Saint Francis Hospital & Medical Center

GH and IGF-I are important regulators of bone homeostasis and are central to the achievement of normal longitudinal bone growth and bone mass. Although GH may act directly on skeletal cells, most of its effects are mediated by IGF-I, which is present in the systemic circulation and is synthesized by peripheral tissues. The availability of IGF-I is regulated by IGF binding proteins. IGF-I enhances the differentiated function of the osteoblast and bone formation. Adult GH deficiency causes low bone turnover osteoporosis with high risk of ver-tebral and nonvertebral fractures, and the low bone mass can be partially reversed by GH replacement. Acromegaly is characterized by high bone turnover, which can lead to bone loss and vertebral fractures, particularly in patients with coexistent hypogonadism. GH and IGF-I secretion are decreased in aging individuals, and abnormalities in the GH/IGF-I axis play a role in the pathogenesis of the osteoporosis of anorexia nervosa and after glucocorticoid exposure. (Endocrine Reviews 29: 535-559, 2008) I. Introduction II. The Growth Hormone (GH)/Insulin-Like Growth Factor-I (IGF-I) Axis III. Mechanisms of GH and IGF-I Action in Bone A. GH B. IGF-I C. IGF binding proteins (IGFBPs) IV. Skeletal Manifestations of GH Deficiency and Excess in Humans A. Adult growth hormone deficiency (GHD) B. Skeletal effects of recombinant human GH (rhGH) in adult-onset GHD C. Skeletal manifestations of acromegaly V. Skeletal Manifestations of Selected Diseases with Abnormal GH/IGF-I Axis A. Postmenopausal and senile osteoporosis B. Anorexia nervosa C. Glucocorticoid-induced osteoporosis VI. Conclusions

Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic proteins (BMP) are unique because they induce the differentiation of mesenchymal cells toward cells of the osteoblastic lineage and also enhance the differentiated function of the osteoblast. However, the activity of BMPs needs to be tempered by intracellular and extracellular antagonists. BMPs bind to specific receptors and signal by phosphorylating the cytoplasmic proteins mothers against decapentaplegic (Smad) 1 and 5, which form heterodimers with Smad 4, and after nuclear translocation regulate transcription. BMP antagonists can be categorized as pseudoreceptors that compete with signaling receptors, inhibitory Smads that block signaling, intracellular binding proteins that bind Smad 1 and 5, and factors that induce ubiquitination and proteolysis of signaling Smads. In addition, a large number of extracellular proteins that bind BMPs and prevent their binding to signaling receptors have emerged. They are the components of the Spemann organizer, noggin, chordin, and follistatin, members of the Dan/Cerberus family, and twisted gastrulation. The antagonists tend to be specific for BMPs and are regulated by BMPs, indicating the existence and need of local feedback mechanisms to temper BMP cellular activities.

Antiresorptive agents help to restore skeletal balance by reducing bone turnover, primarily at the tissue level. Another therapeutic approach is to enhance bone formation with the use of anabolic agents, which differ fundamentally from antiresorptive drugs in their primary mechanism of action. This article reviews the mechanisms of polypeptide anabolic agents and strontium as potential therapeutic options for osteoporosis.

Transforming growth factor beta (TGF beta) stimulates cell replication in fetal rat calvariae, and studies with isolated bone cells suggest that the primary mitogenically responsive cell is of the osteoblast lineage. The effect of TGF beta on bone cell replication is biphasic and depends on both the TGF beta concentration and cell density in monolayer culture. After 23 h of treatment, DNA synthesis in confluent cells is progressively enhanced by 0.15-15 ng/ml TGF beta; but in subconfluent cells, 15 ng/ml is less than maximal; and in sparse cell cultures, it is inhibitory. At all cell densities, however, 15 ng/ml TGF beta stimulates collagen synthesis, an effect which is more pronounced when DNA synthesis rates are declining. Furthermore, 1 mM hydroxyurea, which blocks the mitogenic effect of TGF beta by 85%, only minimally influences the increase in collagen synthesis. Cytoplasmic slot blot analysis reveals alterations in the amount of type I collagen mRNA in TGF beta-treated cells, suggesting that control is exerted, at least in part, at the transcriptional level. Since TGF beta is found in culture medium conditioned by bone explants and in bone tissue extracts, these results support that TGF beta is an important and multifunctional autocrine regulator of bone formation.

