Modelling the lifetime cost-effectiveness of radical prostatectomy, radiotherapy and active monitoring for men with clinically localised prostate cancer from median 10-year outcomes in the ProtecT randomised trial.

BACKGROUND: Optimal management strategies for clinically localised prostate cancer are debated. Using median 10-year data from the largest randomised controlled trial to date (ProtecT), the lifetime cost-effectiveness of three major treatments (radical radiotherapy, radical prostatectomy and active monitoring) was explored according to age and risk subgroups. METHODS: A decision-analytic (Markov) model was developed and informed by clinical input. The economic evaluation adopted a UK NHS perspective and the outcome was cost per Quality-Adjusted Life Year (QALY) gained (reported in UK£), estimated using EQ-5D-3L. RESULTS: Costs and QALYs extrapolated over the lifetime were mostly similar between the three randomised strategies and their subgroups, but with some important differences. Across all analyses, active monitoring was associated with higher costs, probably associated with higher rates of metastatic disease and changes to radical treatments. When comparing the value of the strategies (QALY gains and costs) in monetary terms, for both low-risk prostate cancer subgroups, radiotherapy generated the greatest net monetary benefit (£293,446 [95% CI £282,811 to £299,451] by D'Amico and £292,736 [95% CI £284,074 to £297,719] by Grade group 1). However, the sensitivity analysis highlighted uncertainty in the finding when stratified by Grade group, as radiotherapy had 53% probability of cost-effectiveness and prostatectomy had 43%. In intermediate/high risk groups, using D'Amico and Grade group > = 2, prostatectomy generated the greatest net monetary benefit (£275,977 [95% CI £258,630 to £285,474] by D'Amico and £271,933 [95% CI £237,864 to £287,784] by Grade group). This finding was supported by the sensitivity analysis. Prostatectomy had the greatest net benefit (£290,487 [95% CI £280,781 to £296,281]) for men younger than 65 and radical radiotherapy (£201,311 [95% CI £195,161 to £205,049]) for men older than 65, but sensitivity analysis showed considerable uncertainty in both findings. CONCLUSION: Over the lifetime, extrapolating from the ProtecT trial, radical radiotherapy and prostatectomy appeared to be cost-effective for low risk prostate cancer, and radical prostatectomy for intermediate/high risk prostate cancer, but there was uncertainty in some estimates. Longer ProtecT trial follow-up is required to reduce uncertainty in the model. TRIAL REGISTRATION: Current Controlled Trials number, ISRCTN20141297: http://isrctn.org (14/10/2002); ClinicalTrials.gov number, NCT02044172: http://www.clinicaltrials.gov (23/01/2014).

An analysis of the complementarity of ICECAP-A and EQ-5D-3 L in an adult population of patients with knee pain.

BACKGROUND: The ICECAP measures potentially offer a broader assessment of quality of life and well-being, in comparison to measures routinely used in economic evaluation, such as the EQ-5D-3 L. This broader assessment may allow measurement of the full effects of an intervention or treatment. Previous research has indicated that the ICECAP-O (for older people) and EQ-5D-3 L measure provide complementary information. This paper aims to determine similar information for the ICECAP-A (for the entire adult population) in terms of whether the measure is a substitute or complement to the EQ-5D-3 L. METHODS: Data from the BEEP trial - a multi-centre, pragmatic, randomised controlled trial - were used. Spearman rank correlations and exploratory factor analytic methods were used to assess whether ICECAP-A and EQ-5D-3 L are measuring the same, or different, constructs. RESULTS: A correlation of 0.49 (p < 0.01) was found between the ICECAP-A tariff score and the EQ-5D-3 L index. Using the pooled items of the EQ-5D-3 L and the ICECAP-A a two factor solution was optimal, with the majority of EQ-5D-3 L items loading onto one factor and the majority of ICECAP-A items onto another. CONCLUSION: The results presented in this paper indicate that ICECAP-A and EQ-5D-3 L are measuring two different constructs and provide largely different, complementary information. Results showed a similarity to results presented by Davis et al. using the ICECAP-O. TRIAL REGISTRATION: ISRCTN 93634563.

Type 1 Diabetes Duration Decreases Pulmonary Diffusing Capacity during Exercise.

