 8.3% (NAC 6.3 ± 0.5 versus CON 5.2 ± 0.6 min, P < 0.05). Maximal 3-O-MFPase activity decreased from rest by 21.6 ± 2.8% at 45 min and by 23.9 ± 2.3% at fatigue (P < 0.05). NAC attenuated the percentage decline in maximal 3-O-MFPase activity (%Δactivity) at 45 min (P < 0.05) but not at fatigue. When expressed relative to work done, the %Δactivity-to-work ratio was attenuated by NAC at 45 min and fatigue (P < 0.005). The rise in plasma [K + ] during exercise and the Δ[K + ]-to-work ratio at fatigue were attenuated by NAC (P < 0.05). These results confirm that the antioxidant NAC attenuates muscle fatigue, in part via improved K + regulation, and point to a role for ROS in muscle fatigue.
Physiological reports, 2015
While training upregulates skeletal muscle Na(+), K(+)-ATPase (NKA), the effects of knee injury a... more While training upregulates skeletal muscle Na(+), K(+)-ATPase (NKA), the effects of knee injury and associated disuse on muscle NKA remain unknown. This was therefore investigated in six healthy young adults with a torn anterior cruciate ligament, (KI; four females, two males; age 25.0 ± 4.9 years; injury duration 15 ± 17 weeks; mean ± SD) and seven age- and BMI-matched asymptomatic controls (CON; five females, two males). Each participant underwent a vastus lateralis muscle biopsy, on both legs in KI and one leg in CON. Muscle was analyzed for muscle fiber type and cross-sectional area (CSA), NKA content ([(3)H]ouabain binding), and α1-3 and β1-2 isoform abundance. Participants also completed physical activity and knee function questionnaires (KI only); and underwent quadriceps peak isometric strength, thigh CSA and postural sway assessments in both injured and noninjured legs. NKA content was 20.1% lower in the knee-injured leg than the noninjured leg and 22.5% lower than CON. NKA...
JAMA Otolaryngology–Head & Neck Surgery, 2014
IMPORTANCE The etiology of superior canal dehiscence (SCD) involving the arcuate eminence is not ... more IMPORTANCE The etiology of superior canal dehiscence (SCD) involving the arcuate eminence is not completely understood, but genetic factors may play a role. One hypothesis is that patients are born with a defect of the superior canal, and an acute event (such as head trauma) or progressive loss of bone (eg, due to dural pulsations) may result in the onset of SCD symptoms. Familial SCD has only been briefly mentioned in the literature to date. OBSERVATIONS We report 3 families that each had 2 members with SCD syndrome. We found that first-degree relatives presented with similar complaints and that temporal bone computed tomography scans between relatives showed very similar skull base topography and anatomic SCD defects.
Guanidino Compounds in Biology and Medicine, 2003
The present study investigated whether there were any differences between males and females in re... more The present study investigated whether there were any differences between males and females in respect to creatine transporter (CreaT) gene expression and/or total creatine (TCr) content in human vastus lateralis muscle. Skeletal muscle obtained from young healthy male (n = 13, age: 23.2 +/- 5.0 years) and female subjects (n = 12, age: 21.7 +/- 4.3 years) was analyzed for CreaT mRNA, CreaT protein and TCr content. Total CreaT protein content in the muscle was similar (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 0.05) between the sexes. Two bands (approximately 55 and 73 kDa) of the CreaT protein were detected in all muscle samples. Both the 55 and the 73 kDa bands were present in similar (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 0.05) amounts in males compared with females. The 73 kDa band was in greater abundance (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05) than the 55 kDa band, irrespective of gender. In addition, CreaT mRNA expression relative to beta-actin mRNA and the TCr content (males: 117.8 +/- 2.2, females: 125.3 +/- 4.3 mmol.kg(-1) dry mass) were also unaffected (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 0.05) by gender. These data demonstrate that gender does not influence skeletal muscle TCr content and CreaT gene expression in young human subjects.
The Laryngoscope, 2009
Objectives-Proteins in perilymph may alter the delivery profile of implantable intracochlear drug... more Objectives-Proteins in perilymph may alter the delivery profile of implantable intracochlear drug delivery systems through biofouling. Knowledge of protein composition will help anticipate interactions with delivered agents.