UNLABELLED: We used microCT and histomorphometry to assess age-related changes in bone architecture in male and female C57BL/6J mice. Deterioration in vertebral and femoral trabecular microarchitecture begins early, continues throughout life, is more pronounced at the femoral metaphysis than in the vertebrae, and is greater in females than males. INTRODUCTION: Despite widespread use of mice in the study of musculoskeletal disease, the age-related changes in murine bone structure and the relationship to whole body BMD changes are not well characterized. Thus, we assessed age-related changes in body composition, whole body BMD, and trabecular and cortical microarchitecture at axial and appendicular sites in mice. MATERIALS AND METHODS: Peripheral DXA was used to assess body composition and whole body BMD in vivo, and microCT and histomorphometry were used to measure trabecular and cortical architecture in excised femora, tibia, and vertebrae in male and female C57BL/6J mice at eight time-points between 1 and 20 mo of age (n = 6-9/group). RESULTS: Body weight and total body BMD increased with age in male and female, with a marked increase in body fat between 6 and 12 mo of age. In contrast, trabecular bone volume (BV/TV) was greatest at 6-8 wk of age and declined steadily thereafter, particularly in the metaphyseal region of long bones. Age-related declines in BV/TV were greater in female than male. Trabecular bone loss was characterized by a rapid decrease in trabecular number between 2 and 6 mo of age, and a more gradual decline thereafter, whereas trabecular thickness increased slowly over life. Cortical thickness increased markedly from 1 to 3 mo of age and was maintained or slightly decreased thereafter. CONCLUSIONS: In C57BL/6J mice, despite increasing body weight and total body BMD, age-related declines in vertebral and distal femoral trabecular bone volume occur early and continue throughout life and are more pronounced in females than males. Awareness of these age-related changed in bone morphology are critical for interpreting the skeletal response to pharmacologic interventions or genetic manipulation in mice.

The effects of insulin-like growth factor-I (IGF-I) and insulin on bone matrix synthesis and bone cell replication were studied in cultured 21-day-old fetal rat calvariae. Histomorphometry techniques were developed to measure the incorporation of [2,3-3H]proline and [methyl-3H]thymidine into bone matrix and bone cell nuclei, respectively, using autoradiographs of sagittal sections of calvariae cultured with IGF-I, insulin, or vehicle for up to 96 h. To confirm an effect on bone formation, IGF-I was also studied for its effects on [3H]proline incorporation into collagenase-digestible protein (CDP) and noncollagen protein and on [3H]thymidine incorporation into acid-precipitable material (DNA). IGF-I at 10(-9)-10(-7) M significantly increased the rate of bone matrix apposition and CDP after 24 h by 45-50% and increased cell labeling by 8-fold in the osteoprogenitor cell zone, by 4-fold in the osteoblast cell zone, and by 2-fold in the periosteal fibroblast zone. Insulin at 10(-9)-10(-6) M also increased matrix apposition rate and CDP by 40-50%, but increased cell labeling by 2-fold only at a concentration of 10(-7) M or higher and then only in the osteoprogenitor cell zone. When hydroxyurea was added to IGF-I-treated bones, the effects of IGF-I on DNA synthesis were abolished, but the increase in bone matrix apposition induced by IGF-I was only partly diminished. In conclusion, IGF-I stimulates matrix synthesis in calvariae, an effect that is partly, although not completely, dependent on its stimulatory effect on DNA synthesis.