BACKGROUND: Diabetes damages peripheral tissues; however, its effects on the lung are less known. Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (DM) and pulmonary capillary blood volume (VC), both of which are reduced in adults with type 1 diabetes (T1D). OBJECTIVE: We sought to determine if diabetes duration affects DLCO, DM, VC, and cardiac output (Q). METHODS: 24 T1D patients (10.7-52.8 years) and 24 non-diabetic controls were recruited and had DLCO, DM, VC, and Q measured at rest and during exercise (40, 70 and 90% VO2max). RESULTS: When stratified into two groups based on age (young, <20.6 years old), there were no significant differences in DLCO, DM, VC, or Q (all of which were normalized to body surface area [BSA]) in the young group or in the old group. When stratified by diabetes duration (short duration, 0.33-8.9 years vs. long duration, 9.6-28 years), the T1D patients in the long duration group had lower DLCO/BSA and DM/BSA compared to the controls (p < 0.05). There were no differences in any of the variables in the short duration group. CONCLUSIONS: This study has shown that duration of diabetes is associated with decrements in diffusing capacity and its components.

A longitudinal assessment of the responsiveness of the ICECAP-A in a randomised controlled trial of a knee pain intervention.

PURPOSE: The ICECAP-A is a simple measure of capability well-being for use with the adult population. The descriptive system is made up of five key attributes: Stability, Attachment, Autonomy, Achievement and Enjoyment. Studies have begun to assess the psychometric properties of the measure, including the construct and content validity and feasibility for use. This is the first study to use longitudinal data to assess the responsiveness of the measure. METHODS: This responsiveness study was completed alongside a randomised controlled trial comparing three physiotherapy-led exercise interventions for older adults with knee pain attributable to osteoarthritis. Anchor-based methodologies were used to explore the relationship between change over time in ICECAP-A score (the target measure) and change over time in another measure (the anchor). Analyses were completed using the non-value-weighted and value-weighted ICECAP-A scores. The EQ-5D-3L was used as a comparator measure to contextualise change in the ICECAP-A. Effect sizes, standardised response means and t tests were used to quantify responsiveness. RESULTS: Small changes in the ICECAP-A scores were seen in response to underlying changes in patients' health-related quality of life, anxiety and depression. Non-weighted scores were slightly more responsive than value-weighted scores. ICECAP-A change was of comparable size to change in the EQ-5D-3L reference measure. CONCLUSION: This first analysis of the responsiveness using longitudinal data provides some positive evidence for the responsiveness of the ICECAP-A measure. There is a need for further research in those with low health and capability, and experiencing larger underlying changes in quality of life.

Is lung diffusing capacity lower in expiratory flow limited women compared to non-flow limited women during exercise?

PURPOSE: Women tend to have smaller lungs than men of the same size as well as narrower airways compared to men when matched for the same lung size. Additionally, women with smaller airways relative to lung size are more likely to experience expiratory flow limitation (EFL) as well as exercise-induced arterial hypoxemia (EIAH). One of the possible causes of EIAH includes excessive widening in the alveolar-to-arterial oxygen pressure difference (A-aDO2) due to diffusion limitation. This study investigated if lung diffusing capacity (D LCO) is lower in women with EFL compared to non-flow limited (NEFL) women during exercise. METHODS: D LCO was measured using the rebreathing technique at rest and at 40, 60, and 80 % of [Formula: see text] on a treadmill in healthy women with EFL (n = 7; 21.6 ± 2.3) and without EFL (NEFL, n = 9; 21.2 ± 2.3). Arterial oxygen saturation was measured using pulse oximetry (SpO2). RESULTS: There was no difference (p > 0.05) in D LCO between groups at rest or during exercise; however, SpO2 was significantly lower in the EFL females compared to NEFL females during exercise. CONCLUSION: Due to the lack of differences in D LCO between women with EFL and without EFL, our results suggest that this is not a possible cause for the significant differences in SpO2 between the two groups.

Metabolic accommodation to running on a body weight-supported treadmill.

