World Trade Center exposure, post-traumatic stress disorder, and subjective cognitive concerns in a cohort of rescue/recovery workers.

OBJECTIVE: To determine whether World Trade Center (WTC)-exposure intensity and post-traumatic stress disorder (PTSD) are associated with subjective cognitive change in rescue/recovery workers. METHOD: The population included 7875 rescue/recovery workers who completed a subjective cognition measure, the Cognitive Function Instrument (CFI), between 3/1/2018 and 2/28/2019 during routine monitoring, indicating whether they had experienced cognitive and functional difficulties in the past year. Higher scores indicated greater self-perceived cognitive change. Probable PTSD, depression, and alcohol abuse were evaluated by validated mental health screeners. Logistic regression assessed the associations of WTC exposure and current PTSD with top-quartile (≥2) CFI score, and of early post-9/11 PTSD with top-quartile CFI in a subpopulation (N = 6440). Models included demographics, smoking, depression, and alcohol abuse as covariates. RESULTS: Mean age at CFI completion was 56.7 ± 7.7 (range: 36-81). Participants with high-intensity WTC exposure had an increased likelihood of top-quartile CFI score (odds ratio[OR] vs. low exposure: 1.32, 95%CI: 1.07-1.64), controlling for covariates. Current and early PTSD were both associated with top-quartile CFI (OR: 3.25, 95%CI: 2.53-4.19 and OR: 1.56, 95%CI: 1.26-1.93) respectively. CONCLUSIONS: High-intensity WTC exposure was associated with self-reported cognitive change 17 years later in rescue/recovery workers, as was PTSD. Highly WTC-exposed subgroups may benefit from additional cognitive evaluation and monitoring of cognition over time.

Nested case-control study of selected systemic autoimmune diseases in World Trade Center rescue/recovery workers.

OBJECTIVE: To test the a priori hypothesis that acute and chronic work exposures to the World Trade Center (WTC) site on or after September 11, 2001 were associated with risk of new-onset systemic autoimmune diseases. METHODS: A nested case-control study was performed in WTC rescue/recovery workers who had received a rheumatologist-confirmed systemic autoimmune disease diagnosis between September 12, 2001 and September 11, 2013 (n = 59), each of whom was individually matched to 4 randomly selected controls (n = 236) on the basis of year of hire (±1 year), sex, race, and work assignment (firefighter or emergency medical service). Acute exposure was defined according to the earliest time of arrival (morning of 9/11 versus later) at the WTC site, and chronic exposure was defined as duration (number of months) of WTC site-related work. Rheumatologists were blinded with regard to each subject's exposure status. The conditional odds ratios (CORs) with 95% confidence intervals (95% CIs) for incident autoimmune disease were derived from exact conditional logistic regression models. RESULTS: Rheumatoid arthritis was the most common autoimmune diagnosis (37% of subjects), followed by spondyloarthritis (22%), inflammatory myositis (14%), systemic lupus erythematosus (12%), systemic sclerosis (5%), Sjögren's syndrome (5%), antiphospholipid syndrome (3%), and granulomatosis with polyangiitis (Wegener's) (2%). The COR for incident autoimmune disease increased by 13% (COR 1.13, 95% CI 1.02-1.26) for each additional month worked at the WTC site. These odds were independent of the association between high acute exposure (working during the morning of 9/11) and disease outcome, which conveyed an elevated, but not statistically significant, risk (COR 1.85, 95% CI 0.86-3.89). CONCLUSION: Prolonged work at the WTC site, independent of acute exposure, was an important predictor of post-9/11 systemic autoimmune diseases. The WTC Health Program should expand surveillance efforts for those with extended exposures, as early detection can facilitate early treatment, which has been shown to minimize organ damage and improve quality of life.

The impact of the World Trade Center attack on FDNY firefighter retirement, disabilities, and pension benefits.