PTH was studied for its effects on bone formation in cultured rat calvariae. 0.01-10 nM PTH stimulated [3H]thymidine incorporation into DNA by up to 4.8-fold. Although continuous treatment with PTH for 24-72 h inhibited [3H]proline incorporation into collagen, transient (24 h) treatment enhanced [3H]proline incorporation into collagen 24-48 h after the hormone was removed. The collagen stimulated by PTH was type I and the effect was observed in the periosteum-free bone and was not blocked by hydroxyurea. Furthermore, treatment with 1-100 nM PTH for 24 h increased insulin-like growth factor (IGF) I concentrations by two to fourfold, and an IGF I antibody prevented the PTH stimulation of collagen synthesis, but not its mitogenic effect. In conclusion, continuous treatment with PTH inhibits calvarial collagen, whereas transient treatment stimulates collagen synthesis, and the stimulatory effect is mediated by local production of IGF I.

This European Respiratory Society (ERS) statement provides a comprehensive overview on physical activity in patients with chronic obstructive pulmonary disease (COPD). A multidisciplinary Task Force of experts representing the ERS Scientific Group 01.02 "Rehabilitation and Chronic Care" determined the overall scope of this statement through consensus. Focused literature reviews were conducted in key topic areas and the final content of this Statement was agreed upon by all members. The current knowledge regarding physical activity in COPD is presented, including the definition of physical activity, the consequences of physical inactivity on lung function decline and COPD incidence, physical activity assessment, prevalence of physical inactivity in COPD, clinical correlates of physical activity, effects of physical inactivity on hospitalisations and mortality, and treatment strategies to improve physical activity in patients with COPD. This Task Force identified multiple major areas of research that need to be addressed further in the coming years. These include, but are not limited to, the disease-modifying potential of increased physical activity, and to further understand how improvements in exercise capacity, dyspnoea and self-efficacy following interventions may translate into increased physical activity. The Task Force recommends that this ERS statement should be reviewed periodically (e.g. every 5-8 years).

INTRODUCTION: In the spring of 2017, the American Society for Parenteral and Enteral Nutrition (ASPEN) Parenteral Nutrition Safety Committee and the Clinical Practice Committee convened an interprofessional task force to develop consensus recommendations for identifying patients with or at risk for refeeding syndrome (RS) and for avoiding and managing the condition. This report provides narrative review and consensus recommendations in hospitalized adult and pediatric populations. METHODS: Because of the variation in definitions and methods reported in the literature, a consensus process was developed. Subgroups of authors investigated specific issues through literature review. Summaries were presented to the entire group for discussion via email and teleconferences. Each section was then compiled into a master document, several revisions of which were reviewed by the committee. FINDINGS/RECOMMENDATIONS: This group proposes a new clinical definition, and criteria for stratifying risk with treatment and screening strategies. The authors propose that RS diagnostic criteria be stratified as follows: a decrease in any 1, 2, or 3 of serum phosphorus, potassium, and/or magnesium levels by 10%-20% (mild), 20%-30% (moderate), or >30% and/or organ dysfunction resulting from a decrease in any of these and/or due to thiamin deficiency (severe), occurring within 5 days of reintroduction of calories. CONCLUSIONS: These consensus recommendations are intended to provide guidance regarding recognizing risk and identifying, stratifying, avoiding and managing RS. This consensus definition is additionally intended to be used as a basis for further research into the incidence, consequences, pathophysiology, avoidance, and treatment of RS.

Insulin-like growth factors I and II (IGF-I and -II) are polypeptides secreted by skeletal cells and are considered regulators of bone formation. IGF-I and -II were studied for their effects on collagen synthesis and degradation in cultures of intact fetal rat calvariae and on type I collagen transcript levels in osteoblast-enriched (Ob) cells from fetal rat parietal bone. IGF-I and -II increased [3H]proline incorporation into type I collagen independently of their effect on cell replication. IGF-I and -II also decreased collagen degradation in calvarial cultures. Both factors had similar actions, although IGF-I stimulated collagen synthesis at 10 nM, and IGF-II at 30 nM. In Ob cells, IGF-I and -II also increased [3H]proline incorporation into type I collagen, but the effect was seen at 100 nM, and neither factor decreased collagen degradation. Slot blot analysis of IGF-I- and IGF-II-treated cells, using a rat type I collagen cDNA probe, revealed an increase in type I collagen transcripts. In conclusion, IGF-I and -II increase bone collagen synthesis and decrease collagen degradation in cultures of intact calvariae; the effect on collagen synthesis correlates with an increase in transcript levels in Ob cells.