PURPOSE: Body weight-supported treadmill training using positive air pressure has become increasingly popular, but little is known about the metabolic adaptations to these treadmills. This study aimed to evaluate the existence and length of a metabolic accommodation period to running on a lower body positive pressure (LBPP) treadmill. METHODS: A total of eight recreational runners (5 males and 3 females) ran 15 min trials (5 min at 50, 70, and 90 % body weight) on the AlterG Anti-gravity(®) P200 treadmill. No verbal instruction was given on how to run on the device. Their trial pace corresponded to 70-80 % of their velocity measured at [Formula: see text]O2max on a standard treadmill. Trials were continued until no significant metabolic change was observed. Two-way repeated measures analysis of variance was used to analyze changes in [Formula: see text]O2 across trials and levels of unloading. RESULTS: Participants completed 7 trials. Comparing trial 1 to the average of trials 5, 6, and 7, [Formula: see text]O2 decreased from 29.6 ± 3.8 to 23.6 ± 4.4 ml/kg/min at 50 % body weight (~20 % reduction), from 33.7 ± 4.5 to 29.2 ± 5.1 ml/kg/min at 70 % body weight (~13 % reduction), and from 41.0 ± 7.7 to 36.6 ± 5.6 ml/kg/min at 90 % body weight (~11 % reduction). No significant reduction occurred after trial 4 at any level of support. CONCLUSIONS: An accommodation effect of running on a treadmill with LBPP was observed and reached after 60 min of running (4 trials of 15 min). The accommodation effect was the largest at the greatest level of body weight support. These data suggest the importance of an accommodation period for reliable measures of metabolic cost to be made.

Accuracy of unloading with the anti-gravity treadmill.

Body weight (BW)-supported treadmill training has become increasingly popular in professional sports and rehabilitation. To date, little is known about the accuracy of the lower-body positive pressure treadmill. This study evaluated the accuracy of the BW support reported on the AlterG "Anti-Gravity" Treadmill across the spectrum of unloading, from full BW (100%) to 20% BW. Thirty-one adults (15 men and 16 women) with a mean age of 29.3 years (SD = 10.9), and a mean weight of 66.55 kg (SD = 12.68) were recruited. Participants were weighed outside the machine and then inside at 100-20% BW in 10% increments. Predicted BW, as presented by the AlterG equipment, was compared with measured BW. Significant differences between predicted and measured BW were found at all but 90% through 70% of BW. Differences were small (<5%), except at the extreme ends of the unloading spectrum. At 100% BW, the measured weight was lower than predicted (mean = 93.15%, SD = 1.21, p < 0.001 vs. predicted). At 30 and 20% BW, the measured weight was higher than predicted at 35.75% (SD = 2.89, p < 0.001), and 27.67% (SD = 3.76, p < 0.001), respectively. These findings suggest that there are significant differences between reported and measured BW support on the AlterG Anti-Gravity Treadmill®, with the largest differences (>5%) found at 100% BW and the greatest BW support (30 and 20% BW). These differences may be associated with changes in metabolic demand and maximum speed during walking or running and should be taken into consideration when using these devices for training and research purposes.

Conversion table for running on lower body positive pressure treadmills.

Lower body positive pressure (LBPP) or antigravity treadmills are becoming increasingly popular in sports and rehabilitation settings. Running at a decreased body weight (BW) reduces metabolic cost, which can be offset by running at faster speeds. To date, however, little is known about how much faster someone must run to offset the reduced metabolic cost. This study aimed to develop a user-friendly conversion table showing the speeds required on an LBPP treadmill to match the equivalent metabolic output on a regular, non-LBPP, treadmill across a range of body weight supports. A total of 20 recreational runners (11 males, 9 females) ran multiple 3-minute intervals on a regular treadmill and then on an LBPP treadmill at 6 different BWs (50-100%, 10% increments). Metabolic outputs were recorded and matched between the regular and LBPP treadmill sessions. Using regression analyses, a conversion table was successfully created for the speeds from 6.4 to 16.1 km·h (4 to 10 mph) in 0.8 km·h (0.5 mph) increments on the regular treadmill and BW proportions of 50, 60, 70, 80, 90, and 100% on an LBPP treadmill. The table showed that a greater increase in speed on the LBPP treadmill was needed with more support (p < 0.001) but that the proportion increase was smaller at higher speeds (p < 0.001). This research has implications for coaches or practitioners using or prescribing training on an LBPP treadmill.

Oxygen consumption of elite distance runners on an anti-gravity treadmill®.

