William W. Stringer

Mechanisms of exercise limitation in HIV+ individuals.

Cardiopulmonary exercise testing (CPX) is an important diagnostic tool for both clinical and research purposes in HIV positive (HIV+) individuals. Important information can be obtained from the gas exchange responses that can elucidate heart, lung, peripheral vascular, pulmonary vascular, and muscle abnormalities in this population. A large percentage of these patients are deconditioned, respond well to exercise training, and have no intrinsic limitation to exercise. Results of a progressively increasing CPX can be used to: 1) design an exercise prescription for aerobic training in HIV+ individuals; 2) identify and refer patients with subtle abnormalities of gas exchange for further diagnostic studies to exclude early infectious complications: and 3) evaluate the improvements in maximal oxygen uptake, lactic acidosis threshold, and gas exchange kinetics as result from an aerobic exercise training program. Gas exchange kinetic analysis of constant work rate tests can provide similar information in a nonmaximal, reproducible, readily obtainable format. Both progressively increasing and constant work rate CPX tests provide important information on the changes in oxygen flow from the environment to the exercising muscle that occur with aerobic exercise training. Finally, a case study involving the exercise prescription for HIV+ individuals is reviewed as well as the risk of transmission of HIV during competitive sports competition events.

Oxygen Uptake Efficiency Plateau Best Predicts Early Death in Heart Failure

BACKGROUND The responses of oxygen uptake efficiency (ie, oxygen uptake/ventilation = VO(2)/VE) and its highest plateau (OUEP) during incremental cardiopulmonary exercise testing (CPET) in patients with chronic left heart failure (HF) have not been previously reported. We planned to test the hypothesis that OUEP during CPET is the best single predictor of early death in HF. METHODS We evaluated OUEP, slope of VO(2) to log(VE) (oxygen uptake efficiency slope), oscillatory breathing, and all usual resting and CPET measurements in 508 patients with low-ejection-fraction (< 35%) HF. Each had further evaluations at other sites, including cardiac catheterization. Outcomes were 6-month all-reason mortality and morbidity (death or > 24 h cardiac hospitalization). Statistical analyses included area under curve of receiver operating characteristics, ORs, univariate and multivariate Cox regression, and Kaplan-Meier plots. RESULTS OUEP, which requires only moderate exercise, was often reduced in patients with HF. A low % predicted OUEP was the single best predictor of mortality (P < .0001), with an OR of 13.0 (P < .001). When combined with oscillatory breathing, the OR increased to 56.3, superior to all other resting or exercise parameters or combinations of parameters. Other statistical analyses and morbidity analysis confirmed those findings. CONCLUSIONS OUEP is often reduced in patients with HF. Low % predicted OUEP (< 65% predicted) is the single best predictor of early death, better than any other CPET or other cardiovascular measurement. Paired with oscillatory breathing, it is even more powerful.

A controlled trial of the effects of leg training on breathing pattern and dynamic hyperinflation in severe COPD.

The effects of training on dynamic hyperinflation in stable chronic obstructive pulmonary disease (COPD) were investigated by using a controlled study of 28 subjects with FEV1 = 42.5 (8.3 SD)%pred and 20 matched controls [FEV1 = 44.9 (10.4)%pred]. Training consisted of spending 45 min/day, 4 days/week on a cycle-ergometer for six weeks. Maximal inspiratory and expiratory pressures (MIP and MEP), lung volumes, and two constant-work-rate (CWR) exercise tests (low- and high-intensity) were performed. Significant (p < 0.0l) improvements in the training group were observed in MIP [+8 (12) cmH2O], MEP [+18 (20) cmH2O], and endurance to high-intensity CWR [+7(5) min], and there were significant decreases in respiratory rate and end-expiratory lung volume (EELV) during both exercise tests. At 5 min, EELV decreased 0.1(0.08) L and 0.31(0.13) L and at end of exercise, EELV decreased by 0.09(0.07) L and 0.15(0.11) L respectively, for the moderate- and high-intensity tests. Dyspnea also decreased significantly at both exercise intensities. No changes were observed in the control group. Increased endurance showed independent significant (p < 0.05) correlation with changes in EELV, leg fatigue, and MEP. EELV changes showed a significant negative correlation with resting inspiratory capacity. We conclude that exercise training has beneficial effects on respiratory pattern and dynamic hyperinflation that may partially explain the reduction in dyspnea and the improvement in exercise tolerance.