Glucocorticoids cause profound effects on bone cell replication, differentiation, and function. Glucocorticoids increase bone resorption by stimulating osteoclastogenesis by increasing the expression of RANK ligand and decreasing the expression of its decoy receptor, osteoprotegerin. In accordance with the increase in bone resorption, glucocorticoids stimulate the expression of collagenase 3 by posttranscriptional mechanisms. The most significant effect of glucocorticoids in bone is an inhibition of bone formation. This is because of a decrease in the number of osteoblasts and their function. The decrease in cell number is secondary to a decrease in osteoblastic cell replication and differentiation, and an increase in the apoptosis of mature osteoblasts. Glucocorticoids decrease osteoblastic function directly and indirectly through the modulation of growth factor expression, receptor binding, or binding protein levels. Clinically, patients with glucocorticoid-induced osteoporosis (GIOP) develop bone loss in the first few months of glucocorticoid exposure, and modest doses of glucocorticoids increase the risk of fractures of the spine and hip. Bisphosphonates inhibit bone resorption and prevent and revert the bone loss that follows glucocorticoid exposure. Anabolic agents, such as parathyroid hormone, stimulate bone formation and can increase bone mass in GIOP.

Insulinlike growth Factor I (IGF I), a growth hormone-dependent peptide or somatomedin, was studied for its effects on bone formation by examining the synthesis of DNA, collagen, and noncollagen protein in cultures of 21-d fetal rat calvaria. IGF I caused a dose-dependent stimulation of the incorporation of [3H]thymidine into DNA at concentrations of 0.1--100 nM; the effect appeared after 6 h, was maximal at 12 h, and was sustained for 96 h. IGF I also increased the bone DNA content, IGF I at 0.1--3 nM had a small stimulatory effect on the incorporation of [3H]proline into collagenase-digestible protein (CDP) whereas 30 nM IGF I caused a two- to threefold increment and had a maximal effect. A smaller effect on the labeling of noncollagen protein (NCP) was also observed. The effect of CDP and NCP appeared and was maximal after 12 h and was sustained for 96 h. IGF I increased the total collagen content of bones. The IGF I stimulatory effect on the incorporation of [3H]thymidine was seen in both the periosteum and periosteum-free calvarium, whereas that on the labeling of CDP was seen only in the central, osteoblastic-rich, non-periosteal bone. Histological sections showed a 10-fold increase in the mitotic index after Colcemid arrest in IGF I-treated bones, the mitoses were equally distributed in the periosteum and central portions of the calvarium. Insulin had a stimulatory effect on the incorporation of [3H]proline into CDP and NCP and 1 nM--1 microM similar to the effect of IGF I. In contrast, high insulin concentrations (0.1 and 1 microM) were required to increase the incorporation of [3H]thymidine, and insulin did not affect DNA content. Cortisol decreased the stimulatory effect of IGF I on DNA labeling but greatly enhanced the stimulatory effect of IGF I on the incorporation of [3H]proline into CDP. Triiodothyronine and parathyroid hormone increased the incorporation of [3H]thymidine and were additive to IGF I. Triiodothyronine did not affect the labeling of CDP, but parathyroid hormone inhibited it and opposed the effect of IGF I. These studies indicate that IGF I stimulates bone DNA, collagen, and NCP synthesis in vitro. IGF I and insulin have similar effects on bone collagen synthesis but IGF I stimulates the synthesis of DNA at physiological concentrations, and insulin does not.