BACKGROUND: Our goal was to examine the effect of the World Trade Center (WTC) attack and subsequent New York City Fire Department (FDNY) rescue/recovery activities on firefighter retirements. We also analyzed the financial impact associated with the increased number and proportion of service-connected "accidental" disability retirements on the FDNY pension system. METHODS: A total of 7,763 firefighters retired between 9/11/1994 and 9/10/2008. We compared the total number of retirements and the number and proportion of accidental disability retirements 7 years before and 7 years after the WTC attack. We categorized WTC-related accidental disability retirements by medical cause and worked with the New York City Office of the Actuary to approximate the financial impact by cause. RESULTS: In the 7 years before 9/11 there were 3,261 retirements, 48% (1,571) of which were accidental disability retirements. In the 7 years after 9/11, there were 4,502 retirements, 66% (2,970) were accidental disability retirements, of which 47% (1,402) were associated with WTC-related injuries or illnesses. After 9/11, the increase in accidental disability retirements was, for the most part, due to respiratory-related illnesses. Additional increases were attributed to psychological-related illnesses and musculoskeletal injuries incurred at the WTC site. Pension benefits associated with WTC-related accidental disability retirements have produced an increased financial burden of over $826 million on the FDNY pension system. CONCLUSIONS: The WTC attacks affected the health of the FDNY workforce resulting in more post-9/11 retirements than expected, and a larger proportion of these retirees with accidental disability pensions.

Pulmonary disease in rescue workers at the World Trade Center site.

PURPOSE OF REVIEW: The catastrophic collapse of the World Trade Center (WTC) towers on September 11, 2001 created a large-scale disaster site in a densely populated urban environment. Over the ensuing months, tens of thousands of rescue, recovery and cleanup workers, volunteers, and residents of the adjacent community were exposed to a complex mixture of airborne pollutants. This review focuses on currently described respiratory syndromes, symptoms, and physiologic derangements in WTC rescue, recovery, and cleanup workers, discusses potential long-term effects on respiratory health, and draws parallels to community findings. RECENT FINDINGS: Detailed qualitative and quantitative analyses of airborne pollutants with their changing composition during initial rescue/recovery and subsequent cleanup have been published. Major concerns include persistent aerodigestive tract inflammatory syndromes, such as reactive airways dysfunction syndrome (RADS), reactive upper airways dysfunction syndrome (RUDS), gastroesophageal reflux disease (GERD), and inflammatory pulmonary parenchymal syndromes, as well as respiratory tract and nonrespiratory malignancies. Aerodigestive tract inflammatory syndromes have now been documented in WTC exposed occupational groups, and syndrome incidence has been linked to WTC airborne pollutant exposure intensity. Community based investigations have yielded similar findings. SUMMARY: While it is too early to ascertain long-term effects of WTC dust exposure, current studies already demonstrate a definite link between exposure to WTC-derived airborne pollutants and respiratory disease, both in the occupational and the community setting. A better understanding of causes and effects of this exposure will help in developing appropriate preventative tools for rescue workers in future disasters.

Thermal protective uniforms and hoods: impact of design modifications and water content on burn prevention in New York City firefighters: laboratory and field results.

OBJECTIVES: To determine (1) the effectiveness of hoods in reducing head burns, (2) the impact of clothes worn under the protective outer uniform (modern = long sleeve shirt and long pants; modified modern = short sleeve T-shirt and short pants) on burns, and (3) whether water content (dry, damp or saturated) affects the level of thermal protection. SETTING: Fire Department of the City of New York (FDNY). METHODS: Laboratory tests (fully dressed manikin) evaluated the different uniform and water conditions when exposed to an average 24 cal/cm2 heat flux, approximately 2,250 degrees F air temperature. FDNY field results compared (1) head burns during winters wearing the hood to winters without hood and (2) upper and lower extremity burns during summers wearing traditional, modern, and modified modern uniforms. RESULTS: Laboratory tests showed that thermal protection was: (1) dramatically improved by the hood with protection increasing as water content increased and (2) not significantly different between modern and modified modern uniforms, regardless of water content. FDNY field results confirmed these tests showing (1) significant decreases in neck burns (by 54%), ear burns (by 60%), and head burn totals (by 46%) wearing the hood and (2) no significant differences in upper or lower extremity burns wearing modern compared with modified modern uniforms. CONCLUSIONS: Based on combined laboratory and field results, we strongly recommend the use of modern thermal protective hoods and the modified modern uniform.

The impact of protective hoods and their water content on the prevention of head burns in New York City firefighters: laboratory tests and field results.