The Laryngoscope, 2003
For many complex surgical procedures, larger hospital or surgeon caseload is associated with bett... more For many complex surgical procedures, larger hospital or surgeon caseload is associated with better patient outcome. We examined the volume-outcome relationship for surgical excision of acoustic neuromas. Retrospective cohort study. The Nationwide Inpatient Sample (1996 to 2000) was used. Multivariate regression analyses were adjusted for age, sex, race, payer, geographic region, procedure timing, admission type and source, medical comorbidities, and neurofibromatosis status. At 265 hospitals, 2643 operations were performed by 352 identified primary surgeons. Outcome was measured on a four-level scale at hospital discharge: death (0.5%) and discharge to long-term care (1.2%), to short-term rehabilitation (4.4%), and directly to home (94%). Outcomes were significantly better after surgery at higher-volume hospitals (OR 0.47 for fivefold-larger caseload, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001) or by higher-volume surgeons (OR 0.46, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001). Of patients who had surgery at lowest-volume-quartile hospitals, 12.3% were not discharged directly home, compared with 4.1% at highest-volume-quartile hospitals. There was a trend toward lower mortality for higher-volume hospitals (P =.1) and surgeons (P =.06). Of patients who had surgery at lowest-caseload-quartile hospitals, 1.1% died, compared with 0.6% at highest-volume-quartile hospitals. Postoperative complications (including neurological complications, mechanical ventilation, facial palsy, and transfusion) were less likely with high-volume hospitals and surgeons. Length of stay was significantly shorter with high-volume hospitals (P =.01) and surgeons (P =.009). Hospital charges were lower for high-volume hospitals (by 6% [P =.006]) and surgeons (by 6% [P =.09]). For acoustic neuroma excision, higher-volume hospitals and surgeons provided superior short-term outcomes with shorter lengths of stay and lower charges.
The Journal of Physiology, 2013
Calcium cycling is integral to muscle performance during the rapid muscle contraction and relaxat... more Calcium cycling is integral to muscle performance during the rapid muscle contraction and relaxation of high-intensity exercise. Ca(2+) handling is altered by diabetes mellitus, but has not previously been investigated in human skeletal muscle. We investigated effects of high-intensity exercise and sprint training on skeletal muscle Ca(2+) regulation among men and women with type 1 diabetes (T1D, n = 8, 3F, 5M) and matched non-diabetic controls (CON, n = 8, 3F, 5M). Secondarily, we examined sex differences in Ca(2+) regulation. Subjects undertook 7 weeks of three times-weekly cycle sprint training. Before and after training, performance was measured, and blood and muscle were sampled at rest and after high-intensity exercise. In T1D, higher Ca(2+)-ATPase activity (+28%) and Ca(2+) uptake (+21%) than in CON were evident across both times and days (P &lt; 0.05), but performance was similar. In T1D, resting Ca(2+)-ATPase activity correlated with work performed until exhaustion (r = 0.7, P &lt; 0.01). Ca(2+)-ATPase activity, but not Ca(2+) uptake, was lower (-24%, P &lt; 0.05) among the women across both times and days. Intense exercise did not alter Ca(2+)-ATPase activity in T1D or CON. However, sex differences were evident: Ca(2+)-ATPase was reduced with exercise among men but increased among women across both days (time × sex interaction, P &lt; 0.05). Sprint training reduced Ca(2+)-ATPase (-8%, P &lt; 0.05), but not Ca(2+) uptake, in T1D and CON. In summary, skeletal muscle Ca(2+) resequestration capacity was increased in T1D, but performance was not greater than CON. Sprint training reduced Ca(2+)-ATPase in T1D and CON. Sex differences in Ca(2+)-ATPase activity were evident and may be linked with fibre type proportion differences.