Basic fibroblast growth factor (bFGF) was studied for its effects on bone formation in cultured rat calvariae. bFGF at 0.1-100 ng/ml stimulated [3H]thymidine incorporation into DNA by up to 4.4-fold. bFGF also increased the number of colcemid-induced metaphase arrested cells and the DNA content. Transient (24 h) treatment with bFGF enhanced [3H]-proline incorporation into collagen 24-48 h after the factor was removed; this effect was DNA synthesis dependent and blocked by hydroxyurea. The collagen stimulated by bFGF was type I, and this effect was observed primarily in the periosteum-free bone. In contrast, continuous treatment with bFGF for 24-96 h inhibited [3H]proline incorporation into type I collagen. bFGF did not alter collagen degradation. In conclusion, bFGF stimulates calvarial DNA synthesis, which causes an increased number of collagen-synthesizing cells, but bFGF has a direct inhibitory effect on collagen synthesis.

Bone morphogenetic proteins (BMPs) induce the differentiation of cells of the osteoblastic lineage and enhance the function of the osteoblast. Growth factors are regulated by binding proteins, but there is no information about binding proteins for BMPs in skeletal cells. Noggin specifically binds BMPs, but its expression by cells of the osteoblastic lineage has not been reported. We tested for the expression of noggin and its induction by BMP-2 in cultures of osteoblast-enriched cells from 22-d-old fetal rat calvariae (Ob cells). BMP-2 caused a time- and dose-dependent increase in noggin mRNA and polypeptide levels, as determined by Northern and Western blot analyses. The effects of BMP-2 on noggin transcripts were dependent on protein, but independent of DNA synthesis. BMP-2 increased the rates of noggin transcription as determined by nuclear run-on assays. BMP-4, BMP-6, and TGF-beta1 increased noggin mRNA in Ob cells, but basic fibroblast growth factor, platelet- derived growth factor BB, and IGF-I did not. Noggin decreased the stimulatory effects of BMPs on DNA and collagen synthesis and alkaline phosphatase activity in Ob cells. In conclusion, BMPs induce noggin transcription in Ob cells, a probable mechanism to limit BMP action in osteoblasts.

PTH stimulates bone resorption and formation, but the mechanism of its anabolic effect is unknown. The effects of PTH on bone formation could be mediated by local regulators, either by altering their binding to receptors or by modulating their synthesis. Cell extracts from PTH-treated osteoblast-enriched cultures isolated from fetal rat parietal bones were examined by Northern blot analysis for changes in mRNAs encoding insulin-like growth factor I (IGF-I), transforming growth factor-beta, and beta 2-microglobulin. PTH did not influence transforming growth factor-beta or beta 2-microglobulin transcript levels. In contrast, PTH-(1-34) had a biphasic stimulatory effect on IGF-I transcript levels; 0.1-10 nM PTH increased IGF-I transcripts by 100-200% after a 6-h treatment, while 100 nM PTH induced a 100% increase. In addition, PTH at 0.01-10 nM increased immunoreactive IGF-I (iIGF-I) in culture medium by 40-200% at 24 h. Maximal increases in IGF-I transcripts occurred at 6 h, while iIGF-I accumulated throughout 24 h of culture. These results are compared to the effects of 0.5-50 nM GH, which increased IGF-I transcripts by 30% and iIGF-I by 50-100%. Therefore, PTH enhanced local IGF-I synthesis by increasing IGF-I transcripts, and this effect may in part mediate the anabolic actions of PTH on bone.