The New York City Fire Department (FDNY) is the largest fire department in the United States. In 1996, FDNY added the thermal protective hood to its modern protective uniform. The purpose of this study is to determine 1) the effectiveness of hoods in reducing head burns and 2) whether hood water content (dry, damp, or saturated) affects the level of thermal protection. Laboratory tests (radiant heat performance, thermal protective performance, and fully dressed manikin) and FDNY field results were used. Laboratory tests evaluated 4 different conditions (no hood, dry, damp, and saturated hoods) exposed to 4 different heat fluxes (0.1, 0.25, 0.5, and 2.0 cal/cm2/sec) equivalent to approximate air temperatures of 200, 400, 600, and 2,250 degrees F. Field results compared FDNY head burns during 3 winters wearing the hood to 3 winters without hood. Wearing a hood dramatically reduced head burns. This was true for all laboratory tests, at all heat flux exposures, and all hood water content conditions. At 0.1 cal/cm2/sec, dry hoods were superior to wet hoods. At all other heat flux exposures, thermal protection was either not significantly different between water content conditions or improved as water content increased. Confirming these laboratory tests, FDNY field results showed significant decreases in neck burns (by 54%), ear burns (by 60%), and head burn totals (by 46%). Based on combined laboratory and field results, we strongly recommend the use of modern thermal protective hoods.

Impact of a design modification in modern firefighting uniforms on burn prevention outcomes in New York City firefighters.

Our aim was to determine the impact of three different firefighting uniforms (traditional, modern, and modified modern) on the incidence and severity of thermal burn injuries, the major occupational injury affecting firefighters. Injury data were collected prospectively for the entire New York City Fire Department (FDNY) firefighting force wearing FDNY's traditional uniform (protective over-coat) from May 1, 1993 to August 31, 1993; FDNY's modern uniform (protective over-coat and over-pant) from May 1, 1995 to August 31, 1995; and FDNY's modified modern uniform (short sleeved shirt and short pants, rather than long-sleeved shirt and long pants, worn under firefighter's protective over-clothes) from May 1, 1998 to August 31, 1998. Outcome measures were burn incidence and severity. Adverse outcomes were heat exhaustion and cardiac events. During this 12-month study, 29,094 structural fires occurred. The incidence rate for upper extremity burns was 2341 per 100,000 fires and for lower extremity burns, 2076 per 100,000 fires. With the change from the traditional to modern uniform, the distribution of burns per fire decreased significantly (P = 0.001) for upper extremity burns (86%) and lower extremity burns (93%). With the change from traditional to modern uniform, days lost to medical leave for upper or lower extremity burns decreased by 89%. The majority of burns occurred at the lower arm and mid-leg, and the change to the modern uniform decreased such burns by 87% and 92%. Burn incidence and severity were not significantly affected by the change to the modified modern uniform. The distribution of heat exhaustion or cardiac events per fire was not significantly affected by the change from the traditional to modern uniform, and heat exhaustion was decreased (P < 0.001) by the change to the modified modern uniform. In conclusion, the modern uniform dramatically reduced burn incidence and severity without adverse impact. The modified modern uniform significantly reduced heat exhaustion without significantly affecting thermal protection.

Effects of fire fighting uniform (modern, modified modern, and traditional) design changes on exercise duration in New York City Firefighters.

Fire departments have replaced traditional uniforms with modern, more thermal protective gear. Although the new uniforms afford superior burn protection, they may reduce work time. Our purpose was to determine if exercise time was (1) reduced by wearing the modern versus traditional uniform, and (2) increased by a design change to a modified modern uniform (T-shirt and short pants rather than a shirt and long pants under the outer uniform). Male firefighters (n = 23; age 27 to 59) performed a maximum exercise test in gym clothes (maximal oxygen consumption = 46 +/- 9 ml/kg/min) and then returned on separate days to exercise using a moderately high intensity, constant work rate treadmill protocol while wearing fire fighting breathing apparatus and each of three uniforms. Firefighters exceeded anaerobic threshold by 1 minute and eventually reached or exceeded maximum heart rate and maximal oxygen consumption. Exercise time in modern (15 +/- 3 min) was significantly less than in traditional (18 +/- 5 min) uniform. Exercise time in modified modern (17 +/- 5 min) was significantly greater than in modern and not significantly different than in traditional uniforms. The rate of change in oxygen consumption and water loss were significantly affected by uniform type, with faster rates in modern compared with modified modern or traditional uniforms. These findings show the impact that design changes have on energy demands and exercise duration.