Lower body positive pressure (LBPP), or 'anti-gravity' treadmills® have become increasingly popular among elite distance runners. However, to date, few studies have assessed the effect of body weight support (BWS) on the metabolic cost of running among elite runners. This study evaluated how BWS influenced the relationship between velocity and metabolic cost among 6 elite male distance runners. Participants ran three- 16 minute tests consisting of 4 stages of 4 minutes at 8, 7, 6 and 5 min·mile(-1) pace (3.35, 3.84, 4.47 and 5.36 m·s(-1)), while maintaining an aerobic effort (Respiratory Exchange Ratio ≤1.00). One test was run on a regular treadmill, one on an anti-gravity treadmill with 40% BWS and one with 20% BWS being provided. Expired gas data were collected and regression equations used to determine and compare slopes. Significant decreases in oxygen uptake (V̇O2) were found with each increase in BWS (p < 0.001). At 20% BWS, the average decrease in net VO2 was greater than proportional (34%), while at 40% BWS, the average net reduction in VO2 was close to proportional (38%). Across velocities, the slope of the relationship between VO2 and velocity (ΔV̇O2/Δv) was steeper with less support. The slopes at both the 20% and 40% BWS conditions were similar, especially when compared to the regular treadmill. Variability in VO2 between athletes was much greater on the LBPP treadmill and was greater with increased levels of BWS. In this study we evaluated the effect of body weight support on V̇O2 among elite distance runners. We have shown that oxygen uptake decreased with support, but not in direct proportion to that support. Further, because of the high variability in oxygen uptake between athletes on the LBPP treadmill, prediction equations may not be reliable and other indicators (heart rate, perceived exertion or directly measured oxygen uptake) should be used to guide training intensity when training on the LBPP treadmill. Key pointsWith increasing amounts of body weight-support (BWS), the slope of the relationship between velocity and oxygen consumption (ΔVO2/Δv) decreases significantly. This means the change in oxygen consumption (VO2) is significantly smaller over a given change in velocity at higher amounts of BWS.There is a non-linear decrease in VO2 with increasing BWS. As such, with each increment in the amount of BWS provided, the reduction in VO2 becomes increasingly smaller.This paper provides first of its kind data on the effects of BWS on the cost of running among highly trained, elite runners. The outcomes of this study are in line with previous findings among non-elite runners.

Prior maximal exercise decreases pulmonary diffusing capacity during subsequent exercise.

Pulmonary diffusion (DLCO) increases during exercise due to greater pulmonary capillary volume (Vc) and membrane diffusing capacity (DM). However, after heavy exercise there is a reduction in resting DLCO. It is unclear whether this post-exercise effect will attenuate the normal increase in DLCO, Vc and DM during subsequent exercise and whether this affects SpO2 (pulse oximeter). DLCO, Vc, DM, cardiac output and SpO2 were measured at rest, moderate (~70% VO2peak) and heavy (~90 VO2peak) exercise in 9 subjects during 2 sessions separated by ~90 min. DLCO, Vc and DM increased during exercise (P<0.05). DLCO (P<0.05) and Vc (P<0.10), but not DM or SpO2 were lower in session 2 compared to the first. Reductions in DLCO and Vc appeared to be smallest during rest (1-4%) and greatest at high-intensity exercise (8-20%), but the interaction was not significant. SpO2 decreased by 4.9% and 5.1% from rest to high-intensity exercise during the first and second exercise bout, but these changes were not different. These data confirm that a bout of high-intensity exercise reduces DLCO and Vc, and may indicate that these changes are exacerbated during subsequent high-intensity exercise. Despite these changes, SpO2 was not affected by previous exercise.

Fuel oxidation in relation to walking speed: influence of gradient and external load.

People intuitively walk at a speed that minimizes energy cost per meter. Therefore, the selective advantages of energetic efficiency are thought to drive individuals' preferred walking speed (PWS). This presumption disregards fuel partitioning, which may, in fact, be significant due to the disparate sizes of the carbohydrate (CHO) and fat reservoirs, coupled with the necessity of CHO for high intensity exercise. Potentially, PWS may reflect CHO conservation more than energetic efficiency per se. This study was designed to determine if PWS over a variety of conditions conforms to the CHO sparing hypothesis. Six subjects walked on a treadmill at five speeds: their PWS and speeds 0.45 and 0.22 m/s below and above PWS, under loads of 0, 10, and 20% of body weight, as well as at grades of -6.25, 0 and +6.25%. Oxygen consumption, carbon dioxide production and respiratory exchange ratio were measured over each 10 min bout to calculate total energy, CHO and fat usage. The subjects' mean (±SD) unloaded, level PWS was 1.32 ± 0.11 m/s. PWS was reduced by the 20% load and uphill grade, but not affected by the 10% load or downhill grade. Carbohydrate provided ≥50% of required energy in all conditions. The CHO oxidation rate was related to speed such that the gain was greater at speeds above than below the PWS; however, differences in CHO oxidation between conditions did not correspond to differences in PWS. We conclude that CHO sparing is not the primary determinant of PWS during externally loaded or grade walking.