Effects of live high, train low hypoxic exposure on lactate metabolism in trained humans. .-We de... more Effects of live high, train low hypoxic exposure on lactate metabolism in trained humans. .-We determined the effect of 20 nights of live high, train low (LHTL) hypoxic exposure on lactate kinetics, monocarboxylate lactate transporter proteins (MCT1 and MCT4), and muscle in vitro buffering capacity (m) in 29 well-trained cyclists and triathletes. Subjects were divided into one of three groups: 20 consecutive nights of hypoxic exposure (LHTLc), 20 nights of intermittent hypoxic exposure [four 5-night blocks of hypoxia, each interspersed with 2 nights of normoxia (LHTLi)], or control (Con). Rates of lactate appearance (R a), disappearance (Rd), and oxidation (R ox) were determined from a primed, continuous infusion of L-[U-14 C]lactic acid tracer during 90 min of steady-state exercise [60 min at 65% peak O 2 uptake (V O2 peak) followed by 30 min at 85% V O2 peak]. A resting muscle biopsy was taken before and after 20 nights of LHTL for the determination of m and MCT1 and MCT4 protein abundance. R a during the first 60 min of exercise was not different between groups. During the last 25 min of exercise at 85% V O2 peak, Ra was higher compared with exercise at 65% of V O2 peak and was decreased in LHTLc (P Ͻ 0.05) compared with the other groups. R d followed a similar pattern to Ra. Although Rox was significantly increased during exercise at 85% compared with 65% of V O2 peak, there were no differences between the three groups or across trials. There was no effect of hypoxic exposure on m or MCT1 and MCT4 protein abundance. We conclude that 20 consecutive nights of hypoxia exposure decreased whole body R a during intense exercise in well-trained athletes. However, muscle markers of lactate metabolism and pH regulation were unchanged by the LHTL intervention.
Reading & Writing Quarterly, 1999
Peabody Journal of Education, 1998
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship.
Otology & Neurotology, 2004
To describe the clinical and diagnostic features of superior semicircular canal dehiscence (SSCD)... more To describe the clinical and diagnostic features of superior semicircular canal dehiscence (SSCD) in patients with postpartum vertigo. Retrospective review, meta-analysis. Tertiary neurotologic and audiologic center. Two women who presented with a history of acute postpartum vertigo and SSCD confirmed on high-resolution computed tomography (CT) were included. Our meta-analysis of the surgical SSCD literature comprised a total of 43 patients. Patients with postpartum vertigo and SSCD underwent a complete medical evaluation, audiometric testing, CT imaging, magnetic resonance imaging studies, vestibular evoked myogenic potential testing, and laser Doppler vibrometer testing. Case 2 was managed with a middle fossa craniotomy and SSCD repair. The first patient presented with normal hearing and aural fullness, autophony, and sound sensitivity of the left ear. A 1-mm left-sided SSCD was seen on CT imaging. She is being managed conservatively. The second patient had left-sided conductive hearing loss with sound and pressure sensitivity. The contralateral ear was congenitally deaf. CT imaging revealed a 4-mm left-sided SSCD. Because of her disabling symptoms, the patient underwent a middle fossa craniotomy and superior canal plugging. Her vestibular symptoms resolved with improvement in hearing. Vestibular evoked myogenic potential and laser Doppler vibrometer testing in both cases were consistent with SSCD. This is the first description of patients with SSCD presenting after childbirth and should be included in the differential diagnosis of acute postpartum vertigo or disequilibrium. SSCD plugging can provide a stable repair with resolution of symptoms, reversal of diagnostic indicators, and hearing improvement.