The incidence, prevalence, and severity of sarcoidosis in New York City firefighters.

OBJECTIVE: The etiology of sarcoidosis is unknown, but epidemiology suggests that environmental agents are a factor. Because firefighters are exposed to numerous toxins, we questioned whether sarcoidosis was increased in this cohort. SETTING: The New York City Fire Department (FDNY), employing > 11,000 firefighters and nearly 3,000 emergency medical services (EMS) health-care workers (HCWs). DESIGN: In 1985, FDNY initiated a surveillance program to determine the incidence, prevalence, and severity of biopsy-proven sarcoidosis in firefighters. In 1995, EMS HCWs were added as control subjects. RESULTS: Between 1985 and 1998, 4 prior cases and 21 new cases of sarcoidosis were found in FDNY firefighters. Annual incidence proportions ranged from 0 to 43.6/100,000, and averaged 12.9/100,000. On July 1, 1998, the point prevalence was 222/100,000. For EMS HCWs, annual incidence proportions were zero. Radiographic stage 0 or stage 1 sarcoidosis was found in 19 firefighters (76%), and stage 3 was found in 1 firefighter (4%). Pulmonary function (FVC, FEV(1), and diffusing capacity for carbon monoxide) was normal in 17 firefighters (68%), and reduced to

Impact of a modern firefighting protective uniform on the incidence and severity of burn injuries in New York City firefighters.

The New York City Fire Department (FDNY) is the largest fire department in the United States, with over 11,000 firefighters. In 1994, FDNY changed to a modern firefighting protective uniform. The major difference between traditional and modern uniforms is that modern uniforms include both protective over-coat and over-pant, whereas traditional uniforms include only the over-coat. Furthermore, modern uniforms are manufactured using improved thermal protective textiles that meet or exceed current National Fire Protection Association standards for structural firefighting. The purpose of this study was to determine the impact of the modern uniform on the incidence and severity of FDNY burn injuries. We also evaluated the incidence and severity of other non-burn injuries to determine whether there was serious adverse impact. The number of lower-extremity burns decreased by 85% when 2 years' experience while wearing the modern uniform was compared with 2 years while wearing the traditional uniform. Upper-extremity burns and head burns decreased by 65% and 40%, respectively. Severity indicators (days lost to medical leave, hospital admissions, and skin grafts) for lower- and upper-extremity burn injuries were all substantially reduced. This occurred without significant change in the incidence or severity of trunk burns, heat exhaustion, inhalation injuries (actually decreased), or cardiac events. The reduction in the incidence and severity of burn injuries, the major occupational injury affecting this workforce, has been so dramatic and without untoward effects that the introduction of the modern uniform must be characterized as a sentinel event in the history of firefighter health and safety.

Tuberculin skin test conversion rates in New York City Emergency Medical Service health care workers.

OBJECTIVE: To determine annual tuberculin skin test conversion (infection) rates for prehospital health care workers (EMTs and paramedics) in an urban environment with a high prevalence of Mycobacterium tuberculosis. METHODS: We conducted a prospective study of prehospital health care workers for the New York City EMS, EMS Employee Health Service, and the Fire Department Bureau of Health Service to determine the tuberculin skin test conversion rates. In 1992, all current and new EMS prehospital health care workers without a known history of a positive tuberculin reaction received a baseline tuberculin purified protein derivative (PPD) skin test. Thereafter, (January 1, 1993-December 31, 1996) all EMS health care workers who had negative PPD skin test results received annual tuberculin PPD skin tests. Tuberculin skin test conversion was defined as induration of 10 mm or greater in a worker with a documented prior negative test result. The PPD skin test reaction was measured by trained professional readers. RESULTS: A total of 7,290 PPD test results were read during this study. Compliance with annual testing was 75%. Annual tuberculin skin test conversion rates were 1.3% in 1993, .7% in 1994, .1% in 1995, and .2% in 1996 (average .5%). In a static subgroup with at least 15 years' seniority, compliance with annual testing was 100% and annual tuberculin skin test conversion rates were .5% in 1993, 0 in 1994, .5% in 1995, and 1.5% in 1996 (average .6%). CONCLUSION: Despite the high prevalence of M tuberculosis infection in New York City and the potential for difficulty in the use of respiratory precautions during emergency response operations, EMS prehospital health care workers have an annual tuberculin conversion rate that is relatively low compared with hospital-based health care workers.