HIV and aerobic exercise. Current recommendations.

AbstractAerobic exercise training is an important therapy to offer individuals who are HIV positive (HIV+). Six to 12 weeks of moderate exercise sessions (3 times per week for 1 hour) significantly improves aerobic capacity (V̇O2max and lactic acidosis threshold), apparently without detrimental effects on the immune system. In addition, small but significant beneficial effects on the immune system (skin test reactivity) and quality of life are obtained. The effects on lean body mass with aerobic exercise training have been less marked, but are clearly less costly than androgenic hormone administration in this population. Aerobic exercise training can be recommended with confidence in HIV+ patients.

Non-linear cardiac output dynamics during ramp-incremental cycle ergometry

Published literature asserts that cardiac output (Q̇=V̇O2×1/C(a-v)O2) increases as a linear function of oxygen uptake with a slope of approximately 5–6 during constant work rate exercise. However, we have previously demonstrated that C(a-v)O2 has a linear relationship as a function of V̇O2 during progressively increasing work rate incremental exercise. Therefore, we hypothesized that Q̇ may indeed have a non-linear relationship with respect to V̇O2 during incremental, non-steady state exercise. To investigate this hypothesis, we performed five maximal progressive work rate exercise studies in healthy human subjects. Q̇ was determined every minute during exercise using measured breath-by-breath V̇O2, and arterial and pulmonary artery measurements of PO2, hemoglobin saturation, and content. Q̇ was plotted as a function of V̇O2 and the linear and non-linear (first order exponential and hyperbolic) fits determined for each subject. Tests for linearity were performed by assessing the significance of the quadratic terms added to the linear relation using least squares estimation in linear regression. Linearity was inadequate in all cases (group P<0.0001). We conclude that cardiac output is a non-linear function of V̇O2 during ramp-incremental exercise; the pattern of non-linearity suggests that while the kinetics of Q̇ are faster than those of V̇O2 they progressively slow as work rate (and V̇O2) increases.

Partial anomalous pulmonary venous return: Case report and review of the literature

Isolated partial anomalous pulmonary venous return (APVR) is an uncommon finding. A patient with isolated APVR had pulmonary hypertension without demonstrable left‐to‐right shunting prior to anticoagulant treatment of pulmonary emboli. After anticoagulant therapy, with a fall in pulmonary pressures and resistance to near‐normal levels, left‐to‐right shunting was then detected by oximetry and angiography. The anomaly was visualized on electron beam angiography and confirmed by conventional angiography after anticoagulant therapy. Contrary to the expected obligatory drainage of highly saturated blood associated with APVR, lack of detectable shunting was thought to be due to the obstruction of regional blood due to thromboembolism. Cathet Cardiovasc Intervent 2003;58:548–552.

A matched comparison of serum lipids between hemodialysis patients and nondialysis morbid controls.

The high incidence of cardiac and vascular disease in maintenance hemodialysis (MHD) patients has heightened interest in many investigations concerning the serum lipid levels of these patients. The prevalence and laboratory characteristics of serum lipid concentrations in MHD patients, however, are far from clear. We hypothesized that serum lipids are significantly lower in MHD patients compared to their matched nondialysis counterparts. We compared 2‐year averaged serum levels of total cholesterol (TC), low‐density lipoprotein (LDL), high‐density lipoproteins (HDL), and triglycerides in 285 MHD patients to the same averaged measurements during the same period of time in 285 nondialyzed outpatients from the same geographic area, whose lipid panels were measured in the same laboratory. Matching factors were sex, race and/or ethnicity, diabetes mellitus, and age (± 5 years). The MHD patients and their matched controls were 55.6 ± 13.5 (SD) and 56.3 ± 13.0 years old, respectively. Each group contained 51% women, 31% African Americans, 52% Hispanics, and 37% diabetics; 16% of MHD patients and 38% of controls were receiving statins. Body mass index (BMI) was significantly lower in MHD patients than in controls (26.2 vs. 31.5 kg/m2; p < 0.001). Serum cholesterol levels were significantly lower in MHD patients than in control subjects including after adjustment for BMI and statin use (TC, −51; LDL, −39; and HDL, −10 mg/dL; p < 0.001). Using conditional logistic regression for matched data and after controlling for BMI and statins, all odds ratios for predetermined hypercholesterolemic, but not hypertriglyceridemic, levels were significantly and substantially lower than 1.00, indicating much lower likelihood of hypercholesterolemia in MHD patients. Total and LDL hypercholesterolemia, although very common in nondialysis ambulatory outpatients, are substantially less prevalent in the MHD population, whereas hypertriglyceridemia is approximately equally prevalent between these populations.