The effect of core exercises on transdiaphragmatic pressure.

Abdominal exercises, such as sit ups and leg lifts, are used to enhance strength of the core muscles. An overlooked aspect of abdominal exercises is the compression the abdomen, leading to increased diaphragmatic work. We hypothesized that core exercises would produce a variety of transdiaphragmatic pressures. We also sought to determine if some of the easy exercises would produce pressures sufficient for a training stimulus to the diaphragm. We evaluated the effect of 13 different abdominal exercises, ranging in difficulty, on transdiaphragmatic pressure (Pdi), an index of diaphragmatic activity. Six healthy subjects, aged 22 to 53, participated. Each subject was instrumented with two balloon-tipped catheters to obtain gastric and esophageal pressures, from which Pdi was calculated. Prior to initiating the exercises, each subject performed a maximal inspiratory pressure (MIP) maneuver. Resting Pdi was also measured. The exercises were performed from least to most difficult, with five repetitions each. There was a significant difference between the exercises and the MIP Pdi, as well as between the exercises and resting Pdi (p < 0.001). The exercises stratified into three Pdi levels. Seven of the exercises yielded Pdi ≥ 50% of the Pdi during the MIP maneuver, which may provide a training stimulus to the diaphragm if used as a regular exercise. The Pdi measurements also provide insight into diaphragm recruitment during different core exercises, and may aid in the design of exercises to improve diaphragm strength and endurance. Key pointsPlease provide 3-5 bullet points of the study.The study examined the effect of different core exercises of varying difficulty on activation of the diaphragm.We found that the exercises yielded different pressures, some of which were greater than 50% of the pressures generated during a maximal inspiratory maneuver.The difficulty of the exercise was not always correlated with the magnitude of the pressure.Some of these exercises should be easy enough for subjects in rehabilitation programs to perform and still generate high enough pressures to help strengthen the diaphragm.

Repeated abdominal exercise induces respiratory muscle fatigue.

Prolonged bouts of hyperpnea or resisted breathing are known to result in respiratory muscle fatigue, as are primarily non respiratory exercises such as maximal running and cycling. These exercises have a large ventilatory component, though, and can still be argued to be respiratory activities. Sit-up training has been used to increase respiratory muscle strength, but no studies have been done to determine whether this type of non-respiratory activity can lead to respiratory fatigue. The purpose of the study was to test the effect of sit-ups on various respiratory muscle strength and endurance parameters. Eight subjects performed pulmonary function, maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) measurements, and an incremental breathing test before and after completing a one-time fatiguing exercise bout of sit-ups. Each subject acted as their own control performing the same measurements 3-5 days following the exercise bout, substituting rest for exercise. Following sit-up induced fatigue, significant decreases were measured in MIP [121.6 ± 26 to 113.8 ± 23 cmH2O (P <0.025)], and incremental breathing test duration [9.6 ± 1.5 to 8.5 ± 0.7 minutes (P <0.05)]. No significant decreases were observed from control pre-test to control post-test measurements. We conclude that after a one-time fatiguing sit-up exercise bout there is a reduction in respiratory muscle strength (MIP, MEP) and endurance (incremental breathing test duration) but not spirometric pulmonary function. Key pointsExercise that is primarily abdominal in nature can lead to inspiratory muscle fatigue.This exercise also can cause expiratory muscle fatigue, which would be expected.This study shows a link between a predominantly non-respiratory exercise and decreases in both respiratory muscle strength and endurance.

Are meticillin-resistant Staphylococcus aureus bloodstream infection targets fair to those with other types of healthcare-associated infection or cost-effective?

UK National Health Service Trust hospitals are required to report meticillin-resistant Staphylococcus aureus bloodstream infection (MRSA BSI) and also have targets for their reduction. We argue that the MRSA BSI target influences local priorities, and that the high priority given to control of MRSA BSI is not fair or cost-effective when account is taken of the much larger number of patients who develop other types of serious hospital-acquired infection. Reasons for infection control priorities should be made explicit. Use of a formal and reasoned process of priority setting would also counteract the potential distortion of local priorities by national targets.