Short-term vs long-term dexamethasone treatment: effects on rat diaphragm structure and function.

The effects of dexamethasone treatment duration (2.5 vs 10 weeks) on diaphragm myosin heavy chain isoforms, fiber types, and contractile characteristics were studied in male rats. Compared with ad libitum-fed and pair-fed controls, dexamethasone significantly decreased body weight, costal diaphragm weight, and the relative expression of myosin heavy chain isoform MHC-2B. Compared with pair-fed controls, the effect on MHC-2B expression was greater after 10 weeks than after 2.5 weeks. Type I and type II costal diaphragm fiber atrophy occurred, and type II fiber atrophy was greater after 10 weeks. Costal diaphragm-specific forces were not affected significantly by dexamethasone, regardless of the treatment duration or control group comparison. Fatigue resistance indexes were increased significantly after long term treatment compared with pair-fed controls and after both short-term and long-term treatment compared with ad libitum-fed controls. In conclusion, the effects of dexamethasone on MHC isoform phenotype expression, fiber type costal diaphragm atrophy, and fatigue resistance were dependent on treatment duration, with greater effects after long-term (10 weeks) treatment.

Emergency treatment of acute asthma with albuterol metered-dose inhaler plus holding chamber: how often should treatments be administered?

STUDY OBJECTIVE: To determine the optimal treatment interval for administering albuterol metered-dose inhaler (MDI) with a holding chamber to patients presenting to the emergency department (ED) with acute asthma. DESIGN: Prospective, randomized, double-blind study. SETTING: EDs of two affiliated teaching hospitals in the Bronx, NY. PATIENTS: One hundred adult patients with acute asthma and FEV1 <60% predicted of normal. INTERVENTIONS: At entry (T=0 min), eligible patients all openly received inhaled albuterol (six puffs) via MDI with a spacer. Subsequently, in a double-blind fashion, they received six puffs of albuterol or placebo with new MDIs and spacers at 30, 60, and 90 min such that group 1 (n=34) received albuterol every 30 min, group 2 (n=33) every 60 min, and group 3 (n=33) at 120 min only. FEV1 and vital signs were measured at T=0 and at 15, 30, 60, 90, and 120 min following initial treatment. Potassium levels were measured at T=0 and 120 min. Adverse events, the use of additional inhaled beta-agonists or systemic corticosteroids, and hospitalization rates were recorded. MEASUREMENTS AND RESULTS: At T=0, the groups did not differ in age, FEV1, or prescribed asthma medications. All groups showed significant improvement in FEV1 (p<0.05; T=120 vs 0 min). The conditions of groups 1 and 2 improved significantly more than those of group 3, but did not differ compared to each other. The mean+/-SEM change in FEV1 (T=120 vs 0 min) was 0.993+/-0.108, 0.858+/-0.135, and 0.321+/-0.056 L, respectively, for the three groups. Separate analysis for patients with FEV1% <40% or >40% predicted showed similar results. However, patients who initially were low responders to albuterol treatment (<15 percentage point increase at 15 min) improved significantly with 30-min treatments compared to the other two treatment regimens. Patients who initially responded with >15 percentage point increase in FEV1 at 15 min following initial albuterol inhalation benefited equally from 30- or 60-min treatments compared to 120 min. Potassium levels did not change significantly during the study. Adverse events and hospitalization rates were equivalent. After the conclusion of the study, group 3 patients required a greater number of beta-agonist treatments prior to eventual discharge from the ED. CONCLUSIONS: For acute asthma, albuterol MDI with a holding chamber can be given optimally at 60-min intervals with minimal adverse effects for the majority of patients. However, patients who initially demonstrate a low or poor bronchodilator response to albuterol should be given subsequent treatments at 30-min intervals. This will optimize care and conserve resources for patients who will benefit the most.

Gender-specific effects of dexamethasone treatment on rat diaphragm structure and function.