Bone continuously remodels in response to mechanical and physiological stresses, allowing vertebrates to renew bone as adults. Bone remodeling consists of the cycled synthesis and resorption of collagenous and noncollagenous extracellular matrix proteins, and an imbalance in this process can lead to disease states such as osteoporosis, or more rarely, osteopetrosis. There is evidence that the extracellular matrix glycoprotein osteonectin or secreted protein acidic and rich in cysteine (BM-40) may be important in bone remodeling. Osteonectin is abundant in bone and is expressed in areas of active remodeling outside the skeleton. In vitro studies indicate that osteonectin can bind collagen and regulate angiogenesis, metalloproteinase expression, cell proliferation, and cell-matrix interactions. In some osteopenic states, such as osteogenesis imperfecta and selected animal models for bone fragility, osteonectin expression is decreased. To determine the function of osteonectin in bone, we used contact x-ray, histomorphometry, and Northern blot analysis to characterize the skeletal phenotype of osteonectin-null mice. We found that osteonectin-null mice have decreased bone formation and decreased osteoblast and osteoclast surface and number, leading to decreased bone remodeling with a negative bone balance and causing profound osteopenia. These data indicate that osteonectin supports bone remodeling and the maintenance of bone mass in vertebrates.

PURPOSE: Pegylated recombinant human hyaluronidase (PEGPH20) degrades hyaluronan (HA) and, in combination with chemotherapy, prolongs survival in preclinical models. The activity of PEGPH20 with modified fluorouracil, leucovorin, irinotecan, and oxaliplatin (mFOLFIRINOX) was evaluated in patients with metastatic pancreatic cancer (mPC). MATERIALS AND METHODS: Patients had untreated mPC, a performance status of 0 to 1, and adequate organ function. Tumor HA status was not required for eligibility. After a phase Ib dose-finding study of mFOLFIRINOX plus PEGPH20, the phase II open-label study randomly assigned patients (1:1) to the combination arm or to mFOLFIRINOX alone (n = 138). The primary end point was overall survival (OS). RESULTS: PEGPH20 dosages of 3 µg/kg every 2 weeks were more tolerable than twice-weekly dosages used in the phase I study, so 3 µg/kg every 2 weeks was the phase II dosage. An amendment instituted enoxaparin prophylaxis in the PEGPH20 combination arm as a result of increased thromboembolic (TE) events. The planned interim futility analysis when 35 deaths (of 103 analyzable patients) occurred resulted in an OS hazard ratio (HR) of 2.07 that favored the control arm, and the study was closed to accrual. The treatment-related grade 3 to 4 toxicity was significantly increased in the PEGPH20 combination arm relative to control (odds ratio, 2.7; 95% CI, 1.1 to 7.1). The median OS in the mFOLFIRINOX arm was 14.4 months (95% CI, 10.1 to 15.7 months) versus 7.7 months (95% CI, 4.6 to 9.3 months) in the PEGPH20 combination arm. CONCLUSION: Addition of PEGPH20 to mFOLFIRINOX seems to be detrimental in patients unselected for tumor HA status. This combination caused increased toxicity (mostly GI and TE events) and resulted in decreased treatment duration compared with mFOLFIRINOX alone. The median OS in the mFOLFIRINOX control arm (14.4 months) is, to our knowledge, the longest yet reported and can be considered for patients with good PS.

The aim was to study the overall content and organisational aspects of pulmonary rehabilitation programmes from a global perspective in order to get an initial appraisal on the degree of heterogeneity worldwide. A 12-question survey on content and organisational aspects was completed by representatives of pulmonary rehabilitation programmes that had previously participated in the European Respiratory Society (ERS) COPD Audit. Moreover, all ERS members affiliated with the ERS Rehabilitation and Chronic Care and/or Physiotherapists Scientific Groups, all members of the American Association of Cardiovascular and Pulmonary Rehabilitation, and all American Thoracic Society Pulmonary Rehabilitation Assembly members were asked to complete the survey via multiple e-mailings. The survey has been completed by representatives of 430 centres from 40 countries. The findings demonstrate large differences among pulmonary rehabilitation programmes across continents for all aspects that were surveyed, including the setting, the case mix of individuals with a chronic respiratory disease, composition of the pulmonary rehabilitation team, completion rates, methods of referral and types of reimbursement. The current findings stress the importance of future development of processes and performance metrics to monitor pulmonary rehabilitation programmes, to be able to start international benchmarking, and to provide recommendations for international standards based on evidence and best practice.