Obesity and pulmonary function in Navajo and Hopi children.

BACKGROUND: Although several reports have shown an adverse cardiovascular and metabolic risk profile associated with childhood obesity, few reports have examined the effects of childhood obesity on pulmonary function. OBJECTIVE: The purpose of this study was to examine the influence of obesity on pulmonary function in Navajo and Hopi children. METHODS: Subjects included 256 (110 males, 146 females) Hopi children 6-12 years of age and 557 (274 males, 283 females) Navajo children 6-12 years of age (N = 813). The body mass index was used to classify subjects as normal weight, overweight, or obese on the basis of international reference values. Forced vital capacity (FVC), forced expired volume in one second (FEV1), FEV1% (FEV1 to FVC ratio; FEV1/FVC), and forced expiratory flow between 25%-75% of vital capacity (FEF25-75) were determined according to the American Thoracic Society recommendations. RESULTS: Approximately 26% of Navajo and Hopi children were defined as overweight additional 16% (14.6% of boys and 17.7% of girls) were defined as obese. In general, the patterns showed an increase in pulmonary function between normal weight and overweight children and a decrease in pulmonary function of obese children. Significant differences among groups existed for FEV1% and FEF25-75 in boys and FVC and FEV1 in girls. CONCLUSIONS: The results indicate the pulmonary consequences of obesity in children and provide further evidence of the adverse consequences of pediatric obesity among Native Americans.

Spinal cord injury and contractile properties of the human tibialis anterior.

The purpose of this study was to evaluate contractile properties of the tibialis anterior of paralyzed and non-paralyzed subjects. The contractile properties and the fatigability of the tibialis anterior muscle (TA) were tested in 8 spinal cord injured (SCI) and 8 control individuals. The TA was stimulated at frequencies from 10 to 100 Hz to determine a force-frequency curve. A fatigue bout was also performed by stimulating the muscle at 40 Hz every two seconds for three minutes. The SCI muscles produced lower forces overall, but higher forces relative to maximal force at lower frequencies, shifting the force-frequency curve of the SCI group to the left. The half-relaxation time and rate of relaxation at 40 Hz was slower in the SCI muscles than in the control muscles (127 ± 18.4 ms vs. 78 ± 8.7 ms, 6 ± 1.5 kg·s(-1) 20 ± 4.1 kg·s(-1) respectively). In addition, force loss and slowing of relaxation during the fatigue protocol were not significantly different between the two groups due to high variability in the SCI group. The TA of the SCI group had slower contractile properties than the control group and fatigability was not significantly different between the SCI and control group. The protocol may be useful to assess training effects during rehabilitation of paralyzed muscle. Key PointsStimulated contractions were tested on controls and spinal cord injured subjects to determine differences in contractile characteristics of the tibialis anterior (ta) muscle.Forces were lower in the ta of the spinal cord injured subjects compared to the controls.All indices of contractile speed were slower in the spinal cord injured subjects than in the controls.The reason for possible differences in contractile capabilities and other biochemical indices of contractile speed in disused muscle need to be further evaluated.

The effect of football shoulder pads on pulmonary function.

Restriction of expansion of the lungs or chest wall impedes inflation of the lungs during inhalation. Functional changes occurring during such restriction include reduced pulmonary and/or chest wall compliance, decreases in pulmonary function, and ultimately a decrease in exercise performance. Such restriction can be seen in several pathologic conditions such as scoliosis or obesity, as well as occupational situations such as the wearing of bullet-proof vests. This study investigated the hypothesis that tightened football shoulder pads produce decrements in pulmonary function similar to those shown in previous studies involving other external chest-wall restricting devices. In this study, 24 subjects, all members of a collegiate division IAA football team and used to wearing the pads, performed standard pulmonary function tests while wearing no pads (control, CTRL), wearing pads that were not secured (pads loose, PL) and while wearing pads secured "game-tight" (pads tight, PT). The data showed that both forced vital capacity (FVC) and forced expiratory volume in one second (FEV1.0) were significantly decreased in the PT condition compared to either the CTRL or PL condition, with no changes in the FEV1.0/FVC ratio or peak expiratory flow rate. These results are consistent with a restrictive condition and support our hypothesis that tightened shoulder pads reduce pulmonary function. Further studies remain to be performed to determine whether these changes lead to decreased exercise performance and whether equipment modifications can be made to limit alterations in pulmonary function without decreasing the protective value of the pads. Key PointsThe shoulder pads used in American football extend to the xyphoid process and may provide a restriction to breathing. This was tested in the present study in 24 college-level football players with normal resting pulmonary function.The results showed that there was a decrease in FVC of approximately 150 ml and a similar decrease in FEV1.0.Similar decreases in pulmonary function have been shown to provide a limitation to exercise capacity in otherwise healthy adults.Further study is needed to determine whether these changes lead to decrements in performance.