Cardiopulmonary exercise testing: does it improve perioperative care and outcome?

Purpose of review We reviewed recent articles, guidelines, and meta-analyses concerning the use of cardiopulmonary exercise testing (CPET) in preoperative risk evaluation and fitness for surgery. When the risk of surgery mortality is high (e.g. >5%), and/or the preoperative state of the patient indicates increased propensity toward morbidity and mortality (advanced age, presence of cardiovascular risk factors, multisystem disease, poor functional status, and so on), the thoroughness of the perioperative assessment should be intensified beyond the standard history and physical, basic laboratories, and electrocardiogram stress testing to include CPET. Recent findings The CPET variables of peak oxygen uptake, anaerobic threshold, oxygen pulse, and ventilatory efficiency appropriately focus upon the cardiopulmonary reserve required to respond to metabolic stress and, therefore, are ideal to predict operative surgery outcomes. The focus should not be on using CPET to deny surgery to patients, but rather to define the level of postoperative care required to minimize risk. Summary Using a small number of important variables obtained from CPET an accurate picture of the patients future response to perioperative stress can be obtained. Consideration should be given to performing a CPET in any preoperative patient who has increased risk or is scheduled to undergo a high risk surgical intervention. This strategy assists the anesthetist, surgeon, patients, and their families in appropriate perioperative planning.

Capturing the Diagnosis: An Internal Medicine Education Program to Improve Documentation

BACKGROUND Specific and accurate documentation of patient diagnoses and comorbidities in the medical record is critical to drive quality improvement and to ensure accuracy of publicly reported data. Unfortunately, inpatient documentation is taught to internal medicine trainees and practitioners sporadically, if at all. At Harbor-UCLA Medical Center, a public, tertiary care, academic medical center, we implemented an educational program to enhance documentation of diagnoses and comorbidities by internal medicine resident and attending physicians. METHODS The program consisted of a series of lectures and the creation of a pocket card. These were designed to guide providers in accurate documentation of common diagnoses that group to different levels of disease severity, achieved by capturing Centers for Medicare and Medicaid Services complication codes and major complication codes. We started the educational program in January 2010 and used a pre-post design to compare outcomes. The programs impact on complication codes and major complication codes capture rates, mortality index, and case mix index was evaluated using the University Health Consortium database. RESULTS The median quarterly complication codes and major complication codes capture rate for inpatients on the internal medicine service was 42% before the intervention versus 48% after (P = .003). Observed mortality did not change but expected mortality increased, resulting in a 30% decline in median quarterly mortality index (P = .001). The median quarterly case mix index increased from 1.27 to 1.36 (P = .004). CONCLUSIONS Thus, implementation of an internal medicine documentation curriculum improved accuracy in documenting diagnoses and comorbidities, resulting in improved capture of complication codes.

Arterial H+ regulation during exercise in humans

Resting arterial H+ concentration ([H+]a) is in the nanomolar range (40±2 nm/L) while its production is in the millimolar range/min, with little variation from subject to subject. To determine the precision with which [H(+)]a is regulated during exercise, [H+]a, PaCO2 and ventilation (V˙(E)) were measured during progressively increasing work rate exercise in 16 normal subjects. (V˙(E)) increased with [H+]a, the latter attributable to PaCO2 increase below the lactic acidosis threshold (LAT) (ΔV˙(E)/Δ[H+]a ≈ 15   L   min(-1)   nanomol(-1)). [H+]a and PaCO2 increased, simultaneously, as work rate was increased below LAT. PaCO2 reversed direction of change between LAT and ventilatory compensation point (VCP). Above LAT, [H+]a increase relative to (V˙(E)) increase was greater than below LAT. PaCO2 decreased above the LAT, while [H+]a continued to increase. Thus the exercise acidosis was converted from respiratory, below, to a metabolic, above the LAT. We conclude that [H+]a is increased and regulated over the full range of exercise, but with less sensitivity above the LAT.