The effects of long-term dexamethasone treatment on diaphragm muscle were studied in female and male rats. Compared with pair-fed control animals, dexamethasone treatment did not significantly affect estrous cycling or peak serum estradiol levels; however, testosterone levels were significantly increased in females and decreased in males. Dexamethasone significantly reduced body and costal diaphragm weights, but to a lesser extent in females than in males. Reductions in diaphragm weight were proportional to reductions in body weight. In females and males, dexamethasone treatment significantly decreased diaphragm fiber (types I and II) cross-sectional area and the relative expression of myosin heavy chain isoform 2B. With the exception of type I fiber atrophy, these changes occurred to a lesser extent in females. Dexamethasone did not significantly affect specific forces. Dexamethasone significantly increased twitch one-half relaxation time and fatigue resistance indexes in males but not in females. In conclusion, the effects of long-term dexamethasone treatment were gender specific, with significantly fewer effects in females, and changes in serum testosterone levels were associated with these findings.

Short- and long-term effects of testosterone on diaphragm in castrated and normal male rats.

The effects of short- and long-term testosterone absence or treatment on the diaphragm were studied in castrated and sexually normal male rats. Compared with control rats (untreated normal males), testosterone absence or treatment did not significantly affect costal weight. In untreated castrated males, there were significant decreases in specific forces, type II fiber cross-sectional area, and myosin heavy chain (MHC) isoform 2B after 2.5 wk. In castrated males that received testosterone, there were significant increases in specific forces, type II total fiber proportional area, and relative expression of all adult diaphragm fast MHC isoforms (MHC-2all) after 2.5 wk. In normal males that received testosterone, the only significant finding was an increase in MHC-2B after 2.5 wk. Across all groups, there was close correlation between increases in maximum tetanic forces and MHC-2all. Changes in diaphragm function and composition were closely related to changes in serum testosterone levels at 2.5 wk. The lack of significant change in diaphragm function at 10 wk occurred despite changes in serum testosterone levels and diaphragm composition similar to those at 2.5 wk. These findings support our hypothesis that the effects of testosterone are dependent on basal circulating androgen levels and study duration.

Self-assessment of tuberculin skin test reactions by New York City firefighters: reliability and cost-effectiveness in an occupational health care setting.

OBJECTIVE: To determine whether self-assessment of purified protein derivative of tuberculin (PPD) skin test reactions, done using a simple two-choice approach, is an effective screening method for tuberculosis. DESIGN: Double-blind comparison between self-assessments and trained professional readings of PPD skin test reactions, done 72 hours after test administration. SETTING: The New York City Fire Department's Bureau of Health Services. PARTICIPANTS: 2011 New York City firefighters and fire officers were given PPD skin tests during a mandatory retraining course. Thirty-seven persons were excluded because of a history of a positive PPD skin test result or a bacille Calmette-Guérin vaccination. All others agreed to participate in testing and self-assessment done using simple written instructions. Self-assessment results were submitted just before trained professional readings were done. MEASUREMENTS: Self-assessments and trained professional readings of PPD skin test reactions. RESULTS: 1833 participants (91%) interpreted their test reactions as flat. Of these interpretations, 1824 (99.5%) matched the professional reading and 9 (0.5%) did not. One hundred seventy-eight participants (9%) interpreted their test reactions as not flat; 136 of these interpretations (76.4%) matched the professional reading and 42 (23.6%) did not (kappa = 0.828; lower 95% confidence limit = 0.790). The predictive value of a negative self-assessment reading was 99.5%, and the specificity was 97.7%. CONCLUSION: In this occupational health care setting, we follow (and recommend to others with similar populations) a tuberculin screening program based on self-assessment. Repeated tests with follow-up are required for all persons who do not report their results. All persons with self-assessments of "not flat" should return for readings by trained professionals, counseling, and treatment.

Effect of long-term undernutrition on male and female rat diaphragm contractility, fatigue, and fiber types.