Diaphragmatic responses to graded stimulation of pulmonary C-fibers with capsaicin.

It has been suggested that pulmonary C-fiber stimulation is responsible for the rapid shallow breathing that accompanies pulmonary edema. However, pulmonary C-fiber stimulation also causes apnea. To determine whether it was possible for both responses to occur from one stimulus, we infused varying concentrations of capsaicin (a compound that selectively stimulates C-fiber receptors in the dog) into an in situ vascularly isolated dog lung and measured rates and strengths of diaphragmatic contractions with a strain gauge sutured to the diaphragm and electromyogram electrodes implanted in the diaphragm. There was a dose response to capsaicin in that increased doses were related directly with the duration of cessation of diaphragmatic contractions (2-100 s) and inversely with the latency from the start of stimulation to the beginning of the cessation of diaphragmatic contractions (100-5 s). There was no evidence, however, of rapid shallow breathing in this set of experiments. Either a gradual return to normal rate from prolonged contraction intervals or no change in contraction rate was seen, depending on capsaicin concentration. We conclude that the primary diaphragmatic response to pulmonary C-fiber stimulation is a cessation of diaphragmatic contractions rather than rapid shallow contractions.

Inhibition of skeletal muscle activity by lung expansion in the dog.

The ability of lung expansion to reflexly decrease skeletal muscle activity was tested in anesthetized dogs. In animals whose left lung was vascularly isolated but neurally intact, the left lung was inflated statically to 40 cmH2O pressure or cyclically with tidal volumes of 10, 20, or 30 ml/kg. Responses to these stimuli were compared with those of injecting 120 or 240 micrograms capsaicin into the left pulmonary artery. Skeletal muscle activity was assessed from the electromyogram (EMG) response of the left hindlimb muscles and from the monosynaptic reflex response to a periodic patellar tendon tap of the right leg (knee jerk). Static inflation and cyclic inflations above 10 ml/kg resulted in significant decreases in both EMG and knee jerk responses. The results indicate that lung expansion is capable of initiating a reflex decrease in skeletal muscle activity. Capsaicin injections caused responses that were similar to those caused by lung inflation, suggesting that at least part of this skeletal muscle reflex response to lung inflation can be attributed to the stimulation of pulmonary C-fibers that could be caused by stretch of the lung.

Cardiac output and O2 consumption during inspiratory threshold loaded breathing.

In this study, noninvasive measurements of cardiac output and O2 consumption were performed to estimate the blood flow to and efficiency of the respiratory muscles that are used in elevated inspiratory work loads. Five subjects were studied for 4.5 min at a respiratory rate of 18 breaths/min and a duty cycle of 0.5. Studies were performed at rest without added respiratory loads and at elevated inspiratory work loads with the use of an inspiratory valve that permitted flow only when a threshold pressure was maintained. Cardiac output and O2 consumption were calculated using a rebreathing technique. Respiratory muscle blood flow and O2 consumption were estimated as the difference between resting and loaded breathing. Work of breathing was calculated by integrating the product of mouth pressure and volume. Increases in cardiac output and O2 consumption in response of 4.5 min loaded breathing averaged 1.84 l/min and 108 ml/min, respectively. No increases were seen in response to 20-s loaded breathing. In a separate series of experiments on four subjects, though, cardiac output increased for the first 2 min then leveled off. These results indicate that the increase in cardiac output was a metabolic effect of the increased work load and was not caused primarily by the influence of the highly negative intrathoracic pressure on venous return. Efficiency of the respiratory muscles during inspiratory threshold loading averaged 5.9%, which was similar to measurements of efficiency of respiratory muscles using whole-body O2 consumption that have been reported previously in humans and in dogs.