Otology & Neurotology, 2010
In vitro treatment of Nf2-deficient cells with epidermal growth factor receptor (EGFR) inhibitors... more In vitro treatment of Nf2-deficient cells with epidermal growth factor receptor (EGFR) inhibitors can reduce cellular proliferation. We sought to determine the activity of erlotinib for progressive vestibular schwannoma (VS) associated with neurofibromatosis 2 (NF2). Retrospective case review. Tertiary referral center. Eleven NF2 patients with progressive VS who were poor candidates for standard therapy. Erlotinib 150 mg daily. A radiographic response was defined as &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;or= 20% decrease in tumor volume compared with baseline. A hearing response was defined as a statistically significant increase in word recognition score (WRS) compared with baseline; a minor hearing response was defined as a 10 dB improvement in pure-tone average with stable WRS. : Before treatment, the median and mean annual volumetric growth rate for 11 index VS were 26% and 46%, respectively. Among 10 evaluable patients, the median time-to-tumor progression was 9.2 months. Three patients with stable disease experienced maximum tumor shrinkage of 4%, 13%, and 14%. Nine patients underwent audiologic evaluations. One experienced a transient hearing response, 2 experienced minor hearing responses, 3 remained stable, and 2 developed progressive hearing loss. The median time-to-progressive hearing loss was 9.2 months and to either tumor growth or progressive hearing loss was 7.1 months. Adverse treatment effects included mild-to-moderate rash, diarrhea, and hair thinning, with 2 episodes of grade 3 toxicity. Erlotinib treatment was not associated with radiographic or hearing responses in NF2 patients with progressive VS. Because a subset of patients experienced prolonged stable disease, time-to-progression may be more appropriate than radiographic or hearing response for anti-EGFR agents in NF2-associated VS.
Otolaryngology - Head and Neck Surgery, 1995
With the continued concern over the possible transmission of viral infections through homologous ... more With the continued concern over the possible transmission of viral infections through homologous middle ear implants, there is increasing pressure to develop a truly biocompatible alloplastic middle ear prosthesis. The polymaleinate ionomer, which has been used in dentistry as a filling and luting material for more than 15 years, has recently been used to construct total and partial ossicular replacement prostheses. In an attempt to evaluate these new implants, a multicenter prospective clinical trial was initiated. To date, 92 patients have undergone implantation. The follow-up interval ranged from 3 months to 22 months. Although it is premature to discuss the long-term results, the preliminary surgical experience and audiometric data with these implants are reviewed. From a surgical perspective, the ionomeric prostheses were easily contoured with a diamond burr and were not prone to shattering. Preliminary follow-up audiometric data were available on 80 patients (59 partial ossicular replacement prostheses and 21 total ossicular replacement prostheses). Of the 59 partial ossicular replacement prostheses the air-bone gaps (average of 500 Hz, 1 kHz, 2 kHz and 3 kHz) were as follows: 0 dB to 10 dB, 15 (25%) of 59; 11 dB to 20 dB, 20 (34%) of 59; 21 dB to 30 dB, 11 (19%) of 59; and greater than 30 dB, 13 (22%) of 59. Of the 21 total ossicular replacement prostheses the air-bone gaps were as follows: 0 dB to 10 dB, 6 (29%) of 21; 11 dB to 20 dB, 6 (29%) of 21; 21 dB to 30 dB, 5 (24%) of 21; and greater than 30 dB, 4 (19%) of 21.
Otolaryngology - Head and Neck Surgery, 2007
Osteoarthritis and Cartilage, 2010
Poster Presentations / Osteoarthritis and Cartilage 18, Supplement 2 (2010) S45-S256 S203 1.96 cm... more Poster Presentations / Osteoarthritis and Cartilage 18, Supplement 2 (2010) S45-S256 S203 1.96 cm 3 , SD 3.97) and 2 patients had femoral head cysts (4 cysts, mean total cyst volume/patient 3.98 cm 3 , SD 4.10). 2½ years after surgery 13 patients had acetabular cysts (16 cysts, mean total cyst volume/patient 0.96 cm 3 , SD 1.70) and 2 patients had femoral head cysts (4 cysts, mean total cyst volume/patient 0.80 cm 3 , SD 0.72). Mean total acetabular cyst volume/patient decreased significantly from 1 year to 2½ years after PAO = 0.04. All acetabular cysts were located anterolaterally in the acetabulum except for one that was posterolateral. The femoral head cysts were positioned anterolaterally and anteromedially. The radiographic evaluation on preoperative and postoperative radiographs in the 28 hips showed that the CE angle increased from mean 13 (-27 to 35)°to mean 31 (20 to 41)°after PAO, and the AI angle decreased from mean 18 (7 to 39)°to mean 2 (-4 to 10)°.
Uploads
Papers by Michael McKenna