The effects of long-term undernutrition (10 wk) on diaphragm contractility, fatigue, and fiber type proportions were studied in male and female rats. Contractility and fatigue resistance indexes were measured in an in vitro diaphragm costal strip preparation by using direct stimulation at 37 degrees C. Undernutrition allowed for continued growth in males and females but with substantial reductions in weight gain. Relative to control rats of the same sex, final weights were significantly lower in undernourished males (74 +/- 3%) than females (90 +/- 5%), but weight gain was not significantly different between undernourished males (58 +/- 5%) and females (60 +/- 3%). Only in males did undernutrition significantly reduce costal diaphragm weight (to 77 +/- 5% of control). Diaphragm forces, normalized for cross-sectional area, were not significantly different from male or female control values. Fatigue resistance indexes (fatigue/baseline force) were increased at all stimulation frequencies in undernourished males but not in undernourished females. Costal diaphragm atrophy, involving types I and II fibers, occurred in undernourished males but not in undernourished females. In conclusion, despite long-term undernutrition reducing weight gain to similar levels in males and females (relative to control), there was excellent preservation of diaphragm weight, function, and structure in females but, although diaphragm atrophy occurred, there was preserved contractility and increased fatigue resistance in males.

Effects of short-term and long-term androgen treatment on the diaphragm in male and female rats.

The effects of short-term (2.5 wk) and long-term (10 wk) testosterone propionate (2.5 mg/day; 5 days/wk) treatment on diaphragm contractility, fatigue resistance, and fiber type proportions were studied in male and female rats. Contractility and fatigue resistance indexes were measured in an in vitro diaphragm costal strip preparation by direct stimulation at 37 degrees C. The fatigue paradigm consisted of 30 trains/min at 5 Hz (50% duty cycle) for 10 min. Fatigue resistance indexes were calculated as postfatigue divided by baseline forces. In females but not males, testosterone treatment produced significant increases in body weight, costal diaphragm weight, and contractility and significant decreases in fatigue resistance indexes. The interaction between testosterone treatment and the duration of treatment was significant, with the increase in contractility (females) being significant after short-term but not long-term treatment. No significant difference in fiber type proportions or areas was observed, regardless of treatment duration or the preexperimental, basal circulating level of androgen.

Effects of long-term continuous respiratory resistive loading on rat diaphragm function and structure.

The effects of long-term (24- to 28-wk) continuous respiratory resistive loading on diaphragm mass, contractility, fatigue, and fiber types were studied in male rats. Increased respiratory resistance was produced by extratracheal banding, and results were compared with sham-operated pair-fed controls. At the time the animals were killed, banded tracheal segment internal diameter was reduced by 57% of control values. Diaphragm surface area and muscle mass (normalized for body mass) increased by 19% of control values. Isometric diaphragm contractility and fatigue resistance indexes were measured using an in vitro diaphragm costal strip preparation at 37 degrees C. Twitch and tetanic stimulations were evoked using direct stimulation. Compared with controls, baseline tensions (normalized for diaphragm cross-sectional area) were significantly decreased at low frequencies. Fatigue resistance (endurance) indexes were significantly increased at all frequencies. These findings were consistent with observed increases in number and cross-sectional area of type I (low-tension high-endurance) fibers. We conclude that the diaphragm adapts to chronic long-term resistive loads by sacrificing peak tensions for an increase in endurance capacity.

Effects of starvation and refeeding on adult male rat diaphragm contractility, fatigue, and fiber types.

The effects of 4.5 days of acute starvation, either alone or followed by refeeding (ad libitum), on diaphragm contractility, fatigue, and fiber types were studied in male rats. Contractility and fatigue resistance indexes were measured in an in vitro costal diaphragm strip preparation with direct stimulation at 37 degrees C. Compared with controls, starvation produced a 28 +/- 1% (P < 0.001) reduction in body weight and an 18 +/- 4% (P < 0.001) reduction in costal diaphragm weight. Twitch and tetanic tensions (normalized for weight or cross-sectional area) were not reduced by starvation. Starvation produced significant increases in fatigue resistance indexes after a 5-Hz stimulation paradigm but not after a 100-Hz paradigm, supporting the hypothesis that fatigue resistance is dependent on the energy demand of a given paradigm. The proportions of type I and type II fibers were similar between diaphragms of starved and control rats, but the cross-sectional area of type II fibers decreased significantly by 18 +/- 7% (P < 0.01). Thus, despite the significant decrease in diaphragm weight after starvation, contractility was preserved and fatigue resistance was increased (low-output paradigm). This is consistent with the decrease in type II fiber area. Refeeding restored all parameters so that there were no longer significant differences in body or diaphragm weight, contractility, fatigue, or fiber types.