BACKGROUND: There is heterogeneity in the names and anatomical descriptions of regional anesthetic techniques. This may have adverse consequences on education, research, and implementation into clinical practice. We aimed to produce standardized nomenclature for abdominal wall, paraspinal, and chest wall regional anesthetic techniques. METHODS: We conducted an international consensus study involving experts using a three-round Delphi method to produce a list of names and corresponding descriptions of anatomical targets. After long-list formulation by a Steering Committee, the first and second rounds involved anonymous electronic voting and commenting, with the third round involving a virtual round table discussion aiming to achieve consensus on items that had yet to achieve it. Novel names were presented where required for anatomical clarity and harmonization. Strong consensus was defined as ≥75% agreement and weak consensus as 50% to 74% agreement. RESULTS: Sixty expert Collaborators participated in this study. After three rounds and clarification, harmonization, and introduction of novel nomenclature, strong consensus was achieved for the names of 16 block names and weak consensus for four names. For anatomical descriptions, strong consensus was achieved for 19 blocks and weak consensus was achieved for one approach. Several areas requiring further research were identified. CONCLUSIONS: Harmonization and standardization of nomenclature may improve education, research, and ultimately patient care. We present the first international consensus on nomenclature and anatomical descriptions of blocks of the abdominal wall, chest wall, and paraspinal blocks. We recommend using the consensus results in academic and clinical practice.

Importance: Meta-analyses have suggested that initiating pulmonary rehabilitation after an exacerbation of chronic obstructive pulmonary disease (COPD) was associated with improved survival, although the number of patients studied was small and heterogeneity was high. Current guidelines recommend that patients enroll in pulmonary rehabilitation after hospital discharge. Objective: To determine the association between the initiation of pulmonary rehabilitation within 90 days of hospital discharge and 1-year survival. Design, Setting, and Patients: This retrospective, inception cohort study used claims data from fee-for-service Medicare beneficiaries hospitalized for COPD in 2014, at 4446 acute care hospitals in the US. The final date of follow-up was December 31, 2015. Exposures: Initiation of pulmonary rehabilitation within 90 days of hospital discharge. Main Outcomes and Measures: The primary outcome was all-cause mortality at 1 year. Time from discharge to death was modeled using Cox regression with time-varying exposure to pulmonary rehabilitation, adjusting for mortality and for unbalanced characteristics and propensity to initiate pulmonary rehabilitation. Additional analyses evaluated the association between timing of pulmonary rehabilitation and mortality and between number of sessions completed and mortality. Results: Of 197 376 patients (mean age, 76.9 years; 115 690 [58.6%] women), 2721 (1.5%) initiated pulmonary rehabilitation within 90 days of discharge. A total of 38 302 (19.4%) died within 1 year of discharge, including 7.3% of patients who initiated pulmonary rehabilitation within 90 days and 19.6% of patients who initiated pulmonary rehabilitation after 90 days or not at all. Initiation within 90 days was significantly associated with lower risk of death over 1 year (absolute risk difference [ARD], -6.7% [95% CI, -7.9% to -5.6%]; hazard ratio [HR], 0.63 [95% CI, 0.57 to 0.69]; P < .001). Initiation of pulmonary rehabilitation was significantly associated with lower mortality across start dates ranging from 30 days or less (ARD, -4.6% [95% CI, -5.9% to -3.2%]; HR, 0.74 [95% CI, 0.67 to 0.82]; P < .001) to 61 to 90 days after discharge (ARD, -11.1% [95% CI, -13.2% to -8.4%]; HR, 0.40 [95% CI, 0.30 to 0.54]; P < .001). Every 3 additional sessions was significantly associated with lower risk of death (HR, 0.91 [95% CI, 0.85 to 0.98]; P = .01). Conclusions and Relevance: Among fee-for-service Medicare beneficiaries hospitalized for COPD, initiation of pulmonary rehabilitation within 3 months of discharge was significantly associated with lower risk of mortality at 1 year. These findings support current guideline recommendations for pulmonary rehabilitation after hospitalization for COPD, although the potential for residual confounding exists and further research is needed.